Study On Treatment Of Anaerobically Digested Cattle Manure Wastewater By Chemically Enhanced Combined Membrane Process

Most of the livestock waste produced by intensive livestock and poultry farms in China is treated with anaerobic treatment,but the amount of anaerobically digested wastewater produced by anaerobic fermentation is large.The land is insufficient to complete consume it,so large breeding farms are faced with serious environmental problems.The concentration of COD,ammonia and TP in anaerobically digested wastewater is high,and the concentration of heavy metals exceeds the standard.The direct application of such anaerobically digested wastewater in agriculture will cause serious environmental problems such as groundwater pollution.Compared with anaerobically digested pig manure wastewater,anaerobically digested cattle manure wastewater?ADCMW?contains a large amount of refractory lignin cellulose,humic acid.Therefore,it is urgent to select a chemical strengthening method to realize the solid-liquid separation of anaerobic fermentation liquid,and then carry out the deep treatment of membrane separation combination process Furthermore,the poor biochemical performance increased the difficulty of traditional biochemical treatment.Membrane separation technology has been extensively studied in the field of anaerobic fermentation liquid concentration,but membrane fouling issues had limited the development of this technology.Therefore,it was urgent to explore a pretreatment process to reduce the concentration of contaminants and achieve solid-liquid separation,so as to reduce pollution for subsequent membrane separation technology.This study was mainly divided into two parts.In the first part,we studied an efficient pretreatment method for ADCMW,aiming to improve the sedimentation performance of solid particles in ADCMW,reduce the concentration of pollutants and turbidity in supernatant,and reduce the load and operating cost for subsequent treatment The second part was the deep treatment technology of ADCMW after pretreatment.This technology enabled the treated water to be irrigated and the anaerobic fermentation liquid to be reused.Ozone combination coagulation/Fenton technique and MW-H₂O₂ combined technique were used for pretreatment of ADCMW.In ozone oxidation pretreatment,COD removal efficiency reached 46.5%under the optimal conditions,but the settlement performance was poor at this time.In order to further achieve the effect of solid-liquid separation,crystalline aluminum chloride was selected as a coagulant.Although the optimal sedimentation ratio of the combined process reached 14%and the removal efficiency of COD reached 82%,the addition of aluminum chloride lead to the content of chloride ion in the supernatant up to 3625 mg/L.In the ozone combined Fenton and Fenton-like pretreatment experiment,the COD removal efficiency was only 49.5%,and the treatment effect was not obvious.In the Fenton treatment,the COD removal efficiency can reach 84.5%,from 21528 mg/L to 3334 mg/L,and the sedimentation ratio was reduced to 18%.However,due to the addition of ferrous sulfate,the supernatant contained277 mg/L of iron ions,and a certain amount of iron mud precipitated.That made subsequent processing more difficult.In the pretreatment experiment of MW-H₂O₂ combined technique,the suitable microwave radiation can promote the stability of the colloid and improve the settling property of the mixture.Under the optimal treatment conditions,COD removal efficiency reached 68.8%and effluent COD decreased to 7536 mg/L.MW-H₂O₂ combined technique only added a certain amount of H₂O₂,without the addition of other ions,thus TDS removal efficiency reached 62.0%,so the cost was the lowest.After centrifugation,it showed little difference in settlement properties of the three processes.The MW-H₂O₂combined technique was selected as the pretreatment process,because it can not only effectively realize solid-liquid separation and reduce the concentration of pollutants in superant liquid,but also effectively control the treatment cost.Ceramic membrane microfiltration–PES?10kDa?ultrafiltration-NF245nanofiltration-NF90 nanofiltration was used in the pretreatment liquid membrane separation combination process.The final effluent COD,NH₄⁺-N and TP were reduced to 350.0 mg/L,255.1 mg/L and 18.2 mg/L respectively,and EC was reduced to 2.41ms/cm,and the effluent water quality was significantly improved.Microfiltration reduced SS from 337 mg/L to 145 mg/L and that increased the membrane flux in the ultrafiltration process from 11.3 L/m²h to 18.2 L/m²h.When the pressure of PES?10kDa?was 0.1MPa,the removal efficiency of COD,NH₄⁺-N and TP reached 28.7%,6.27%and 4.31%respectively,which was the best treatment effect among the four membranes,but the removal efficiency on ES was limited.When NF245 was combined with PES?10kDa?ultrafiltration membrane,the final effluent COD,NH₄⁺-N and TP were reduced to 589.3mg/L,503.4 mg/L and 53.2 mg/L,respectively.NF90 was selected for the secondary nanofiltration,which had high removal efficiency of NH₄⁺-N and TP.