In addition, the shutdowns caused huge environmental problems because without adequate backup power, the pumping stations and treatment plants could not perform their tasks, and many were forced to dump untreated wastewater into rivers and in the street. New York City, for instance, was particularly impacted by the blackout, as many of its plants had no choice but to dump raw sewage into rivers and basins. It is believed that sewage plants spilled nearly half a billion gallons of untreated wastewater into New York Harbor over a two-day period. The City is still trying to determine the environmental effects of this huge spill. Seven stations in the greater New York metropolitan area were particularly impacted by the blackout either because they did not have backup generation or because the backup emergency system did not perform well. The shutdowns at the 13th Street wastewater station in Manhattan and the Newton Creek plant in Greenpoint, Brooklyn, were particularly troubling because they are located near densely populated residential areas.

The biogas-fueled microturbine combined heat and power system in Lewiston, NY, has surpassed more than 20,000 hours of operation.

The great blackout not only exposed the vulnerability of the US electric grid but also forced policy-makers to begin planning for potential future outages by making sure that essential public services, such as trains, subway systems, wastewater treatment plants, and communication systems, continue to operate during a sustained power interruption.

For wastewater treatment plants there are two broad alternatives that can potentially alleviate the negative repercussions of blackouts: First, a more limited short-term solution would be the installation of more powerful backup generators. This solution would provide critical backup power to make sure that the sewage plants continue operating during a rolling blackout at least at partial load. Second, a more long-term solution would be onsite combined heat and power with part or no reliance on the local electric grid. This solution, where warranted, would not only provide backup power generation but also increase the overall energy efficiency of the sewage plants. This would be a more capital-intensive alternative but one that would provide long-term operating benefits in the form of reduced energy expenses for the plants. The combined heat and power plant would either be based on an internal-combustion engine­generator set or on gas turbine­generators. Installations of 1,000 kilowatts or less generally use engine-generators while gas turbines are the equipment of choice for capacities of 6,000 kilowatts or more.

Wastewater Plants in New York

In the early 1990s, the New York State Energy Research Development Agency (NYSERDA) began thinking of ways to improve the state's overall energy efficiency. One of the early concepts was to apply combined heat and power at wastewater treatment plants. NYSERDA estimates that the state's wastewater treatment plants each year consume about 1.5 billion kilowatt-hours of electricity for sewage treatment and sludge management (Pakenas 1996). In addition, NYSERDA estimates that wastewater treatment plants use 170 million therms of natural gas and 16 million gallons of fuel oil each year for space heating and sludge processing. A single treatment plant is estimated to use as much as 1,700 kilowatt-hours of electricity to treat 1 million gallons of sewage and dispose of the resulting sludge and residuals.

In addition to blackout prevention, onsite generation could play a major role in reducing this huge amount of energy used. Natural gas to fuel the onsite energy plant could be purchased and/or produced by anaerobic sludge digesters (biogas), a byproduct of the wastewater treatment process. In this way, combined heat and power would displace electricity purchases from the utility and the waste heat from the system could be recovered to heat the plant and for thermal load applications, including sludge drying and digester heating. Sludge management in particular has become increasingly costly because the disposal process has become more complicated given the greater distance between the sewage plants and the disposal sites.

The potential market for combined heat and power is very large. There are more than 570 wastewater treatment plants in New York State. Some plants are very small, treating 100,000 gallons of water a day, while others are very large, treating up to 300,000 gallons per day (gpd). According to NYSERDA estimates, approximately 20 million gallons, or 1,000 dry tons, of sludge are produced by the sewage plants in the state. The largest plants are found in New York City, Albany, Buffalo, and Rochester and in the populous suburbs of Westchester and Long Island. Approximately 75 plants in the New York metropolitan area treat 60% of the state's total wastewater flow of 3.5 billion gpd.

Recent Projects

The New York Power Authority (NYPA) has spearheaded the installation of CHP units at sewage plants. A 200-kilowatt unit was installed at the Westchester County wastewater treatment plant in Yonkers. While most fuel cells run on natural gas, the Yonkers project is the world's first commercial fuel cell to use the anaerobic digester gas that is a byproduct of wastewater treatment, avoiding the environmental impacts of burning off the gas into the air. This significantly cuts the pollution that would result from burning off the gas - and helps the county meet federal Clean Air Act requirements. The fuel cell meets part of the treatment plant's electricity needs, and the waste heat is used in the wastewater treatment process. Anaeorbic digester gas also powers two 30-kilowatt microturbines that NYPA has installed on behalf of the Town of Lewiston's wastewater treatment plant in Niagara County. The units have cut emissions to the air by about 90% compared with a previous diesel generator. Waste heat from power production supplies hot water for the treatment plant.

Another very encouraging initiative was launched in February 2004 when New York City's Mayor Bloomberg and NYPA unveiled a new program that will convert waste gas at four of the city's sewage treatment plants into electricity. The initiative will help avert blackouts and electricity price spikes. It will also boost the city's energy efficiency since it will save up to 3,000 barrels of fuel oil a year. The surrounding communities will be positively impacted by the initiative as well since it will also reduce fumes from the wastewater plants. NYPA has installed eight 200-kilowatt fuel cells at four sewage plants in the Bronx, Brooklyn, and Staten Island. The fuel cells are manufactured by United Technologies Corporation (UTC), the supplier of the world's only commercially available fuel cell system. UTC supplies fuel cell devices that combine hydrogen and oxygen to produce electricity, heat, and water. Because hydrogen is often not readily available, the fuel cells use a fuel processor to convert hydrocarbon fuels, typically natural gas, into a hydrogen-rich stream that is fed into the fuel cell. These fuel cells are virtually pollution free. Besides generating 200 kilowatts of electricity, the fuel cells provide more than 900,000 Btu/hr of heat that can be used for space heating, hot water heating, or absorption chilling and air conditioning.

At the unveiling of the project Mayor Bloomberg said, "We are using the fumes generated by our own sewage to clean our own sewage. And this will not only make the plants more energy-efficient; they will also be a lot better neighbors to the surrounding area."

Hopefully this initiative will encourage other managers of water treatment plants across the state to look into the viability of combined heat and power.

Reference

Pakenas, Lawrence J. Energy Efficiency in Municipal Wastewater Treatment Plants. NYSERDA. 1996.

DE - July/August 2004