eden food waste technology trial · 2011-09-21 · food waste is collected from the central food...

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Eden Project Food Waste Technology Trial

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Prepared for The Eden Project by Tim Stokes, environmental consultant, 07809 762545 The author has taken due care in the preparation of this report to ensure that all facts and analysis presented are as accurate as possible within the scope of the project. However no guarantee is provided in respect of the information presented, and the author is not responsible for decisions or actions taken on the basis of the content of this report.

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CONTENTS

Title

Page no.

Executive summary...................................................................................................... 1 1. Introduction.................................................................................................................... 3 2. Background................................................................................................................... 4 2.1 The issue of waste........................................................................................................ 4 2.2 Eden Projects Waste Neutral Programme................................................................... 6 2.3 Food waste at the Eden Project.................................................................................... 7 2.4 Aim of the food waste technology trial.......................................................................... 7 2.5 The choice of technology.............................................................................................. 7 3 Overview of the composting process used in the food waste technology trial.............. 8 3.1 Collecting, sorting, transportation and storage of feed-stocks...................................... 8 3.1.1 Food waste.................................................................................................................... 8 3.1.2 Green waste.................................................................................................................. 9 3.1.3 Carbon supplements..................................................................................................... 10 3.2 Inputting feed-stock into the Neter 30 composter......................................................... 10 3.3 Description of the Neter 30 composter.......................................................................... 11 3.4 Energy input.................................................................................................................. 13 3.5 Staff input...................................................................................................................... 13 3.6 Outputs of process........................................................................................................ 14 4 Findings of the trial........................................................................................................ 15 4.1 Background................................................................................................................... 15 4.2 Effectiveness of composting process............................................................................ 17 4.2.1 Temperature.................................................................................................................. 17 4.2.2 Acidity............................................................................................................................ 18 4.2.3 Moisture levels.............................................................................................................. 18 4.2.4 Rate of progress of composting mass........................................................................... 19 4.3 Effectiveness of compost as a horticultural product...................................................... 20 4.3.1 Growth medium trials.................................................................................................... 21 4.3.2 Mulching medium trials.................................................................................................. 21 4.3.3 BSI PAS 100 tests......................................................................................................... 22 4.4 Bioaerosol tests............................................................................................................. 24 4.5 Gas emissions....................................................................................................... 25 4.6 Design, operational and other issues arising from the trial........................................... 26 4.6.1 Design issues................................................................................................................ 26 4.6.2 Operational and other issues........................................................................................ 27 5. Financial appraisal........................................................................................................ 29 5.1 Introduction................................................................................................................... 29 5.2 Set-up costs.................................................................................................................. 29 5.3 Management, administration and research and development costs............................. 29 5.4 Operational and maintenance costs.............................................................................. 30 5.5 Cost benefit analysis..................................................................................................... 32 5.5.1 Assumptions.................................................................................................................. 32 5.5.2 Annual running costs and savings................................................................................ 33 5.5.2 Environmental and social impacts................................................................................. 34 5.5.3 Summary of costs and benefits projected for 2007/8.................................................... 35 5.5.4 Potential savings using Neter and other in-vessel technology...................................... 37 5.5.5 Conclusions of financial analysis.................................................................................. 39 6. Conclusions................................................................................................................... 40 7. Recommendations........................................................................................................ 42

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Food Waste Technology Trial Report� Page��

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EXECUTIVE SUMMARY

As a society, the UK is consuming resources at an unsustainable rate. At the heart of our unsustainable consumption of resources is the issue of waste. Around 100 million tonnes of waste are generated by commerce, industry and households every year. Food waste makes up a considerable proportion of the total waste stream that is sent to landfill where it rots down under anaerobic conditions to produce methane, a powerful greenhouse gas that is contributing to global climate change.

The Eden Project is pioneering an approach to waste called Waste Neutral aimed at stimulating the market for recyclates and encouraging people to think of waste as a resource. As part of this approach, it installed a Neter 30 in-vessel composter in April 2005 and set up a trial to test the efficacy of this technology for the processing of food waste.

This report is an open account of the Eden Projects experience of setting up and operating the composter. The aim of the report is to inform others considering investing in this technology of the benefits and potential pitfalls of such an approach.

The Neter 30 operates on the principle of aerobic digestion - a process through which micro-organisms consume organic matter in the presence of air and convert it into a stabilised compost that can be applied to land.

Food waste is collected from the central food preparation facility and seven catering outlets on the site and transported to the Waste Neutral Recycling Compound (WNRC). Here it is fed into the Neter 30 alongside shredded green waste and wood pellets which help to improve the composting process.

After initial teething problems, the Neter 30 has been producing compost since September 2005. The compost produced has been submitted to various tests to ascertain its quality and in the main has been shown to be suitable as a soil improver for use on the site. In particular, samples submitted for testing under the British Standards Institute Publicly Available Specification 100 (BSI PAS 100) scheme have passed in two out of three instances.

The quantity of food waste being processed by the composter is lower than originally expected and well below the capacity of the machine. This is mainly due to problems that have been experienced in establishing the optimum feed-stock for the Neter. Also, the level of food waste available was overestimated at the design stage of the project partly due to the success of sustainability initiatives across the site which have subsequently reduced food waste.

The most reliable feed-stock mix identified to date consists of approximately two parts food waste to one part green waste, with a 15% addition of wood pellets.

Analysis of the financial costs and savings arising from the use of the composter indicates that the process operating at the Eden Project cannot currently be justified from an economic perspective. The operational costs incurred outweigh the savings made from diverting food waste from landfill and producing compost for use on the site.


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However, the Eden Project is committed to the principles of sustainability and there are environmental and social benefits that arise from diverting food waste from landfill. In particular, treating food waste on site follows the proximity principle of managing waste close to where it is produced. Composting food waste also results in a reduction in emissions of methane, a powerful greenhouse gas.

Furthermore, the findings indicate that the economic viability of the technology tends to increase with the throughput of food waste and as knowledge of appropriate feed-stock mixes increases. The rising costs of sending food waste to landfill by virtue of increasing environmental taxation will also substantially increase cost savings over time from diverting food waste from landfill.

Arising from the Eden Projects experience of in-vessel composting using the Neter 30, the following recommendations are made:

1. Organisations considering investing in an in-vessel composter should:

• seek to understand their food waste issue and take appropriate steps to minimise the amount of food waste being generated;

• make an accurate assessment of the amount of food waste generated as it could have a major bearing on the financial payback;

• seek to ensure that the capacity of the machine purchased closely matches the volume of food waste and other feed-stocks composted;

• ensure that they have given full consideration to the implications of complying with the relevant legislation including amongst others ABPR 2005 and the EPA 1990; and

• be committed to the principles of sustainability and thereby have a full appreciation of the benefits of the process, over and above the current financial returns.

2. At lower levels of throughput, in addition to the aforementioned precautions, the following conditions should ideally apply:

• A suitable free or low cost source of carbon should be available as a supplement to the feed-stock.

• A steady source of green waste should also be available free or at low cost

• The compost produced should be either of use to the operator as a soil improver or processed into a saleable product.

• Any additional operational capacity employed in the processing of food waste needs to be closely matched to the nature and level of work.

3. It is important to input an appropriate mix of feed-stock into the composter. Failure to do so could result in a situation where the machine will be operating inefficiently or not at all.


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1. INTRODUCTION

The Eden Project was conceived to celebrate the wonder and variety of the plant world and to raise awareness of the interdependency of people and plants. Since its opening in 2001 it has consistently welcomed over one million visitors every year to view its iconic biomes.

The Eden Project strives to ensure that its visitors enjoy the whole experience of their visit. For this reason, there is a range of catering outlets on the site where a variety of meals and refreshments are served. Inevitably in such an operation, there will be left-over food. But what happens to this food waste? In most commercial catering establishments, it will be put in a bin, for collection and transportation to a landfill site. There, it will rot down along with other waste emitting, in particular, methane a powerful greenhouse gas which is contributing towards global climate change. With no other option available at the time, the Eden Project used to send all its food waste to landfill. This approach was very much at odds with the ethos of sustainability underpinning its activities. It also contravened the proximity principle which recognises both the need to avoid passing on the environmental cost of waste disposal to communities that are not responsible for its generation and the need to reduce the financial and environmental costs of transporting waste. However, the Eden Projects food waste stream constituted ’catering waste’ and as such was governed by the UK Animal By-product Regulations (ABPR 2005) and required special treatment. This necessitated using new, in-vessel composting technology capable of safely processing food waste containing animal by-products. To close the loop, the compost produced would be used on site as a growing medium, soil improver or mulch, thus returning nutrients to the soil, improving its structure, and aiding plant growth.

After considerable research, the chosen solution came in the form of the Neter 30 in-vessel composting system manufactured by a company called Susteco. Though a number of smaller composting facilities using similar technology are now operating in the UK, this was the first time that an installation of this scale and capacity had been installed. It was also only the third Neter composter to be installed in the world.

Recognising its potential for improving resource efficiency amongst small to medium sized enterprises (SMEs), the Eden Project decided to set up a trial to examine the operational, environmental and financial implications of investing in this technology.

This report is an open account of the Eden Projects journey down that route. It is hoped that this experience in attempting to deal with its food waste more sustainably will help others seeking to go down the same path, raising awareness of the benefits and potential pitfalls of such an approach.


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2. BACKGROUND 2.1 The issue of waste

As a society, the UK is consuming resources at an unsustainable rate, estimated to be three times the carrying capacity of the earth.

At the heart of our unsustainable consumption of resources is the issue of waste. Waste is one of the biggest environmental issues currently facing the UK. Around 100 million tonnes of waste are generated by commerce, industry and households every year1.

Existing landfill sites are fast approaching capacity and the space and desire to open fresh landfill sites is rapidly diminishing. Indeed, in Cornwall, full capacity will be reached in a matter of a few years. Moreover, it is now widely acknowledged that disposal of waste in such a manner is an unsustainable practice. Food waste represents a significant proportion of the total waste stream that is sent to landfill. The decomposition of organic wastes in landfill produces methane, a powerful greenhouse gas which is contributing towards climate change. It is estimated that approximately 40% of the UKs methane emissions arise from uncontrolled emissions from landfill sites. Methane emissions account for around 8% of the UKs total greenhouse gas emissions2. Food waste in itself has a considerable impact on the environment even if it is not sent to landfill, simply from the embodied energy used in its production, transportation and preparation. There are a number of reasons why food waste arises. Some food waste is unavoidable as inedible or unpalatable components of meat, fish, vegetables and fruit have to be discarded in the preparation of food. In a commercial catering setting there are a number of other causes of food waste including:

• Poor planning which can result in food going off before it is used • Providing portions that are too large • Providing menus that are too broad in a setting where food is pre-prepared, thereby

consigning less popular dishes to the bin • Providing poor quality food • Buying more food than is required particularly a s a consequence of buy one, get one

free offers Recently EU and UK legislation, and fiscal measures have been introduced to discourage the disposal of food waste (and other wastes) in landfill sites.

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The Landfill Directive (99/31/EC) has set binding targets for the UK to reduce quantities of biodegradable municipal waste (BMW) sent to landfill. The targets are as follows: • By 2010 to reduce the amount of BMW landfilled to 75% of that produced in 1995. • By 2013 to reduce the amount of BMW landfilled to 50% of that produced in 1995. • By 2020 to reduce the amount of BMW landfilled to 35% of that produced in 1995.

The Waste and Emissions Trading Act (WET) 2003 has been introduced as the main mechanism for meeting the Landfill Directive targets in the UK. The WET Act provides the framework for the Landfill Allowance Trading Scheme (LATS) which through a system of tradable allowances and permits will help waste disposal authorities to reduce the amount of BMW that is sent to landfill.

The Landfill Tax Escalator is set to increase landfill tax from £24/tonne in 2007/8 by £8 per tonne per annum until at least 2010/11, by which time the landfill tax will have doubled to £48 per tonne. The banning of non-hazardous liquid waste and untreated waste from landfill under the Landfill Directive from October 2007 may also place upward pressure on the cost of disposing of catering waste. In practice, these initiatives will result in increased costs for commercial organisations wishing to send food waste to landfill, and so, they will be incentivised to seek out alternative methods of disposing of food waste. Options for the disposal of food waste include:

• Mechanical and Biological Treatment (MBT) combines mechanical and biological

processes to treat municipal, non-hazardous and commercial wastes. Essentially, a range of mechanical processes are used to separate out dry recyclables, and biological processes such as biological drying are used to stabilise the organic fraction of the incoming waste. The resultant outputs can be used to produce an energy rich refuse derived fuel, an organic fraction that is suitable for composting or anaerobic digestion and a biologically stable residue that is suitable for composting. It is, in essence, a method of pre-treating waste.

• Mass burn incineration treats unsorted municipal waste by combustion in air under controlled conditions, reducing refuse to dry ash. Most incineration plants now generate electricity and heat from the burning of refuse.

• Pyrolysis and gasification turn waste into energy rich fuels. Pyrolysis is the thermal degradation of waste in the absence of oxygen to produce char, pyrolysis oil and syngas. Gasification breaks down hydrocarbons into a syngas by carefully controlling the amount of oxygen present. The by-products of these processes can be used as fuel and as a feedstock for petrochemical and other applications.

• There are now a number of commercial companies operating in the UK employing aerobic digestion technology to produce compost or anaerobic digestion technology to


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generate electricity and heat and produce a digestate that can be used as a soil improver.

• Companies can, under licence from the Environment Agency (exemptions can apply), compost their own waste on site employing aerobic or anaerobic digestion technology.

2.2 Eden Projects Waste Neutral Programme

The Eden Project can play an important role in raising awareness of alternative ways of thinking about waste in particular the recognitio n that potentially there is no such thing as waste, only unrecognised resources.

In 2004, the Eden Project set up its Waste Neutral Programme. The aim of the programme is to make best use of the resources that the Eden Project uses, minimising waste, and ultimately leading to a situation where the volume of waste and recyclates leaving the site after reduction and re-use, is equal to or less than the volume of products made from recyclates that are bought in. This approach encourages both the careful use of resources and the purchase of goods made from recyclates thereby stimulating the market for waste, recognising that unless recyclates become part of the resource chain, they will simply become value-added landfill.

The mantra of the Waste Neutral Programme is Reduce, Re-use, Recycle and Reinvest. It is the reinvestment in products made from recycled materials that stimulates the market for waste.

The Waste Neutral Programme is being implemented as follows:

• Environmental and waste criteria have been fully integrated into the Eden Projects purchasing policy, and accounting and auditing systems.

• The Eden Project is working proactively with its suppliers and service providers to

minimise waste and maximise the use of recyclates, redesigning products and services if necessary in order to achieve this aim.

• The Eden Project is promoting the programme to individuals, communities and

organisations through on-site and off-site educational programmes to encourage them to adopt a similar approach.

• Recycling stations have been set up throughout the Eden Project site to enable visitors

to participate in the Waste Neutral programme and to allow for the separation of recyclables.

• The Waste Neutral Recycling Compound (WNRC) has been set up to sort, store and

process waste arising from the Eden Projects activities.


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• In April 2005 the Neter 30 in-vessel composter was installed in the WNRC in order to process food waste generated on the site

2.3 Food waste at the Eden Project

Food waste is a significant concern for Eden. Prior to the inception of the Food Waste Technology Trial and installation of an in-vessel composting system, an estimated 230kg per day of catering waste was being sent to landfill. The cost of sending this waste to landfill in financial terms was at least £5,000 per annum, a figure that was likely to increase rapidly with the rising costs of disposing of waste in landfill. There was also a cost to the environment in using this form of disposal. For example:

• The material had to be picked up and transported to landfill consuming vehicle fuel and causing exhaust emissions to the environment

• Once landfilled, the material would most likely break down anaerobically to produce methane which would have a negative impact on the environment unless recovered and used as a fuel to generate electricity.

Finally, there was an opportunity cost of sending a resource to landfill that could otherwise be put to use on the Eden Project site.

2.4 Aim of the food waste technology trial

The aim of the food waste technology trial was to investigate the viability of new technology for complete, in-vessel treatment of food waste as a solution for comparatively small-scale on-site producers of food waste such as SMEs, schools, prisons, hospitals and community-based composting partnerships for the disposal of their food waste. The trial was set up to assess:

• The performance of the technology in treating food waste and producing usable outputs (e.g. compost, digestate, biogas);

• the ability of the technology to meet UK animal by product regulations (ABPR) in relation to the treatment of food waste; and

• the operational, financial and environmental implications of utilising in-vessel technology.

2.5 The choice of technology

Though other solutions for the treatment of food waste are available, the Eden Project narrowed its focus to a choice between two in-vessel treatment processes that it felt would have greatest applicability to the scale and nature of its catering operations, namely aerobic and anaerobic digestion. The final decision to utilise aerobic digestion for the trial was made for the following reasons:


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• The energy input required for aerobic digestion is comparatively low because it is

essentially a natural process.

• Anaerobic digestion technology needed to be scaled-down to match the Eden Projects food waste output. Even the smallest scale anaerobic digester would normally process higher quantities of food waste than produced by the Eden Project. The capital cost of the anaerobic digester option was also comparatively high making it less economic to operate at lower levels of throughput.

• Aerobic technology is generally easier to control and operate than anaerobic

technology, having fewer outputs and less complex maintenance requirements. The financial savings likely to arise from diverting small quantities of food waste from landfill would be too low to justify the base-level operational and maintenance costs of an anaerobic digester.

• Aerobic digestion is more complementary to other composting processes taking place

on site (e.g. of green waste) and to the home composting process. It was therefore felt that the installation of this technology and accompanying interpretation would reinforce the Eden Projects support for home composting.

• It was felt that the simpler design of an aerobic system would be easier to replicate in

SMEs.

3. OVERVIEW OF COMPOSTING PROCESS USED IN THE FOOD WASTE TECHNOLOGY TRIAL

This section sets out the process through which food waste and other inputs are converted to compost, tracing the route of the inputs to the composting vessel and describing the composting process and its outputs.

3.1 Collection, sorting, transportation and storage of feed-stocks

The achievement of optimum conditions for the production of compost in an in-vessel system is dependent on the mixture of the feedstock applied. In particular, it is important to attain the correct carbon to nitrogen ratio, moisture levels and levels of acidity. The three key material inputs of the composting process at the Eden Project are food waste, green waste and carbon supplements.

3.1.1 Food waste

All food is cooked at a central preparation facility located next to the Foundation Building. Many of the vegetables received by this facility are pre-prepared off-site by the Eden Projects catering suppliers. The proportion of food waste that constitutes raw vegetable material is as


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a consequence quite low. The vegetable waste generated by the Eden Projects catering suppliers is used as a feedstock for pigs and goats on a farm. Food waste generated at the central preparation facility is deposited into 90 litre wheelie bins.

The food is distributed from the central preparation facility to the seven catering facilities that operate on the Eden Project site, five of which are for visitors and two of which are for staff. At these facilities some final preparation takes place including the presentation of food on plates for customers. The total capacity of these facilities is 1180 covers.

At the restaurants and cafes, left-over food, packaging and utensils are separated by restaurant staff to minimise contamination of the food waste by items which are unsuitable for composting. Certain non-food items are permitted including serviettes and kitchen towel, some egg boxes, coffee filters, wooden cutlery, tea bags and occasional small bits of paper. The food waste is again deposited in 90 litre wheelie bins.

The food waste arising from the catering operations at the Eden Project consists of cooked and raw meat, carcases and bones (e.g. from chickens), bread, cereals, some vegetable waste and some compostable packaging and eating utensils.

The wheelie bins are collected at regular intervals (along with other waste and recycling) by staff from the WNRC in a diesel tipper van with a tail-lift and transported to the Waste Neutral Recycling Compound.

At the WNRC food waste is either input into the Neter, or picked up by the Eden Projects waste carrier and taken to landfill, dependent on the operational status of the composter and balance of feedstock required to ensure the optimal functioning of the composting process.

In recent times, the breadth of options available on menus has been reduced in order to minimise wastage. The decision to reduce choice was based on financial grounds as much as it was on the level of waste that was arising from lack of take-up of certain dishes on the menus.

The overall volume and weight of food waste produced is not routinely monitored. However, the weight of food waste was monitored during August 2006 and November 2006 providing an indication of the scale of the catering operation at the Eden Project. During August 2006, the total weight of food waste produced was 9532kg (173,037 visitors). During November 2006, the total weight of food waste was 4571kg (35,095 visitors). Generally August is the busiest month of the year and November is one of the quietest. So the two weights probably represent the opposite ends of the scale for food waste.

3.1.2 Green waste

Through its extensive horticultural activities, the Eden Project produces large amounts of green waste. Most of this is shredded and then composted in open bays on site. Some of this green waste is shredded and transported to the WNRC to be used as a feed-stock in the in-


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vessel composting process to help increase pH and to provide suitable microbial populations potentially lacking in the food waste that would aid the composting process.

3.1.3 Carbon supplements

The optimum carbon to nitrogen ratio for composting is considered to be between 30 35:1 3. The manufacturer of the composter, Susteco, recommended the use of wood pellets made up of compressed sawdust to help increase the carbon ratio and reduce the moisture content. The Eden Project has trialled other carbon sources such as wood shavings, shredded office paper, shredded paper towels, shredded corrugated board, waste dust collected from the corrugated board shredding process, and chopped straw. Currently, the wood pellets are favoured due to their efficacy and the stability of supply. However, wood pellets are externally sourced and represent a cost to the Eden Project and to the environment (e.g. transportation and embodied energy). The pellets are supplied at a cost of approximately 31p per kg.

3.2 Inputting feedstock into the Neter 30

The food waste is fed into the Neter along a conveyor belt which transports the feed-stock to a shredder. Although some segregation of food waste and green waste is inevitable, efforts are made to ensure that the two feed-stocks are fed into the Neter together as this has been found to improve the efficiency of the composting process. The wheelie bins containing food waste are automatically raised and emptied onto the conveyor belt providing an opportunity for an operative to remove any unsuitable items from the food waste stream.

The conveyor belt transports the food to a spiral conveyor that terminates with a knife system. From here it passes to a shredder which mashes it into fragments of approximately 2cm in diameter. Wood pellets and green waste, if necessary, can be fed into the in-auger via a hopper to allow early incorporation of these feed stocks. The volume of green waste and wood pellets added is adjusted to take account of the nature and moisture content of the food waste. The mixture of food waste, green waste and wood pellets is transported by the in-auger into the composting cylinder.

The machine is designed to process up to 1800kg of material per day, operating on a range of inputs including vegetable and meat waste, and garden waste. The mix of inputs determines the quality and utility of the compost produced.

The cylinder rotates periodically, slowly moving the food waste from the front to the back end of the machine. The rotation increases access of the contents to atmospheric oxygen, enabling the material to be aerobically digested. After a period of time (usually 40-60 days under optimum operational conditions), the material is fully broken down through a process of aerobic digestion into compost and discharged from the rear of the machine via an out-auger.

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3.3 Description of Neter 30 composter

The composter consists of a horizontal, stainless steel cylinder which is approximately 8.5 metres long and 2 metres in diameter with a central spindle. The cylinder is rotated by externally mounted hydraulic rams against fixed end walls. (see fig 1 below).

Figure 1

The composter is housed in a partially insulated, stainless steel outer-casing which is 9.5m long, 2.7m wide and 2.6m high. The outer casing acts as a safety barrier against the hazards of the machines moving parts and provides a degree of buffering from external temperature fluctuations.

The rotation of the cylinder tumbles the material being composted, mixing and aerating it whilst moving it along the vessel. The periods of rotation (run) and standing (wait) can be altered according to the requirements of the composting process at any one time.

Five circular steel plates are affixed to the central spindle at 1.4m intervals. Each plate holds four temperature sensors and one water inlet nozzle for adding moisture to compost as required (see figure 1, picture B inset).


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Figure 2

Air is drawn by a fan across the top of the composting mass during the wait periods and through the mass during the run periods. This removes unwanted gases, water vapour and excess heat and replenishes oxygen levels (see figure 2). The fan speed can be adjusted to suit internal conditions. The exhaust air is passed through a biofilter to be cleansed prior to being discharged into the atmosphere. The biofilter uses natural processes to eliminate odours and contains bark which is periodically treated with an enzyme solution

There are four inspection hatches through which the process can be observed and any maintenance requirements can be administered.

The compost is produced through an aerobic process, through which micro-organisms consume organic matter in the presence of air and convert it into a stabilised compost.

Theoretically, there are three temperature phases through which the organic matter must normally pass in order to break down into compost. Under optimum operating conditions, the matter quickly enters the thermophilic phase which is characterised by high moisture content of the composting material and temperatures of between 55 - 65= C. This phase should last for 12 to 18 days. The next stage is the mesophilic stage during which the volume of the material diminishes and the temperature of the compost falls to between 25 and 40= C. This stage normally lasts for between 18 to 24 days. The final phase is called the maturation phase. This lasts for approximately 10 15 days du ring which there are further reductions in volume and in the temperature of the composting matter.

The reduction in bulk of the original material is between 70 to 90% of its original input. Subject to meeting the ABPR 2005 the compost material derived through this process can be used in a range of applications.


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3.4 Energy input The Neter composting process involves an exothermic reaction, thereby providing its own

heat, though a small electric heater has been incorporated into the machine in case of extreme (cold) weather conditions. The machine uses electricity to power the:

• conveyor belts; • spindle for revolving the inner cylinder; • shredder; • aeration fan; • temperature sensors; and • electronic information systems

The average power consumed per day is around 48kwh/day broken down as follows: Component Average kwh/day

Feeding machinery 14.45 Cylinder and fan 29 Out-conveyor 0.55 Sensors 4.2 Total 48.22

. 3.5 Staff input

Five permanent and one seasonal members of staff are engaged in operational roles relating to the Neter. Two staff collect wheelie bins containing food waste from the catering facilities on the site and deposit them at the WNRC. Their role also involves the collection of other waste and recyclables deposited in the recycling and waste bins that are located throughout the site. All staff are involved in operating the Neter. Activities include:

• feeding the Neter, • checking the volume of compost in the Neter, • checking backend compost • emptying compost into the compost bay • general maintenance of Neter and bio-filter

• checking and logging temperatures • checking equipment is operating

correctly • cleaning the Neter • cleaning bins

In addition to high visibility jackets worn by all staff working in the WNRC, operatives feeding the Neter are required to wear the following additional personal protective equipment:

• Heavy duty gloves • Waterproof trousers and jackets • Safety wellington boots

• Particulate respirator face masks • Ear protectors


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A number of staff from other sections also have roles in relation to the Neter, principally in relation to monitoring the biological functioning of the Neter, its emissions and the quality of the compost. The level of input from such staff has necessarily been higher than would be the case under normal operating circumstances as they have been involved in developing the knowledge base for the trial. Nonetheless, it is anticipated that other users of this technology would require access to a degree of scientific knowledge of the composting process and compost outputs.

WNRC operatives and Edens science team liaise closely in order to determine feed-stocks for the Neter. WNRC staff will use their experience to report any concerns regarding the status of the biodegrading feedstock to the science team. The science team will on occasion specify new feed-stock regimes for the purpose of the trial.

3.6 Outputs of the process (i.e. compost, emissions , waste)

The aim of the process is to produce a compost that can be used (ideally without further treatment) for a range of applications. Emissions to air and water are minimal through this process. However, it is important that a suitable use can be found for the compost, otherwise it effectively becomes waste. The Animal By Products Regulations (ABPR 2005) require composting material with a maximum particle size of 40cm to reach at least 60= C for two days, twice, with a barrier between the 2 treatments to prevent cross contamination - or, alternatively two periods at a temperature of greater than 70= C for at least one hour, with a maximum particle size of 6cm4. The legislation also requires that measures be put in place to ensure that pre-treated and composted materials cannot be cross-contaminated. In practice, this means that there should be a dirty area where food waste is delivered to the site, an area where vehicles and equipment can be cleaned, and a clean area where the finished compost is stored. Ideally a physical barrier should be installed. Failing this, procedures should be in place to ensure that operatives loading food waste into the composter do not transgress into the clean area without taking precautions to ensure that they are clean. Procedures to achieve this have been set out for composters using Hazard Analysis and Critical Control Point (HACCP)5.

Compliance of the composting process with Animal By-Products Regulations need not be achieved for compost produced from catering waste that is generated, composted and used on a single premises provided no ruminant animals or pigs are kept on the site and the composting waste is not accessible to poultry.

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4. FINDINGS OF TRIAL

4.1 Background

The Neter 30 composter was installed on 20th April 2005. The trial period for the purpose of this report lasted until July 2007. However, there are a number of different permutations of food waste that require composting and so in practice the Eden Project will continue to trial different combinations of additives and operating conditions in order to improve its knowledge of the composting process. It is hoped that others considering or already using similar technologies can learn from the Eden Projects experience.

During the trial period in question, a total of 33 different treatments (see table 1) were tested involving different mixtures of feed-stocks and running parameters. The number of treatments reflects not only a desire to gain a wide knowledge of the different permutations of feed-stocks, but also the reality of an operational environment in which volume and types of food waste available as a feed-stock are variable. A number of different combinations of run and wait times and fan speeds were also trialled to determine optimum operating conditions for the aeration and mixing of inputs.


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Table 1: �Effects of feed stock treatments T1 T33 on temper atures, pH and moisture contents measured at sampling point A (figure 1) at which thermophillic conditions should be well established� Turn cycle Temperature Category No Treatment Wait (h) Run

(min) Fan speed

(m s-1) n Range Mean (SD) pH (SD) %

moisture (SD)

Progress A/D/U/S (Ascending,

Descending, Uneven or Stable)

T1 Food waste + carbon 4 12 7.8 76 20-34 28.5 (2.89) - - U T3 Food waste + carbon 4 12 7.8 21 28-40 36.2 (2.95) - - U T2 No feeds 4 12 7.8 19 21-27 23.6 (1.80) - - S T23 Food waste + green waste + carbon 2 6 3.2 10 36-39 37.0 (1.33) 4.3 (0.14) - S T33 Food waste + green waste 8 8 3.2 22 37-43 39.4 (1.56) 4.4 (0.05) 59.6 (0.74) S T17 Food waste + carbon 2 6 3.2 5 37-42 38.6 (2.07) - - A

1

T24 No feeds - - - 38 30-49 38.7 (5.38) 4.6 (1.05) 27.7 (-) A T5 Food waste (


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4.2 Effectiveness of composting process 4.2.1 Temperature

The temperature of the composting mass was measured through the built-in temperature sensors, the use of temperature probes and through data-loggers that were passed through the machine between 28/4/2006 and 10/7/2007.

Thermophilic temperatures have been achieved at some point within the composter since August 2005 and usable compost is being produced. However, frequent, and at times considerable, teething problems were experienced at the beginning of the trial.

Initially, problems were centred on the excessive moisture content of the food waste. Indeed during the first four months of the trial, temperatures within the vessel were insufficiently high to produce compost. A period during which only green waste was fed into the machine helped to stabilise the process before food waste could be re-introduced.

The temperature of material within the composter was monitored at sampling points throughout the vessel. However, it was the impact of feed-stocks on the temperature between sampling points A and B (see fig 1, page 11) which was of greatest interest since themophilic temperatures (55 - 65= C) would be required in this section of the vessel in order to ensure that the process was operating optimally.

Temperature data provided by the internal sensors indicated that the majority of feed-stock treatments (22 out of 33) did not result in thermophilic temperatures being attained between sampling points A and B, thereby representing non-functional states at that point (see table 1). The remaining eleven treatments did result in temperatures at or above the minimum required for thermophilic processes to take place

Whilst achieving thermophilic conditions near the front of the vessel is desirable for the effective and efficient operation of the Neter 30 composter, compost can still be produced as long as thermophilic temperatures have been achieved at some point within the vessel. And this was the case during much of the trial period with the exception of the period between April and August 2005 (see figure 3). Additional temperature data provided by the data-loggers placed in the composting vessel between 28/4/06 and 10/7/07 indicated that:

• during the period in question, temperatures increased in the machine with progress through the vessel; and

• when temperatures in the vessel were higher, the rate of composting was faster, and the transit time of material through the vessel was shorter.


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Figure 3

Interestingly, for 60% of the periods during which thermophilic temperatures were achieved at points A and B, green waste made up a significant proportion ranging between 100 - 33% of the feedstock. The biggest temperature spikes achieved during treatments 9, 10, 26 and 27 (see table 1) were also achieved when green waste made up a significant proportion of the feed-stock.

4.2.2 Acidity

A strong relationship was also observed between acidity levels of the feed-stock and the rate of change from mesophilic to thermophilic conditions. The most effective treatments produced pH values of 5.9 and 7. Eden Projects food waste was generally measured at pH5, prior to treatment, but dropped quite rapidly following the shredding process on entry into the composting vessel. The lower pH values that resulted from the food waste were generally associated with a slower transfer from mesophilic to thermophilic conditions between sampling points A and B.

4.2.3 Moisture levels

Moisture levels in the materials of between 55% and 65% and pH values of between 4 and 5 were associated with a cluster of lower temperature readings. These conditions occurred when macerated food waste was added with the wrong balance of accompanying feed-stocks. They were also associated with periods of electrical/mechanical breakdown resulting in materials at the front end of the composter not being mixed or moved for a period of time. This situation allowed acidogenic fermentation to take place in the macerated food component.


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Once acidic conditions became established at the front end of the compost, they tended to persist. Better conditions could be re-established through the addition of large quantities of finished compost from the out auger through the foremost inspection hatch, or in later treatments through the hopper system. Suspending the addition of feed-stocks for a period of several weeks also tended to increase pH, though this could not be guaranteed. The relationship between moisture, pH and temperature is set out in figure 4 below.

Figure 4

4.2.4 Rate of progress of composting mass A range of markers of varying sizes and shapes were placed in the composter in various locations to determine the rate of progress of the composting mass through the machine. These included rubber balls of varying sizes and densities and plant labels cut to different lengths (see fig 5), the aim being to determine whether objects of different sizes and weights would pass through the composter at different rates of progress. The progress of the larger balls was also used to assess the risks of damage or loss to data-loggers of a similar shape and size that would be used to monitor the temperature of the compost. In addition to the markers, some feed-stocks were used to mark the point of change between two treatments. For example, large pieces of shredded plant material present in green waste were used to track the progress of compost mixes containing this feed-stock.


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Figure 5 The marker tags took between 150 and 255 days to pass through the vessel. The size of the tags did not seem to have any significant bearing on their rate of progress through the vessel. Once it had been established that the risk of loss of, or damage to the dataloggers was low, nine egg dataloggers were placed into the composting vessel at a point close to the foremost inspection hatch. These provided temperature data and transit times for discrete batches of compost material as they passed through the composter. These took on average, 95 days to pass through the vessel. The main influences on the rate of progress of materials through the vessel were the volumes of feedstock loaded into the vessel, and the rate at which finished materials were removed at the out-auger.

4.3 Effectiveness of compost as a horticultural pro duct

Though there was always an intention to use the compost produced by the Neter on the Eden Project site, the principal driver for the trial was the need to reduce waste from catering operations. Though the composting initiative has succeeded in reducing the weight of catering waste sent to landfill by approximately 29% (April 05 to July 07), unless the compost produced was suitable for use on the Eden Project site, a waste problem albeit reduced, would persist. Moreover, if good compost could be produced by the Neter, this would reduce the need for the Eden Project to purchase compost from external sources, thereby saving money. It was considered that the compost might be suitable both as a growing and a mulching medium. Three trials were therefore conducted to assess the suitability of the Neter compost for use as a growing medium and a further three trials were conducted to assess its suitability


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as a mulching medium. The detection of any potentially phyto-toxic effects was of great importance since the presence of such would severely restrict the utility of the compost.

4.3.1 Growth medium trials

The trials were conducted on two commonly grown vegetables:

• Lactuca sativa - Little Gem lettuce (two trials) • Lycopersicon esculentum - Gardeners Delight tomatoes (one trial)

The progress of vegetables grown in 100% Neter compost was compared with that of those grown in a commercially available, peat free preparation used for the majority of propagation and container growing at the Eden Project. Mixtures containing different ratios of Neter compost to the peat free compost were also prepared.

Importantly, no signs of phyto-toxicity were found in any of the plant trials conducted. Measurements of plant growth in the Neter compost produced variable results. Growth in the lettuce was substantially increased by the presence of Neter compost in the mix. In fact the greater the concentration of the Neter compost, the stronger the growth in the shoots. Conversely, the growth of the tomatoes was weaker, the greater the concentration of Neter compost in the mix. It is not yet understood why this was the case though the trials took place at different times of the year and variations in feedstock and accordingly the end-product may have influenced these results.


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Figure 6

4.3.2 Mulching medium trials

The mulching medium trials were conducted on:

• Lactuca sativa Little Gem lettuce • Capsicum annuum - De Cayenne peppers • A newly planted mixed hedge

The lettuce and pepper seeds were propagated in the normal peat free preparation used by the Eden Project up to a point where small seedling plants had developed. Freshly produced Neter compost was compared with proprietary green waste compost (West Country Compost, Ecosci,) as a mulching medium. Plants were also grown in untreated compost as a control for the test. In the pot experiments with the lettuce and pepper plants, no significant differences were seen in shoot growth between the Neter compost, the West Country Compost and the control. Plant heights were only recorded in the pepper plant trial. These were significantly higher for plants treated with the Neter compost and West Country Compost than they were for those left untreated.


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In the field trial, the mean heights of the plants used in the hedge were not found to be significantly different amongst the different treatments applied. However, because all plants assessed in the hedge are hardy and long-lived, further assessment of height will be made over time. Mineral analysis of the soil under the hedge indicated that neither the Neter nor the West Country Compost mulches have had any significant impact on the mineral composition of the underlying soil to date.

Again, no signs of phyto-toxicity were observed during the mulching medium trials.

4.3.3 BSI PAS 100 test

The British Standards Institution Publicly Available Specification for Compost Materials or BSI PAS 100 test specifies minimum standard requirements for the processing of source segregated biowastes. The aim of the scheme is to give end users and specifiers the confidence that compost meeting the standard is quality assured, traceable, safe and reliable. It covers all the key elements of the composting process including:

• Process control • Input materials • Composting activity (sanitisation and

stabilisation) • Compost quality requirements • Product preparation

• Compost maturation • Compost sampling and analysis • Classification of compost • Labelling and marking • Monitoring and traceability

The Eden Project submitted three samples of Neter compost for testing. Two samples have passed the test, but one failed on stability, plant top growth, and on an unacceptably high level of contaminant particles (which in this case were predominantly shreds of office paper which had failed to biodegrade). A summary of the findings can be found in table 2 below. Table 2

Sample number PAS 100 upper limit 1 2 3

Sample date - 11/01/07 26/02/07 16/05/07 Passed or failed PAS 100 - Passed Failed Passed Probable treatment number & category (see Table 1)

- T21/T22 (2)

T23/T24 (1)

T26/T27 (4)

Human pathogens

Escherichia coli (Colony forming units (cfu) g-1

1000


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Copper (mg kg-1) 200.00 10.3 22.3 16.4 Lead (mg kg-1) 200.00 3.44 6.27 4.97 Mercury (mg kg-1) 1.00 4mm (% of air dry sample)

16.00 1.24 0.86 0.07

Stones in other than mulch >4mm (% of air dry sample)

8.00 1.24 0.86 0.07

Plant growth tests

Plants germinated (no. as % of controls)

80.0 93.3 93.3 103.0

Plant top growth (mean g plant-1 as % of controls)

80.0 93.0 74.7 89.8

*Particles were predominantly paper

4.4 Bioaerosol tests

Bioaerosol tests were undertaken by a representative from the University of Hertfordshire to assess the level of potentially harmful micro-organisms arising from the composting process. Air was sampled at eight stations situated in and around the WNRC to assess counts for total bacteria, total filamentous fungi and Aspergillus fumigatus.

The total number of bacterial colony forming units (cfu) m-3 present in the samples were less than the nominal reference value of 1000 cfu m-3 limit proposed by the Environment Agency (2001) in all except one site. The limit was breached at the sampling station next to the finished compost bin where a reading of 1780 cfu m-3 was taken. The reading was taken with the bin cover off. With the bin cover replaced, the reading dropped to 167 cfu m-3.

The count of total filamentous fungi exceeded the maximum of 1000 cfu m-3 at three sampling stations. However, the concentration of spores was considerably less than the level at which sensitisation might occur under conditions of continuous exposure. The report from University of Hertfordshire recommended that workers wear face masks as a precaution when working in the vicinity of the compost collection bin, when the cover is off at the feeding station and when accessing the biofilter.


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Aspergillus fumigatus was found at all stations but in all cases at significantly lower levels than the 1000 cfu m-3 limit and were largely within the normal background range. A summary of these findings is set out in table 3 overleaf.


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Table 3

Counts of colony forming units (cfu m -3) Sample Sample location Total

bacteria Total

filamentous fungi

Aspergillus fumigatus

1 Background On roadside footpath upwind of

the Waste Neutral compound 127 600 14

2 Biofilter

(uncovered) On top of the biofilter unit (figure 2) with cover open

200 1130 36

3 Filter tube End of the filter tube with the filter

removed 136 400 109

4 Compost bin

(cover on) Above the finished compost bin with the plastic cover sheet in position

167 430 42

5 Compost bin

(cover off) Above the finished compost bin with the plastic cover sheet removed

1780 1160 67

6 Food waste input Directly above the conveyor belt

during food waste loading operation

504 1736 18

7 Hatch 1 Open Hatch 1 (figure 1) during

loading of food waste* 736 722 41

8 Hatch 3 Open Hatch 3 (figure 1) during

loading of food waste* 263 345 41

*Sample collected 30 minutes after rotation was switched off. 4.5 Gas emissions

A schedule has been devised to test for concentrations of oxygen, carbon dioxide, methane, hydrogen sulphide and carbon monoxide using a gas analyser. The concentrations of oxygen and carbon dioxide were found to be well within expected and safe levels confirming that the composting processes within the Neter vessel are most likely operating aerobically as designed. The results of gas emissions tests undertaken to date are set out in table 4.


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Sampling date

Sample location & conditions

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pellets and green waste to be mixed with the food after it had been shredded. This was fitted to the in-feed auger connecting at a point on the vessel side of the shredder.

4.6.2 Operational and other issues The average daily amount of food waste composted at Eden between January 2006 and

September 2007 was 66kg. In the last six months (April 2007 to September 2007), this rate has risen to an average of 88kg per day. The principal reason for the relatively low throughput of waste is the difficulty which has been experienced in maintaining high front-end temperatures for the composting mass. As knowledge of the optimum feed-stock balance has increased, so the volume of food waste composted has increased. Down time resulting from mechanical breakdown and from falling temperatures within the vessel has also been a contributory factor to the relatively low throughput of waste.

Figure 6

Wood pellets are currently being used as a carbon supplement for the composting process. Though they are effective in promoting a good composting process, their use incurs a financial cost to the Eden Project. They are also inert, and do not contribute any microbial activity to the composting mass. Their biggest disadvantage is that they have to be transported to the site and are not part of the Eden Projects waste stream. The Eden Project recognises this issue and is exploring alternatives. A brief summary of materials trialled is set out below:


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• Initial trials of wood shavings have indicated that the compost mixture produced has a good structure. Supply of this material is limited.

• Dust from corrugated card has a high pH value (which helps counteract the low pH of the other feed stocks) but supply is limited.

• The Eden Project is considering using woody green waste as it is felt that this may help

both increase the carbon to nitrogen ratio and improve the structure of the compost • Shredded paper (towels and office) and corrugated card did not completely break down

- the shredded paper was partially responsible for the failure of one of the PAS 100 trials.

• Straw has been rejected as a feedstock because it tends to create a wattle and daub

effect within the vessel disrupting the mixing and flow of composting materials. The recent addition of a hopper may provide scope for using a mix of wood shavings, dust (from corrugated card) and woody green waste according to supply and the nature of the food waste being input.


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5. FINANCIAL APPRAISAL

5.1 Introduction

It is recognised that there are a number of factors that can influence the cost of running an in-vessel composter such as:

• The nature and volume of feed-stocks available • Staff costs and availability • Staff knowledge of the composting process • Potential for use or sale of the compost produced • Disposal costs for food waste

Summary of key findings:

• Thermophilic temperatures have been achieved at some point in the vessel for most of the duration of the trial. Adding substantial quantities of green waste to the feedstock appears to raise temperatures and pH levels and encourage good composting conditions.

• Excessively moist food waste tends to reduce pH. It is important to input the right proportion of green waste and carbon supplements when waste of this nature is fed into the composter.

• The compost has passed two out of three BSI PAS 100 tests. The failure was due to the lack of compost maturity, poor plant top growth and to the presence of shredded paper which failed to break down in the composter.

• Trials of the compost as a growing medium have produced mixed results though there is evidence that it is nutrient rich and in most circumstances promotes plant growth. All trials of the compost as a mulch have produced positive results.

• There are no concerns in relation to bioaerosol or gaseous emissions.

• Finding the right balance of feed-stocks has been difficult. At times the rate of the composting process has consequently been slow, resulting in relatively low levels of food waste being processed on a daily basis.

• Issues relating to the design of the front end of the composter have also slowed the rate at which food waste is being composted.

• The Neter 30 has been relatively easy to operate and understand and the process has been positively embraced by staff.


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• Economies of scale

Each individual organisation seeking to operate an in-vessel composter will have its own unique set of circumstances. However, there is much that can be learnt from the Eden Projects experience in this regard.

5.2 Set-up costs The set up costs incurred at the start of this trial were as follows:

Item Cost Neter 30 purchase and installation £179,000

5.3 Management, administration and research and dev elopment costs Because Eden has been trialling this technology, there have been considerable management,

and research and development costs associated with the project. These have tended to increase as the project has progressed (see figure 7), reflecting in particular, the time implications of undertaking scientific research, responding to operational issues and improving the design of the composter. The two graphs overleaf set out the costs incurred on a monthly basis for the last financial year (2006/7).


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Figure 7

5.4 Operational and maintenance costs

Operational and maintenance costs have tended to reduce over time (see figure 8), though there was a significant jump in costs in March 2007. This related to additional maintenance costs, incurred due to the connection of a hopper to the front end of the composter for feeding in wood pellets and green waste.


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Figure 8 If operational costs are separated from maintenance costs, a clearer indication of declining day-to-day costs can be observed. This may reflect the development of a better understanding over time of the factors that affect the operation of the Neter and a consequent reduction in operational input.

Figure 9

The Eden Project site may be atypical of most catering establishments with several dispersed outlets operating on site. Travel time between catering outlets and the WNRC is therefore probably higher than would be experienced in a typical catering scenario.


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5.5 Cost benefit analysis An analysis of costs and benefits has been undertaken in order to ascertain the value of

adopting such an approach to the disposal of food waste. The following assumptions have been made:

5.5.1 Assumptions Projected data for the period April 2007 to March 2008 have been used to reflect the most current operational cost data available. Projections are based on actual results for the first half of the 2007/2008 financial year. An assumption has been made that similar conditions will persist from October 2007 to March 2008 as no significant seasonal factors are currently influencing the amount of food waste composted. To illustrate this point though the overall level of food waste is likely to fall during the quieter winter months, it is still likely to exceed the amount of food waste being composted given the current rate of throughput. Data from 2006/7 is also set out to provide a comparison. Only costs relating to the operation of the Neter have been incorporated into this cost benefit analysis. The research and development, and management costs incurred by the Eden Project relating to the process of trialling this technology are disregarded since they are not relevant to the ongoing, operational costs of running a Neter composter. However, it is likely that some scientific input will be required by early adopters of this technology, if the degree of trial and error involved in establishing feed-stock combinations that work is to be minimised.

The Eden Project is fortunate to have scientific staff at hand who have been able to contribute from the start of the project to the process of producing compost using the Neter. Their input has been invaluable in the quest to establish a range of feed-stock mixes and operating conditions that will produce a safe and satisfactory compost, and a reasonably efficient process. Although a degree of trial and error has been inevitable, the scientific staff have been able to minimise the potential for error. Their monitoring has also meant that lessons have been learnt from unsuccessful feed-stocks as well as from those that have resulted in good composting conditions.

Technical support is available from Susteco, and no doubt from other providers of similar composting technologies. However, the availability of in-house scientific expertise has been invaluable to the trial. Other organisations considering installing in-vessel technology to deal with their food and green waste may not be so fortunate as to have access to such scientific expertise and may therefore need to consider the procurement of such advice in their cost projections. The estimate of savings from food waste being diverted from landfill is based on a cost of £67 per tonne during 2006/7 and £70 per tonne during 2007/8 for the collection and disposal of such waste. These costs are estimates only. Charges will vary amongst different waste carriers and waste disposal authorities. The £3 increase in charge between 2006/7 and


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2007/8 represents the increase in Landfill Tax over that period. From April 2007, Landfill Tax is set to rise by £8 per annum until 2010/11. The value of the compost produced is based on the cost of composted green waste which is supplied to the Eden Project at a rate of £11.58 per tonne. Smaller scale operations are likely to be purchasing compost at a much higher rate and therefore greater savings are possible. To some extent, the composted green waste can be displaced by the Neter compost. However, the high nutrient content of the Neter compost means that it will usually need to be mixed with a lower nutrient compost such as composted green waste in order to provide a satisafactory growing medium for plants on the site. Energy consumption is assumed to be constant at a rate of 48kwh per day. Electricity is assumed to be purchased at a rate of 7.8p per kwh, though a small amount of energy consumption will occur overnight when this rate is reduced to 4.8p per kwh. Wood pellets are purchased by the Eden Project for 31.25p per kg.

5.5.2 Annual running costs and savings

Running costs of the Neter 30 composter for the per iod April 2006 to March 2007 Item Quantity Cost Wood pellets 3,069.8kg £959.31 Operational staff time 1,678.25 hours £12,413.20 Maintenance and repair costs 43.5 hours £1,157.06 Energy consumption 17,264.5kwh £1,346.63 Total cost £15,876.20

Savings from Neter 30 composter for the period Apri l 2006 to March 2007

Item Quantity Saving Food waste diverted from landfill 22,906kg £1,534.70 Compost displaced 6,872 kg £79.58 Total cost £1,614.28

Projected running costs of the Neter 30 composter f or the period April 2007 to March 2008

Item Quantity Cost Wood pellets 4,896 kg £1,530 Operational staff time 1,139 hours £8,679.18 Maintenance and repair costs 28 hours £455 Energy consumption 17,264.5kwh £1,346.63 Total cost £12,010.81

Projected savings from Neter 30 composter for the p eriod April 2007 to March 2008

Item Quantity Saving Food waste diverted from landfill 32,500 kg £2,275 Compost displaced 9,750kg £112.91 Total cost £2,387.91


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The results and projections indicate that the composting operation is currently operating at a substantial loss. The main reasons for this situation are as follows:

• The amount of food waste being composted on a daily basis is relatively low both by comparison with the amount of food waste generated and with the capacity of the Neter 30.

• Operational costs are comparatively high for the scale of the operation. Should a

substantial increase in food waste be composted, economies of scale are likely to apply.

5.5.3 Environmental and social impacts

There are a range of environmental benefits that arise from Edens use of this technology, against the alternative of disposing of food waste in landfill. These are as follows:

• Composting food waste helps to avoid the negative environmental impacts that might

normally arise from disposing of such waste in landfill. For example:

� Food waste that is disposed of in landfill without further treatment will rot down. Often, it will be covered by other waste which markedly reduces the amount of oxygen available. These anaerobic conditions lead to the production of methane, a greenhouse gas that is estimated to be 21 times more powerful than carbon dioxide6. In some instances, the negative impacts of this will be mitigated where the landfill has facilities for generating heat and power from landfill gases. These facilities do not exist at the two principal landfill sites in Cornwall

� Food waste has to be transported to a landfill site and processed. The main environmental impact of this activity is the carbon dioxide emissions that arise from fuel consumption

� Putrescible waste at landfill sites is the main cause of unpleasant odours experienced in and around landfill sites.

• The Eden Project is practicing a more sustainable approach to the disposal of its food

waste and actively promoting this to its visitors and to a wider audience. Through this approach it can influence the way in which households, businesses and other organisations view and dispose of their food waste.

• Provided the compost produced is of appropriate quality and contains adequate nutrients, it can displace some of the compost purchased from external sources, thereby avoiding the use of fuel (and accompanying emissions) that would arise from the production and transportation of the compost.

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• By dealing with its food waste on-site, Eden is following the proximity principle which recognises the need to avoid passing on the environmental cost of waste disposal to communities that are not responsible for its generation.

The main negative environmental impact of using this technology is the embodied energy of the composter. For example, the machine is largely made of stainless steel. Energy will have been used in the reprocessing of steel and manufacture of the composting vessel. Energy will also have been used in the transportation of the machine onto the site. It should be noted, that though the machine uses approximately 48kwh per day, the electricity is currently supplied through a green tariff from renewable energy sources and therefore is rated as having no impact on carbon dioxide emissions.

5.5.4 Summary of costs and benefits

A summary of the costs and benefits projected for 2007/8 is set out below in table 5:


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Table 5 Financial:

Costs Benefits Item Value Item Value Wood pellets £1,530 Food waste diverted from landfill £2,275 Operational staff time £8,679.18 Compost displaced £115.77 Maintenance and repair costs £455 Energy consumption £1,346.63 Total £12,010.81 Total £2,390.77

Environmental & social:

Costs Benefits

Item Value Item Value Resources used in manufacture of Neter assuming reprocessed steel used (energy)

Increased CO2 emissions arising from energy use

Reduced methane emissions from 32.5 tonnes of food waste diverted from landfill

Reduction in methane emissions estimated to be in the region of 13,000m3

Reduced vehicle emissions arising from transportation of food waste and compost

Reduced CO2 and particulate emissions

Promotion of zero waste message to households

Potential impact on climate change and more sustainable resource usage

Managing food waste on-site (proximity principle)

Social and environmental impacts of managing waste off-site in a community that did not generate the waste are theoretically avoided


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5.5.5 Potential savings using Neter and other in-ve ssel technology

Though the Eden Projects composting operation is currently running at a financial loss, the following factors should have a positive impact on the cost-effectiveness of the composting operation:

• Improved knowledge of the process should lead to an increased throughput of food waste

• Greater use of alternative (to wood pellets) carbon sources from the Eden Projects own waste stream should reduce costs

• The cost of sending food waste to landfill is also set to rise substantially As landfill costs rise, the market for alternative processing methods will become more attractive to investors. Indeed, this is one of the intended consequences of the landfill tax escalator. This may lead to an increase in larger scale biogas plants or other food waste handling facilities whose operating costs will be immune to increases in the rate of landfill tax. Disposal of food waste through such a route is likely to be less expensive than sending waste to landfill. However, it is likely to take time for food waste handling capacity to be developed through the installation of such facilities, not least due to the scale of investment required and the time that it generally takes to obtain planning permission for such installations. It may be safe to assume for the next few years at least, that for most commercial organisations the only viable option for the disposal of food waste will be landfill along with its associated costs Table 7 overleaf sets out the potential savings that could arise at different levels of throughput and taking account of the impact of the landfill tax escalator which will increase the cost of disposal by at least £24 per tonne by the year 2010/11. The Government has not yet set out its plans for the level of landfill tax beyond 2010/11 and accordingly it is difficult to project savings from composting food waste beyond that financial year.


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Table 6 Kg/day food waste composted

Tonnes/annum food waste composted

Annual saving @ £70/tonne (2007/8)




Tonnes/annum compost * x 4 years

Value of compost @ £12/tonne �

Total saving (2007/8 to 2010/11)

100 36.3 £2,541 £2,831.4 £3,121.8 £3,412.2 43.56 £522.72 £12,429.12

200 72.6 £5,802 £5,662.8 £6,243.6 £6,824.4 87.12 £1,045.44 £25,578.24

400 145.2 £10,164 £11,325.6 £12,487.2 £13,648.8 174.24 £2,090.88 £49,716.48

600 217.8 £15,246 £16,988.4 £18,730.8 £20,473.2 261.36 £3,136.32 £74,574.72

800 290.4 £20,328 £22,651.2 £24,974.4 £27,297.6 348.48 £4,181.76 £99,432.96

1000 363 £25,410 £28,314 £31,218 £34,122 435.6 £5,227.2 £124,291.2

*assumes weight of compost produced is 30% of the weight of food waste composted, and that the proportion of feed-stock additives (green waste and carbon) to food waste remains constant.

� Savings based on Eden Projects costs and are likely to be higher for organisations purchasing lower quantities of compost.


�

5.5.5 Conclusions of financial analysis

Historically and at present, the Eden Project is diverting only relatively small amounts of food waste from landfill resulting in an estimated saving of just £1570.49 (food waste and compost) for the year April 2006 and March 2007. The amount of food waste composted is increasing, but even if Eden were to compost all of its estimated 84 tonnes of food waste per annum, a saving of only £5,880 would be achieved (at 2007 waste collection and disposal rates). This is less than current operating cost for the Neter. As landfill tax rises, and the composting operation at Eden becomes more efficient, it is likely that the breakeven point will be reached. However, it is unlikely that the capital cost of th

eden food waste technology trial · 2011-09-21 · food waste is collected from the central food...

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