Energy optimization considerations for wastewater treatment plants in South Africa – A realistic perspective

Rudi Scheepers*, Marlene vd Merwe-Botha**

*Arcus GIBB (Pty) Ltd, P.O. Box 3965, Cape Town, 8000, South Africa. Email: rscheepers@gibb.co.za

**WaterGroup (Pty) Ltd, South Africa ABSTRACT Engineers and wastewater treatment plant owners have historically not considered power consumption as a critical design parameter in the South African wastewater industry, as the country has experienced an

abundance of low priced electricity for many years. This picture has changed dramatically. ESKOM’s

introduction of energy tariff increases of 25% per annum over a three year period up to 2012, followed by further annual increases estimated at 7% over a 7 year period. To add to the pressure, the Department of Water Affairs is increasing regulatory pressure on municipalities to comply with stricter effluent discharge standards. Literature indicate that current trends are to opt for advanced treatment technologies with associated high energy requirements in order to achieve the more exacting effluent quality requirements. The cumulative effect is that energy has become the highest single cost item (along with man-hours) on the balance sheet of municipalities and a critical performance driver and enabler. Plant Managers are already faced with the challenge to reduce treatment costs with limited budgets, burdened by ageing plants with mechanical equipment which are not operated with energy efficiency as precursor. The net impact is that the ever increasing costs of providing municipal water services within the boundaries of legislation is likely to be passed on to the consumer via higher public municipal tariffs. It is has become imperative to optimize energy efficiency and develop opportunities for energy generation from wastewater and sludge as part of the municipal wastewater business. International best estimates indicate that energy gains and savings of 5-30% are realistic, and that 100% self-sustainability in power supply is possible. Local indications are that up to 60% of the energy requirements can be achieved by the implementation of cell lysis processes with CHP production. These opportunities can only be realized if the key players have a baseline from where to conceptualize and formulate a cohesive development plan to address the key risks associated with the water-energy nexus. The paper focuses on setting a baseline to support higher order energy considerations in the wastewater industry, in order to influence perspectives and advance principles and incentives that would guide regulators and parastatals in assuming a development role in a sustainable and compliance future municipal wastewater sector.

INTRODUCTION

Key issues are to be addressed if government, municipalities and water sector stakeholders (professional service providers and private operators) are to prepare adequately for a sustainable and compliant wastewater treatment industry. Apart from man-hours, energy is becoming the single most critical performance enabler and cost driver on the balance sheets of municipal wastewater treatment plants in South Africa, with potentially far reaching economic, social and environmental consequences. The cost of municipal services tariffs are escalating at a rate that exceed the ability of the consumer to pay, as is evident in the increasing number of municipalities that battle to achieve acceptable payment levels. Whereas this has previously affected smaller towns and municipalities, the trend is spreading to

also impact on cities and metropolitan municipalities (CoGTA, 2009). It is against this backdrop that the rationale that effluent quality requirements and the associated costs to achieve such qualities, must be assessed. Higher levels of service (e.g. waterborne sewers) and more advanced treatment technology (e.g. activated sludge BNR) are generally associated with higher costs. If higher levels of service are not affordable, the ability of a municipality to recover its costs is negatively affected, threatening the revenue base and the financial sustainability of the municipality. Energy efficiency is a critical component along the value chain of sustainable service provision and responsible life cycle infrastructure development. The global water sector is already seen to look beyond the ambit of conventional treatment to also concentrate on a sustainable relationship between water and energy (electricity). South Africa is already exploring and pilot-scaling project associated with the supply- and demand side in the greater uptake of energy from the wastewater sector (Burton et al. , 2009).

Water-Energy Nexus

Energy and water have a symbiotic relationship and wastewater treatment plants (WWTPs) contribute to this connection. WWTPs in the United States contribute between 0.1 to 0.3 % of the total energy consumption of the country (WEF, 1997). It becomes increasingly evident that the impact of the rising demand for both of these recourses is eminent. The global water industry is exploring methods of moving and treating water and wastewater that are environmentally sustainable and economically viable. This global approach is to balance these two resources are illustrated in Figure 1. Figure 1: Schematic illustration of the Water–Energy Resource Nexus showing the connectivity amongst the three entities in a balanced sphere. Over and above the risking demand for higher levels of service and technologies, climate change is also affecting the water cycle. Some of its impacts can be mitigated through technical developments and social, economic and environmental response, as is demonstrated in Australia. Key energy demand areas are: pumping over wide service areas, asset condition and pipe leakage, treatment by aeration and pumping raw and treated effluent (Global Water Research Coalition 2010, Turton 2008). Electricity cost has become an important driver to treat wastewater which results in new and amended technology introduced to the market in the last 20 years. The standard approach across the globe will be to optimize the equipment and systems for a sustainable and cost effective future. There is strong evidence that up to 15% of wastewater energy demand can be offset by biogas generation and CHP. Pumping represents upwards of 30% for wastewater, however, aeration presents up to 60% or more of

the usage for the service (Global Water Research Coalition 2010). The best opportunities seems for reducing energy demand seems to be linked to the high usage components.

Electricity Supply in South Africa

ESKOM generates 95% of South Africa‟s electricity and 45% of Africa‟s electricity that are exported to Namibia, Botswana, Zimbabwe, Mozambique, Swaziland and Lesotho. Coal contributes 92% towards the country‟s electricity supply (Eskom 2010). According to ESKOM‟s Annual report in 2009 revealed that South Africa is a net importer of water which the trend will continue in the future (Eskom 2009). The cost to generate energy from fossil fuels will increase as power generation is still a large consumer of water which accounts for about 2% of all water used in South Africa.

In January 2008 South Africa has experienced electricity shortages known as “load shedding” for the first time in history. According to ESKOM, various capacity limitations were experienced that resulted in reduced demand to the grid supply and affected the entire country in all economic sectors of industry for almost an entire year. The water sector was greatly affected by these impacts. To date the total effect of these power supply disruptions to treatment plants and pumpstations has not yet been completely investigated and quantified. It is however, fair to observe that the external and secondary costs incurred as result of downtime and damage to equipment and processes responsible for collection and treatment of wastewater is significant, and affected the end user, environment and the economy significantly. Since April 2008, electricity consumers have felt the effects of price increases, which compounded to a 260% increase including the last increase of 25,8% hike in April 2011. ESKOM however, has indicated that it would be applying to the National Energy Regulator of South Africa (NERSA) for further 25% increases for each of 2013 and 2014, which are the first two years of the next Multi -Year Price Determination (MYPD). If the applied increases are awarded, the compounded average electricity price would increase by more than five times in the seven year period from April 2008 to April 2014 (Moneyweb 2011). Both certainty and uncertainty indicators give rise to multiple questions posed in the wastewater industry:

Are wastewater collection and treatment facilities equipped to effectively adapt further power disruption events in the country?

Are treatment technologies upgraded and new facilities designed with an energy efficiency perspective and realistic electricity cost centers, preferable ringfenced, to manage and contain operational and maintenance costs?

How will the treatment industry in South Africa present itself by 2050 when the global water sector focuses on self-efficient treatment facilities?

Is the water regulator sufficiently cognizant of the trade-off between stricter effluent quality requirements and energy intensity to deliver such qualities with a shrinking technical skills sector?

Are municipal infrastructure funding agencies geared to evaluate energy requirements as a critical sustainability parameter over the asset life cycle chain when considering motivations for high-end technologies?

Is ESKOM putting sufficient and practical incentives in place to reward energy generation or savings initiatives by municipalities, and are avenues explored to partake in capital renewal projects with high uptake and energy benefits?

OBJECTIVE OF STUDY This study seeks to contextualize and illustrate current application and trends in the South African municipal wastewater industry as pertaining to treatment technologies, plant capacity, electricity consumption trends and good practices applied in electricity supply- and demand management. The paper also intent to raise discussion and awareness amongst the sector players regarding the respective roles in:

Viewing and planning for WWTPs as energy producers and cost conservers as opposed to a facility to „treat sewage‟ without any further benefit;

Initiate opportunities to have the first full scale self efficient WWTP in Africa in the near future;

Municipal wastewater practitioners, process controllers and scientists are scarce professions and critical enablers in realizing any opportunity associated with energy optimization, cost recovery and sustainable management and compliance.

METHODOLOGY

The methodology followed in the study is presented via specific subject areas as follows:

Situation Analysis of Existing Technology Types The Green Drop 2009 and 2011 Assessments were used to evaluate the various technologies (treatment processes) applied by municipalities across the nine provinces in South Africa (DWA 2009, DWA 2011). A framework was developed to categorize the various technologies, consisting of 16 technology types. Further simplification of the technology types was done by reducing the various technology types into three generic technology groups: i) Activated sludge processes and variations thereof, ii) trickling biofilters, iii) pond and lagoon systems. The approach was followed to use updated (2010/11) information where available and only revert to 2009 information where data was lacking. Where a plant comprises of two or more technology types, each type would count for one technology. Only municipal plants with a verification tract record were processed.

Trend Analysis in Technology Applications A total of 18 plants were selected (DWA licensing database, 2010) to determine the best spread of plants across the 9 provinces for technology trends assessment against the following assessment framework:

Assessment Criteria Reference Framework

Legislative requirements

Water use license, General Authorisation, previous Exemptions (General / Special Standard)

Environmental landscape Present Ecological State and Condition (PESC)

Technology levels employed (existing and new)

Low, medium and high-end technologies as available in market place

Municipal environment and technology impact.

CoGTA spatial analysis framework (Municipal size, Social-economic vulnerability, National Treasury (NT) classification, Audit outcomes, and the extent to which the municipality is undertaking all of their possible local government functions (as a %)).

The data results were processed to determine the movement in technology trends from recent-current process employed to current-future process planned or employed, in terms of the three broad technology types investigated. This study was conducted in cooperation with Water Research Commission and SALGA (Bhagwan et al. 2011).

Energy Consumption per Technology Types and Capacity The Green Drop Report (DWA 2011) was used to adopt data relating to municipal plant capacity and actual flow received at plants. These design capacities were used to determine the number of plants in micro, small, medium, large and macro size categories. The energy usage per unit process was derived work done by the USA Electric Power Research Institute (EPRI) Energy Audits (1994) and used to evaluate the energy consumption (kWh/day) on two levels:

Per plant capacity (size) category

For activated sludge and biofilters technology groupings* The energy consumption (kWh) per volume was evaluated according to the treatment processes of the plant. Only medium size plants (2-10 Mℓ/day) to a macro size plants where evaluated from published energy consumption data.

Energy as Running Cost in Municipalities Financial ring-fencing of water services provision is a legal requirement (Water Services Act of 1997) where it is stated that: “When performing the functions of a water services provider, a water services

authority must manage and account for those functions separately” (Sect 20.(1)). The above however leads to two problems statements which are:

Definitive information as to the extent of ring fencing is not readily available, although the Green Drop initiative is focussing more attention on this compliance parameter. Energy is a real and comprehensive element of the cost of the wastewater treatment service and should be recovered via responsible tariff setting, offsetting, etc.

Section 10 of same Act need to be complied with when formulating tariffs. This would require financial sustainability (adequate budget for O&M), recovery of cost reasonable associated with providing the service, the need for return on capital investment for the provision of the serv ice, etc (Moshidi et al. 2011)

As a first step to ensure cost reflective recovery of services cost as part of municipal financial sustainability, it is necessary to establish broad comparative and costing comparisons as pertaining to different treatment technologies in the municipal sector. To present such first order material as part of this study, linkage is made to studies undertaken with the Department of Water Affairs, Water Services Regulation in extracting actual figures from treatment plants that reported ringfenced costs for the respective treatment plants during the 2011 Green Drop Assessments. The baseline costing reported in “Municipal Wastewater Treatment: First Order Costing Of Capital And Additional Operations And Maintenance Funding Requirements Based On Risk Based Indices (DWA, 2009)” were used to expand and escalate on the cost configurations, which were based on actual tender prices in 2008 to provide for a 2011 baseline estimate.

Improved Application: Energy Efficiency Opportunities for improved efficiency are various, and attempt was made to comment on practical ways of optimizing energy efficiencies, as applicable to the technology types under discussion, in the following context:

Improved energy efficiency through demand side management: Integrate 1st order analysis data

from the energy utilization by typical types of wastewater treatment plants (WWTPs) in the country.

Improved energy efficiency through supply side management and energy generation: Projections of 1

st order analysis to various energy generation potentials mainly to large (10-25

Mℓ/day) and macro WWTPs (>25 Mℓ/day).

RESULTS AND DISCUSSIONS

Situation Analysis of Existing Technology Types

A total of 975 technology counts were made during the analysis of the data. Activated sludge plants (and variation thereof) counted the highest applications of 395, followed by pond systems (368) and biofilters (145). 100 counts were made in total for remaining processes such as Pasveer ditch, RBC, various package plant types and include unknown or poorly specified processes. Table 1: Summary of the various treatment technology types as depicted per province.

Wastewater Treatment Technology Types

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

PROVINCE

Technology # per provin

ce

Activa

ted

Slu

dg

e

Activa

ted

Slu

dg

e &

B

NR

Activa

ted

Slu

dg

e &

D

iffu

se

d A

ir

Activa

ted

Slu

dg

e &

E

xte

nd

ed

Ae

ration

Activa

ted

Slu

dg

e &

M

BR

A

ctiva

ted

Slu

dg

e &

S

BR

A

ctiva

ted

Slu

dg

e &

M

echa

nic

al

Ae

ratio

n

Ae

rate

d L

ag

oon

s/

Oxid

ation

Po

nd

s

Ana

ero

bic

C

on

tacto

rs

Ana

ero

bic

Pond

s/

Facu

lta

tive

Pon

ds

Bio

log

ica

l (T

ricklin

g)

Filt

ers

Pasve

er

Ditc

h

Ro

tatin

g B

iolo

gic

al

Con

tacto

rs

Packa

ge

pla

nts

Oth

er

Unkno

wn

or

no

t spe

cifie

d

Limpopo 75 13 3 0 0 0 0 0 44 0 0 14 0 0 1 0 0

Mpumalanga 94 39 4 0 0 0 0 0 24 0 1 22 0 2 0 0 2

Gauteng 69 24 19 0 1 0 1 0 2 0 0 19 0 0 0 3 0

North West 42 19 4 0 2 0 0 0 12 0 0 5 0 0 0 0 0

Free State 134 36 3 0 0 0 0 1 49 0 14 27 1 0 0 0 3

Northern Cape 75 11 1 0 1 0 1 0 52 0 2 6 0 0 0 1 0

KwaZulu Natal 158 58 2 17 5 1 1 4 38 0 7 21 0 1 2 1 0

Eastern Cape 146 45 4 0 0 0 1 0 61 0 2 19 2 2 6 2 2

Western Cape 182 65 1 4 0 0 2 2 57 0 3 12 3 3 3 1 26

Totals 975 310 41 21 9 1 6 7 339 0 29 145 6 8 12 8 33

975 1- 7:

Activated sludge and variations

i) 8 & 10 ii) Ponds and

lagoons

iii) 11: Biofilter

9 & 12-16: Other

975 395 368 145 100

Figure 2 shows the distribution of technologies across the technology types. Almost 38% of all WWTPs in the country use a type of lagoon or pond treatment system, with the majority (in number) found in the Eastern- Western and Northern Cape regions. Most of the macro size WWTPs are using activated sludge technology with various and additions like BNR (Biological Nutrient Reactor, MBR (membrane bioreactor), SBR (Sequencing Batch Reactor) and other systems, with the majority (by number) found in KZN, Western Cape and Gauteng. The third most common treatment technology is biological trickling filters which the Free State Province has the highest number (27). Figure 2: General treatment technology types in South Africa.

39540%

36838%

14515%

677%

Activated Sludge & Additionals

Lagoons and Various Ponds

Biological Trickling Filters

Other

Trend Analysis in Technology Applications

Analysis of the assessment results of the 18 test cases indicated the following trend:

Current Scenario: Oxidation pond systems account for 39%, activated sludge plants for 61% (of which 36% include BNR) and 6% package plants.

Future Scenario: Oxidation pond system will reduce to 17%, whilst activated sludge systems will increase to 78%.

The results indicate that a more complex and potentially costly level of technology (medium) enjoys higher preference to the low to medium level technology. Although this could be ascribed to effluent treatment requiring a higher level of technology, land availability, initial cost of expansion and repairs of existing versus capital cost of new system, etc, it is observed that this is not always the situation. Often, insufficient attention is directed towards investigating sustainable low to medium leve l alternatives, and/or that the long term cost implication (lack of skills, cost recovery, power consumption) of the high level technology is not realised. This is concerning as sustainability of higher level technologies may not always be within reach of some of the municipalities.

Figure 3: Technology level trends from 18 test sites with existing and planned upgrades

It also appeared from the study that in terms of demand growth, the trend is often not to resolve the process limitations and optimise the existing systems or to extend the existing plant and maintain the technology level, but to upgrade to a higher technology level as shown in Figure 3. This is disconcerting as not all municipalities are necessarily equipped to sustainably manage such a change in circumstances, specifically with regard to skills and financial resource availability. If therefore following the literature whereby it is reported that more sophisticated technology have higher energy, and therefore cost, requirements, then the results point towards a trend that energy-intensive technologies are opted for (i.e. BNR and extended aeration activated sludge systems) in preference to lower energy requirement processes (such as pond systems). The influence by the consulting engineer and the legal requirement for strict effluent standards, as well as the lack of feasibility studies that consider energy as a critical cost component when motivating for grant or other funding, are key considerations and a pivotal point to redress if energy efficiency is to be tackled in a resource-scarce future (Bhagwan et al 2011).

Energy consumption per technology types and capacity Following from the findings under the “Situation analysis of technology types”, the energy consumption

per variation can be expected to vary significantly across the vastness of the difference technology types. For purpose of 1

st order evaluation, the categories were regrouped under 4 main categories, as

discussed, in order to profile the results to a single technology type. Based on the data of the generic treatment technology, an energy consumption evaluation was conducted by using information contributed by the USA Electric Power Research Institute (EPRI Energy Audits, 1994) to evaluate the energy consumption in kWh/day for the two treatment technology types. Table 2: Energy consumption ranges for a typical trickling filter treatment technology across difference plant sizes (capacity) and per process unit

ENERGY REQUIREMENT FOR A TRICKLING FILTER TREATMENT PLANT

Process unit kWh/day

Micro Size

Plants

Small Size Plants

Medium Size Plants Large Size Plants Macro Size Plant

<0.5 Mℓ/d

>0.5 Mℓ/d

2 Mℓ/d >2 Mℓ/d 10 Mℓ/d 10 Mℓ/d 25 Mℓ/d 25 Mℓ/d 100 Mℓ/d

Pumping 22.59 22.59 90.35 90.35 391.31 391.31 925.92 925.92 3380.07

Inlet Works 6.74 6.74 26.95 26.95 48.64 48.64 89.82 89.82 334.18

Primary Clfrs 1.98 1.98 7.93 7.93 42.63 42.63 102.37 102.37 409.47

Trickling Filters 46.49 46.49 185.98 185.98 994.11 994.11 1669.56 1669.56 6189.54

Secondary Clfrs 1.98 1.98 7.93 7.93 42.63 42.63 102.37 102.37 409.47

Disinfection 0.13 0.13 0.53 0.53 2.73 2.73 17.83 17.83 70.01

Sludge Mngt 132.88 132.88 531.51 531.51 768.95 768.95 996.59 996.59 3587.45

Lights & Building

26.42 26.42 105.67 105.67 218.61 218.61 528.34 528.34 1585.03

TOTALS 239.2 239.2 956.8 956.8 2509.6 2509.6 4432.8 4432.8 15965.2

Consumption ratio (kWh/Mℓ)

478.41 478.41 478.41 478.41 250.96 250.96 177.31 177.31 159.65

The results presented in Table 2 indicate the kilowatt hours (kWh) per day used for each process unit in the treatment process. To determine the energy consumption per volume, the electricity use (kWh) is divided by the volume per Mega liters (Mℓ) of the plant size. The results appear in the bottom row. It is evident that the consumption rate per plant capacity unit decrease with increase in volumetric plant capacity. The results for small and micro plants could not be evaluated sufficiently as the EPRI baseline data was only available from medium size plants and above. It is probable that energy consumption rates will further increase for small to micro size plants. The process units that prescribes „pumping‟ relates to all various transfer pumping activities within and along the treatment process. Sludge management concludes to all activities that relate to sludge handling, digestion, processing and disposal. The 15% (145) trickling filters plants across the provinces contribute to the second lowest energy consumer per volume next to lagoons and ponds. From Table 3, it can be deducted that the energy consumption per volume for a typical activated sludge treatment systems are between 20 to 40% higher than trickling filter systems. Table 3: Energy consumption ranges for a typical activated sludge process across difference plant sizes (capacity) and per process unit

79185

330476

277

409

608

1,030

0

200

400

600

800

1,000

1,200

Lagoons Trickling Filter Plants

Activated Sludge Plants

Oxidation Ditches / Extended Aeration

Plants

ENERGY REQUIREMENT FOR ACTIVATED SLUDGE TREATMENT PLANT

Process unit kWh/day

0.5 Mℓ/d >0.5Mℓ/d 2 Mℓ/d >2 Mℓ/d 10 Mℓ/d 10 Mℓ/d 25 Mℓ/d 25 Mℓ/d 100 Mℓ/d

Pumping 28.53 28.53 114.12 114.12 507.71 507.71 1205.28 1205.28 4336.37

Inlet Works 6.74 6.74 26.95 26.95 48.64 48.64 89.82 89.82 334.18

Primary Clfrs 1.98 1.98 7.93 7.93 42.63 42.63 102.37 102.37 409.47

Aeration 70.27 70.27 281.08 281.08 1453.73 1453.73 4705.55 4705.55 17908.18

Secondary Clfrs

1.98 1.98 7.93 7.93 42.63 42.63 102.37 102.37 409.47

Disinfection 0.13 0.13 0.53 0.53 2.73 2.73 17.83 17.83 70.01

Sludge Mngt 159.30 159.30 637.18 637.18 1424.77 1424.77 1194.72 1194.72 4379.96

Lights & Buildings

26.42 26.42 105.67 105.67 218.61 218.61 528.34 528.34 1585.03

TOTALS 295.34 295.34 1181.37 1181.37 3741.45 3741.45 7946.28 7946.28 29432.67

Consumption ratio

(kWh/Mℓ) 590.69 590.69 590.69 590.69 374.15 374.15 317.85 317.85 294.33

With reference to the trends analysis results, it can be expected that energy costs will further escalate and increase if pond systems and biofilters are replaced with activated sludge plants. Whilst the main argument used for the increased implementation of activated sludge systems, it is notable that the majority of activated sludge plants do not necessarily deliver compliant effluent quality in terms of stricter phosphate, ammonia and nitrogen concentrations (DWA 2011). Anecdotal evidence is to the contrary, where a pond system is much more forgiving if appropriate resources are not allocated for maintenance and operations, as opposed to activated sludge systems which become a major health and public risk hazard if neglected. The balance of the argument also carries weight, whereby a densely and urbanized area will have the benefit of a centralized system where skills and resources could be pulled for a high performance plant and complaint effluent. The economies of scale in terms of lower energy consumption rates may then out-scale the use of other novel technologies. When comparing the South African energy consumption variation within a technology type (Figure 4), the difference between consumptions per technology type can be observed. High consumption figures are found with extended aeration plants, and lower consumption patterns for ponds/lagoons and biofilters systems. The exponential trend curve indicates the rapid increase in consumption as a direct function of the energy requirements by more sophisticated systems. Figure 4: Energy consumption ranges (kWh/Mℓ) for various types of WWTPs. The South Africa profile correspondents with patterns in the USA against similar technology types (EPRI Energy Audit, 2006). This baseline trend could be used to link with actual electricity costs, manpower

requirements, energy generation offsetting projections and many more studies, and further research is encouraged against this baseline. It becomes more important that design engineers advice municipalities of the impact of energy. Sector leaders could assist in the process to ensure energy costing as a pre-requisite to any funding, in order to allow the designer and municipality to determine appropriate energy efficient technology which is affordable and suitable to local conditions. The establishment of baseline information in terms of WWTP energy consumption may further improve the planning, implementation and monitoring systems for the operational staff.

Energy as a Running Cost in Municipalities Internationally the “Running Cost” or Operation Cost of wastewater treatment plant mainly includes the following components as a percentage of the monthly cost: Table 4: Running cost breakdown of a typical plant in a 1

st world country application

Description Percentage

Wastewater discharge fee (similar to the SA “Waste Discharge Charge System Levy”) 18%

Electricity cost 27%

Chemical cost 6%

Staff cost 18%

Maintenance and replacement cost 10%

Sludge disposal and transport 13%

Administration cost 9%

The South African scenario is quickly moving in the same direction where electricity becomes the main line item on the municipal balance sheet. Using 2008 actual tender pricing,(Moshidi et al. (2011) indicated that electricity made up 5% of lower end technology types budget, and 10% if more sophisticated processes are employed. If these figures are escalated to 2011, using an annual 10% escalation for all the components, except for electricity, where the NECSA figures (27% [2008], 31% [2009], 35% [2010] and 35% for 2011) are used, the electricity components increase to 11 and 20% respectively. Table 5: Breakdown of cost elements of two technology scenario WWTPs

20

11

Description

Low end technology plants High end technology plants

Percentage Cost (R/kℓ)

Percentage Cost (R/kℓ)

Maintenance 28% R 0.200 35% R 0.639

Staffing 52% R 0.366 31% R 0.559

Electricity 11% R 0.076 20% R 0.364

Chemicals 9% R 0.067 13% R 0.240

Full O&M 100% R 0.708 100% R 1.801

Annual municipal budget per cost centre

R 258,429.976

R 657,485.884

Further escalations (as reported) will place electricity on par with international trends, after a period of abundant and cheap electricity in South Africa. Figure 5: A comparative analysis of operational cost between SA- and international WWTPs (with specific reference to electricity cost)

From the above the following observations can be made:

the impact of electricity cost is going to have a substantial effect on the actual cost of the service, once again highlighting the need to ensure that the selection of technology take electricity costs into account and need to be as cost effective as possible;

it is critical that operations at the works must be effective and optimised and maintained to prevent works becoming unsustainable, which would include dedicated energy efficiency optimisation.

Improved Application: Energy Efficiency It may be economically viable and best practice for large WWTPs to invest in an energy conservation study when the facilities consumption cost reach multi-million Rand projects on a multi-year basis, and when the municipal policy prescribe to cleaner production and self- sufficiency principles. The savings to reduce its energy account by 5% per annum is a considerable investment to the municipality and to the municipal consumer base. Smaller treatment plants may not experience the benefit of such a study and may opt for simple energy savings opportunities to ameliorate the treatment process in the long term. Performance targets can be set for various treatment areas, plant life expectancies, machinery and instruments. (Deacon et al. 1998).

Furthermore, a detailed economic analysis of applicable energy saving options may assist to identify which options are best suited for effective implementation to a particular plant. Economic analysis models such as the present capital value of the plant and the investment repayment time for investing in energy saving initiatives can be determined. Despite the economic advantages of reducing the electrical consumption and cost for a WWTP, other objectives such as treatment quality must take precedence over just energy savings. The following table summarizes a range of practical energy savings opportunities that would benefit any size WWTP, from a demand side management perspective. Table 6: Energy savings applications against various plant equipment aspects (no priority assigned)

18

27

0 0 0 0 00

119

52

28

00

22

30 3135

0

wastewater discharge fee (SA situation

this would be a Waste

Discharge

Charge System levy, were applicable)

electricity cost chemical cost staff cost maintenance and

replacement cost

sludge disposal and transport

administration cost

International bencmark (%)

SA trend when using lower technology (%) (BF, OP)

SA trend when using higher technology (AS, BNR)

Energy Savings Opportunities for WWTPs

Area/Section Suggestion/Opportunity

Electrical Network

Introducing updated power factor corrections (PFC) control systems from the power supply line (Substation) to the WWTP.

Test all power supply cables for possible power leakages at damaged wire insulation including connection points.

Motor Efficiency

Motor efficiency programmes can be implemented by developing an in situ monitoring and diagnostic programme. A core replacement programme may also be beneficial to upgrade old low efficient motors. Various literatures show that careful selection of high-efficiency motors with high power factors can improve the economic benefit of replacing old standard efficiency motors as much as 30%. Energy efficient motors are more expensive, but the energy savings result to lower operating cost.

Motors may be oversized as much as 50%. Replace such motors with the correct size and efficiency.

Implementation of a variable speed drive (VSD) programme for appropriate motor technology for example mixers, lifting pumps and aeration.

Increase of pump impeller size or adjusting the size accordingly can ensure efficient application.

Introduce solar water pumping systems to suitable applications that only require pumping during daytime.

Oxygen demand requirements to oxidation ponds may be solved with floating solar aeration systems.

Gearbox Drives

The gearbox systems consist mostly of gears and bearings for mixers, aerators and smaller applications. The energy transfer loss from the electric motor to the gear system may be tremendous if the gearbox is oversized for the application and/or grease maintenance have not been regularly conducted. Various publications state that aeration accounts for 50-70% of a treatment plant‟s power consumption.

Pumps Select pumps based on existing flows with the ability to increase impeller size to handle larger flows. Use supplementary pumps to assist with peak flows.

Minimize the elevation change for a pump to lift liquids as far as possible.

Pumpstations

Introduce storage capacity during peak flow durations to reduce “on-peak” hour pumping capacity and additional emergency pumping.

Ensure that pumpflows are matched properly to avoid use of additional pumps.

Alternating pumps – The one pump must be turned off before another pump is started.

Generators

Large WWTPs with installed stand-by generators must be used regularly during “on-peak” hours which will reduce treatment energy consumption during such peak scheduled times and ensuring that such equipment are efficient during emergency procedures. The cost of fuel per kWh must be recognized to validate the viability.

Treatment Process

Aeration process with mixers or by other means to supply oxygen must match the oxygen required in the aeration tank. The installation of Dissolved Oxygen (DO) probes can be installed to continuously monitor the supply and requirement levels. The aeration is automated and controlled by the DO monitoring system. The disadvantage of course is the continuous maintenance of the DO probes. The energy savings does outweigh the maintenance and regular cleansing requirement of the probes. According to Elliot (2003) the energy required to remove the first 30% of the Biological Oxygen Demand (BOD) is 5%.

Energy Monitoring System

Introduce power use monitoring systems to equipment that is part of the critical treatment process.

Large instrumentation control systems are suggested to have alternative energy sources such as diesel generation or renewable energy systems to measure and control the treatment operations when main source electricity are not available for long time durations.

Other Components

Introduce photovoltaic (PV) solar panel or/and micro wind power generation systems with large energy storage for emergency lights and measuring equipment including computer systems.

Implement solar power for generating hot water to the building of the treatment facility.

Introduction to low energy light fittings for internal and external application with latter switching either through “daylight” switches or through remote sensing to reduce light usage on a treatment facility.

Overall management best practice

Optimize energy consumption and identify energy savings opportunities by means of an energy audit. Such audits require plant operational data and monthly electrical accounts for the plant. Drawings and data of electrical equipment will ease the process of such an assessment. The price structure of the plant‟s electrical account will benefit in understanding the cost structure for the WWTP during assessment stages. Issues such as electrical load management during peak demand periods must be clear and understood by the plant operations staff.

Elliot (2003) point out that there are energy savings opportunities from demand side management (DSM) programmes which includes reduction in energy costs by shifting the power consumption from “on-peak” to “off-peak” hours. Such options need careful consideration for large treatment plants. Small and seasonal WWTPs may benefit from such an opportunity.

From an energy supply point of view, the US-based Water Environment Research Foundation (WERF) can be quoted in their chemical analytical findings that sewage represents the potential of 9,3 times more energy to be derived from wastewater than is currently used to treat it (WERF, 2009). This statement accurately describes the relationship between supply and demand side opportunities. In South Africa, energy generation opportunities have been limited to feasibility studies and pilot-scale applications at best. Strong initiatives are starting to follow, for example the City of Johannesburg Combined Heat and Power (CHP) application which commenced in 2011 (Deacon, 2011). Combined Heat and Power (CHP) refers to the thermodynamics of cleaning and combustion of gas that will result in 60% of the energy source as heat and 40% as electrical power. CHP is done via prime movers such as generators or reciprocating engines, following a recommended course of cell lysis and biogas scrubbing. The value of the latter 2 processes is in its ability to disintegrate cell membranes with subsequent increase in biogas yield and the removal of impurities from the biogas to extend the life value of the asset and keep maintenance in balance. CHP is capable of producing 10.2 MW electrical energy and 256.8 MWh/d heat from 5 wastewater treatment plants treating 1 047 000 m

3/day in Johannesburg.

The Water Research Commission has commissioned a study to capture good practice in energy efficiency in South Africa as part of a global network with partners being UK and USA. A Compendium of Best Practice will be published in 2012/13 to reflect some of the developments and applications in South Africa.

CONCLUDING REMARKS AND COMPARISONS It is evident that the cost to generate energy will continue to rise and will increase drastically when fossil energy resources become a limiting factor on global scale. The nexus between energy and water has become a pivotal instrument to supply and treat water and wastewater within a sustainable environment. It is a fact that some of the equipment on current WWTPs has reached its useful life and need to be replaced very soon. Various opportunities present it through applying energy audits, ringfencing of cost centers energy efficiency improvement, reinvesting in appropriate technologies, cleaner production and high performance wastewater treatment in the municipal business through supply- and demand side management. A long-term aspiration that could be held in view is to see a self-sufficient WWTP on own soil in the nearby dated future. Europe is currently the global leader on energy efficient WWTP and there may be various reasons for setting the benchmark which may be due to available land constraints and resources including strict environmental regulations. Strass WWTP is the first treatment facility in Europe to reach a 108% energy

self sufficient plant, in terms of the process, carbonaceous and nitrogen conversions, mass flow and mass balance of the plant and energy efficiency. The additional 8% electricity produced is returned to Austria‟s national electrical grid for use. Table 7: Percentage self-efficient wastewater treatment plant in the world (Cao Ye Shi 2011)

Sweden

(Average of all WWTPs)

Czech Republic (Centre WWTP, Prague)

Singapore (Jurong WWTP)

UK (Average of the

WWTPs)

Switzerland (Werdhölzli

WWTP, Zurich)

Austria (Strass WWTP)

Energy Efficiency (%)

9% 83,5% 40% 50% 100% 108%

Unfortunately, the baseline information and practices are scarce and critical drivers are not focused on the water energy nexus and the risk and opportunity it presents. The non-compliance of WWTPs is underscored by the lack of technical and management skills to manage, maintain and operate plants to their design specification and capability (Manus & vd Merwe-Botha 2010). The development of a comprehensive Energy Efficient Resource Guideline for WWTPs in a South African environment is set in the horizon which will assist municipal decision makers, designers and plant managers with the integration of energy efficient systems into the design and operation of WWTPs.

Funding for Energy Efficiency Programmes Energy efficient initiatives require high initial capital outlay. The benefit is only evident when considering the life cycle cost benefit and environmental tradeoffs. Funding and financing agents that oversee projects against the Regional Bulk Infrastructure Grant (RBIG), Municipal Infrastructure Grant (MIG), Accelerated Community Infrastructure Programme (ACIP), and Development Bank South Africa (DBSA) based funding may benefit from a more direct interest, incentives and practical means to lead energy efficiency drives by local government. The United States of America currently have an energy efficient programme to upgrades refurbish WWTP by means of loans with zero interest obligations. Tax write-off incentives in the first year of the capital cost to reduce electricity demand encouraged municipalities to adoption such initiatives on their treatment plants. The Department of Energy (DoE) and ESKOM could introduce Energy Efficient Demand Side Management (EEDSM) subsidies for wastewater (sewage and industrial) to implement such initiatives which will further reduce the electricity demand in the long-term. Specific tariff schemes to wastewater treatment facilities could be provided for from ESKOM once a treatment plant has reached a certain percentage energy efficiency target. The details in terms of the financial implications of alternative tariff price scenarios still need to be investigated. Commitments between DWA, DoE, ESKOM, banks with green philosophies and other stakeholders could ensure early initiation of energy efficient policies and escalated interest in planning and implementation. European countries (e.g. the Netherlands) committed to reduce the total energy demand per annum for the treatment of water and wastewater by 2% until 2030. Such a commitment is a joint effort by everyone understanding the long-term outcome. “Save water saves energy: save energy saves water” represent the simplicity and yet the value in the energy water nexus for South Africa.

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