Effect of peracetic acid, ultraviolet radiation, nanofiltration-chlorine in the disinfection of a non conventional source of water (Tula Valley).

Water supply for human consumption requires certain quality that reduces health risks to consumers. In this sense, the process of disinfection plays an important role in the elimination of pathogenic microorganisms. Even though chlorination is the most applied process based on its effectiveness and cost, its application is being questioned considering the formation of disinfection by-products (DBPs). Therefore, alternative disinfectants are being evaluated and some treatment processes have been proposed to remove DBPs precursors (organic matter. This paper reports the results of disinfection of a non conventional source of water (aquifer recharged unintentionally with raw wastewater) with peracetic acid (PAA) and ultraviolet radiation (UV) as well as nanofiltration (NF) followed by chlorination to produce safe drinking water. The results showed that a dose of 2 mg/L PAA was needed to eliminate total and faecal coliforms. For UV light, a dose of 12.40 mWs/cm2 reduced total and faecal coliforms below the detection limit. On the other hand, chlorine demand of water before NF was 1.1-1.3 mg/L with a trihalomethane formation potential (THMFP) of 118.62 microg/L, in contrast with chlorination after NF where the demand was 0.5 mg/L and THMFP of 17.64 microg/L. The recommended scheme is nanofiltration + chlorination.     

Evaluation of electrochemically generated ozone for the disinfection of water and wastewater.

Effective wastewater treatment is critical to public health and well-being. This is especially true in developing countries, where disinfection of wastewater is frequently inadequate. People who live in these areas may benefit from wastewater disinfection using ozone. This study evaluated the ability of a new electrochemical process of ozone generation, which produced ozone continuously at high pressure and concentration by the electrolysis of water, to disinfect tap water and secondarily treated wastewater. Inactivation of Klebsiella terrigena, Escherichia coli, MS2 bacteriophage and poliovirus 1 was evaluated first in reverse osmosis (RO) treated water. Inactivation of K. terrigena (6-log), E. coli (6-log), MS2 (6-log) and poliovirus 1 (>3-log) was observed after 1 min of ozonation in a 1 L batch reactor. Experiments were then performed to assess the microbiological impact of disinfection using ozone on secondarily treated municipal wastewater. The effect of ozonation on wastewater was determined for total and faecal coliforms, bacteriophages and heterotrophic plate count (HPC) bacteria. Electrochemical ozone generators provided an effective, rapid and low-cost method of wastewater disinfection. Based on the results of this research, electrochemically generated ozone would be well suited to remote, small-scale, disinfection operations and may provide a feasible means of wastewater disinfection in developing countries.     

城市污水再生利用中病原菌指示微生物及其限值研究

在对目前国内外再生水中病原菌指示微生物进行调研的基础上,结合再生水厂运行数据对再生水中病原菌指示微生物及其限值进行了探讨。研究结果表明,以粪大肠菌群作为再生水病原菌指示微生物更能够反映出水体中病原菌的存在状况,目前的再生水处理和消毒技术要达到《城市污水再生利用城市杂用水水质》(GB/T 18920—2002)对总大肠菌群≤3个/L的要求需要投加大量的消毒剂,增加了再生水的处理成本以及再生水中的消毒副产物。     

Combined use of microbiological and non-microbiological data to assess treatment efficacy.

The treatment efficacy for reducing Campylobacter concentrations by a drinking water treatment plant was assessed using a stochastic Monte Carlo model. The goal of the study was to reduce uncertainty of the results by combining microbiological and non-microbiological data in an advanced treatment assessment. Combining raw water Campylobacter and E. coli data reduced the uncertainty on raw water (peak) concentrations five-fold. Similar improvement was achieved for rapid sand filtration. Ozone disinfection was modelled based on ozone concentrations, contact time and temperature. Since this data was available, whereas most microbiological analyses at this point were negative, uncertainty was reduced three-fold. The slow sand filtration assessment could not be improved; however, since previous steps contained less uncertainty, this did not increase uncertainty by much. The study showed that using appropriate data for each treatment step can greatly reduce uncertainty in treatment assessment.     

Setting up microbiological water reuse guidelines for the Mediterranean.

Water reuse is a widespread practice in most Mediterranean countries. Some countries have no wastewater treatment facilities and direct reuse of raw wastewater is occurring while others have a well-established national reuse policy. Water reuse microbiological standards, when existing, significantly differ from one country to another. Some countries have adopted regulations close to the California's Water Recycling Criteria whereas other countries have chosen criteria based on the World Health Organisation (WHO) guidelines. California standards are technologically based requirements aimed at eliminating the presence of pathogens. The WHO guidelines relied on epidemiological evidences though few were available. Their revision on the basis of new epidemiological investigations and quantitative microbiological risk assessment (QMRA) provided by Blumenthal et al., together with added QMRA data, helped proposing Mediterranean guidelines. Acceptable annual risks related to bathing and potable water drinking were taken as benchmarks. This proposal is designed to protect individuals against realistic maximum exposures and to provide minimum and affordable requirements which should constitute the basis of water reuse regulations in every country of the region. Inadequacies of the actual knowledge do not allow a definitive position regarding the guideline limits; other scientific and technical basis are still required.     

Study on the introduction of hazard analysis and critical control point (HACCP) concept of the water quality management in water supply systems.

In the latest revision in 2004, the 3rd edition, the Water Safety Plans (WSP) was newly introduced into the World Health Organization (WHO) Guidelines for Drinking Water Quality. The Hazard analysis and critical control point (HACCP) is a basic concept that underlies the WSPs, and is also known as the product quality management method in the field of food and the medical manufacturing industries. In the amendments of the Drinking Water Quality Standards in Japan, water suppliers are required to reasonably achieve both safe water and efficient water quality management. Therefore, the HACCP concept is focused as an adequate management method covering a whole process of water supply systems, in a systematic way. The purpose of this study is to investigate a practical procedure in introducing the HACCP into water quality management in Japan. In comparison to conventional applications of the HACCP, unmanageable variations of raw water quality, continuous treatment and supply, and numerous standards of water quality items need to be considered. The HACCP system is expected to achieve a quick response to improvements in water quality, accountability towards consumers and a decrease in accidents.     

Control of disinfection byproduct formation in Feng-Shan reservoir by the traditional treatment processes plus O3-pilot-plant test.

Two processes in the pilot plant were studied and compared to reduce the disinfection byproduct risk of the potable finished water of Feng-shan treatment utility in Taiwan. For 5 months study, two processes have both demonstrated to achieve a significant removal on the organic precursors of DBPs, including NPDOC and A-254. With the analysis of molecular weight distribution of organics in raw water, the study found the post ozonation plus BAC can provide additional enhancement in degrading organic contents. A process of coagulation/sedimentation/rapid sand filtration/post ozonation/BAC would be suggested as the advanced treatment process improving the supply quality of Feng-shan utility.     

Comparison of the role of attachment, aggregation and internalisation of microorganisms in UVC and UVA (solar) disinfection

In this comparative study, the impact of two microbial protective mechanisms against simulated UVA disinfection was assessed by using protocols previously developed for UVC disinfection assays. (i) The impact of natural microorganism aggregation and attachment to particles was assessed by targeting total coliform bacteria in natural surface water samples. (ii) The impact of bacteria internalisation by zooplankton was assessed by using C. elegans nematodes as a model host and E. coli as a bacterial target for UVA inactivation. Dispersion of natural aggregates by blending prior to UVA exposure was shown to enhance the inactivation rate of total coliforms as compared to untreated raw water. Removal of particles by an 8-microm membrane filtration did not improve UVA disinfection efficiency. Twenty-four per cent of the highest applied UVA fluence was found to reach internalised E. coli in nematodes. Both aggregation and internalisation showed similar impact as protective mechanisms against UVA and UVC bacterial inactivation.     

Safe household water treatment and storage using ceramic drip filters: a randomised controlled trial in Bolivia.

A randomised controlled field trial was conducted to evaluate the effectiveness of ceramic drip filters to improve the microbiological quality of drinking water in a low-income community in rural Bolivia. In four rounds of water sampling over five months, 100% of the samples were free of thermotolerant (faecal) coliforms (TTC) compared to an arithmetic mean TTC count of 1517, 406, 167 and 245 among control households which continued to use their customary sources of drinking water. The filter systems produced water that consistently met WHO drinking-water standards despite levels of turbidity that presented a challenge to other low-cost POU treatment methods. The filter systems also demonstrated an ability to maintain the high quality of the treated water against subsequent re-contamination in the home.     

Microbiological quality of groundwater sources used by rural communities in Limpopo Province, South Africa.

A survey of the microbiological quality of water from 194 boreholes (97 privately owned and 97 communal boreholes) in the rural Thitale-Hlanganani area of the Limpopo Province, South Africa was carried out between August 2002 and August 2003. Very little information on the microbiological quality of privately-owned boreholes in rural communities is available raising concerns about the safety of these groundwater supplies. In this study, levels of total coliforms, thermotolerant (faecal) coliforms, faecal enterococci, Clostridium perfringens (vegetative cells and spores) and somatic coliphages were determined for community and privately-owned borehole water. The average counts for total coliforms, faecal coliforms, faecal enterococci and Clostridium perfringens exceeded the South African recommended guideline limits of 0-10 counts.100 ml(-1) for total coliforms and 0 counts. 100 ml(-1) for faecal coliforms, faecal enterococci and Clostridium perfringens respectively. Comparisons between the levels of indicator bacteria present in private and communal boreholes during dry seasons indicated a statistical difference for faecal enterococci bacteria (p = 0.005) and Clostridium perfringens (p = 0.08). Comparisons between the levels of indicator bacteria present in private and communal boreholes during rainy seasons indicated statistical differences between total coliforms (p = 0.05), faecal coliforms (p = 0.03) and Clostridium perfringens (p = 0.009) bacteria. No significant differences in the presence of somatic coliphages in both private and communal borehole water were see. The results indicated the need for environmental impact assessment studies to monitor the microbiological quality of groundwater sources in rural communities.     

Application of a virological tracer method for the assessment of pathogen removal by physicochemical treatment and chemical disinfection.

Coxsackie B3 (CoxB3) virus was used as a virological tracer for an assessment of the efficiency of pathogen removal by several typical physicochemical treatment and chemical disinfection processes, such as coagulation-filtration, ultra-filtration, and disinfection using chlorine and ozone, with regard to the pathogenic quality of the treated domestic wastewater for reuse purposes. The CoxB3 virus was seeded to sterilized secondary effluent to make a raw water of known pathogenic level. After applying the raw water to each treatment or disinfection process, the residual virus in the finished water was concentrated, and virus assay was carried out by the Tissue Culture Infectious Dose technique. TCID50 was used as an indicative parameter of CoxB3 virus in the raw and treated water. Parallel experiments were also conducted to evaluate the effectiveness of each process for the removal of coliform bacteria. It was noticed from the experiment that both coagulation-filtration and ultrafiltration could achieve substantial removal of TCID50 at about the same level (2-log removal). However, the effect of the two processes on the removal of coliform bacteria was much different: 2-log removal by coagulation-filtration and 4 to 5-log removal by ultrafiltration. The TCID50 removal correlates more closely with the removal of turbidity than that of coliform bacteria. Chlorine was found to be effective in coliform removal but almost had no effect on TCID50. As ozone was applied, a high removal of both coliform bacteria and TCID50 could be obtained.     

富营养湖泊的藻类现存量控制和供水处理的藻类去除

我国城镇供水正面临湖泊(水库)富营养化的严峻挑战.评述了高藻类现存量干扰水处理过程导致的供水问题,以及高藻类生物量控制对策和供水处理除藻工艺的国内外发展现状.就国内外现有藻类生物量控制对策和供水处理除藻工艺提出若干结论,并对我国今后在该领域的进一步研究提出建议.     

Investigation of opportunistic pathogens in municipal drinking water under different supply and treatment regimes.

Changing regulations to lower disinfectant byproducts in drinking water is forcing utilities to switch disinfection from chlorine to monochloramine. It is generally unknown whether this will impact positively or negatively on the microbiological quality of drinking water. A utility in Florida, using water with relatively high organic carbon levels from deep wells in several wellfields, made the decision to change its disinfection regime from chlorine to chloramine in order to meet the new regulations. To assess the impacts of such a change on the microbiology of its water supplies, it undertook a number of studies before and after the change. In particular, the presence of the opportunistic pathogens Legionella and Mycobacterium, and also the composition of drinking-water biofilms, were examined. A preliminary synthesis and summary of these results are presented here. Legionella species were widely distributed in source waters and in the distribution system when chlorine was the disinfectant. In some samples they seemed to be among the dominant biofilm bacteria. Following the change to monochloramine, legionellae were not detected in the distribution system during several months of survey; however, they remained detectable at point of use, although with less species diversity. A variety of mycobacteria (21 types) were widely distributed in the distribution system when chlorine was the disinfectant, but these seemed to increase in dominance after chloramination was instituted. At point of use, only four species of mycobacteria were detected. Other changes occurring with chloramination included (a) an altered biofilm composition, (b) increased numbers of total coliforms and heterotrophs and (c) nitrification of water storage tanks. The results suggested that consideration should be given to the microbiological effects of changing disinfection regimes in drinking-water and distribution system biofilms.     

Water Quality Monitoring and Hydraulic Evaluation of a Household Roof Runoff Harvesting System in France

The quality of harvested rainwater used for toilet flushing in a private house in the south-west of France was assessed over a one-year period. Twenty-one physicochemical parameters were screened using standard analytical techniques. The microbiological quality of stored roof runoff was also investigated and total flora at 22°C and 36°C, total coliforms, Escherichia Coli, enteroccocci, Cryptospridium oocysts, Giardia cysts, Legionella species, Legionella pneumophila, Aeromonas, and Pseudomonas aeruginosa were analysed. Chemical and microbiological parameters fluctuated during the course of the study, with the highest levels of microbiological contamination observed in roof runoffs collected during the summer. Overall, the collected rainwater had a relatively good physicochemical quality but variable, and, did not meet the requirements for drinking water and a microbiological contamination of the water was observed. The water balance of a 4-people standard family rainwater harvesting system was also calculated in this case study. The following parameters were calculated: rainfall, toilets flushing demand, mains water, rainwater used and water saving efficiency. The experimental water saving efficiency was calculated as 87%. The collection of rainwater from roofs, its storage and subsequent use for toilet flushing can save 42 m³ of potable water per year for the studied system.     

控释消毒剂及其在饮用水消毒保质上的应用前景

控制释放技术作为一种新型且安全有效的方法 ,已引起越来越多有关专业人员的重视 ,正在形成一个崭新的研究领域。就此简要介绍了控制释放技术 ,分析了控释消毒剂制备中消毒剂和载体聚合物的选择问题及三种可行的制备方法 ,指出了控释消毒剂在饮用水消毒保质上应用的优点和存在的问题 ,并对其应用前景进行了展望。     

Use of Ozone in Wastewater Treatment to Produce Water Suitable for Irrigation

The use of ozone to disinfect sewage is becoming increasingly important, especially when a high degree of treatment is required. Ozone is a strong disinfectant with a high oxidation potential and is one of the most effective ways of inactivating pathogens. In order to observe and evaluate the effect of this disinfectant on the physical, chemical and microbiological characteristics of wastewaters, we analyzed the effluent input and output of an ozone disinfection plant located in Almeria, southeast Spain. The ozone input rate is adjusted according to the residual ozone content in the effluent output. The effluent is currently reused to irrigate vegetable crops. Another objective of this study has therefore been to verify the adequacy of this water treated process for preparing water for this purpose. Among the results obtained, it is important to highlight the fact that the ozone disinfection treatment was sufficient to inactivate faecal coliforms. We achieved reductions in these pathogens of around 89%. This treatment was respectful towards elements that give the reuse of effluent an added value in irrigation (N, P, K, etc) and also kept the quality of the waters within the authorized limits. Thus, we achieved up to 88% removal of COD, a maximum 68% removal of BOD₅ and up to 75% removal of suspended solids. Based on the results of the parameters analyzed in this ozonized effluent, we concluded that ozone-treated water is suitable for reuse in the irrigation of fresh consumption crops in accordance with the guidelines established in related legislation.     

The use of immersed membranes for upgrading wastewater treatment plants

Membranes can be installed in the clarifier (or aeration tank) of an existing activated sludge plant to enhance the biomass separation function of the system, thereby effectively overcoming any operating constraints associated with sludge settleability. The resulting upgraded plant can be operated at high biomass concentrations (10–20 gMLSS/L), leading to an increase in its treatment capacity. The membranes also ensure a treated water consistently free of suspended solids and a superior disinfection performance. The system offers an enhanced operating flexibility, and allows to operate at high sludge ages leading to a low excess sludge production.Such an immersed membrane activated sludge process (BIOSEP^®) has been developed and applied to the treatment of raw sewage. When treating screened raw sewage with this process, with a sludge concentration of 15 gMLSS/L and a volumetric loading of 1.2 kgCOD/m³/d, a 96% COD reduction and a 95% Total Kjeldahl Nitrogen (TKN) reduction have been obtained. The disinfection performance of the system was over 6 Log removal for fecal coliforms. The resulting production of sludge was 0.20 kgMLSS/kgCOD.Two desk case studies are given for 900 m³/day upgraded plants. In one case, the primary objective was to increase the treatment efficiency and develop nutrient removal for the original plant, while in the other case the primary objective was to increase the capacity of the original 460 m³/day plant.     

Control of Cryptosporidium: From reservoirs to clarifiers to filters

Control of Cryptosporidium in potable waters requires an integrated multiple barrier approach of source water protection of water supply reservoirs and treatment technology through clarification, filtration, and disinfection. Pristine lakes and protected reservoirs have far lower concentrations of oocysts (mean values less than 10 oocysts/100 L) than unprotected supplies. Coagulation is critical to the effective control of Cryptosporidium by clarification and filtration. Coagulation conditions that produce filtered waters of low turbidities, particle counts, and effectively remove natural organic matter also produce high removals of Cryptosporidium. Dissolved air flotation (DAF) can achieve oocyst removals of 3 log compared to about 1 log by sedimentation. DAF and filtration provide two effective barriers to Cryptosporidium with cumulative log removals of 4 to 5 compared to log removals of 3 to 4 by sedimentation and filtration.     

Secondary effluent reclamation: combination of pre-treatment and disinfection technologies.

A study was carried out to evaluate the efficiency of secondary effluent additional treatment, using a combination of pre-treatments (ring filter, physico-chemical and infiltration-percolation) followed by disinfection methods (chlorine dioxide, peracetic acid and ultraviolet light). Three different indicator microorganisms were determined: E. coli, total coliforms and somatic bacteriophages. The results show better efficiency of physico-chemical and infiltration-percolation processes. Bacteriophages were eliminated to a lesser extent than bacterial indicators in all the treatment systems. Chlorine dioxide and peracetic acid seems to be more efficient in disinfection than ultraviolet light when a ring filter is the pre-treatment used. For the same doses and contact times, the efficiency of the disinfection methods is higher when the pre-treatment used is the physico-chemical or the infiltration-percolation system. The final effluent quality from the physico-chemical treatment train and the infiltration-percolation treatment train, followed by the disinfectants, achieves an E. coli content that allows the reuse in most of the uses described in the Spanish legislation for wastewater reuse.     

On-site greywater treatment and reuse in multi-storey buildings.

The paper presents a study of a pilot plant treating light greywater for seven flats. The pilot plant combines biological treatment (RBC) with physicochemical treatment (sand filtration and disinfection). The pilot plant produced effluent of excellent quality, meeting the urban reuse quality regulations, and was very efficient in TSS turbidity and BOD removal: 82%, 98% and 96%, respectively. COD removal was somewhat lower (70-75%) indicating that the greywater may contain slowly-biodegradable organics. The RBC (attached growth biological system) was able to retain most of the solids as a result of bioflocculation; further it was proven to have very stable and reliable performance. Faecal coliforms and heterotrophic reductions were very high (100% and 99.99%, respectively) producing effluent that also met drinking water standards. The combination of low organic matter, nutrients and microbial indicators reduces the regrowth and fouling potentials in the reuse system, thus ensuring safe reuse of the treated greywater for toilet flushing.