Meeting Stringent Phosphorus Limits Without A Tertiary System

The Marlborough, Mass., Easterly Wastewater Treatment Facility, originally constructed in the early 1970s, is one of two facilities serving the Marlborough area. The facility’s influent is mainly commercial and residential. It also treats a small stream from an on-site composting station.

The treated effluent discharges into a small tributary leading to the Hop Brook and, ultimately, into the Concord River. The facility has a design capacity of 5.5 MGD with a high hydraulic peaking factor of 4:1. It features primary clarification, as well as two-stage aeration with intermediate and final clarifiers, followed by chlorination/dechlorination. Sludge is dewatered prior to being sent to composting. The two-stage aeration system was originally designed to remove biochemical oxygen demand in the first stage and achieve nitrification in the second stage.