Phosphorus Removal From Wastewater By Suspended Sludge Filtration

The construction of small sewage treatment plant will be the focus point of the new municipal constructions. The difficulty we are facing is how to make the operation of small sewage treatment plant simple, and the effluent reaching A standard of sewage discharge at the same time. One of the most difficult problems is how to make the phosphorus meet A standard of sewage discharge. In order to solve the problem, the combination of the traditional biological phosphorus removal process and chemical phosphorus removal process is becoming a new choice. The main treatment process includes the depth processing of effluent technology and the side stream phosphorus removal technology. But conventional chemical phosphorus removal method has some problems like the buildings cover a large area, the structure are complex, large precipitant dosage and so on. Suspended sludge filtration(SSF) technology designs a small tank that merges the coagulation, sedimentation and filtration processes in sewage treatment process. Phosphorus removal is achieved by chemical precipitation, when precipitant is introduced. This research studied the efficiency of phosphorus removal in the process of the side stream phosphorus removal, in an improved A2/O process containing suspended sludge filtration technology.The experiment results show that using ferric chloride as the precipitant and polyacrylamide as the coagulant agent, the hydraulic load of suspended sludge filtration technology can reach up to 1.6 m/h, the hydraulic retention time(HRT) is 48 min, and the total phosphorus removal rate of effluent is 56.3%. According to the optimization of operation parameters in the suspended sludge filtration technology, we can draw some conclusions: the optimal dosage of Fe Cl3 is 36 mg/L; the optimal dosage of PAM is 0.5 mg/L, in the process of start-up, the optimal p H range for the rapid formation of stable floc layer is between 8.5~9.0; increasing the pre coagulation stage before the suspended sludge filtration device can improve the phosphorus removal efficiency, the optimal time for flocculation is 10 min; the start-up time of the suspended sludge filtration technology device is 14 h; when the floc layer is formed, the restart time is shortened to 1 h.After strengthening the suspended sludge filtration technology by adding micro sand, the afforded hydraulic load of the device can increase to 2.6 m/h. HRT is shortened to 23 min. At the same time, the start-up time of the device is shortened to 9 h after reinforcement, the restart time is shortened to 0.5 h, the total phosphorus removal rate of effluent can increase 21% than the SSF technology without reinforcement and the Fe/P molar ratio is 1.6. After the reinforcement by the introduction of sludge recirculation system, the dosage of Fe Cl3 can be reduced 30% and the dosage of PAM can be reduced 20% when the total phosphorus removal rate of effluent maintains the same with before that without reinforcement. Through the research, the optimum sludge reflux ratio is 7%. Through the reinforcement of the suspended sludge filtration technology with fiber filter, the total phosphorus removal rate of effluent increased 25%; the removal rate of SS increased 38%.Selecting the effluent which flows from the anaerobic tank of the improved A2/O as the research object, the efficiency of side stream phosphorus removal with the suspended sludge filtration technology is inspected. In the operational conditions without strengthening, after the device runs 20 days, the average total phosphorus, SS, and COD removal rate of effluent respectively is 58.1%, 53% and 40.9%. After the reinforcement and 20 days stable operation with the micro sand, the sludge recirculation system and the fiber filtration, the average total phosphorus, SS, and COD removal rate of effluent respectively is 82.3%, 94% and 55.1%.The advantage of suspended sludge filtration technology can be concluded that, the Fe/P molar ratio is 1.2~1.6, the afforded hydraulic load of the device can reach 2.6 m/h, the total HRT is 33 min, and this technology need not the large mechanical equipments.