On-site wastewater treatment system in Høyås farm, Ås Norway
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- Master's theses (IPM) 
Norway has endorsed strict regulations regarding wastewater discharge also in rural areas. In areas defined as vulnerable i.e. most inland area the phosphorus (P) discharge limit is 1 mg P/l or 90% removal. Both package treatment plants and nature based systems (constructed wetlands, soil infiltration) are used. Constructed wetlands or filterbed system (wetlands without macrophytes) have excellent purification performance, but require a large area according to current guidelines resulting in large investment costs. When using the phosphorus sorbing material Filtralite P, leaching of calcium in the early stage of the system may clog outlet pipes or form a white layer of CaCO3 at the discharge point. The lost calcium may also reduce the longevity of the systems P-removal. At Høyås farm in Ås municipality a compact filter bed system with post polishing sand filter to trap the leaching calcium has been built. A compact Pfilter combined with a polishing sandfilter has not been tested in Norway before. Two different Psorbing materials Filtramar and Filtralite P are tested and compared in the two 4m3 P-filter units of the system. to find the maximum phosphorus retention capacity in order to increase the life time and to reduce the investment cost. Samples were collected during the first month of system operation in October 2012. Samples were taken at an interval of around two weeks. Samples were analyzed for pH, conductivity BOD5 (mg/l), COD (mg/l), total phosphorus (mg/l) and orthophosphate (mg/l). In addition a batch experiment has been conducted to find the phosphorus sorption capacity of Filtralite P and Filtramar. The Batch experiment results showed that the sorption isotherms of Filtralite P and Filtramar had different behaviors at high initial concentrations (50-480 ppm) and at low initial P concentrations (0-50 ppm). With an initial concentration of 480 ppm, Filtramar (shellsand) had a P sorption capacity of 8.22 g P/kg, while Filtralite P was found to have a P sorption capacity of 1.23g P/kg. At low initial concentrations comparable to real wastewater concentrations Filtramar (shellsand) had a P sorption capacity of 149 mg P/kg, while Filtralite P was found to have a P sorption capacity of 476 mg P/kg. Thus at lower initial concentrations of phosphorus, Filtralite P had higher P-sorption capacity than Filtramar did. The use of Langmuir equation to calculate the maximum sorption capacity and the saturation points of the filter materials showed that Filtramar had life time (26.2 years) ten times more than service life of Filtralite P (2.45 years). However it is not wise to determine replacement time of filter materials based on batch experiments results only. Batch experiments can only be used to compare and rank filter materials according to their phosphorus retention capacity and not for estimation of their life time. The overall removal of the Høyås treatment system in its first three months of operation was 90% BOD5 removal, 76% COD removal, 98% total phosphorus removal and 99% orthophosphate removal. The results meet or exceed current discharge limits for the recipient with eutrophication risk and user interests. Insulation of bio-filter and sand filter by tree bark is a good solution to protect from frost but it leaches organic substances and produces color in wastewater and that may increase COD in the effluents and also block P-sorption sites of the filter media. The bark should be replaced.