Experimental Study And Process Establishment Of Simultaneous Recovery Of Phosphorus From Calcium Peroxide Reduced Sludge

The activated sludge process is the most widely used urban sewage treatment method in the world,and produces a large amount of residual activated sludge.The cost of a large amount of sludge treatment and disposal is huge.Phosphate mines are unevenly distributed around the world and have limited reserves.It is predicted that global phosphate resources will be depleted within 45 to 100 years.90%of the phosphorus in the municipal wastewater is transferred to the sludge after the enhanced biological phosphorus removal process,so the sludge is a very promising raw material for phosphorus recovery.In view of this,it is imperative to reduce the excess sludge production while recovering the phosphorus.Most of the urban sewage plants in China use chemical dephosphorization process,but the addition of chemical agents cannot take into account the sludge reduction when dephosphorization,and even increase the sludge production.Pretreatment is usually carried out before sludge digestion,but conventional pretreatment methods usually focus only on sludge reduction or sludge dewatering performance,and little attention is paid to phosphorus recovery.As an environmentally friendly inorganic oxidant,CaO₂ can improve sludge dewatering and anaerobic digestion to reduce sludge,enhance sludge hydrolysis and acidification,ie inhibit methane production,and enable a large number of short-chain fatty acids?VFA?.Accumulation promotes the anaerobic phosphorus release of polyphosphate bacteria.On the other hand,CaO₂ dissolves in water to cause an alkaline environment,and Ca²⁺and HPO₄^2-easily form calcium phosphate crystal precipitates to recover phosphorus.Using the characteristics of CaO₂ to construct SBR-sludge reduction and simultaneous recovery of phosphorus,determine the optimal dosage of CaO₂,anaerobic sludge age,optimal operating conditions for phosphorus recovery,and long-term continuous operation of the process to ensure effluent quality Under the conditions,the effects of sludge reduction and phosphorus recovery were investigated.The main research contents and results are as follows:The phosphorus recovery rate in the sludge depends on the amount of phosphorus released from the sludge,and the amount of phosphorus released is positively correlated with the VFA content.Through static test,the effect of CaO₂ on sludge reduction and phosphorus release was investigated.The results showed that with the increase of CaO₂dosage,the VFA yield accumulated significantly,and the methane production was significantly inhibited.When the dosage of CaO₂ is 0.1g/gVSS and the age of anaerobic digestion is 8d,the total solids?TS?reduction rate of the reduction tank is up to 20%,and the sludge specific resistance is the lowest;the reduction tank?I?When the sludge ratio of the phosphorus release tank?II?was 4:6?40%:60%?,the phosphorus release effect of the II pool was the best,which was 72.5%higher than that of the control group.In addition,CaO₂ was applied to the dairy wastewater sludge for comparison.The results showed that the TS reduction rate was about 10%,and the sludge specific resistance increased.When the I and II tanks received a sludge ratio of 3:7,the phosphorus release from the II pool.The effect was the best,which was 60.9%higher than the control group.The design conditions of the phosphorus recovery tank were optimized based on the Box-Behnken principle using Design Expert V8.0 software.Based on the single factor test,the initial pH value,the Ca/P molar ratio,the reaction time were selected as the variables,the phosphorus removal rate was the response value,and the three-factor and three-level tests were designed.The results showed that the phosphorus removal rate reached 96%at the initial pH of 9,the Ca/P molar ratio was 2.7,and the reaction time was 65 min.The test results show that the optimization results are credible.Continuous operation of SBR-sludge reduction and phosphorus recovery system for90d,the effluent quality meets China's"Urban Sewage Treatment Plant Pollutant Discharge Standard?GB18198-2002?"national first-class B emission standard,when the sludge returns to SBR and the reflux ratio is At 20%,total phosphorus meets the Class A standard.The TS reduction rate of the I pool sludge is 20%,the specific resistance of the sludge is reduced from 6×10¹22 m/kg to 0.5×10¹22 m/kg,the dewatering performance is improved,and the phosphorus recovery rate in the sludge is 95%,which is equivalent to the influent.The total phosphorus recovery rate is 60%or more.Estimating the cost of the entire system,the SBR-sludge reduction and phosphorus recovery system?new system?is about 145,000 yuan/t sludge lower than the conventional sludge treatment system?original system?,but the operating costs are Increased.In addition,as the system achieves the dual effects of sludge reduction and phosphorus recovery in the overall operation phase,the secondary pollution to the environment and the eutrophication of the water body are reduced.