id44 paper191 scheepers r

8/17/2019 ID44 Paper191 Scheepers R

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Energy optimization considerations for wastewater treatmentplants 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: [email protected]

**WaterGroup (Pty) Ltd, South Africa

ABSTRACT

Engineers and wastewater treatment plant owners have historically not considered power consumption asa 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 byfurther 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 dischargestandards. Literature indicate that current trends are to opt for advanced treatment technologies withassociated 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) onthe balance sheet of municipalities and a critical performance driver and enabler. Plant Managers arealready 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 netimpact is that the ever increasing costs of providing municipal water services within the boundaries oflegislation 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 generationfrom 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 powersupply is possible. Local indications are that up to 60% of the energy requirements can be achieved bythe implementation of cell lysis processes with CHP production.

These opportunities can only be realized if the key players have a baseline from where to conceptualizeand formulate a cohesive development plan to address the key risks associated with the water-energynexus. The paper focuses on setting a baseline to support higher order energy considerations in thewastewater industry, in order to influence perspectives and advance principles and incentives that wouldguide regulators and parastatals in assuming a development role in a sustainable and compliance futuremunicipal wastewater sector.

INTRODUCTION

Key issues are to be addressed if government, municipalities and water sector stakeholders (professionalservice providers and private operators) are to prepare adequately for a sustainable and compliantwastewater treatment industry. Apart from man-hours, energy is becoming the single most criticalperformance enabler and cost driver on the balance sheets of municipal wastewater treatment plants inSouth 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 topay, as is evident in the increasing number of municipalities that battle to achieve acceptable paymentlevels. Whereas this has previously affected smaller towns and municipalities, the trend is spreading to

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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 toachieve such qualities, must be assessed. Higher levels of service (e.g. waterborne sewers) and moreadvanced treatment technology (e.g. activated sludge BNR) are generally associated with higher costs. Ifhigher levels of service are not affordable, the ability of a municipality to recover its costs is negativelyaffected, 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 andresponsible life cycle infrastructure development. The global water sector is already seen to look beyondthe ambit of conventional treatment to also concentrate on a sustainable relationship between water andenergy (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 tothis connection. WWTPs in the United States contribute between 0.1 to 0.3 % of the total energyconsumption 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 movingand treating water and wastewater that are environmentallysustainable and economically viable. This global approachis to balance these two resources are illustrated in Figure 1.

Figur e 1: Schematic i l lustrat ion o f the Water –Energy

Resource Nexus show ing the con nect iv i ty amongst the

three ent i t ies in a b alanced sphere.

Over and above the risking demand for higher levels ofservice and technologies, climate change is also affectingthe water cycle. Some of its impacts can be mitigatedthrough technical developments and social, economic andenvironmental response, as is demonstrated in Australia.Key energy demand areas are: pumping over wide serviceareas, 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 amendedtechnology introduced to the market in the last 20 years. The standard approach across the globe will beto optimize the equipment and systems for a sustainable and cost effective future. There is strongevidence 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 forreducing 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 toNamibia, Botswana, Zimbabwe, Mozambique, Swaziland and Lesotho. Coal contributes 92% towards thecountry‟s electricity supply (Eskom 2010).

According to ESKOM‟s Annual report in 2009 revealed thatSouth Africa is a net importer of water which the trend will continue in the future (Eskom 2009). The costto generate energy from fossil fuels will increase as power generation is still a large consumer of waterwhich accounts for about 2% of all water used in South Africa.


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In January 2008 South Africa has experienced electricity shortages known as “load shedding” for the firsttime in history. According to ESKOM, various capacity limitations were experienced that resulted inreduced demand to the grid supply and affected the entire country in all economic sectors of industry foralmost an entire year.

The water sector was greatly affected by these impacts. To date the total effect of these power supplydisruptions 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 anddamage 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 a260% increase including the last increase of 25,8% hike in April 2011. ESKOM however, has indicatedthat 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 PriceDetermination (MYPD). If the applied increases are awarded, the compounded average electricity pricewould increase by more than five times in the seven year period from April 2008 to April 2014 (Moneyweb2011).

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 powerdisruption events in the country?

Are treatment technologies upgraded and new facilities designed with an energy efficiencyperspective and realistic electricity cost centers, preferable ringfenced, to manage and containoperational and maintenance costs?

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

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

Are municipal infrastructure funding agencies geared to evaluate energy requirements as acritical 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 orsavings initiatives by municipalities, and are avenues explored to partake in capital renewalprojects with high uptake and energy benefits?

OBJECTIVE OF STUDY

This study seeks to contextualize and illustrate current application and trends in the South Africanmunicipal wastewater industry as pertaining to treatment technologies, plant capacity, electricityconsumption 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 afacility 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 professionsand critical enablers in realizing any opportunity associated with energy optimization, costrecovery and sustainable management and compliance.

METHODOLOGY


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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). Aframework 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 intothree generic technology groups: i) Activated sludge processes and variations thereof, ii) tricklingbiofilters, iii) pond and lagoon systems.

The approach was followed to use updated (2010/11) information where available and only revert to 2009information where data was lacking. Where a plant comprises of two or more technology types, each typewould 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 andtechnology impact.

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

The data results were processed to determine the movement in technology trends from recent-currentprocess employed to current-future process planned or employed, in terms of the three broad technologytypes investigated. This study was conducted in cooperation with Water Research Commission andSALGA (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 andactual flow received at plants. These design capacities were used to determine the number of plants inmicro, small, medium, large and macro size categories. The energy usage per unit process was derivedwork done by the USA Electric Power Research Institute (EPRI) Energy Audits (1994) and used toevaluate 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 theplant. Only medium size plants (2-10 Mℓ/day) to a macro size plants where evaluated from publishedenergy 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


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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 GreenDrop initiative is focussing more attention on this compliance parameter. Energy is a real andcomprehensive element of the cost of the wastewater treatment service and should berecovered via responsible tariff setting, offsetting, etc.

Section 10 of same Act need to be complied with when formulating tariffs. This would requirefinancial sustainability (adequate budget for O&M), recovery of cost reasonable associated withproviding 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 financialsustainability, it is necessary to establish broad comparative and costing comparisons as pertaining todifferent treatment technologies in the municipal sector. To present such first order material as part of thisstudy, linkage is made to studies undertaken with the Department of Water Affairs, Water ServicesRegulation in extracting actual figures from treatment plants that reported ringfenced costs for therespective 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 tenderprices 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 ofoptimizing energy efficiencies, as applicable to the technology types under discussion, in the followingcontext:

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 thecountry.

Improved energy efficiency through supply side management and energy generation:

Projections of 1st order analysis to various energy generation potentials mainly to large (10-25Mℓ/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 (andvariation 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, variouspackage plant types and include unknown or poorly specified processes.

Table 1: Summ ary of the various treatment technolo gy 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


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PROVINCE

Technology# perprovin

ce A c t i v a t e d S l u d g e

A c t i v a t e d S l u d g e &

B N R


D i f f u s e d A i r


E x t e n d e d A e r a t i o n


M B R


S B R

c t v a t e

u

g e

M e c h a n i c a l

A e r a t i o n

A e r a t e d L a g o o n s /

O x i d a t i o n P o n d s

A n a e r o b i c

C o n t a c t o r s

A n a e r o b i c P o n d s /

F a c u l t a t i v e P o n d s

B i o l o g i c a l

( T r i c k l i n g ) F i l t e r s

P a s v e e r D i t c h

R o t a t i n g B i o l o g i c a l

C o n t a c t o r s

P a c k a g e p l a n t s

O t h e r

U n k n o w n o r n o t

s p e c i f i e 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

9751- 7:

Activated sludge and variations

8 & 10Ponds and

lagoons

11:Biof ilter

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 inthe country use a type of lagoon or pond treatment system, with the majority (in number) found in theEastern- Western and Northern Cape regions.

Most of the macro size WWTPs are using activated sludge technology with various and additions likeBNR (Biological Nutrient Reactor, MBR (membrane bioreactor), SBR (Sequencing Batch Reactor) andother 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 Provincehas the highest number (27).

Figu re 2: General treatment techno logy typ es in South Africa.

39540%

36838%

14515%

677%

Activated Sludge & Additionals

Lagoons and Various Ponds

Biological Trickling Filters

Other


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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% (ofwhich 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) enjoyshigher preference to the low to medium level technology. Although this could be ascribed to effluenttreatment requiring a higher level of technology, land availability, initial cost of expansion and repairs ofexisting 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 highlevel technology is not realised. This is concerning as sustainability of higher level technologies may notalways be within reach of some of the municipalities.

Figur e 3: Techn olog y level trends from 18 test sites with exist ing and planned up grades

It also appeared from the study that in terms of demand growth, the trend is often not to resolve theprocess limitations and optimise the existing systems or to extend the existing plant and maintain thetechnology level, but to upgrade to a higher technology level as shown in Figure 3. This is disconcertingas 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 higherenergy, and therefore cost, requirements, then the results point towards a trend that energy-intensivetechnologies 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 engineerand the legal requirement for strict effluent standards, as well as the lack of feasibility studies thatconsider energy as a critical cost component when motivating for grant or other funding, are keyconsiderations and a pivotal point to redress if energy efficiency is to be tackled in a resource-scarcefuture (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


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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 wasconducted 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 cons ump tion ranges for a typical trickl ing f i l ter treatmen t techn ology acro ss

dif ference plant sizes (capacity) and per proc ess unit

ENERGY REQUIREMENT FOR A TRICKLING FILTER TREATMENT PLANT

Process unit kWh/day

MicroSize

Plants

Small SizePlants

Medium Size Plants Large Size Plants Macro Size Plant

0.5Mℓ/d

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

Consumptionratio (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 inthe treatment process. To determine the energy consumption per volume, the electricity use (kWh) isdivided 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 plantcapacity. The results for small and micro plants could not be evaluated sufficiently as the EPRI baselinedata was only available from medium size plants and above. It is probable that energy consumption rateswill further increase for small to micro size plants.

The process units that prescribes „pumping‟ relates to all various transfer pumping activities within andalong the treatment process. Sludge management concludes to all activities that relate to sludgehandling, digestion, processing and disposal.

The 15% (145) trickling filters plants across the provinces contribute to the second lowest energyconsumer per volume next to lagoons and ponds.

From Table 3, it can be deducted that the energy consumption per volume for a typical activated sludgetreatment systems are between 20 to 40% higher than trickling filter systems.

Table 3: Energy cons ump tion ranges for a typical act ivated sludge process across d if ference

plan t sizes (capacity) and per pr ocess u nit


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79185

330476

277

409

608

1,030

0

200

400

600

800

1,000

1,200

Lagoons Trickling FilterPlants

Activated SludgePlants

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

SecondaryClfrs

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

Consumptionratio

(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 escalateand increase if pond systems and biofilters are replaced with activated sludge plants. Whilst the mainargument used for the increased implementation of activated sludge systems, it is notable that themajority of activated sludge plants do not necessarily deliver compliant effluent quality in terms of stricterphosphate, 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 maintenanceand operations, as opposed to activated sludge systems which become a major health and public riskhazard if neglected.

The balance of the argument also carries weight, whereby a densely and urbanized area will have thebenefit of a centralized system where skills and resources could be pulled for a high performance plantand 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), thedifference between consumptions per technology type can be observed. High consumption figures arefound with extended aeration plants, and lower consumption patterns for ponds/lagoons and biofilterssystems. The exponential trend curve indicates the rapid increase in consumption as a direct function ofthe energyrequirements bymoresophisticatedsystems.

Figure 4:

Energy

consumpt ionranges

( kWh/Mℓ ) fo rvar ious types

of WWTPs.

The South Africa profile correspondents with patterns in the USA against similar technology types (EPRIEnergy Audit, 2006). This baseline trend could be used to link with actual electricity costs, manpower


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requirements, energy generation offsetting projections and many more studies, and further research isencouraged against this baseline. It becomes more important that design engineers advice municipalitiesof 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 energyefficient technology which is affordable and suitable to local conditions. The establishment of baselineinformation in terms of WWTP energy consumption may further improve the planning, implementation andmonitoring 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 thefollowing components as a percentage of the monthly cost:

Table 4: Running cost b reakdown of a typical plant in a 1 st wo rld country appl ication

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 mainline item on the municipal balance sheet.

Using 2008 actual tender pricing,(Moshidi et al . (2011) indicated that electricity made up 5% of lower endtechnology types budget, and 10% if more sophisticated processes are employed. If these figures areescalated to 2011, using an annual 10% escalation for all the components, except for electricity, wherethe NECSA figures (27% [2008], 31% [2009], 35% [2010] and 35% for 2011) are used, the electricitycomponents increase to 11 and 20% respectively.

Table 5: Breakdo wn of cost elements of two technolo gy scenario WWTPs

2 0 1 1

Description

Low end technology plants High end technology plants

PercentageCost(R/kℓ)

PercentageCost(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 percost centre

R 258,429.976 R 657,485.884

Further escalations (as reported) will place electricity on par with international trends, after a period ofabundant and cheap electricity in South Africa.Figur e 5: A comparat ive analysis of operat ional cost between SA - and in ternat ional WWTPs (with

sp ecif ic reference to electric i ty co st)


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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 costsinto 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 toprevent works becoming unsustainable, which would include dedicated energy efficiencyoptimisation.

Improved Application: Energy Efficiency

It may be economically viable and best practice for large WWTPs to invest in an energy conservationstudy when the facilities consumption cost reach multi-million Rand projects on a multi-year basis, andwhen the municipal policy prescribe to cleaner production and self- sufficiency principles. The savings toreduce its energy account by 5% per annum is a considerable investment to the municipality and to themunicipal consumer base.

Smaller treatment plants may not experience the benefit of such a study and may opt for simple energysavings opportunities to ameliorate the treatment process in the long term. Performance targets can beset 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 identifywhich 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 energysaving initiatives can be determined.

Despite the economic advantages of reducing the electrical consumption and cost for a WWTP, otherobjectives 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 anysize WWTP, from a demand side management perspective.Table 6: Energy savings applicat ions against various plant equipment aspects (no priori ty

assigned)

18

27

0 0 0 0 00

119

52

28

00

22

30 31

35

0

wastewaterdischarge fee(SA situation

this would be aWaste

DischargeCharge System

levy, wereapplicable)

electricity cost chemical cost staff cost maintenanceand

replacementcost

sludge disposaland transport

administrationcost

International bencmark (%)

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

SA trend when using higher technology (AS, BNR)


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Energy Savings Opportunities for WWTPs

Area/Section Suggestion/Opportunity

Electrical Network

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

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

Motor Efficiency

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

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

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

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

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

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

Gearbox Drives

The gearbox systems consist mostly of gears and bearings for mixers, aerators and smallerapplications. The energy transfer loss from the electric motor to the gear system may betremendous if the gearbox is oversized for the application and/or grease maintenance havenot been regularly conducted. Various publications state that aeration accounts for 50-70%of a treatment plant‟s power consumption.

PumpsSelect pumps based on existing flows with the ability to increase impeller size to handlelarger 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 pumpingcapacity 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.

GeneratorsLarge WWTPs with installed stand-by generators must be used regularly during “on-peak”hours which will reduce treatment energy consumption during such peak scheduled timesand ensuring that such equipment are efficient during emergency procedures. The cost offuel 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 oxygenrequired in the aeration tank. The installation of Dissolved Oxygen (DO) probes can beinstalled to continuously monitor the supply and requirement levels. The aeration isautomated and controlled by the DO monitoring system. The disadvantage of course is thecontinuous maintenance of the DO probes. The energy savings does outweigh themaintenance 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 MonitoringSystem

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

Large instrumentation control systems are suggested to have alternative energy sourcessuch as diesel generation or renewable energy systems to measure and control thetreatment 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 withlarge energy storage for emergency lights and measuring equipment including computersystems.

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 latterswitching either through “daylight” switches or through remote sensing to reduce lightusage on a treatment facility.


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Overall management

best practice

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

Elliot (2003) point out that there are energy savings opportunities from demandside management (DSM) programmes which includes reduction in energy costsby shifting the power consumption from “on-peak” to “off -peak” hours. Suchoptions need careful consideration for large treatment plants. Small and seasonalWWTPs 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 moreenergy to be derived from wastewater than is currently used to treat it (WERF, 2009). This statementaccurately 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 JohannesburgCombined Heat and Power (CHP) application which commenced in 2011 (Deacon, 2011). CombinedHeat and Power (CHP) refers to the thermodynamics of cleaning and combustion of gas that will result in60% of the energy source as heat and 40% as electrical power. CHP is done via prime movers such asgenerators 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 subsequentincrease in biogas yield and the removal of impurities from the biogas to extend the life value of the assetand keep maintenance in balance. CHP is capable of producing 10.2 MW electrical energy and 256.8MWh/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 energyefficiency in South Africa as part of a global network with partners being UK and USA. A Compendium ofBest 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 fossilenergy resources become a limiting factor on global scale.

The nexus between energy and water has become a pivotal instrument to supply and treat water andwastewater within a sustainable environment.

It is a fact that some of the equipment on current WWTPs has reached its useful life and need to bereplaced very soon. Various opportunities present it through applying energy audits, ringfencing of cost

centers energy efficiency improvement, reinvesting in appropriate technologies, cleaner production andhigh performance wastewater treatment in the municipal business through supply- and demand sidemanagement.

A long-term aspiration that could be held in view is to see a self-sufficient WWTP on own soil in thenearby dated future.

Europe is currently the global leader on energy efficient WWTP and there may be various reasons forsetting the benchmark which may be due to available land constraints and resources including strictenvironmental regulations. Strass WWTP is the first treatment facility in Europe to reach a 108% energy


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self sufficient plant, in terms of the process, carbonaceous and nitrogen conversions, mass flow andmass 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-ef f ic ient wastewater treatment plan t in the wo rld (Cao Ye Shi 2011)

Sweden(Average ofall WWTPs)

CzechRepublic(CentreWWTP,Prague)

Singapore(JurongWWTP)

UK (Averageof the

WWTPs)

Switzerland

(WerdhölzliWWTP,Zurich)

Austria(StrassWWTP)

EnergyEfficiency (%)

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

Unfortunately, the baseline information and practices are scarce and critical drivers are not focused onthe water energy nexus and the risk and opportunity it presents. The non-compliance of WWTPs isunderscored by the lack of technical and management skills to manage, maintain and operate plants totheir design specification and capability (Manus & vd Merwe-Botha 2010). The development of acomprehensive Energy Efficient Resource Guideline for WWTPs in a South African environment is set inthe horizon which will assist municipal decision makers, designers and plant managers with theintegration of energy eff icient 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 consideringthe life cycle cost benefit and environmental tradeoffs. Funding and financing agents that overseeprojects 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 energyefficiency drives by local government. The United States of America currently have an energy efficientprogramme to upgrades refurbish WWTP by means of loans with zero interest obligations. Tax write -offincentives in the first year of the capital cost to reduce electricity demand encouraged municipalities toadoption such initiatives on their treatment plants.

The Department of Energy (DoE) and ESKOM could introduce Energy Efficient Demand SideManagement (EEDSM) subsidies for wastewater (sewage and industrial) to implement such initiativeswhich will further reduce the electricity demand in the long-term. Specific tariff schemes to wastewatertreatment facilities could be provided for from ESKOM once a treatment plant has reached a certainpercentage energy efficiency target. The details in terms of the financial implications of alternative tariffprice scenarios still need to be investigated.

Commitments between DWA, DoE, ESKOM, banks with green philosophies and other stakeholders couldensure 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 forthe treatment of water and wastewater by 2% until 2030. Such a commitment is a joint effort by everyoneunderstanding the long-term outcome.

“Save water saves energy: save energy saves water ” represent the simplicity and yet the value in theenergy water nexus for South Africa.

REFERENCES


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i. Bhagwan J, Moraka W, Van der Merwe-Botha M, 2011, The use of sustainabili ty drivers to make appropriate

wastewater treatment technology choices within the current municipal- and legislative environment, WaterQuality Conference, Cape Town, June 2011

ii. Burton S, Cohen B, Harrison S, Pather-Elias S, Stafford W, van Hille R and von Blottnitz H, 2009, Energyfrom wastewater – a feasibility study technical report, WRC Report no 1732/1/09

iii . Deacon S, Biogas to Energy Presentation to the South African City Managers Forum, 2011.

iv. Deacon S, Boyd R & Pitman, 1998 WISA Biennial Conference, Cape Town, The Control of OperationalExpenditure at Northern Wastewater Treatment Works – Johannesburg (1998)

v. Elliot T, 2003, Energy-Savings Opportunities for Wastewater Facilities, report, Wisconsin, USA (2003).

vi. EPRI, Energy Audit Manual for Water/Wastewater Facilities (1994)

vii. ESKOM 2009. Annual Report 2009 – Market Overview. Accessed 4 January 2011. Available athttp://www.financialresults.co.za/eskom_ar2009/ar_2009/market_overview_02.htm

viii. ESKOM 2010. Annual Report 2010 – Market Overview. Accessed 4 January 2011. Available athttp://www.eskom.co.za/annreport10

ix. Global Water Research Coalition Report no 10/CL/11/3, Energy efficiency in the water industry: Acompendium of best practices and case studies, 2009-2010

x. (CoGTA) Cooperative Governance and Traditional Affairs, State of Local Government in South Africa,Overview Report, November 2009

xi. Manus L, vd Merwe Botha M, 2010 WISA Biennial Conference, Durban, Raising Wastewater TreatmentPerformance Through Incentive- & Risk-Based Targeted Regulation (2010).

xii. Moneyweb. 2011. Electricity price increases. Accessed 29 November 2011. Available athttp://www.moneyweb.co.za/mw/view/mw/en/page295023?oid=534394&sn=2009%20Detail

xiii. Moshidi S, Quilling G, van der Merwe-Botha M, 2011, A publication to communicate a brief comment oncurrent situation relating to municipal tariffs as pertaining to wastewater services. Municipal Water QualityConference, Cape Town, June 2011

xiv. Snyman H, v Niekerk A, Rajasakran N, 2008 WISA Biennial Conference, Sun City, Sustainable WastewaterTreatment – What has gone wrong and how do we get back on track? (2008)

xv. Scheepers R, 74

th

IMESA Conference, East London, How can Green Drop Results Trickle Down to GoodEffect?(2010)

xvi. Turton A, 2008. Three Strategic Water Quality Challenges that Decision-makers Need to Know About andHow the CSIR should respond, CSIR Conference, South Africa (2008)

xvii. Water Wheel 2009, article, New Water Framework Counts Every Drop ,May/Jun edition (2009)

xviii. WEF, Water Environment Federation, Energy Conservation in Wastewater Treatment Facilities Manual ofPractice, pp 1-142 (1997)

xix. WERF, Energy Opportunities in Wastewater and Biosolids, report, April 2009.

xx. Ye Shi C 2011, Mass Flow and Energy Efficiency of Municipal Wastewater Treatment Plants, p54, (2011)
http://www.financialresults.co.za/eskom_ar2009/ar_2009/market_overview_02.htmhttp://www.financialresults.co.za/eskom_ar2009/ar_2009/market_overview_02.htmhttp://www.eskom.co.za/annreport10http://www.eskom.co.za/annreport10http://www.moneyweb.co.za/mw/view/mw/en/page295023?oid=534394&sn=2009%20Detailhttp://www.moneyweb.co.za/mw/view/mw/en/page295023?oid=534394&sn=2009%20Detailhttp://www.moneyweb.co.za/mw/view/mw/en/page295023?oid=534394&sn=2009%20Detailhttp://www.eskom.co.za/annreport10http://www.financialresults.co.za/eskom_ar2009/ar_2009/market_overview_02.htm

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