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/m(3) d and 0.0023 kg-CN/m(3) 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. (C) 2007 Elsevier B.V. All rights reserved.