| The purpose of this study was to address two important questions: (1) Should wastewater disinfection be practiced? (2) If the answer is yes, how should disinfection be accomplished? Long-term effects of disinfection on wastewater effluents were assessed from both microbiological and chemical viewpoints. Microbial quality was characterized on the basis of viable indicator microorganism (fecal coliform) concentration as well as the community change, and aerobic respiration activity following different treatments using effluent samples collected from four municipal wastewater treatment facilities. Treatments used in this study included: chlorination/dechlorination, UV irradiation, no treatment and control. Oxygen utilization during incubation was recorded in real-time. Results indicated that UV irradiation can cause more respiratory inhibition than chlorination/dechlorination on wastewater effluents with high ammonium concentration. Analyses of community change were based on variations of viable indicator organism concentration against the total bacteria, and results were further classified into nine possible scenarios. Experimental results indicated that both chlorination/dechlorination and UV irradiation led to regrowth of indicator organisms and total bacteria after disinfection. Furthermore, the regrowth pattern was a function of nitrogen composition.; Chlorine-based disinfection processes can have important effects on water chemistry, especially in terms of nitrogenous compounds. Four aliphatic amines (methylamine, N-propylamine, ethylmethylamine and trimethylamine) were chosen as model organic-N compounds. Chlorination was conducted under different pH and CI/N ratios. Organic chloramines and DBPs formed during chlorination of these amines were detected and identified by Membrane Introduction Mass Spectrometry (MIMS). Acute toxicity assays of the precursors and chlorinated amines were conducted using a Microtox system with Phosphobacterium phosphoreum . In addition, an inhibition test was conducted using the oxygen utilization rate (OUR) test with an enhanced nitrifier culture. Results indicated that aliphatic amines could cause a toxicity response and respiratory inhibition. The EC50 values of these aliphatic amines from the Microtox test decreased by one order of magnitude after chlorination. Collectively, results of this research indicated that while disinfection can effectively reduce indicator microorganism concentration, the regrowth potential of wastewater effluents was increased after disinfection. In addition, nitrogenous compounds can have long-term effects on respiration, and may cause toxicity problems after disinfection. |
