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Inactivation of MS2 coliphage by sequential ultraviolet (UV) light/free chlorine exposure, sequential UV light/monochloramine exposure, simultaneous UV light/free chlorine exposure, and simultaneous UV light/monochloramine exposure using either low-pressure (LP) or medium-pressure (MP) UV lamps was evaluated in this study. At a UV dose of 51 mJ/cm2, the sequential exposure to UV or the simultaneous exposure in the primary disinfection stage enhanced MS2 inactivation rates during the secondary disinfection stage by chlorine by 1.5–2.7 times, compared to the rates solely by free chlorine. At the same dose, the sequential exposure to UV or the simultaneous exposure in the primary disinfection stage enhanced MS2 inactivation rates during the secondary disinfection stage by monochloramine by four to five times. The enhancement was similar with the different UV lamps but less significant with a UV dose of 17 mJ/cm2, while the enhancement from the sequential exposure was higher than that after the simultaneous e...

A switch from free chlorine to chloramine disinfectant triggered problems with excessive lead in Washington, D.C., drinking water. High levels of lead originated in the service lines, but excessive lead was also derived from solder or brass plumbing materials. In many cases, the highest lead concentrations emerged from the tap after about 1 min of flushing-a troublesome outcome, given that routine public notification recommended that consumers flush for about a minute to minimize lead exposure. Bench-scale testing found that chlorine reacts with soluble Pb +2 to rapidly precipitate a red-brown-colored lead solid that was insoluble even at pH 1.9 for 12 weeks; this solid did not form in the presence of chloramine. Further experiments indicated that chloramines sometimes dramatically worsened lead leaching from brass relative to free chlorine, whereas new lead pipe was not strongly affected.

Bench-scale experiments determined the inactivation rates of adenovirus serotype 2 with low-pressure, high-output ultraviolet (UV) light, chlorine (Cl 2 ), and preformed chloramines. Studies with sequential chloramines were also done to mimic water treatment practices. Sequential experiments with adenovirus serotype 2 suspended in laboratory-grade water and natural waters containing ammonia were exposed to either UV light followed by Cl 2 /chloramines or the reverse sequence. Adenovirus log reductions were quantified through cell culture techniques. A free Cl 2 C × T (concentration x time) of 1.22 mg-min/L resulted in a 3.72-log reduction, a preformed chloramine C x T of 264.5 mg-min/L resulted in a 1.2-log reduction, a sequential chloramine C x Tof 40.5 mg-min/L resulted in a 1-log reduction, and a UV dose of 40 mJ/cm 2 resulted in a 1-log reduction. Up to 4-log reductions were achieved with a UV dose of 40 mJ/cm 2 followed by a sequential chloramine C × T of 27.2 mg-min/L. This suggests that sequential disinfection may be the best option for dealing with UV-resistant organisms such as adenoviruses.

Biofilm in drinking water systems is undesirable. Free chlorine and monochloramine are commonly used as secondary drinking water disinfectants, but monochloramine is perceived to penetrate biofilm better than free chlorine. However, this hypothesis remains unconfirmed by direct biofilm monochloramine measurement. This study compared free chlorine and monochloramine biofilm penetration into an undefined mixed-culture nitrifying biofilm by use of microelectrodes and assessed the subsequent effect on biofilm activity and viability by use of dissolved oxygen (DO) microelectrodes and confocal laser scanning microscopy (CLSM) with LIVE/DEAD BacLight. For equivalent chlorine concentrations, monochloramine initially penetrated biofilm 170 times faster than free chlorine, and even after subsequent application to a monochloramine penetrated biofilm, free chlorine penetration was limited. DO profiles paralleled monochloramine profiles, providing evidence that either the biofilm was inactivated with monochloramine's penetration or its persistence reduced available substrate (free ammonia). While this research clearly demonstrated monochloramine's greater penetration, this penetration did not necessarily translate to immediate viability loss. Even though free chlorine's penetration was limited compared to that of monochloramine, it more effectively (on a cell membrane integrity basis) inactivated microorganisms near the biofilm surface. Limited free chlorine penetration has implications when converting to free chlorine in full-scale chloraminated systems in response to nitrification episodes.

The primary focus of this paper is to elucidate the influence of mixtures of natural organic matter (NOM) and free chlorine and NOM and monochloramine on the reduction of PbO2 in drinking water. Parallel experiments using PbO2 particles of two different sizes (approximately 20 and approximately 200 nm) were conducted to explore the effects of particle size on this process. In the absence of NOM, reduction of PbO2 was observed in monochloramine solutions but not in free chlorine solutions. In the presence of NOM, significant Pb(II) formation was observed in disinfectant-free solutions. The release of Pb(II) was suppressed by the additional presence of free chlorine until the point in time when free chlorine was exhausted. Monochloramine also repressed Pb(II) formation in the presence of NOM but not as significantly as free chlorine. The presence of NOM and monochloramine does not necessarily act additively or synergistically due to complex interactions including reduction of PbO2 by NOM, monochloramine mediated reduction of PbO2, and oxidation of NOM by monochloramine. Higher surface area-normalized Pb(ll) formation was found in experiments using larger PbO2 particles. The high reactivity generally associated with nanoparticles was not observed in our study.

The formation of disinfection by-products (DBPs) from chlorination and monochloramination of treated drinking waters was determined. Samples were collected after treatment at 11 water treatment works but before exposure to chlorine or monochloramine. Formation potential tests were carried out to determine the DBPs formed by chlorination and monochloramination. DBPs measured were trihalomethanes (THMs), haloacetic acids (HAAs), halonitromethanes (HNMs), haloacetonitriles (HANs), haloaldehydes (HAs), haloketones (HKs) and iodo-THMs (i-THMs). All waters had the potential to form significant levels of all the DBPs measured. Compared to chlorine, monochloramination generally resulted in lower concentrations of DBPs with the exception of 1,1-dichloropropanone. The concentrations of THMs correlated well with the HAAs formed. The impact of bromine on the speciation of the DBPs was determined. The literature findings that higher bromide levels lead to higher concentrations of brominated DBPS were confirmed.

The kinetics of chlorine isotope exchange between chloramine-B /CAB/ and chloride has been studied using ion-exchange separation and tracer technique. McKay's plot are linear. The exchange reaction is fast in acidic medium, very slow in neutral medium and does not take place in alkaline medium. In the acidic range the exchange is maximum at pH 3.3. The rate of exchange decreases at pH >3.3 and 5. Addition of neutral salt or parent compound has no effect on the rate of exchange. Activation energy and activation entropy for this exchange reaction have been calculated. ? 1989 Akad�miai Kiad�.

Hydrogen sulphide at trace level can be determined by radiorelease technique using radiochloramine-T. The minimum detection level is 0.25 ppm. Zinc acetate is used to fix H2S from air samples. CS2 does not interfere. Interference by SO2 can be eliminated by oxidizing it with H2O2. ? 1989 Akad�miai Kiad�.