Output Water Quality Research Articles

Development and Performance Evaluation of an Economical Solar Still for Water Purification

Aim: The study aims to address the global challenge of clean water scarcity by exploring a cost-effective and efficient solar still for purifying various types of contaminated water using solar energy. Methodology: An experimental investigation was conducted using a solar still designed with acrylic sheets, an inner mirrored surface, and aluminum fins. The study evaluated the solar still's performance in purifying seawater, brackish water, and polluted water, comparing input and output water quality. The experiments were carried out with and without aluminum fins, using a solar still with an area of 0.25 m². Results: The solar still successfully reduced the total dissolved solids (TDS), salinity, and pH of the input water. For seawater with an initial TDS of 14,700 PPM, salinity of 18.13 PSU, and pH of 9.15, the output values were 15 PPM TDS, 0.01 PSU salinity, and a pH of 7.4. The highest water volumes were achieved with aluminum fins: 410 ml for seawater, 380 ml for brackish water, and 380 ml for polluted water, compared to 170 ml without fins. The maximum water yield of 1.64 l/m2 was achieved for sea water using this solar still. Conclusion: The study demonstrates that the solar still, particularly when equipped with aluminum fins, effectively transforms high-TDS, high-salinity, and high-pH water into clean, potable water. The findings suggest that solar distillation is a viable solution for producing safe drinking water from contaminated sources.

Integration of Hydrate-Based Desalination (HBD) into Multistage Flash (MSF) Desalination as a Precursor: An Alternative Solution to Enhance MSF Performance and Distillate Production

This study considers the integration of multistage flash (MSF) desalination with hydrate-based desalination (HBD) precursor to improve MSF performance in terms of distillate production, longevity, and operational conditions. This is accomplished by a comprehensive analysis of the rate of scale formation, distillate production, and the MSF performance ratio by means of mathematical modelling conducted in Simulink software. To calibrate the effectiveness of HBD as precursor to the MSF desalination process, two MSF models were created: the once-through (OT) and brine recycle (BR) configurations. The MSF models were validated in terms of stagewise distillate production, brine temperature, and coolant temperatures with data from the literature, while neglecting the non-equilibrium allowance. The operational performance of the proposed integration approach was evaluated in terms of the deposition rates of CaCO3, scale thickness, fouling resistance, overall heat transfer coefficient, performance ratio, and production ratio. The examination was conducted from the perspective of water salinity and stream temperature for the integrated HBD-MSF systems. The results show that due to the quality of output water in terms of salinity and temperature, the integration of HBD and MSF improved the performance of MSF by substantially reducing scale formation rates as well as increasing the production of distillate where the scale formation rates were 40.6% and 36.3% lower for the hybrid HBD-MSF-OT and HBD-MSF-BR systems, respectively.

Optimization of Sedimentation System through AHP and AHP-TOPSIS Methods in Water Treatment Steam Power Plant

Steam power plants consist of systems such as Water Treatment Plant (WTP), boiler, turbine-generator, and balance of plant. WTP system consists of sedimentation, desalination, and demineralization. The coagulation mechanism triggered by the mass grave of suspended solids during the sedimentation process, and if it is less than optimal, so will be modified by injecting coagulant-flocculant chemicals. The most common problem is the high dose chemicals used in the rain and tidal sea conditions. However, the output water quality that produced still does not reach the standard requirements. This condition would affect the high costs of water treatment operations. It also would have an impact on the poor feed the next system. The jar-testing technique is research using process and operational variables that theoretically influence the efficiency of the coagulant-flocculant such as doses, setting times, and rotates agitator. Evaluation of experiments using water quality criteria and data results processed by AHP and AHP-TOPSIS. The sensitivities of both methods are analyzed thus compared to select a consistent alternative that obtained sequence the first alternative for D60W30P80 and the second alternative for D40W20P80. The optimal sedimentation process could potentially save 40-60% of the water treatment operational cost while operating conditions achieved.

Investigating the Error Propagation from Satellite-Based Input Precipitation to Output Water Quality Indicators Simulated by a Hydrologic Model

This study investigated the propagation of errors in input satellite-based precipitation products (SPPs) on streamflow and water quality indicators simulated by a hydrological model in the Occoquan Watershed, located in the suburban Washington, D.C. area. A dense rain gauge network was used as reference to evaluate three SPPs which are based on different retrieval algorithms. A Hydrologic Simulation Program-FORTRAN (HSPF) hydrology and water quality model was forced with the three SPPs to simulate output of streamflow (Q), total suspended solids (TSS), stream temperature (TW), and dissolved oxygen (DO). Results indicate that the HSPF model may have a dampening effect on the precipitation-to-streamflow error. The bias error propagation of all three SPPs showed a positive dependency on basin scale for streamflow and TSS, but not for TW and DO. On a seasonal basis, bias error propagation varied by product, with larger values generally found in fall and winter. This study demonstrated that the spatiotemporal variability of SPPs, along with their algorithms to estimate precipitation, have an influence on water quality simulations in a hydrologic model.

Assessment of microbial quality of household water output from desalination systems by the heterotrophic plate count method.

Point-of-use household water desalination systems (HWDSs) are becoming popular in Iran because of the deterioration of drinking water. This study aimed to determine the microbial quality of output water from HWDSs in Qom, Iran by using the heterotrophic plate count (HPC) method. Samples of input and output water from 30 HWDSs were collected over a six-month period. Heterotrophic bacteria were tested using the pour plate technique. At the first sampling stage, the HPC level in 23% of samples exceeded the 500 CFU/ml threshold level. On average, for 50% of samples, the HPC level of input samples was 0-10 CFU/ml, for 42% it was 10-100 CFU/ml and for 8% it was 100-500 CFU/ml. For output samples, for 25%, the level of HPC was 0-10 CFU/ml, for 43% it was 10-100 CFU/ml, for 24% it was 100-500 CFU/ml and for 8% it exceeded 500 CFU/ml. For total coliforms the most probable number test was positive for the first and third stages of sampling (3% input samples). The comparison of the averages with national standard values shows that in some cases, the contamination of output water from HWDSs in the city of Qom has been above the standard values.

A simulation study of surface water purifying through a polystyrene foam filter

The study has improved the mathematical model of water purification in view of the physicochemical properties of surface water, the type of filter loading, and the filtration characteristics of filtering structures. The advanced mathematical model takes into account the inverse influence of the process characteristics on the filtration parameters, changes in the diameters of the loaded grains throughout the height, the direction of filtering, and the turbidity of water at the inlet. The authors performed a comparative analysis of the work of filters with homogeneous and non-uniform loading for water filtration in different directions and carried out statistical processing of the results of the study with the establishment of the adequacy and the possibility of its use for a mathematical description of water treatment processes. Physicochemical properties of surface water entering filtration structures are taken into account in the model in the form of kinetic coefficients. The kinetic coefficients, which characterize the intensity of contaminants’ separation from and adhesion to the loaded grains, were obtained using the dimension theory method and were deduced for floating densities. It has been determined that the optimum loading height is 1.0 m for the ascending and descending filtration directions, where the output water quality is of the normative values. The improved mathematical model can help select the optimal design (the loading height and area, the granulometric composition, etc.) and the technological parameters (velocity and direction of filtration, degree of vaporization of incoming water) of polystyrene foam filters; it allows producing simulation of filters’ work in different conditions. A simulation of the work of polystyrene foam filters with different parameters of operation was carried out, which made it possible to specify optimal structural and technological parameters of the polystyrene foam filters for purifying water of the Horyn River (Rivne Oblast, Ukraine), the composition of which is typical for most plain rivers in Ukraine

A NOVEL APPLICATION OF CHAOTIC PROPERTIES IN WATER TREATMENT PLANT

This paper aims at presenting a new optimization proposal to enhance the flocculation process in Water Treatment (WT) plant using a better flash mixing, located at KELAVERAPALLY, in Krishnagiri district, Tamil Nadu, India. Further, Sludge removal is done efficiently which decreases the water wastage as well as improvement in output water quality. Though WT plants are already equipped with systematic and sequential physicochemical processes, still they need to be optimized to obtain a better treated drinking water to maintain the quality standards as prescribed by World Health Organization. Chaotic behavior in chemical systems has been used to optimize the performance of WT plant. Measurement systems implemented in WT plant yield several chaotic based measurement parameters which are used to control the system operations to maintain the target water quality. This intelligible data extraction through the proposed measurement  systems in a short span of time improves the plant performance without adding any costly systems except few changes in the existing plant setup.  Chaotic behavior is ensured through Lyapunov Exponents and Kolmogorov-Sinai Entropies. Both, water quality improvement and water wastage reduction is achieved simultaneously in the proposed work when a dosage prediction is done using Feed Forward Neural Networks. The treatment plant investigated has a maximum capacity of 14 MLD (Million litres per day) using two parallel streams with 7 MLD each

Predicting the Hydraulic Conductivity of Metallic Iron Filters: Modeling Gone Astray

Since its introduction about 25 years ago, metallic iron (Fe0) has shown its potential as the key component of reactive filtration systems for contaminant removal in polluted waters. Technical applications of such systems can be enhanced by numerical simulation of a filter design to improve, e.g., the service time or the minimum permeability of a prospected system to warrant the required output water quality. This communication discusses the relevant input quantities into such a simulation model, illustrates the possible simplifications and identifies the lack of relevant thermodynamic and kinetic data. As a result, necessary steps are outlined that may improve the numerical simulation and, consequently, the technical design of Fe0 filters. Following a general overview on the key reactions in a Fe0 system, the importance of iron corrosion kinetics is illustrated. Iron corrosion kinetics, expressed as a rate constant kiron, determines both the removal rate of contaminants and the average permeability loss of the filter system. While the relevance of a reasonable estimate of kiron is thus obvious, information is scarce. As a conclusion, systematic experiments for the determination of kiron values are suggested to improve the database of this key input parameter to Fe0 filters.

ASSESSMENT OF HOUSEHOLD REVERSE-OSMOSIS SYSTEMS IN HEAVY METAL AND SOLUTE ION REMOVAL IN REAL AND SYNTHETIC SAMPLES

In this study, the efficiency of household reverse-osmosis system (HROS) with and without neutralizer accessory was investigated in both real and synthetic samples. The real samples were collected from rural and urban public drinking-water systems with and without primary refinery treatment. The selected areas were situated in the Kurdistan province, Iran. The HROS model RO100GPD with and without neutralizer accessory was used in all experiments to prevent effects of the membrane used, age of devices, and length of time in service. In order to assess sample quality, some more common physico-chemical analyses consisting of hardness, Ca 2+ , Mg 2+ , total dissolved solids (TDS), electrical conductivity (EC), alkalinity, Cl - , Br - , SO 4 2- , PO 4 3- , NO 3 - , NO 2 - , and heavy metals were performed based on standard methods. The results indicate that HROS and neutralizer accessory have significant effects on the physico-chemical properties of feed water. However, the results indicate the instability of HROS output water quality, but they verify that this instability cannot reduce the output quality. Finally, results emphasize that HROS output water meets standard levels regardless of the input water quality and application of neutralizer accessory.

Comparative Analysis of Desalination Technologies

As the world population is growing, the need for fresh water is increasing. Water desalination is a mean for producing fresh water from saline water abundant in seas and oceans. Various technologies have been used to desalinate saline water with different performance characteristics. This work outlines current desalination technologies and compares their performance in terms of input and output water quality, amount of energy required, environmental impact and cost. It was found that adsorption desalination technology is a promising method for desalinating seawater due to its low running cost and low environmental impact as it uses waste energy resources.

Kristal® 2000 PVDF hollow fiber UF membrane in the pretreatment for seawater desalination

Membrane technology has emerged as a dominant solution to seawater desalination due to its superior advantages such as stable output water quality, lower energy consumption, ease of operation and smaller footprint. However, the design of spiral wound reverse osmosis (RO) membranes used in desalination does not allow for backwash or air scouring, thus rendering the RO membrane highly susceptible to fouling. Pretreatment for the RO system is therefore essential to ensure a long service life of the RO membranes. For waters containing suspended solids of up to 75 mg/L (such as that in the SingSpring Desalination Plant at Tuas, Singapore), conventional pretreatment methods (such as dissolved air floatation and filtration (DAFF), chemical dosing and cartridge filtration) require regular operator intervention to produce a permeate of reasonably quality. Ultrafiltration (UF) as a pretreatment for seawater desalination can offer better treated water, lower operating costs, a smaller footprint, and flexibility in dealing with poor or varying feed water quality. By improving the pretreatment permeate water quality, reducing operating costs and the footprint, capital expenses can be lowered. Greater stability is also achieved during times of poor or variable feed water conditions (such as periods of algalbloom). A pilot study was conducted at SingSpring to track the performance of Hyflux's Kristal® 2000 hollow fiber UF membranes as pretreatment for the seawater reverse osmosis (SWRO) system. The results of the pilot study will enable the design of future large-scale UF-SWRO membrane projects for seawater desalination.

Testing for aerobic heterotrophic bacteria allows no prediction of contamination with potentially pathogenic bacteria in the output water of dental chair units.

Background: Currently, to our knowledge, quality of output water of dental chair units is not covered by specific regulations in the European Union, and national recommendations are heterogeneous. In Germany, water used in dental chair units must follow drinking water quality. In the United States of America, testing for aerobic heterotrophic bacteria is recommended. The present study was performed to evaluate whether the counts of aerobic heterotrophic bacteria correlate with the presence of potentially pathogenic bacteria such as Legionella spp. or Pseudomonas aeruginosa. Methods: 71 samples were collected from 26 dental chair units with integrated disinfection device and 31 samples from 15 outlets of the water distribution pipework within the department were examined. Samples were tested for aerobic heterotrophic bacteria at 35°C and 22°C using different culture media and for Legionella spp. and for Pseudomonas aeruginosa. Additionally, strains of Legionella pneumophila serogroup 1 were typed with monoclonal antibodies and representative samples of Legionella pneumophila serogroup 1 were typed by sequence based typing.Results: Our results showed a correlation between different agars for aerobic heterotrophic bacteria but no correlation for the count of aerobic heterotrophic bacteria and the presence of Legionella spp. or Pseudomonas aeruginosa.Conclusion: Testing for aerobic heterotrophic bacteria in output water or water distribution pipework within the departments alone is without any value for predicting whether the water is contaminated with potentially pathogenic bacteria like Legionella spp. or Pseudomonas aeruginosa.

English

Advanced bioremediation in waste water and sewage treatments currently represents one of the important aspects of biotechnology. The removal of pathogenic microorganisms, complex hydrocarbons, heavy metals and nutrients were intensively investigated. The present work aims to improve the efficiency of involved bacteria in aeration tanks for maximizing mineralization process of organic substances and consequently reduce the time of the treatment process. Other target is the elimination of nutrients (N & P) to avoid their environmental and hazardous effects. In order to achieve these goals, isolation and identification of dominant microflora in aeration tanks were carried out and highly active strains were selected. Trails are newly done for hybridization or cloning one or more of dominant strains to increase their oxidizing efficiency. A pilot experiment was established in a green house to stimulate biological stage of municipal plant and to test the achieved genetically modified strains (Modell experiment). Also, monthly data were recorded of 20 parameters to highlight and controlling input and output of wastewater station of Taif city. Biological oxygen demand (BOD5) and chemical oxygen demand (COD) clearly decreased in out fluent indicating lower organic load. The decrease of total organic carbon (TOC), total dissolved solids (TDS) and total suspended solids (TSS) assured the previous obtained data. Presence of large amount of dissolved oxygen (DO) in the out fluent means the efficiency of aeration pumping process.  Nitrate content (NO3-) and nitrite content (NO2-) were sharply decreased in the out fluent indicating the higher requirement of H-acceptors. NH3 (ammonia content) decrease, however total Kjeldahl Nitrogen (TKN) increase were due to intensive microbial bodies load. Total hardness (TH) decrease, which means lower conc. of Ca++ and Mg++ and better quality of output water. pH values were slightly decreased because of microbial acidic products.  Turbidity was dramatically reduced because of different precipitation process. Phosphorous (P) content and Sulfate (SO4 =) content decreased indicating consumption or fixion in microflora bodies. Otherwise, chloride (Cl-) content were increased in outfluent because of chlorination process. Oil and grease were quite reduced in the outfluent. Finally, different heavy metals and hydrocarbons were found in the limit or lower than the permit levels globally. Total microbial count increased considerably in outfluent, especially in summer months; however, fermentative bacteria were very low because of enough O2 present in outfluent. Only 15 strains of 280 isolates (about 5.4%) were found to be highly active in mineralizing organic substances which were completely identified. The most active one was used to modify the dominant strains by cloning technology and reinoculated in the pilot experiment   Key words: Waste water bioremediation, sewage microflora, mineralization of organic pollutants, eutrofication phenomena, microbial cloning, ligation reaction.

The Genotoxicity of the Organics in Effluent From Different Treating Processes of 6 Water Works in Shenzhen

PP-31-192 Background/Aims: To detect and assess the genotoxicity of the organic extracts in effluent of 6 water works in Shenzhen. Methods: The Salmonella mutagenicity test was used to detect the mutagenicity of water samples collected from 6 water works (A, B, C, D, E, and F) on May and June, 2008, Shenzhen. Results: Except for the water sample from active carbon pool of B water works, all other showed positive result for Ames test, and the type of mutagenicity was mainly code-shifting. The intensities of mutagenicity of every water samples during the treatment were as follows: A: output water > precipitated-filtrated water > source water > second chlorinated water > tap water > prechlorinated water; B: source water > second chlorinated water > precipitated-filtrated water > tap water > output water > active carbon filtrated water; C: prechlorinated water > output water > precipitated-filtrated water > source water > tap water > second chlorinated water; D: tap water > precipitated, filtrated water > prechlorinated water > output water > source water; E: output water > prechlorinated water > tap water > precipitated-filtrated water > second chlorinated water > source water; F: second chlorinated water > precipitated-filtrated water > source water > output water > tap water. The comparisons of mutagenicity of output water among 6 water works: TA98 (−S9): E > D > C > A > F > B; TA98(+S9):E > C > F > D (A, B were negative); TA100 (−S9): E > F > C > A (D, B were negative); TA100 (+S9): only E was positive. Conclusion: The mutagenicity of Dongjiang river decreased after the treatment of B and F water works, increased after the treatment of A and C; the mutagenicity of Dongjiang river plus reservoir water source increased after the treatment of D and E. The treatment techniques of pre-O3-O3-bioactive carbon filtration had positive effect in reducing the mutagenicity of output water. During the treatment techniques, cancelling of the prechlorination or using the dioxochloride replaced for chlorine as the disinfectant might have positive effect toward optimizing the quality of output water.

Application of the combined ultrafiltration and reverse osmosis for refinery wastewater reuse in Sinopec Yanshan Plant

The refinery wastewater reuse system of Sinopec Yanshan Plant in Beijing (China) has been in operation for more than four years. The water reuse system combines biological treatment, media filtration with a combination of ultrafiltration (UF) and reverse osmosis (RO). After more than 30?times of chemical cleaning, the current RO system salt rejection is still above 97% at 80% system recovery. The normalized permeate flow of the three RO trains vary with the operation time but after chemical cleaning, they recover to above the design flow of 100 m3/h. The data presented in this study indicate the fouling nature of the RO feed water on the 1st stage RO. However, according to the experience of Sinopec Yanshan Plant the output water quality meets the customer requirements. This is one of the first publications which show that the combination of UF and RO technology can be applied to reuse the refinery wastewater. The TOC rejection of the UF process is determined at 34%, which is highly dependent on the molecular weight of the organics. Low molecular weight organics could pass the UF unit and foul the RO membrane surface, causing serious organic fouling. Furthermore, the periodic pressure drop increase of the 1st stage RO system showed that there was serious bio-fouling. Therefore, addition of other pretreatment technology before UF, such as activated carbon cartridge filter and dosing non-oxidized biocides, are proposed alternatives that could help to increase the life-span of UF and RO elements.

Lack of cytotoxicity by Trustwater Ecasol™ used to maintain good quality dental unit waterline output water in keratinocyte monolayer and reconstituted human oral epithelial tissue models

We previously showed that residual treatment of dental chair unit (DCU) supply water using the electrochemically-activated solution Trustwater Ecasol™ (2.5 ppm) provided an effective long-term solution to the problem of dental unit waterline (DUWL) biofilm resulting in DUWL output water quality consistently superior to potable water. Objectives To investigate the cytoxicity of Ecasol using cultured keratinocyte monolayers and reconstituted human oral epithelial (RHE) tissue and to extend the study of Ecasol's effectiveness in maintaining the microbiological quality of DUWL output water. Methods TR146 human keratinocyte monolayers and RHE tissues were exposed to Ecasol (2.5–100 ppm) for 1 h periods after removal of growth medium and washing with phosphate-buffered saline (PBS). Experiments were repeated using Ecasol that had been exposed for 30 min to 1–2 mg/mL bovine serum albumin (BSA), equivalent to protein concentrations in saliva. To quantitatively determine cytotoxic effects on monolayers following Ecasol exposure, the Alamar Blue proliferation assay (assesses cell viability) and the Trypan Blue exclusion assay (assesses plasma membrane integrity), were used. Cytotoxicity effects on RHE tissues were assessed by the Alamar Blue assay and by histopathology. Results Ecasol at >5.0 ppm resulted in significant ( P < 0.001) cytotoxicity to keratinocyte monolayers following a 1 h exposure. These effects, however, were completely negated by BSA pretreatment of Ecasol. No cytotoxicity was observed in the more complex RHE tissue at any of the Ecasol concentrations tested. In a 60-week study of 10 DCUs, tested weekly, the average density of aerobic heterotrophic bacteria in Ecasol-treated (2.5 ppm) DCU supply water was <1 cfu/mL and in DUWL output water was 6.5 cfu/mL. Conclusions Ecasol present as a residual disinfectant in DUWL output water is very unlikely to have adverse effects on human oral tissues at levels effective in maintaining DUWL output water quality at better than potable standard water quality.

Valuation of shrimp ecosystem services – a case study in Leizhou City, China

The economic valuation of ecosystem services is an effective way to understand the multiple benefits provided. Effluent and other environmental problems must be properly managed if shrimp aquaculture is to achieve sustainability. Evaluation of shrimp ecosystems can facilitate voluntary improvements in the environmental performance of shrimp farms. This study evaluated shrimp ecosystem services in Leizhou City, Guangdong Province, using the market method (MM), carbon tax rate method (CRM), reforestation cost method (RCM) and contingent valuation method (CVM), based on results of input–output analysis and water quality of shrimp ponds. We examined both direct and indirect value of shrimp ecosystem services at large and small spatial scales. This study has quantified the multiple benefits and costs of shrimp ecosystems, suggests a more feasible basis for coastal environmental management and sustainability of shrimp aquaculture.

A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol™ maintains dental unit waterline output at better than potable quality: A 2-year longitudinal study

Most studies addressing biofilm formation in dental chair unit waterlines (DUWLs) have focused on a range of individual dental chair units (DCUs) and no studies on a centralised approach in a large number of DCUs have been reported to date. Objectives To develop a centralised, automated water quality and biofilm management system serving the distribution network providing water to Dublin Dental Hospital's 103 DCUs, capable of maintaining DUWL supply and output water at better than potable quality standards in the long-term and requiring a minimum of human intervention. The potable water standard for the European Union does not specify an upper limit of aerobic heterotrophic bacteria, whereas a maximum of 100 cfu/mL is permitted in bottled water. Methods Mains water of varying quality was treated by specifically selected automated filtration units to provide DCUs with water of consistent chemical composition. This water was then automatically disinfected using an electrochemically activated solution Ecasol™ (Trustwater Group, Clonmel, Ireland) (2.5 ppm) prior to distribution to DCUs. Microbiological quality of both DUWL supply and output water was monitored weekly by culture on R2A agar for 10 sentinel DCUs for a 100-week period. DUWLs were tested for the presence of biofilm by electron microscopy. Results Chemical composition of processed mains water consistently bettered potable water standards. DUWL supply water and output water aerobic heterotrophic bacterial counts averaged <1 and 18.1 cfu/mL, respectively, from the 10 DCUs, compared to 88 cfu/mL for unprocessed mains water. This correlated with the absence of biofilm in DUWLs. No adverse effects due to Ecasol™ treatment of supply water were observed for DUWLs or DCU instruments. Conclusions This centralised and automated water treatment and biofilm management system consistently maintains DUWL output water at better than potable quality simultaneously in a large number of DCUs over the long-term.

Water environmental capacity and total water pollution quantity control of Chaping River, Sichuan Province

以流经四川绵阳市安县河流茶坪河为研究对象,在对该河流水污染负荷、水环境现状及水环境功能充分调查的基础上,结合该河流的水文特征和排水规划以及四川省绵阳市环境监测站2005年实测的数据,采用二维浅水水动力学—水质模型方程组对茶坪河的各监测断面CODCr和NH₃-N的浓度场进行了计算模拟和对比,并用一维水环境容量计算模型计算了该河流的水环境容量,提出了具体的总量控制措施.结果表明:用二维浅水水动力学—水质模型方程组计算各监测断面的CODCr和NH₃-N与实测值相差不大;茶坪河水环境容量CODCr为123.96t/a,NH₃-N为42.95t/a,所排放的CODCr量、NH₃-N量已经超过该流域容量,出水水质已超过水质保护目标Ⅲ类标准.;The object of research is Chaping River which flows over Anxian County in Mianyang City, Sichuan Province. Based on agreat number of investigations on the load of water pollutants, the situation and function of water environment of the river, theriver-basin hydrological character, the river draining plan, and observation date at environmental monitoring station of MianyangCity Sichuan Province in 2005, two-dimensional hydrodynamic shallow-water model equations were used for monitoring COD and NH₃-N concentrations in section of the Chaping River and the simulations were compared. A one-dimensional model was used tocalculate the water volume capacity of the river's water environments and the ways controlling the total quantity were provided.Results indicated that using two-dimensional hydrodynamic shallow-water model equations to calculate the monitoring sectionshowed a small measured difference for COD and NH₃-N. For the water environmental capacity of Chaping River, COD was 123.96t/a and NH₃-N 42.95 t/a. The COD and NH₃-N emission volume would exceed the capacity in the basin, and the quality of outputwater would exceed the III grades of water protecting standards.

Optimisation of the long-term efficacy of dental chair waterline disinfection by the identification and rectification of factors associated with waterline disinfection failure

Although many studies have highlighted the problem of biofilm growth in dental chair unit waterlines (DUWs), no long-term studies on the efficacy of DUW disinfection using a large number of dental chair units (DCUs) have been reported. To investigate the long-term (21 months) efficacy of the Planmeca Waterline Cleaning System (WCS) to maintain the quality of DUW output water below the American Dental Association (ADA) recommended standard of < or =200cfu/mL of aerobic heterotrophic bacteria using once weekly disinfection with the hydrogen peroxide-and silver ion-containing disinfectant Planosil. Microbiological quality of DUW output water was monitored by culture on R2A agar for 10 DCUs fitted with the WCS. The presence of biofilm in DUWs was examined by electron microscopy. During the first 9 months a high prevalence (28/300 disinfection cycles; 9.3%) of intermittent DUW disinfection failure occurred in 8/10 DCUs due to operator omission to disinfect all DUWs (10/28 failed cycles), incorrect compressed air pressure failing to distribute the disinfectant properly (4/28 failed cycles) and physical blockage of disinfectant intake valves due to corrosion effects of Planosil (14/28 failed cycles). On rectification of these faults through engineering redesign and procedural changes, no further cases of intermittent DUW disinfection failure were observed. Independently of these factors, a rapid and consistent decline in efficacy of DUW disinfection occurred in 4/10 DCUs following the initial 9 months of once weekly disinfection. There was a highly significant difference (P<0.0001) in the prevalence of strongly catalase-positive Novosphingobium and Sphingomonas bacterial species (mean average prevalence of 37.1%) in DUW output water from these 4 DCUs compared to the other 6 DCUs and DCU supply water (prevalence <1%), which correlated with biofilm presence in the DUWs and indicated selective pressure for maintenance of these species by prolonged disinfectant usage. Planosil was reformulated to a more concentrated form (Planosil Forte) and when used once weekly was found to maintain bacterial density in output water below the ADA standard for all 10 DCUs. A variety of factors can contribute to failure of DUW disinfection in the long-term, including human error, disinfectant corrosion of equipment and natural selection of naturally disinfectant-tolerant bacterial species.