Effects of pistachio processing wastewater on treatment efficiency of urban wastewater using activated sludge process

Background: In this study, the effect of wastewater produced by pistachio processing in processing terminals on wastewater treatment plants with activated sludge process was investigated. Methods: The pilot of activated sludge was constructed at the laboratory scale similar to wastewater treatment plant in Kerman and it was investigated in different ratios of the wastewater of pistachio processing with urban wastewater and return sludge ratios of 50% and 75%. The best reactor efficiency in treating pistachio processing wastewater was obtained at a ratio of 5% with urban wastewater and return sludge of 50% plus 5 and 10% with urban wastewater and return sludge of 75%. Results: The removal efficiency in the reactor in the aforementioned ratios was obtained to be 96.9%, 98%, and 96.2% for COD, 95.7%, 97.2%, and 93.3% for BOD5, and 7.1%, 99%, and 96.97% for phenolic compounds, respectively. The removal efficiency of BOD5 and COD reduced with the increase in the ratios of pistachio processing wastewater especially with the presence of phenolic compounds. The one-way analysis of variance (ANOVA) indicated that in the aforementioned ratios of pistachio processing wastewater with urban wastewater, the mean COD and BOD5 in the output wastewater were significantly lower than the standards of Iranian environmental organization and guidelines of World Health Organization (WHO). Conclusion: Activated sludge process is able to remove organic compounds of pistachio processing wastewater at a ratio of 5% and return sludge of 50% along with ratios of 5 and 10% and return sludge of 75% with urban wastewater with a high efficiency.