| The wastewater from textile printing and dyeing industry is one of the main source of industrial wastewater, with the top5th of the discharge volume in the whole domestic industry. The caustic soda consumption and discharge is the largest chemical reagent in the mercerization process in the textile printing and dyeing plants, meanwhile there are high levels of COD and SS (consist of fibers and impurities) in the discharged wastewater. The quality of the products would be descended if using the waste alkali liquor without treatment. Large amount of acid will be consumed to neutralize the alkali when the wastewater is treated for discharge. The unsuitable neutralization will influence the subsequent bio-treatment seriously and increase the difficulty of the bio-treatment system; meanwhile the large consumption of acid dosage not meet the requirements of clean production. It is necessary to purify and recover the alkali from the waste alkali liquor of the mercerization process.This study derives from a sub-project of the integrated technology research on water-saving and discharge-decreasing and clean production in the key industrial zone in Liaohe watershed, which belongs to the national significant special program in12th Five Years Plan. The nanofiltration process was employed in recover the alkali from the practical mercerized waste alkali liquor from Anshan Boyi Printing and Dyeing Company in this pilot-scale study. The recovered alkali could be reused to mercerization or other printing and dyeing processes, thus reached the objectives of water and alkali conservation and decrease in enviromental pollution. The pre-treatment process, equipment design and manufacture, the optimization of operational parameters of the membrane equipment, and operational stability of the equipment sets were investigated in these study.(1) The result of coagulation pretreatment shows that the turbility removal efficiency reached above90%under the suitable following parameters. The optimal operational parameters are120mg/L of PAC dosage and4mg/L PAM dosage,40℃of temperature,300r/min and3minutes for rapid stirring,50r/min and2minutes for slow stirring, and45minutes for settlement. While the natural precipitation after temperature decrease could be also used as pretreatment. The coagulation air floatation process and natural precipitation after temperature decrease could be chosen in the practical project. (2) The nanofiltration set-up, consisted of Koch’s special alkali-resistant nanofiltration membrane (Model:MPS-34A2Z),50micron bag filter and5micron microfiltration membrane as pretreatment for nanofiltration membrane was used in this test. After settlement pretreatment, the various waste alkali liquor from mercerization wastewater were used as influent for nanofiltration process (the waste alkali liquor was diluted by tap water for preparation of low concentration waste alkali liquor). The experimental results show that a higher alkali permeability of up to80-97%for various concentrations of influents; the COD removal efficiency reached up to77-84%; and the SS and turbidity removal efficiencies could be near100%. In the condensing experiments, the results show that the recovery efficiencies of alkali liquor and alkali reached95%and90%respectively, and COD removal efficiency was above80%. The membrane flux could be recovered by above99%by suitable cleaning agents and operating parameters in the destructive test. The experimental results was also satisfied in treating the influent with alkalinity up to71.2g/L and COD of1000mg/L by nanofiltration process.After three membrane modules could be installed in the set-up for increase in treating capability, the experimental set-up in this pilot-scale test could be used in the practical project by suitable improvement. |
PDF Full Text Request