Treating dairy parlor wastewater using subsurface-flow constructed wetlands

Two horizontal subsurface flow reed beds to treat parlor effluent as well as domestic sewage, each 75 m(2), were built in 1999. The goal of the project is to verify the efficiency of this treatment system to reduce the polluting load of parlor effluent, which are more polluted than domestic sewage. Throughout the first year of the trial the two wetlands operated one after the other in succession and wastewater inflows and outflows were sampled 20 times. Analyses were made for pH, TSS, COD, BOD5, TKN, NH4-N, NO3-N, P, Cu and Zn. The reduction of suspended solids and organic load remained consistently at levels greater than 90%; those of the nutrients N and P were over 40% and 50%, respectively. The monitoring of the heavy metals Cu and Zn made it possible to verify that their load was reduced consequent to deposit in the sediments in moving through the system, while the phenomenon of assimilation by the reeds was shown to be insignificant. Mycorrhizae were found in the roots of the reeds of both wetlands, which indicates a possible strengthening of the assimilation activity of the plants.