| dc.description.abstract | The objectives of this study were intended to investigate the acute toxicity of practical wastewater in one municipal treatment plant, industrial treatment plant and science-based industrial treatment plant by the Microtox tests. Moreover, the detoxification of biological processes and chemical coagulation processes were understood, and the primary source of acute toxicity was determined by means of linear regression for several parameters of water quality and toxicity unit (TU) of Microtox tests. Furthermore, this study also identified bacteria of biological processes by Biolog identification and then investigated the effect of acute toxicity on the microbial community.
Results indicated the effluent of municipal treatment plant exhibited high acute toxicity because NaOCl was used as the disinfectant, and the maximum value of TU5min and TU15min was 21.7 and 28.6, respectively. In addition, none of acute toxicity was identified in the wastewater of science-base industrial treatment plant because the toxic compounds were suggested to be at very low concentration. The acute toxicity of influent and effluent was generally low in the industrial treatment plant even high acute toxicity was once observed in the influent. Moreover, the activated sludge process (ASP) has obvious performance of detoxification. The maximum reduction of acute toxicity in TU5min and TU15min was estimated to be 71% and 63%, respectively. Pure oxygen activated sludge process also has the function of detoxification. However, the performance of detoxification was unstable due to low concentration of MLSS and inadequate HRT. Notably, the function of detoxification was not observed in one chemical coagulation process of industrial treatment plant. The acute toxicity of industrial wastewater increased due to overdosage of coagulant PAC. The maximum value of TU5min and TU15min was 4.4 and 5.1 in the effluent of chemical coagulation process, respectively.
Additionally, there was a fine correlation of linear regression between the value of TU5min and TU15min in each sample. Thus, the time of Microtox tests could be shorten to 5 min. For the industrial treatment plant, the values of TU15min and dissolved organic carbon (DOC) also exhibited 0.86 of correlation coefficient in the effluent of ASP. Also, the value of TU increased with the increase of total dissolved solid (TDS) in the effluent of chemical coagulation process. This result showed that the use of PAC increased TDS and then resulted in the increase of acute toxicity.
Furthermore, Biolog identification showed Aeromonas spp. was only the predominant bacteria in the ASP of municipal treatment plant. However, Acinetobacter spp., Burkholderia spp. and Pseudomonas spp. was identified as the predominant bacteria in the ASP of industrial treatment plant. The predominant percentage of this three genus of bacteria increased apparently when the TU5min and TU15min increased to 3.8 and 6.7 in the influent of ASP, respectively. | en_US |