Application of a horizontal subsurface flow constructed wetland on treatment of dairy parlor wastewater

Two horizontal subsurface flow reed beds of 75 m2 each, treating dairy parlor effluent and domestic sewage (about 6.5 m3/day), were set-up to determine the efficiency of this system in reducing the polluting load in an isolated mountain rural settlement. A total suspended solids value of about 0.70 g/l and chemical oxygen demand (COD) and biological oxygen demand (BOD5) values of about 1200 and 450 mg/l O2, respectively, were characteristic of the influent waters. Removal of suspended solids and organic load constantly remained at levels above 90%, while those of the nutrients N and P were about 50% and 60%, respectively. The total number of coliform bacteria and Escherichia coli was reduced by more than 99%, and faecal streptococci by more than 98%. Nitrates, chlorides, sulfates, anionic and non-ionic surface-active agents and heavy metals were detected only in low concentrations. Concentration and localization of metals was also quantified in Phragmites tissues by microanalysis. Results demonstrated the use of reed beds as an appropriate treatment to reduce pollutants in wastewater from rural activities to values acceptable for discharge into surface waters.