Anaerobic Treatment of Domestic Wastewater with EGSB Reactor

An expanded granular sludge bed (EGSB) reactor was employed to promote COD removal from domestic wastewater in psychrophilic range (13-26degC). Reactor performance and sludge properties were investigated. It was found that COD removal increased with the increase of organic loading rate (OLR) and the shortening of HRT. At temperature above 15degC, the average COD removal were 75, 81, 81 and 82% with the corresponding OLR of 6, 9, 13 and 16 kgCOD/(m³-d) when HRTs were set at 1.6, 1.2,0.75 and 0.6 h. The reactor could endure OLR as much as 38.1kgCOD/(m³-d) with 93% COD removed. However, the average COD removal cut down to 66% at HRT of 0.75 h when temperature decreased to 13degC. Both sludge size reduction and degranulation occurred when liquid upflow velocity (V_up) was higher than 3.1 m/h, which resulted in sludge bed move upward thus increased the risk of sludge washout. The specific methanogenic activity (SMA) of sludge built up from the original 0.69-0.76gCODCH₄/(gVSS-d) to the final 0.96- 1.34gCODCH₄/(gVSS-d), which indicated an improved reactor efficiency. Therefore, increasing OLR by shortening HRT is an efficient way to enhance the reactor efficiency for EGSB to treat low strength domestic wastewater.