Study On The Pre-treatment Of Centrifugal Mother Liquid In Polyvinyl Chloride Production By Iron-carbon Micro-electrolysis And Air-fenton Technique

Polyvinyl chloride (PVC) is one of the largest general-purpose resins, whoseyield is second only to polyethylene (PE). Since2005, China has become the world’slargest manufacturer of PVC. At present, the production of PVC is based onsuspension polymerization. Centrifugal mother liquid (CML) is one of the mainsources of wastewater generated during the production of polyvinyl chloride (PVC) inchlor-alkali industry. Therefore, to study the pretreatment technique has greatsignificant meaning to the whole chlor-alkali industry on the pollution control andemission reduction. CML is characterized as low biodegradability and high turbidity,which limits the application of biotreatment and membrane technique on its treatment.Currently, the pretreatment of CML is a new field for lack of pretreatment theory andpractical engineering research.Among all the tested5factors of iron-carbon micro-electrolysis technique, pHhad the most significant effect on the removal of COD and PVA. The optimalcondition for COD and PVA degradation was4h for reaction time,30g/L for Fedosage,1:2for m(Fe)/m(C) ratio,2for pH and0.8L/min for aeration rate. Under thiscondition, the residual COD and BOD in the effluent was about57mg/L,28mg/Land the removal efficiency of COD, PVA and TOC was67%±2%,98%±1%and55%±3%, respectively. The biodegradability (BOD/COD) of CML increasedsignificantly, with BOC/COD increased from0.29to around0.5. Besides, the increaseof initial temperature resulted in further increase in COD removal.In the chosen ranges of the6factors of air-Fenton techneque, the dosage ofFeSO4·7H2O and initial temperature had the most significant effects. The optimaltreatment condition for COD and PVA was1.125mmol/L for FeSO4·7H2O dosage,4for pH,6for [H2O2]/[Fe2+],0.2L/min for aeration rate,30min for reaction time,40℃for initial temperature and1.125mmol/L for FeSO4·7H2O dosage,4for pH,6for[H2O2]/[Fe2+],0.8L/min for aeration rate,30min for reaction time,30℃for initialtemperature. Under these two conditions, the residual COD and BOD in the effluent were about44mg/L,30mg/L and50mg/L,34mg/L respectively. The degradationrate of COD, PVA and TOC was74±1%,96%±2%,53±3%and71±3%,98±1%,52±2%, respectively. In addition, the biodegradability of CML increased to0.68.Both of iron-carbon micro-electrolysis and air–Fenton techniques could meet thedemands on the pretreatment of the PVC centrifugal mother liquid. In addition, eachof them showed great potential in removing ammonia nitrogen, decreasing turbidity,improving biodegradability and had low residual total iron ion. Compared toiron-carbon micro-electrolysis technique, air–Fenton technique had shorter reactiontime, milder treatment condition and relatively low requirement for equipment.