ANAEROBIC DIGESTION OF PRIMARY AND SECONDARY SLUDGE IN TWO SERIAL UASB REACTORS

The present research studies of mesophilic hydrolysis (AM) and stabilization under thermophilic methanogenic conditions (MT) for a mixture of primary Sludge (PS) and secondary sludge (SS) using two serial Upflow Anaerobic Sludge Blanket reactors (UASB). The AM and MT reactors were operated at 32 +/- 2 degrees C and 56 +/- 1 degrees C, respectively with different rates of PS:SS in the supply, without stir or recirculation at different hydraulic retention times (HRT). The AM reactor showed the optimal results in the stage V, HRT of 2 days. solid retention times (SRT) of 18.1 for a PS:SS rate of 50:50, and volumetric loading (Bv) of 3.6 kg DQO/m3.d., and it was observed a COD removal efficiency of 56.8%, soluble COD production of 48.3%, volatile suspended solids (VSS) removal or 68.6% using a hydrolysis rate of 0.16 kg/m3.d. The MT reactor showed the optimal stabilization for HRT on the 6(th) day of operation, methane (CH4) production of 107.7 mL CH4/ Kg VSSremoved, VSS removal of 66%, faecal coliform elimination of 8.5 Log(10) and-reduction for helminth eggs of 85%. Partition in two stages of the sludge anaerobic treatment allowed us to achieve higher hydrolysis of the organic matter with lower SRT than those reported for completely stirred reactors. furthermore reduction of helminth eggs was similar to other previous reports.