Study On Pre-treatment Of Centrifugal Mother Liquid Based On The Combination Of Ozonation Technique

Polyvinyl chloride (PVC) is one of the world’s most important plastic products.It has such mechanical and corrosion resistance properties that it has great potentialfor wide-scale use. Also the energy consumption and the cost of its production is low,thus it has a great market prospect. In China, PVC is mainly made of vinyl chloridemonomer, using electricity stone production suspension polymerization method.PVC centrifugal mother liquid is one of the main wastewater emissions inproduction process. It has poor biodegradability and can easily generate foam so thatit affects the reoxygenation ability of water. If directly emitted, it would terriblypollute the environment. When using conventional biological treatment andmembrane treatment, PVC centrifugal mother liquid is poorly biodegradable becauseit can’t be easily biodegraded and can easily clog the membrane.In this article, oxidation technology and coagulation sedimentation-Ozonationwas employed in pre-treatment of PVC centrifugal mother liquid. They identifiedfactors that influence treatment effect, got the optimum processing conditions andprovided the basis for the pre-treatment of the mother liquid.In oxidation technology pre-treatment,4factors influencing the polyvinylalcohol (PVA) and COD removal efficiency were studied. The ozone dosing quantityand pH affect efficiency significantly. Initial temperature and residence time affectefficiency to a less extent. By considering those4factors, the optimal treatmentconditions for PVA and COD removal were obtained through orthogonalexperiments. The results showed that the maximum removal of COD and PVA couldbe reached under the following conditions: reaction time was20minutes, initialtemperature was30℃, pulse density of the ozone generator was25%, pH=7, andaeration rate was100L/h. The removal efficiency of COD and PVA was72±2%and85±0.2%, respectively, and the residual concentration of COD and PVA was48.7mg/L and0.36mg/L, respectively. Under this condition, ozone dosage was4.2±0.2g/L. Biodegradability of the wastewater (BOD/COD) was improved from0.26to0.46. In coagulation sedimentation-ozonation technology pre-treatment, the dosageof3coagulants including Al2(SO4)218H2O, FeCl36H2O, PAM were studied. Then,the effects of pH and the best dosage of ozone were determined through single factorexperiment. Finally determined polyvinyl alcohol (PVA) and COD removalefficiency. The result showed that when we used Al2(SO4)3as coagulant, the dosagewas40-80mg/L, pH ranged from5-7, and then we did5minutes of ozonationpretreatment: pulse density of the ozone generator was15%, aeration rate was100L/h, the related pollution indexes had good removal efficiency: COD, PVA,ammonia nitrogen and turbidity was78±5%,96±2%,50±3%,100%, respectively.Biodegradability of the wastewater (BOD/COD) was improved from0.26to0.52.Under these condition, ozone dosage was0.5±0.1g/L.Both oxidation technology and coagulation sedimentation–ozonationtechnology can be used to pretreat the PVC mother liquid to remove the PVA andCOD. After subsequent biological and advanced treatment, the PVC mother liquidcan be reused. The oxidation technique requires less investment and doesn’t causesecondary pollution. But it needs much more ozone and the removal of PVA andturbidity is not thorough. Combing coagulation technology with ozone dosage, wecan get good effect meanwhile cost low money, mild conditions, low equipment. Theprice of Al2(SO4)3is so cheap that the combination can be used largely in theindustrial water treatment.