Backround
Up until the construction of major intercepting sewers and a wastewater treatment facility in early 1970’s, the Lewiston and Auburn sewer systems were a series of combined sanitary and stormwater drainage systems that discharged directly to the Androscoggin River and its tributaries. This system of combined sewers had evolved over a period of approximately 100 years as the Lewiston-Auburn area developed. However, as populations and waste quantities increased in the Lewiston – Auburn area, it became apparent that the continual discharge of raw, untreated sewerage to area receiving waters was a public health threat and a significant water quality problem.

The Lewiston – Auburn Water Pollution Control Authority (Authority) was subsequently formed to provide common wastewater treatment for the cities of both Lewiston and Auburn.

Facility Description
The Authority began operation in 1974, and is designed and licensed to provide secondary (activated sludge) treatment for an average daily flow of 14.2 million gallons per day (MGD) of wastewater from the cities of Lewiston and Auburn, as well as septage from surrounding communities. In 2004, the Authority treated a total of 4 billion 42 million gallons of wastewater or an average daily flow of 11 MGD. The lowest monthly average flow was in July when the average flow was 9.66 mgd while the highest monthly average flow occurred in April at 16.1 MGD.

Treatment Process
Secondary treatment is provided using an activated sludge process and solids are dewatered by belt filter presses. After metering, flow from the two cities is combined and screened to remove large solids. An aerated grit chamber is used to remove sand, grit and other small inorganic particles that could cause abrasion and premature wear of pumps, piping and other downstream equipment. Primary sedimentation is used to remove floating materials and settleable solids. The settled solids are called primary sludge. The wastewater then flows to the aeration basins where it is mixed with acclimated microorganisms and aerated for approximately ten hours. The microorganisms use biodegradable materials in the wastewater as food. This process turns soluble pollutants into solid organisms which are subsequently removed by sedimentation in the secondary clarifiers. While the majority of the settled microorganisms are returned to the aeration basins to remove additional pollutants, it is necessary to remove a portion of the organisms to maintain a healthy system. The portion thus removed is called waste activated sludge or secondary sludge.

Primary sludge is thickened in gravity thickeners and secondary sludge is thickened in dissolved air flotation thickeners before being combined for dewatering. Polymer is added to the combined sludge as a conditioning and flocculating agent prior to dewatering. After dewatering, the sludge cake can be mixed with quick lime or hydrated lime in a pug mill to achieve a pH of 12 after two hours contact time and 11.5 after 24 hours in order to comply with State requirements. This material can then be applied to farm land (as a “class B” material) or may be utilized under site specific license for landfill closure or other beneficial use. The Authority complies with the management practices outlined in both State and Federal regulations.

A portion of the Authority's sludge is composted to produce a high-quality "class A" material. The Authority's facility is an agitated bin, in vessel composting system. This material is sold to contractors, landscapers, nurseries, colleges, public works departments and the general public for use as a soil amendment and low strength fertilizer.

Biosolids Generation
In 2004, the Authority produced 25,879 cubic yards of biosolids having an average solids content of approximately 18% before lime addition and approximately 25% after lime addition (when class B material was produced for direct farm application). The Authority administers an extensive testing program on the biosolids produced at the treatment facility. Testing for solids content and pH is performed daily. Testing is performed on a monthly basis for percent solids, volatile solids, Total Kjeldahl Nitrogen, organic nitrogen, ammonia nitrogen, nitrate, nitrite, total phosphorus, total potassium, cadmium, copper, chromium, nickel, lead, zinc, calcium, magnesium, iron, arsenic, chloride, sodium, mercury, molybdenum, and selenium. The Authority’s class B biosolids are tested annually for dioxins and furans, pesticides, PCBs and other required priority pollutants.

The Authority’s compost product (class A biosolids) is tested daily for pH and percent solids and the time and temperature of the compost in production is sampled and recorded at least daily. Monthly analyses include salmonella, pH, arsenic, boron, cadmium, calcium, chromium, copper, iron, lead, magnesium, mercury, molybdenum, nickel, potassium, selenium, sodium, zinc, chloride, nitrate nitrite, total organic nitrogen, Total Kjeldahl Nitrogen, ammonia nitrogen, total phosphorus, total volatile solids, total solids, specific conductance, and pH. The compost is also is tested annually for dioxins and furans, pesticides, PCBs, and other required priority pollutants.

A summary of the results of these tests are on file at the treatment facility and at the Department of Environmental Protection, Bureau of Hazardous Materials and Solid Waste Control.