Disinfection of secondary effluents using tin oxide anodes.

Direct current applied to a tin oxide anode submersed in water has the potential to generate hydroxyl radicals, a strong chemical oxidant. Tin oxide anode systems, which may represent a viable alternative disinfectant, were investigated for the disinfection of secondary effluents. Coliform bacteria in the effluent were effectively inactivated in a bench-scale tin oxide disinfection system. The number of anodes in the tin oxide disinfection system influenced the steady-state concentration of hydroxyl radicals and, consequently, the contact time necessary to achieve a specified dose. The life expectancy of the anodes was greater than 30 days and no appreciable loss of tin was observed over a 5-day period. A preliminary estimate of the capital and operating costs of a pilot- or full-scale tin oxide disinfection system designed to meet a discharge requirement of 23 most probable number/100 mL at a 3 785-m3/d (1-mgd) facility was comparable to UV and chlorination/dechlorination facilities. Based on this preliminary assessment, tin oxide disinfection systems are a promising alternative disinfectant for secondary effluents.     

Removal of genotoxicity in chlorinated secondary effluent of a domestic wastewater treatment plant during dechlorination

Purpose  

Dechlorination with tetravalent sulfur is widely used in wastewater treatment processes after chlorination. Dechlorination can remove certain genotoxic disinfection by-products (DBPs). However, the reactions occurring during dechlorination of chlorinated secondary effluent and their genotoxic chemicals are still very complex, and the related genotoxicity changes remain unknown. Therefore, the effects of dechlorination on genotoxicity in secondary effluent and its fractions and typical genotoxic chemical after chlorination were evaluated.     

Effects of thiocyanate on the formation of free cyanide during chlorination and ultraviolet disinfection of publicly owned treatment works secondary effluent.

Cyanide has been detected in effluent of some publicly owned treatment works (POTWs) at levels exceeding influent concentration. Thiocyanate (SCN-) is a cyanide-related compound encountered in most POTW influents and may be decomposed to free cyanide (CN-) under some circumstances. Effects of SCN- on the formation of cyanide during chlorination and UV disinfection were studied through a laboratory study with synthetic solutions and POTW secondary effluent. Results indicated that CN- was detected in SCN- solutions after chlorination in which the chlorine dose or reaction time was not sufficient to destroy SCN-completely, thus ensuring no residual chlorine to destroy any CN-produced. It was also found that SCN can be broken down to yield cyanide by UV irradiation. In addition, SCN- was observed to cause significant positive error in the conventional total cyanide analysis technique involving acidic distillation and colorimetric measurement when nitrate was present in the sample.     

Insights to false positive total cyanide measurements in wastewater plant effluents.

Many publicly owned treatment works in North America are exceeding permitted limits for total cyanide in their wastewater treatment effluents. A recently introduced rapid, segmented, flow-injection analysis procedure using UV digestion and amperometric detection of the membrane-separated cyanide was used to investigate the various scenarios by which elevated cyanide levels might be present in wastewater treatment plant effluent. A number of significant interferences can produce false positive bias during sample analysis with the traditional acid distillation technique, but are minimized or absent with the new analytical method. However, increased levels of cyanide were found in some chlorinated wastewaters compared to the levels before chlorination, suggesting a fast reaction mechanism associated with the disinfectant and some precursor in the wastewater. In particular, the contact of chlorine with nitrite in the presence of a carbon precursor appears to contribute to cyanide formation during wastewater treatment and sample handling. This paper explores the scenarios under which cyanide can form during wastewater treatment as well as those in which a false bias for total cyanide can be obtained during sample processing and provides guidance for appropriate sample handling, screening, and processing to ensure valid analytical results.     

Wastewater disinfection by peracetic acid: assessment of models for tracking residual measurements and inactivation.

With its potential for low (if any) disinfection byproduct formation and easy retrofit for chlorine contactors, peracetic acid (PAA) or use of PAA in combination with other disinfectant technologies may be an attractive alternative to chlorine-based disinfection. Examples of systems that might benefit from use of PAA are water reuse schemes or plants discharging to sensitive receiving water bodies. Though PAA is in use in numerous wastewater treatment plants in Europe, its chemical kinetics, microbial inactivation rates, and mode of action against microorganisms are not thoroughly understood. This paper presents results from experimental studies of PAA demand, PAA decay, and microbial inactivation, with a complementary modeling analysis. Model results are used to evaluate techniques for measurement of PAA concentration and to develop hypotheses regarding the mode of action of PAA in bacterial inactivation. Kinetic and microbial inactivation rate data were collected for typical wastewaters and may be useful for engineers in evaluating whether to convert from chlorine to PAA disinfection.     

Spectroscopic changes on fulvic acids from a kraft pulp mill effluent caused by sun irradiation

Large volumes of wastewater with a high organic load are generated by the pulp and paper industry that negatively affect the quality of receiving waters. The main waste products in the pulp mill effluents are lignin derived macromolecular compounds, which are similar to natural humic substances and very resistant to wastewater treatments. Fulvic acids (FA) represent the higher percentage of these humic substances and it was observed that solar irradiation modify their properties. Several analytic tools, namely, UV–Visible, molecular fluorescence and FTIR spectroscopies, were used to assess the effect of solar exposition on fulvic acids from a kraft pulp mill effluent. It may be concluded that sun irradiation may alter to a high extent the physicochemical properties of macromolecular organic matter, namely fulvic acids, released by kraft pulp mill effluents. After solar exposition, the aromaticity decreases, the aliphatic structures become more oxygenated, and the fulvic acids from the pulp mill effluent remaining in solution are more similar to aquatic fulvic acids from non polluted sites.     

Point-of-use water disinfection using UV light-emitting diodes to reduce bacterial contamination

The treatment process described in this research explores the impact of exposing water samples containing fecal coliforms to the radiation produced by single ultraviolet (UV) light-emitting diodes (LEDs) operating at 265 nm. UV LEDs are long lasting, compact in size and produce more efficient light output than traditional mercury-vapour bulbs, making them ideal for application in point-of-use disinfection systems, such as in remote areas. In this study, contaminated water samples containing either a pure culture of Escherichia coli or tertiary effluent from the City of Regina Wastewater Treatment Plant were used to study the application and efficiency of using UV LEDs for water disinfection. The results indicate that bacterial inactivation was achieved in a time-dependent manner, with 1- and 2.5-log E. coli reductions in water following 20 and 50 min of UV LED exposure, respectively. Ultraviolet radiation was less effective in reducing coliform bacteria in wastewater samples due to the elevated turbidity levels. Further work remains to be completed to optimize the application of UV LEDs for point-of-use disinfection systems; however, the results from this study support that bacterial inactivation using UV LEDs is possible, meriting further future technological development of the LEDs.     

二氧化氯和氯复合消毒剂对城市污水的消毒效果

试验研究了二氧化氯和氯复合消毒剂用于经城市污水处理厂处理后的城市污水消毒的效能 ,结果表明 ,二氧化氯和氯复合消毒剂的使用减低了生成的亚氯酸根离子的浓度 ,增加了残余的二氧化氯的浓度 ,粪大肠菌灭活效果良好。     

Removal and formation of chlorinated triclosan derivatives in wastewater treatment plants using chlorine and UV disinfection

Triclosan, a common antimicrobial agent, may react during the disinfection of wastewater with free chlorine to form three chlorinated triclosan derivatives (CTDs). This is of concern because the CTDs may be photochemically transformed to tri- and tetra-chlorinated dibenzo-p-dioxins when discharged into natural waters. In this study, wastewater influent, secondary (pre-disinfection) effluent, and final (post-disinfection) effluent samples were collected on two occasions each from two activated sludge wastewater treatment plants, one using chlorine disinfection and one using UV disinfection. Concentrations of triclosan and three CTDs were determined using ultra performance liquid chromatography-triple quadrupole mass spectrometry with isotope dilution methodology. Triclosan and the CTDs were detected in every influent sample at levels ranging from 453 to 4530 and 2 to 98 ng L⁻¹, respectively, though both were efficiently removed from the liquid phase during activated sludge treatment. Triclosan concentrations in the pre-disinfection effluent ranged from 36 to 212 ng L⁻¹, while CTD concentrations were below the limit of quantification (1 ng L⁻¹) for most samples. In the treatment plant that used chlorine disinfection, triclosan concentrations decreased while CTDs were formed during chlorination, as evidenced by CTD levels as high as 22 ng L⁻¹ in the final effluent. No CTDs were detected in the final effluent of the treatment plant that used UV disinfection. The total CTD concentration in the final effluent of the chlorinating treatment plant reached nearly one third of the triclosan concentration, demonstrating that the chlorine disinfection step played a substantial role in the fate of triclosan in this system.     

The occurrence of cyanide formation in six full-scale publicly owned treatment works.

This paper presents results from an intensive monitoring program implemented at six full-scale publicly owned treatment works (POTWs) to investigate the fate and formation of cyanide in wastewater treatment processes, with a focus on chlorination and dechlorination processes. A review of historical monitoring data for cyanide species in these POTWs was also conducted. This POTW monitoring program provided a database for the investigation of cyanide formation in wastewater secondary treatment. Data from participating POTWs showed evidence of cyanide formation in this 1-year monitoring effort, although the cyanide formation pattern varied significantly from one plant to another and among seasons. Generally, the chlorination of thiocyanate (SCN-) seems to be the most important mechanism for the formation of cyanide in wastewater treatment processes, especially in chlorination and dechlorination. This hypothesis is supported by the findings of a related laboratory study of mechanisms of cyanide formation in POTWs. It is recommended that POTWs monitor SCN in influent and secondary effluent to identify its presence and adjust chlorine dose appropriately.     

回用生活污水的电化学消毒试验研究

对北京某中水站回用于杂用水的生活污水进行电化学消毒试验。试验结果表明 ,生活污水经生物接触氧化、活性炭吸附后 ,流经电化学消毒器停留 2 0s、耗电 0 .30kWh/m3 、消毒器出水放置 1h后 ,总大肠菌群数 <3个 /L ,满足生活杂用水的卫生学指标。当余氯浓度及接触时间相等的条件下 ,电化学消毒法的杀菌效果好于加氯消毒。E .coli细胞经电化学消毒和加氯消毒处理后 ,扫描电镜观察的结果表明 :2种方法作用后的细胞在形态上的变化是不相同的 ,说明电化学消毒的消毒机制不仅仅取决于电解产氯的作用 ,还有其他的杀菌作用     

污水紫外消毒微生物光复活原理及其控制技术

紫外消毒技术因其具有操作简单、无有害副产物、经济高效等优势,在污水处理中越来越广泛被应用.但其无剩余消毒能力,微生物在光照条件下进行修复而实现复活,从而导致出水微生物数量增多.综述了国内外紫外消毒出现的光复活现象,阐述了污水紫外消毒微生物光复活原理和控制技术.     

Making chlorine greener: performance of alternative dechlorination agents in wastewater

The residual chlorine in chlorine-disinfected and dechlorinated wastewater was characterized using a liquid chromatograph that was switched between reversed-phase separation and flow injection analysis modes, permitting measurement of fractionated and total residual chlorine, respectively. Residuals were detected in the effluent of an operating wastewater treatment plant employing chlorine disinfection and sulfite dechlorination. Despite dechlorination, an estimated total residual chlorine of 3 microM (0.2 ppm as Cl2) was detected in the effluent. To improve dechlorination effectiveness, four alternative agents (ascorbic acid, iron, sulfite plus iodide mediator, thiosulfate) were compared to sulfite on laboratory-chlorinated wastewater. Listed in order of decreasing relative effectiveness, we found: iron metal > sulfite plus iodide approximately = thiosulfate > sulfite > ascorbic acid. Only the iron metal column was completely effective at rapidly removing all traces of residual chlorine.     

Effect of chlorination and ultraviolet disinfection on tetA-mediated tetracycline resistance of Escherichia coli

Antibiotic-resistant bacteria are an emerging threat to public health during drinking water consumption and reclaimed water reuse. Several studies have shown that the proportions of antibiotic-resistant bacteria in waters may increase when exposed to low doses of UV light or chlorine. In this study, inactivation of tetracycline-resistant Escherichia coli and antibiotic-sensitive E. coli by UV disinfection and chlorination was compared to determine the tolerance of tetracycline-resistant E. coli to UV light and chlorine, and tetracycline resistance of a tetracycline-resistant E. coli population was studied under different doses of the disinfectants. Our results showed that relative to antibiotic-sensitive E. coli, tetracycline-resistant E. coli had the same tolerance to UV light and a potentially higher tolerance to chlorination. The mortality frequency distributions of tetracycline-resistant E. coli exposed to tetracycline were shifted by both chlorination and UV disinfection. When compared to the hemi-inhibitory concentrations (IC₅₀) of tetracycline-resistant E. coli with no exposure to UV or chlorination, the IC₅₀ of tetracycline-resistant E. coli treated with tetracycline was 40% lower when inactivation by UV light or chlorination reached 3-log but was 1.18 times greater when inactivation by chlorination reached 4.3-log. Chlorination applied to drinking water or reclaimed water treatment may increase the risk of selection for highly tetracycline-resistant E. coli.     

Distribution and fate of metals in the dispersion plume of a major municipal effluent

The environmental impacts of municipal wastewater discharges on receiving waters are numerous and inputs of contaminants such as metals can cause toxicity to organisms in receiving waters. The effluents generated by the treatment plant of the city of Montreal, Canada, the largest such facility in the St. Lawrence Valley, was investigated to determine the environmental fate of trace metals in the receiving waters. Total and extractable metal concentrations were determined and physico-chemical parameters were measured to characterize the receiving waters and evaluate their influence on the fate and behaviour of metals released from the urban effluent. Our results showed that particulate metals near the effluent discharge point are highly reactive and their distribution seems to be significantly influenced by the abundance of HCl-reactive iron and manganese, which act as trace-metal carriers. The partitioning of metals between dissolved and particulate phases varies along the effluent dispersion plume and therefore could strongly influence the exposure routes for aquatic organisms that are exposed to the various contaminants released from the effluent.     

鼠伤寒沙门氏菌的紫外灭活及光复活抑制的研究

研究了鼠伤寒沙门氏菌的紫外失活动力学、在日光灯下的光复活现象以及氯对其光复活的抑制。结果表明,鼠伤寒沙门氏菌的紫外失活动力学曲线分为滞后区、一级动力学区、拖尾区三阶段,在PBS中的一级动力学失活速率常数为0.9041 cm2/mJ。而紫外灭活后的鼠伤寒沙门氏菌在日光灯下存在光复活。当紫外剂量为10 mJ/cm2时,鼠伤寒沙门氏菌在日光灯下照射3 h内发生明显的光复活,浓度从8.6×103CFU/mL增加到4.1×106 CFU/mL;但是在紫外消毒后,投加1 mg/L的氯可以有效抑制该细菌的光复活,投加2 mg/L的氯可以在10 min内全部灭活。因此,紫外-氯联合消毒能够有效的抑制鼠伤寒沙门氏菌细菌光复活,使其得到高效灭活。     

Reduction of photoreactivation with the combined UV/peracetic acid process or by delayed exposure to visible light.

Photoreactivation of microorganisms following UV inactivation is a well-known, but complex, phenomenon. It is affected by several factors, including UV fluence, wavelength, light intensity, and exposure time to photoreactivating light. The effect on photoreactivation of a combined peracetic acid (PAA)/UV process has not been investigated. Accordingly, this study compared the degree of photoreactivation, under both sunlight and artificial lights, following UV and combined PAA/UV inactivation of fecal coliforms. Effluent samples from the Montreal Wastewater Treatment Plant (MWTP) (Quebec, Canada) were exposed, for 3 hours, to both low- and high-intensity artificial lights and sunlight. All resulted in similar photoreactivation levels. However, average photoreactivation for UV-treated wastewater samples was 1.2 logs, compared with 0.1 log for the combined PAA/UV treatment. Hence, the use of PAA in combination with UV can significantly reduce the potential for photoreactivation. To simulate the photoreactivation conditions of the MWTP effluent (which passes through a 4-km outfall tunnel with approximately 3 hours detention time), UV-treated samples were kept in the dark for 3 hours before photoreactivating light exposure. After this period, photoreactivation levels were close to zero. Hence, the effects of photoreactivation may be diminished by use of a combined disinfection scheme and/or by delaying exposure of the disinfected wastewater to light.     

Spectroscopic changes on fulvic acids from a kraft pulp mill effluent caused by sun irradiation

Large volumes of wastewater with a high organic load are generated by the pulp and paper industry that negatively affect the quality of receiving waters. The main waste products in the pulp mill effluents are lignin derived macromolecular compounds, which are similar to natural humic substances and very resistant to wastewater treatments. Fulvic acids (FA) represent the higher percentage of these humic substances and it was observed that solar irradiation modify their properties. Several analytic tools, namely, UV–Visible, molecular fluorescence and FTIR spectroscopies, were used to assess the effect of solar exposition on fulvic acids from a kraft pulp mill effluent. It may be concluded that sun irradiation may alter to a high extent the physicochemical properties of macromolecular organic matter, namely fulvic acids, released by kraft pulp mill effluents. After solar exposition, the aromaticity decreases, the aliphatic structures become more oxygenated, and the fulvic acids from the pulp mill effluent remaining in solution are more similar to aquatic fulvic acids from non polluted sites.     

In situ and laboratory bioassays to evaluate the impact of effluent discharges on receiving aquatic ecosystems

Effluents are a main source of direct and often continuous input of pollutants into aquatic ecosystems with long-term implications on ecosystem functioning. Therefore, the study of the effects of effluent exposure on organisms, populations or communities within the framework of impact assessment has a high ecological relevance. The aim of this study was to assess the toxicological impact of two effluents, one household wastewater treatment effluent (Effluent 1) and one industrial effluent (Effluent 2), on the receiving aquatic ecosystem using two test species under both in situ and laboratory conditions. Zebra mussel (Dreissena polymorpha) and common carp (Cyprinus carpio) were exposed under laboratory conditions in an online monitoring flow-through system (receiving different concentrations of Effluent 2) and under in situ conditions along the pollution gradient established by these two effluent discharges. Bioassays focussed on growth and condition related endpoints (i.e. condition, growth, lipid budget), since these are key functional processes within organisms and populations. Under laboratory conditions, increasing concentrations of the industrial effluent (Effluent 2) had a negative effect on both zebra mussel and carp energy reserves and condition. Under in situ conditions, the same negative impact of Effluent 2 was observed for zebra mussels, while Effluent 1 had no apparent effect on exposed zebra mussels. Carp growth and condition, on the other hand, were significantly increased at the discharge sites of both effluents when compared to the reference site, probably due to differences in food availability. The results indicate that a combination of in situ and laboratory exposures can illustrate how ecological processes influence bioassay studies. The incorporation of indirect, ecological effects, like changes in food availability, provides considerable benefit in understanding and predicting effects of effluents on selected species under realistic exposure conditions.     

Exposure of caged mussels to metals in a primary-treated municipal wastewater plume

The biological availability of metals in municipal wastewater effluents is strongly influenced by the physical and chemical conditions of both the effluent and the receiving water. Aquatic organisms are exposed to both dissolved and particulate (food ingestion) forms of these metals. In the present study, the distribution of metals in specific tissues was used to distinguish between exposure routes (i.e. dissolved vs. particulate phase) and to examine metal bioavailability in mussels exposed to municipal effluents. Caged Elliptio complanata mussels were deployed at sites located between 1.5 km upstream and 12 km downstream of a major effluent outfall in the St. Lawrence River. Metals in surface water samples were fractionated by filtration techniques to determine their dissolved, truly-dissolved (<10 kDa), total-particulate and acid-reactive-particulate forms. At the end of the exposure period (90 days), pooled mussel soft tissues (digestive gland, gills, gonad, foot and mantle) were analyzed for several metals. The results showed that gills and digestive gland were generally the most important target tissues for metal bioaccumulation, while gill/digestive gland metal ratios suggest that both exposure routes should be considered for mussels exposed to municipal effluents. We also found that Ag and Cd in the dispersion plume nearest the outfall, in contrast to other metals such as Cu and Zn, are more closely associated with colloids and were generally less bioavailable than at the reference site in the St. Lawrence River.