Two-stage Filtration System Research Articles

Performance evaluation and parameter estimation of the advanced primary filtration (APF) process in wastewater treatment plants

Conventional technologies employed in wastewater treatment plants (WWTPs) demand significant energy consumption. Concurrently, the wastewater infrastructure is experiencing a heavy strain as a result of the increased influent loads and pollutants. Advanced primary filtration (APF) is an emerging wastewater treatment process for early removal of suspended solids from raw wastewater. In this work, the APF process comprises of a two-stage filtration system, consisting of a proprietary rotating belt filter (RBF) (collectively known as microsieve) followed by a proprietary continuous backwash upflow media filter (CBUMF). The principal focus of this study is the assessment of the APF process performance, and the prediction of the total suspended solids (TSS) effluent concentrations of the APF process, using a parameter estimation method. According to pilot scale experimental results, the percentages of TSS (average TSS removal rate of 51 %) and biological oxygen demand (BOD5) (average BOD5 removal rate of 30 %), removed by the microsieve were notably higher compared to conventional primary treatment (sedimentation). The removal efficiency of the APF process during stable operation, varied from 69 to 86 % for TSS, as compared to 50–70 % typically achieved with primary sedimentation. The removal performance of BOD5 varied from 44 to 82 %, as compared to 25 to 40 % typically achieved with primary sedimentation. The chemical oxygen demand (COD) removal rates for the APF process ranged between 62 and 90%, as compared to 25–40 % typically achieved with primary sedimentation. The early removal of TSS prior to aeration tank has the potential to significantly enhance the capacity of the WWTP and decrease the energy requirements of the aeration tank. A high degree of concordance between model predictions and experimental data was observed. This study demonstrated the potential of using the APF process for the early removal of TSS from raw municipal wastewater just upstream of the aeration tank.

Experimental Study of a PowerCore Filter Bed Operating in a Two-Stage System for Cleaning the Inlet Air of Internal Combustion Engines

Small dust grains cause a higher intensity of increase in the flow resistance of the fibrous filter bed, which, due to the established value of the permissible resistance, results in a shorter period of operation of the air filter and the vehicle. At the same time, the mass of dust per unit of filtration area takes on smaller values. Such a phenomenon occurs in the two-stage “multicyclone-baffle filter” engine inlet air filtration system. The main objective of this study was to experimentally determine the mass of dust retained per unit of filtration area (dust absorption coefficient km) of the PowerCore filter bed operating under two-stage filtration conditions, which cannot be found in the available literature. The original methodology and conditions for determining the dust absorption coefficient km of a PowerCore filter bed operating under two-stage filtration conditions are presented. Tests were carried out on the characteristics of filtration efficiency and accuracy, as well as on the flow resistance of a filtration unit consisting of a single cyclone and a PowerCore test filter with an appropriately selected surface area of filter material. During the tests, conditions corresponding to the actual conditions of vehicle use and air filter operation were maintained, including filtration speed and the dust concentration in the air. The experimentally determined dust absorption coefficient of the PowerCore research filters operating in a two-stage filtration system took on values in the range of km = 199–219 g/m2. The dust absorption coefficient km of the PowerCore research filter operating under single-stage filtration conditions reached a value of km = 434 g/m2, which is twice as high. Prediction of the mileage of a car equipped with a single-stage and two-stage “multi-cyclone-partition” filtration system was carried out, showing the usefulness of the experimentally determined dust absorption coefficients km.

Influence of Oil Content on Particle Loading Characteristics of a Two-Stage Filtration System

Filter media may encounter aerosols mixed with solid and oil ingredients from various sources, such as industries, transportation, and households, in the air purification process, while the influence such oil content has on the loading performance of single-stage and two-stage filtration systems is under-reported. Thus, this study aims to evaluate oil fraction effects on the loading performance of single-stage and two-stage filtration systems. First, to reveal the oil–solid mixed particle deposition mechanisms, the filter media parameters, i.e., specific cake resistance ε and cake porosity K2, were tested, indicating that a slight amount of oil can increase the dust holding capacity (DHC) of filters by forming a more porous cake, while an excess of oil results in reduced DHC by forming impermeable liquid films on the solid skeleton. Further two-stage experimental results indicate that the effectiveness of a pre-stage filter can be significantly affected by the properties of incoming aerosol and main-stage filters. The utilization of a pre-stage filter unintentionally deteriorated the service lifetime of the main-stage filter when challenged with contaminants with certain oil particles. This counter-intuitive negative phenomenon is due to the special loading behaviors of oil–solid mixed particles. The existing pre-stage filters allow a higher fine oil particle fraction to reach the main-stage downstream, while the induced cake filtration scenario leading to a film clogging scenario adversely reduced the lifetime of the main-stage filter. The findings suggest that the feasibility of a pre-stage in the filtration system requires compressive evaluations according to the specific oil-coated contaminants.

Effect of main-stage filter media selection on the loading performance of a two-stage filtration system

This study experimentally evaluates the performance of a two-stage indoor air filtration system with the focus on main-stage filter media selection. The impact of the main-stage filter media properties on the effectiveness of adding a pre-stage filter media is compared among three main-stage filter media types commonly used in heating, ventilation, and air conditioning (HVAC) filtration system: cellulose, melt-blown, and expanded PTFE membrane. The pre-stage filter media effectiveness was found to be significantly affected by the incoming aerosol size distribution. Although counter-intuitive, having an additional pre-stage filter was found to cause a service lifetime drop for cellulose-type main-stage filters depending on incoming aerosol size distribution, while universally enhanced life spans were found for melt-blown and PTFE membrane-coated main-stage filters. The mechanism that causes a shortened service life of cellulose main-stage filter with the presence of a pre-stage filter was explored in detail and was found to be associated with the special particle loading behavior of conventional cellulose media. The rapid pressure drop increase of cellulose media in depth and transitional filtration regimes was strongly affected by the incoming aerosol size distribution, with a steeper slope (faster pressure drop increase) associated with finer particles penetrating more deeply into the inhomogeneous pores of cellulose media. The pre-stage filter alters the particle size distribution of the main-stage faces, with an increased fraction of fine particles that negatively impacts the main-stage filter loading behavior. This observation and mechanism analysis are the first time being reported, which suggests a careful selection of the combination of pre-stage and main-stage filter types with the consideration of incoming contaminant properties. It is essential for researchers and engineers in designing energy-efficient two-stage filtration systems.

Influence of pre-stage filter selection and face velocity on the loading characteristics of a two-stage filtration system

A two-stage filtration test system was successfully developed previously, and the objective of this study is to investigate the effect of pre-filter selection and face velocity of pre-stage and main-stage on the loading characteristics of a two-stage filtration system. Three different types of pre-stage filter media with different capture efficiency, i.e., G3, G4 and M5 pre-filters, were selected as filter type variables. Three different face velocities on pre-stage, i.e., 26.3, 45.0 and 65.2 cm·s−1, and three different face velocities on main-stage, i.e., 2.1, 3.6, 5.2 cm·s−1 were chosen as face velocity variables. Self-defined indexing parameters were used to analyze the effect of pre-filter in this study. The experimental results indicated that although M5 pre-filter with the highest capture efficiency presents the best protection to mitigate the pressure drop growth of main-filter, the pressure drop of M5 pre-filter itself increases the fastest, resulting in the shortest effective protecting time of M5 pre-filter in front of a main-stage filter, so the overall effectiveness of M5 pre-filter fades out due to the limited protection period. On the other hand, G4 pre-filter can run for a relative longer time while maintaining the pressure drop of the whole two-stage filtration system to increase relatively slowly. G4 pre-filter achieves highest T** value, outperforming the lowest efficient G3 pre-filter by its higher efficiency and the highest efficient M5 pre-filter by longer effective protection period. With the decrease of face velocity on either the pre-stage or the main-stage, the effectiveness of pre-filter on main-filter and the whole two-stage filtration system improves, by slowing down the pressure drop increasing rate of main-stage filter, which further contributes to extend the service lifetime of the main-filter and increase dust holding capacity of the whole filtration system. Besides, the specific resistance k2 of the dust cake formed on main-filter were found deeply affected by the main-stage face velocity. With the face velocity on the main-stage increased, the specific cake resistance k2 increased obviously, which implies that the dusts structure on the main-filter changed and became more compacted under higher main-stage filtration velocity. To better illustrate the relatively importance between pre-filter grade and filtration velocity selection, the analyzed performance indexing parameters were further arranged in a set of contour plots, which unveils the predominance of pre-filter grade over filtration velocity within the variation ranges tested in current study.

Particle loading characteristics of a two-stage filtration system

A two-stage filtration testing system, consisting of a pre-stage filter and a main-stage filter was successfully developed, which proves capable of being used to investigate the loading characteristics of a two-stage filtration system. A G4 filter media was selected as pre-stage media sample while an E11 filter media was tested as main-stage sample. Bi-modal aerosols consisting of both super-micrometer A2 coarse dusts and sub-micrometer KCl fine particles with varied mixing ratios were employed to challenge the two-stage filtration system to investigate the influence of aerosol size distributions. Two sets of self-defined performance-based indexing parameters were introduced to quantify the effectiveness of the pre-stage filter and simplify the comparison among various test conditions. It was found installing a pre-filter in front of a main-filter can improve the performances of the entire filtration system, by extending the service lifetime of the main-stage filter and increasing the dust holding capacity of the whole filtration system. Moreover, the effectiveness of pre-stage filter was found to be strongly influenced by the particles size distribution: the protection by a pre-stage filter is more pronounced for large particles and tends to fade out with increasing fraction of fine particles. The specific cake resistance K2 of the main-stage filter was found to increase with increasing fraction of fine particles, and was higher at the presence of a pre-stage filter than the corresponding reference case without a pre-filter.

The application of ceramic membranes for treating effluent water from closed-circuit fish farming

Abstract The aim of the study was to analyze and assess the possibility of using a two-stage filtration system with ceramic membranes: a 3-tube module with 1.0 kDa cut-off (1st stage) and a one-tube module with 0.45 kDa cut-off (2nd stage) for treating effluent water from a juvenile African catfish aquaculture. The study revealed that during the 1st filtration stage of the effluent water, the highest degrees of retention were obtained with respect to: suspended solids SS (rejection coefficient RI=100%), turbidity (RI=99.40%), total iron (RI=89.20%), BOD5 (RI=76.0%), nitrite nitrogen (RI=62.30%), and CODCr (RI=41.74%). The 2nd filtration stage resulted in a lower reduction degree of the tested indicators in comparison to the 1st filtration stage. At the 2nd stage, the highest values of the rejection coefficient were noted in for the total iron content (RIV=100%), CODCr (RIV=59.52%; RV=64.28%, RVI=63.49%) and turbidity (RIV and RV = 45.0%, RVI=50.0%). The obtained results indicate that ceramic membranes (with 1.0 and 0.45 kDa cut-offs) may be used in recirculation aquaculture systems as one of the stages of effluent water treatment.

Passive solid–liquid separation of anaerobically digested dairy manure using two-stage filtration

Solid–liquid separation makes further treatment and disposal of dairy manure easier. High concentrations of solids and long times-to-filter of anaerobically digested dairy manure present a challenge to cost-effective solid–liquid separation. This study operated a two-stage filtration system by batch modes to develop passive solid–liquid separation of anaerobically digested dairy manure. In the 1st-stage, pebble filters attained solid–liquid separation through surface filtration and evaporation. Filtration was completed after 7–33 d into each cycle of batch operation. Evaporation became the predominant mechanism for manure dewatering 2–3 weeks after each batch loading. Filtration was faster at higher temperatures, higher initial solids concentrations, and shorter times-to-filter. Two weeks after batch loadings, the pebble filters had removed 81.4–97.7% of total solids and 87.1–98.8% of total volatile solids from the filtrate and the manure retained on the pebble beds was thickened to 6.3–24.6% solids. Dewatering on the pebble beds was faster at a lower loading rate and more efficient at a higher loading rate (0.20 versus 0.16 and 0.12 m3 m−2). In the 2nd-stage, the sand filters removed suspended solids via depth filtration.

Performance of two-stage filtration system for treating high turbidity water

Two-stage filtration is a potentially promising technology for treating water. It has been estimated that most of the water treatment carried out today can be achieved efficiently with this technology, although some design and operational aspects relating to high turbidity of the influent water have yet to be fully studied. In the study reported here, a pilot plant was built comprising 2 two-stage filtration systems: system 1 involved an upflow coarse sand filter and system 2 consisted of an upflow gravel filter as the first stage of filtration. Both were followed by a downflow fine sand filter as the second stage. The experimental investigation was carried out using influent I with a turbidity of approximately 100 NTU and influent II with a turbidity of approximately 300 NTU. Coagulation was achieved using aluminium sulphate to obtain a final zeta potential of approximately zero. The main conclusions were that both systems can clarify influent I and influent II and that the downflow filter plays an essential role in the production of filtered water with a turbidity of less than 0.5 NTU. Intermediate downflushes on the upflow filters are more advantageous in increasing filter run times and in preventing the formation of any sludge blanket at the top of the upflow filters and the occurrence of breakthough in the rapid downflow sand filter. Another conclusion drawn from this research is that the effective water production is related to influent water turbidity, filtration rates, intermediate downflushes and the hydraulic head necessary for the retention of solids in the two filters of each two-stage filtration system.

Evaluation of two-stage filtration systems in drinking water treatment

Two parallel pilot plants, PP1 and PP2, each consisting of a two-stage filtration system, were evaluated; the first stage of PP1 consisted of an upflow coarse sand filter while that of PP2 consisted of an upflow gravel filter. Both pilot plants had a rapid downflow sand filter as a second stage. System pretreatment performance was determined based on the efficiency of filtering surface raw water previously coagulated with aluminium sulphate. Filter run lengths were longer in PP1 than in PP2. Coagulant doses were determined and controlled by using a bench-scale sand filter, the dominant mechanism being adsorption-destabilization with partial charge neutralization. Results of turbidity, apparent colour, total iron and manganese concentrations in the final effluent in both pilot plants were shown to meet Brazilian standards. The quality of effluents from both systems showed no variation and thus the two filtration systems were equivalent. Conclusively, both systems were found to be technically feasible processes for water clarification and compare favourably with conventional clarification systems of flocculation, sedimentation and filtration when treating raw water with turbidity lower than 20 NTU and true colour below 50 HU.