Speaker(s)

Description

Electrical-grid powered aeration is used intensively in reactor basins at activated-sludge wastewater treatment plants (WWTPs) to supply the mixing and oxygenation needed for digestion. Personnel at the Eden WWTP investigated alternatives to grid-powered aeration to reduce the plant’s operational expense and carbon footprint. A U.S. Environmental Protection Agency qualitative assessment indicated that solar powered circulation (SPC) technology could replace some or all of the mixing and oxygenation supplied by grid-powered aeration (U.S. EPA 2005). The goal of the initial Eden WWTP study was to meet National Pollution Discharge Elimination System (NPDES) limits while operating a single SPC unit in one reactor basin and reducing aeration.

The study was conducted in a basin of surface area=1.74 ac, and operating volume=7.0 MG. The pre-SPC period, June 2008 through May 2009, was followed by the during-SPC treatment period, June 2009 through May 2010. Three-to-six of the 12, 20-horsepower aerators were deactivated over the course of the during-SPC period. Parameters monitored throughout the study were wastewater flow rate, total suspended solids (TSS), biochemical oxygen demand, acidity or alkalinity (pH), dissolved oxygen, ammonia nitrogen, total nitrogen, total phosphorus (TP), fecal coliform, and electrical-grid power usage and expenditures.

No NPDES water quality violations occurred during either study period. Water quality parameters were generally unchanged or improved during the SPC treatment period, with statistically significant reductions seen in TSS, pH and TP. Mean monthly electrical-grid power use declined by 1,692,000 kWh (42%), eliminating 2,268,972 lbs of CO₂ emissions to air. Annual electricity expenditure decreased by $61,101 (31%) as the cost of electricity rose. The cost savings on electricity resulted in a 10.7 month pay-back period.

The study results indicated that water quality parameters remained stable or improved as use of aeration declined from 240 to 120 HP during the SPC treatment period. The WWTP’s operating costs and carbon footprint decreased with electrical-grid power use. These results obtained at an activated-sludge WWTP were consistent with the conclusions reached in the U.S. EPA evaluation of SPC use at four pond-based WWTPs. The Agency concluded that SPC reduced grid-powered aeration usage, electricity consumption and operational costs, associated greenhouse gas emissions, odor events, and sludge buildup.

Conference

NC AWWA-WEA
Wilmington Convention Center - Wilmington, NC, March 2011