WWTP energy efficiency benchmarking confirms need for continuous improvementIntroductionEnergy is a large portion of a Wastewater Treatment Plant’s (WWTP’s) operating costs. Understanding specific energy requirements of a plant and benchmarking against other similar plants is the first step to reducing energy costs and greenhouse gas emissions. In 2013/14, the Water Services Association of Australia (WSAA) conducted a first round of specific energy benchmarking of 142 WWTPs across Australia. This study repeated the benchmarking exercise for the 2015/16 period and included 245 WWTPs in Australia and Auckland, New Zealand. The purpose of the project was to compare the performance of WWTPs to the previous benchmarking exercise and assess new energy related benchmarks.

3

Number of WWTP utilities

17

6

111 1

1

MethodThis study’s approach followed current best practice from Germany, tailored to the local water industry. It involved collection of a large volume of data from the participating utilities including imported, generated and exported electricity, influent and effluent flow and quality, influent and effluent pumping and sub-metered data. An adopted Equivalent Population (EP) was then calculated based on Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and Nitrogen (N) loads to the plant.

WWTPs were categorised according to size and type based on definitions applied in German WWTP energy benchmarking manuals.

Definition of plant types

Type Features

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

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

3 Extended aeration activated sludge, including aerobic digestion Sub-types recognised

4 Trickling filters

5 Lagoon and/or wetland systems

6 Rotating biological contactors

0

2022

Type 1

Breakdown of WWTPs surveyed by TypeTotal No = 245 (previous 142)

Type 2 Type 3 Type 4 Type 5

40

60

80

120

100

140

Num

ber

of W

WTP

s

This roundPrevious round

18 2416

81

13 10

53

17

133

The following metrics were benchmarked:

1. A primary benchmark of specific energyuse, expressed as kilowatt-hour(kWh)/EP/year;

2. A secondary benchmark measuring theextent of electrical energy self-supply (%);and

3. New benchmarks of kWh per kg ofCOD removed and BOD removed andN removed.

Energy benchmark values adopted for this study were defined for each size and type category as:

1. Guide Values - average (or typical)performance of a WWTP; and

2. Target Values - ‘top’ performance or currentbest practice (top 10%) of a WWTP.

Representation of system boundary for WWTP energy use applied in this study.

Grid electricity generation and transmission (energy losses)

Imported electricityImported fuels (gas/liquid)for energy production

Exported electricity

Co-generation energyproduction on site> Biogas> Supplementary fuelsOther onsite energy production> Wind> Solar> Other

Treated effluent propertiesand pumping

Water recycling(advanced treatment)

Recycled watercredits (offsets)

WWTP electricity useWWTP fuels (gas/liquid),use for electrical energyproduction

IncludedExcluded

Raw wastewater,influent propertiesand pumping

Treated withmain stream

Co-digested

Imported waste,properties(eg tanker waste)

Fuel production and transport(energy loss/use)Other fuel uses (eg site maintenance)

ResultsThis study showed that many WWTPs in Australia do not perform as well as their European counterparts in terms of energy efficiency benchmarks. However, slightly more than half the plants that participated in both the previous and current benchmarking round have improved their performance against the benchmarks.

Performance of participating plants ranked by specific energy

Ranking Number of plants

Specific energy (kWh/EP/year)

Implications

Top 10%

25 <25 Limited opportunities for further energy efficiency improvements or lowering energy use.

Above average

75 25-50 Some opportunities to improve efficiency or lower energy use.

Average 24 51-60 Some opportunities to improve efficiency or lower energy use.

Below average

75 61-110 Significant opportunities to improve efficiency or lower energy use.

Bottom 10%

46 >110 Opportunities to substantially improve energy efficiency or reduce energy use, potentially involving revised plant design or operations.

The two figures below are examples of how a WWTP’s performance can fluctuate over a year. In this case, the Western Treatment Plant’s specific energy (kWh/PE/year) met the Guide value but fell short of the Target value. The plants electrical self-supply (%) was always better than the Guide value but never reached the Target value. Its specific energy performance had not changed from the previous benchmarking round but improved slightly on its energy self-supply. The plant was highlighted as a top performing Type 1 plant.

3,500,000

3,000,000

2,500,000

2,000,000

1,500,000

1,000,000

500,000

00

20

40

60

80

100

120

7/07/15 26/08/15

kWh/EP/Year kWh/Kg-N Removed kWh/EP/Year Guide Value

kWh/EP/Year Target Value Adopted EP

15/10/15 4/12/15 23/01/16 13/03/16 2/05/16 21/06/16

Equ

ival

ent

Per

sons

kWh/

EP

/Yea

r of

kW

h/kg

-N R

emov

ed

Specific electrical energy consumption and equivalent persons

0

20

40

60

80

100

120

7/07/15 26/08/15 15/10/15 4/12/15 23/01/16 13/03/16 2/05/16 21/06/16

% E

nerg

y S

elf

Sup

ply

Plant electrical energy self sufficiency

% Energy self-supply % Ess guide value % Ess target value

The graph below shows that smaller WWTPs generally use more energy relative to EP and vice versa for the larger WWTPs.

Electrical self-supply was a secondary benchmark used in this study. Of the 22 plants with energy self-supply, seven plants achieved the Guide Value of 60% and a further two were greater than 50%.

Metrics based on kWh/kg COD removed or kWh/kg BOD removed were strongly correlated with the primary benchmark and therefore are not likely to add value. The metric of kWh/kg N removed was less correlated with the primary benchmark. This was attributed to nitrogen removal being more variable over the range of WWTP types and sizes covered and therefore most likely to provide value as an additional benchmark in a local context.

Summary data for primary and alternative benchmarks

Type WWTP count

Average kWh (EP.y)

Average kWh/kg - COD removed

Average kWh/kg - BOD removed

Average kWh/kg - N removed

Average % COD removal

Average % BOD removal

Average % N removal

Type 1 22 40.5 1.1 2.2 11.9 93% 98% 57%Type 2 24 63.5 1.4 3.0 14.8 94% 93% 80%Type 3 133 107.3 3.6 6.2 26.3 94% 98% 90%Type 4 13 75.9 N/A 3.9 14.4 N/A 93% 56%Type 5 53 61.8 1.8 3.2 15.6 81% 82% 76%

All 245 85.6 2.8 4.8 21.0 92% 93% 81%

ConclusionsWhile some plants met their respective specific energy benchmark values, there clearly remains room for significant improvement in terms of energy efficiency at many WWTPs. There also remains room to improve energy self-supply when compared to their German counterparts. There is likely value in water utilities improving sub-metering to support the adoption of the proposed benchmark of the power required to remove nitrogen from the treatment process (kWh/kg N removed). The recommendations for future benchmarking are to:

Develop guidelines for augmenting and designing new plants based on energy benchmarks;

Propose an additional benchmark based on the metric kWh/kg N removed

Host the benchmarking database centrally, allowing users to enter their own data and compare WWTP energy performance against industry benchmarks.

AcknowledgementsThe authors would like to acknowledge the support of all water utilities that participated in the benchmarking exercise. The Water Services Association of Australia (WSAA), Intelligent Water Networks, and the Project Delivery Team were also critical in delivering the program to a successful and informative completion.

Utilities Treatment PlantsNSW 3 44VIC 17 93QLD 6 61TAS 1 10WA 1 21NZ 1 2SA 1 12ACT 1 2

73% increasein WWTP

participation

>50% of plants that also participated in a previous benchmark round improved theirbenchmark performance

A secondary benchmark of self-supply of energy for WWTPs

improved by 7%

Presented by

56373 SW OZWATER A1 POSTERS v5.indd 2 27/03/2018 9:50 AM

WWTP ENERGY EFFICIENCY BENCHMARKING CONFIRMS NEED FOR CONTINUOUS IMPROVEMENT

Greg Appleby 1, Nirmala Dinesh 2, George Charakos 3, David De Haas 4, Jennifer Bartle-Smith 5

1. Sydney Water, NSW, Australia

2. SA Water, South Australia, Australia

3. Melbourne Water, Victoria, Australia

4. GHD Pty Ltd, Brisbane, Australia

5. WSAA, Victoria, Australia Keywords

Energy, Benchmark, Wastewater, Treatment, Efficiency, Greenhouse, Emissions

EXECUTIVE SUMMARY

Energy benchmarking of 245 wastewater treatment plants (WWTPs) in Australia and Auckland, was carried out for the period 2015 to 2016. The study showed that many WWTPs in Australia do not perform as well as their European counterparts in terms of energy efficiency but had improved on average overall compared to a previous benchmarking exercise carried out for the period 2013 to 2014. The study also highlighted a new benchmark based on energy required for nitrogen removal, that could be utilised by water utilities in the future.

INTRODUCTION

Energy is a large portion of a WWTP’s operating cost. Understanding specific energy of a plant and benchmarking against other similar plants is the first step to reducing energy costs and greenhouse gas emissions. In 2013/14, the Water Services Association of Australia (WSAA) conducted a first round of specific energy benchmarking of 142 WWTPs across Australia. This study repeated the benchmarking exercise for the 2015/16 period and included 245 WWTPs in Australia and Auckland, New Zealand. The purpose of the project was to compare the performance of WWTPs to the previous benchmarking exercise and assess new energy related benchmarks.

HIGHLIGHTS

Participation in the benchmarking exercise increased from 142 to 245 WWTPs

A number of plants improved their specific energy performance

A secondary benchmark of self-supply of energy for WWTPs improved by 7%

Benchmarking the metric kWh/kg of Nitrogen removed by the WWTP will add value

A standard data collection template and sub metering guidelines were developed.

METHODOLOGY/ PROCESS

This study’s approach followed current best practice from Germany, tailored to the local water industry, and involved collection of a large volume of data from the participating utilities including imported, generated and exported electricity, influent and effluent flow and quality, influent and effluent pumping and sub-metered data. An adopted Equivalent Population (EP) was then calculated based on organic (BOD and COD) and nitrogen loads to the plant.

WWTPs were categorised according to size and type based on definitions applied in German WWTP energy benchmarking manuals.

The following metrics were benchmarked:

1. A primary benchmark of specific energy use, expressed as kWh/EP/year; 2. A secondary benchmark measuring the extent of electrical energy self-supply (%); and 3. A new benchmark of kWh per kg of Chemical Oxygen Demand (COD) removed and/or Biochemical

Oxygen Demand (BOD) removed and/or Nitrogen (N) removed.

Energy benchmark values adopted for this study were defined as:

1. Guide Values - average (or typical) performance of a WWTP for each size and type category; and 2. Target Values - ‘top’ performance or current best practice (top 10%) of a WWTP for each size and

type category.

RESULTS/ OUTCOMES

Primary Benchmark - kWh/(EP.year)

This study showed that many WWTPs in Australia do not perform as well as their European counterparts in terms of energy efficiency benchmarks, although slightly more than half the plants that participated in both the previous and current benchmarking round have improved their performance against the benchmarks.

25 WWTP’s with specific energy use of less than 25 kWh/EP/y are in the ‘top 10%’ and approaching or exceeding industry best practice. Such plants are likely to have limited opportunities for further energy efficiency improvements or lowering energy use

75 WWTP’s with specific energy use between 25-50 kWh/EP/y are better than ‘average’ and are likely to have some opportunities to improve efficiency or lower energy use

24 WWTP’s with specific energy use between 51-60 kWh/EP/y are considered to have energy performance around ‘average’ in the Australian context

75 WWTP’s with specific energy use between 61-110 kWh/EP/y are considered to be ‘below average’ and might have significant opportunities to improve efficiency or lower energy use

46 WWTP’s with specific energy use greater than 110 kWh/EP/y are amongst the least energy efficient and for these plants, there are opportunities to substantially improve energy efficiency or reduce energy use, potentially involving revised plant design or operations.

Secondary Benchmark - % self-supply

Of the 22 plants with energy self-supply, seven plants achieved the Guide Value of 60% and a further two were greater than 50%. There was a 7% increase in self-supply from the previous benchmarking project.

Alternative Benchmarks

Metrics based on kWh/kg COD removed or kWh/kg BOD removed were strongly correlated with the primary benchmark and therefore are not likely to add value. The metric of kWh/kg N removed was less correlated with the primary benchmark. This was attributed to nitrogen removal being more variable over the range of WWTP types and sizes covered and therefore most likely to provide value as an additional benchmark in a local context.

Recommendations

A number of recommendations are made for future benchmarking including:

1. Develop guidelines for augmenting and designing new plants based on energy benchmarks 2. Propose additional benchmark values based on the metric kWh/kg N removed 3. Host the benchmarking database centrally, allowing users to enter their own data and compare

WWTP energy performance against industry benchmarks.

CONCLUSION

While some plants met their respective specific energy benchmark values, there clearly remains room for significant improvement in terms of energy efficiency on many of the WWTPs. There also remains room to improve energy self-supply when compared to their German counterparts. There is likely value in water utilities improving sub-metering to support the adoption of the new benchmark of the power required to remove nitrogen from the treatment process (kWh/kg N removed).

Figure 1: WWTPs surveyed in this study compared to previous study, according to Type (Type definitions listed below)

Table 1: Summary of WWTP total plant specific energy performance from this study

Type Average kWh/EP/year

Minimum kWh/EP/year

Average kWh/EP/year Guide Value

Average kWh/EP/year Target Value

Comments

Type 1 41 [45]

15 [14]

40 [30]

26 [20]

Room for improvement in 50% of plants to achieve Guide Values

Type 2 64 [66]

26 [10]

40 [38]

25 [24]

Room for significant improvement in many plants

Type 3 107 [68]

25 [5]

50 [44]

32 [26]

Room for significant improvement in many new plants to this benchmarking exercise

Type 4 76 [68]

2.5 [11]

32 [27]

24 [17]

Room for significant improvement in many plants

Type 5 62 [57]

1.3 [1]

35 [34]

22 [17]

Room for improvement in most plants

Values in parentheses are from the previous WSAA benchmarking round (2013-14) Table 2: Proposed (interim) Guide and Target values for alternative benchmarks based on pollutant removal specific energy use

Data

2015-16 data

Proposed

2015-16 data

Proposed

2015-16 data

Proposed

Type Average Guide Value

Target Value

Average Guide Value

Target Value

Average Guide Value

Target Value

Units: kWh/kg COD removed kWh/kg BOD removed kWh/kg N removed

Type 1 1.1 (1.0) (0.5) 2.2 (2.0) (1.0) 11.9 10.0 5.0

Type 2 1.4 (1.0)

(0.6)

3.0

(2.0)

(1.0)

14.8

14.0

6.7

Type 3

3.6

1.2

0.8

6.2

3.4

2.0

26.3

18.0

10.0

Type 4

6.3

N/A

N/A

3.9

(1.4)

(0.4)

14.4

10.0

4.0

Type 5

1.8

(0.6)

(0.2)

3.2

(2.0)

(0.5)

15.6

8.0

3.0

Type summary definitions as follows:

Type 1: With primary sedimentation, anaerobic sludge digestion and co-generation from biogas

Type 2: With primary sedimentation and anaerobic sludge digestion but without co-generation from biogas

Type 3: Extended aeration activated sludge

Type 4: Trickling filters, including trickling filter-activated sludge combinations

Type 5: Lagoon plants, including aerated lagoons

Size summary definitions as folloows:

Size Class 1: ≤ 1,000 EP

Size Class 2: 1001 – 5,000 EP

Size Class 3: 5001 – 10,000 EP

Size Class 4: 10,001 – 100,000 EP

Size Class 5: >100,000 EP