Filtered Water Turbidity Research Articles

Downflow and upflow sand filtration for removing turbid particles with diverse morphological and surface-charge characteristics: Comparisons of filtered water quality and head loss distribution

Besides the physicochemical characteristics (e.g., size, structure, charge nature, etc.) of turbid particles, the filtration flow direction may affect their migration and adhesion behaviors inside the filtration unit. Unfortunately, there has been a lack of research regarding the combined effects of these above factors on filtered water quality and head loss development during filtration. In this study, different turbid particles were prepared by flocculating water samples containing kaolin and humic acid. Filtration experimental results of these flocculated waters revealed that downflow and upflow filtration modes had different durations of effective filtration under identical PAC-dosage cases, and upflow filtration led to faster increases in filtered water turbidity at the breakthrough stage compared to downflow filtration. During 180-min downflow filtration, the average size of residual turbid particles increased, but this did not occur in upflow filtration. Furthermore, differently from downflow filtration, upflow filtration had a more uniform distribution of head loss across all filter layers. The ease of backwashing differed between the two filtration modes, reflected by the different times required for reaching a relatively stable turbidity during 10-min backwashing. Lastly, based on SEM, FTIR and XPS analyses for characterizing the coagulated particle surface morphology, element composition, and functional groups, a series of conceptual models for particle removal by downflow and upflow filtrations were developed to clarify the influencing mechanisms of different turbid particles on filtration. It highlighted the advantages of upflow filtration, including improved distribution of flow resistance, better removal of larger-sized turbid particles, and enhanced pollutant-holding capacity of the filter media.

<b>Intelligent system for improving dosage control

Coagulation is one of the most important processes in a drinking-water treatment plant, and it is applied to destabilize impurities in water for the subsequent flocculation stage. Several techniques are currently used in the water industry to determine the best dosage of the coagulant, such as the jar-test method, zeta potential measurements, artificial intelligence methods, comprising neural networks, fuzzy and expert systems, and the combination of the above-mentioned techniques to help operators and engineers in the water treatment process. Current paper presents an artificial neural network approach to evaluate optimum coagulant dosage for various scenarios in raw water quality, using parameters such as raw water color, raw water turbidity, clarified and filtered water turbidity and a calculated Dose Rate to provide the best performance in the filtration process. Another feature in current approach is the use of a backpropagation neural network method to estimate the best coagulant dosage simultaneously at two points of the water treatment plant. Simulation results were compared to the current dosage rate and showed that the proposed system may reduce costs of raw material in water treatment plant.

Rapid gravity filtration operational performance assessment and diagnosis for preventative maintenance from on-line data

Rapid gravity filters, the final particulate barrier in many water treatment systems, are typically monitored using on-line turbidity, flow and head loss instrumentation. Current metrics for assessing filtration performance from on-line turbidity data were critically assessed and observed not to effectively and consistently summarise the important properties of a turbidity distribution and the associated water quality risk. In the absence of a consistent risk function for turbidity in treated water, using on-line turbidity as an indicative rather than a quantitative variable appears to be more practical. Best practice suggests that filtered water turbidity should be maintained below 0.1 NTU, at higher turbidity we can be less confident of an effective particle and pathogen barrier. Based on this simple distinction filtration performance has been described in terms of reliability and resilience by characterising the likelihood, frequency and duration of turbidity spikes greater than 0.1 NTU. This view of filtration performance is then used to frame operational diagnosis of unsatisfactory performance in terms of a machine learning classification problem. Through calculation of operationally relevant predictor variables and application of the Classification and Regression Tree (CART) algorithm the conditions associated with the greatest risk of poor filtration performance can be effectively modelled and communicated in operational terms. This provides a method for an evidence based decision support which can be used to efficiently manage individual pathogen barriers in a multi-barrier system.

Comparison of backwashing with conventional cleaning methods in slow sand filters for small-scale communities

The application of slow sand filtration technology for domestic water supply was investigated, with particular attention to the issue of periodic maintenance (cleaning the filter layer). The study used raw lake water with a high algal density to allow results to be obtained in a short time. Two filters were constructed with the same filter layer characteristics and were operated in parallel under the same conditions (filtration rate 0.16 m/h and hydraulic load variable maximum 0.80 m). Periodic maintenance was performed when the hydraulic load on the filtration layer reached 0.80 m. One filter was cleaned conventionally and the other by backwash. Nine filtration runs were performed, with an average duration of 14 d. Both filters provided significant improvements in water quality: filtered water turbidity less than 1 NTU, apparent color average of 15 Pt/Co, and removal of total coliforms and Escherichia coli around 1.5 log. In general, the quality of filtered water from the two filters was similar. However, the results obtained indicated that the backwash facilitates the operation of slow sand filters by simplicity (opening one valve) and time consumption (7 min), and ensures the water quality in terms of the parameters evaluated, justifying increased use of this technology, especially in small communities and rural areas. Nevertheless, this technology is applicable in small filters (up to 93 m2), because uniform backwash does not occur in filters with large dimensions.

Experimental evaluations of water treatment systems using a pilot-scale plant for adaptations to a sharp increase in raw-water turbidity caused by climate change

One effect of climate change on the water supply systems in Japan may be a sharp increase in the raw-water turbidity following heavy rain. The objective of this study was to evaluate water treatment performance with a sharp increase in raw-water turbidity. This evaluation was carried out from the perspective of turbidity response by a pilot-scale plant using sand filtration and membrane filtration with coagulation–sedimentation pretreatment. Two coagulants were used; namely, polyaluminum chloride with a basicity of either 72% (PACl-72%) or 51% (PACl-51%). Raw-water turbidity was increased from 5 to 300 TU by adding kaolin suspension. In the case of sand filtration, the filtered-water turbidity increased during the filter stabilization period. An increase in the coagulant dosage produced a more rapid decrease in the filtered-water turbidity and shortened the filter stabilizing period. Filtered-water turbidity decreased more rapidly for PACl-72% than for PACl-51%. In the case of membrane filtration, an increase in raw-water turbidity caused no significant increase in filtered-water turbidity or transmembrane pressure. These results demonstrated that, although neither filtration technique completely failed, membrane filtration was more robust than sand filtration against a sharp increase in raw-water turbidity.

Comparison of two online flocculation monitoring techniques for predicting turbidity removal by granular media filtration

Particulate matter removal in drinking water treatment via direct granular filtration requires specific flocculation conditions (a process typically termed ‘high energy flocculation’). Predicting filtered water turbidity based on flocculated water characteristics remains difficult. This study has sought to establish a relationship between filtered water turbidity and the flocculated water characteristics. Flocculation of low‐turbidity raw water was evaluated online using a Photometric Dispersion Analyser (PDA) and a Dynamic Particle Analyser in a modified jar test followed by a bench‐scale anthracite filter. Coagulants used were alum, PASS100 and ferric sulphate, in addition to a polydiallyldimethylammonium chloride (polyDADMAC) cationic polymer. They were dosed in warm and cold waters, and flocculated with intensities (G) from 0 to 100 s−1. Of the two instruments selected to analyse flocculation performance, the Dynamic Particle Analyser was shown to be the most sensitive, detecting small changes in floc growth kinetics and even floc growth under low flocculation conditions which remained undetected by the PDA. Floc size was shown to be insufficient in predicting particulate matter removal by direct granular filtration as measured by turbidity, although a threshold dv value (50 µm) could be identified for the test conditions evaluated in this project, above which turbidity was systematically lower than 0.2 NTU.

Application of Artificial Neural Networks for Filtration Optimization

Granular media filtration is an important process in drinking water treatment to ensure the adequate removal of particle-bound pathogens (i.e., Giardia and Cryptosporidium). Filtration performance is typically monitored in terms of filtered water turbidity. However, particle counts may provide further insight into treatment efficiency, as they have a greater sensitivity for detecting small changes in filtration operation. Artificial neural networks (ANN) models were applied to optimize filtration at the Elgin Area water treatment plant (WTP) in terms of postfiltration particle counts. Process models were successfully developed to predict postfiltration particle counts. Two inverse-process models were developed to predict the optimal coagulant dosage required to attain target particle counts. Upon testing each model, a high correlation was observed between the actual and predicted data sets. The ANNs were then integrated into an optimization application to allow for the transfer of real-time data between the models and the online supervisory control and data acquisition (SCADA) system.

Advanced Oxidation Treatment of Drinking Water: Part II. Turbidity, Particles and Organics Removal from Lake Huron Water

Pre-coagulation ozonation has been reported to be effective in drinking water treatment processes. Limited data are available on the impact of advanced oxidation processes (AOPs) on Lake Huron water which serves as a primary source of drinking water for many communities around the Great Lakes region. Impact of ozone/hydrogen peroxide based AOP on Lake Huron water was studied. The results show that AOPs can achieve higher particles removal in finished water and deliver improved filtered water turbidity compared to the conventional treatment process. Sharp decline in ultraviolet absorbance at 254 nm (UV254) was observed immediately following AOP treatment while only minimal overall decrease in dissolved organic carbon (DOC) was achieved.

Assessing the feasibility of a water treatment plant quality index

Research Article| August 01 2009 Assessing the feasibility of a water treatment plant quality index Marcelo Libânio; Marcelo Libânio Search for other works by this author on: This Site PubMed Google Scholar Vanessa Cristina Lopes Vanessa Cristina Lopes Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2009) 58 (5): 354–362. https://doi.org/10.2166/aqua.2009.002 Article history Received: January 17 2009 Accepted: May 09 2009 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Marcelo Libânio, Vanessa Cristina Lopes; Assessing the feasibility of a water treatment plant quality index. Journal of Water Supply: Research and Technology-Aqua 1 August 2009; 58 (5): 354–362. doi: https://doi.org/10.2166/aqua.2009.002 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex This paper focuses on the development of a quality index applied to conventional water treatment plants (WTPQI) with the objective of providing a more consistent way of evaluating performance and comparing different plants. The methodology, based on the Delphi method, relies on the same principles used at the beginning of the 1970s in the formulation of the Water Quality Index (WQI). Afterwards, the WTPQI was applied to ten different Brazilian conventional water treatment plants, with horizontal sedimentation basins and variable sizes (average flow rates range from 100–4,300 L s−1) and the results pointed out its usefulness as an instrument for plant evaluation. A significant correlation between plant performance and the WTPQI values was confirmed based on the filtered water turbidity, mainly for the rainy season when the raw water quality becomes harder to reach compliance with the drinking water standards. Therefore, these results open up the perspective of the use of the WTPQI as a reliable tool for the management of water supply systems. Delphi method application, water treatment plant evaluation, water treatment plant index This content is only available as a PDF. © IWA Publishing 2009 You do not currently have access to this content.

Drinking water turbidity and emergency department visits for gastrointestinal illness in Atlanta, 1993–2004

The extent to which drinking water turbidity measurements indicate the risk of gastrointestinal illness is not well understood. Despite major advances in drinking water treatment and delivery, infectious disease can still be transmitted through drinking water in the United States, and it is important to have reliable indicators of microbial water quality to inform public health decisions. The objective of our study was to assess the relationship between gastrointestinal illness, quantified through emergency department visits, and drinking water quality, quantified as raw water and filtered water turbidity measured at the treatment plant. We examined the relationship between turbidity levels of raw and filtered surface water measured at eight major drinking water treatment plants in the metropolitan area of Atlanta, Georgia, and over 240,000 emergency department visits for gastrointestinal illness during 1993-2004 among the population served by these plants. We fit Poisson time-series statistical regression models that included turbidity in a 21-day distributed lag and that controlled for meteorological factors and long-term time trends. For filtered water turbidity, the results were consistent with no association with emergency department visits for gastrointestinal illness. We observed a modest association between raw water turbidity and emergency department visits for gastrointestinal illness. Our results suggest that source water quality may contribute modestly to endemic gastrointestinal illness in the study area. The association between turbidity and emergency department visits for gastrointestinal illness was only observed when raw water turbidity was considered; filtered water turbidity may not serve as a reliable indicator of modest pathogen risk at all treatment plants.

The Effect of Ozone on Cold Water Coagulation

The application of pre-coagulation ozone in drinking water treatment to provide primary disinfection, has an impact on coagulation and flocculation, and needs to be evaluated further for cold water temperatures, especially when accompanied by episodes of high alkalinity and dissolved organic carbon (DOC). Ozone application to raw water, prior to the addition of coagulants and coagulant aides, was shown to reduce coagulant and coagulant aide doses, and improve settled and filtered water turbidity. The impact on particle count was also noticeable, filtered water particle count was reduced after the application of pre-coagulation ozonation. Pilot-scale experiments were conducted at the Walkerton Clean Water Centre, Walkerton, Ontario, Canada, to investigate the effect of pre-coagulation ozonation, on filtered water turbidity, particle count, and filter performance, during periods when water temperatures could be lower than 5°C.

Performance of Dual-Media Down-Flow Rapid Gravity Filters

The present study was conducted to evaluate the effect of variation of influent raw water turbidity, bed composition, and filtration rate on the performance of mono (sand) and dual media (sand and anthracite) rapid gravity filters in response to the effluent filtered water turbidity and headloss development. In order to evaluate each filter pe1formance, sieve analysis was made to characterize both media and to determine the effective size and uniformity coefficient. Effluent filtered water turbidity and the headloss development was recorded with time during each experiment.

Drinking Water Quality and Emergency Department Visits for Gastrointestinal Illness, 1993–2004

P-237 Introduction: Evidence suggests that drinking water quality contributes to endemic gastrointestinal (GI) illness in the US, but the determinants of this relationship and the proportion of illness attributable to drinking water are poorly understood. Contaminated drinking water can reach the end user through inadequate treatment and through intrusion of pathogens into the distribution system. These sources of contamination are considered in this set of analyses. Methods: We collected emergency department data from 41 of 42 hospitals serving a major US city from 1993 through 2004. A total of 7,952,826 visits are being analyzed, 446,559 (5.63%) for GI illness. Six major drinking water utilities serving three million residents are participating in this study, providing water quality and distribution system network data. To better understand the role of inadequate water treatment in contributing to GI illness we are considering temporally variable water quality measurements, including turbidity and disinfection efficiency, taken at each plant and the differences in raw water sources and treatment techniques among plants. We are evaluating the role of the distribution system by considering temporally variable water quality measurements, including chlorine levels and detection of indicator bacteria, in samples taken from the distribution system. We are also evaluating the potential for distribution system contamination, as quantified by the estimated distance from treatment plant to end user and the time the water travels, or water age. Water age is being estimated using hydraulic models. We are examining the association between these water quality factors in each zip code and emergency visits for GI illness among people residing in that zip code. Poisson generalized linear models are being fit, controlling for potential confounders. Results: An average of 102 emergency visits for GI illness occurred per day in the study area, out of an average of 1810 total emergency visits per day. The maximum turbidity of the source waters serving the treatment plants, including both lakes and rivers, ranged from 0.6 to 472 nephelometric turbidity units (NTU). The average filtered water turbidity ranged from 0.03 to 0.166 NTU. The average distance from plant to end user was estimated to be 9.50 miles (range: 0.96–23.6 miles). The described epidemiological analyses are ongoing and will be presented. Discussion: Results from this study, the most comprehensive of its kind to date, will contribute important new evidence regarding the role of drinking water quality in endemic GI illness.

Evaluation of Mono-Media and Dual Filter Media for Improving Water Quantity and Quality

Water is a unique substance and in the coming decades, there will be increasing competition for water supplies worldwide. Alexandria city has eight water treatment plants with an average daily production of 2 million m3 of drinking water. The most common types of sand filters used in them are Italba deep filter. Increasing rates of filtration by using existing deep sand filter, deep mono-anthracite, and dual sand/anthracite media was studied aiming at increasing plant production without deterioration in water quality. Pilot water treatment plant with three pilot filters [mono-sand, mono-anthracite, and dual sand/anthracite] was used and the applied filtration rates were 8 m/hr [current rate], 12 m/hr, and 15 m/hr. Comparison between mono and dual media at the three rates was evaluated according to performance criteria. These criteria are: Filter effluent turbidity =0.2 NTU, head loss =120 cm, Unit filter run volume [UFRV] ≥400 m3/m2, and the percent removal of turbidity and algae. The results revealed that dual filter media [sand/anthracite] achieved the criteria of filter performance at rates of 8, 12, and 15 ml/h at filter runs of 56, 43, and 30 h. Mono-sand and mono-anthracite achieved these criteria after short run time as a result of development of head loss quickly. So, it is recommended to modify an existing mono-sand deep filter into dual media [sand/anthracite] with increasing filtration rates to 12 m/h to get an increase in water quantity with gross production =528 m3/m2 instead of 384 m3/m2 at 8 m/h by mono-sand and the same water quality with turbidity =0.2 NTU. However, by increasing the filtration rate to 15 m/h, the filtered water turbidity was not affected and UFRV=450 m3/m2 but filter run was decreased and may need to fix surface wash system and/or to use filter aid to avoid buildup of slime growth on filter bed.

Improvement and Optimization of the A. H. Weeks Water Treatment Plant Processes, Windsor, ON, Canada

ABSTRACT After the ozone system was implemented at the A.H.Weeks Water Treatment Plant in June 2001, the plant was monitored to evaluate the effects that ozone had on the plant operation and filtered water quality. Filter performance showed an improvement since ozone was applied. Longer filter run time and lower filtered water turbidity and particle count were achieved. Average treated water turbidity was 0.07 NTU for the year before ozone was applied and 0.05 NTU for the year after ozone was applied. An optimization process was conducted to improve the operation. The benefits of the ozone system optimization resulted in more consistency in meeting performance objectives. Ozone generator power requirement was decreased while ozone generator efficiency was increased. Overdosing of ozone quenching agent was less frequent. Reduction in total operational cost was also observed for the year ozone was applied.

Evaluation of Natural Coagulants for Direct Filtration

In the present study surjana (Moringa oleifera) seed, maize (Zea mays) and chitosan were used in direct filtration of Bilaoli lake water and evaluated for their efficiency in removing turbidity and microorganisms from water. The experiments with these natural coagulants gave filtered water turbidity less than or almost equal to 1NTU and thereby met the turbidity criteria for drinking water as per WHO guidelines. Bilaoli lake water had low ionic strength and low turbidity which represents one of the most difficult raw waters to treat, but natural coagulants in direct filtration achieved good filtrate quality. The head loss development across the filter bed with chitosan was more than that of alum, while with maize it was comparable to that of alum. With M. oleifera seeds the head loss was much less in comparison to alum. The average most probable number (MPN) reductions obtained with M. oleifera seeds, maize and chitosan were 97.35%, 95.4% and 87.1% respectively, whereas, with alum it was only 7.7%.

Effect of Ozonation and UV Irradiation with Direct Filtration on Disinfection and Disinfection by-Product Precursors in Drinking Water Treatment

Pilot plant studies were conducted to evaluate the effect of pre-ozonation and ultraviolet irradiation on disinfection, disinfection by-product precursors and water quality in a direct filtration water treatment system. Disinfection parameters including total coliforms, faecal coliforms and heterotrophic plate count were investigated. Total organic carbon (TOC), trihalomethanes (THMs), total organic halides (TOX), filtered water turbidity and colour were also evaluated. It was found that advanced pre-oxidation processes (ozonation and UV irradiation) significantly increase the level of disinfection of raw water. Removal of total trihalomethanes and total organic halides precursors improved with ozonation and UV irradiation, compared to no oxidation treatment in direct filtration and/or in conventional water treatment. All coliforms (total and faecal) were completely destroyed by ozonation alone, and also with ozonation in conjunction with UV irradiation. However, the heterotrophic plate count was not significantly reduced at an ozone residual concentration of 0.1 mg l−1. This suggests that disinfection efficiency is strongly influenced by competition reactions of organic and inorganic compounds with ozone. Precursors of total trihalomethanes and total organic halides were reduced by 90% and 98%, respectively, with advanced pre-oxidation processes. Water quality parameters were improved by the pre-ozonation and UV irradiation treatment system.

Effects of SPENT FILTER BACKWASH recycle ON CRYPTOSPORIDIUM REMOVAL

Pilot studies were conducted to investigate the effect of recycling spent filter backwash water (SFBW) on Cryptosporidium and particle removal during conventional sedimentation and dual‐media filtration. When SFBW recycle configurations (3,000–19,000 oocysts/100 L) were used, Cryptosporidium concentrations in settled water were as low as or lower than when no recycle was used (6,000–22,000 oocysts/100 L). Filtered water oocyst concentrations were typically below the detection limit of 1 oocyst/120 gal (~0.25/100 L). Overall process removal was about 5 log without recycle and about 5.7 log for each recycle scenario based on calculations using raw Cryptosporidium concentrations and filtered water detection levels. As with Cryptosporidium removal, removal of turbidity and particles > 2 μm for the entire process (sedimentation + filtration) was similar for operations with and without recycle. Typical median filtered water concentrations for particles > 2 μm were < 0.5 particles/mL for all recycle scenarios, including no recycle. Similarly, settled and filtered water turbidity levels for all studies were typically < 2 and < 0.03 ntu, respectively.

Achieving Low‐level Turbidities in Filtered Water

Maintaining a consistent low‐level filtered water turbidity is a regulatory requirement promulgated by the Interim Enhanced Surface Water Treatment Rule. This article discusses how to achieve a recommended treatment goal for filtered water with a turbidity of less than 0.1 ntu. Topics covered include: accurate turbidity measurement; eliminating turbidity spikes; and, examining filters.

Effective Management and Operation of Coagulation and Filtration

The most commonly used water filtration technique involves coagulation and rapid rate filtration, either in conventional plants with flocculation and sedimentation, or in direct filtration plants in which the sedimentation process is omitted. Both versions of coagulation and filtration can be effective for controlling Giardia cysts and Cryptosporidium oocysts, but research done by several investigators has shown that coagulation and filtration must be operated very carefully to attain the best results. When filtered water turbidity is 0.1 ntu or lower, the process is most effective. Careful control of coagulation chemistry and of filtration rate increases, continuous monitoring of filtered water turbidity, and proper management of backwash water are keys to successful filtration.