Wastewater Treatment Energy Efficiency

1

Technical Papers

WASTEWATER TREATMENT ENERGY EFFICIENCY A review with current Australian perspectives D de Haas, M Dancey

ABSTRACT Energy use for wastewater treatment is typically among the largest contributors to total energy use faced by urban water and wastewater utility providers. This is especially relevant in Australia, given that a recent benchmarking study noted that the majority of Australian wastewater treatment plants (WWTPs) by number are small- to medium-sized plants of the extended aeration activated sludge type that lack energy recovery systems and have relatively poor economies of scale. Interestingly, though, the major part of the combined equivalent population wastewater load in Australia is treated in medium to large WWTPs that have better economies of scale and either have energy recovery systems or potential to install and/or optimise energy recovery, principally from biogas. This paper draws on data from a recent Australian WWTP energy use benchmarking study, providing a detailed breakdown of energy use for 12 selected plants for illustrative purposes. The selected plants represent three basic types (all using activated sludge processes). These three types either have primary sedimentation (PSTs) plus anaerobic digestion (either with or without cogeneration from biogas), or do not have PSTs (extended aeration). The units for energy efficiency benchmarking are discussed, with reference to similar studies elsewhere and Germany in particular. The differences are highlighted between energy efficiency benchmark values in load (equivalent persons) specific terms, compared with that in flow-specific terms. Potential savings associated with improving WWTP energy in Australia are discussed and referenced against similar studies elsewhere.

INTRODUCTION The water-energy nexus is receiving attention worldwide in the search to meet growth in demand due to an increase in both population numbers and levels of consumption (Olsson, 2012;

Kenway, 2013). For example, according to Kenway (2013), water-related energy associated with urban water provision and use in Australia in 2006–07 accounted for 6,811 GWh of equivalent primary energy use per one million people. This was equal to 13% of Australia’s electricity use plus 18% of natural gas consumption, representing 9% of the equivalent primary energy use and 8% of Australia’s GHG emissions (Kenway, 2013). Most of the urban water energy use was associated with residential, industrial and commercial uses and dominated by residential hot water use. Energy use for utilities in the provision of water and wastewater services accounted for, on average, around 10% of water-related energy, of which approximately half was associated with wastewater pumping and treatment (Kenway, 2013). Therefore, from a global perspective, it is tempting to conclude that the energy associated with wastewater is relatively small and, therefore, less important. However, from a local government or water utility perspective, the energy use for wastewater treatment is a major contributor to energy use and greenhouse gas emissions profiles (Kenway et al. 2008; Hall et al., 2009; Cook et al., 2012; de Haas et al., 2014). Yet, understanding the reasons for this can be complex. This paper provides an overview of energy use for wastewater treatment in the urban water context, followed by a breakdown of energy use for 12 typical current wastewater treatment plants (WWTPs) in Australia that represent the most common types of process configuration. Data is drawn from a recent benchmarking study conducted by the Water Services Association of Australia (WSAA, 2014). Attention is drawn to key potential opportunities associated with energy efficiency improvement in Australian WWTPs and compared with a similar study recently conducted for plants in the US (WERF, 2014).

UNITS FOR ENERGY EFFICIENCY COMPARISONS For water or wastewater systems, energy efficiency is often expressed on a flow-specific basis (e.g. kWh. ML-1) (Hall et al., 2009; Ohlsson, 2012) and is sometimes benchmarked on this basis (AWWA, 2007). However, a major difference between water and wastewater treatment systems is that a much larger proportion of wastewater treatment plant energy use is due to aeration and internal plant recirculation systems that are related to the removal of contaminants. Broadly, the raw wastewater contaminants are made up of organic compounds and nutrients (mainly nitrogen and phosphorus). Hence, a significant portion of WWTP energy use is linked to raw influent mass load, which in turn is linked to the catchment population served (typically expressed as “per capita” or “per equivalent population, EP”). Therefore, for WWTPs, comparison of energy efficiency on a load-specific basis (e.g. kWh.EP-1.year-1) is preferable since wastewater composition is taken into account (Crawford, 2010). Pumping systems by themselves may be compared on a volume basis (typically kWh.ML-1 or Wh.m-3). Unfortunately, neither a loadspecific nor flow-specific measurement of energy efficiency by itself is adequate in all instances for WWTPs. The user has to make an appropriate choice of which units to use for benchmarking purposes. Therefore, it is useful to understand the conversion between units applied. Energy use data for urban water systems of seven cities in Australia and New Zealand (Kenway et al., 2008; Cook et al., 2012) shows a wide range, with wastewater treatment averaging around 580 kWh.ML-1 wastewater collected or 51 kWh.capita-1.year-1. For these datasets, the actual population numbers served (capita) were sourced from the relevant water utilities. For WWTPs where the population served is not known exactly, the term

November 2015 water

2

Technical Papers “equivalent population” (EP) (or “person equivalents”, PE) is often used and may include trade wastes. One EP (or 1 PE) is typically defined as 60 g.d-1 biochemical oxygen demand (BOD) load in the raw wastewater in energy benchmarking manuals from several European countries (Crawford, 2010; Krampe, 2013). It is recognised that benchmarks based solely on BOD load might not be appropriate in some situations, such as in Australia, where raw wastewaters tend to have a high N/C ratio, which has a significant impact on overall WWTP energy efficiency (e.g. due to higher aeration requirements) (Krampe, 2013). Balmér (2000) compared specific energy efficiency for Nordic WWTPs, based on TKN load (kWh.EPTKN12-1.year-1) assuming 12 gN.EP-1.d-1 as Total Kjeldahl Nitrogen (TKN). In a recent benchmarking study covering 142 WWTPs in Australia, WSAA (2014) assessed equivalent population (EP) for load-specific energy determination as the average of that calculated from: 120 g.EP-1.d-1 chemical oxygen demand (COD) (or 60 g.EP-1.d-1 BOD where COD data was unavailable); and 12 gN.EP-1.d-1 (or TN where TKN data was unavailable). Included in the background datasets of Kenway et al. (2008) and Cook et al. (2010) from Australian and New Zealand cities was total water supply, which equated to an average of 346 and 331 L.capita-1.d-1 respectively. The wastewater collected was on average 66% (Cook et al., 2010) to 72% (Kenway et al., 2008) of the total water supplied. Therefore, if normalised to units of kWh. ML-1 total water supplied, the average energy use on a per ML basis would be approximately 1.4 to 1.5 times lower than values tabulated per unit flow of wastewater collected. This highlights the importance for urban water systems of carefully defining the flow basis when considering WWTP energy use in flowspecific terms. It is also important to note here that electrical energy use in most of the literature, including that from the recent benchmarking study for Australian WWTPs (WSAA, 2014), is based on end-use kilowatt-hour consumption recorded. Other studies (e.g. AWWA, 2007; WERF, 2014) have included primary energy use (e.g. in British Thermal Units), which may be indicatively three times greater than electricity end use, depending on the extent of losses in power generation, transmission and other fuels used (e.g. liquid or gaseous fuels) to operate WWTPs.

water November 2015

VARIATIONS IN WWTP ENERGY USE The data of Kenway et al. (2008) and Cook et al. (2010) suggest average energy use for wastewater treatment across cities in Australia and New Zealand ranges 27 to 67 kWh.capita-1.year-1 (assuming 1 capita = 1 EP). In practice the range of actual averages for individual WWTPs is even larger, being somewhere between approximately 1 and 270 kWh.EP-1.year-1 (WSAA, 2014). Reasons for this variation include: • Type of treatment technology; • Level of treatment and effluent quality targets (e.g. basic removal of organic contaminants only; advanced nutrient removal; treatment for reuse, including advanced disinfection); • Size of WWTP (in general, with larger plants tending to be more energy efficient than smaller ones, for reasons relating to economies of scale and type of technology used); • Trade waste contribution to load in EP terms; • Type and efficiency of aeration systems used; • Extent to which pumping occurs on the plant (including influent or effluent pumping and internal pumping for recirculation, pumping head requirements, etc) and pump efficiency; • Extent and type of tertiary treatment systems (e.g. filtration; disinfection, etc); • Effluent reuse (related to tertiary treatment and the need for additional pumping, etc);

• Energy requirements for sludge handling and treatment (e.g. thickening, mixing, dewatering, drying, etc); • Presence (or not) and extent of on-site energy generation and self-supply (e.g. from biogas), and how self-supplied or exported energy is accounted for in plant reporting.

DISTRIBUTION OF AUSTRALIAN WWTPs For benchmarking purposes, five WWTP types can be broadly defined, based on treatment technologies that currently commonly occur (Table 1). These types were defined in the recent Australian WWTP energy benchmarking study (WSAA, 2014; de Haas et al., 2015) and align with WWTP categories defined in a German WWTP energy manual (Baumann and Roth, 2008) and related benchmarking studies (Haberkern et al., 2008; Krampe, 2013). The German datasets collectively covered several thousand WWTPs, classified according to size (based on personequivalent raw influent load) and type. The WSAA (2014) benchmarking study covered 142 WWTPs operated by 17 water utilities across seven states and territories in Australia and has been summarised by de Haas et al. (2015). Looking at the distribution of data from the WSAA (2014) study, Figure 1A shows that, in terms of number of WWTPs, Type 3 (extended aeration activated sludge) dominated, representing more than half the plants, with the other four types each representing 7% to 13% of the number surveyed. However, Figure 1B shows a rather different distribution of plant type when broken down by size (based on adopted EP from the average of current COD or BOD and nitrogen loads).

Table 1. Definition of WWTP types. Type

Description/Features

Type 1

Activated sludge treatment with separate sludge stabilisation, including those with primary sedimentation, anaerobic digestion (or alternative – Note 1) and with on-site co-generation (on-site energy produced from biogas).

Type 2

Activated sludge treatment with separate sludge stabilisation, including those with primary sedimentation, anaerobic digestion (or alternative – Note 1) but without on-site co-generation (no on-site energy produced from biogas).

Type 3

Extended aeration activated sludge, including aerobic digestion. No biogas production and no on-site co-generation (Note 2).

Type 4

Trickling filters or trickling filter-activated sludge combinations. Such plants often include primary sedimentation and anaerobic digestion, sometimes with on-site co-generation (on-site energy produced from biogas).

Type 5

Aerated or unaerated lagoons. No biogas production and no on-site co-generation.

Note 1: Alternative sludge stabilisation includes: Incineration; Covered anaerobic lagoons; Chemical (e.g. lime) treatment etc. Plants with aerobic digestion for sludge stabilisation are classified as Type 3. Note 2: Membrane bioreactor plants are included in Type 3 if no primary treatment is present with separate sludge stabilisation (as in Types 1 & 2).

3

Technical Papers

Breakdown of WWTPs by Type and Adopted EP

Breakdown of WWTPs surveyed by Type Total No. = 142

90

81

Number of WWTPs

80

60%

70

59.5%

50%

60 50

40%

40

30%

30 18

20

10

Type 2

Type 3

Type 4

34.1% 26.7%

Percent of Imported Electrical Power (Averages)

20.7% 12.4%

10%

0 Type 1

Percent of Total EP

43.3%

20%

17

16

10

A

Total EP (Sum of All Class Sizes) = 22,603,300 EP

70%

Type 5

B

0.5% 0.9%

0% Type 1

Type 2

Type 3

0.9% 1.0%

Type 4

Type 5

Figure 1. Plants covered in WSAA (2014) energy benchmarking study, showing breakdown of: (A) WWTP number surveyed by Type; and (B) Adopted equivalent person (EP) load on WWTP surveyed by type (refer to Table 2 for definitions). Type 1 dominates the EP load representation, followed by Type 3 and Type 2, with the other two types (those with Trickling Filters or Lagoons) being relatively insignificant in EP terms. The WSAA (2014) study did not cover all the WWTPs in Australia; some regional metropolitan and rural towns were not included. Nevertheless, the data suggest that approximately 60% of the Australian population’s wastewater load is treated by WWTPs that do have primary treatment, anaerobic digestion and energy recovery from biogas (Type 1), and a further 12% has primary treatment and anaerobic digestion with the potential for energy recovery systems from biogas to be added (Type 2). The Type 3 plants would need significant modification or upgrades to add energy recovery from biogas. Nevertheless, anaerobic digestion of waste-activated sludge alone is technically feasible (Gloag et al., 2014), although typically constrained by biological nutrient removal considerations and economies of scale, given that digesters and biogas systems tend to be more capital intensive than extended aeration systems. Economies of scale can be illustrated from the WSAA (2014) data, when the plants surveyed are

grouped by size class (based on adopted EP load) irrespective of type. It becomes apparent that, although the largest size class (SC5 for >100,000 EP) represented only about one-quarter of the number of WWTPs (35 in number surveyed – Figure 2A), it represented 88% of the total EP for all plants surveyed and, on average, 78% of the imported electrical power (Figure 2B). Collectively, the two largest classes (SC4 and SC5) represent WWTPs >10,000 EP and nearly 99% of the total EP for all plants surveyed (Figure 2B). As might be expected, the smaller plants (in EP load terms) and Types 2 to 5 (that lack energy recovery or self-supply from cogeneration) tend to use more imported electrical power on a relative basis (Figure 1B and Figure 2B). Clearly, investment in the larger plants represents the best opportunity to improve energy efficiency and recovery in Australian WWTPs. Table 2 presents a sample of summary electrical energy use data taken from the WSAA (2014) study for 12 plants of Types 1, 2 and 3. These plants were selected on the basis of size (>10,000 EP) and a breakdown of sub-process data was also available to allow more detailed analysis. Also in Table 2 are the German benchmark

Number of WWTPs

Breakdown of WWTPs surveyed by Size Class 80 70 60 50 40 30 20 10 0

The size of WWTPs represented in Table 2 ranged from approximately 60,000 EP (for a medium-sized Type 3 plant) to over 2.2 million EP (for a large Type 1 plant). The specific electrical energy use varied over a wide range and consistent trends are difficult to discern from such small datasets. This is due to a number of possible factors contributing to energy use, such as those already listed. Bigger datasets (Haberkern et al., 2008; de Haas et al., 2015) tend to show economies of scale with larger plants being more energy-efficiency than smaller plants, as might be expected. However, a number of site-specific factors can strongly influence energy use for a given plant. Such factors are expected to underlie, for example,

Breakdown of WWTPs by Size and Adopted EP

Total No. = 142

Total EP (Sum of All Class Sizes) = 22,603,300 EP

68

100%

88.4%

90%

20

78.0%

80%

35

70%

Percent of Total EP

60%

13

50%

6

40% 30% 20% 10% 0%

A

Target and Guide Values derived from information presented by Baumann and Roth (2008) and Haberkern et al. (2008). The Target Value is indicative of ‘top’ or ‘best practice’ performance, while the Guide Value is indicative of ‘average’ performance from the German benchmark data. The WSAA (2014) study also collected data on WWTP energy supply from gaseous or liquid fuels but only benchmarked the electrical energy use, which was predominant for all the plants.

B

Percent of Imported Electrical Power (Averages)

20.1% 0.05% 0.01%

SC1

0.6% 0.2%

SC2

1.2% 10.8% 0.5%

SC3

SC4

SC5

Figure 2. Plants covered in WSAA (2014) energy benchmarking study, showing breakdown of: (A) WWTP number surveyed by size class; and B) Adopted equivalent person (EP) load on WWTP surveyed by size class (refer to legend for definitions).

November 2015 water

4

Technical Papers

Table 2. Sample Australian WWTP electrical energy use data for Types 1, 2 and 3. Average EP

Average Flow ML.d-1

Average WWTP Electrical Energy Use kWh.d-1

Average Load-specific Elec. Energy Use kWh.EP-1. year-1

German Benchmark Guide Value kWh.EP-1. year-1

German Benchmark Target Value kWh.EP-1. year-1

Percent Energy SelfSupply (Ess) %

Plant A

2,227,556

395.9

388,063

965

63.6

27

18

31%

Plant B

271,220

61.2

60%

21,491

323

28.9

27

18

34%

60%

Plant C

76,501

18.0

9,196

488

43.9

30

20

44%

60%

Plant D Plant E

465,563

86.9

61,890

708

48.5

33

22

352,797

78.5

57,888

733

59.9

27

18

Plant F

130,474

21.5

37,501

1701

104.9

31

20

0% (All)

0% (All)

Plant G

110,973

26.1

23,091

882

75.9

27

18

Plant H

295,086

58.2

29,921

499

37.0

44

27

Plant I

169,507

37.1

36,572

980

78.7

34

20

Plant J

141,240

36.0

32,652

920

84.4

30

18

0% (All)

0% (All)

Plant K

103,843

19.7

12,170

595

42.8

30

18

Plant L

61,911

18.9

14,729

756

86.8

114 (Note 3)

62 (Note 3)

Plant Type & Name Type 1

Average Flow-specific Elec. Energy Use kWh.ML-1

(Note 1)

German Guide Value Percent Ess %

(Note 2)

Type 2

Type 3

Source: Data from WSAA (2014). Note 1: WWTP Electrical Energy Use includes energy generated on site (for Type 1 plants by co-generation from biogas), less energy exported (where applicable). Note 2: Ess denotes ‘Energy Self Supply’. The Ess Target Value is 100% and Guide Value is 60% for Type 1 plants of >5000 EP size. Note 3: Includes energy supplement adopted for Membrane Bioreactor by extrapolation from German values (proposed by Haberkern et al., 2008).

the observation from Table 2 that plants of nominally similar size (>100,000 EP) and type (Type 2 or Type 3) have specific energy use spanning roughly a two-fold range, both in terms of flow (kWh.ML-1) and load (kWh.EP-1.year-1). Therefore, a more detailed breakdown of energy use for each plant is usually necessary in order to characterise sub-process efficiency and potentially bring about improvements. It is worth noting from Table 2 that energy use efficiency is separately benchmarked from the extent of energy self-supply, usually from cogeneration using biogas (in Type 1 plants). Table 2 also shows that for the example plants of Types 1, 2, and 3 none of the WWTPs listed met the German benchmark Target Value, and only two (or three) plants met or approached the Guide Value. This is not surprising considering that most Australian WWTPs have designs that pre-date more recent periods when rising energy costs or energy efficiency and greenhouse gas emissions have emerged as leading issues (e.g. ComLaw, 2007). Apart from weak historical legislative or cost drivers for energy efficiency, other reasons for relatively high WWTP energy consumption in Australia include: • More advanced treatment for improved effluent quality (e.g. nutrient removal) driven by higher standards for environmental regulation around receiving water;

water November 2015

• More advanced treatment and pumping associated with water recycling, driven by water scarcity; • Terrain (e.g. influent and/or effluent pumping due to lack of gravity alternatives in flat terrain such as in many coastal locations); • Need for effluent pumping, driven by environmental regulations around discharges to local waterways (e.g. creeks with limited or highly seasonal natural flow); • Lack of anaerobic digestion, energy recovery or co-generation facilities; • Planning and population distribution considerations around the number, size and location of WWTPs (i.e. centralised vs. decentralised, with associated sewerage and transfer systems). Plant L (Type 3) stands out in terms of its load-specific energy performance relative to higher German benchmarks, due to it being a membrane bioreactor plant and, therefore, receiving a relatively generous benchmark energy ‘supplement’ (Haberkern et al., 2008). This plant is an example of a trend among some Australian water utilities, where membrane bioreactor applications have become popular in the last decade due to drivers of tighter effluent quality standards and the push toward water recycling as a water conservation measure.

POTENTIAL OPERATING COST SAVINGS Operating costs for WWTPs can be reduced by improving the efficiency of energy use or increasing on-site energy self-supply, typically from co-generation using biogas, or a combination of both. Since electrical energy use and extent of electrical energy self-supply can be separately benchmarked (Krampe, 2013; de Haas et al., 2015), it is possible to use benchmarking data to estimate operational cost savings potential from these two approaches. Operational expenditure (Opex) savings potential was estimated for Australian WWTPs covered in the WSAA (2014) study, in two ways as follows: • Due to efficiency improvements (i.e. reduced total electrical energy use), assuming that these translate directly into reduced imported grid electrical power consumed (i.e. end use in kWh, not taking into account peak demand or other tariffs); • Due to improved reduced imported grid electrical power consumed as a result of energy self-supply for all Type 1 plants (already equipped with cogeneration from biogas) and assuming the largest (SC5 for >100,000 EP current load) Type 2 plants (already equipped with primary sedimentation and anaerobic digestion) could be cost-effectively upgraded to include co-generation from biogas.

5

Technical Papers

Table 3. Potential operating cost savings due to improved efficiency of electricity energy use on Australian WWTPs (based on WSAA, 2014 data).

Type

No. of plants

Energy saving potential due to energy use improvement (GWh/ annum)

Opex potential savings @ 10c/kWh

Opex potential savings @ 20c/kWh

(Million $/year)

(Million $/year)

NPV of Opex potential savings @ 10c/kWh

NPV of Opex potential savings @ 20c/kWh

(Million $)

(Million $)

to Guide Value

to Target Value

to Guide Value

to Target Value

to Guide Value

to Target Value

to Guide Value

to Target Value

to Guide Value

to Target Value

Type 1

18

142

228

$14.2

$22.8

$28.5

$45.5

$211

$338

$422

$675

Type 2

16

50

74

$5.0

$7.4

$10.1

$14.7

$75

$109

$150

$218

Type 3

81

70

118

$7.0

$11.8

$13.9

$23.6

$103

$175

$207

$350

TOTAL

115

262

419

$26.2

$41.9

$52.5

$83.9

$389

$622

$778

$1,243

Net Present Value (NPV) assumptions: 25 year period; 4.5% p.a. discount rate; inflation excluded.

The extent to which a plant can achieve savings by realising both improved energy use efficiency and self-supply would need to be evaluated on a sitespecific basis for each plant, taking into account the revenue potential associated with a plant becoming a net exporter of energy (either as biogas or electricity). Capital and operating (e.g. maintenance) costs associated with improved energy efficiency or self-supply improvements also require a site-specific financial assessment. Nevertheless, the data summarised in Table 3 (for energy efficiency improvement) and Table 4 (for energy selfsupply) provide some cost perspectives for Australian WWTPs Type 1, 2 and 3 plants based on the WSAA (2014) data. For the plants included (115 of these three types) total annual Opex savings potentials from improved energy efficiency lie in the range indicatively of $26 million to $84 million per annum, depending on the assumed average unit cost of grid electricity (range 10c/kWh to 20 c/kWh) and whether the plants are improved to achieve the benchmark Guide or Target values. In Net Present Value (NPV) terms, these Opex savings amount to between approximately $390

million and $1.24 billion over 25 years at a discount rate of 4.5% per annum, excluding inflation. Similarly, considering only savings from energy self-supply for Type 1 plants (18 and seven Type 2 plants (>100,000 EP), total annual Opex savings potentials from improved energy efficiency lie in the range indicatively $21 million to $116 million per annum, depending on the assumed average unit cost of grid electricity (range 10c/kWh to 20 c/kWh) and whether the plants are improved to achieve the benchmark Guide or Target values. In Net Present Value (NPV) terms, the Opex savings amount to between approximately $313 million and $1.72 billion over 25 years at a discount rate of 4.5% per annum, excluding inflation. Although further financial analysis is required, the data in Table 3 and Table 4 suggest that improved energy selfsupply and efficiency is likely to be most cost-competitive when targeted at the largest plants and among those already well-placed for potential self-supply from cogeneration (biogas). A similar conclusion was reached in a recent WERF (2014) study covering more than 1,000 medium-to-large plants in the US (>19

ML/d average flow), taking into account capital cost estimates and commercial alternatives for distributed renewable energy supply. Reducing dependence of WWTPs on grid electricity also has the potential to reduce national greenhouse emissions (de Haas et al., 2014).

CONCLUSIONS Wastewater treatment is a significant contributor to energy use in the urban water cycle. Benchmarking is a useful means by which to compare energy use between different plants or systems. Benchmarking of WWTP total energy use in load-specific terms may be preferable to applying only flow-specific benchmarks since a major part of the energy use on a WWTP is directly related to pollutant load. Benchmarking in terms of equivalentperson influent load (e.g. kWh.EP-1.year-1) is useful, particularly if WWTPs are grouped according to size and type. WWTPs have the potential to ‘recover’ a high proportion of total plant energy through self-supply systems, particularly co-generation of electricity and heat from biogas. Energy self-supply should be benchmarked separately from energy efficiency, with the latter being based on total plant energy use (usually largely in the

Table 4. Potential operating cost savings due to improved electrical energy self-supply on Australian WWTPs (based on WSAA, 2014 data).

Type

No. of plants

Energy saving potential due to energy self-supply improvement (GWh/ annum)

Opex potential savings @ 10c/kWh (Million $/year)

Opex potential savings @ 20c/kWh (Million $/year)

NPV of Opex potential savings @ 10c/kWh (Million $)

NPV of Opex potential savings @ 20c/kWh (Million $)

to Guide Value

to Target Value

to Guide Value

to Target Value

to Guide Value

to Target Value

to Guide Value

to Target Value

to Guide Value

to Target Value

Type 1

18

145

470

$14.5

$47.0

$29.0

$94.0

$215

$697

$429

$1,394

Type 1 (SC5 only)

14

143

464

$14.3

$46.4

$28.6

$92.8

$212

$688

$424

$1,376

Type 2 (SC5 only)

7

66

110

$6.6

$11.0

$13.2

$22.1

$98

$164

$196

$327

TOTAL

25

211

580

$21.1

$58.0

$42.2

$116.1

$313

$861

$626

$1,721

Net Present Value (NPV) assumptions: 25-year period; 4.5% p.a. discount rate; inflation excluded. SC 5: Size Class 5 (>100,000 EP current load)

November 2015 water

6

Technical Papers form of electricity, regardless of supply source). Self-supplied energy will lower imported (grid) electrical power and fuel requirements (liquid or gas) for supplementary heating, if present. Distinct from energy recovery, ultimately it is improved plant design, maintenance, and control that enable energy-efficient WWTP operation. Data from a recent (2014) benchmarking study for Australian WWTPs suggested that there is room for improvement in terms of energy efficiency, compared with benchmark Guide (average) and Target (best practice) values based on similar studies in Europe, and Germany in particular. The Australian dataset also illustrates existing economies of scale with all the large plants (>100,000 EP current loading) representing only one-quarter of the total number of plants surveyed but covering nearly 90% of the associated current total equivalent person loading. This represents a significant opportunity to realise operating cost and greenhouse gas savings associated with improved energy use efficiency and self-supply from biogas as a renewable source. The majority of these large plants in Australia are already equipped with primary sedimentation, anaerobic digestion and co-generation facilities from biogas, and there is potential to upgrade a relatively small number of similarly sized plants (indicatively less than 10) that only lack co-generation facilities. Comparing current performance to benchmark values, the indicative operating cost-saving potential from improved energy self-supply from cogeneration alone for 25 such large Australian WWTPs is estimated to lie between $313 million and $1.7 billion in whole-of-life present cost terms over 25 years, based on an average price of 10 to 20 c/kWh for grid electricity use saved. Further potential savings of the same order may be possible from reduced grid electricity use due to improved energy efficiency of treatment processes for 115 WWTPs in Australia that represent the most common types, covering approximately 98% in terms of current total equivalent person loading. Further research is recommended to better quantify net whole-of-life savings potential, including capital and maintenance costs.

ACKNOWLEDGEMENTS The Water Services Association of Australia (WSAA), its contributing members and relevant Project Delivery Team are gratefully acknowledged for permission to reproduce selected data in this paper from the WWTP Energy Benchmarking Study (WSAA, 2014).

water November 2015

THE AUTHORS Dr David de Haas (email: David.deHaas@ ghd.com) is a principal professional (municipal wastewater treatment) at GHD in Australia. He has 30 years’ experience in municipal water and wastewater treatment, including research and development, process design, operation, planning and advisory functions. He has also undertaken research projects focusing on greenhouse gas emissions and energy use in wastewater treatment plants in Australia. He has participated in a number of research projects through the University of Queensland, the Australian Water Recycling Centre of Excellence in collaboration with the University of New South Wales, and a range of other industry partners. Murray Dancey (email: murray.dancey@ wannonwater.com.au) is a Project Manager at Wannon Water, specifically working on energy efficiency and innovation projects. Murray is a member of the Intelligent Water Networks (IWN) Energy Optimisation Working Group and the IWA Energy and Greenhouse Special Interest Groups (SIG). He was the Project Manager of the WSAA Wastewater Treatment Plant (WWTP) Benchmarking project and a Project Board member of the WSAA Pumping Efficiency Benchmarking project.

REFERENCES AWWA (2007): Energy Index Development for Benchmarking Water & Wastewater Utilities. AWWA Research Foundation, Denver, Colorado CO. Balmér P (2000): Operation Costs and Consumption of Resources at Nordic Nutrient Removal Plants. Water Science and Technology, 41, 9, pp 273–279. Baumann P & Roth M (2008): Senkung des Stromverbrauchs auf Kläranlagen, Leitfaden für das Betriebspersonal (Reduction of the Energy Consumption of WWTPs – Manual for Operators), Heft 4. DWA Landesverband Baden-Württemberg, Stuttgart (in German). ComLaw (2007): National Greenhouse and Energy Reporting Act 2007. Australian Government, Canberra. www.comlaw. gov.au/Series/C2007A00175 Cook S, Hall M & Gregory A (2012): Energy Use in the Provision and Consumption of Urban Water in Australia: An Update. Report prepared for Water Services Association of Australia by CSIRO (Water for a Healthy Country Flagship Report), May 2012, Water Services Association of Australia, Melbourne.

Crawford G (2010): Best Practices For Sustainable Wastewater Treatment Initial Case Study Incorporating European Experience And Evaluation Tool Concept. WERF Report No. OWSO4R07a, Water Environment Research Foundation, Alexandria VA. De Haas D, Foley J, Marshall B, Dancey M, Vierboom S & Bartle-Smith J (2015): Benchmarking Wastewater Treatment Plant Energy Use in Australia. Paper presented at Ozwater’15 Conference, 12–14 May 2015, Adelaide Convention Centre, Adelaide. De Haas D, Pepperell C & Foley, J (2014): Perspectives on Greenhouse Gas Emission Estimates Based on Australian Wastewater Treatment Plant Operating Data. Water Science & Technology, 69, 3, pp 451–463. Haberkern B, Maier W & Schneider U (2008): Steigerung der Energieeffizienz auf kommunalen Klaeranlagen (Increasing the Energy Efficiency of WWTPs). Umweltbundesamt (German Federal Environment Agency), Dessau-Roßlau (in German). Gloag G, Batstone D, Simonis J, Robertson D, Jensen P, O’Halloran K & Longley V (2014): WAS Only Mesophilic Anaerobic Digestion at Coombabah WWTP. Paper presented at Ozwater’14 Conference, 29 April–1 May, 2014, Brisbane Convention Centre, Brisbane. Hall M, West J, Lane J, de Haas D & Sherman B (2009): Energy and Greenhouse Gas Emissions for the SEQ Water Strategy. Technical Report No. 14, Urban Water Security Research Alliance, Brisbane. www.urbanwateralliance. org.au/publications/UWSRA-tr14.pdf Kenway S (2013): The Water-Energy Nexus and Urban Metabolism – Connections in Cities. Technical Report No. 100, Urban Water Security Research Alliance, Brisbane. www. urbanwateralliance.org.au/publications/ UWSRA-tr100.pdf Kenway S, Priestley A, Cook S, Seo S, Inman M, Gregory A & Hall M (2008): Energy Use in the Provision and Consumption of Urban Water in Australia and New Zealand. Report prepared for Water Services Association of Australia (WSAA) by CSIRO (Water for Healthy Country National Research Flagship Report series), Water Services Association of Australia, Melbourne. Krampe J (2013): Energy Benchmarking of South Australian WWTPs. Water Science and Technology, 67, 9, pp 2059–2066. Olsson G (2012): Water and Energy – Threats and Opportunities. IWA Publishing, London. WERF (2014): Utilities of the Future – Energy Findings. Report prepared by Black & Veatch for Water Environment Research Foundation (WERF), Alexandria, Virginia USA. WSAA (2014): WWTP Energy Benchmarking (Part 2, Technical Report). Report prepared for Water Services Association of Australia by GHD Pty Ltd, September 2014, Water Services Association of Australia, Melbourne.