Studies On Treatment Performance Of Different Membrane Combinations For Pig Manure Digested Slurry

In view of the difficulties of pretreatment and the uncertainty of processing efficiency,the selection of membrane concentration processes has become more difficulty and lack of foundation.In this study,the performance for treatment of digested slurry based pig manure by different pore size ceramic membranes?CM?was studied.The key parameters for ceramic membrane were optimized,and the cleaning effects of different cleaning strategies were investigated.The influences of operating pressure on the operating parameters such as volume reduction factor?VRF?and membrane flux were examined.The concentration of antibiotics and heavy metals may increase due to the use of membrane technology,and fewer investigations have been carried out on antibiotics and heavy metals.Therefore,antibiotics concentrations and heavy metals concentrations were measured to determine their species and distributions.The main findings obtained are as follows:?1?The running tests of ceramic membranes at different pore sizes and pressures shown that the ceramic membrane can be used as pretreatment of pig manure digested slurry,and the optimized operating conditions were 200 nm pore size and 0.3 MPa.The membrane flux can reach100.6 L/?m²·h?for 200 nm CM with the operating pressure of 0.3 MPa and the removal efficiencies of phosphorus,total organic carbon,ammonia nitrogen,total nitrogen and potassium were 61%,35.0%,3.8%,6.2%and 3.0%respectively.At 0.3 MPa operating pressure,both of the turbidity removal efficiency of 50 and 200 nm CM can reach more than 99%.The COD removal efficiency between 50and 200 nm CM were 36.2%±0.6%and 32.6%±1.5%,respectively.However,under the same operating pressure of 0.3 MPa,the membrane flux of 200 nm CM was 52.8%higher than that found in50 nm CM.The maximum membrane flux recovery rate was achieved by combination of 1%concentration of sodium hydroxide and 1%concentration citric acid,and the membrane flux recovery rate was around 95%of original membrane flux.?2?The comparison tests of three membrane concentration processes?NF,RO₁,NF+RO₂?shown that the NF+RO₂ two-stage concentration process can reduce the operating pressure of concentration system and increase membrane flux of reverse osmosis.With VRF were 6,the ammonia nitrogen removal efficiencies?NH₄⁺-N?for NF,RO₁ and RO₂ were 13.7%,88.5%and 85.4%,respectively.The ammonia nitrogen removal efficiency for reverse osmosis?RO₁?was 74.8%higher than that of nanofiltration.Under the same operating pressure of 1.5 MPa,the membrane flux of RO₂was 98%higher than that of RO₁.As the pretreatment of reverse osmosis,nanofiltration membranes can reduce the operating pressure of concentration system.Therefore,NF+RO₂ two-stage concentration processes were used to concentrate the digested slurry.When VRF was 6,ammonia nitrogen concentrations for NF and RO₂ concentrates were 1.7 times and 3.8 times of their influent,respectively.Total potassium?TK?concentrations for NF and RO₂ concentrates were 1.7 times and 3.6 times of their influent,respectively.NF+RO₂ two-stage concentration processes can effectively recover the nutrients of pig manure digested slurry.?3?The detection results of heavy metals and antibiotics for concentrate and permeate showed that removal of heavy metals mainly occurred in ceramic membrane filtration stage,and antibiotics mainly existed in the concentrate of nanofiltration and reverse osmosis.The Zn concentrations of ceramic membrane concentrate reached 0.46 mg/L,which was 3.5 times higher than that of the influent;the Cu concentrations of ceramic membrane concentrate was 0.12 mg/L,which was over 3 times higher than that of the influent.The concentrations of sulfadiazine?SD?,sulfamethazine?SMZ?,sulfamonomethoxine?SMZ-J?,tetracycline?TC?,and oxytetracycline?OTC?in nanofiltration membrane concentrates were 22.05 ng/mL,905.65 ng/mL,and 19.57 ng/mL,32.55 ng/mL,675.94ng/mL,and were 1.25 times,1.25 times,1.52 times,1.13 times,and 4.77 times higher than that of their influent.Reverse osmosis membranes can further retain antibiotics in permeate of the nanofiltration membrane.The concentrations of sulfadiazine?SD?,sulfamethazine?SMZ?,tetracycline?TC?,and oxytetracycline?OTC?in reverse osmosis concentrates were 11.52 ng/mL,525.8 ng/mL,46.47 ng/mL,and 112.44 ng/mL,and were 4.1 times,3.2 times,1.5 times,and 3.2 times higher than that of the influent,respectively.