1.
Kinetics and mechanism of 17β-estradiol chlorination in a pilot-scale water distribution systems.
Li, C, Dong, F, Crittenden, JC, Luo, F, Chen, X, Zhao, T
Chemosphere. 2017;:73-79
Abstract
The kinetics and mechanisms of 17β-estradiol (E2) chlorination in water distribution systems (WDS) were studied. We examined the impacts of different factors, including pH, temperature, humic acid concentration and type, and flow velocity. The experimental results showed that the rate constants in beaker tests and WDS were described by a pseudo-first-order model. pH had the greatest impact on E2 chlorination in the beaker tests. However, temperature had the greatest impact on E2 chlorination in WDS. Mechanistic analysis of E2 chlorination showed that chlorine attacked E2 in three stages: 1) halogenation of the aromatic ring, 2) cleavage of the benzene moiety and chlorine or bromine substitution formation, and 3) formation of trihalomethanes (THMs) and halogenated acetic acids (HAAs) from phenolic intermediates through benzene ring opening with chlorine and/or bromine substitution of hydrogen on the carbon atoms. In the third stage, the concentrations of THMs and HAAs increased rapidly.
2.
Evaluating simultaneous chromate and nitrate reduction during microbial denitrification processes.
Peng, L, Liu, Y, Gao, SH, Chen, X, Ni, BJ
Water research. 2016;:1-8
Abstract
Sulfur-based autotrophic denitrification and heterotrophic denitrification have been demonstrated to be promising technological processes for simultaneous removal of nitrate NO3(-) and chromate (Cr (VI)), two common contaminants in surface and ground waters. In this work, a mathematical model was developed to describe and evaluate the microbial and substrate interactions among sulfur oxidizing denitrifying organism, methanol-based heterotrophic denitrifiers and chromate reducing bacteria in the biofilm systems for simultaneous nitrate and chromate removal. The concomitant multiple chromate reduction pathways by these microbes were taken into account in this model. The validity of the model was tested using experimental data from three independent biofilm reactors under autotrophic, heterotrophic and mixotrophic conditions. The model sufficiently described the nitrate, chromate, methanol, and sulfate dynamics under varying conditions. The modeling results demonstrated the coexistence of sulfur-oxidizing denitrifying bacteria and heterotrophic denitrifying bacteria in the biofilm under mixotrophic conditions, with chromate reducing bacteria being outcompeted. The sulfur-oxidizing denitrifying bacteria substantially contributed to both nitrate and chromate reductions although heterotrophic denitrifying bacteria dominated in the biofilm. The mixotrophic denitrification could improve the tolerance of autotrophic denitrifying bacteria to Cr (VI) toxicity. Furthermore, HRT would play an important role in affecting the microbial distribution and system performance, with HRT of higher than 0.15 day being critical for a high level removal of nitrate and chromate (over 90%).
3.
[Relation analysis of phosphorus removal and BOD5 loading using PHB monitoring in A2/O process].
Gao, S, Dai, XC, Chen, X, Gao, Y, Zhu, Y, Huang, Y, Huang, MS, Wang, GH
Huan jing ke xue= Huanjing kexue. 2008;(11):3093-7
Abstract
In a pilot-scale anaerobic-anoxic-oxic experimental system for municipal wastewater treatment, PHB consumption in an oxic tank and PHB production in an anaerobic tank had been monitored overtime, and relations among PHB consumption/production, phosphorus removal/release and BOD5 loading had been analyzed. The results indicated that the consumption of PHB was positively related with phosphorus removal, and about 140 mg PHB consumption could result in 1 mg P removal. In the anaerobic tank, about 1.17 mg P release could result in 100 mg PHB production. The PHB production at the loading of 0.176 g/(g x d) was 4 mg/g MLSS less than that at 0.413 g/(g x d). No significant relevance was observed between PHB and BOD5 removal. The PHB of microorganism synthesizes was increased with the increase of temperature. Compared with the lowest temperature (17.1 degrees C), 20% of the total PHB content was increased at the maximum temperature (33.2 degrees C) in active sludge.