| Nitrogen and phosphorus are the main elements that cause water eutrophication,and they are also the main pollutants removed by urban sewage treatment plants in China.In recent years,China has attached great importance to the issue of water environment and has strict control over the drainage water quality of various sewage treatment plants.This is an opportunity and a challenge for the improvement of water pollution control technology.Denitrifying phosphorus removal and short-cut nitrification technologies are emerging as efficient nitrogen and phosphorus removal technologies in recent years.Denitrifying phosphorus removal technologies use denitrifying phosphate-accumulating bacteria to use nitrates or nitrites instead of oxygen as electron acceptors for anoxic phosphorus absorption.Achieve"one carbon dual purpose",with the advantages of energy saving and reduced sludge yield.Short-cut nitrification involves nitrification only at the nitrite stage.If the coupling of short-cut nitrification and denitrifying phosphorus removal can be realized,this will greatly reduce the reaction time and energy loss,thereby improving the economic and environmental benefits,and will also be used to explore nitrogen removal.Phosphorus technology opens up new roads.CAST technology has become the preferred process for many sewage treatment plants due to its advantages of low investment,low operating costs,and the ability of the selector to prevent sludge swelling and flexible operation.In addition,the sludge reduction technology is one of the important approaches to solve the problem of excess sludge in urban sewage,which has become a research hotspot at home and abroad.Therefore,research on biological phosphorus removal,nitrogen removal and sludge reduction in nitrite-based CAST process has certain theoretical research value and engineering significance.In this study,the CAST reactor was used to examine the biological phosphorus removal and nitrogen removal performance and sludge reduction in the nitrite-based CAST process in four stages.In the first stage,the domestic sewage was used as the research object to examine the biological phosphorus and nitrogen removal performance of the CAST system under different conditions.The study showed that the change of COD removal performance of the system was small when the influent C/P was changed,when C/P=100 The total nitrogen removal rate is 88%,and the effluent phosphorus concentration is less than 0.5 mg·L-1.The system has good nitrogen and phosphorus removal performance.Under the condition of low C/P?50?,reducing the reflux ratio?12.5%or 0?can save operating costs,but the system's phosphorus removal performance has no substantial improvement.At the same time,it was found that sludge“starvation”caused by short-term idleness of the CAST system can improve the system's phosphorus removal performance.Under the conditions of low temperature?14°C±1°C?,the phosphorus removal rate of the system is high and above 90%.Under high temperature short-cut nitrification conditions,the phosphorus removal effect of the system is only 14%due to insufficient carbon source,indicating that low temperature It is more conducive to the removal of phosphorus in the system.Phosphorus experiments showed that the systemic sludge at the normal temperature can absorb phosphorus with O2,NO3-,and NO2-as electron acceptors,while the low-temperature system sludge absorbs phosphorus with O2 and NO3-as electron acceptors.Mud can only absorb phosphorus with O2 as electron acceptor.In the second stage,simulated wastewater was used to examine the effect of temperature on the nitrification,denitrification,and phosphorus removal of the CAST process.The control temperatures were:22°C,25°C,and 28°C.Studies have shown that temperature has little effect on the COD and NH4+-N removal performance of the system.When the temperature is22°C and 25°C,the phosphorus removal rate is above 85%,and the system has better phosphorus removal performance.During the high-temperature short-cut nitrification?28°C?stage,the phosphorus removal performance of the system was suppressed due to NO2--N accumulation(average 13.03 mg·L-1),and the phosphorus removal performance deteriorated rapidly,and the phosphorus removal rate was only 68.7%.Phosphorus absorption experiments showed that the control temperatures were 22°C,25°C,and 28°C,and the specific phosphorus uptake rate of sludge with O2 and NO3-as electron acceptors was negatively correlated with temperature.However,the specific phosphorus uptake rate with NO2-as an electron acceptor is almost constant with increasing temperature.In the third phase of the study,the influent ammonia nitrogen was increased to 75 mg·L-1.Based on the short-cut nitrification,the nitrogen and phosphorus removal performance of the CAST process was examined.The results showed that during the short-range operation,the effluent TN removal rate was 79%,The effluent TN increased more than the entire denitrification.The effluent P concentration of the system was 1.08 mg·L-1,and the P removal rate was 89.7%.Compared with the whole nitration process,the P removal rate was increased by 0.7%,but the increase was small.During this period,the average NO2--N concentration was The mean accumulation rate of 8.86 mg·L-1 and NO2--N was 80.33%.In this process,microorganisms can resist the toxic impact caused by the accumulation of NO2--N,and the system has good denitrification and phosphorus removal capability.Phosphorus small test system can be seen,the system of the maximum specific phosphorus uptake rate and the average specific phosphorus uptake rate of change is the same law:aerobic than the rate of phosphorus absorption>NO2-type than the rate of phosphorus absorption>NO3-type than the rate of phosphorus absorption.During the operation of the reactor,the settling performance of the system sludge was good and there was no problem such as sludge swelling.In addition,the experiment also found that during the short-range nitrification,the sludge concentration and sludge specific resistance remained in a dynamic equilibrium.In the fourth stage,NO2--N with concentrations of 5,10,15,and 20 mg·L-1 were added to the CAST system in the aerobic stage to examine the effect of nitrite on biological phosphorus and nitrogen removal and sludge reduction in the CAST process.Impact.Studies have shown that the addition of NO2--N to the CAST system at concentrations of 5,10,and15 mg·L-1 has a large fluctuation in the phosphorus removal rate at the beginning of the reactor operation,but after 10,6,and 34 days respectively.After acclimation,the phosphorus removal rate is greatly improved and maintained at a stable level above 95%.When the dosage is 20 mg·L-1,the process phosphorus removal performance deteriorates rapidly,but the nitrite-type anoxic phosphorus absorption capacity of sludge is The significant increase was 10.4 times before acclimation,indicating that the deterioration of the phosphorus removal performance caused by adding a certain concentration of nitrite can be eliminated,and long-term addition of NO2--N is also favorable to the enrichment of system NO2-type denitrifying phosphorus accumulating bacteria.The experiment also found that aerobic addition of a certain concentration of nitrite system sludge settlement performance is good and the sludge concentration continues to decrease,which has certain guiding significance for sludge reduction.In the fifth stage,the SBR reactor was used as the research object,and the inhibitory effect of phenol on the phosphorus removal of EBPR system was investigated.The results showed that the removal rate of COD and PO43--P was more than 85%when the concentration of phenol was?50 mg·L-1,and the system had better pollutant removal performance;however,high concentration of phenol(?100 mg·L-1)was added.),the phosphorus removal performance of the reactor is greatly reduced;when the phenol concentration is 200 mg·L-1,the system only loses the phosphorus removal performance after 22 cycles,and the COD average removal rate drops to 61.3%,and in the short term Difficult to restore.At the same time,it was found that the long-term dosing of phenol led to the suppression of the phosphorus removal performance of EBPR system sludge,and the inhibition of aerobic phosphorus uptake was greater than that of anaerobic phosphorus release.In addition,under low-concentration phenol(?50 mg·L-1),the sludge gradually adapts to phenol toxicity,and the system sludge gradually disappears due to the micro-expansion phenomenon,but the sludge swelling caused by high-concentration phenol is difficult to recover.Short-term impact tests show that the fluctuations of effluent COD and phosphorus concentration caused by the addition of phenol can gradually recover with the removal of phenol.It can be seen that the inhibition of the phosphorus removal performance of the system by phenol impact is reversible.The phenol dosing concentration was controlled to 50 mg·L-1.When the MLSS concentration was 1500±100 mg·L-1,the COD removal rate was only 67.1%,and the sludge concentration was increased to 3500±100 mg·L-1.At 4800±100 mg·L-1,the experiment found that it had little effect on the COD removal rate of the system.When the sludge concentration is 1500±100 mg·L-1,due to the small amount of microorganisms,the impact caused by phenol can not be resisted,resulting in the deterioration of the system's phosphorus removal performance;increasing the biomass can resist the toxic impact of phenol on the EBPR system.The greater the concentration of sludge,the stronger its ability to resist impact,and the better the phosphorus removal performance.Coupling of phenol with Cu2+accelerates the rate of deterioration of phosphorus removal in the EBPR system. |
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