LOW-COST PROCEDURE FOR NUTRIENT REMOVAL IN SMALL RURAL WASTE-WATER TREATMENT PLANTS

Nutrient removal in small wastewater treatment plants is often benefic ial especially if the effluent must be discharged into sensitive or gu arded waters or into groundwater. The presented studies optimised an i nexpensive method of subsequent enhanced wastewater treatment. The dev eloped reactor is similar to a concentrated subsoil passage. The fixed bed reactor is divided in two sections to achieve aerobic and anoxic conditions for nitrification/denitrification processes. To enhance pho sphorus removal, ferrous particles are addedto the aerobic zone. Two s eries of column tests were carried out and a technical pilot plant was built to verify the efficiency of the process. The results show that this method can be implemented successfully. The aerobic processes, ni trification and phosphorus removal by absorption, were not problematic . Elimination rates higher than 90 % were measured. The capacity of ph osphorus removal is principally limited. After consumption of the ferr ic ions the reactor filling must be renewed. Denitrification strongly depends on the availability of a degradable organic substrate. To bala nce the substrate load and the nitrate flow a Simple device was create d. Weekly monitoring of the BOD and nitrate effluent concentration see ms to be sufficient to find an appropriate adjustment. A technical-sca le pilot plant was built and the first test drives have been started. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.