Study On The Treatment Of Pig Wastewater By Magnetic Coagulation + Magnetically Strengthened Biological Aeration Filter

China is the main country that produces pigs,in order to meet the growing demand for pork,China’s pig industry has gradually become large-scale and intensive.The rapid development of pig breeding industry has produced a large amount of pig wastewater,because the concentration of pig wastewater is generally 20000～30000 mg/L,high treatment costs and inadequate maintenance of facilities can easily lead to high concentration of pig wastewater tailwater.If not properly treated,arbitrary discharge will inevitably cause serious environmental pollution.Tailwater ammonia nitrogen is generally 100～200 mg/L,COD is generally 200～400 mg/L,which is a typical low C/N wastewater,which is difficult to properly treat by conventional tailwater treatment methods.And in most areas,the effluent standard of pig wastewater needs to meet the primary and secondary standards of the comprehensive sewage discharge standard or the agricultural irrigation standard,and the discharge limits of ammonia nitrogen and COD are higher,which forces the transformation and upgrading of relevant water treatment technologies.In view of this,in view of the problem that the tailwater of pig wastewater still has high concentration and low C/N,and the traditional advanced treatment method is difficult to meet the standard discharge,the actual pig tailwater of a large-scale pig farm in Jingzhou City,Hubei Province is used as the object,and the process of magnetic coagulation+magnetic strengthening biological aeration filter is used to deeply treat the tail water of pig breeding wastewater,the coagulation effect of self-made magnetic coagulant is studied,the magnetic biological filler is prepared and the process conditions such as film hanging start and stable operation in the biological aeration filter are explored.The following conclusions are drawn:（1）The new magnetic coagulant MPFS was synthesized by hydrothermal method by magnetic nanoparticles and polyferric sulfate（PFS）,and the optimal preparation conditions were as follows:m（Fe₃O₄）:m（PFS）=1:10.The particle size of Fe₃O₄ is 75 nm;The ripening temperature was 40℃,and the turbidity and COD removal rates of pig wastewater tailwater were 79.96%and 43.08%.The microscopic characterization of coagulant structure by SEM,FTIR and XRD was carried out,and it was found that MPFS was a multinuclear polymer containing hydroxyl,nano-Fe₃O₄ and SO₄^2-,and the nano-Fe₃O₄ particles were closely distributed on the surface of PFS,showing a spherical superposition structure,which effectively increased the specific surface area of PFS.（2）The experimental results show that the flocculation effect of MPFS is significantly stronger than that of polyferric sulfate（PFS）and polyaluminum chloride（PAC）,and the removal rates of COD,turbidity and total phosphorus in tailwater reach56%,90%and 97%,and the dissolved organic components of the tailwater are removed to varying degrees after MPFS coagulation treatment,and the aromatic compounds are significantly reduced.After the optimization results of the response surface method,under the optimal process parameters of MPFS dosage of 2.6 g/L,raw water pH of 7.4 and PAM dosage of 2.9 mg/L,the effective removal rate of COD can reach 58.91%,and it is found that the COD removal rate is affected by three factors when the MPFS dosage is 2-3 g/L:pH value>MPFS dosage>PAM dosage,and there is a certain interaction between the factors.（3）Using dewatered activated sludge from urban sewage treatment plant as the main raw material,kaolin and ferric oxide powder as auxiliary materials to fire magnetic ceramic particles,the optimal ratio of ingredients was studied by single-factor experiment:kaolin:magnetic powder=30%:20%:50%.At the same time,the particle density,magnetic field strength and compressive strength were selected by orthogonal test with particle density,magnetic field strength and compressive strength as the detection index,and the best firing process conditions were:drying temperature 105℃,3 min;Under the preheating conditions of 400℃,10 min,and the roasting conditions of 1000℃,6 min,the magnetic ceramic particles with the best compressive strength can be fired,the compressive strength is 5.7 Mpa,the magnetized magnetic field strength is 200 mT,and the magnetic field strength on the surface of the magnetic ceramic grain can be stabilized to 2.8 mT when the magnetization time is 25 min（4）Under the same starting conditions,the magnetic ceramic BAF can be started quickly after about 20 days,and the removal rate of COD reaches 68.8%,the removal rate of ammonia nitrogen is 74.2%,while the removal rate of ordinary ceramic filler is not stable until about 22 days,and the removal rate of COD and ammonia nitrogen is56.8%and 59.5%.Under different ammonia nitrogen influent concentrations,the ammonia nitrogen removal rates of magnetic ceramic BAF in the first,second and third stages were about 75%,73%and 71%,respectively,while the ammonia nitrogen removal rates of ordinary ceramic BAF were 62%,56%and 55%.When the HRT is 8h,DO=4-5 mg/L,the treatment effect of magnetic ceramic BAF is the best,the removal rate of COD and ammonia nitrogen is 76.1%and 93.8%,and the effluent meets the first-class standard of GB 8978-1996.