TREATMENT OF SEPTAGE USING SINGLE AND 2-STAGE ACTIVATED-SLUDGE BATCH REACTORS SYSTEMS

The cyclic or sequencing batch activated sludge process was applied fo r the treatment of septage originating from cesspools serving non-sewe red areas. Single and two stage systems were investigated in bench sca le units. The single stage aerated system was capable in removing prac tically all the biodegradable COD and producing a well stabilised exce ss sludge with excellent settling and thickening characteristics. With respect to nitrogen the average removal rate was to the order of 70%, but the performance was unstable due to periodic strong inhibition of the nitrification process. Subsequent treatment in a second stage aer ated unit improved nitrification but did not result in higher nitrogen removal rates due to the increased concentrations of oxidised nitroge n, An anoxic second stage post denitrification unit resulted in an ove rall nitrogen removal of 88%, through a substantial reduction of nitra tes. Further improvement of the system, with nitrogen removal of about 95% and average effluent nitrogen concentrations lower than 10 mg.l(- 1), can be achieved by adoption of a two stage system consisting of a first aerated stage unit, followed by a second stage unit with alterna ting aerated and anoxic cycles and addition of external carbon during the anoxic cycle.