~ Pergamon

pn: S0273-1223(97)OOI 90-X

Wal. Sci. Te('h. Vol. 35. No.9. pp. 121-133. 1997.C 1997 IAWQ. PublIshed by Elsevler SCIence Ltd

Printed in Grea' Britain0273-1223/97 $17'00 +0'00

SUSTAINABLE WATER AND WASTEMANAGEMENT IN URBAN AREAS

Ralf Otterpohl*, Matthias Grottker** and Jorg Lange***

• Otterpohl Wasserkonzepte. KanalstrafJe 52. D-23552 Lubeck. Germany•• Fachhochschule Lubeck, FD Siedlungswasserwinschajt. Stephensonstr. 3.D-23562 Lubeck. Germany••• ATURUS. Holbeinstr. 19. D·79100 Freiburg, Germany

ABSTRACf

Sewerage system and centralised aerobic wastewater treatment plants (WTP) should not be considered asthe only possible solution for sanitation. Systems with source control can avoid many problems of the end­of-pipe technology by respecting different qualities of wastewater and by treating them appropriately forreuse.

Different qualities of waste and wastewater in human settlements and appropriate treatment technologiescan be: I. low diluted faeces with/without urine and bio waste (composter or anaerobic digester), 2. greywater/aerobic biofilm plan1. 3. storm water (usage and infiltration) and 4. non-biodegradable waste (reuse

as raw material). In order to perform resource management, the material originating from agriculture shouldbe returned to the soil as fertiliser. Of similar importance is the organic material. This helps maintaining orbuilding up humus and creates a sink for carbon when the C-content in the soil is increased. Energy will besaved, too: energy-intensive aerobic treatment with nitrification is obsolete as well as the production of therespective amount of replaced artificial fertiliser. A pilot project for a new settlement for about 300inhabitants in LUbeck, Germany, shall demonstrate the feasibility of a new integrated system with vacuumtoilets and pipes for the collection of black water. This will be mixed with shredded bio waste and fed to asemicentralised biogas plant that produces liquid fertiliser without dewatering. Grey water will be treated indecentralised biofilm systems. Storm water is collected, retained and infiltrated in a trench system. This waythe expensive centralised sewera,e;e system can be avoided for this settlement.© 1997 IAWQ. Published by Elsevier Science Ltd

KEYWORDS

Sustainable sanitation, vacuum toilets, vacuum sewerage, wastewater treatment; biogas plant, renewable en­ergy, anaerobic treatment, digester, composter, constructed wetlands, domestic waste, bio waste, nutrients,agriculture, global warming, material intensity, sustainable communities, eco city, city planning

121

122 R. OTfERPOHL ellJ/.

DISADVANTAGES OF THE TRADITIONAL SANITATION CONCEPTOF INDUSTRIALISED COUNTRIES

Centralised wastewater treatment plants solve acute pollution problems efficiently and require relativelysmall treatment capacities per inhabitant. Flushing sewers can be a very energy efficient way of transport ifthey have a reasonably small length per inhabitant. However, there are several disadvantages that becomeexceedingly important with tOOay's world-wide promotion of this type of system with consideration of alarger time scale.

The traditional sanitation concept of industrialised countries produces linear material flows causing accumu­lation and mixes the food and water cycles. Reuse of material and directing the flows to advantageous placesis limited (Figure I). The question of carbon flows has to be considered in urban waste and water manage­ment (Strong and Arrhenius, 1993; Arrhenius, 1992). For phosphorus (P) Beck et al. (1994) consider theinfluence of the urban water management on the flows of P-bearing materials as the most important factor.On its way from the mines through the city and the urban drainage system P is converted from a rather im­mobile adsorbable form into a soluble form that ends up in the water bodies. Many of the disadvantages ofthe unified flushing sewer system listed below are well known, others are rarely addressed:

• Nutrient losses even with the best affordable treatment plants are over 20% for nitrogen (N), over 5% forphosphorus (P) and more than 90% for potassium (K). The discharged nutrients are accumulated in the

sea. P and K resources that are used to replace these losses are likely to run out within a time span ofconcern (order of magnitude of 10 human generations with a wide variation in different publications).

• High energy demand for destruction of the organic wastewater contents and for the nitrification. In addi­tion, the synthesis of ammonia from nitrogen for production of fertiliser is very energy intensive.

nitrogen

phosphatefron Africa

potassIum­mining "'­

FERTIUSER FACTORYAGRiCULTURE. "food

~ .....

( Bonly 10to 20"

High .

water.consumption

Figure 1: Linear mass flow in the traditional sanitation system of industrialised countries

• High pollution loads in the sewage sludge and missing potassium makes its use as an agriculturalfertiliser often impossible. Non-recycling of organic compounds of human- and bio waste to the soil does

Susulinable water and waste management in urban areas 123

not maintain the humus layer and does not create a carbon sink for carbon by increasing C-contents in thesoil (ArrtIenius, 1992).

• A high amount of water is necessary for flushing human wastes to the treatment plant (leads to disastersespecially in water scarce metropolitan areas).

• Hygiene problems in receiving waters after combined sewer overflows and WTP effluents. Severeproblems without adequate treatment in low-income countries (even existing plants often fail within acouple of years)

• The joint presence of sulphur (S) and heavy metals can lead to a mobilisation of the metals (Beck et al.,1994).

• High operation and rehabilitation costs for the drainage system and the sewage treatment plant. Most mu­nicipalities do not rehabilitate the average I % to 2% of the drainage and treatment system per year due tothe systems lifetimes of 50 to 100 years.

• Little sense of responsibility for the water cycle and the fate of pollutants is developed on the users sidedue to the invisibility and invulnerability (mainly by dilution, not by final degradation of chemicals) ofthe wastewater infrastructure in the local environment.

The effects of the mentioned points are not showing a 'doomsday scenario', They rather contain a strongpotential for a slow degradation of the performance of the natural systems used for food production and fish­ery, With such a development social injustice can be increased by rising prices for water and food.

The disadvantages of the unified flush-system indicates that the evaluation of new concepts and their com­parison to the traditional approach is necessary. Furthermore the propagation of this concept for world-wideusage requires further development of appropriate systems for different geographical and social conditionswith consideration of global requirements.

EVALUATING THE SUSTAINABILITY OF SANITATION SYSTEMS

It is very difficult to find a scientific approach to define the sustainability of sanitation systems. Somepossible methods for additional information about the performance of systems are Life Cycle Analysismethods (SETAC, 1993), the MIPS-concept (Material Intensity per Service unit, mass and energy related)(Schmidt-B1eek, 1993) and the Sustainability Index (land usage) (Moser, 1994). Without a proper method ofassessment, the concept of sustainability is often misused by labelling slightly improved conventionaltechnology "sustainable". For the urban water cycle the following 4 principles should be considered:

• less energy and material usage for the same or more activities;

• no transfer of problems in space or time or to other persons;

• no reduction or degradation of water and soil resources, even in the long run,

• Integrate humans activities preferably into the natural cycles;

These ideal principles can guide to the improvement of drainage and treatment concepts. The traditional uni­fied flushing sewer system does not allow to follow most of these principles.

A MIPS-study is presently carried out to compare the traditional system with the vacuum system proposedin this paper and a system based on composters for faeces with bio waste (ReckerzUgl, 1997). Theprovisional results indicate some strong advantages of the decentralized and semicentralized systemsconcerning material intensity (conventional system: high intensity for sewerage systems), energyconsumption and loads of pollutants and nutrients emitted to the receiving waters. Further results arepresented below. The disadvantage of this method is that the same service of the systems has to be assumed.

124 R. OlTERPOlll. el al.

It might be more realistic to include the fertiliser production that is necessary if N. P and K are wasted by therespective system.

CLASSIFICATION OF DOMESTIC WASTE AND WASTEWATER WITHREGARD TO DIFFERENTIATING SANITATION SYSTEMS

The process of defining a different sanitation concept starts with an assessment of the various waste andwastewater fractions. Classification of the residues in human settlements leads to the four groups repre­sented in table 1. In addition appropriate treatment methods are indicated.

TABLE 1:

Classificationfor treatment

CLASSIFICATION OF DOMESTIC WASTE AND WASTEWATER FOR ADEQUATETREATMENT PROCESSES

appropriatetreatment

Group I:Biodegradable solid waste and low-dilutedfaeces with urine (or further separation ofurine)

Group 2:Grey wastewater (grey water) frombathrooms. washing machines and kitchenwith little nutrients

Group 3:Storm water runoff

Group 4:Non-biodegradable solid waste(small fraction with reuse of packages)

anaerobic orcomposting(urine processing)

aerobic withbiofilm plants

usage and localinfiltration

processing to rawmaterial

related to thefood cycle

related to thewater cycle

related to thewater cycle

Group I contains nearly all of the nutrients nitrogen, phosphorus and potassium. Most of these are concen­trated in the urine. The separation of faeces and/or urine from the domestic wastewater can be considered asthe most important step towards sustainable water concepts. Besides composters which are often not ac­cepted by people and which should be further developed vacuum toilets connected to anaerobic digestersseem to be a promising technology to drain faeces with urine and treat them together with bio waste.Vacuum toilets were chosen for the integrated concept described in detail below, since they seem tocombine a high comfort with reliability. Alternatively separating flushing toilet systems or systems with avery small amount of water needed for flushing could be used.

The development of optimised toilets is a key issue for the implementation of sustainable sanitation systems.It is also important to help by saving clean water that becomes increasingly scarce in many parts of the world.

Even the latest models of toilets often have a rather poor performance although they often use large amountsof water. A scientific optimisation with proper modelling and considering of separation demands would bevery beneficial. One first step can be to start installing urine separating toilets even without making furtheruse of the separation for now. These toilets exist (Lange and Otterpohl. 1997) and can reduce the water de­mand for flushing to a total of less than 10 litre per person and day. The urine bowl needs a flush of just

Sustainabk watcr and W,L'IC managcmcni in urban arC:L' 12~

about 200 ml, the faecal bowl can be adjusted to local requirements (e.g. gradient of pipes). These toilets areextremely cost effective and allow a future change to sustainable systems. Based on this source control sys­tem the ANS-system (Larsen and Gujer, 1996) and even biogas systems can be established in future.

In the 19th century Liernur (1873) constructed a differentiating system in the Netherlands with vacuumpipes for black water. The background was not to pollute the water and to get nutrients back to the soil. Thistype of system served thousands of people in Amsterdam and other cities. However at the time there weresome technical problems that hindered a further spread out.

URBAN WATER MANAGEMENT AND GLOBAL WARMING

Carbon plays an important role in the material balances of urban drainage systems. This problem is coupledwith the usage of fossil energy (COremissions) for aerobic treatment and nitrification, that also causes a faslrelease of C to the atmosphere (whereas anaerobic treatment can replace some fossil energy). II is also aquestion of the possible creation of a carbon sink in the top soil by the application of treated matter thatcontains C. This is about the only possibility of anthropogenic action against global warming besides savingfossil energy and not reducing wooded areas. In addition a rising content of C in the soil improves thefertility and a further degradation can be stopped (Arrhenius. 1992). The traditional flushing system returnseven under the best circumstances only a small proportion of the carbon to the soil even when all sludge isused in agriculture. Figure 2 presents a comparison of the best possible scenario of a traditional system withcomposting of bio waste (still rare in urban areas) to a system with separate anaerobic treatment of faeces,urine and bio waste.

~=---

=---

co, . EmlaUon. to~

/'_c

\4OOlCC • FlXIIlon In 101Ipluo Irlnopo1t

_CC • Fballlon In 101Ipluo IrInOjlOf\

Traditional wutltwatltrtreatment plantplua compoatlng ofblow..t.

81og.. aystem forfa_a, urln.and blowaatlt

Figure 2: Estimated carbon balance for the traditional treatment and a system with separate anaerobictreatment of faeces, urine and bio waste

For the wastewater treatment plant the usage of sludge in agriculture was assumed. In practice this is oftenimpossible because of high concentrations of heavy metals and micropollutants in the sludge caused by the

126 R. OTIERPOHL tlal.

unified collection and treatment. For the energy balance the anaerobic system saves the aeration energy andproduces valuable gas replacing fossil resources for example in a heat and power generating plant.

SUSTAINABLE SANITATION CONCEPTS FOR URBAN AREAS IN­CLUDING DIFFERENT CLIMATES

There is a wide range of possible solutions for more sustainable sanitation systems respecting the differentqualities of wastewater. There are many traditional concepts in the different areas of the world with certainadvantages. Some options of economically and technically feasible and more sustainable sanitation conceptsare:

1. Vacuum closets (VC), anaerobic treatment with hygienisation and co-treatment of organic householdwaste (biogas plant), application of the produced liquid fertiliser to agriculture in growth periods(decentralised/semicentralised biogas plant with vacuum pipes, optional larger biogas plants on farmswith a capacity related to nutrient requirement and with storage, gas usage).

2. Composters for faeces and organic household waste, application of compost to agriculture (some care ofusers necessary, houses of up to 3 storeys, diluted leachate used for garden, compost removal in appro­priate season). Moisture has to be kept in a range of about 50 to 60% - difficult in warm climates.

3. Drying of faeces in warm climates in desiccation toilets with solar panels, moisture < 20% (Winblad,1996), easy control (the dryer the better). Problems in countries with wet anal cleaning, reuse in agricul­ture after sufficient storage. Not appropriate in colder climates - high energy consumption.

4. Traditional flushing sewerage with urine separating toilets (save most of the water, too), decentralizedstorage of stabilised urine and release by remote control according to required transport time in thesewerage systems in early morning hours; treatment of the concentrated nutrient rich flush in WTP(Larsen & Gujer, 1996) (Implementation within the existing structures is possible, sufficient gradient ofsewers necessary).

5. Water closets (WC), aerobic treatment without nitrification, digester for sludge, usage of effluent for irri­gation and as fertiliser, unpolluted sludge to agriculture (Only for countries without winter seasons orwith greenhouses or aquaculture).

Table 2 gives a tentative overview of some advantages/disadvantages of the different concepts. The table ismeant to give a rough idea, however, general statements are difficult due to the wide variety of aspects foreach row. The traditional system of industrialised countries with flushing toilets (WC), central sewerage sys­tem and advanced treatment plants is shown in column no 6. for comparison. Social and/or religious con­straints have to be considered for all concepts when they shall be realised in a certain place. All of the non­separating concepts can be modified with source control of urine, too. For the strategies I to 3, grey watertreatment has to be carried out in central or decentralized facilities.

TABLE 2. TENTATIVE QUALITATIVE COMPARISON OF DIFFERENT SANITATIONCONCEPTS, INCLUDING THE TRADITIONAL APPROACH OF INDUSTRIALISEDCOUNTRIES (THE WC)

sanitation concept no. 1. VC- 2. 3. 4. Urine 5. WC- 6.concern Digester Compost Drying separate irrigation (WC)

pathogens (rw= receiving waters) (op: + +op + -rw -rwgood operation)

Susf,'linable water and waste management in urban areas 127

carbon sink against global warming +

water consumption +

++ ++

++ ++

++ ++

needed possible

++ ++

++ ++

++

+ reuse

no no

+ +

+

+

++

++

++

+

no

+

+

++

+++

+

++

+++

++

++

+

++

+

+

++

++

possible

nutrient recycling to agriculture(proper dosage in growth periods nec­essary)

co-treatment of household bio waste

arid regions

overall energy efficiency

climates with winter seasons

centre of large cities

rural areas

smaller towns and outskirts

operation and maintenance

low-tech solution ++ ++

+ System behaves positive, is adequate or appropriate

Vacuum toilets in concept no. I can be replaced by flushing toilets with very little water usage or urine sepa­rating toilets. A good gradient for flushing sewers or other ways of transport will be needed then. Figure 3presents the main mass flows in sanitation concept no. I. This sketch shall represent the basic pathways ofmaterial flows in an idealised way. The cycle is not a cycle in reality but a concept, the pathways should bepreferably longer than to grow food with the liquid fertiliser just produced. It might as well be used onindustrial crops or for energy forests. The objective is to perform resources management by creating matterthat is needed and can be offered at market prices (of the future). A local market has to be developed as a

part of a sanitation concept. There are many areas with an excess of fertiliser due to a massive import offood for cattle. This kind of practice is non-sustainable anyway and has to be stopped if a sustainabledevelopment is wanted. However the areas with excess manure are not the ideal places for starting with newsanitation concepts.

t21l

no productionof artln.,.1fertlllaer

SOIL

\c.P.N~

R. O1TERPOHL el al.

Improvinghumu••011

gaIn of renewable energy

Figure 3: Mass flows in a possibly sustainable sanitation systems

The concept with vacuum toilets and biogas plant will be implemented in a pilot project of technical scale.Construction will be started in the middle of 1997. This project is described below in more detail.

A Pll..OT PROJECf FOR THE VACUUM-BIOGAS SYSTEM FOR UR­BAN AREAS

An integrated sanitation concept with vacuum toilets, vacuum sewers and a biogas plant for black waterwill be implemented for the new settlement 'F1intenbreite' within the city of LUbeck (Baltic Sea, Ger­many). The area with a total of 3.5 ha will not be connected to the central sewerage system. The system isplanned by the authors of this paper for the construction company Trautsch Bau that develops this area inco-operation with the city of Uibeck. The settlement will be inhabited by about 300 inhabitants and ismeant as a pilot project to demonstrate the concept in practice. However, all components of the projecthave been in use in different fields of application for many years and are therefore well devel~ped.vacuum toiletsare used in ships, aeroplanes and trains. There are already some implementations in apartment houses forsaving water. Unified vacuum sewerage serves hundreds of communities. Anaerobic treatment is in usein industrial wastewater treatment, bio waste treatment, on many farms and for faeces in ten thousands ofapplications in South East Asia and elsewhere. The system that will be built in LUbeck consists mainlyof:

• vacuum closets (VC) with collection and anaerobic treatment with co-treatment of organic householdwaste in decentralisedlsemicentralised biogas-plants, recycling of digested anaerobic sludge to agricul­ture with further storage for growth periods; use of biogas in a heat and power generator (heat forhouses and digester) in addition to other fuel (here: natural gas).

• decentralised treatment of grey wastewater in constructed wetlands (very energy efficient)

• storm water collection for reuse, collection of excess storm water in a through and drain trench for re­tention and infiltration (Grothehusmann, 1993).

The heat for the settlement will be produced by a combined heat and power generating engine which isswitched to use biogas when the storage is filled. It will also be used to heat the biogas plant. In addition

SlL~tainable water and waste management in urb.1O llre.U 129

there will be passive solar systems to support heating of the houses and active solar systems for wannwater production. A sketch of such a system is presented in figure 4. The figure is not meant for showingall the details but shall give an idea of the concept with collection and treatment of faeces.

At the digester a vacuum pumping station will be installed. The pumps have an extra unit in the case offailure. Pressure in the system is 0.3 bar operating both the vacuum toilets and the vacuum pipes. Pipesare dimensioned 50 mm to allow good transport by the air. They have to lie deep enough to be protectedagainst freezing and must have down-bows about every ~o metres to create plugs of the transported mat­ter. Noise is a concern with vacuum toilets but modem units are not more noisy than flushing toilets andgive only a short lasting noise.

Faeces mixed with the shredded bio waste (only black water for mixing) will be hygienised by heatingthe feed to 70°C for 30 minutes. The energy is reused by a heat exchanger that preheats the incomingflow. The digester shall be operated thermophilically at around 55°C with a capacity of 35 mJ• which ishalf of the size compared to mesophilic operation (around 37°C). However, problems may occur inoperation arising from high concentrations of NHJNHJ which are predicted to be around 2000 mg/l. Incase of difficulties, the operation will be switched to mesophilic conditions using an additional tank, asthe proportion of NH3 under mesophilic conditions is lower at the same pH-value. Another concern is theamount of sulphur in the biogas. This can be minimised by controlled input of oxygen into the digester orinto the gas flow.

The biogas plant is meant to be a production unit for liquid fertiliser as well. It is important to considerpathways of pollutants from the beginning. Import:J.!1t sources for heavy metals are copper o!.zinc .plated pipes for drinking water. These materials will be avoided and polyethylene pipes will be used. Thesludge will not be dewatered in order to have a good composition of the fertiliser and in order to avoidtreating the filtrate. The relatively small amount of water added to the black water keeps the volumessmall enough for transportation. There will be a 2 weeks storage tank for the collection of the digestereffluent. Biogas will be stored in the same tank within a balloon that gives more flexibility in operation.The fertiliser will be pumped off by a truck and transported to a fw:m that has a storage tank for 8 month.These tanks are often available anyway or can be built with little investment.

Decentralised treatment of grey wastewater should be done by biofilm processes. Appropriate technolo­gies with very limited space are aerated sand tilters, rotating disk plants and trickling filters (Nolde. 1995)with infiltration of treated grey water within the storm water storage- and infiltration system. Constructedwetlands are also a possible solution for urban areas - they can be integrated in gardens and parks. Greywater is relatively easy to treat because it has low contents of nutrients. There may even be a lack ofnutrients for incorporation during the start-up of the grey water treatment system. As soon as there is asufficient biofilm the micro-organisms can reuse nutrients released by lysis. Several projects on technicalscale have demonstrated the feasibility and good to excellent performance of decentralised grey watertreatment. These plants allow reuse of the water for toilet flushing, which is not economically feasible inthe LUbeck project because of the low water consumption of the vacuum toilets. Grey water inF1intenbreile will be treated in decentralised vertically fed constructed wetlands with sizes of 2 m2 perinhabitant. These are relatively cheap in construction and especially in operation. The pumping wells willserve as a grit chamber, for grease control and will have filters for larger particles above the waterline.The effluent will preferably be infiltrated in the drain trench system for storm water.

The infrastructure for F1intenbreite including the integrated sanitation concept will be pre-financed by theconstruction company and a private company where participating companies. planners and later thehouse- and flat-owners are financially integrated and will have the right to vote on decisions. Parts of theinvestment are covered by a connection fee. just like in the traditional system. Money saved by nothaving to construct a flushing sewerage system, by smaller freshwater consumption and by co-ordinatedconstruction of all pipes and lines (vacuum sewers. local heat and power distribution, water supply,

:\11 R. OTIERPOHL et uf.

phone- and TV-lines) are essential for the economical feasibility of this concept. The fees for wastewaterand bio waste charged later will cover operation, interest rates on additional investment and rehabilitationof the system. A part of the operation costs has to be paid for a part-time operator. but this also offerslocal employment. The company cares for operation of the whole technical structures including heat andpower generation and distribution, active solar systems and an advanced communications system.

, .,'#

vacu~­toiletaVC

I

II

I

~~'

\ LIi_II-l:!II

" "',- ....

" " " " "

TralUlport toqriculture

-~- .....AaAerobic rea'Mpr

JI44 vacuum PUDl"- \, \

I \, ,I I, I\ ,

-".::11/'"-- -"

Figure 4: Principle of the vacuum system for collection and transport of faeces with bio waste andsemi-centralised anaerohic treatment

The material and energy intensity of the structure is presently studied with the MIPS-method in compari­son to a traditional system at the Wuppertal Institute in Germany (RcckerzUgl, 1997). Material and energyintensity is less than half for the decentralised system as for a conventional central system serving a me­dium densely populated area (see table 3). For the central system most of the material intensity resultsfrom the construction of the sewerage system. The predicted effluent values hased on averages ofmeasurements of grey water effluent qualities are presented in comparison to average values of a moderntreatment plant with an advanced nutrient removal and good performance.

Table 3 indicates some major advantages for the new system which justify further research. Thecumulated savings of emissions to the seas and of energy- and material usage for an average lifetime of70 years for one person would be: ahout 700 m' of freshwater, 230 kg of COD, 4.2 kg of P, 42 kg N, 85kg of K, 10000 kWh of energy and about 160 tons of material usage. The saved emissions can replacefertiliser production from fossil resources and synthesis of nitrogen, 100. This can be calculated asanother 7 000 kWh of energy saved (Boisen. 1996). These numbers are important with respect to a largeworld population and decreasing fossil resources.

Sustainable water and waste management in urban areas 131

TABLE 3: ESTIMATED EMISSIONS, ENERGY CONSUMPTION AND MATERIAL INTENSITYOF THE PROPOSED SYSTEM COMPARED TO A TRADmONAL SYSTEM

Advanced traditional sanitation New sanitation system

COD

BODsTotal P

Total N

Total K

(** assumption, no data)

3.6 Kg/PIa

0.4 Kg/PIa

0.07 KglP/a

0.73 KglP/a

( > 1.4 Kg/PIa)··

COD 0.3· Kg/PIa

BODs 0.1· Kg/PIa

Total P 0.01· Kg/PIa

Total N 0.13· Kg/PIa

Total K ( < 0.2 KglP/a)*·

(. official measurements HH-AliermOhe•• assumption, no data)

Energy demand for water supply

(0.5 Kwh/m3) 25 kWh/PIa

(wide variation)

Typical demand for wastewatertreatment 85KWhlP/a

Total demand 12.5 W = 110KWh/P/a

Material intensity 3.6 tlPla(MIPS-study ReckerzOgl, 1997)

Energy demand for water supply

(>20% water savings) 20 kWh/PIa

Vacuum system ~5KWh/P/a

Grey water treatment 2 kWh/PIaTransport of sludge

(21month. 50 km return) 20 kWh/PIaNet win biogas (12.5 roo 110 kWhlP/a

Total production 5 Will - 43 kWhlP/a(computations from design procedure)

Material intensity 1.3 tlPla(MIPS-study ReckerzOgl, 1997)

FURTHER OPTIONS FOR INTEGRATED SANITAnON CONCEPTSBASED ON BIOGAS PLANTS

The interest in the integrated concept described above has dramatically increased since the first publication(Otterpohl and Naumann, 1993) and the beginning of the planning for the project in LUbeck. There are otherprojects where this type of concept shall be built. The system in general could well be cheaper all In all thanthe traditional system. This depends on the possibility to infiltrate storm water locally, whlch is just becomingthe standard approach. It also depends on the size of the area that is served and on the number of inhabitants.An optimum size may be an urban area with around 500 to 2000 inhabitants. Smaller units are feasible if theback water and bio waste mixture is only collected and transported to a larger biogas plant that would pref­erably be situated on a farm. The treatment of grey water can be done in an existing wastewater treatmentplant if the sewerage system is nearby. In some cases this is the most economical way. If a certainpercentage of the population is served by separate back water treabnent, nutrient removal can be Improved.At a certain proportion nitrification would be obsolete.

132 R. 01TERPOffi. et al.

The size of cities is of concern because of the transport distances. However even in metropolitan areas therewould be possibilities to deal with this problem. The liquid fertiliser or the raw back water-bio wastemixture can either be pumped or transported by rail out of peak load times for passenger transportation.These are questions of long-term planning in close connection to city planning. From the point of view ofsustainable sanitation, for food production and transport and for a closer contact of city dwellers to naturecities of the future should be developed in the shape of stars with rural areas in between.

The proposed system is based on vacuum toilets, but there are other ways to collect back water. Urine sepa­ration toilets and a type of pressure flush toilet with a lid instead of a water siphon to prevent smells (Langeand Otterpohl, 1997) that are both developed in Sweden can be used as well. The latter type needs a pipegradient above 5% at least to a collection pit. Further transport could be done by a vacuum or a pressuresystem. Systems based on biogas plants should have a heat and power generator if there is a demand of heataround the plant, typically in the settlement served by the system (colder climates). A charming conceptcould be the production of bio diesel with fertiliser from the digester. There are engines that can be run witha mixture of bio diesel and biogas.

CONCLUSIONS

The traditional sanitation concept has several severe disadvantages: it needs too much water, dilutes faecesand raises nutrient levels in the seas even with very advanced treatment. For the definition of new sanitationconcepts, waste and wastewater from settlements can be split into four groups: 1. Biodegradable solid wasteand faeces with urine (or further separation of urine), 2. Grey water (bathrooms, washing machines andkitchen), 3. Storm water runoff and 4. Non-biodegradable solid waste. There are several sanitation concepts,each with advantages and disadvantages under different conditions. A more sustainable sanitation conceptfor urban areas is:

• separation of faeces and urine with vacuum toilets and treatment with bio waste in biogas plants;

• decentraJised aerobic treatment of grey water in constructed wetlands;

• infiltration of storm water to avoid a centralised sewerage system completely.

A comparison for emissions to receiving waters, energy balances and material intensities show many ad­vantages of this system. The main disadvantage of this type of system is that it is incompatible with thetraditional sanitation system of industrialised countries. The system will be installed in a new settlementfor 300 inhabitants in the city of LUbeck. Germany. It is a system that may represent an adequate solutionfor comfortable sanitation in urban areas. Performance and actual costs of operation can be derived fromthis and future projects under planning now. If there is a clear advantage for this type of concepts, theycould be implemented in new settlements and in connection with the complete renovation of houses.City planning has to consider the effects of further application with a view on the existing sewerage andtreatment systems. Time for a finally complete change to the differentiating sanitation would be when theexisting sewerage and treatment plants are technically written off.

REFERENCES

Arrhenius, Eric (1992) Population, Development and Environmental Disruption - An Issue on Efficient Natural ResourceManagemenl,Ambio. Vol.21. No. I

Beck, M. B.; Chen, 1.; Saul. A.1.; Butler, D. (1994) Urban Drainage in the 21st Century: Assessment of new technology on thebasis of global material flows. Water Science 4< Technology. Vol. 30, No.2. ppl-J2

Boisen, Thorkil. (1996) (TV Denmark. Dept. of Building and Energy), personal information

Sust.'linable water and waste management in urban areas 133

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