Uprating and rescuing small wastewater treatment facilities by adding tertiary treatment reed beds

A water utility developed use of gravel-filled constructed reed beds operat ing in a subsurface flow mode to polish secondary effluent to meet demandin g standards for 5-day biochemical oxygen demand (BOD5) and total suspended solids. Results collected by the regulatory environmental agency (EA) for 4 3 sites completed before the end of 1993 are given. The average BOD5 concen tration was 1.9 mg/ L. The benefit of affluent polishing is further demonst rated by influent and effluent data from two sites that have operated since June 1990 and September 1991, respectively. Environmental agency effluent quality data are also given for 39 sites at which reed beds either treat st ormwater and secondary effluent together or have been installed as remedial treatment for works struggling to meet secondary treatment standards. The average BOD5 concentration for these sites was 3.0 mg/L. Remedial, or treat ment plant rescue, application is illustrated by four contrasting case stud ies where constructed reed beds brought facilities back into compliance.