Response surface optimization of acid red 119 dye from simulated wastewater using Al based waterworks sludge and polyaluminium chloride as coagulant

In this research, the performance of Polyaluminium Chloride (PAC) and Polyaluminium Chloride sludge (PACS) as coagulants for acid red 119 (AR119) dye removal from aqueous solutions were compared. The sample of PACS was collected from "Baba Sheikh Ali" water treatment plant (Isfahan, Iran) where PAC is used as a coagulant in the coagulation/flocculation process. A response surface methodology was applied to evaluate the simple and combined effects of the operating variables including initial pH, coagulant dosage and initial dye concentration and to optimize the operating conditions of the treatment process. Results reveal that the optimal conditions for dye removal were initial pH 3.42, coagulant dosage of 4.55 g dried PACS/L and initial dye concentration of 140 mg/L for PACS, while the optimal initial pH, coagulant dosage and initial dye concentration for PAC were 3.8, 57 mg/L and 140 mg/L, respectively. Under these optimal values of process parameters, the dye removal efficiency of 94.1% and 95.25% was observed for PACS and PAC, respectively. Although lower amount of PAC in comparison with PACS was needed for specific dye removal, the reuse of PACS as a low-cost material can offer some advantages such as high efficiency for AR119 dye removal and economic savings on overall water and wastewater treatment plant operation costs.     

Bacterial pretreatment enhances removal of heavy metals during treatment of post-methanated distillery effluent by Typha angustata L

A combination of bacterial pretreatment followed by free water surface flow through wetland plants was investigated to determine its effect on removal of heavy metals in bioremediation of post-methanated distillery effluent (PMDE). The bacterial pretreatment was intended to transform the metal complexes and organic pollutants into simpler, biologically assimilable molecules. The 10% and 30% v/v concentrations of PMDE favored luxuriant bacterial growth; the 50% concentration supported less growth, whereas the undiluted effluent (i.e., 100%) supported very little bacterial growth. The use of bacterial pretreatment combined with the constructed wetland system greatly increase the overall bioaccumulation of all heavy metals by the plants compared with the control treatment. However, the integration of bacterial pretreatment of PMDE with the Typha angustata resulted in enhanced removal of Cd (34.02–61.50% increase), Cr (35.90–57.60% increase), Cu (32.88–54.22% increase), Fe (32.50–51.26% increase), Mn (35.99–82.85% increase), Ni (35.85–59.24% increase), Pb (33.45–59.51% increase) and Zn (31.95–53.70% increase) compared with a control that lacked this pretreatment. In addition to the bioaccumulation of these heavy metals, several physico-chemical parameters also improved at the 30% effluent concentration: color, BOD, COD, phenol and total nitrogen decreased by 98.33%, 98.89%, 98.50%, 93.75% and 82.39%, respectively, after 7 days of free water surface flow treatment. The results suggest that bacterial pretreatment of PMDE, integrated with phytoremediation will improve the treatment process of PMDE and promote safer disposal of this waste.     

Decolorization and Complete Degradation of Methyl Red by a Mixed Culture

Synthetic dyes, azo dyes in particular, are widely found in the effluents from textile industries. The persistence and toxicity of these compounds cause adverse impacts in the receiving streams. A mixed culture isolated from a domestic wastewater treatment plant was found to remove the colour of the azo dye, methyl red, efficiently. Total decolorization and degradation occurred within 18 h. The mixed culture could degrade 700 mgl^–1 of methyl red efficiently in the presence of 200 mgl^–1 of glucose, whereas in the absence of glucose it could degrade only 100 mgl^–1 of methyl red. The mixed culture, when suspended in phosphate buffer along with methyl red at 100 mgl^–1 concentration could degrade methyl red efficiently within 2 h of incubation. The pH of the medium decreased continuously during degradation. After the complete removal of initial methyl red, another 100 mgl^–1 was added to the culture filtrate and incubated further. The mixed microbial cultures could degrade methyl red efficiently through three cycles but further degradation was not possible as the pH of the medium decreased to 3.5.     

Review of fluoride removal from drinking water

Fluoride in drinking water has a profound effect on teeth and bones. Up to a small level (1–1.5 mg/L) this strengthens the enamel. Concentrations in the range of 1.5–4 mg/L result in dental fluorosis whereas with prolonged exposure at still higher fluoride concentrations (4–10 mg/L) dental fluorosis progresses to skeletal fluorosis. High fluoride concentrations in groundwater, up to more than 30 mg/L, occur widely, in many parts of the world. This review article is aimed at providing precise information on efforts made by various researchers in the field of fluoride removal for drinking water. The fluoride removal has been broadly divided in two sections dealing with membrane and adsorption techniques. Under the membrane techniques reverse osmosis, nanofiltration, dialysis and electro-dialysis have been discussed. Adsorption, which is a conventional technique, deals with adsorbents such as: alumina/aluminium based materials, clays and soils, calcium based minerals, synthetic compounds and carbon based materials. Studies on fluoride removal from aqueous solutions using various reversed zeolites, modified zeolites and ion exchange resins based on cross-linked polystyrene are reviewed. During the last few years, layered double oxides have been of interest as adsorbents for fluoride removal. Such recent developments have been briefly discussed.     

Removal and recycling of copper from aqueous solutions using treated Indian barks

Removal of copper from aqueous solutions containing 100–1000 ppm, using different Indian bark species, was performed on laboratory scale. The percentage removal of metal ions depends on the solution pH, bark species and time. The efficiency of copper removal by the used raw barks increases with a rise of solution pH and reaches a maximum of about 65–78% around pH 4–5. However, the decontaminated aqueous solutions were colored due to the dissolution of soluble organic compounds contained in the raw bark. This increases the biological and chemical oxygen demand (BOD and COD) of the solutions as well as the total organic carbon content (TOC). For this reason, raw bark should be treated either by chemical or biological means. Such treatment will allow the extraction of the soluble organic compounds and increase the chelating capacity and efficiency of the treated bark. Depending on the pH value, the chelating efficiency of treated barks is about 1.2–2.2 times that of the raw ones. Moreover, the retention capacity of the Indian treated bark varies from about 42–51 mg/g of dry bark. It is equal to or higher than that of common European species. About 1.8 mols of H₃O⁺ are released, by the treated barks, for every mol of chelated copper ions. Moreover, scanning electron microscopy (SEM) observations show uniform distribution of metal ions throughout the copper saturated bark. Infra red (IR) spectra suggest that the copper ions are chelated to hydroxyl and/or carboxyl functional groups of organic compounds contained in the treated bark. It seems that the interaction of the copper ions with the bark follows a cation exchange mechanism. This hypothesis is supported by elution experiments that allow recovery of about 99% of the contained copper. The retention capacity of the treated bark is almost constant after five cycles of chelation–elution, suggesting that the ‘life time cycle' is sufficiently long for continuous industrial application. The spent copper loaded barks can either be incinerated or pyrolysed. It generates solids containing either ≈80% of CuO or ≈14% of Cu°, respectively. Such materials can be used either in the secondary or primary copper production, thus offering a friendly environmental solution of effluents' treatment. The suggested process can be used as an alternative to the classical technologies for effluent decontamination. It is also efficient for polishing effluents treated by other methods.     

Solar oxidation and removal of arsenic from water: An experimental study

Arsenic poses a significant threat to both human health and the environment. Arsenic removal through solar oxidation has been investigated in a batch process. Arsenic was artificially added to both deionized and tap water to conduct the experiments. Clean, colorless, transparent, Polyethylene Terephthalate (PET) bottles were used for Solar Oxidation and Removal of Arsenic (SORAS) experiments. Various parameters including concentration of arsenic, iron, and photo-catalyst were varied during the experiments. The maximum arsenic removal efficiency obtained was 94% and 88% for deionized water and tap water respectively when ferrous ammonium sulphate and lemon juice were used. Maximum efficiency of 88% and 82% was obtained for deionized and tap water respectively when locally available ferrous alum and glacial acetic acid were used. The change in volume of the photo-catalyst (lemon juice and glacial acetic acid) also did not affect the SORAS process significantly. Therefore, the recommended volume for the photo-catalyst was 1–2 ml/L. SORAS can very well be used for areas contaminated with arsenic having concentrations less than 100 μg/L.     

Utilization of waste product (tamarind seeds) for the removal of Cr(VI) from aqueous solutions: Equilibrium, kinetics, and regeneration studies

In the present study, an adsorbent was prepared from tamarind seeds and used after activation for the removal of Cr(VI) from aqueous solutions. The tamarind seeds were activated by treating them with concentrated sulfuric acid (98% w/w) at a temperature of 150 °C. The adsorption of Cr(VI) was found to be maximum at low values of initial pH in the range of 1–3. The adsorption process of Cr(VI) was tested with Langmuir, Freundlich, Redlich–Peterson, Koble–Corrigan, Tempkin, Dubinin–Radushkevich and Generalized isotherm models. Application of the Langmuir isotherm to the system yielded a maximum adsorption capacity of 29.7 mg/g at an equilibrium pH value ranging from 1.12 to 1.46. The adsorption process followed second-order kinetics and the corresponding rate constants obtained were 2.605 × 10⁻³, 0.818 × 10⁻³, 0.557 × 10⁻³ and 0.811 × 10⁻³ g/mg min⁻¹ for 50, 200, 300 and 400 mg/L of initial Cr(VI) concentration, respectively. The regenerated activated tamarind seeds showed more than 95% Cr(VI) removal of that obtained using the fresh activated tamarind seeds. A feasible solution is proposed for the disposal of the contaminants (acid and base solutions) containing high concentrations of Cr(VI) obtained during the regeneration (desorption) process.     

壳聚糖对酸性染料的吸附性能

在不同的壳聚糖浓度、pH和温度条件下，采用分光光度法测得吸附后的染料浓度，得到了壳聚糖对酸性染料的最佳吸附条件，即在固定染料浓度和体积的情况下，壳聚糖的投入量在500mg、pH值为6、温度为室温、吸附时间为2h左右条件下吸附最佳，其结果将为利用壳聚糖处理印染废水提供一定的理论根据。     

Biosorption of Reactive Black 5 from aqueous solutions by chitosan: Column studies

Fixed-bed column studies were carried out to investigate the dynamic sorption of Reactive Black 5 (RB5) onto chitosan. The effect of operating parameters such as initial dye concentration, superficial flow velocity, bed height and particle size on the sorption of RB5 onto chitosan was studied. Column regeneration, dye recovery and the possibility of reusing the regenerated chitosan were also investigated. The results show that both the breakthrough curves and the adsorption parameters of the column were strongly affected by the operating parameters studied. An analysis of the breakthrough curves indicated that adsorption was affected by mass transfer limitations, probably due to intraparticle diffusion. An empirical model was applied to describe the breakthrough curves, while the Bohart–Adams and BDST models were used to determine the operating parameters useful in the process design. Elution of the column with 0.01 mol L^?1 NaOH allowed the chitosan to be regenerated and the dye to be recovered and concentrated. The concentration factor was 10. Several cycles of adsorption–elution showed that the regenerated chitosan retained good adsorption efficiency and the elution efficiency was always higher than 80%.     

Electrocoagulation of blue reactive,red disperse and mixed dyes,and application in treating textile effluent

This study investigated the efficiency of electrocoagulation in removing color from synthetic and real textile wastewater. Two representative dye molecules were selected for the synthetic dye wastewater: a blue reactive dye (Reactive Blue 140) and a disperse dye (Disperse Red 1). The electrochemical technique showed satisfactory color removal efficiency and reliable performance in treating both individual and mixed dye types. The removal efficiency and energy consumption data showed that, for a given current density, iron was superior to aluminum in treating both the reactive dye and the disperse dye. With an initial dye concentration of 100 mg L^?1, the energy cost in achieving >95% color removal was on the order of 1 kWh m^?3 for both dyes. The effect of changing the initial pH of the samples on the removal efficiency and energy consumption was also studied. It was found that the design parameters used for the synthetic wastewater were less effective for treatment of real textile wastewater, with 1 in 5 tests on real wastewater failing.     

Fly ash for the treatment of Zn(II) rich effluents

Summary The ability of fly ash to remove Zn(II) from water by adsorption has been tested at different concentrations, temperatures and pH of the solution. It was found that low adsorbate concentration, small particle size of adsorbent and higher temperature favoured the removal of Zn(II) from aqueous solution. The Langmuir isotherm was used to represent the equilibrium data at different temperatures. The apparent heat of adsorption has been found to be 17.325 Kcal mol^–1, which indicates the process to be endothermic. The uptake of Zn(II) is diffusion controlled and the mass transfer coefficient is 3.56 × 10^–5 cm s ^–1.The maximum removal was noted at pH 7.5. Dr V.N. Singh is Professor and Head of the Department of Applied Chemistry, Dr A.K. and Prof. D.P. Singh are members of the Department of Mining Engineering; all are situated in the Institute of Technology at Banaras Hindu University.     

Surface water and wastewater treatment using a new tannin-based coagulant. Pilot plant trials

A new tannin-based coagulant-flocculant (Tanfloc) was tested for water treatment at a pilot plant level. Four types of water sample were treated: surface water (collected from a river), and municipal, textile industry (simulated by a 100 mg L^?1 aqueous solution of an acid dye), and laundry (simulated by a 50 mg L^?1 aqueous solution of an anionic surfactant) wastewaters. The pilot plant process consisted of coagulation, sedimentation, and filtration. The experiments were carried out with an average coagulant dosage of 92.2 mg L^?1 (except in the case of the surface water for which the dosage was 2 mg L^?1). The efficacy of the water purification was notable in every case: total turbidity removal in the surface water and municipal wastewater, about 95% dye removal in the case of the textile industry wastewater, and about 80% surfactant removal in the laundry wastewater. Filtration improved the removal of suspended solids, both flocs and turbidity, and slightly improved the process as a whole. The efficiency of Tanfloc in these pilot studies was similar to or even better than that obtained in batch trials.     

Loofa egyptiaca as a novel adsorbent for removal of direct blue dye from aqueous solution

In this paper, Loofa egyptiaca (LE), an agricultural plant cultivated in Egypt, was used to prepare low-cost activated carbon (LE_C1 and LE_C2) adsorbents. The adsorbents (LE, LE_C1 and LE_C2) were evaluated for their ability to remove direct blue 106 dye from aqueous solutions. Batch mode experiments were conducted using various parameters such as pH, contact time, dye concentration and adsorbent concentration. The surface chemistry of LE, LE_C1 and LE_C2 was analyzed by scanning electron microscopy (SEM). The experimental data were examined using Langmuir, Freundlich, Temkin and Harkins–Jura isotherms. The results showed that the adsorption of direct blue 106 was maximal at the lowest value of pH (pH = 2). Removal efficiency was increased with an increase in dye concentration and a decrease in amount of adsorbent. Maximum adsorption capacity was found to be 57.14, 63.3 and 73.53 mg/g for LE, LE_C1 and LE_C2 respectively. Kinetics were also investigated using pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The experimental data fitted very well with the pseudo-first-order and pseudo-second-order kinetic models. The results indicate that LE, LE_C1 and LE_C2 could be employed as adsorbents for the removal of direct blue dye from aqueous solutions.     

Performance assessment of a wastewater treatment plant producing effluent for irrigation in Egypt

A conventional activated sludge treatment facility was the subject of this study. The assessment was directed at determining the characteristics of the raw wastewater, the quality of the treated effluent and the efficiency of the various treatment units. Furthermore, the water quality along the effluent irrigation canal was monitored. The assessment of the quality of the treated effluent for irrigation is based on the guidelines established by the World Health Organization and the Egyptian decree 9/89 for the use of wastewater in agriculture. The results of the study indicated that the concentration of the raw wastewater was considered moderate. The mean values of the COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand) and total suspended solids (TSS) were around 250, 102 and 142 mg l–1, respectively. This was attributed to the high quantities of wastewater from industrial sources. The overall efficiency of the treatment facility was good. The mean residual COD, BOD and TSS were 25, 8 and 21 mg l–1 and the corresponding percentage removal values were 90, 92 and 85%, respectively. The maximum percentage removal of oil and grease was 84% with a mean residual concentration of 24 mg l–1. The total viable count (22°C and 37°C), faecal coliform and aecal streptococci were reduced by 99.9% compared to only 99.5% for Salmonella. Bacteriological examination of the dried sludge indicated a reduction of nine logs of faecal coliform and faecal streptococci, as compared to thickened sludge. Analysis of the Ni, Cu, Pb and Cr in the dried sludge indicated that their concentrations are within the permissible limits. Zinc exceeded the consent standards by 50%. The results of the analyses of samples collected at the beginning of the irrigation canal indicated insignificant changes from the characteristics of the final effluent. Samples collected at a distance of 2km along the irrigation canal showed mean reductions in the COD and BOD of 28.6 and 47%, respectively, which could be attributed to sedimentation and/or a self-purification effect. An increase in the total nitrogen, total phosphorus and total viable count was also recorded, which could be due to seepage from the agricultural land. From the data available it is evident that the treated wastewater could be used for restricted irrigation. The design and implementation of a monitoring programme is recommended.     

Removal of Pb(II) ions from aqueous solution using activated tea waste: Adsorption on a fixed-bed column

An inexpensive and effective adsorbent was developed from waste tea leaves for the dynamic uptake of Pb(II). Characterization of the adsorbents showed a clear change between physico-chemical properties of activated tea waste and simply tea waste. The purpose of this work was to evaluate the potential of activated tea waste in continuous flow removal of Pb(II) ions from synthetic aqueous effluents. The performance of the system was evaluated to assess the effect of various process variables, viz., of bed height, hydraulic loading rate and initial feed concentration on breakthrough time and adsorption capacity. The shape of the breakthrough curves was determined for the adsorption of Pb(II) by varying different operating parameters like hydraulic loading rate (2.3–9.17 m³/h m²), bed height (0.3–0.5 m) and feed concentration (2–10 mg/l). An attempt has also been made to model the data generated from column studies using the empirical relationship based on the Bohart–Adams model. There was an acceptable degree of agreement between the data for breakthrough time calculated from the Bohart–Adams model and the present experimental study with average absolute deviation of less than 5.0%. The activated tea waste in this study showed very good promise as compared with the other adsorbents available in the literature. The adsorbent could be suitable for repeated use (for more than four cycles) without noticeable loss of capacity.     

Use of additives to enhance the removal of phenols from water treated with horseradish and hydrogen peroxide

Use of additives, such as polyethylene glycol (PEG), selected surfactants, chitosan gel, or activated carbon, has been shown to enhance enzymatic treatment of water polluted with organic compounds. In this study, additives were used to facilitate the removal of 2,4-dichlorophenol (2,4-DCP) from water using minced horseradish (Armoracia rusticana P. Gaertn. et al.) as a carrier of peroxidase activity. The specific objectives of the study were to (i) enhance the pollutant removal activity of minced horseradish by the addition of PEG and other additives (e.g., Tween 20, Triton X-100, and rhamnolipid); (ii) eliminate colored reaction products by the addition of chitosan; and (iii) eliminate color by amending treated water with activated carbon. The disappearance of 2,4-DCP in horseradish-treated water samples amended with PEG or various surfactants (75-90%) was greatly increased over that observed in nonamended samples (29%). The effect of PEG depended on its average molecular weight. As indicated by visible spectrophotometry, enclosing horseradish pieces between two sealed chitosan films completely eliminated colored reaction products; however, the decolorization was accompanied by a reduction in 2,4-DCP removal (from 95 to 60%). On the other hand, commercially available activated carbon completely removed colored reaction products from the treated water without reducing the removal efficiency. Based on the results obtained, it can be concluded that the use of additives may considerably improve the quality of wastewater treated by plant materials.     

An imprecise fuzzy risk approach for water quality management of a river system

Uncertainty plays an important role in water quality management problems. The major sources of uncertainty in a water quality management problem are the random nature of hydrologic variables and imprecision (fuzziness) associated with goals of the dischargers and pollution control agencies (PCA). Many Waste Load Allocation (WLA) problems are solved by considering these two sources of uncertainty. Apart from randomness and fuzziness, missing data in the time series of a hydrologic variable may result in additional uncertainty due to partial ignorance. These uncertainties render the input parameters as imprecise parameters in water quality decision making. In this paper an Imprecise Fuzzy Waste Load Allocation Model (IFWLAM) is developed for water quality management of a river system subject to uncertainty arising from partial ignorance. In a WLA problem, both randomness and imprecision can be addressed simultaneously by fuzzy risk of low water quality. A methodology is developed for the computation of imprecise fuzzy risk of low water quality, when the parameters are characterized by uncertainty due to partial ignorance. A Monte-Carlo simulation is performed to evaluate the imprecise fuzzy risk of low water quality by considering the input variables as imprecise. Fuzzy multiobjective optimization is used to formulate the multiobjective model. The model developed is based on a fuzzy multiobjective optimization problem with max–min as the operator. This usually does not result in a unique solution but gives multiple solutions. Two optimization models are developed to capture all the decision alternatives or multiple solutions. The objective of the two optimization models is to obtain a range of fractional removal levels for the dischargers, such that the resultant fuzzy risk will be within acceptable limits. Specification of a range for fractional removal levels enhances flexibility in decision making. The methodology is demonstrated with a case study of the Tunga–Bhadra river system in India.     

Screening analysis of volatile organic contaminants in commercial inorganic coagulants used for drinking water treatment

A method for quality screening is suggested to detect volatile impurities in inorganic coagulants that are used for drinking water treatment. Static headspace gas chromatography with mass spectrometry detection (HS–GCMS) is sensitive and selective to detect volatiles in low concentrations. This study has discovered that volatile organic impurities are detectable in ferric and aluminium-based coagulants which are used for drinking water treatment. For ferric chloride, 2-propanol was detected at a level of 17–24 μg ml⁻¹, acetone at 0.7–1.7 μg ml⁻¹, 1,1,1-trichloroacetone at 0.02–0.04 μg ml⁻¹, trichloromethane at 0.01–0.02 μg ml⁻¹ and toluene at 0.01–0.12 μg ml⁻¹. For ferric chloride sulfate, acetone was detected at a level of 0.12 μg ml⁻¹, 1,1,1-trichloroacetone at 0.06–0.08 μg ml⁻¹, trichloromethane at 0.13–0.23 μg ml⁻¹, bromodichloromethane at 0.04–0.06 μg ml⁻¹ and dibromochloromethane at 0.04–0.05 μg ml⁻¹. For aluminium hydroxide chloride, only trichloromethane was detectable, but below the method detection limits (MDL). Although the concentrations of these impurities in commercial coagulants are low, this observation is important and should have impact on water industries for them to pay attention to the chemicals they are using for drinking water production.     

Anaerobic/aerobic treatment of meat processing wastewater

The meat processing industry is believed to produce highly polluted wastewater. Analysis of such wastewater indicated that the waste was highly contaminated with organic compounds as indicated by COD (1544mgO2l–1), BOD (646mgO2l–1), and TSS (1155 mgl–1). Moreover, oil and grease concentrations reached 144mgl–1 treatment of raw wastewater using Upflow Anaerobic Sludge Blanket (UASB) followed by Rotating Biological Contactors (RBC) was studied. Efficiency of the UASB for the removal of CODtotal, BODtotal, TSS, and oil and grease was 56%, 56%, 85%, and 58%, respectively. The quality of the UASB effluent barely complies with the regulatory standards for discharging wastewater into the sewerage network. UASB effluent was subjected for further treatment using a RBC unit to improve the quality of the treated effluent for reuse in irrigation purposes. Residual COD, BOD, TSS, and oil and grease, following RBC, was 132mgO2l–1, 40mgO2l–1, 44mgl–1, and 10mgl–1 respectively. The overall efficiency of the treatment units provided good quality effluent. The overall percentage removal of COD, BOD, TSS, and oil and grease was 91.5%, 94%, 96%, and 91%, respectively. Based on the quality of the treated effluent and guidelines recommended for wastewater reuse, it may be concluded that a slight to moderate restricted irrigation is applicable to reuse the treated effluent in the green belt around the factory. Disinfection should be applied to ensure the safety of such a process.     

A Baseline Study on Water Resources of the Tourist Island, Pulau Perhentian, Peninsular Malaysia, from an Ecological Perspective

Ambient water quality and bacterial populations in the water resources of Pulau Perhentian, a Marine Park of Malaysia, were studied during a peak tourist arrival, off-monsoon period. The overall water and bacteriological quality of swimming/boating sites in the island is at an acceptable condition, although the conductivity (0.88–60 mS m^–1) due to high dissolved solid concentrations is slightly high, when compared with the recommended standard and published guidelines for the protection/maintenance of recreation water and its aesthetic enjoyment (Universiti Malaya, Department of Environment, Malaysia, 1986). However, the bacteriological quality of the drinking/bathing water wells is poor, with faecal coliform counts (2 up to 1,600 MPN per 100 ml sample water) exceeding the permissible levels defined for raw water supplies (with or without treatment). This suggests that the groundwater, seepage and run-off into the wells is contaminated. Contrary to the belief of the water users being interviewed in a social survey, the untreated drinking/bathing water is not bacteria-free. The excessive counts are attributable to deoxygenated conditions (12–42 percent corresponding to 0.9–3.3 mg l^–1) prevailing in the wells, high total suspended solids (up to 202 mg l^–1) which promote bacterial growth, lack of adequate sewerage systems to receive effluents from lavatories of dwellings, chalets and resorts, as well as the lack of centralised water treatment plants and storage tanks to cope with water scarcity and waterway contamination.