Greywater Treatment in combined Biofilter/Constructed Wetlands in Cold Climate

In Norway systems consisting of an aerobic biofilter followed by a subsurface horizontal flow constructed wetland has been very successful in reducing organic matter, indicator bacteria, nitrogen and phosphorus in greywater. Because of phosphate free detergents are used in Norway and no toilet waste is included, the average influent total phosphorus concentrations (measured as septic tank effluent-STE) are about 1mg P/l and the average influent total nitrogen concentrations are in the range 8-10 mg N/l. The aerobic biofilter prior to the wetland is essential to remove BOD in a climate where the plants are dormant during the cold season. When combined with a horizontal flow constructed wetland the concentrations of indicator bacteria in the effluent meets European standards for swimming water quality. The effluent concentrations for phosphorus are generally < 0.2 mg P/l and for nitrogen < 5mg N/l. The combined biofilter /constructed wetland systems require 1-3m 2 surface area per person. The