Process Optimization Of Ink Wastewater Treatment For Printed Circuit Board Manufacturing

Since the ink wastewater from printed circuit board(PCB) manufacturing is characterized as high concentration of organic matters, high toxicity, and poor biodegradability. Acid precipitation/aerobic biological technology are traditionally applied for its treatment. However, acid precipitation process is ineffective to remove the organic matters and improve the biodegradability, resulting in the effluent chemical oxygen demand(COD) below the standard and biological nitrification inhibition. Meanwhile, the total nitrogen(TN) after the current treatment process is unable to meet the updated emission standard. In this case, the combination of physico-chemical pretreatment, denitrification-biological aerated filter(AAS-BAF) theories were introduced in present study for the ink wastewater treatment. It is not only capable to reduce the amount of organic matters and improve the biodegradability, but also to strengthen the efficiency of TN removal.Based on the comparision of acid precipitation and coagulation using as the primarily pretreatment precess for ink wastewater treatment, the iron-carbon micro electrolysis and Fenton oxidation technology were studied for the following step. The results indicated that compared with coagulation process, which is effective only in the decrease of SS, the acid precipitation was preferred for the removal of COD(69%), chroma(90%), and SS(100%) under the condition of p H 3. Besides, both the iron-carbon micro electrolysis and Fenton oxidation technology were helpful to further enhace the degredation of organic matters and the biodegradability. After the treatment of oxidation processes, COD removal efficiency could reach 21.42% for the former and 24.48% for the latter; and the corresponding effluent B/C increased from 0.04 to 0.26 and 0.39, respectively.The effluent obtained from “ acid precipitation + microelectrolysis” and “acid precipitation + Fenton” process were then applied to carry out the biological treatment experiments separately. The optimum treatment process was determined based on the analysis of removal efficiency and economical cost. Compared with single acid precipitation process, “ acid precipitation + microelectrolysis” and “acid precipitation + Fenton” had no obvious effect on denitrification, but they were helpful to improve the nitrification effect, and the corresponding nitrification rates raised from 4.54 mg/h to 6.32 mg / h and 7.66 mg/h respectively. Economical cost analysis showed that “ acid precipitation + microelectrolysis” treatment process costed 4.71 yuan/ton of water, far below the “ acid precipitation + Fenton process” of 11.66 yuan/ton of water. According to above conclusions, “ acid precipitation + microelectrolysis” treatment process was choosen for the treatment of ink wastewater.The continuous dynamic experiments were conducted to evaluate the process efficiency of “acid precipitation + microelectrolysis + AAS-BAF”. The results showed that the treatment process was capable to effectively remove the COD, ammonia and TN of ink wastewater. Under the condition of 150 mg COD/L methanol as external carbon source, the removel efficiencies of COD, ammonia and TN were 55,1.44 and 12.82 mg/L, which could achieve the related emission standards.