The following is the second part in a series about recent upgrades to an
Easton wastewater treatment plant, and how these improvements have helped support our clean water efforts. Read the first part in the series here.
Construction began in 2005, and the plant began operating on June 30, 2007, (the fifth and--at the time--largest BRF plant to go online). The design for the plant incorporates sophisticated new practices for removing phosphorus and nitrogen, the latter being especially difficult to catch because its waste compounds dissolve so easily in water. It includes advanced filter systems and twin five-stage bacteria-driven bioreactors, making Plant Manager Doug Abbott and his staff shepherds of livestock as surely as any dairy farmer.
Over the course of the 1.75 days (on average) that a batch of wastewater flows through the plant, the "bugs" process it in those five stages, gradually breaking down nitrogen compounds until the element vents off as a stable, odorless gas. In the bioreactor stages, the system alternately adds and takes away oxygen. Adding means spraying it in extremely fine bubbles, for more surface area to make it readily available to the bugs. "In champagne and sewage treatment," Doug Abbott remarked with a chuckle during the 2009 visit, "it's all about the size of the bubbles."
Screens and filters remove solid material containing most of the phosphorus and some nitrogen. It goes through aerated holding tanks, de-watering centrifuges, and drying systems into a silo for storage for sale to local farmers, who use it as a soil conditioner. Final disinfection comes from intense ultraviolet radiation. The plant is highly automated, with an alphabet soup of Supervisory Control sensors; Programmable Logic Controllers to optimize efficiency of valves, pumps, aerators, and chemical feeds; and alarm systems that allow the staff of six people to operate the plant on one shift, with members on call if an alarm goes off. Abbott noted that both monitors and sensors are rapidly becoming more sensitive and reliable.
In just its second year of operation, the Easton plant won an award for operations and maintenance excellence from EPA's Region 3. By our 2009 visit, the plant was already running well below its permit loads of 4 milligrams per liter of nitrogen and 0.3 mg/l of phosphorus. "There's still a lot to learn about Enhanced Nutrient Removal," Doug Abbott said. He was referring to challenges like how to meet the discharge permit's goals on a daily basis, including how to adjust to varying inflow, fine-tuning for weather, and giving the bugs the consistent conditions they need to thrive.
--John Page Williams
CBF's Senior Naturalist
Stay tuned tomorrow for more on how this revolutionary new plant came to be, and what it means for our waters and Bay. In the meantime, learn more about wastewater treatment plant issues here on our website.