Head Loss Development 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.

Pilot studies for the application of triple media filtration at Morton Jaffray Water Works, Harare, Zimbabwe

Abstract Lake Chivero, Harare's main source of raw water for drinking water, is algae infested thus affecting water treatment processes at Morton Jaffray Water Treatment Works (MJWTW). Consequently, several challenges have been encountered including frequent filter backwashing, leading to a reduced plant output. In this study, the potential of substituting single-media filters (currently used at MJWTW) with triple-media filters was investigated. This was done using pilot filters of a single-media filter (SMF) and a triple-media filter (TMF) and piloted using clarified water from MJWTW. Electrical conductivity (EC), pH, total dissolved solids (TDS), turbidity, and temperature were the water quality parameters that were monitored. Headloss and flow rate were the filter operation parameters that were monitored. Both water quality and operational parameters were monitored at hourly intervals until one filter reached the maximum allowable headloss or turbidity limit. The variation in effluent turbidity, TDS, EC, and pH between the filters was insignificant. Nevertheless, the headloss development for the TMF was significantly slower than that of the SMF resulting in the SMF reaching the maximum headloss earlier. Therefore, the TMF performed better overall. Therefore, the adoption of TMF could result in a longer filter run and improve filtration and water production at MJWTW.

Effect of filtration rates on the performance and head loss development in granular filters during the post-treatment of anaerobic reactor effluent.

This study investigated the performance of a granular filtration system (GFS) composed of a rock filter (RF), a rapid sand filter (RSF), and an activated carbon filter (ACF), applied to the post-treatment of an anaerobic reactor effluent. Four filtration rates (FR) were applied to the GFS (in m3·m-2·d-1): 100-60-60, 100-90-90, 200-120-120, and 200-160-160, for RF-RSF-ACF, respectively. A clarified final effluent with low turbidity (~ 10 NTU), solids (~ 6.5mg TSS.L-1), and organic matter content (~ 40mg COD.L-1) was obtained when the GFS worked with FR up to 100-90-90 m3·m-2·d-1. For higher FR, the effluent quality was a little poorer. Principal component analysis showed when the RSF operated at 120 or 160 m3·m-2·d-1, it presented an effluent with higher turbidity which did not affect negatively the ACF performance. The hydraulic load limits in the RSF were reached in periods of 45, 30, and 24.5h for the FR of 60, 120, and 160 m3·m-2·d-1, respectively, and head loss analysis depicted a more distributed solid retention through the sand depth with the lower FR. Thus, the results revealed that the RF-RSF-ACS system is a promising alternative for effluent polishing of anaerobic reactor, especially when the FR is set at 90 m3·m-2·d-1 or even higher.

Exploring the feasibility of dual media filtration at Morton Jaffray Water Works (Harare, Zimbabwe)

Lake Chivero, Harare’s main potable raw water source, is eutrophic. This has complicated water treatment at Morton Jaffray Water Treatment Works (MJWTW) leading to frequent filter backwashing and reduced plant output. This study investigated the use of dual media filters (DMF) as an alternative to single media filters (SMF) currently employed using pilot filters. Key operational parameters (headloss and flow rate) and water quality parameters [electrical conductivity (EC), pH, total dissolved solids (TDS), turbidity and temperature] were monitored hourly. The change in EC, pH, TDS, and turbidity across the SMF and DMF was 6.3% and 6.3%; 0.5%. and 0.2%; 5.5% and 4.5%; 68% and 69%, respectively thus showing no significant difference. However, headloss development for the SMF was significantly higher reaching 247.3 m compared to 134.6 m for the DMF. Use of DMF could increase the filter run and production at MJWTW.

Pilot-scale evaluation of sulfite-activated ferrate for water reuse applications

Ferrate is a promising, “green” (i.e., iron-based) pre-oxidation technology in water treatment, but there has been limited research on its potential benefits in a water reuse (wastewater recycling) paradigm. Recent studies have shown ferrate treatment processes can be improved by activation, the addition of reductants (i.e., sulfite) to the reaction. Prior bench scale experimentation suggests sulfite-activated ferrate may be a feasible option for water reuse applications; however, extent questions need to be addressed. This study evaluated the viability of sulfite-activated ferrate in water reuse treatment through continuous-flow experiments using synthetic and field-collected secondary wastewater effluents. The effluents were processed through the piloting system which included various physicochemical processes such as ferrate pre-oxidation, coagulation, clarification, and dual-media filtration. In each trial, the system was run continuously for eight hours with data collected via grab samples and online instrumentation with real-time resolution. Results demonstrate that reuse systems using activated ferrate pre-oxidation can produce effluents with water quality meeting most regulatory requirements without major impacts on downstream physicochemical processes. When compared to traditional ferrate pre-oxidation, activation showed several improvements such as lower byproduct yields. Operationally, activated ferrate does increase the development of headloss across the dual-media filter. In general, sulfite-activated ferrate is viable in a water reuse setting, resulting in several improved water quality outcomes. Results from this work create a pathway for adaptation at scale.

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.

Filtration Process and Alternative Filter Media Material in Water Treatment

In drinking water treatment, filtration plays an important role in the multi-barrier approach employed for the removal of pathogens. The presence of suspended solids and other particulate matter in water increases the resistance of most microbes to disinfection. Therefore, high performance in the removal of particles achieved by granular filtration can increase the disinfection efficiency. Although sand is one of the major filter media, alternative media have been developed and used in recent years. In this review, the performance of alternative media is compared with traditional sand/anthracite for drinking water treatment. Advantages in the use of alternative media, especially glass media, have been found, including high filtration performance in removing residual particles and turbidity, minor modification requirements to the existing filtration configuration and slow head loss development. However, before the employment of them in industry, additional tests are recommended. In particular, full scale tests with variations in the operating conditions and analyses of pathogen removal should be performed. Moreover, this paper reviews the filtration processes and operating configurations which provide overall references to those who are studying and working in the field of water technology and treatment. In this paper, legislations/standards of safe drinking water are summarized as they are the driving force of developing new treatment technologies; mathematical modules for predicting the media filtration performance are briefed. Finally, future work on the application of alternative filter media is recommended.

Investigation of backwash strategy on headloss development and particle release in drinking water biofiltration

Biofiltration is known for its many benefits, such as its ability to remove dissolved organic carbon (DOC) and disinfection by-product (DBP) precursors, decrease bacterial regrowth in the distribution system, all while maintaining desired turbidity removal and controlling taste and odor. However, the sensitivity of biofilter performance associated with backwash regime is under studied, particularly headloss development and particle release. A pilot scale study was conducted on two dual media anthracite/sand biofilters under warm (15–25 °C) and cold (0–5 °C) temperature conditions. Biofilters were subjected to various backwash regimes, including the addition of air scour and extended terminal subfluidization washes (ETSW), to evaluate their effects on headloss development, turbidity and particle passage during filter ripening. Media age was also considered. The biofilters were also assessed with respect to organics removal, DBP formation and microbial activity. Headloss was minimized by the addition of air scour and ETSW during backwashes by 11–18%. The turbidity spike during ripening of 0.35 NTU significantly (p < 0.05) improved with the addition of single and double stage ETSW, with maximum turbidity values of 0.14 and 0.09 NTU, respectively. Particle release during ripening followed the same trend, with the lowest particle counts observed with a double stage ETSW applied during backwashing.

Analyzing the performance of biological versus conventional drinking water filtration under warm and cold water conditions: A pilot scale study

Conventional filtration practices typically operate with a pre-chlorination step for the disinfection of harmful pathogens. Without pre-chlorination, biofilters will develop, which are capable of reducing the formation of disinfection by-products (DBPs) and can decrease bacterial regrowth in the distribution system. However, concerns, particularly in North America, still exist with the implementation of biofiltration and there is a lack of side-by-side comparisons with pre-chlorinated filters in literature. A pilot scale study comparing conventional and biological dual media anthracite/sand filters was conducted to assess their performance under warm (15–25 °C) and cold (0–5 °C) water conditions. The filters were operated under various backwash conditions, including the addition of air scour and extended terminal subfluidization wash (ETSW). The biofilter effluent exhibited significantly lower (p < 0.05) DBP formations under both temperature conditions, with trihalomethanes (TTHM) and haloacetic acids (HAA9) concentrations 33–35% and 36–46% lower than the conventional filters, respectively. There was no significant difference when it came to particle passage or turbidity during ripening for both filter types, however the conventional filter proved to be more vulnerable to changes in terms of particles between backwashes. The biofilter exhibited greater average headloss development by 8.8 cm and 4.5 cm under warm and cold water conditions, respectively. Biofilter headloss was found to be minimized by 18% when applying air scour and ETSW during backwash compared to water only, under warm temperature conditions.

Impact of carbon-based nutrient enhancement on biofiltration performance for drinking water treatment

Incorporation of a carbon-based nutrient enhancement strategy for drinking water biofiltration is an attractive option, especially for source waters which contain recalcitrant organics. This study compared biofilters that were operated in parallel and individually enhanced with amino acids (including alanine, phenylalanine, and tryptophan), inulin, and sucrose to increase biomass concentration and promote biodegradation of dissolved organic carbon (DOC) in the source water, including disinfection by-product (DBP) precursors. Biomass activity was characterized by measuring adenosine tri-phosphate (ATP), dissolved oxygen (DO) consumption, and through the use of laccase and esterase enzyme assays. Performance was evaluated in terms of headloss, turbidity, pH, DOC, UV254, and DBP formation potential (DBP FP). The introduction of carbon-based nutrients significantly increased biomass activity, where ATP values peaked at 976 ng/g of filter media, 853 ng/g, and 513 ng/g for amino acids, inulin, and sucrose-spiked biofilters, respectively, while a non-spiked control only reached 104 ng/g. DO utilization by the enhanced biofilters was significantly higher than the control, with a strong correlation between ATP and DO uptake observed for all filters (R2 > 0.74). Laccase and esterase enzyme activities of enhanced biofilters were also elevated (p > 0.05), suggesting greater biodegradation potential. Operational parameters such as headloss development and turbidity control were not impaired by carbon supplementation strategies or an increase in biomass concentration and activity. However, the enhancement strategy did not provide improvement in terms of source water carbon removal (DOC and UV254) or DBP FP when treated filters were compared to a control.

Characterizing solids retention, head loss development and micropollutant removal in the case of direct powdered activated carbon dosage upstream of deep bed filtration

The dynamics of micropollutant removal and powdered activated carbon (PAC) separation were studied in a combined PAC/deep bed filtration process.

Study of biological up-flow roughing filters designed for drinking water pretreatment in rural areas: using ceramic media as filter material

ABSTRACTRoughing filters have been successfully employed as a pretreatment method in rural water supply, but few studies have reported the performance of up-flow roughing filters (URFs) packed with ceramic media. In this study, two pilot-scale URFs filled with ceramic media were designed. Filter performance, height profiles and head loss development were fully investigated. The average DOC, UV254 absorbance, NH4+-N and total bacterial counts removal efficiencies of filters were found to be close to 8%, 10%, 70% and 0.6 log (75%), respectively. Both filters could remove about 60–90% of turbidity with influent turbidity ranging from 1 to 500 NTU and high removal efficiencies (∼60%) were achieved when influent turbidity was lower than 2.5 NTU at a hydraulic load up to 2 m h−1. Height profiles revealed that UV254 absorbance, NH4+-N and turbidity were primarily removed in the former part of filter columns and that the separated solids stored within 20 cm of ceramic media layer above the bottom contributed to over 90% of total head loss. Filter run times were estimated to be around 60–80 days with a maximum head loss of 30 cm and an average influent turbidity of 10 NTU. The results indicated that the two URFs, combining low-cost operation and simple maintenance with good performance, were well suited to small waterworks in rural areas.

ADVANCED WASTEWATER TREATMENT BY HYDRAULIC AUTOMATIC FLOATING MEDIA FILTER

A pilot scale experiment was carried out in tertiary wastewater treatment using hydraulic automatic floating filter. The hydraulic automatic floating media filter has been working with 120 cm depth of polystyrene bed. Wastewater from secondary biological treatment of WWTP was treated in the pilot filter with filtration velocity of 4 m/h. Oxygen concentration was remained constantly at level 2.0 mg/l by using an ejector. Headloss development and evaluation of SS, COD, NH4+ removals during filtration were objectives of the study. The experiment results showed that concentrations of SS, COD and NH4+ in effluent wastewater were kept lower than 5 mg/l, 30 and 0.5 mg/l respectively for almost filtration cycle. Effects of treatment in SS, COD and NH4+ were 88.27 %, 68.54 % and 5.59 %, respectively.

Deployment of Recyclable Polycarbonate as Alternative Coarse Media in Dual-media Rapid Filters

Sand and anthracite coal/granular activated carbon are commonly employed in traditional dual-media rapid filters to remove physical impurities present in influents. With increasing emphasis on sustainability, more water treatment facilities worldwide are opting for the use of eco-friendly materials which include recycled crushed glass, wood chips, and coconut shell based carbons. For instance, some filtration facilities of private pools in the United States have adopted recycled glass and obtained high quality effluent. The deployment of eco-friendly filter media in rapid filters deserves attention. In this study, sewed polyester bags which contained recyclable polycarbonate pellets (RPCs) were deployed as an alternative coarse media in a lab-scale dual-media rapid pressure filter setup. By coupling RPCs with sand, the following performance criteria were attained during the experimental runs when compared with the traditional dual-media: (a) similar rate of head loss development while maintaining acceptable effluent quality, and (b) improved clogging distribution within the filter. Life-cycle analysis (LCA) was also carried out with the Gabi Education software to assess the environmental footprint associated with various dual-media combinations. It is hopeful that the obtained LCA results would provide useful insights to industrial decision-makers who wish to improve the company’s environmental performance index.

The effect of high hydraulic loading rate on the removal efficiency of a quadruple media filter for tertiary wastewater treatment

It is well known that filtration removal efficiency falls with an increase in flow rate; however, there is limited supporting experimental data on how removal efficiency changes for filters with multiple layers of media and for wastewater filtration, a practice that is becoming more common. Furthermore, information is not available on the characteristics of particles that are removed at different flow rates. Here, a quadruple media filter was operated at hydraulic loading rates (HLRs) between 5 and 60 mh−1 with subsequent measurement of total suspended solids, turbidity and particle size distribution (PSD). Samples were collected from the filter influent, effluent and also from between media layers. Pressure changes across the filter layers were also measured. The solids removal efficiency of the filter varied inversely with the increase in filtration rate. However, the multiple media layers reduced the negative impact of increased HLR in comparison to a single media filter. High filtration rates were shown to transport solids, such that particle retention and headloss development was distributed across the entire depth of the multi-media filter. There was also a progressive decrease in the suspension particle size leaving each of the filter layers. The particle hydrodynamic force simulation was consistent with the changes in measured PSD through the filter layers.

Assessment of recycled glass and expanded clay in a dual media configuration for drinking water treatment

ABSTRACTThe aim of this study was to investigate the overall performance of different types of recycled glass media with the optimized coagulation conditions for drinking water treatment. Tests were performed using a laboratory-based filtration unit, with dual filter media configurations and synthetic raw water. The glass media showed comparable performance for both filtration and backwashing and avoided the breakthrough of particles in the effluent. Moreover, the promising performance of the glass media was a slow head loss development which should grant longer filtration runs, less backwashing requirement and thus possible clean water and energy savings. Finally, the optimized combination of filtration media and coagulation operations can lead to the best filtration performance.

Performance comparison of granular media filter beds

Particle capture, head loss development, and efficiency of in-line coagulation in contact filtration were studied using two types of laboratory filters with varying coagulants. One filter consisted of sand and anthracite, whereas the other filter contained crushed glass and anthracite. Effects of in-line coagulation on filter performance were evaluated using a charge measuring device. Performance of filters was monitored in terms of effluent quality as a function of time and development of head loss by anthracite layer and by the entire filter bed. Filterability index was used to provide a measure of effectiveness of filter media and/or operational variables such as coagulant type and dosage. This study found that the crushed glass–anthracite filter was as effective at removal of particles and metals (Fe and Al) as sand–anthracite filters.

Arsenic removal from simulated groundwater using household filter columns containing iron filings and sand

Recent investigations have found zero-valent iron [Fe(0)] as promising material for removal of arsenic from groundwater. This study aimed at improving the arsenic removal efficiency of a household level filter unit containing iron filings and sand. A novel methodical approach was used to assess the aeration (oxygen transfer) capacity of the filter unit. The calculations suggest that the designed unit possessed sufficient capacity to oxidize ferrous ion to ferric ion and resulted in co-oxidation of arsenite (As3+) to arsenate (As5+). The modifications made to the system reduced the problems of clogging, excessive headloss development and enabled prolonged leaching of iron leading to better arsenic removal efficiency. Under laboratory conditions, the modified unit was able to treat simulated groundwater containing 500μg/L of As3+, 2mg/L of P, and 20mg/L of Si to arsenic levels below WHO standard of 10μg/L without adding any chemical oxidant. The Fe/As ratio of 88.46 was required to bring the arsenic concentrations below 10μg/L which is much less than that are achieved by other researchers under similar conditions. The removal of arsenic by zero-valent iron [Fe(0)] is attributed to adsorption by iron hydroxides generated from the oxic corrosion of Fe(0) and/or precipitation of iron arsenate within the system. Results indicated that a filtration system consisting of iron filings and sand could be effectively used at household level to bring the total arsenic levels below WHO standard of 10μg/L in drinking water.

A modified BAF system configuring synergistic denitrification and chemical phosphorus precipitation: Examination on pollutants removal and clogging development

The performance of a BAF system configuring simultaneous chemical phosphorus precipitation in the pre-denitrification stage was examined using a continuously operated setup to treat real domestic wastewater. The effects of using no chemical, dosing sole Fe2+, and dosing combined Fe2+, PAM, and NaHCO3 in the pre-denitrification tank were assessed by monitoring COD, nitrogen, and phosphorus removal and hydraulic headloss development in the BAF column. Though dosing sole Fe2+ significantly enhanced phosphorus removal, it would consume alkalinity through hydrolysis and form smaller-sized sludge flocs in the pre-denitrification tank, and hence resulted in affected NH4+-N, insoluble COD, and SS removal in the BAF. Dosing combined Fe2+, PAM, and NaHCO3 can enhance sludge flocculation to form larger flocs and compensate alkalinity consumption. It exhibited sound performance on COD, nitrogen, and phosphorus removal, and led to less frequent BAF backwashing by slowing clogging development in the BAF filter layer.

Investigation of geometric properties of media particles and operating conditions on floating media filtration

Filtration is an effective process in removing particles that are present in water. Floating medium filter has been used in direct filtration because of its flexibility, cost savings gained by less land requirements, and less water and energy required for backwashing. The aim of this work was to investigate the effect of geometric properties of a floating medium in upflow filtration mode. A pilot plant was designed and constructed to evaluate the filtration process. Effect of physical parameters on filtration performance was also investigated. The experiments were carried out using a commonly available polypropylene floating medium. Four median grain sizes (2.28, 3.03, 3.30, and 4.07 mm) of polypropylene plastic pellets were used. Two media shapes (cubic and disc) were evaluated. Bentonite (250 mg/L ≈ 60 NTU) was used to make up the raw feed water. Three parameters that could influence the filtration performance were identified, namely: filtration velocity, media depth, and coagulant dose. The results showed that the best conditions to remove turbidity were found to be: low filtration rate (36.8 L/m2 min), longer media depth (600 mm) and optimum coagulant dose (23 mg/L). The results also indicated that the smaller plastic medium (2.28 mm) was more efficient in terms of turbidity removal than the larger medium. However, headloss development associated with smaller media was higher (109 mm of water) than that associated with larger medium (42 mm of water).