Research For Combined Process Of Micro-Flocculation Depth Filtration And Ultrafiltration Applied In Advanced Treatment Of Printing And Dyeing Wastewater

Compared with conventional technologies of advanced treatment of printing and dyeing wastewater, micro-flocculation depth filtration is an economical integrated process of high efficiency, which is characterized by small floor space and low investment and running cost. With the development of membrane materials, mature of membrane manufacturing technology and improvement of cleaning methods, ultrafiltration is of simplicity in separation process and low in investment and energy consumption which will be increasingly applied in advanced treatment of printing and dyeing wastewater.This study introduced the process which was combined ultrafiltration with micro-flocculation depth filtration using high stretch yarn terylene fiber-ball filter as the filtration media in advanced treatment of printing and dyeing wastewater. Then the particle entrapped mechanism of fiber-ball filter and pollutants removal characteristics and efficiency of the combined process were analysed and discussed at the same time.The test results showed that high stretch yarn terylene fiber-ball filter was of high porosity, great specific surface area, fast filtering velocity, strong pollutants entrapped capacity and long filtering cycle. Through the treatment of micro-flocculation depth filtration, the effluent turbidity could maintain below 1NTU. The addition of flocculant PAFC (polymeric aluminium ferric chloride) strengthened the removal effect of turbidity. And variation of filtering velocity had little influence on running condition and effluent water quality. Therefore, the process had a widely applied future in the field of advanced treatment of wastewater.By the analysis of theoretical models and test results, we found that the average concentration and diameter of particulates presented a successive depressed trend along the depth direction of filter bed. In accordance with variation of volume distribution for entrapped particulate diameter of different filter height, the particle diameter of depth filtration effluent was between 1μm and 30μm. However, the proportion of particle diameter about 1μm was the most basing on the variation of number and length distribution for entrapped particulate diameter of different filter height.Combined with the oxidization of NaClO , the color, UV₂₅₄ and V₅₁₂ could beefficiently reduced by micro-flocculation depth filtration process. When the quantity of PAFC and NaClO were both 10mg/L, the color of wastewater could be depressed from 160 times to 2 times, and UV₂₅₄ and V₅₁₂ were partially removed either. The addition of NaClO was helpful to the removal of TOC with a small degree increase, but the removal of DOC was below 8%. At the same time, the removal of NH₄⁺ - N reached above 90% because of theoxidization of NaClO.The material that had accumulated within the fiber-ball filter could be removed efficiently by the backwash mode of air scouring-water and air backwash-water scouring. And the filtering media could be sufficiently fluidized when the air and water scouring intensity were 25L/(s·m²) and 8L/(s·m²), respectively. By the shear and washing forces created by backwash water using in conjunction with the surface scrubbing of air, the suspended matter with the filter could be removed and washed away, and the water consumption was smaller than other granular filtering media's.The combined process had significant effect on the removal of turbidity. In a degree, as the pretreatment process of ultrafiltration, micro-flocculation depth filtration could alleviated the load of ultrafiltration membrane greatly, and reduce the probability of membrane fouling occurrence. Meanwhile, the problem of effluent turbidity increase on the initial stage of depth filtration because of the increase of filtering velocity, could be settled by ultrafiltration, and the effluent turbidity could stabilize between 0.5NTU and 0.7NTU. The removal of TOC was also good as well as UV₂₅₄ and V₅₁₂, and their removal ratio reached 41%-53%, 81% and 83%, respectively.