Filtration Period Research Articles

Modelling of Postproduction Suspensions’ Concentration Processes by “Batch” Membrane Microfiltration

Abstract The mathematical model of postproduction suspension concentration by microfiltration has been developed. This model describes a process conducted in a batch system with membrane washing by reverse flow of permeate. The model considerations concern filtration pseudocycles consisting of the filtration period and the membrane washing period. The balances of continuous phase volume, dispersed phase mass and energy, for each period of pseudocycle respectively, have been presented.

Assessment of biological activity in contact flocculation filtration used as a pretreatment in seawater desalination

Contact flocculation filtration (CFF) is a promising pretreatment method to improve feed water quality prior to seawater reverse osmosis (SWRO). CFF is the combination of deep bed filtration and in-line flocculation. To date, CFF has been used mainly as a barrier for particle removal in the filter bed itself with hydrophobic organic compounds removal by flocculation. In this study, the potential of CFF was investigated as a biofilter in addition to its major function of flocculation and particle/floc separation. Two different media (sand; S-CFF and anthracite; A-CFF) were tested on CFF. Bacterial activity in the filter bed was assessed in terms of cell number and adenosine tri-phosphate (ATP) measurement. The microbial community test in the filtration bed was carried out over 50d in case of sand filter (S-CFF) and 90d for anthracite filter (A-CFF) filtration periods. With the growth of an active microbial population on the filter bed medium, significant removal of organic compounds, especially low molecular weight (LMW) organics, from the seawater was achieved. The results indicated that CFF functions both as flocculation and separation unit and also as biofilter with moderate efficiency in reducing biofouling potential. The results also showed that A-CFF needed longer time to achieve bio-stabilization but it showed more effective biofiltration potential than S-CFF.

Effect of IX dosing on polypropylene and PVDF membrane fouling control

The performance of ion exchange (IX) resin for organics removal from wastewater was assessed using advanced characterisation techniques for varying doses of IX. Organic characterisation using liquid chromatography with a photodiode array (PDA) and fluorescence spectroscopy (Method A), and UV254, organic carbon and organic nitrogen detectors (Method B), was undertaken on wastewater before and after magnetic IX treatment. Results showed partial removal of the biopolymer fraction at high IX doses. With increasing concentration of IX, evidence for nitrogen-containing compounds such as proteins and amino acids disappeared from the LC-OND chromatogram, complementary to the fluorescence response. A greater fluorescence response of tryptophan-like proteins (278 nm/343 nm) for low IX concentrations was consistent with aggregation of tryptophan-like compounds into larger aggregates, either by self-aggregation or with polysaccharides. Recycling of IX resin through multiple adsorption steps without regeneration maintained the high level of humics removal but there was no continued removal of biopolymer. Subsequent membrane filtration of the IX treated waters resulted in complex fouling trends. Filtration tests with either polypropylene (PP) or polyvinylidene fluoride (PVDF) membranes showed higher rates of initial fouling following treatment with high IX doses (10 mL/L) compared to filtration of untreated water, while treatment with lower IX doses resulted in decreased fouling rates relative to the untreated water. However, at longer filtration times the rate of fouling of IX treated waters was lower than untreated water and the relative fouling rates corresponded to the amount of biopolymer material in the feed. It was proposed that the mode of fouling changed from pore constriction during the initial filtration period to filter cake build up at longer filtration times. The organic composition strongly influenced the rate of fouling during the initial filtration period due to competitive adsorption processes, while at longer filtration times the rate of fouling appeared to depend upon the amount of biopolymer material in the feed water.

Fouling characterization and nitrogen removal in a batch granulation membrane bioreactor

A submerged membrane bioreactor (MBR) combined with aerobic granulation reactor was investigated for the simultaneous organic/nitrogen removal and membrane fouling control. Total nitrogen (TN) removal was 59% (1.76 mg TN/g VSS h) in the aerobic granulation reactor. The filtration of granulation effluent or low operating F/M condition of the MBR could extend the filtration period of up to 78 days without any need for physical cleaning The soluble fraction was the main contributor to fouling compared to colloids and solids. The soluble polysaccharides (sPS) had more adverse effects than that of soluble protein (sPN). The deposition on a unit of the membrane's surface area was 11 mg sPS/L m2 and 8 mg sPS/L m2. As a result, the BG-MBR could be an alternative treatment process for simultaneous organic/nitrogen removal and fouling control.

A comparison study on the removal of suspended solids from irrigation water with pumice and sand–gravel media filters in the laboratory scale

In this study, different bed materials in media filter systems were examined. For this purpose a laboratory experiment was established to determine the solids removal efficiency, total outlet flow volume and outlet flow velocity of pumice that has numerous open spaces, vesicles and irregular cavity, sand–gravel and combination of pumice and sand–gravel. In the experiment, two different filter column diameters (150 and 200 mm) and two different inlet flow pressures (100 and 150 kPa) were used. The results show that the total outlet flow volumes increased logarithmically as the filtration test period progressed, while the outlet flow velocities and the outlet concentrations of suspended solids decreased logarithmically for all filter types. Pumice media filters provided higher total outlet flow volumes and lower solid removal efficiency in comparison with sand–gravel media filters. However, the highest average solid removal efficiency was determined by pumice plus a sand–gravel media filter at 90.5%. The average outlet flow velocity value for this filter type was 34.2 m3 h-1 m-2, which was higher than the other filter types at the same experimental conditions. Pumice plus sand–gravel media filters increased the filtration period according to the sand–gravel media filters as well.

침전이 수반되는 케이크 여과 II: 새로운 분석과 케이크에 도입되는 현탁액의 고체 질량분율

Filtration on horizontal filter medium facing upward is accompanied by sedimentation. When sedimentation phenomenon is not considered, the average specific cake resistance by filtration could be in error more than two times. In the previous paper on this subject, it was insisted that the solid mass fraction of suspension changes in filtration period by sedimentation. But we could not find out the degree of change. At the first half of this paper, the average specific cake resistance measured by permeation will be proved to be exact in several means. The average specific cake resistance conventionally measured by filtration does not give correct results because it uses initial solid mass fraction of suspension. Then we calculated the changed solid mass fraction of suspension due to sedimentation during filtration by the experimental values obtained filtration-permeation method. We also determined the solid mass fraction at a certain moment of filtration from the suspension height and a new equation derived in this study. The two results were compared and proven that they almost matched.

Pilot Study of a Hybrid Process Combining Oxidation- Coagulation- Microfiltration for Drinking Water Production from Surface Water

In this study, microfiltration (MF) combined with oxidation and coagulation was investigated for production of drinking water by Huangpu River. The experiment focused on the effects of various oxidants on reduction in fouling and improvement in quality of treated water. 0.5mg/L of ozone, 1.5mg/L of sodium hypochlorite and 0.3mg/L of potassium permanganate were added before membrane to reduce the fouling. The results showed that significant differences in permeate water and trends of TMP exhibited by adding different oxidants. With ozone as pre-oxidation, permeate water could meet China Drinking Water Regulations (CDWR), however, part of water quality met CDWR with sodium hypochlorite and potassium permanganate as pre-oxidation. TMP increased slowly during filtration period for a long time when ozone and sodium hypochlorite were added. With potassium permanganate as pre-oxidation, rapid increase in TMP was observed, which can be attributed to a lot of manganese oxides deposited in the membrane by analyzing chemical cleaning water. Chemical cleaning of membrane could decrease TMP to initial level. Analysis of chemical cleaning solution indicated that organic matters was responsible for the most fouling, and ozone could reduce membrane fouling effectively.

Flux Improvement during Cross-flow Microfiltration of Wheat Starch Suspension using Turbulence Promoter

The objective of this study was to investigate the effects of the process variables (transmembrane pressure, flow rate, and concentration) on the permeate flux during the microfiltration of model starch suspensions, and to determine the conditions under which the use of Kenics statics mixer as a turbulence promoter is justified. A response surface methodology was used to examine the influence of the selected operating conditions on starch suspension microfiltration using a single channel ceramic membrane with 200 nm pore size. The experimental results clearly show that the improved performance of starch suspension cross-flow microfiltration can be obtained by using a Kenics static mixer, especially at lower flow rates. Compared to the operation without the turbulence promoter, the average permeate flux improvement during the filtration period ranged from 30% to 230%. As a result of the statistical analysis, the optimal conditions for starch suspension microfiltration were determined and applied to microfiltration of starch industry wastewater.

Filtration and drying characteristics of casein

Casein precipitated by acidolysis of the skimmed milk was filtered under constant pressure conditions followed by the cake drying in a vacuum tray dryer. Filtration characteristics of the cake were expressed in terms of average specific cake resistance (αav) and cake solids fraction or porosity. An interesting trend was observed at lower feed concentrations of casein in the filtration slurry. In the initial period of filtration, αav, was found to be lower under the prevailing conditions as compared to the increased value of αav in the later part of filtration. This phenomenon accentuates the strong relationship between the differential pressure across the filtration unit and αav. To corroborate these findings, the pressure drop across the cake was found to influence its compressibility, n, that varied between 0.4 and 0.8. The differential pressure studied was in the range of 0.5–2.5bar. The influence of gas deliquoring on cake saturation (S) was studied to obtain the threshold pressure, an useful design parameter for pressure filtration.The drying of casein cake in a vacuum tray dryer showed the typical drying rate curve with constant rate period followed by the extended falling rate period. The drying curve was analyzed in terms of moisture diffusivity, which in turn was found to be a strong function of temperature. To overcome long drying time of few hours, the casein cake after partial dehydration was extruded to get the benefit of higher surface area to volume ratio. The extruded pellets were effectively and efficiently dried to the final desired moisture content. It was shown that the total drying time and drying technique influence to a large extent the protein denaturation.

Microfiltration characteristics of Bacillus subtilis fermentation broths

The microfiltration characteristics of Bacillus subtilis broths under different culture conditions were studied. In the no medium addition culture condition the major component in the broth was sole B. subtilis cells. The filtration curve of dt/dv vs. v (reciprocal of filtration flux vs. filtrate volume) can be divided into three regions. After a short relaxation time the tangent slope increases drastically. This implies that significant cell deformation and cake compression occurs in the second region. The average specific cake filtration resistance will reach the maximum value at the filtration curve inflection point. The cake compressibility gradually decreases in the third region because most solid compressive pressures are depleted by the formed compact cake. In the medium addition culture condition the B. subtilis cells and extracellular polymer substances (EPS) flocs concentrations in the broth increase markedly with culture time. The filtration curve tangent slope increases continuously during the entire filtration period because of the highly compressible cake. All proteins in the extra-cellular polymeric substances are retained by the filter cake and membrane during a filtration, while most polysaccharides have the opportunity to penetrate into the filtrate when the culture time exceeds 1 day. Polysaccharide rejection increases with increasing filtration pressure for the 1-day culture broth. However, the filtration pressure has a trivial effect on the polysaccharide rejection for longer culture times. The filter cake resistance formed by B. subtilis cells and EPS flocs plays an important role in determining the overall filtration resistance. A longer culture time and lower filtration pressure are beneficial for protein/polysaccharide separation using microfiltration.

Influence of biofilm carriers on membrane fouling propensity in moving biofilm membrane bioreactor

In moving biofilm membrane bioreactor (MB-MBR) sponge carriers for biofilm growth were coupled with conventional submerged membrane bioreactor (C-MBR). This study compared the fouling propensity of C-MBR with MB-MBR and investigated factors affecting fouling variations in both the systems. Membrane fouling tendencies were monitored in terms of trans-membrane pressure (TMP) and the fouling characterization included membrane fouling resistances in situ and specific cake resistance (SCR) in batch filtration cell. Comparison of TMP profiles depicted prolong filtration periods in MB-MBR. Cake layer resistance (Rc), pore blocking resistance (Rp) as well as SCR were higher in C-MBR. The study reveals that hybrid biomass in MB-MBR creates relatively more porous cake structure in the absence of filamentous bacteria which were found in abundance in C-MBR. Filamentous bacteria were also responsible for the release of high concentration of carbohydrates in the form of soluble extra polymeric substance (EPS) contributing to higher Rp in C-MBR.

Evaluation of cake filtration biological reactors (CFBR) vs. membrane biological reactors (MBR) in a pilot scale plant

In this study, cake filtration biological reactors (CFBR) and membrane biological reactors (MBR) were operated in the same environment. The initial flux of CFBR was 1,517.5L/h/m2 and the start-up cake resistance was around 6kPa. The flux dropped sharply during the first run, and at the end of first run flux was 110L/h/m2. During the second run, the flux declined further from 60L/h/m2 to 48L/h/m2 and during the last 4,000hours period flux was considered to be stable. However, the pressure difference (∆p) increased steadily for about 2,300hours until it reached a stable ∆p value at the termination of the run. On the other hand, the design operation flux of the membranes was 17.5L/h/m2. The system was operated around design flux values; however, more stable operation was achieved when the flux was around 9L/h/m2. Both the cloth filter and the membrane produced effluents with suspended solid concentrations of less than 10mg/L, but the effluent quality of the cloth filter was inferior to the membrane with respect to coliform removal. Activated sludge cake, which formed on cloth media during filtration, was evaluated according to conventional cake filtration theory using the plots of V vs. t and t/V vs. V. The plot of V vs. time t for filtration of different MLSS concentrations in laboratory cell was best fitted to second order polynomial regression (R2>0.98); a linear relationship between t/V against V was not observed. Separately, an evaluation of V vs. t showed that CFBR was best fitted to second order polynomial regression (R2=0.995 for first run and R2=0.989 for second run); however, a linear relationship between the reciprocal of filtration rate (t/V) and the cumulative volume was observed individually. A transition between two linear plots was considered to be a change in the filtration characteristics. Standard blocking model plots of CFBR were fitted better (R2>0.95) than complete blocking and intermediate blocking models with the measured data for the initial period of filtration; the latter period of filtration was best fitted to the cake filtration model (R2>0.99).

Flux decline behaviors in inclined dead-end ultrafiltration of BSA solutions

Inclined dead-end ultrafiltration experiments were conducted for bovine serum albumin (BSA) solutions by using a specially-designed, unstirred batch filtration cell with the filtering surface of a square. Variations of the filtration rate were measured over time during filtration. Initially, short-term, severe flux decline occurred in the early period of filtration due to the formation of the thin filter cake over the membrane surface. Thereafter, the filtration resistance gradually increased over the long term of filtration. It was found from observations of the filter cake during filtration that the filter cake, which gradually slipped, grew on the lower side of the inclined membrane keeping its surface horizontal. Considering the decrease in the effective filtration area caused by the thick cake formed on the lower side of the membrane in addition to the formation of the thin filter cake over the membrane surface, a model was proposed to describe the dynamic behaviors of the filter cake during the long-term filtration and utilized to evaluate the variations of the filtration rate with time. On the basis of the cake accumulation model presented, the time evolutions of the filtration rate were evaluated for the different values of the inclined angle of the membrane, the solution pH, and the BSA concentration. It was shown that the calculations were in reasonable agreement with the experimental data.

Measurements of Growth Rate of Filter Cake in Vertical Single-Pass Ultrafiltration Using Hollow Fiber Membrane Module

Vertical ultrafiltration experiments of silica colloid and bovine serum albumin solution were conducted in the single-pass mode by using a hollow fiber membrane module and beneficial in measuring the time evolution of the growth rate of the filter cake during filtration. The extremely small mass flux of the concentrate enabled us to highly concentrate the feed solution on the principle of vertical ultrafiltration in which the filter cake formed on the membrane surface is exfoliated continuously. Both growth and re-entrainment rates of the filter cake formed in vertical ultrafiltration were evaluated from the experimental data of the filtration rate and the mass fraction ratio of the concentrate on the basis of the mass balance within the hollow fiber membrane module. As a consequence, it was found that the re-entrainment rate of the filter cake increased almost linearly with the filtration time in the initial period of filtration and then tended to rapidly approach a constant value. The filter cake stopped growing under this dynamically balanced condition. The variations of the average specific resistance of the filter cake with time were also determined from the time evolutions of both the filtration rate and the growth rate of the filter cake.

RO Membrane Filtration of Pretreated Swine Manure with High Levels of Suspended Solids

Sustainable practices require that manure nutrients be reused within the agricultural sector. Reverse osmosis (RO) is one of the few technologies capable of producing nitrogen and potassium concentrates that can be transported to fertilize distant cultivated fields. However, solid-liquid separators produce a liquid fraction that could significantly foul RO membranes because of high colloidal and particulate concentrations. This project investigated the effect of high suspended solids (SS) concentrations, ranging from 258 to 3897 mg L-1, in pretreated manure on the performance of a spiral-wound RO membrane. The effluents were first concentrated to 47% of the initial volume. The concentrates, containing from 453 to 6893 mg SS L-1, were then filtered in full-recycle mode for a total of 22.5 h. Permeate flux stabilized during the full-recycle filtration period at SS levels up to 4000 mg L-1 in RO concentrate, but it was 13% lower at 4016 than at 453 mg SS L-1. At the highest SS level of 6893 mg L-1 in concentrate, flux decreased throughout the full-recycle filtration period, and it was 27% below that measured at 453 mg L-1 after 22.5 h. Lower flux was attributed to the formation of a concentrated gel layer at the membrane surface. While the thickness or density of the gel layer appeared to stabilize below 4000 mg SS L-1 in concentrate, it kept increasing at the highest tested SS level. However, with all effluents, the gel layer was easily removed by rinsing the membrane with tap water, and water flux recovery after rinsing (82.3% 1.6%) and chemical cleaning (99.1% 1.2%) were similar at all SS concentrations. Results thus suggested that spiral-would RO membrane systems could be used to directly process swine manure pretreated by physically based solid-liquid separators, but permeate flux will be significantly reduced at SS concentrations above 4000 mg L-1 in the membrane element.

Membrane flux dynamics in the submerged ultrafiltration hybrid treatment process during particle and natural organic matter removal

Particles and natural organic matter (NOM) are two major concerns in surface water, which greatly influence the membrane filtration process. The objective of this article is to investigate the effect of particles, NOM and their interaction on the submerged ultrafiltration (UF) membrane flux under conditions of solo UF and coagulation and PAC adsorption as the pretreatment of UF. Particles, NOM and their mixture were spiked in tap water to simulate raw water. Exponential relationship, ( J P/ J P0 = a×exp{–k[t–( n–1) T]}), was developed to quantify the normalized membrane flux dynamics during the filtration period and fitted the results well. In this equation, coefficient a was determined by the value of J P/ J P0 at the beginning of a filtration cycle, reflecting the flux recovery after backwashing, that is, the irreversible fouling. The coefficient k reflected the trend of flux dynamics. Integrated total permeability (Σ J P) in one filtration period could be used as a quantified indicator for comparison of different hybrid membrane processes or under different scenarios. According to the results, there was an additive effect on membrane flux by NOM and particles during solo UF process. This additive fouling could be alleviated by coagulation pretreatment since particles helped the formation of flocs with coagulant, which further delayed the decrease of membrane flux and benefited flux recovery by backwashing. The addition of PAC also increased membrane flux by adsorbing NOM and improved flux recovery through backwashing.

Effects of membrane morphology and operating conditions on microfiltration particle fouling

The effects of membrane morphology and operating conditions on the particle fouling in dead-end microfiltration are studied to verify the criteria for membrane selection. Three kinds of membranes, Isopore, Durapore and MF-Millipore membranes, with similar mean pore sizes around 0.45 μm are used for filtering 0.15 μm PMMA particles. The blocking index and resistance coefficient used for membrane blocking models are analyzed during microfiltration. The membrane pore blocking is dominant and the blocking index decreases gradually in the early filtration period. The blocking index drops suddenly to zero when a critical condition reaches; and the filtration follows up the cake filtration model thereafter. A membrane blocking chart is established for relating the blocking index and operating conditions for the used membranes. Comparing the results under a fixed filtration pressures, the blocking occurred in Isopore membrane is the most serious. The use of MF-Millipore membrane causes a filter cake to more easily form on the membrane surface. While the use of Durapore membrane results in the highest filtration flux due to its antifouling behavior. To analyze the critical filtration flux and particle accumulation at the changing point of blocking models, the sequence of difficulty in transforming to cake filtration is Isopore > Durapore > MF-Millipore membrane. The force analysis on depositing particles shows that a power relationship exists between the overall filtration resistance and filtration pressure at the critical condition. The critical overall filtration resistance has a sequence of Isopore > Durapore > MF-Millipore membrane under a fixed filtration pressure.

The performance and impact of a bubble-wash bead filter in a recirculating green water larval culture system for delta smelt ( Hypomesus transpacificus)

Delta smelt are cultured at the UC Davis Fish Conservation and Culture Lab (FCCL) for research purposes. The culture systems used are based on recirculation technology to ensure optimum water quality for the fish at each life stage. Larval culture takes place in recirculation systems with green water to which a Nannochloropsis algal concentrate is added to maintain a turbidity of approximately 9 NTU. A bubble-wash bead filter is used to remove total suspended solids (TSS) from the recirculation system. The performance of the bubble-wash bead filter has been evaluated by testing the TSS and particle size distribution in two parallel systems operated in the same way. The need for bubble-wash bead filter backwashing and the impact of the backwash method were evaluated also. The results show that the bubble-wash bead filter removed a great deal of the TSS, including the algae added to maintain the turbidity. An improper backwash method could result in a short term but significantly high TSS peak in the system immediately after the backwash event. Testing over an extended filtration period with a prolonged backwash interval showed that the TSS in the system remained stable up to 150 h post backwash, at which time it increased rapidly. The TSS accumulation in the system with a bubble-wash bead filter that was not backwashed was greater than that in a parallel system without a bubble-wash bead filter. No significant mortality increase was found in the system without a bubble-wash bead filter for 34 days, which provides a possible alternative in order to lower the rearing cost. Nevertheless, there are benefits of using a bead filter, and these are discussed in the paper.

Fouling of ultrafiltration membrane during secondary effluent filtration

Ultrafiltration (UF) membranes have been increasingly used for the pretreatment of secondary effluent in reverse osmosis wastewater reclamation plants. The fouling behavior of UF membranes during secondary effluent filtration was studied under constant pressure conditions in a cross flow filtration unit. The rate of flux decline was found to be strongly dependent on the permeate flux level, and drastic flux decline was observed at high flux during the initial period of filtration (within the first 30 min of each fouling test). Further flux decline was insignificant and a limiting flux behavior was observed. Membranes with high initial flux (>the limiting value) approached asymptotically to an identical stable flux, i.e., the limiting flux. The stable flux was strongly affected by solution chemistry (both pH and calcium concentration), with more severe membrane fouling occurred near the isoelectrical point of the foulant (pH 6) or at greater calcium concentration. Zeta potential measurements revealed that the stable flux may be correlated to the square of zeta potential of fouled membrane samples. The current study seems to suggest that foulant-foulant electrostatic repulsion plays a significant role in membrane fouling by effluent organic matter.

High voltage impulse electric fields: Disinfection kinetics and its effect on membrane bio-fouling

A high voltage impulse (HVI) technique was applied for the control of membrane bio-fouling caused due to the filtration of microorganisms. Escherichia coli was used as a model microorganism for membrane filtration. The death rate of the cells increased with increasing electric fields (E) strength from 5 to 20 kV/cm. In particular, the cell numbers decreased from 3.7 × 10 5 to 2.5 × 10 3 CFU/ml (99.3% reduction) when subjected to an HVI of 20 kV/cm for 60 min. The model equation for HVI disinfection; E 1.94 · t = 1.3 × 10 4, was obtained by plotting the contact time (t) vs. E for 2-log removal (99% reduction) of microorganisms. E. coli Suspensions, both with and without HVI induction, were filtered through an ultrafiltration membrane to verify if the HVI enhanced the filtration performance. The flux of the suspension subjected to HVI was constantly maintained throughout the entire filtration period; whereas, that of the control (without HVI induction) abruptly decreased after the onset of membrane filtration. The main reason for the improved flux was the reduced cake resistance (R c) as a result of the increased cell particle sizes after HVI induction. E coli cells became coagulated after being subjected to HVI and; thus, the particle size increased. The HVI system could be used as an alternative method for the control of membrane bio-fouling.