| The investigation shows that the concentration of inorganic suspended solids(ISS)in the influent of municipal wastewater treatment plants in China is higher than the average level of European developed countries due to the sewer leakage and combined drainage system.Especially during the rainfall period,due to the scouring effect of rainwater on the surface,a large number of inorganic substances enter into the sewage confluence pipeline together with the rainwater,resulting in the increase of inorganic solid concentration in the influent of the sewage plant.Part of the inorganic matter in the influent then enters the subsequent wastewater biological treatment unit,resulting in the reduction of sludge activity,MLVSS/MLSS ratio,wastewater denitrification efficiency and higher sludge yield.The high concentration of inorganic matter in the influent makes it difficult for the wastewater treatment plant to operate efficiently.Therefore,in order to ensure the effect of sewage treatment,it is very important how the inorganic matter in the influent affects the sewage treatment plant quantitatively.However,there are few relevant studies in the scope of literature review.Based on this,aiming at the problem of high inorganic suspended solids(ISS)load in wastewater treatment plant,this paper uses the activated sludge mathematical model No.1,combined with the inorganic model proposed by ekama,to quantitatively analyze the impact of inorganic suspended solids on the operation of wastewater treatment plant.In this paper,ISS/cod is used to characterize the inorganic load,and the effects of high inorganic load on sludge activity,sludge yield and nitrogen removal efficiency are discussed.According to the unique water quality characteristics of China,reasonable suggestions are put forward on how to improve the quality and efficiency of sewage treatment plants.The operation of municipal sewage treatment plants is unsustainable due to high inorganic load.According to the experimental results,we can draw the following conclusions:1.There is a common phenomenon of high inorganic matter in wastewater treatment plants in China,which makes it difficult for wastewater treatment plants to operate efficiently.In this paper,the influent samples of sewage pipe network lifting pumping station and sewage plant in a city of Jiangsu Province were taken,and the COD,ammonia nitrogen,SS and VSS concentrations of sewage were tested.The experimental data analysis showed that the COD concentration of each pumping station in the city was low.about 49%of the pumping stations had COD concentration less than 200mg/L,and 75%of the pumping stations had COD concentration less than 300mg/L.The concentration of inorganic matter in some pumping stations is high,especially in rainy days.The ratio of ISS/SS is about 0.4～0.5,the concentration of inorganic matter in the influent is high,and there are many fine inorganic particles in the influent.The particle size less than 100um is about 70%,and the particle size less than 200um is about 90%.The experimental results show that the grit chamber has a certain removal effect for particles larger than 200um.The results show that the size of suspended solids in the influent of WWTP in winter and summer is different.In summer,due to the rainy season,the particle size distribution of sewage inflow is less than 100 μ The ratio of ISS/SS is about 0.5 in summer,which indicates that the content of inorganic matter in sewage is higher than that in winter,which is about 0.3.The results show that the activated sludge concentration is about 7000mg/L,while the MLSS/MLVSS ratio is low,about 0.4～0.5.Under the condition that the influent organic matter(VSS)is relatively constant,the MLSS concentration in the aeration tank increases,which eventually leads to the decrease of MLVSS/MLSS value,which is far lower than the normal value of 0.75.The experimental results show that the source value of activated sludge is lower than the reference value due to high inorganic influent,and the degradation rate of ammonia nitrogen is reduced due to high inorganic influent.2.The simulation results show that the inorganic matter in the influent is the cause of the activated sludge inorganic.When the concentration of ISS in influent is normal,ISS/COD=0.03,and the ISS in activated sludge mainly comes from the contribution of biological phosphorus removal;When the ISS concentration in the influent is high,ISS/COD=0.4,the ISS in the activated sludge mainly comes from the influent.Moreover,with the increase of SRT.the MLVSS/MLSS ratio has little change,and the decrease of MLVSS/MLSS ratio has little relationship with the longer SRT.3.The high inorganic matter in the influent leads to the increase of sludge yield.When the ISS/COD ratio increased from 0 to 0.5,the MLVSS/MLSS ratio decreased from 0.8 to 0.4,and the corresponding sludge yield increased from 0.45 to 0.87(kg/kg COD removal).With the increase of ISS/COD ratio,the sludge yield also increased significantly.4.High inorganic matter influent reduces nitrogen removal efficiency.The results of mathematical simulation show that the high ISS in the influent makes it difficult to complete the low temperature nitrification process under normal MLSS concentration.When the influent ISS/COD ratio is 0.4,the MLSS concentration must be kept above 6000 mg/L in order to achieve complete nitrification in winter.When the ISS/COD ratio of influent increases to a certain extent,the nitrifying bacteria AOB will be eliminated,the nitrification reaction is difficult,and the concentration of ammonia nitrogen in effluent will increase. |
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