Energy Efficiency in Wastewater Facilities

Prepared by

Tongyan Li

Treated SourceWater Treatment

100-16,000kWh/MG

Treated WastewaterWastewater Collection

& Treatment

Water End Use

Conveyance0-14,000kWh/MG

Distribution700-1,200Wh/MG

Treated wastewater discharge

Energy Opportunities• Use efficient pumping systems (pumps,

motors, variable frequency drives)• Capture energy from water moving

downhill• Store water to avoid pumping at times of

peak energy cost

Energy Opportunities• Install SCADA software• Use efficient pumping systems• Install efficient disinfection equipment• Implement lighting • HAVC improvements

Energy Opportunities• Use efficient pumping systems• Reduce distribution leaks• Implement automatic meter reading

Energy Opportunities• Improve efficiency of aeration

equipment and anaerobic digestion• Implement cogeneration and other

onsite renewable power options • Implement lighting, HVAC

improvements• Fix leaks• Install SCADA software• Use efficient pumping systems• Recycle water

Energy Opportunities• Use efficient pumping systems• Capture energy from water moving

downhill

Figure 1 Energy Intensity of Each Stage in the Water Cycle [1]

WHY DOES ENERGY EFFCIENCY MATTER FOR WASTEWATER TREATMENT FACILITIES?

Water and wastewater systems are significant energy consumers with an estimated 3%-4% of total U.S. electricity consumption used for the movement and treatment of water and wastewater [2].

A secondary treatment plant may use as much as 1500 to 1700 kilowatt hours (kWh) of electricity to treat one million gallons of sewage and manage the resulting sludge and residuals [3].

Electricity is a critical input for delivering municipal water and wastewater services. Electricity costs are usually between 5 to 30 percent of total operating costs among water and wastewater utilities (WWUs) worldwide [4].

The Oregon Department of Energy reports that a city’s electrical power cost for wastewater treatment can consume 25 percent or more of the entire city’s electrical bill. Nationwide, that’s more than $4 billion annually [5].

Figure 2 Process flow diagram of a typical wastewater treatment plant

1.65%

8.67%

1.23%

19.24%

0.48%68.73%

Tertiary treatment

Sludge treatment

Lighting and other

Pretreatment

Primary treatment

Secondary treatment

Figure 3 Energy consumption in different processes [6]

Secondary Treatment

Microorganisms break down organic material, such as sugar s, fats, and proteins,that were not removed in the primary sedimentation process. This processreduces the majority of BOD5 and suspended solids

Pretreatment

Remove coarse materials such as paper, rocks, plastic, and rags

Tertiary Treatment

Biological treatment for nitrogen or phosphorus removal, chemical precipitationfor phosphorus or metals removal, air stripping for ammonia removal

Disinfection

Remove the remaining pathogens and bacteria

Primary Treatment

The remaining settleable and floatble materials are removed during primarysedimentation

0

50

100

150

200

250

300

Trickling Filter Activated Sludge Physical Chemical Other

Trickling Filter

Activated Sludge

Physical Chemical

Other

Figure 4 Number of treatment plants in New York State that use various forms of secondary wastewater treatment [3]

Activated sludge

Trickling filter

Non-electric secondary filtration

CONVENTIONAL SECONDARY TREATMENT PROCESSES

Oxidation ponds

Wastewater Plants Energy Consumption

Figure 5 Typical wastewater treatment energy use distribution [1]

Sewage aeration at an activated sludge

WWTP accounts for about 30 to 80 percent ofthe total plant electricity demand.

At the Fort Collins, Colorado, wastewater treatment facility. In 2012,the facility upgraded the controls on its blower system, installing anautomated control system with much better turndown capabilitiesand a blow-off valve to improve system performance. Along withother blower upgrades, the improved controls helped reduceenergy consumption from the aeration system by about 30 percent.

Figure 6 Typical blower efficienciesTurndown capability is an indication of the blower’s ability to meet a range of airflow requirements

Aeration

Aeration electric demand and energy consumption could be reduced by using fine-pore diffused-air systems and aeration process controls, or lowering the sludge age.

A cross section of a typical coarse-bubble aerationtank at an activated sludge treatment plant

A cross section of a typical fine-bubble aerationtank at an activated sludge treatment plant

Aeration systems consist of blowers and diffusers are the most significant consumers of energy in a wastewater treatment system

Installing variable-speed drives for blowers and matching the blower output with air requirements can reduce energy use

Fine bubble diffusers coupled with variable flow compressors and energy efficient motors can reduce aeration energy consumption by 50%

The Jackson, Wy., wastewater treatment plant replaced its 75 and 40 hpaerator mixers with 50 and 25 hp models, and replaced the 250 hp fixedspeed blower with a high efficiency 150 hp variable speed blower. This hasreduced the annual demand of 5.9 million kWh by about 1.95 million kWhand saved the plant around $85,000 a year.

Understanding Energy Use in Wastewater Treatment Facilities

Size Category Energy Use kWh/ML (kWh/MG)

<4MLD (<1MGD) 990 (3,749)

4-19MLD (1-5MGD) 403 (1,527)

19-76MLD (5-20 MGD) 394 (1,490)

76-284MLD (20-75MGD) 413 (1,562)

>284MLD (>75MGD) 282 (1,067)

Table 1 Comparison of Energy Use for Wastewater Treatment

Magnitude of energy use and demand in different facilities

Daily and seasonal load patterns/Facility size

The role of energy-intensive equipment in the wastewater treatment process

Type of processing

Efficiency levels of the equipment

Dependence of energy use on the quality of the waste stream (the level of treatment required to meet regulations, the treatment technologies used)

Figure 7 Municipal Wastewater Treatment Facility Load Pattern

According to EPA’s ENERGY STAR program, municipalities can reduce energy costs for water and wastewater treatment by as much as 10 percent through cost-effective changes to their operations [7].

CASE STUDY: NYSEDA municipal wastewater treatment plant energy evaluation Town of Tonawanda wastewater treatment plant

NYSERDA: New York State Energy Research and Development Authority

Figure 8 Electrical demand and usage

Power metering was installed at eachplant to accurately determine theenergy consumption and savings of theevaluated processes. Through the use ofsubmetering data and a thoroughunderstaning of wastewater treatmentprocesses, many opportunities toreduce plant energy costs whilemaintaining or increasing treatmentand/or capacity were identified

Figure 9 Total plant hourly kW draw

Figure 10 Change in usage

NYSERDA Energy Saving Measures

Capital Improvements

Replacement of existing sludge stabilization and dewatering facilities Modification or replacement of UNOX mixers with more efficient mixing equipment Replacement of existing cryogenic oxygen generation system with vacuum-assisted

pressure swing adsorption technology High pressure service water pump modifications Replacement of constant speed standard efficiency motors with premium efficiency

motors

Operation modifications

Operational modifications to reduce energy usage and cost

Lighting/HVAC modifications

GE Energy-Neutral Wastewater TreatmentReplace conventional aeration process with ZeeLung Membrane Aerated Biofilm Reactor (MABR) [8]

Four times more energyefficient than theconventional fine-bubbleaeration systems manymunicipalities arecurrently using

ZeeLung MABR Features

Simple Low Energy Nutrient Removal Small Footprint

The Metropolitan Water Reclamation District ofGreater Chicago began a demonstration project toevaluate GE’s new ZeeLung MABR technology toincrease the removal of nutrients in the existingplant footprint and reduce the energy required forbiological aeration by 40%

U.S. EPA offers energy-efficient equipment, technology and operating strategies

Step 1: BENCHMARK

your energy use

Step 2: Perform

an energy AUDIT

Step 3: IMPLEMENT audit

recommendations

Step 4: Share your sucesses and REPEAT,

for continuous improvement

Equipment and Collection System Upgrades Install Variable-Frequency Drives Upgrade to Energy Efficient Motors and Motor Systems Heating, Cooling, Ventilation System Upgrades Bright Lights Bring Energy Savings

Operating StrategiesManaging your electrical load Biosolids management Operation and maintenance Inflow and infiltration control

Energy Efficient Technology Cogeneration or combined heat and power Cogeneration using landfill gas

Renewable Energy In conduit hydro-power Solar powerWind power

Source: https://www3.epa.gov/region9/waterinfrastructure/technology.html

The city of Pacifica, California, recently began operating 1,800 solar panels to supply a portion of the Calera Creek Water Recycling Plant’s electric needs. The solar panels provide 10 to 15 percent of the treatment plant’s energy needs. The facility estimates $100,000 per year in energy savings

California Energy Commission

A multitude of energy efficient equipment, technologies and operating strategies are available to help take a bite out of the energy costs in water and wastewater facilities.

• Variable frequency drives

• Energy-Efficient Motors

• Heating, Cooling, Ventilation Improvements

• Lighting Improvements

• Electrical Load Management Strategies

• Cogeneration Optimization

• Fuel Cells

California water and wastewater agencies spend more than $500 million each year on energy costs

Source: http://www.energy.ca.gov/process/water/wastewater_treatment.html

The role of big data in wastewater treatment plants

SCADA systemsRetrieve

information on plant operation

and other systems

Predicting pipe failurePredictive weather data

Managing water costs

Energy management

Measuring asset condition

Energy monitoring can be used to helpunderstand and quickly intervene when energyconsumption at plant or component levelincreases. Data analytics can then be used toprevent efficiency excursions before they happenand to identify further reductions by a change ofoperation or equipment. Many water companieshave extensive energy data at plant level, butrarely at component level, but this is improving.

The water and wastewater industry is currently in transition from business-as-usual operations, employing traditional engineering solutions, to a new approach – Smarter Water Management – which uses big data and advanced analytics to create new insights that can improve operational efficiencies.

IBM Research, working in partnership with aEuropean wastewater utility, developed anend-to-end water resource recovery plantoptimization that can save as much as 15percent or more of costs associated withenergy consumption, biosolids handling, andchemical usage. Using a big data approachthat integrates dynamic plant simulationforecasting and mathematical optimization,activated sludge treatment processes can besignificantly improved in the areas ofresources recovery, cost efficiency, andregulatory compliance.

Programs

Federal programs

ENERGY STAR Water and Wastewater

ENERGY STAR Green Buildings and Energy Efficiency

U.S. EPA Office of Water, Energy Efficiency for Water and Wastewater Utilities

U.S. EPA Combined Heat and Power (CHP) Partnership

U.S. EPA Green Power Partnership

U.S. EPA Wastewater Management Website

U.S. EPA WaterSense Program

U.S. EPA State and Local Climate and Energy Program

Useful Resources

EPA’s Energy Use Assessment Tool is a free, downloadable, Excel‐based energy audit tool.The tool allows both water and wastewater systems to conduct a utility bill analysis, determine baseline energy consumption and cost in total and also broken down to the process‐level and equipment‐level, and identify the most energy‐intensive areas of the system. In addition, the tool highlights areas of inefficiency that users may find useful in identifying and prioritizing ECMs. The tool can be found at: http://water.epa.gov/infrastructure/sustain/energy_use.cfm.

EPA’s EnergyStar Portfolio Manager is a free, online tool drinking water systems can use to develop a simple energy baseline based on utility bill data and track changes in energy use and GHG emissions over time. The tool can be found at: http://www.energystar.gov/index.cfm?c=evaluate_performance.bus_portfoliomanager.

Understanding Your Electric Bill is a Wisconsin Focus on Energy Fact Sheet that can be found at: http://water.epa.gov/infrastruture/sustain/Understanding‐Your‐Electirc‐Bill.pdf

Electric Power Research Institute (EPRI) Energy Audit Manual for Water /Wastewater Facilities can be found at: http://www.cee1.org/ind/mot‐sys/ww/epri‐audit.pdf.

How to Hire an Energy Auditor is a California Energy Efficiency document that can be found at: http://www.energy.ca.gov/reports/efficiency_handbooks/400‐00‐001C.PDF.

California Energy Commission (Process Energy-Water/Wastewater Treatment) http://www.energy.ca.gov/process/water/wastewater_treatment.html

Reference

1. Efficiency, E., Energy Efficiency in Water and Wastewater Facilities.

2. Daw, J., et al., Energy efficiency strategies for municipal wastewater treatment facilities. Contract, 2012. 303: p. 275-3000.

3. Pakenas, L. J. (1995). Energy Efficiency in Municipal Wastewater Treatment Plants: Technology Assessment, New York State Energy Research and Development Authority.

4. Liu, F., et al., A primer on energy efficiency for municipal water and wastewater utilities. 2012.

5. https://energytrust.org/library/GetDocument/3441

6. Tao, X. and W. Chengwen (2009). Energy consumption in wastewater treatment plants in China. IWA world congress on water, climate energy.

7. ICF International. 2008. Water and Energy: Leveraging Voluntary Programs to Save Both Water and Energy. http://water.epa.gov/scitech/wastetech/upload/Final‐Report‐Mar‐2008.pdf

8. http://www.gewater.com/products/zeelung.html