Valuation of OSA process and folic acid addition as excess sludge minimization alternatives applied in the activated sludge process

The aim of this study was to investigate the ability of the oxic-settling-anaerobic (OSA)-process and the folic acid addition applied in the activated sludge process to reduce the excess sludge production. The study was monitored during two distinct periods: activated sludge system with OSA-process, and activated sludge system with folic acid addition. The observed sludge yields (Y_obs) were 0.30 and 0.08 kgTSS kg^–1 chemical oxygen demand (COD), control phase and OSA-process (period 1); 0.33 and 0.18 kgTSS kg^–1 COD, control phase and folic acid addition (period 2). The Y_obs decreased by 73 and 45% in phases with the OSA-process and folic acid addition, respectively, compared with the control phases. The sludge minimization alternatives result in a decrease in excess sludge production, without negatively affecting the performance of the effluent treatment.