High Efficiency And Low Cost Nitrogen Removal In Printed Circuit Board Wastewater

With the rapid development of electronics industry in China, different kindsof wastewater were produced in the manufacturing process of electronic products.The amount of wastewater is very large in the production of printed circuit board(PCB). After many years of research and development, various stable and efficientmethods have been created for the removal of a wide variety of most contaminantsin the PCB wastewater. However, there is a lack of treatment process for highefficiency and low cost nitrogen removal. The combined process of complex-breaking pretreatment+anoxic activated sludge (AAS)+biological aerated filter(BAF) was proposed in the study of nitrogen wastewater treatment in this paper.The removal efficiency of nitrogen was investigated in the process by pilot-scaletest and dynamic experiment. In order to provide some reference for the designand operation of the actual project, the appropriate operating parameters wereindicated by running optimum operating conditions.The pretreatment effect on nitrogen wastewater was compared by usingsodium sulfide precipitation and ferrous sulfate replacement method. The resultsshowed that the optimal condition of sodium sulfide precipitation method was thatthe molar ratio of S2-/Cu was1.2:1, concentration of PAC was300mg/L andconcentration of PAM was0.3mg/L. In the optimal condition of ferrous sulfatereplacement method, the molar ratio of Fe2+/Cu was5:1, pH was8.0andconcentration of PAM was0.3mg/L. Under this condition, the two processes havebetter pretreatment effect. And after pretreatment the wastewater can achievedischarge standards with total copper less than0.5mg/L.The possible residual ions (including S2-, Cu2+, Fe2+) effect on subsequentbiological systems were compared by using the two complex-breakingpretreatment methods through a pilot-scale test. The results suggested that varyingdegrees of toxicity inhibition were produced by Cu2+or S2-for nitrification anddenitrification sludge, respectively. But the addition of Fe2+has no effect onsludge. The results of instantaneous effect displayed that the median effectiveconcentrations (EC50) of Cu2+and S2-were4.65mg/L and7.01mg/L, respectivelyfor nitrification sludge. For the denitrification sludge, EC50were3.15mg/L and14.71mg/L, respectively. The results of cumulative effect indicated that themaximum tolerance concentrations of Cu2+and S2-were0.5mg/L and5mg/L,respectively for nitrification sludge. For the denitrification sludge, maximumtolerance concentrations were1mg/L and20mg/L, respectively. Therefore, Compared with nitrification sludge, the denitrification sludge has more toxicitytolerance.The combined process of complex-breaking pretreatment+anoxic activatedsludge (AAS)+biological aerated filter (BAF) was investigated for the treatmentefficiency of nitrogen wastewater through continuous dynamic experiment. Theresults showed that the indicators can reach national emission requirements andeffluents water quality at stable operation conditions were that NH4+-Nconcentration of0.8mg/L, TN concentration of8.4mg/L, COD concentration of63.9mg/L, at the inflow water quality conditions with NH4+-N concentration of23.0mg/L, TN concentration of36.7mg/L, COD concentration of330.8mg/L,HRT of2h in denitrification and nitrification section, nitrification liquid refluxratio of200%and carbon dosage of120mg/L (Methanol, using CODCrcalculated).Compared with the existing process, reaction time and treatment cost of theprocess can be effectively reduced. The total HRT fell down to590min from770min with a decrease of23%; the dosing cost reduced from4.4yuan/ton to1.8yuan/ton with a decrease of59%; the amounts of sludge production reduced from1195mg/L to760mg/L with a decrease of36%.