Like many municipalities in urban and suburban areas, San Bruno, Calif.’s source water comes both from its own groundwater supply and through a...
Howard County, Md., facility helps protect Chesapeake Bay with enhanced nutrient removal
The Little Patuxent Water Reclamation Plant (LPWRP) serves the heart of Howard County, Md. The sewage collection system recently underwent a $92 million upgrade to improve the quality of the plant’s effluent discharge and reduce the amount of harmful nutrients that reach Chesapeake Bay.
With a geographic footprint of 64,229 sq miles, Chesapeake Bay ranks as the nation’s largest estuary and receives flows from 150 rivers and streams. The multistate region’s growth over the past 50 years has brought an inevitable surge in byproduct nutrients from wastewater treatment plants that has steadily eroded the vitality of the Bay’s water environment.
In the estuary and along its tributaries, nitrogen and phosphorus are major problems attributed to several sources, but caused in large part by wastewater treatment plant discharges reaching the bay.
Following exhaustive evaluations, consulting firm Atkins Global recommended an enhanced nutrient removal (ENR) upgrade comprised of seven deep-bed monomedia Leopold elimi-NITE 2.0 denitrification filters, along with FilterWorx control systems and related ancillary equipment.
Other equipment was also supplied by Xylem, including a 400-lamp WEDECO TAK 55 UV disinfection system, Flygt-brand propeller mixers and related head works screening and dewatering and clarification equipment.
An additional 7,000 Sanitaire ceramic diffusers were added to the process reactor aeration grids, and the existing centrifugal blowers were replaced with a new turbo-type unit. The capacity of the existing biological nutrient removal (BNR) process was expanded with a new process reactor, a secondary clarifier, launder covers on the secondary clarifiers and a new solids-processing centrifuge.
The ENR system now in operation can scrub the effluent down to 3 or 4 mg/L of total nitrogen, compared to the 8 mg/L achieved by the earlier BNR method.
In tandem with the phosphorous removed upstream in the process reactors, total phosphorous can now be reduced to 0.2 mg/L or less.
The LPWRP’s daily reductions equate to an impressive 37,000 lb of suspended solids, 4,730 lb of nitrogen and 965 lb of phosphorous. The plant will increase the statewide nitrogen reductions achieved by earlier upgrades across the state’s wastewater treatment infrastructure by more than 16 million lb. Adding ENR to the state’s 66 largest plants could potentially reduce nutrient loading by another 7.5 million lb of nitrogen and 260,000 lb of phosphorus per year.