THE EFFECT OF NITRATE AND TREATMENT PROCESS ON PHOSPHATE RELEASE IN BATCH GRAVITY THICKENER

This paper includes the results of an experimental investigation carri ed out on thickening of excess sludge to observe the phosphate behavio ur in the presence and absence of nitrate and to study the effect of t he wastewater treatment process on sludge properties which have a grea t influence on phosphate release to the supernatant of gravity thicken ers. The main results obtained are as follows: (1) the rate of phospha te release under anaerobic conditions is influenced by the chemicals w hich are used in the aeration tank to precipitate P. In case of no P p recipitation, the P released to the supernatant after 24 h detention t ime (DT) was about 6% of the influent P load of the wastewater treatme nt plant; (2) as initial nitrate concentration increases, the phosphat e release rate decreases; (3) up to a DT of 12 (sludge age, 3.5 days) to 20 h (30 days), the N release to the supernatant is rather low and can be neglected in regard to the wastewater treatment process; (4) a DT of less than 18-24 h is advantageous in regard to nutrient release for thickening of ES in case of activated sludge treatment plant witho ut primary sedimentation process.