Recycling of dicing and grinding wastewater generated by IC packaging and testing factories－A case study using UF membrane technology

Abstract With the increasing awareness of environmental protection and establishment of strict policy measures requiring more than 85% recovery rate of wastewater in the Science Park, water recycling has become an important issue in several electronic industries such as semiconductor, photovoltaic, and solar energy industries. Among the different types of wastewater, the dicing and grinding wastewater generated in the IC packaging and testing industry is a colloid containing insoluble SiO2 particles. Such wastewater exhibits high turbidity and low electrical conductivity, and can be recovered by simple physical methods. However, the recovery efficiency of the equipment used for recycling wastewater is often degraded by clogging due to the high turbidity of wastewater. In addition, the high chemical stability of the suspended SiO2 particles makes it difficult for them to sediment from the suspension state and presents a greater challenge to remove these, even by conventional methods such as the addition of chemicals which facilitate coagulation and sedimentation. Therefore, the SiO2 particles produce a considerable amount of sludge which causes secondary pollution. In view of the above, recycling tests of cutting and grinding wastewater were performed in this study, using a suitable ultrafiltration (UF) membrane without the addition of any extra chemicals. The results of the study show that the most important factors associated with the application of a UF membrane, in addition to basic material strength, selection of pore size, low water turbidity, and good water quality, are the performance recovery of the membrane after it is blocked and methods for improving the recycling rate of the device. To avoid the formation of a permanent blockage, the UF membrane must be backwashed within 2 h of its use for collecting wastewater. In addition, the effect of cleaning on the UF membrane after it is blocked is related linearly to the concentration of the chemical used for cleaning and the temperature of the cleaning agent, when the concentration and temperature are lower than 0.15% and 45℃, respectively. To increase the recovery rate, the wastewater is collected and recycled in the dead-end mode, whereas the collection time and backwashing frequency are reduced or increased according to the increase in turbidity of the wastewater. In this study, it was observed that the UF membrane was very effective in reducing the turbidity and Suspended solids of wastewater due to the presence of pore structures in the membrane; however, the appropriate filtration mode of the UF membrane should be selected based on the actual quality of the wastewater and results of pilot tests. The use of a UF membrane was established to be the most environmentally benign method for recycling wastewater, without the addition of chemicals.