Biological Flocculation Coupled With Electrodialysis For The Treatment Of Swine Wastewater

The continuous expansion of the scale of pig farming caused a large amount of swine wastewater.It is difficult to treat swine wastewater because of the characteristics of high COD,high SS and high ammonia nitrogen.At present,anaerobic-aerobic biological treatment technology is widely used,but the removal rate of organic matter in the anaerobic stage is low,and the effluent concentration of SS and ammonia nitrogen are usually still high,which limits the treatment of the subsequent aerobic stage.Therefore,it is of great significance to develop a new process for effectively treating swine wastewater.Based on the principle and technology of flocculation and electrodialysis,this study tried to use electrodialysis coupled flocculation process to treat swine wastewater.The main research contents and results were as follows:（1）The turbidity,COD,and TP of swine wastewater were greatly reduced after biological flocculation,and the removal effect of NH₃-N and TN was not good.Orthogonal experiments determined that the best stirring intensity for flocculation was fast stirring(290S^-1);fast stirring time（1.5 min）;slow stirring(20 S^-1);slow stirring time（15 min）.The bacterial solution after 72 hours of cultivation has the greatest flocculating activity on swine wastewater,and the removal rate of COD,TP,and turbidity were 89.21%,97.76%,98.79%,respectively.For the treatment of wastewater with a p H of 5/6/7/8/9,the best dosages were 2%,8%,10%,10%,10%,respectivity,and the removal rate of turbidity and TP were above 95%,and COD was above 89%.For the treatment of wastewater with TS of0.2/0.4/0.6/0.8/1.0%,the removal rate of COD,TP,and turbidity all reach the maximum when the dosage is 10%.Zeta potential results showed that the electric neutralization has a certain contribution on the biological flocculation process.（2）Biological flocculation could greatly reduce the DOM of swine wastewater,after biological flocculation,the NH₃-N and TN were completely removed using electrodialysis,and the effluent quality reaches the national swine wastewater discharge standard（GB18596-2001）.Biological flocculation,PAC-PAM and centrifugation were used to pre-treat swine wastewater,the biological flocculation treatment effect is better than PAC-PAM and centrifugalation.After biological flocculation,the aromatic protein substances（Ⅱ）,soluble microbial metabolites,and humic acids in the wastewater were greatly reduced,and the changes after PAC-PAM and centrifugal treatment were not obvious.Using single factor experiments determined the best operating conditions,current density was 8 m A/cm²,flow rate was 3 L/min·m²,p H 6,and maximum operating voltage was 25 V.The denitrification rate for different initial p H and different initial NH₃-N concentration could reach more than 95%.The removal rate of TN and NH₃-N of wastewater after different pre-treatments by electrodialysis reached 100%,and the concentrated water and fresh water ratio of bioflocculation-electrodialysis,PAC-PAM-electrodialysis,centrifugal-electrodialysis was 11%and 89%.（3）The loss of Ca²⁺,Mg²⁺,Cu²⁺,Zn²⁺and organic matter was the main reason of the fouling of the electrodialysis membrane,and biological flocculation could alleviate the membrane fouling during electrodialysis treatment.The main mechanisms of Ca²⁺and Mg²⁺contaminated electrodialysis membranes were（1）deposition on the cation membrane in the form of Ca（OH）₂ and Mg（OH）₂;（2）precipitation deposition on the surface of the anion membrane in the form of Ca CO₃ and Ca SO₄.The main mechanisms of Cu²⁺,Zn²⁺polluted of electrodialysis membranes were（1）complex with DOM in wastewater to form a complex and deposit on the anion membrane;（2）Cu²⁺,Zn²⁺form Cu（OH）₂ and Zn（OH）₂ on the cation membrane.The decrease in TOC was due to the retention of the membrane instead of entering the concentrated water through the ion exchange membrane.The three-dimensional fluorescence results showed that the main components of the DOM in the polluted membrane in the swine wastewater are aromatic protein（Ⅱ）,humic acid and soluble microbial metabolites.The main mechanisms of biological flocculation to alleviate membrane pollution are（1）effectively remove the DOM of swine wastewater,so that reduce the complexation of Cu²⁺and DOM,and indirectly alleviate the complex pollution caused by the complexation of Cu²⁺and organic matter;（2）effectively remove aromatic protein（Ⅱ）substances,humic acid substances and soluble microbial metabolites that could easily lead to membrane organic matter pollution.This study provides a new idea to treat swine wastewater and alleviate membrane fouling,also provides a theoretical basis for the practical application of electrodialysis technology.