Research On Treatment Of Sludge Filter Pressing Wastewater By MAP And SBBR Process

anaerobic digestion is a process of sludge treatment, the dewater of anaerobic digestion sludge produce a great quantity of wastewater, ammonia nitrogen concentration is 500~1000mg/L, difficult to treat, not suitable for direct biochemical treatment. Physicochemical treatment method for treating high ammonia nitrogen wastewater include magnesium ammonium phosphate(MAP) precipitation, Air stripping method and ion exchange method, etc. Among these,the magnesium ammonium phosphate precipitation method has advantage like fast response, simple operation, no secondary pollution and product can be used as a fertilizer, but MAP method exist problem high cost of sedimentation agent, in order to solve this problem, this paper selects waste phosphoric acid producting from polishing of mobile phone touch screen as MAP method phosphorus source to be tested. MAP method can remove a large number of ammonia nitrogen and reduce ammonia nitrogen concentration to within biochemical treatment range(less than 200 mg/L) then use SBBR process to treat wastewater further,make effluent reach the standard.In order to make the MAP-SBBR process to achieve good results, this study includes two parts MAP pretrement experiment and MAP-SBBR process running tests. Specific research includes:(1) MAP pretrement experiment: study influence of types of phosphorus and magnesium sources, reaction time, p H value, the molor ratio of nitrogen, phosphorus and magnesium, the initial concentration of ammonia nitrogen and setting time on ammonia removal effect and the residual concentration of phosphorus, and determine the optimal reaction conditions, analysis of MAP handling costs.(2) SBBR process running test: using SBR as contrast, through determination of COD, ammonia nitrogen, phosphorus, p H, nitrite and nitrate-nitrogen and TN concentrations in system to study the SBBR process capability. The results are as follows:(1) Waste phosphoric acid as phosphorus sedimentation agent of MAP method to treat ammonia-nitrogen in sludge filter pressing wastewater is no significant difference compare to phosphorus salt reagent. At normal atmospheric temperature, optimal reaction conditions is p H=9, n(N):n(Mg):n(P)=1:1:1, aeration agitation 10 min, ammonia nitrogen removal rate up to 84.91%, the residual phosphorus concentration 6.49mg/L,effluent ammonia concentration below 200 mg/L, benefit to the follow-up biological treatment.(2) No significant difference of Magnesium salt precipitator on ammonia nitrogen removal efficiency, but ammonia nitrogen removal efficiency is poor when use Mg O as a precipitant due to low solubility in short reaction time.The effect on removing ammonia-nitrogen by MAP precipitation by reaction time and setting time effects is small, greatly influenced by p H and the molor ratio of phosphorus to nitrogen and magnesium. Aeration before MAP can raise wastewater p H, reducing follow-up reagent required to adjust p H and cost savings, p H should be controlled at about 9 in the actual production.The molor ratio of nitrogen, magnesium and phosphorus control at 1:1:1 can get preferable ammonia nitrogen removal rate and ensure low residual phosphorus concentration. Increase dosages of phosphorus, ammonia nitrogen removal rate can be improved, but the residual phosphorus concentration in the water will also improve. Increase the dosage of magnesium can control the phosphorus residual phosphorus concentration in the water. While reducing the dosage of phosphorus and magnesium precipitated at the same time compared to alone reduce the dosage of phosphorus precipitation reagent make no significant different effect on remove of ammonia nitrogen.In the same certain p H and molor ratio of magnesium, nitrogen and phosphorus conditions, higher ammonia concentration, higher removal efficiency.(3) SBBR present strong resistance to shock loads and remain stable ammonia removal effect compare to SBR. MAP-SBBR process running one month, average concentration of ammonia nitrogen of effluent is 12.03mg/L, reaching wastewater discharge standard(GB 8978-1996) secondary standards. Concentration of ammonia nitrogen of inffluent is from145.00 mg/L to 431.39 mg/L, SBBR ammonia nitrogen removal rate is above 90%, best 99.89%. The COD removal rate of SBBR is fluctuate, removal rates between 4.74%-64.49%. SBBR present poor phosphorus removal, when n(P):n(N):n(Mg)=0.9:1.0:1.0 of MAP pretreatment,phosphorus concentration of SBBR effluent can reach three-level standard of wastewater discharge standard(GB 8978-1996). High ammonia concentration is more favorable for SBBR to accumulate of nitrite nitrogen. Poor biochemical quality and low ratio of carbon to nitrogen cause disruptions to denitrification, poor TN removal effect and high ammonia concentration need add alkali to maintain normal p H, guarantee the removal of ammonia-nitrogen. To sum up, use the waste phosphoric acidcity as the phosphorus source of MAP treatment to treat ammonia nitrogen in the effluent of anaerobic sludge dewatering liquid is feasible. The concentration of ammonia nitrogen in wastewater can be reduced to 200mg/L by MAP precipitation method with waste phosphoric acid as the source of phosphorus.At the same time, the phosphorus element was introduced to adjust the ratio of nitrogen, phosphorus and magnesium in wastewater, creating conditions for subsequent biological treatment. SBBR process has better ammonia removal effect, simple operation, good stability, effluent can reach the comprehensive sewage discharge standards. The study provides guidance for comprehensive treatment of wastewater sludge dewatering and promote the development of sludge treatment industry.