Biological removal of cyanide compounds from electroplating wastewater (EPWW) by sequencing batch reactor (SBR) system

Biological treatment system especially, sequencing batch reactor (SBR) system could not be applied to treat the raw electroplating wastewater (EPWW) due to the low organic matter concentration of 10+/-3 mg-BOD5/L and toxic of high cyanide concentration of 23.0+/-2.2 mg-CN/L. However, EPWW could be used as the nitrogen source for the bio-sludge of SBR system. And 10% of EPWW (the final cyanide concentration of 2.3+/-0.2 mg/L) was most suitable to supplement into the wastewater as the nitrogen source. SBR system showed the highest COD, BOD5, TKN and cyanide removal efficiencies of 79+/-2%, 85+/-3%, 49.0+/-2.1% and 97.7+/-0.7%, respectively with 4-times diluted Thai-rice noodle wastewater (TRNWW) containing 10% EPWW and 138 mg/L NH4Cl (BOD5: TN of 100:10) at SRT of 72+/-13 days (under organic and cyanide loadings of 0.40 kg-BOD5/m3 d and 0.0023 kg-CN/m3 d, respectively). However, the effluent ammonia was still high of 22.6+/-0.4 mg-N/L while the effluent nitrate and nitrite was only 9.9+/-0.4 and 1.2+/-0.9 mg-N/L, respectively. And SVI and effluent SS of the system were higher than 95 and 75 mg/L, respectively.