| The wastewater discharge of printing and dyeing industry is very large.The wastewater quality in these fields is complex and difficult to treat.The goal of current printing and dyeing wastewater treatment is mainly to discharge in accordance with standards,which not only pollutes the environment but also wastes the water resources.If the standard discharge wastewater can be reused and extract the salt from it to achieve zero discharge,it can not only achieve water saving and emission reduction,but also avoid serious harm to the water environment by a large amount of high-salt and refractory wastewater.At present,there are few successful experiences and cases about zero discharge of printing and dyeing wastewater.In this paper,the wastewater discharged from a printing and dyeing industrial park in Guangdong province is taken as the research object,proposed to use membrane treatment to reuse,separate and concentrate salt from it,and achieve zero discharge through evaporation crystallization finally.The main research contents and results are as follows:(1)Through ultrafiltration and reverse osmosis process achieved that more than 60%of the discharged wastewater was treated to meet the water reuse standard and reused directly.Meanwhile,the salt in the raw water has been preliminarily concentrated.Putting forward that ultrafiltration with TIPS membrane preparation method and smaller filter aperture is more suitable for refractory water quality like printing and dyeing.The results show that the SDI of UF product water is less than 3,under the operating conditions of that running flux is 69.4 L/(m~2.h)and water recovery is 93.7%,which meets the design requirements and maintain a long period of stable operation.In the application of reverse osmosis,the actual operation situation of reverse osmosis is investigated and the influence of water temperature and inter-stage pressurization design on reverse osmosis is discussed.The results show that the average desalting rate of the system is 97.8%and TOC rejection rate is greater than 98%under the condition:water temperature is 36.9℃,the average inter-stage pressurization is 3.1 Bar,the designed operating flux is 16.6L/(m~2.h)and the system recovery rate is 65.9%.The product water completely meets the standard of reuse water.(2)Nanofiltration is used to separate and concentrate the bivalent ions mainly including sulfate in RO concentrated water of middle water reuse system to avoid that form miscellaneous salt in final evaporation and crystallization process.The results of this study showed that the final high-pressure nanofiltration concentrated TDS and sulfate radical concentration to 162,740 mg/L and 94,426 mg/L.Research on membrane fouling in low pressure nanofiltration system shows that:fouling on first membrane element in first stage was mainly caused by organic matter,the proportion of pollutant organic matter reached 85.9%.The proportion of inorganic pollutant in the membrane element at the end of the third stage was 69.4%,of which Si accounted for 21.71%and Al for 11.36%,The degradation of its performance is mainly caused by silicon and silicate scale.(3)Zero discharge RO concentration system achieves the salt concentration in product water of all pressure levels nanofiltration,it mainly including medium pressure,high pressure and ultra-high pressure RO systems.The results of this study show that the operating pressure of final ultra-high pressure RO system is over 90 Bar,inlet conductivity is about 65,000μs/cm and concentrated water conductivity is more than110,000μs/cm.In this study,through the combination of different membrane processes in the treatment of printing and dyeing wastewater,not only achieved the reuse of water resources,but also separated and highly concentrated the salt in wastewater,which greatly reduces the operation cost of subsequent evaporation crystallization.It is verified that membrane water treatment technology is an effective way to achieve zero discharge of printing and dyeing wastewater,and provides reference of large-scale practical application cases and technical support for it. |
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