Effectiveness Of Disinfection Processes Research Articles

Effect of disinfection on the photoreactivity of effluent organic matter and photodegradation of organic contaminants

Chlorine, UV254, and ozone are three typical processes commonly used for wastewater disinfection, which could change the photoreactivity of dissolved organic matter (DOM) in effluents of wastewater treatment plants (WWTPs). The photoinduced reactive species (RS) from DOM, primarily including the excited triplet state of DOM (3DOM*), singlet oxygen (1O2), and hydroxyl radical (•OH), play important roles in the attenuation of contaminants. However, the effect of disinfection processes on the photosensitized degradation of contaminants is poorly understood. This paper presents the first evidence that 3DOM*, 1O2, and •OH interaction with three typical contaminants (diphenhydramine, cimetidine, and N,N-diethyl-m-toluamide (DEET)) was largely impacted by DOM after disinfection. The results of electron spin resonance (ESR) spectrometry and laser flash photolysis (LFP) experiments demonstrated that the chlorination increased the formation rate of 3DOM* and 1O2, while UV254 irradiation and ozonation decreased the formation rate of these RS. All these three disinfection processes promoted the photoproduction of •OH and increased the photodegradation rate constants (kobs) of DEET by 26−361%. The kobs of diphenhydramine, cimetidine, and DEET correlated positively with the formation rate of 3DOM*, 1O2, and •OH, respectively. The bimolecular reaction rate constant of 3DOM* with diphenhydramine increased by ∼41% after chlorination. These findings suggest that disinfection processes altered the photogeneration of RS from DOM, which significantly impacts the fate of trace pollutants in aquatic environments.

Disinfection Procedures and Their Effect on the Microorganism Colonization of Dental Impression Materials: A Systematic Review and Meta-Analysis of In Vitro Studies.

Dental impressions are contaminated with potentially pathogenic microorganisms when they come into contact with patient blood, saliva, and plaque. Numerous disinfectants are used; however, no sole disinfectant can be designated as universal for all the impression materials. Thus, the aim of this study is to systemically review the literature to evaluate the effect of the existing disinfection procedures on the bacterial colonization of dental impression materials. This systematic review and meta-analysis was conducted according to the PRISMA statement. PubMed (MEDLINE), Web of Science, Scopus, EMBASE, and SciELO databases were screened up to April 2021. Eligibility criteria included in vitro studies reporting the antibacterial activity of disinfectant solutions in dental impression materials. The meta-analysis was performed using Review Manager (version 5.3.5). A global comparison was performed with the standardized mean difference based on random-effect models at a significance level of α = 0.05. A total of seven studies were included in the meta-analysis. The included studies described the effect of disinfection processes with chlorhexidine gluconate, alcohol, sodium hypochlorite, glutaraldehyde, and hydrogen peroxide in alginate, polyvinyl siloxane, and polyether impression materials. The meta-analyses showed that the use of chlorhexidine, alcohol, glutaraldehyde, and sodium hypochlorite reduced the colony-forming units by a milliliter (CFU/mL) in alginate (p < 0.001). On the other hand, glutaraldehyde, sodium hypochlorite, and alcohol reduced the CFU/mL in polyvinyl siloxane (p < 0.001). Finally, alcohol and glutaraldehyde reduced the CFU/mL in polyether material (p < 0.001). High heterogenicity was observed for the alginate and polyvinyl siloxane materials (I2 = 74%; I2 = 90%). Based on these in vitro studies, the disinfection of impression materials with several disinfection agents reduces the CFU/mL count.

UV Disinfection of Human Norovirus: Evaluating Infectivity Using a Genome-Wide PCR-Based Approach.

The removal and inactivation of infectious human norovirus (HuNoV) is a major focus in water purification, but the effectiveness of disinfection processes on norovirus is largely unknown owing to the lack of a readily available infectivity assay. In particular, norovirus behavior through unit processes may be over- or underestimated using current approaches for assessing HuNoV infectivity (e.g., surrogates, molecular methods). Here, we fill a critical knowledge gap by estimating inactivation data for HuNoV after exposure to UV254, a commonly used disinfection process in the water industry. Specifically, we used a PCR-based approach that accurately tracks positive-sense single-stranded RNA virus inactivation without relying on culturing methods. We first confirmed that the approach is valid with a culturable positive-sense single-stranded RNA human virus, coxsackievirus B5, by applying both qPCR- and culture-based methods to measure inactivation kinetics with UV254 treatment. We then applied the qPCR-based method to establish a UV254 inactivation curve for HuNoV (inactivation rate constant = 0.27 cm2 mJ-1). Based on a comparison with previously published data, HuNoV exhibited similar UV254 susceptibility compared with other enteric single-stranded RNA viruses (e.g., Echovirus 12, feline calicivirus) but degraded much faster than MS2 (inactivation rate constant = 0.14 cm2 mJ-1). In addition to establishing a HuNoV inactivation rate constant, we developed an approach using a single qPCR assay that can be applied to estimate HuNoV inactivation in UV254 disinfection systems.

Effect of disinfection processes and anthropogenic pollutants on comparative formation of trihalomethanes and N-nitrosodimethylamine

Chloramination and chlorination contribute to the formation of N-nitrosodimethylamine and trihalomethanes, respectively, both of which are defined as disinfection by-products. To be able to select the most appropriate water treatment scheme, it is important to comparatively evaluate the formation of both of these disinfection by-products during the application of different disinfection methods. In this study, chlorination, chloramination and stepwise chloramination methods have been applied to surface water samples that have been spiked with known N-nitrosodimethylamine precursors. Experimental results showed that ranitidine can be an effective N-nitrosodimethylamine precursor in distilled water, when chloraminated with high concentrations (140 mg/L) for a long time (10 days), resulting in approximately 450 ng/L of N-nitrosodimethylamine. However, neither dimethylamine nor ranitidine leads to significant trihalomethanes or N-nitrosodimethylamine formation in lake water when chloramination is conducted with low concentration (2 mg/L) for 2 h. These results suggest that N-nitrosodimethylamine concentration measured in the effluent of the drinking water treatment plant may underestimate the N-nitrosodimethylamine concentration that will reach the consumers since chloramination reactions will continue in the distribution system. On the other hand, when only N-nitrosodimethylamine formation potential is used, it will overestimate the N-nitrosodimethylamine that might form in the distribution system due to high disinfectant concentration, high contact time and adjusted pH values used in the N-nitrosodimethylamine formation potential test.

Treatment challenge of a cyanobacterium Romeria elegans bloom in a South Australian wastewater treatment plant – a case study

ABSTRACTA bloom of the non-toxic cyanobacterium Romeria elegans in waste stabilisation ponds (WSPs) within Angaston waste water treatment plant (WWTP) has posed an unprecedented treatment challenge for the local water utility. The water from the WSPs is chlorinated for safety prior to reuse on nearby farmland. Cyanobacteria concentrations of approximately 1.2 × 106 cells mL−1 increased the chlorine demand dramatically. Operators continuously increased the disinfectant dose up to 50 mg L−1 to achieve operational guideline values for combined chlorine (0.5-1.0 mg L−1) prior to reuse. Despite this, attempts to achieve targeted combined chlorine residual (CCR) failed. In this study, samples from the waste stabilisation pond at Angaston WWTP were chlorinated over a range of doses. Combined chlorine, disinfection by-product formation, cyanobacteria cell concentration, Escherichia coli inactivation, as well as dissolved organic carbon and free ammonia were monitored. This study shows that, in the occurrence of cyanobacterial blooms, CCR does not directly suggest pathogen removal efficiency and is therefore not an ideal parameter to evaluate the effectiveness of disinfection process in WWTP. Instead, E. coli removal is a more direct and practical parameter for the determination of the efficiency of the disinfection process.

Formation and control of emerging C‐ and N‐DBPs in drinking water

A survey of 16 US drinking water treatment plants was conducted regarding the occurrence, formation, and control of emerging disinfection by‐products (DBPs), with a focus on drinking waters that were impacted by treated wastewater and/or algae. The formation and control trends of certain emerging carbonaceous (haloacetaldehyde) and nitrogenous (haloacetonitrile, halonitromethane, cyanogen halide, nitrosamine) DBPs were different from those of the regulated trihalomethanes (THMs). This was due to differences in the sources of precursors (e.g., humic substances versus proteinaceous materials) plus differences in the effect of disinfection processes on these DBPs. For example, ozone increased the formation potential (FP) of chloropicrin (median = 226%), whereas biofiltration typically decreased the FP of the ozonated water (median = 48%), which—together with coagulation or softening—resulted (in general) in a net decrease (median = 33%) in FP through the ozone plants. Alternatively, coagulation with the polymer polyDADMAC (a source of N‐nitrosodimethylamine [NDMA] precursor) increased the FP of NDMA (43‐82%), whereas ozonation often destroyed NDMAFP (median to maximum = 10‐87%). This article discusses how utilities can minimize and balance the formation of THMs and haloacetic acids with that of certain emerging DBPs.

Degradation of Selected Acidic and Neutral Pharmaceutical Products in a Primary-Treated Wastewater by Disinfection Processes

Anti-inflammatory and anti-convulsive drugs are being detected in measurable quantities in municipal wastewaters. Some of these emerging substances undergo major transformation at the sewage treatment plant after biological and chemical treatments. The degradation of pharmaceutical products from high-quality treated wastewaters by disinfection processes is well documented. However, the effect of disinfection processes on these products in physicochemical primary-treated municipal effluents remains to be investigated. Pilot projects using ozone, performic acid and UV-radiation disinfection processes were carried out at the Montreal wastewater treatment plant. Residues of pharmaceutical products like salicylic acid, clofibric acid, ibuprofen, naproxen, triclosan, carbamazepine, diclofenac, and 2-hydroxy-ibuprofen were found in the treated wastewaters before disinfection at concentrations ranging from 42 to 2556 ng/L. Most of these substances were eliminated at a rate greater than 50% at an ozone dose of 10 mg/L. Higher removal rates (as high as 70%) were observed when 20 mg/L of ozone was used. Removal rates for UV radiation, on the other hand, were often below 10% among the substances studied. Limited removal rate was observed after UV radiation for diclofenac and triclosan (25 and 40% efficiency, respectively). The irradiation used here (25 mJ/cm2) for bacterial treatment appeared, as previously reported, to be too low to cause the significant breakdown of many of the pharmaceutical substances contained in these wastewaters. Poor reduction efficiencies (< 8%) were observed with the performic acid treatment. Further investigations on analytical methodologies are therefore needed to assess the potential impact of degradation by-products on the environment and on human health.