Sustainable wastewater treatment involves the reuse of the process’s byproducts for the treatment plant’s operations. A typical wastewater treatment plant offers several options for generating energy or carrying out other conservation measures. Carefully planned wastewater treatment can provide the following benefits: (1) the natural flow of water due to gravity can act as an energy source; (2) methane and hydrogen production from anaerobic digestion serve as energy sources for powering the facility; (3) the reactions inside the digester produce heat that can be rerouted to other biological processes; (4) the treatment plant’s gray water may be reused for flushing toilets; and (5) nutrient-rich sludge exiting the digester serves for landscaping the facility’s grounds or may be sent to local farmers. In summary, in sustainable wastewater treatment, everything is used and reused to the maximum.
The wastewater industry resembles other industries today in trying to meet stricter pollution requirements while reducing energy use. Water and wastewater treatment in the United States uses only 2 percent of the country’s total amount of energy, but with concerns over fuel and energy costs the industry faces the need to build more sustainable operations. Electricity needs of wastewater treatment plants vary by the amount of incoming wastewater they treat each day and the concentration of waste in the water.
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| Sustainable wastewater treatment plants allow water to naturally purify and consume minimal energy for pumping water. Methane gas from the treatment plant’s anaerobic digester can provide some or all of this energy. The Earth purifies the water due to the soil’s ability to remove particles and bind to many organic compounds. |
Sustainable practices in wastewater treatment provide some or all of the energy needs for running pumps for the aeration step and other pumps, heating, and lighting. Methane serves as the most efficient energy source for these purposes, helped to a smaller degree by hydrogen gas. Wastewater-to-energy plants recover methane in a three-step process that involves (1) dehydration, (2) gas cooling, and (3) removal of hydrocarbon compounds heavier than methane. This process results in pure methane of natural gas quality. Methane contains a heating value of 55.5 megajoules per kg of material compared with natural gas’s 53.0 MJ/kg. Other fuels do not provide as much energy as methane: gasoline (48.1 MJ/kg); home heating oil (45.5); coal (28.5 MJ/kg); and wood (about 15 MJ/kg). Wastewater-to-energy therefore holds exciting promise for leading the way in new waste-to-energy technologies.
