Head Loss Development Research Articles

A comparative study on in-line flocculation and spiral flocculation followed by media filtration as a pre-treatment of seawater

In this study the efficiency of two different flocculation systems namely in-line flocculation and spiral flocculation followed by media filtration (sand or anthracite) have been investigated as a pre-treatment of seawater to reverse osmosis. The performances of these filtration systems were assessed in terms of turbidity removal, head loss development, ultra filter-modified fouling index (UF-MFI) and organic matters removal. Both systems showed 60–70% removal of turbidity. In-line flocculation and filtration showed 2–3 times higher head loss development than spiral flocculation filtration. These filtration systems helped to reduce the fouling potential (in terms of UF-MFI) by 50–73%, whereas dissolved organic carbon-removal efficiency was 30–45%. The fractionation of organic matter showed that both systems removed 70% of hydrophobic organic matters. The removals of hydrophilic organics were around 30–40%. Among the hydrophilic compounds, the removal of biopolymer and lower molecular weight neutrals and acid were higher than that of humic substances’ and building blocks’.

Particles Capturing and Correlation with Head Loss in a Pilot-Scale Biological Aerated Filter

Experimental observations of particle capturing through the biological aerated filter bed indicated that air flow rate plays an important role in head loss development by influencing the suspended solids distribution along the depth of the bed as well as the morphology of the deposits. The active height for the SS removal prolonged with the increasing of the air velocity based on the mechanism of first-order kinetics. With the increasing of the superficial air velocity, the effluent SS concentration and the time need to reach the stead-states after backwash both increased. The value of the SS spike in the effluent after backwash at superficial air velocity of 27 m/hr was nearly twice as much as that of 5.4m/hr. Distribution of the deposits at higher air velocity was more uniform. Deposits at lower velocity with air flow rate produced higher head loss gradient. The headloss increased with the increasing of deposits and the increase rate was faster when the deposits exceeded higher value.

Seawater biofiltration pre-treatment system: comparison of filter media performance

Biological filtration is an effective pre-treatment method to remove organic matter and particulate matter from seawater. Three biofilter columns were operated packed with granular-activated carbon (GAC), anthracite and sand as a filter media. The biofilters were run for 120 d at a slow filtration velocity of 0.12 m/h. Biofiltration performances were evaluated in terms of turbidity, different fouling indices, and dissolved organic carbon(DOC). The removal efficiencies of turbidity by the three biofilters were similar with low headloss development. The fouling potential of treated seawater (filtrate) was evaluated using three different fouling indices such as microfiltration, ultrafiltration, and microfiltration at a cross flow. The analyses of three different fouling indices showed that the reduction in fouling potential was the following order GAC ##xgt; sand ##xgt; anthracite. In terms of DOC removal efficiency, GAC biofilter showed higher and stable removal efficiency (41–88%), than sand biofilter (7–76%) and anthracite biofilter (3–71%). All biofilters used in this study removed most of hydrophobic organic compounds (around 94%). On the other hand, hydrophilic organic removal varied depending on the media filter. GAC biofilter removed more organic biopolymers (51%), humic substances (75%) and building blocks (50%) compared with sand and anthracite biofilters. Therefore, GAC biofiltration can be used as an effective pre-treatment to alleviate organic fouling.

Slow sand filtration pre-treatment with alum is efficient, but is it effective?

Enhancing the performance of slow sand filter pre-treatment with alum (i.e. direct or contact filtration) has been proposed as an alternative to overcome limitations of conventional gravel (roughing) pre-filtration. Experimental results revealed high turbidity reduction efficiencies in alum-dosed pre-filtration. However, due to the alum coagulation, the nature of the particulates in the pre-treatment effluent changed and had a potential to shorten the downstream slow sand filter run lengths by approximately 50% under the conditions tested. Hence, depending on the effluent turbidity levels the effectiveness of the alum-dosed pre-treatment could be compromised, despite its high efficiency. Relatively low turbidity levels (<2 NTU) were needed to minimise excessive headloss development in alum-dosed filters. However, the necessary resources to achieve such process control may not be available in developing country contexts. Furthermore, full-scale field experiences indicated the limited effectiveness of alum dosing prior to slow sand filters and the difficulties in maintaining an adequate chemical dosing in under-resourced settings.

Modeling of Headloss Development in Biological Aerated Filter (<i>BAF</i>) —Ⅱ. Simulation

In order to evaluate the feasibility of the hybrid physical– biologically filtration equation of Biological Aerated Filter (BAF) developed previously, the parameters of the filtration equations were determined through the numerical simulation and experimental fitting, and the empirical formula was carried out finally. The results showed that experimental data were in agreement with the simulated data very well, illustrated that the determined parameter was reasonable and the equation can be used to forecast the headloss development of the tested filter.

Modeling of Headloss Development in Biological Aerated Filter (<i>BAF</i>) —Ⅰ. Equations Development

Biological Aerated Filter (BAF) has been global applied in secondary and tertiary wastewater treatment process in the past decades. As the increasing application of BAF, it was required to get deeper understanding of the operational discipline, parameter optimization and structural characteristics of BAF to improve the treatment efficiency and to operate stability constantly. In this paper, a physical filtration equation of clean filter bed was established firstly based on an average porosity ratio equation and Kozeny-Carman filtration equation. And then the influence of biological oxidation and biofilm development were introduced, of which the Eckenfelder mode and oxygen transfer were considered, to induce a hybrid physical- biologically equation to describe the headloss development in the BAF.

Soil aquifer treatment using advanced primary effluent

Soil aquifer treatment (SAT) using primary effluent (PE) is an attractive option for wastewater treatment and reuse in many developing countries with no or minimal wastewater treatment. One of the main limitations of SAT of PE is rapid clogging of the infiltration basin due to high suspended solid concentrations. Some pre-treatment of PE before infiltration is likely to reduce this limitation, improve performance of SAT and help to implement this technology effectively. The effects of three pre-treatment options namely sedimentation (SED), coagulation (COAG) and horizontal roughing filtration (HRF) on SAT were analyzed by conducting laboratory-scale batch and soil column experiments. The sedimentation and coagulation pre-treatments led to less head loss development and reduction of clogging effect. The head loss development in soil column using PE + COAG and PE + SED was reduced by 85 and 72%, respectively, compared to PE alone without any pretreatment. The overall dissolved organic carbon (DOC) removal of pre-treatments and soil column collectively were 34, 44, 51 and 43.5% for PE without any pre-treatment, PE + SED, PE + COAG and PE + HRF, respectively. Coagulation pre-treatment of PE was found to be the most effective option in terms of suspended solids, DOC and nitrogen removal. Sedimentation pre-treatment of PE could be attractive where land is relatively less expensive for the construction of sedimentation basins.

Optimum backwash method for granular media filtration of seawater

In order to determine an effect backwash method in granular media filtration of seawater, effectiveness of three backwash methods was evaluated in this study. The first method (W) is water wash alone at fluidization velocity. The second method (AW) is air scouring followed by fluidized water wash. The third method (SAW) is simultaneous air scouring and sub-fluidized water wash. These methods were evaluated by four parameters; turbidity of backwash waste, mass of suspended solids in backwash waste, head loss development, initial turbidity breakthrough. According to this study results, simultaneous air scouring and sub-fluidized water wash (SAW) was the most effective backwash in seawater filtration and water wash alone (W) was the least effective. Subsequent analysis of computational fluid dynamics (CFD) confirmed the effectiveness of the SAW method. Calculation of shear rate and fluid velocity around the media showed that values of these parameters were the highest when a filter was backwashed by simultaneous air scouring and sub-fluidized water wash.

Effects of intermittent polyelectrolyte addition on water quality in direct filtration

The effects of intermittent polyelectrolyte addition on the quality of effluent water and on the development of filter headloss were studied. Anionic and cationic polyelectrolytes were applied to two similarly constructed pilot sand filters. The surface water used in the study was obtained from Ömerli, which is one of the main drinking water reservoirs of Istanbul. Six sets of experiments were carried out. The objective of the experiments in the first three sets was to determine the type and dose of suitable polyelectrolyte. The polyelectrolytes were then added intermittently and continuously in the last three sets. Intermittent addition of polyelectrolyte produced better effluent quality and reduced the polyelectrolyte consumption by half with much less headloss. Ives' Filterability Index, which incorporates the important filtration design parameters such as effluent quality, the headloss and the velocity of filtration into a dimensionless number, was used for the comparison of the experimental results.

Hybrid filtration method for pre-treatment of stormwater

In this study the hybrid filtration process (combining fibre filter with deep bed dual media filtration) was investigated as pre-treatment to stormwater. This process was investigated in-terms of reduction in turbidity, dissolved organic carbon (DOC), colour, headloss development across the filters, suspended solids removal, organic matter removal, nutrients and heavy matter (such as iron, copper, lead, zinc) removal efficiency. A comparison was made between the hybrid filter with single media (sand) deep bed filter and fibre filter. It was found that the hybrid filtration system successfully removed turbidity (98%), colour (99%), suspended solids (99%), and DOC (55%). The removal efficiency of heavy metal was relatively low as the concentration of heavy metals present in stormwater was low. The removal efficiency of nitrate, nitrite and phosphorous (as orthophosphate) was 27, 35 and 72% respectively. Hybrid filtration processes showed a better reduction of Modified Fouling Index (MFI) value (from 15.500 s/l(2) to 9 s/l(2)) compared with single media sand, anthracite and fibre filter which were 35 s/l(2), 13 s/l(2)and 14 s/l(2) respectively when operated at FeCl(3) dose of 15 mg/l.

Pre-Ozonation-Coagulant Interactions in Direct Filtration

Abstract Pre-ozonation–coagulant interactions effects in relation to the coagulant type and dosage in direct filtration of surface waters were investigated. The performance of the process was evaluated by monitoring the effluent quality and head loss development through the filter bed. Two identical pilot scale filter columns filtering the same raw water were operated in parallel. The raw water was brought from Ömerli Reservoir in Istanbul. Before filtering, the raw water flow was split into two equal flows. One of the streams was pre-ozonated and the other was aerated using contact chambers with equal volumes equipped with same number and type of diffusers. In coagulation experiments, one of the filters was operated using aluminum sulfate as a coagulant while the other one was run with ferric chloride. For similar filter run times, the effluent quality was always better with pre-ozonation compared to aeration. It was also observed that, aluminum sulfate application gave more favorable results for both particle and turbidity removal compared to ferric chloride. Ives’ filterability index which incorporates the important filtration design parameters such as: effluent quality, the headloss and the velocity of filtration into a dimensionless number was used for the comparison of the experimental results.

Deep bed filter as pre-treatment to stormwater

This paper presents the results of experiments on the application of dual media and single media deep bed filters as pre-treatments to stormwater. In-line flocculation-filtration experiments were conducted with dual and single media filter. The single filter media (80 cm) consisted of either anthracite or sand, and the dual media filter consisted of sand (40 cm at the bottom) and anthracite (40 cm on top). Filtration velocities of 5 m/h, 10 m/h and 15 m/h were examined. The removal efficiency for turbidity, suspended solids and TOC was found to be 95%, 99% and 30–45% respectively at a flocculant dose of FeCl3 of 15 mg/L. The anthracite filter media showed a lower headloss development (26 cm, operated at 5 m/h filtration velocity with FeCl3 dose of 5 mg/L). The removal efficiency for nitrogen was lower than phosphorus which was relatively good (up to 50%). The removal efficiency for heavy metals such as Cd, Pb, Cr and Ni was found to be very low for all tested filtration systems because concentrations of these metals in the influent were also low. This filter can be used as a pretreatment to a membrane filter as the modified fouling index was reduced from 750 s/L2 (for stormwater) to 15 s/L2 (for filtered effluent). Detailed submerged membrane filter experiments conducted with pre-treated water showed that the membrane filter can be successfully be used as post-treatment to in-line flocculant-filter at a sustainable flux of 10 L/m2.h to remove the remaining solids and pathogens. An increase of air scouring in the membrane unit decreased the pressure development although it did not have any effect on increasing the critical flux beyond 10 L/m2.h.

Predicting the efficiency of deposit removal during filter backwash

The long-term performance of granular media filters used in drinking water treatment is ultimately limited by the efficiency of the backwash process. This paper demonstrates that it is possible to develop quantitative predictions of backwash efficiency based on filter operating conditions. An experimental investigation into the effect of backwash rate, type of coagulant, degree of clogging and accumulation of residual deposits (not removed by backwash) on the efficiency of fluidised bed filter backwash in laboratory scale filters is described. A natural raw water was used and small variations in the raw water characteristics (manifested as variations in raw water turbidity, temperature, pH, rate of head loss development and turbidity removal efficiency) within each set of experiments appeared to affect the efficiency of backwash in addition to the parameters varied deliberately. Stepwise linear regression and statistical analysis of model significance were used to determine which of several possible filtration and backwash parameters were the best predictors of backwash performance. Backwash rate, filter run time, rate of head loss development and mass of residual deposits accumulated during previous runs were found to be the best predictors of backwash efficiency for any given filter cycle. Floc deposits appeared to become more difficult to remove the longer they remained in the filter, while rate of head loss development appeared to provide some indication of the strength of cohesive deposits for filter runs of similar length. The efficiency of detachment of freshly deposited floc appeared to increase as the mass of residual deposits and mud balls in the filter increased. The numerical correlations developed in this study are site specific but the methodology can be adapted to any filter operation and backwash regime.

Biofilter as pretreatment to membrane based desalination: Evaluation in terms of fouling index

The removal of particulate matter and dissolved organic matter from seawater by the use of biofiltration was investigated. Granular activated carbon (GAC) and anthracite were used as biofilter media at two different filtration velocities. Filtrate quality was measured in terms of silt density index (SDI), modified fouling index (MFI) and turbidity removal. Reverse osmosis (RO) was used as a post-treatment. Both biofilters demonstrated similar fouling reduction behavior in terms of SDI and MFI. Fouling potential in terms of MFI values decreased to 10 s/L 2 within the first 10–15 days of operation and kept constant up to the remaining experimental period of 55 days of operation for both GAC and anthracite biofilter. The filtrate turbidity was steady after 10 days and remained low at a value of 0.2–0.3 NTU and 0.28–0.31 NTU for anthracite and GAC biofilter, respectively. Furthermore, the headloss development was low and within 20 cm for biofilter operated at a low velocity of 5 m/h. A post-treatment of reverse osmosis after a pretreatment of GAC and anthracite biofilters showed a reduction in normalized flux decline ( J/ J 0) from 0.22 to 0.12 and 0.35 to 0.21 during the first 20 h, respectively. The RO flux for seawater declined at a faster rate and continued even after 3 days when no pretreatment was provided.

Enhanced performance of crumb rubber filtration for ballast water treatment

Waste-tire-derived crumb rubber was utilized as filter media to develop an efficient filter for ballast water treatment. In this study, the effects of coagulation, pressure filtration and dual-media (gravity) filtration on the performance of the crumb rubber filtration were investigated. The removal efficiencies of turbidity, phytoplankton and zooplankton, and head loss development were monitored during the filtration process. The addition of a coagulant enhanced the removal efficiencies of all targeted matter, but resulted in substantial increase of head loss. Pressure filtration increased filtration rates to 220m3h−1m−2 for 8-h operation and improved the zooplankton removal. Dual-media (crumb rubber/sand) gravity filtration also improved the removal efficiencies of phytoplankton and zooplankton over mono-media gravity crumb rubber filtration. However, these filtration techniques alone did not meet the criteria for removing indigenous organisms from ballast water. A combination of filtration and disinfection is suggested for future studies.

Head loss performance and modeling of burnt oil palm shell in deep bed filtration

Filtration is a common unit operation in a water treatment plant. The effectiveness of granular filter media in treating surface water and removing suspended solids is already well established. However, less effort in the mathematical modeling towards the design of the filtration unit is observed. The current study involved head loss performance evaluation and development of a mathematical model to correlate maximum service time of filter at a maximum allowable head loss with various effective sizes and flow rates. Sand and burnt oil palm shell (BOPS) used as filter media in single and dual media filters were subjected to different effective sizes and flow rates. The average influent water turbidity for each filter (at specific effective size and flow rate) before entering the filtration unit was from 1 to 5 NTU. This was a pilot a study on settled water that was conducted in a Malaysian water treatment plant. Results suggest that all filters are capable of producing water with acceptable turbidity unit (<1 NTU). The total running time and filtrate water quality produced by BOPS/sand dual media filter was much better (i.e. the running time of BOPS/sand was four to nine times greater than sand single media filter) than BOPS and sand single media filters. The experimental data were well represented by a newly developed model and results of fitting show a high correlation coefficient (R2) of 0.991. The maximum allowable head loss was selected as 240 cm with an acceptable filtrate water quality (less than 1 NTU). In addition, the current results will be a supplementary tool for engineers in designing a proper filtration unit.

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.

Laboratory evaluation of a water-treatment sequence using Moringa oleifera seed coagulant

A water extract of Moringa. oleifera seed was applied to a treatment sequence comprising coagulation-flocculation-sedimentation-sand filtration. Model waters (kaolinite suspensions) of turbidities 10, 100, 300 and 700 NTU were prepared. For the 10 NTU water, the optimum dose was only evident when sand filtration was incorporated into the treatment sequence. For the higher water turbidities tested, a relatively broad optimum dose range exists post filtration. After filter ripening, the filtrate turbidities obtained for the 300 and 700 NTU raw water turbidities were 1 NTU and 3 NTU respectively. Headloss development was gradual giving relatively long filter runs.

Deterministic-Based Model of Slow Sand Filtration. II: Model Application

This paper describes the use of a deterministic slow sand filter process model to investigate and assess some of the fundamental aspects and mechanisms operating during slow sand filtration (SSF). These include the role of the schmutzdecke, biomass development, and the initial condition of the filter, to the overall process performance. The SSF process model has been developed recently and is described in a companion paper by Campos et al., in 2006. It attempts to provide a simulation of the physicochemical and biological processes responsible for the filtration mechanisms operating in SSF. The simulation of filter runs has been carried out with the help of extensive pilot plant data provided by Thames Water Utilities Ltd., involving both uncovered and covered filter beds. The results demonstrate that the presence and nature of a schmutzdecke layer profoundly influence the spatial and temporal development of interstitial biomass within the sand and, consequently, the headloss profile. Microbial interactions in the filter bed play a fundamental role in the process and are involved in setting the pattern and magnitude of headloss development. The model also demonstrates the significance of residual deposits within the filter after surface cleaning, on the subsequent filter behavior.

Deterministic-Based Model of Slow Sand Filtration. I: Model Development

Slow sand filtration (SSF) is widely used throughout the world for the treatment of drinking water. However, relatively little attention has been given to the development of a comprehensive process model. Previous studies have considered separate aspects of the SSF process, such as developing an improved representation of the schmutzdecke layer, and a more detailed description of the microbial dynamics. The objective of this work was to develop a deterministic simulation model of the SSF process incorporating fundamental physicochemical and biological dynamics within a classical filtration framework. The model was based on a temporal and spatial finite difference method and was calibrated and verified using operational data from pilot-scale SSF units. Results from the calibration showed that the model satisfactorily predicts headloss development in SSF units. There was no significant difference between many of the most sensitive model parameter values for two successive runs of the same filter. However, a few individual model parameters (e.g., in the fundamental headloss equations) were found to vary with filtration run and it is speculated that this is due to seasonal factors.