Study On Wastewater Reuse In PTA Process By Ultrafiltration And Reverse Osmosis Integrated Membrane Technology

Purified terephthalic acid(PTA)is an important basic raw material for chemical fiber products.In the PTA production process,a large amount of industrial wastewater is produced.Reclaimed water reuse technology,which could be used to reduce the wastewater discharge and save operating cost,is now widely used in industries.In this thesis,a reclaimed water reuse process is designed based on the ultrafiltration and reverse osmosis double membrane technology for a PTA industry.The main contents and conclusions are as described below.According to the onsite water supply and wastewater drainage condition,as well as the reclaimed water quality requirement,membrane separation technology is chosen as the core of a reclaimed water reuse system.The whole system consists of five units,which are pre-treatment unit,slush dewater unit,ultrafiltration system,reverse osmosis system for generating circulating cooling water,and reverse osmosis system for generating process reusable water.The detailed design of parameters and equipment for each unit are made.Ultrafiltration system is the pretreatment unit of the reverse osmosis system.It could provide protection for the reverse osmosis membrane.Three ultrafiltration membrane with different molecular weight cutoff are chosen to conduct the tests of the removal rates of COD,turbidity and heavy metal in the wastewater.By comparison,the removal rates of X-company ultrafiltration membrane with the molecular weight cutoff 0.08 ? m to COD is 30%and to turbidity is 99%.The X-company ultrafiltration membrane has the best comprehensive properties.The Asahi Kasei ultrafiltration membrane are tested in different operation pressure and the best operation pressure is obtained to be-0.02MPa.The sodium hypochlorite concentration,pH and temperature could influence the cleaning effect of the ultrafiltration membrane.According to the tests,the optimized chemical cleaning conditions are obtained.The cleaner pH should be controlled between 11-12,the temperature be about 30 C and the sodium hypochlorite concentration be about 2000ppm.The best immersion time is 90 minutes.The main function of the reverse osmosis membrane is to remove heavy metal ions.Three different brand of reverse osmosis membrane which have similar parameters are chosen to test the properties in standard sodium chloride and modeling wastewater.The results show that the desalination rate of G-company RO membrane is above 98%and the performance is stable.The variation law of the membrane flux and desalination rate to the supplied water pressure and temperature are studied.The best operation pressure is 0.8MPa and the best inlet water temperature is 25 ?.The designed reclaimed water reuse system is operated and monitored to get the unit properties and the water supply and wastewater drainage condition.The monitored data shows that after the Ultrafiltration and Reverse Osmosis Double Membrane system,the COD in the product water is below 5 mg/L and SS is below 10mg/L.The RO system has very significant effect to the removal of the heavy metal ion and the concentration of the heavy metal ion in the product water is below 0.01 mg/L.The product water hardness is below 1.5mg/L?The treated water after ultrafiltration system and reverse osmosis system could meet the required water quality standards.The treated water could be reclaimed as process supply water and circulating water.The designed system with the capacity of 600m3/h could save cost by 4.18 million RMB.The reclaimed water reuse system achieves remarkable economic benefits.