Wastewater treatment by greywater separation:: Outline for a biologically based greywater purification plant in Sweden

The current system of wastewater treatment in industrial societies severely restricts the possibility of nutrient recycling. One of the biggest constraints is the mixing of the part of the sewage water containing a high concentration of nutrients with greywater, which contains fairly low amounts. The MIx-First-and-Separate-LAter (MIFSLA) approach to waste water management has led to a wastewater system the function of which is to first mix and then to remove urine and faeces from the greywater. The aim of this article was to analyse this problem and to propose a method for wastewater treatment where the different components of the wastewater are treated according to their individual qualities. The focus is placed on the treatment of greywater with ecotechnological methods. The greywater purification plant is designed to enhance the subsurface flow of water and biological interactions of plants and microorganisms ill a triplicate riparian ecotone. Preliminary calculations of the efficiency of such a system indicate that the residual nutrient content of the water would be about 0.06 mg N 1(-1) and 0.02 mg P 1(-1), which is less than 1/10 of drinking water standards. After one year of use, tests have given the results of 0.007 mg N 1(-1) and 0.02 mg P 1(-1). Bacteria was reduced with 3-4 powers of ten (to detection level) in the pond system, and nor detected after final treatment. (C) 2000 Elsevier Science B.V. All rights reserved.