Study On Combination Process Of Aerobic Granular Sludge-Dense Filtration For Domestic Wastewater

Compared with traditional wastewater biological treatment,aerobic granular sludge?AGS?has gradually been paid more attention in wastewater treatment due to the higher removal efficiency,faster settling velocity,and smaller land area.However,high concentration of suspended solid?SS?and phosphorus in effluent have limited the widely promotion and application.Therefore,this study analyzed the characteristics of sludge and effluent by constructing an AGS system and optimized the best combination technology among three post-treatment methods based on the domestic sewage treatment efficiency.We operated continuously the sequencing batch AGS reactor?AGS-SBR?with the cultural method to shorten the settling time gradually.The results showed that AGS could generate after about 25 days and remained stable for about 45⁵0 days.And AGS has the performance of light-yellow globular sludge with an average particle size of 1.25 mm and SVI of 33.9 mL/g.When we set the optimal parameters of organic loading rate?OLR?=2.94 kg/m³·d,aeration volume=4 L/min,HRT=4h,the removal rates of COD,NH₄⁺-N and TN were reach about 94.1%,98.4%and74.1%,respectively.Moreover,the effluent SS fluctuated within the range of22¹67 mg/L drastically and the effluent TP shown the positive correlation with SS in the range from 0.7 to 3.5 mg/L.To solve the problem of AGS effluent,we compare three post-processes were added after the AGS system based on the operation performance.The effluent SS in the post-sedimentation process could reach less than 10 mg/L after a long setting time and there was phosphorus releasing during the sedimentation.Thus,the effluent TP raised after an initial declined and the minimal concentration was about 0.83 mg/L.In addition,the post-contact oxidation process had an optimum operating condition with gas-water ratio of 10:1 and HRT of 1 h.And the effluent COD and NH₄⁺-N could conform to one-class A permitted criteria.The effluent SS was 7¹1 mg/L depending on the adhesion effect of biofilm and TP was 0.6 mg/L.However,the effluent NO₃^--N was about 18.56 mg/L so that TN could not meet the emission standard.Furthermore,we selected sieves with pore size of 30?m?500 mesh?of the post-precision filtration process to control the effluent SS and TP effectively.When the flow rate less than 1.70 cm/s and backwashing strength greater than 0.38 L/?s·m²?,the SS and TP could be removed efficiency and the clogging time of sieves could be delayed.Therefore,the post-precision filtration had the best performance among these post processes to solve the problem of high effluent SS and TP without reducing the removal efficiency of other pollutants.We selected AGS-precision filtration combined process for further pilot-scale study with a daily domestic sewage treatment capacity of 450 L/d.The AGS system was successfully started after about 60 days and operated stably with the average particle size of 0.82 mm and SVI of 39.12 mL/g.Besides,the effluent SS was about9.6 mg/L and TP was less than 0.45 mg/L.The effluent SS can be further reduced along with clogging which would occur around 40 d.Additionally,though the effluent TN was up to 20.27 mg/L,it could be controlled less than 15 mg/L after adding the anoxic unit.