Low Turbidity Source Water Research Articles

Optimisation and improvement of in-line filtration performance in water treatment for a typical low turbidity source water

ABSTRACTForest catchments can produce high quality source water with a low turbidity. However, the combination of low turbidity, low organic carbon, and low temperature water conditions presents operating challenges in conventional water treatment processes. In this study, in-line filtration was tested using pilot-scale filter columns, and was found to be an appropriate option to treat a typical low turbidity water originating from the Rocky Mountains near Calgary, Alberta, Canada. When alum and cationic polymer were dosed simultaneously, in-line filtration produced high quality effluent with a turbidity and a particle count value of less than 0.1 NTU and 50 counts/mL, respectively. However, the alum and polymer doses and their ratios played important roles in the filtration efficiency. In general, short filter ripening times (i.e. <15 min) required an alum dose of at least 3 mg/L and an alum to polymer dose ratio of less than 180:1. A longer filter stable period was associated with lower alum and polymer doses, as long as their doses were at least 2 and 0.024 mg/L, respectively, and their dose ratio was maintained in the range of 30:1 to 130:1. The optimal alum and polymer doses were observed to be 3 and 0.072 mg/L, respectively. Filter performance was enhanced when higher alum and polymer doses were used for ripening, and lower doses were applied during the stable filtration period. In addition, in-line filtration resulted in the reduction of microspheres by 3.6 logs under the tested water conditions. Hence, a similar removal efficiency is anticipated for Cryptosporidium.

Activated starch as an alternative to polyacrylamide-based polymers for in-line filtration of low turbidity source water

Polyacrylamide-based polymers are commonly used as coagulant aids in water treatment, but there is some concern about their potential toxicity. This work investigated a novel alternative, Hydrex TM 3841 activated starch polymer, as a coagulant aid for alum to treat low turbidity source water at pilot scale using in-line filtration. Compared to two typical polyacrylamide-based polymers, Magnafloc ® LT22S and Superfloc ® A-100, at an alum dose of 0.95 mg Al/L, activated starch could reach a similarly optimal unit filter run volume (∼116 m 3 /m 2 ), while the required dose (0.48 mg/L) was approximately 2–10 times higher than those for the other two types of polymers. Since polymer cost has been reported to be a minimal proportion of the total chemical cost at a water treatment plant, activated starch may be a promising alternative to polyacrylamide.

The impact of recycling sludge on water quality in coagulation for treating low-turbidity source water

There is an alternative method for the treatment of low-turbidity source water that reuses coagulation sludge as low-turbidity raw water to enhance conventional coagulation efficiency. This research investigated the impact of the recycling ration by volume of coagulation sludge on enhancing the removal efficiency of specific water quality parameters in a pilot-scale experiment with a capacity of 5 m3/h. This novel test was first continuously run for 150 h (15 recycling runs), and the recycling sludge was cycle used. The results showed a significantly higher removal efficiency of turbidity from the raw water than that of the traditional process, which was probably attributed to the special long-range Van der Waals attractive force, the enhancement of the collision ratio among particles, and the similar “second dosage of coagulant” strategy after the recycling process. Charge neutralization and absorption have mainly enhanced the removal efficiency of organic matter with recycling sludge. To some extent, this enhancement is due to the open and porous structure of the reused sludge, which could absorb the metal ions and further remove them following the sedimentation process. Recycling sludge is a feasible and successful method to enhance pollutant removal and has a significant effect on the treatment of low-turbidity source water.

Impact of recycling alum sludge on coagulation of low-turbidity source waters

This research project evaluated the recycling performance of alum sludge (AS), formed during sedimentation process in drinking water treatment, to enhance coagulation of low-turbidity source water. The results indicated that the recycling of AS effectively enhanced coagulation, when the optimal blended water turbidity was in the range of 13.6–21.7 NTU, with solid content of 0.072–0.124%. Furthermore, recycling AS could reduce up to 40% of fresh coagulant dosage in coagulation–sedimentation process. Bench-scale experiment results showed recycling AS prior to coagulation had insignificant effect on effluent water quality for all measured parameters: color, NH3-N, CODMn, UV254, aluminum, and manganese. Scanning electron microscopy evidence revealed that the floc structures with AS were more smooth and more compact than that without AS. It was postulated that the aluminum hydroxide precipitate in AS provide nucleating sites for physical collision and that sweep coagulation might play a key role in the enhancement of coagulation in low-turbidity source water.

Household effectiveness vs. laboratory efficacy of point-of-use chlorination

Treatment of water at the household level offers a promising approach to combat the global burden of diarrheal diseases. In particular, chlorination of drinking water has been a widely promoted strategy due to persistence of residual chlorine after initial treatment. However, the degree to which chlorination can reduce microbial levels in a controlled setting (efficacy) or in a household setting (effectiveness) can vary as a function of chlorine characteristics, source water characteristics, and household conditions. To gain more understanding of these factors, we carried out an observational study within households in rural communities of northern coastal Ecuador. We found that the efficacy of chlorine treatment under controlled conditions was significantly better than its household effectiveness when evaluated both by ability to meet microbiological safety standards and by log reductions. Water treated with chlorine achieved levels of microbial contamination considered safe for human consumption after 24 h of storage in the household only 39–51% of the time, depending on chlorine treatment regimen. Chlorine treatment would not be considered protective against diarrheal disease according to WHO log reduction standards. Factors that explain the observed compromised effectiveness include: source water turbidity, source water baseline contamination levels, and in-home contamination. Water in 38% of the households that had low turbidity source water (<10 NTU) met the safe water standard as compared with only 17% of the households that had high turbidity source water (>10 NTU). A 10 MPN/100 mL increase in baseline Escherichia coli levels was associated with a 2.2% increase in failure to meet the E. coli standard. Higher mean microbial contamination levels were seen in 54% of household samples in comparison to their matched controls, which is likely the result of in-home contamination during storage. Container characteristics (size of the container mouth) did not influence chlorine effectiveness. We found no significant differences between chlorine treatment regimens in ability to meet the safe water standards or in overall log reductions, although chlorine dosage did modify the effect of source conditions. These results underscore the importance of measuring both source water and household conditions to determine appropriate chlorine levels, as well as to evaluate the appropriateness of chlorine treatment and other point-of-use water quality improvement interventions.

Treatment of low-turbidity source water by permanganate pre-oxidation: In situ formed hydrous manganese dioxide as filter aid

This pilot study investigated the effects of in situ formed manganese dioxide (in situ δMnO2), produced from KMnO4 reduction, on the removal efficiency for turbidity and particles and the run length of filters through this pilot-scale study. The sedimentation effluent showed an insignificant difference in turbidity but a remarkable decrease in particle concentration after dosing KMnO4. The residual particle concentration decreased from 1504units/mL to 359, 302, 164units/mL in the anthracite filter effluent and from 994units/mL to 219, 134, 99units/mL in the granular activated carbon (GAC) effluent at KMnO4 dosages of 0.2, 0.3, and 0.4mg/L respectively. However, this effect was achieved at the expense of a rapid increase of water head loss (WHL), and the average run length decreased from 70h to 54, 52, and 48h accordingly. After dosing KMnO4 at 0.2, 0.3, and 0.4mg/L, the contributive ratios of the uppermost 200mm layers on WHL increased from 68.5% to 81.9%, 76.0%, and 82.2%, respectively.

Coagulation optimization for low temperature and low turbidity source water using combined coagulants: a case study

abstract Coagulation optimization using coagulants of ferric chloride (FeCl3), polymer–polyaluminum ferric chloride (PAFC) and their combinations (FeCl3/PAFC) was evaluated by performing jar tests for treating source water with low temperature (<10°C) and low turbidity (1.5–8 NTU) i,n a typical North-China water treatment plant (WTP), Tanggu WTP. The results indicated that compared to single coagulant, the combined coagulants showed superior coagulation performance in terms of turbidity, UV254, CODMn, iron, and aluminum removal. The optimal dosage was determined as 20 mg/L using the combined PAFC/FeCl3 (3:1 by mass) and dosing PAFC with a 5–20 s interval followed by FeCl3. Scanning electron micrographs further showed that the coagulations combination can form a more compact structure that increases the settleability of the flocculation flocs.

Pilot Study of Coagulation-Direct Filtration for Low-Temperature and Low-Turbidity Source Water

A pilot study was carried out for direct filtration assisted with low-dose coagulation to treat low temperature and low turbidity reservoir water for drinking water. The impacts of filtration rate, gap between coagulation and filtration, coagulant dosage and filtering material were examined. The tested ranges were as following: filtration rate 4-10 m/h, gap between coagulation and filtration 1-5 min, coagulant dosage 4- 20 mg/L. The results show that direct filtration with low-dose coagulation was very effective in treating the low temperature and low turbidity source water. The optimal conditions were as following: PAC dose of 12 mg/L, filtration rate of 6 m/h, gap between coagulation and filtration of 3 min. The effluent turbidity was 0.5 NTU, COD was 2.4 mg/L, and the filtration cycle was 9 h. The coagulant dose was only 40% of that of conventional treatment.

Pilot-Scale Study on Treatment of High-Algae and Low-Turbidity Source Water by Air Flotation in South China

The pilot-scale experiment of air flotation was carried out for reservoir water treatment of Shenzhen in order to provide reference for waterplant. The results show the turbidity of raw water is higher or lower than 15NTU, the optimum dosage of poly aluminum chloride (PAC) is 1.65mg/L and 1.25mg/L respectively. When the turbidity of raw water is between 3NTU and 32NTU, the amount of algae is less than 1.08×107unit/L, the removal rate of air flotation for turbidity and algae is 89.3% and 92.7% respectively; besides, the average removal rate of air flotation on CODMn is 32.6%, 21.2% of TOC is removed at least. Air flotation has preferable treatment effect on high–algae and low-turbidity water, adapts to treat micro-polluted water in South China.

Effect of Hydrous Manganese Dioxide on the Treatment of Low-Turbidity Source Water: Plant-Scale Experience

The effect of potassium permanganate (KMnO(4)) preoxidation on the treatment of low-turbidity reservoir water was investigated through two years of operational data in a large-scale drinking water treatment plant (DWTP). KMnO4 facilitated the removal of pollutants [e.g., turbidity and chemical oxygen demand (COD(Mn))] by different units such as clarification, sand filtration, and granular activated carbon (GAC) adsorption. Although the addition of KMnO(4) increased the color and total Mn concentrations, the results of removal by clarification and filtration are promising. The average run length of anthracite filters decreased from 48 to 40.8 hours after the introduction of KMnO(4) and exhibited a negative correlation with KMnO(4) dosages (r(2) = 0.6912). The hydrous manganese dioxide in situ formed (delta MnO(2)) dominated in aiding coagulation and improving filtration to enhance pollutant removal in the KMnO(4) preoxidation process, and these effects were achieved at the expense of more frequent backwashing of anthracite filters. DOI: 10.1061/(ASCE) EE. 1943-7870.0000349. (C) 2011 American Society of Civil Engineers.

Effects of Recycling-Sludge Operation on the Structure and Moisture Content of Floc in Water Treatment Plant

Recycling-sludge operation is applied in the Feng-Yuan Water Treatment Facility to treat low turbidity source water. By employing fractal dimension analysis and the dilatometry technique, the effects of recycling-sludge operation on the structure and moisture content of sludge flocs are studied. As the results show, the recycling-sludge operation can decrease the average bound water content by nearly 13–24% and increase the effective floc density, thereby forming a compact structure with a high fractal dimension and low floc porosity. The results also indicate that a significant correlation arises between the fractal dimensions and the bound water content of the sludge flocs.