Study On Polypropylene Base Sustained-release Carbon Source Filler In Improving Water Quality In Rivers And Lakes

With the rapid development of society,river and lake pollution events occur frequently.As one of the main components of ecosystem,river and lake play an important role in ecology.Therefore,water quality purification is of great significance to the overall improvement and sustainable development of river and lake system.Due to the characteristics of low C/N and high NO₃^--N in river and lake water bodies,the denitrification process needs additional carbon sources to carry out completely.Therefore,it is necessary to find a solid carbon source with high efficiency,stability,low price and good nitrogen removal effect to enhance the microbial nitrogen removal performance of the lake water of low carbon nitrogen ratio river.In this paper,anhydrous sodium acetate was selected as the carbon source,vacuum negative pressure method or blending method was used to prepare the sustained-release carbon source filler with different polymers as the carrier matrix（polyvinyl alcohol,polypropylene,foamed-polypropylene,etc.）.By comparing the effluent COD,the filler with better sustained-release effect was screened out,and the carbon release test and nitrogen removal test were conducted.The hydrophilic modified and optimized slow-release carbon source filler was used in a self-designed double-membrane coupled river and lake water purifier,and the continuous flow biofilm test was carried out after inoculation with activated sludge.The effects of flow rate,influent nitrate load,aeration mode and other operating parameters on the removal of COD,TN,NH₄⁺-N,NO₃^--N,NO₂^--N and TP were investigated.Specific research results are as follows:（1）Analysis of carbon release properties of different carrier substrates.Polyvinyl alcohol,polypropylene,porous polypropylene and hydrophilic porous polypropylene were selected as the slow-release carbon source carrier matrix.The static carbon release experiment was carried out after carbon source adsorption by vacuum negative pressure method.The results showed that the hydrophilic porous polypropylene filler had the best carbon release performance,carbon source release followed the second-order kinetic equation,R²=0.9961,and the secondary pollution risk was the lowest.The results showed a good performance of enhanced nitrogen removal.According to the results of material characterization,the hydrophilicity of the substrate was HEPP-C>PVA-C>EPP-C>PP-C,andthesurfaceroughnesswas HEPP-C>EPP-C>PP-C>PVA-C.（2）Study on the performance of EPP-C and HEPP-C under intermittent denitrification and continuous flow.Intermittent denitrification and continuous flow experiments showed that the hydrophilic modification could significantly enhance the membrane hanging efficiency of the filler,accelerate the growth and propagation of functional bacteria,and improve the efficiency of nitrogen and phosphorus removal.The nitrogen removal effect of HEPP-C is the best in stable stage.In the intermittent denitrification process,the NO₃^--N and TN concentrations in effluent were the lowest,the average concentrations were 1.04 mg/L and 1.57 mg/L,the removal rates were89.6%and 89.5%,the COD was 26.90 mg/L,and there was no NO₂^--N accumulation.In the process of continuous flow denitrification,the average concentrations of NH₄⁺-N,NO₃^--N and TN in effluent are 0.11 mg/L,0.64 mg/L and 0.78mg/L,respectively.The removal rates are 97.8%,93.6%and 94.8%,and the COD is 27.10 mg/L,without the accumulation of NO₂^--N.（3）With HEPP-C as the external carbon source of the double-membrane coupled river and lake water purifier,the influent water quality is changed during the start-up period,and the film hanging speed is faster when the influent COD is 100 mg/L.After successfully hanging the film,the inlet flow rate was changed.The experimental results showed that when the flow rate was 0.02cm/s,the purification effect was the best.With the increase of influent nitrate concentration,the water purification effect decreases gradually.When influent nitrate concentration is less than 20 mg/L,the purification effect is better.By changing the aeration mode,it is found that the aeration mode is8h-4h,which can not only meet the metabolic activities of microorganisms,but also have higher economic benefits and feasibility.At this time,the effluent COD concentration of the reactor is 28.70 mg/L,TN=1.47 mg/L,NH4+-N=0.72 mg/L,which meets the standard of surface water ClassⅣ.HEPP-C,as the external carbon source of the double-membrane coupled river and lake water quality purifier,can achieve efficient and stable nitrogen removal effect.