Abstract:
This research studied the efficiencies, COD removal rates, and kinetic parameters of a completely mix activated sludge process treating real wastewater from hardboard mill after pretreatment of anaerobic process. Flow rate was controlled at 8 l/d, 5 liters reactor was used for studied sludge ages of 0.4, 0.7, 1.03, and 1.62 day, and 10 liters reactor was used for studied sludge ages of 6.1, 10.4, 10.6, and 15.5 day. Analytical parameters were pH, DO, TCOD, sCOD, MLSS, MLVSS, TS, and microscopic examination. Results showed that low efficiencies clarifier disposed a lot of sludge with effluents resulting in the reduction of sludge age by 54.6% to 0.4, 0.7, 1.03, 1.62, 6.1, 10.4, 10.6, and 15.5 days instead of 0.5, 1, 2, 5, 10, 15, 20 and 30 days, respectively. During first period, average TCOD and sCOD inputs were 7,040±6.80 mg/L and 6,240±70 mg/L, respectively. Results showed that TCOD and sCOD removal rates at sludge age of 1.62 days were the highest at 4.21±0.10 and 4.85±0.41 kg.COD/m3-d. The best efficiency of sCOD removal was at 48% at sludge age of 1.62 days, and 24, 26, and 43% at sludge age of 0.4, 0.7, and 1.03 days, respectively. SVI were 25-92 ml/g indicated the proper sedimentation but because of wasting too much sludge, the system couldnt maintain good treatment efficiencies. During 2nd period, average TCOD and sCOD inputs were 4,324±34 mg/L and 4,237±4 mg/L, respectively. TCOD and sCOD removal rates at sludge age of 6.1 days were the highest at 1.45±0.06 and 2.01±0.09 kg.COD/m3-d. The best efficiency of sCOD removal was at 59% at sludge age of 6.1 days, and 51, 48, and 48% at sludge age of 10.4, 10.6, and 15.5 days, respectively. SVI were 125-190 ml/g indicated the fair sedimentation, due to various problems such as sludge bulking. The treated water still had high COD and was in dark color, which was not acceptable by standards of disposal water. Therefore, recycle method such as irrigation or other treatment methods were needed. Low growth yield of 0.15 mg-cellsCOD/mg-COD was observed. Non-biodegradable COD was about 22%. COD removal rates were found to be a 1st-order kinetic reaction with effluent biodegradable COD with k1 of 0.012 L/mgs/d.