|M.Sc Student||Lew Beni|
|Subject||UASB for Municipal Wastewater Treatment|
|Department||Department of Agricultural Engineering||Supervisor||Professor Emeritus Michal Green|
The performance of an upflow anaerobic sludge blanket reactor (UASB) was investigated for the treatment of domestic wastewater at different operational temperatures (28 ºC, 20 ºC, 14 ºC and 10 ºC) and loading rates. A laboratory scale 5.3 liters reactor inoculated with granular sludge was fed with domestic wastewater from the Neve Sha'anan neighborhood in Haifa (600 mg COD/l) after a primary sedimentation.
Under all temperatures studied constant percentage total COD removal (not affected by HRT) was observed as long as the upflow velocity was lower than 0.35 m/h, corresponding to HRT of 3 hours. However, for each temperature studied the constant percentage COD removal decreased with the decrease in temperature, mainly due to non-biodegradability of a range of compounds comprising heterogeneous composition of domestic wastewater at lower temperatures: 82% COD removal at 28 ºC, 76% at 20 ºC, 68% at 14 ºC and 44% at 10 ºC. At HRTs shorter than 3 hours (upflow velocities higher than 0.35 m/h) a reduction in the total COD removal was observed, due to washout of influent SS.
COD removal in the UASB reactor resulted from both biological degradation and accumulation in the reactor. At lower temperatures higher accumulation of organic matter was observed.
A constant 200 g sludge mass was observed at 28º C. At lower temperatures an increase in the amount of reactor sludge was observed, which was attributed to inflow matter accumulation. The average daily increase in the reactor sludge was greater as the temperature decreased and explains the similar removal efficiency at 28 ºC, 20 ºC and 14 ºC, since particulate matter accumulation in the reactor contributes to COD removal.
During the transition from winter to summer conditions (10 ºC to 28 ºC), methane production initially increased, and then gradually declined over time. This was accompanied by an increase in COD removal indicating that the TSS accumulated during the winter was exhausted and influent degradation remained.
The UASB reactor can be a good alternative for domestic wastewater treatment in Israel. During low temperatures, when the bacterial activity is lower, solids accumulation in the reactor is more pronounced. The sludge that accumulates during the winter is subsequently digested in the following summer.