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Jae K. Park

Energy in Water and Wastewater Treatment Plants

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Energy CostMunicipal wastewater treatment plant can see

up to 40~55% of their operating budget dedicated to energy.

Industrial wastewater plants can see up to 70% of their operating budgets spent on energy.

WTPs and WWTPs account for approximately 3% of the electric load in the United States.

As populations grow and environmental requirements become more stringent, demand for electricity at such plants is expected to grow by approximately 20% over the next 15 years (Carns 2005).

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Energy CostEnergy represents a substantial and rising cost

to water and wastewater utilities.In recent survey of utility directors, energy cost

was rated as one of the top five long term concerns

Many utilities are implementing energy management and cost control programs.

New technologies in drinking water treatment are more energy intensive

In wastewater treatment, older conventional technologies are given way to lower energy options

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Wisconsin Energy UsageEnergy cost (% of total expenses): 10.5%

2001 2002 2003 2004 2005 2006 2007 20080

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http://dnr.wi.gov/environmentprotect/gtfgw/documents/MhTF20080501.pdf

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Electricity Bill Two methods

By the amount of energy used over a specific period (kilowatt-hours)

By demand, the rate of the flow of energy (kilowatts)

Electric utilities structure their rates on the basis of the user’s required voltage level, the electricity usage at different hours of the day, and the peak demand. A WWTP might be operating equipment when electricity is at peak rates, resulting in unnecessary costs.

Plant personnel should become familiar with the energy rate structure to determine whether they can operate equipment at off-peak hours or reduce energy consumption during peak-demand hours.

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Industrial Electricity Bill StructureEnergy charge Similar to flat rate Pays for each killowatt-hour of electrical energy

used Off-peak and on-peak rates

Demand or capacity charge A dollar amount usually based on the highest

"power" demand by the user in any hour of the previous month or quarter or year.

e.g., :Don't start all the motors in the plant at the same time, and let's generate some or all of our own electricity!”

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Technology ShiftWater/wastewater reuse is growing also

increasing use of energy intensive technologies:Membrane BioreactorsReverse OsmosisUltra and Micro FiltrationUltraviolet disinfection

Reuse of wastewater allows us to use water wisely and more effectively but can result in an additional 20~40% increase in energy use over conventional treatment methods

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Ultra- and Micro-FiltrationTreat wastewater resulting in high quality

effluent but increase energy use by 10%.

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UV and OzoneOzone and UV provide significant water quality

benefits but consume from 100 to 400% more energy than traditional treatment methods.

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Reverse Osmosis An effective method for desalting sea water and reuse

of wastewater, but requires 500% more energy than conventional water or wastewater treatment.

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Effective Energy ManagementLike most initiatives, successful energy

management depends on good people.Energy management is a cultural thing.Significant quick wins can be achieved with

minor organizational change and new business practices.

Consider ‘supply and demand’ in energy management program.

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Effective Energy Management- continued

In many cases, largest savings come through real-time optimization using SCADA.

Diligence in operations is required for continuous improvement in energy management.

Energy management is a continuous operational process.

Setting & tracking goals is key to successful energy management.

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Ways of Reducing Energy CostsReview the power rate for each stationReduce demand chargesKnow when the station power meter is readDedicate a staff member to monitor the

power billsTake advantage of time-of-use metering

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Additional Consideration forReducing Power Optimization

Analyze pump stations for pressures, flows, and storage requirements for peak operational demands and fire/emergency requirements.

An opportunity may exist for reducing the storage if there is excessive storage.

The impeller can be trimmed if there is surplus pump discharge pressure.

It may be more cost effective to install soft starts or VFD (variable frequency drives) at major power users.

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Organizational ProcessesOperate pumps and valves to minimize energy

costs & use.Develop the system operating plan.Measure system performance, respond to events

and update the plan.

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Key Components of Energy Management Plan

Create a system to track energy usage and costsPerform energy audits of major operationsUpgrade equipment, systems, and controls,

including facility and collection system improvements to increase energy efficiency

Develop a cost-effective electric supply purchasing strategy

Optimize load profiles by shifting operations where possible

Develop in-house energy management training for operators

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Example Modifications - 1100-horsepower surface aerator replaced with a

25-horsepower subsurface aerator. An aerated grit chamber that used

approximately 2,900 megawatts per year replaced with a vortex system.

Installed high-efficiency influent and effluent pumps, high-efficiency motors, and variable-frequency drives.

Discontinuing second-stage activated-sludge mixing.

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Example Modifications - 2Add plastic balls to prevent heat loss and

evaporation losses in the oxygen production vaporizer pit.

Tie in pipes on gas recirculation blowers to allow one blower to service two mixing tanks.

Installed high-efficiency influent and effluent pumps, high-efficiency motors, and variable-frequency drives

As a result, an estimated annual savings of $2,796,000 (California Energy Commission, EBMUD Case Study, 2003) or energy savings of approximately 70% per year achieved.

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Example Modifications - 3Installation of an equalization basin allows the

plant to even out pumping needs, and so allows for “peak shaving” by running pumps during off-peak hours

Reducing infiltration and inflow in the collection system also can pay for itself in energy savings. By rehabilitating damaged or deteriorated sewer lines and eliminating improper connections to the system, the overall flow to the WWTP is reduced, thus reducing the amount of energy required to treat the flows.

Installation of Supervisory Control and Data Acquisition (SCADA) system.

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Auxiliary and Supplemental Power Sources (ASPS) or Energy Recovery Equipment

Cogenerate electricity and thermal energy on site. Capture and use anaerobic digester gas (or bio-gas). Ex.

EBMUD: Generates 50% of energy needs, $1.7 million savings annually.

Bio-gas fueled internal combustion engines, microturbines, wind turbines, fuel cells, and solar cells.

Some ASPS available do not conserve energy but replace off-site generation with on-site generation.

The city of Pacifica, California, 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% of the treatment plant’s energy needs. The facility estimates $100,000 per year in energy savings (Manekin, 2006).

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Example Modifications – 4Industrial Application

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Helixchanger®

A high efficiency heat exchanger and a proprietary product

Quadrant-shaped plate baffles are placed at an angle to the tube axis in a sequential arrangement to create a helical flow pattern. The helical flow offers improved thermal effectiveness, enhanced heat transfer, reduced pressure drop, lower fouling, and significantly reduced vibration hazards.

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Microturbines

Background reading materials: http://www.energy.ca.gov/distgen/equipment/microturbines/microturbines.html

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Fuel CellAn electrochemical energy conversion deviceWorks by a catalyst such as a platinum group metal

or alloyReplacement for diesel generatorsBackground reading materials

http://www.fuelcells.org/

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WWTP in Amman, Jordan

Approach used to tackle energy issues

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Summary Serving for 2.2 million people

Qaverage = 267,000 m3/dayQmax = 530,000 m3/day

Hydraulic turbines upstream and downstream and gas turbines powered by methane gas from anaerobic digesters: 95% of the electricity required for the plant

Contract signed between the Samra Plant Company (owned by SUEZ ENVIRONNEMENT, Infilco Degrémont Inc. and The Morganti Group Inc.) and the Jordanian Government, represented by the Ministry of Water and Irrigation: design, financing, construction and 22-year operation of the treatment plant for a price of USD169 million.