Rapid Gravity Filters Research Articles

Feasibility of rapid gravity filtration and membrane ultrafiltration for the removal of microplastics and microlitter in sewage and wastewater from plastic industry

Wastewater treatment plants (WWTPs) act as barriers in reducing uncontrolled microplastic and microlitter (MP-ML) emissions from both urban and industrial wastewaters. Despite removing most of the MP-ML, large quantities of this waste still enter the environment through WWTP effluents, which means further post-treatment technologies are needed. This study contains a technical evaluation of MP-ML removal from urban wastewater (UWW) and from the wastewater from the recycling plastic industry (PIWW) using two different pilot-scale post-treatment systems: rapid gravity filtration (RGF) and ultrafiltration (UF) membranes. The MP-ML mass concentrations contained in UWW and PIWW were measured by a simplified method adapted for the long-term monitoring of WWTP operations. The method was validated on standard samples. Despite the RGF system consumed less energy than UF treating UWW (0.097 kWh·m−3 and 0.156 kWh·m−3, respectively), RGF was not efficient enough to properly decrease the risk of MP-ML emissions (39.5 ± 34.6 % of MP-ML removal). With respect to PIWW, the energy consumption of the UF plant decreased up to 0.059 kWh·m−3. The combination of RGF and UF technologies was expected to reduce membrane fouling but it did not show significant differences in the mid-term operation.

Design of Water Supply Scheme for Bisur Village

Abstract: In order to meet the water demand of the continuously growing population of Bisur village and failure of current water supply system it is essential to provide the sufficient and uniform quantity of water through the design of various units of water treatment plant, so for design work we have collected information of proposed area like Main water source, Population, Demand of water, quality of water, distribution network and water tanks etc. from MJP (Maharashtra Jeevan Prabhakaran) and local authorities. After analysed above data we calculated (i) Future population (ii) Water characteristics (iii)Design Period (iv)Water demand [101 LPCD]. After conducting and analysis of survey data we proposed an efficient new alignment for water distribution system and we designed various units of water treatment plant like Aeration, Alum Tank, Tube settler, Rapid Gravity filter, rising main, Jack Well, Sump etc. This proposed design of the water supply scheme for proper supply of water is sufficient to meet the daily requirement of water in selected area. Keywords: RRWS, ESR, Water Demand, MJP, WTP, Population

Exploring the use of flow cytometry for understanding the efficacy of disinfection in chlorine contact tanks

A pilot scale chlorine contact tank (CCT) with flexible baffling was installed at an operational water treatment plant (WTP), taking a direct feed from the outlet of the rapid gravity filters (RGF). For the first time, disinfection efficacy was established by direct microbial monitoring in a continuous reactor using flow cytometry (FCM). Disinfection variables of dose, time, and hydraulic efficiency (short circuiting and dispersion) were explored following characterisation of the reactor's residence time distributions (RTD) by tracer testing. FCM enabled distinction to be made between changes in disinfection reactor design where standard culture-based methods could not. The product of chlorine concentration (C) and residence time (t) correlated well with inactivation of microbes, organisms, with the highest cell reductions (N/N0) reaching <0.025 at Ctx¯ of 20 mg.min/L and above. The influence of reactor geometry on disinfection was best shown from the Ct10. This identified that the initial level of microbial inactivation was higher in unbaffled reactors for low Ct10 values, although the highest levels of inactivation of 0.015 could only be achieved in the baffled reactors, because these conditions enabled the highest Ct10 values to be achieved. Increased levels of disinfection were closely associated with increased formation of the trihalomethane disinfection by-products. The results highlight the importance of well-designed and operated CCT. The improved resolution afforded by FCM provides a tool that can dynamically quantify disinfection processes, enabling options for much better process control.

Microplastic Removal from Urban and Industrial Wastewaters Using Rapid Gravity Filtration and Membrane Ultrafiltration Technologies

Microplastic Removal from Urban and Industrial Wastewaters Using Rapid Gravity Filtration and Membrane Ultrafiltration Technologies

Microplastic Removal from Urban and Industrial Wastewaters Using Rapid Gravity Filtration and Membrane Ultrafiltration Technologies

Microplastic Removal from Urban and Industrial Wastewaters Using Rapid Gravity Filtration and Membrane Ultrafiltration Technologies

Feasibility of Rapid Gravity Filtration and Membrane Ultrafiltration for the Removal of Microplastics and Microlitter in Sewage and Wastewater from Plastic Industry

Feasibility of Rapid Gravity Filtration and Membrane Ultrafiltration for the Removal of Microplastics and Microlitter in Sewage and Wastewater from Plastic Industry

Anthracite as filter Media in Filtration Process

This research was carried out to see the performance of anthracite as filter media in filtration process. The study also aimed to compare two filter media in terms of turbidity it removed, head loss development with time and filter run with increase in influent turbidity. Two rapid gravity filter(RGF) columns were prepared having internal dimensions of 11x11x290 cm3, one with anthracite and another with sand as filter media. The uniformity coefficient of sand and anthracite of 1.54 and 1.4 were maintained from sieve analysis. Constant Filtration rate of 3m/h was set and other ancillary activities were made same for both filter models. The experiments were repeated seven times with different influent turbidity ranges of 0-25, 25-50, 50-100, 100-150, 150-200, 200-250, 250-300 NTU. Both the Filters were back washed with back washing velocity of 24 m/h, when the terminal head loss of 165.4 cm was obtained. The effluent quality of anthracite obtained was better for all the filter run. The head loss development with time was more for sand filter in all filter runs. The filter run time for sand vary from 150 to 8 hours and for anthracite, it varies from 172 to13 hours from first to seventh filter run.

Analiza rada postrojenja za kondicioniranje vode u općini Ilijaš

The operation of the Karašnica Water Treatment Plant, forming part of the water system in Ilijaš Municipality, in Bosnia and Herzegovina, is analysed in the paper. Two distinct water treatment lines are described and analysed. The first line consists of an internal circular settling tank and rapid sand gravity filters, while the second line consists of an external circular settling tank and pressure filters. In order to evaluate operating efficiency, a tour of the system facilities was made, interviews with the employees were conducted, the existing documentation was examined, and additional physicochemical and bacteriological analyses of appropriate water samples were conducted. Following analysis of all available data, appropriate conclusions and significant recommendations were made toward more efficient operation of the water treatment plant.

Evaluation of energy performance of drinking water treatment plants: Use of energy intensity and energy efficiency metrics

One of the United Nations Sustainable Development Goals is to provide access to safe and clean drinking water. However, treating raw water in facilities currently involves using a non-negligible amount of energy, and the fossil fuels used are both expensive and emit greenhouse gases when combusted. Previous studies have evaluated the energy performance of drinking water treatment plants by estimating the amount of energy consumed per volume of water. However, such studies have not accounted for differences between treatment technologies and have assumed a common standard water treatment technology. To overcome these limitations, this study employed metafrontier data envelopment analysis to evaluate and compare the energy performance of four types of treatment technologies. This approach integrates energy intensity with pollutant removal efficiency into a single, synthetic index to deliver an energy-efficiency score. A comparison of the four treatment technologies showed that facilities using rapid-gravity filtration and coagulation-flocculation processes provided the highest energy efficiencies. However, energy intensity and energy efficiency metrics delivered contradictory results, which thus illustrates the importance of including pollutant removal efficiency data in performance assessments. This study provides valuable information for policy-makers when planning and developing new drinking water treatment plants and for water utility managers when identifying energy reduction opportunities in plants.

Functional Channel Membranes for Drinking Water Production

Drinking water production utilities rely on, among other processes, different filtration technologies like bank filtration and slow sand filters, as well as pressure, roughing, or rapid gravity filters that, together with low- and high-pressure operating membranes, help to ensure high quality drinking water for millions of customers all over the world. The global market of membrane separation technologies is projected to reach USD 11.95 Billion by 2021, encompassing water treatment, wastewater treatment, food and beverage processing, industrial gas processing, and pharmaceutical and biomedical applications. In addition to the current, polymer-based membrane separation technologies, new promising strategies using embedded functional motifs, water and ion channels, are expected to play a key role in the next generation of membranes for separation purposes, which are of paramount relevance for drinking water production utilities. In this review, we summarize the different strategies for developing new advanced membranes with a wide variety of functional motifs, like biological and artificial water and ion channels, and their possible impact on drinking water applications.

Inadequate water treatment quality as assessed by protozoa removal in Sarawak, Malaysia.

ABSTRACTProviding safe drinking-water to human civilization is indispensable; it is one of the most cost-effective means of reducing the disease burden of diarrhea. Unfortunately, water supply quality monitoring from public water treatment plants (WTPs) is often neglected or taken for granted. To determine the produced water quality, WTPs in Sarawak, Malaysia were assessed for their protozoa removal ability. A self-administered questionnaire based on the regulations in the Drinking-water Standards for New Zealand (DWSNZ) was developed. Optional 10-liter raw water samples were collected from willing WTPs for the detection of protozoan cysts. Routine physical and microbial testing of WTP parameters were also requested for raw water quality overview. Two of the nine assessed WTPs achieved three log credits in the treatment component, one of which belonged to Peninsular Malaysia. No log credits were obtained in the other tested components for any samples. Most of the WTPs employed “Coagulation, Sedimentation, and Filtration” using rapid gravity filters without enhancement (P < 0.05). Giardia cysts were detected in raw water sources used for treatment, and the geographical location was identified as an influencing factor for raw water quality. There is an urgent requirement for active collaboration and holistic approaches to review existing water management policies and interventions. WTPs in Sarawak did not achieve the log credits required to safeguard the microbial quality of the water supplied; however, only Giardia cysts were detected in 10-liter raw water samples despite routine microbial parameter monitoring showing disturbing contamination levels.

Medium shapes the microbial community of water filters with implications for effluent quality

Little is known about the forces that determine the assembly of diverse bacterial communities inhabiting drinking water treatment filters and how this affects drinking water quality. Two contrasting ecological theories can help to understand how natural microbial communities assemble; niche theory and neutral theory, where environmental deterministic factors or stochastic factors predominate respectively. This study investigates the development of the microbial community on two common contrasting filter materials (quartz sand and granular activated carbon-GAC), to elucidate the main factors governing their assembly, through the evaluation of environmental (i.e. filter medium type) and stochastic forces (random deaths, births and immigration). Laboratory-scale filter columns were used to mimic a rapid gravity filter; the microbiome of the filter materials, and of the filter influent and effluent, was characterised using next generation 16S rRNA gene amplicon sequencing and flow-cytometry. Chemical parameters (i.e. dissolved organic carbon, trihalomethanes formation) were also monitored to assess the final effluent quality. The filter communities seemed to be strongly assembled by selection rather than neutral processes, with only 28% of those OTUs shared with the source water detected on the filter medium following predictions using a neutral community model. GAC hosted a phylogenetically more diverse community than sand. The two filter media communities seeded the effluent water, triggering differences in both water quality and community composition of the effluents. Overall, GAC proved to be better than sand in controlling microbial growth, by promoting higher bacterial decay rates and hosting less bacterial cells, and showed better performance for putative pathogen control by leaking less Legionella cells into the effluent water.

Energy intensity of treating drinking water: Understanding the influence of factors

To provide safe drinking water to urban populations, raw water must be treated in drinking water treatment plants, which are energy-intensive facilities. Previous studies have assessed energy intensity (EI: unit of energy required per unit of treated water) of conventional drinking water treatment plants, but they ignored variations related to water treatment trains. By modeling 179 facilities of four water treatment trains, we explored factors potentially affecting energy intensity, such as removal efficiencies of pollutants and treatment capacities of drinking water treatment plants. We also investigated the economies of scale in energy intensity of drinking water treatment plants. Our results illustrated that the energy intensity of water facilities using pressure filter systems is affected by several pollutant removal efficiencies, but not by plant capacity. In contrast, the volume of water treated is the main factor responsible for the energy intensity in plants using rapid gravity filter systems and, therefore, their energy intensities are significantly affected by economies of scale. The results of this study should be useful to policy makers planning new facilities and developing policies to reduce the carbon footprints of urban water treatment plants.

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.

Ecological patterns, diversity and core taxa of microbial communities in groundwater-fed rapid gravity filters.

Here, we document microbial communities in rapid gravity filtration units, specifically serial rapid sand filters (RSFs), termed prefilters (PFs) and after- filters (AFs), fed with anoxic groundwaters low in organic carbon to prepare potable waters. A comprehensive 16S rRNA-based amplicon sequencing survey revealed a core RSF microbiome comprising few bacterial taxa (29–30 genera) dominated by Nitrospirae, Proteobacteria and Acidobacteria, with a strikingly high abundance (75–87±18%) across five examined waterworks in Denmark. Lineages within the Nitrospira genus consistently comprised the second most and most abundant fraction in PFs (27±23%) and AFs (45.2±23%), respectively, and were far more abundant than typical proteobacterial ammonium-oxidizing bacteria, suggesting a physiology beyond nitrite oxidation for Nitrospira. Within the core taxa, sequences closely related to types with ability to oxidize ammonium, nitrite, iron, manganese and methane as primary growth substrate were identified and dominated in both PFs (73.6±6%) and AFs (61.4±21%), suggesting their functional importance. Surprisingly, operational taxonomic unit richness correlated strongly and positively with sampling location in the drinking water treatment plant (from PFs to AFs), and a weaker negative correlation held for evenness. Significant spatial heterogeneity in microbial community composition was detected in both PFs and AFs, and was higher in the AFs. This is the first comprehensive documentation of microbial community diversity in RSFs treating oligotrophic groundwaters. We have identified patterns of local spatial heterogeneity and dispersal, documented surprising energy–diversity relationships, observed a large and diverse Nitrospira fraction and established a core RSF microbiome.

Dissolved organic carbon and trihalomethane precursor removal at a UK upland water treatment works

The removal of dissolved organic carbon (DOC) during potable water treatment is important for maintaining aesthetic water quality standards, minimising concentrations of micro-pollutants, controlling bacterial regrowth within distribution systems and, crucially, because it contains a sub-component that can act as trihalomethane (THM) precursors. In this study, the concentration and characteristics of raw water DOC and THM formation potential (THMFP) entering an upland potable water treatment works were analysed over twelve months. Correlations between raw water DOC characteristics, standardised THMFP (STHMFP) and % DOC removal were also investigated. DOC and THM precursor removal during a series of treatment stages was examined over this period, as well as potential selectivity in the removal of DOC fractions, to assess the importance of different treatment stages for DOC removal and THM amelioration. Though THMFP removal remained high and fairly stable throughout the study period (83–89%), the data suggest that this was mostly the result of high DOC removal rates rather than the selective removal of THM precursors. Whilst this chemical agnosticism makes DOC removal more robust, it may make the overall process more vulnerable to exceeding permissible THM concentrations under changing climatic conditions. The kinetics of the reaction between DOC and chlorine appeared to vary seasonally, indicating temporal changes in the proportions of fast- and slow-reacting precursors with implications for THM concentrations at the point of delivery to the consumer. The initial treatment stages, comprising coagulation–flocculation and dissolved air floatation (DAF) were by far the most important in terms of bulk DOC removal and the preferential removal of THM precursors, though, surprisingly, DOC quality was also modified following chlorination and secondary rapid gravity filtration (RGF). Though net THM concentration decreased following initial treatment stages, a doubling in the proportion of brominated THMs (BrTHMs), which are reported to be more carcinogenic, was also observed.

Pilot - Plant Experiments For The Removal of Thms, Haas and Doc from Drinking Water by Gac Adsorption- Galatsi Water Treatment Plant, Athens

A pilot-plant study was carried out with the water supply to Athens water works filtered through a granular activated carbon (GAC) filter- adsorber. The objective of this study was to evaluate the performance of GAC for the removal from drinking water of the two main groups of disinfection by -products (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), as well as of dissolved organic matter. The pilot treatment facility is located at the Water Treatment Plant of EYDAP in Galatsi, Athens, and was operated as a rapid gravity filter - adsorber. It was fed with chlorinated water, coming from the overflow of the sedimentation tanks, and operated continuously in parallel with a full-scale sand filter. At regular time intervals water samples were taken from both filters and analysed for THMs, HAAs and DOC. Other parameters were measured too. The operation of the GAC filter-adsorber continued until the GAC adsorption capacity for THMs and HAAs was almost exhausted. The results of the analyses showed that GAC was more effective in removing the dissolved organic matter than the smaller molecules of THMs and HAAs, fact which is in agreement with the relevant literature. GAC was also proved more effective in removing HAAs than removing THMs. The removal of THMs and the most part of the removal of HAAs and DOC must be attributed to adsorption by GAC, while that of a smaller part of DOC and HAAs may be attributed to biological activity in the filter bed, where chlorine had been totally removed by the catalytic action of the activated carbon surface.

Reduction in cryptosporidiosis associated with introduction of enhanced filtration of drinking water at Loch Katrine, Scotland.

Previous evidence has suggested an association between cryptosporidiosis and consumption of unfiltered drinking water from Loch Katrine in Scotland. Before September 2007, the water was only micro-strained and chlorinated; however, since that time, coagulation and rapid gravity filtration have been installed. In order to determine risk factors associated with cryptosporidiosis, including drinking water, we analysed data on microbiologically confirmed cases of cryptosporidiosis from 2004 to 2010. We identified an association between the incidence of cryptosporidiosis and unfiltered Loch Katrine drinking water supplied to the home (odds ratio 1.86, 95% confidence interval 1.11-3.11, P = 0.019). However, while filtration appears to be associated with initially reduced rates of cryptosporidiosis, evidence suggests it may paradoxically make those consumers more susceptible to other transmission routes in the long-term. These findings support implementation of similar treatment for other unfiltered drinking-water supplies, as a means of reducing cryptosporidiosis associated with drinking water.

Pilot plant study of alternative filter media for rapid gravity filtration

Sand has been the main filter media used in rapid gravity filtration since its introduction. The dominance of sand has been due to its low cost and availability. Extensive experience has led to sand filters with a dependable and predictable performance. Sand remains the preferred filter medium but usually with a larger sized anthracite capping to reduce the onset of head loss. Other approved filter media are now commercially available and this paper compares sand with recycled glass, Filtralite(®) and slate at pilot scale. The results have reaffirmed the basic importance of particle size on head loss and turbidity performance rather than surface activity or specific surface area. The results did suggest, however, that particle shape and packing exerted a stronger influence on performance than previously acknowledged. These could be used to improve the design and the contribution to sustainability made by rapid gravity filters.

Control of the biofouling bryozoan, Plumatella repens, using pulsed chlorine treatment

Bryozoans are common biofoulers of under-drain filter nozzles in rapid gravity filters in water treatment works. A potential method for controlling bryozoan biofouling is the use of chlorine in backwash water. Repeatedly exposing bryozoan colonies with chlorine for 20 min every 24 h in an experimental setting, to replicate what would occur if the backwash was chlorinated, caused significant reduction in colony growth and size. After 10 days repeated treatment in good conditions for bryozoan propagation, the EC50 (the chlorine concentration required to decrease growth such that treated colonies were half the size of control colonies) was 1.6 ppm (SE 0.3). In sub-optimal conditions for propagation, the impact of chlorine was greater. The majority of colonies treated with 1 ppm and above did not grow or even decreased in size over 5 days. However, a chlorine concentration of 5 ppm was necessary, even in sub-optimal conditions, to ensure all colonies decreased in size over 5 days of treatment; this is too high to be acceptable to water companies due to the risk of carcinogenic by-products. Nevertheless, the observed decline in feeding activity of bryozoans exposed to chlorine levels >1 ppm suggests that repeated backwashing with chlorine may cause colony death over time, especially in sub-optimal conditions. Chlorine backwashes may therefore be an effective long-term control strategy, especially in locations such as rapid gravity filters where it is suggested that upstream processes are likely to create sub-optimal conditions for bryozoan growth.