Study On Recovery Of Polyvinyl Alcohol In Desizing Wastewater

At present, wastes from textile industry has greatly threatened the environment while recycling on most of these wastes has drawn more attraction recently. This paper is focusing on the pollution control and waste recycle in textile industry. As for the treatment of desizing wastewater containing polyvinyl alcohol, which is a difficult problem in textile industry, process of salting-out recovery is studied. PAC, as one kind of agent-assist, is utilized to optimize the process, in order to reduce the cost of agent. Therefore, it can reduce pollution and get benefits if PVA can be recycled or reused from wastewater.In this dissertation, PVA was treated by salting-out recovery, the main process factors were studied, as well as performance of recycled PVA. The detailed contents are as follows:Firstly, a way to determine the consistency of PVA solution by spectrophotometry was established, and a curve related the consistency of PVA solution to the absorbance was constituted. Meanwhile the connection between COD and consistency of PVA was researched, with a curve showing the relationship between consistency of PVA and COD, which is beneficial to the following steps. COD engendered by different PVA wastewater is about 1.4～2.1kgCOD/kgPVA, which is largely responsible for the COD load in the textile industry, while the amount of desizing wastewater accounts for only 3 %～5 %.Secondly, factors such as consistency of sodium sulfate, borax, pH, reaction temperature, reaction time and consistency of PVA, were studied respectively. The experimental results have indicated that the elementary technologic condition is: sodium sulfate 14g/L, borax 1.4g/L, reaction time 20min, pH=8.5～9.5, reaction temperature 50℃. It shows that when the consistency of PVA reaches 12 g/L, the recovery rate of PVA is 90.59 % and the removal efficiency of COD is 82.48 %.Furthermore, the best component ratio of new salting agent is gained through orthogonal experiment, and PAC was selected to be one kind of agent-assist. The best technologic condition is: sodium sulfate 8g/L, borax 1.2g/L, PAC 1.0g/L and the recovery rate of PVA is 90.8%. It is found that the amount of sodium sulfate and borax to be added is reduced by 42. 8% and 14. 3% respectively. Besides, the consistency of salt in effluent was reduced from 14.87g/L to 5.92g/L, reaching 60. 2%, which can reduce the cost of agent and is beneficial to the following treatment. Finally, the molecular weight and DP of reclaimed PVA is tested by ubbelohde viscometer. Then the structure of recovered PVA is analysed by infrared spectrum analysis method, resulting in the same performance. In a word, salting-out recovery with a new agent-assist PAC can reduce pollution and get benefits as PVA can be recycled or reused fromwastewater.