Tak Kai Pang, PhD, PE, Utility Infrastructure Technical Director, American Structurepoint ([email protected]

Every community is coping with its aging wastewater treatment infrastructural, regulatory modifications, and technical challenges, all of which require significant investment. This investment can result in higher sewer rates to be paid by the rate payers within the communities. Historically, wastewater has been treated as waste when in fact, it is a resource rich in water, nutrients, and energy. Proven technologies exist to reclaim, reuse, and repurpose these valuable resources while continuing to meet regulatory requirements, minimize operating costs, improve the environment, and stimulate regional economic development.

With water being the obvious resource, proven technologies are available to treat the wastewater safely for reuse. Reclaimed water can be used for agricultural irrigation, landscaping irrigation, to recharge ponds and lakes for recreational use, and to recharge the groundwater. Each of these reuses allows a community to minimize its reliance on groundwater/surface water for fresh potable water.

The nutrients, in particular, phosphorus, can be recovered from the wastewater to produce fertilizer and result in several benefits for our communities and the environment.   Phosphorus is a key nutrient in the food grown today. Phosphorus is an essential element for plant life, but when there is too much of it in water, it can use up large amounts of oxygen and cause algae to grow. With economically viable phosphorus mines diminishing worldwide, harvesting the phosphorus going through our treatment plants provides a marketable product, removes the nutrient from our waterways, and reduces the occurrence of harmful algae bloom. Red tides and blue-green algae are examples of harmful algae blooms that can severely impact human health, aquatic ecosystems, and the economy.

Biosolids generated from wastewater treatment plants are another nutrient rich resource. This product can be reused on agricultural land to supplement commercial fertilizers or to produce compost for landscaping.

The anaerobic digestion process is a means to stabilize biosolids produced at a treatment plant. The stabilized biosolids can be a beneficial reuse as mentioned above, and the digester gas generated from the anaerobic digestion process can be recovered to use as a combustible fuel. This fuel can be used directly to provide heat to the digesters and/or heat for buildings within the treatment plant. The gas may also be cleaned of impurities and used to generate electricity through the combined heat and power process. Generated electricity helps offset the rising cost to power a treatment plant, or in some cases, to reach a net zero electrical cost. Another beneficial use gaining in popularity is renewable natural gas (RNG), which is the digester gas produced in the anaerobic digester by removing all impurities and creating a fuel that is nearly pure methane (>97%). This fuel is commonly used as transportation fuel in the form of compressed natural gas (CNG), or it may be injected into a nearby gas pipeline.

Additional waste, in the form of food waste and fat, oil, and grease (FOG), can be introduced in the anaerobic digester to produce more digester gas. This in turn reduces the need to send this material to a landfill, which results in prolonging the service life of a landfill. The community can also benefit by charging tip fees for the treatment of these materials in the wastewater treatment plant, thus generating another revenue stream to offset the plant’s operating cost.

If you want to know more about how you might implement some of these practices at your wastewater plant, please contact our expert, Tak Kai, at American Structurepoint at 317-547-5580.

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