Fosforrening i enskilda avlopp med rotzonsanläggning

Sammanfattning: A HSSF CW – Horizontal Subsurface Flow Constructed Wetland was constructed at Alnarp, Scania, Sweden, for onsite wastewater treatment in cooperation with the company AlnarpCleanwater Technology AB, working with onsite wastewater treatment. The aim with the wetland was to reach at least a 70 % decrease in phosphorus concentration as required for areas with “normal protection” according to the Swedish EPA. Previous studies on HSSF CW´s have shown great variation in phosphorus retention (31 % - 99.5 %). Calcium, Aluminium and Iron content in the substrate has been pointed out as the most important factors determining phosphorus retention. There was a significant difference between phosphorus concentration in incoming and outgoing waste water and a retention of 85 % (CI: 75-95 %) was found. The sand in the HSSF CW had a Ca-content of approximately 5 % and Glyceria maxima, Iris pseudacorusand Typhalatifolia were planted in the sand.Uptake from plants could play an important role if the phosphorus loading is not very high (10-20 mg P/m2/year). In theory, the plants in the study remove approximately 15-24 % of the incoming phosphorus. In Sweden there are 745 000 households with onsite waste water treatment, and the majority of these do not fulfill the requirements from the Swedish EPA when it comes to phosphorus retention. These households contribute to eutrophication with important amounts of phosphorus, making up 19 % of the anthropogenic discharge of phosphorus. There is great potential in reducing eutrophication if more HSSF CW were to be constructed for onsite wastewater treatment. In a near future, there will be lack of phosphorus for fertilizing farmland. The plants and the sand in the HSSF CW could be used as relatively clean sources of phosphorus for farmland.