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Removal of Pathogenic Bacteria, Viruses, and Protozoans
Published in Samuel D. Faust, Osman M. Aly, Chemistry of Water Treatment, 2018
The Greater Vancouver Water District (GVWD) is a wholesale supplier of drinking water for 1.6 million people in the Lower Mainland of British Columbia.174 Surface water impoundments are located in three uninhabited, mountainous waterbeds to the north of the general service area. Since raw water quality is excellent, treatment for most of the water system consisted of screening at source inlets and disinfection with free chlorine. In 1988, GVWD initiated a comprehensive water quality study to address problems associated with bacterial regrowth, corrosion, turbidity events, tastes, and odors that had been identified in its system. A portion of this study was an evaluation of chloramination for secondary disinfection of the regrowth problem (seasonal occurrence of coliform bacteria and high HPCs). Subsequently, service areas were selected and a secondary disinfection plant was designed to simultaneously chlorinate and chloraminate the water supply. This demonstration plant commenced operation in early September 1988. Water quality monitoring during 1989–1991 found chloramines to be more effective than Cl2 for reducing HPC and coliform levels in the test area. For example, no more than 3% of the samples collected from the chloramine test area during any one month were found to have HPCs greater than 500 cfu/mL in 1989 and 1990. Biofilms collected from the chloramine test area had a much lower incidence of coliforms and somewhat lower concentration of heterotrophic bacteria than biofilms in the chlorine test area. The reader is directed to Reference 175. Residuals in the chloramine test area were much more stable than in the chlorine area. Chloraminated water was found to be more acceptable from a taste-and-odor standpoint than chlorinated water based on a flavor profile analysis. However, there is a negative aspect of chloramination treatment. Based on public response; i.e., consumer complaints, chloramine produced more negative reaction at the beginning of the treatment program chlorine. It is imperative for a PWS to conduct an extensive public education program prior to a conversion to chloramine treatment.
Detection of CNX cyanogen halides (X = F, Cl) on metal-free defective phosphorene sensor: periodic DFT calculations
Published in Molecular Physics, 2021
Mahdi Ghadiri, Mehdi Ghambarian, Mohammad Ghashghaee
Cyanides such as cyanogen halides, which are rich in electrons, are known to be highly lethal to human beings and animals since they restrain the utilisation of oxygen by the tissue [9,10]. Specifically, cyanogen chloride is a common disinfection by-product found in chloraminated waters [11–13]. Cyanogen chloride is a condensable colourless gas [10,14]. It is highly volatile chemical warfare (blood agent) with the military designation CK [10]. Exposure to CNCl can be rapidly fatal. It can severely influence the whole body by ingestion, inhalation, or skin/eye contact, thus affecting the central nervous, cardiovascular, and pulmonary systems. Its vapours are extremely irritating, chocking, and corrosive. It is also used for synthesis of different chemicals and fumigation in commercial scale [10]. CNCl is highly poisonous and its metabolisation to cyanide in the human body is so quick [10,13]. It can become explosive due to polymerisation, and its permissible exposure limit (PEL) is equal to 0.3 ppm or 0.6 mg/m3 [10]. Cyanogen bromide (CNBr) is another member of the halogen cyanide family, which has been used as a common reagent in organic synthesis as well as biochemical applications, such as protein immobilisation and cleavage. Thus, the effective monitoring of this compound, in particular in aqueous systems is critical as well. One may note, however, that CNBr is often not an ideal reagent of choice, as it is much more expensive and more poisonous than free cyanide [15].
Halogenated acetaldehydes in water: A review of their occurrence, formation, precursors and control strategies
Published in Critical Reviews in Environmental Science and Technology, 2019
Jianan Gao, Francois Proulx, Manuel J. Rodriguez
Compared to THM4, the CH concentration could be as high as 66% of overall THM concentrations, according to the study conducted by Koudjonou et al. (2008). Depending on the disinfectant used in this study, the CH/THMs ratios (wt/wt) varied significantly with the lowest ratio observed in chloraminated water (4–22%) and the highest ratio in water treated with ozone-chlorination (12–52%) (Koudjonou et al., 2008). The wide range of CH/THMs ratios (2–66%) reported in this study emphasizes the importance of monitoring CH levels, considering its presumable relatively high occurrence in drinking water.
Ammonia-oxidizers’ diversity in wastewater treatment processes
Published in Environmental Technology, 2018
Ji Hye Jo, Woong Kim, Juntaek Lim
AOB distribution patterns in the environments reflect the physiological properties of distinct AOB isolates observed in the laboratory. In general, oxygen concentration, ammonia concentration, and salinity are thought to be extremely important environmental parameters that affect the nitrification rate and determine the nitrifier community [24]. Residual ammonia concentration is likely to be the most important factor for the distribution of AOB species [21]. Sequences of the N. cryotolerans-cluster are often recovered from oligotrophic environments, including freshwater sediment, wastewater treatment systems receiving low-ammonia influents, and chloraminated drinking water distribution systems, whereas members of the N. europaea-cluster comprise the majority of AOB in eutrophic environments rich in ammonia [21]. The members of N. nitrosa are known to prefer eutrophic environments as well [25]. AOB distribution patterns in A and C were consistent with the above statement. In system A, the ammonium concentrations at the steady-state condition were between 1.8 and 2.0 mM, nearly the level of Ks values of N. europaea, and the N. europaea-cluster was the predominant AOB in this system. In system C, the ammonium concentrations were below detection limit throughout the steady-state period and the N. cryotolerans-cluster was the dominant AOB in this system. However, the result from B contradicted the above. In system B, although the ammonium concentration at the steady-state condition was below detection limit, eutrophic AOB member of the N. nitrosa-cluster was the dominant AOB in this system throughout the experiment. This result implied that it would be necessary to consider other environmental parameters together with ammonium concentration to better correlate AOB diversity in the nano-scale with process performance. It was demonstrated that theVAL is the factor influencing the inclusion of AOB species [26]. VAL of A, B, and C calculated from the influent ammonium concentration, flow rate, and reactor volume were 12.6, 7.5, and 2.1 mM/d, respectively. In this study, the oligotrophic AOB group of the N. cryotolerans-cluster was the predominant AOB when the VAL was 2.1 mM/d, whereas eutrophic AOB groups of N. europaea- and N. nitrosa-clusters comprised the majority of AOB populations in the systems with a VAL of 7.5 mM/d or higher. This is consistent with a previous study that a VAL of 2.4 mM/d was the threshold of dominancy of eutrophic AOB over oligotrophic AOB in a nitrification system [26]. N. europaea has been reported to dominate in medium with low salinity because it is mainly found in freshwater [27]. On the other hand, N. cryotolerans is known to be found in medium containing high salt because it is found mainly in relatively seawater [28]. The physiological characteristics of N. nitrosa are still unknown.