Poor Filterability Research Articles

Enhanced methanogenic degradation and membrane fouling associated with protein-EPS by extending sludge retention time in a high-solid anaerobic membrane bioreactor treating concentrated organic sludge

The improvement of organic sludge destruction efficiency and methanogenic performance is a key concern during anaerobic digestion toward maximum energy recovery. In this study, a high-solid anaerobic membrane bioreactor (AnMBR) was operated continuously for the treatment of organic sludge from Japanese small-scale collective wastewater treatment facility (Johkasou), and digestion efficiency was enhanced by the optimizing solid retention time (SRT). Degradation efficiency of the substrate improved from 36 % to 52 % and the biogas yield was enhanced from 0.37 to 0.51 L/g-VSfed when the SRT was extended from 30 to 60 d. The net energy yield of AnMBR at SRT 60 days was 9.83 kJ/g-VSfed, and the corresponding energy sufficiency ratio was 181 %, indicating that SRT extension could enhance substrate destruction with significant energy recovery potential. However, a long SRT is characterized by high mixed liquor total solids (MLTS), small particle size, high extracellular polymeric substances content, and poor filterability, which exert detrimental effects on membrane operation. Membrane fouling was effectively controlled by regulating the flux at a sustainable rate. The low fouling region and transition region of operating flux were determined as 0.21–4.6 L/m2/h (LMH) and 1.5–5.7 LMH, respectively, when MLTS was 25–50 g/L, and the main contributors to membrane fouling were high protein fractions and small sludge flocs. The current study proposes a promising method to promote digestion efficiency and provided adequate guidance for membrane operation at super-high MLTS by presenting practical engineering applications of AnMBRs in solid waste treatment.

The filtration of aqueous clay mineral suspension in the presence of bitumen

Typical mine tailings can be dewatered by filter press to filter cakes containing >=85 wt% solids that are ready for reclamation, but Alberta oil sands tailings could only reach about 60 wt% solids using the same technology, even when the dominant particle sizes are similar. In this work, the effects of residual bitumen, one of the distinguishing features of oil sands tailings, were investigated. The residual bitumen in the oil sands tailings exists in the forms of bulk bitumen, emulsified bitumen, and adsorbed bitumen. The roles of the three forms of bitumen were investigated in the filtration of primarily a model mineral kaolinite mineral slurry supplemented by rutile, quartz and montmorillonite slurries. Generally, bulk bitumen was found not to affect filtration significantly, emulsified bitumen facilitated filtration possibly by mopping the ultrafine particles, while bitumen adsorbed on mineral surfaces had more complex effects: a thin bitumen coating improved filtration because of the induced surface hydrophobicity, while a thick bitumen coating impeded filtration due to its mobile and deformable nature. The poor filterability of oil sands tailings may be partly caused by the mobile and deformable bitumen coating on the sands/clay mineral surfaces. This study elucidated the effects of a third deformable organic phase on the filtration of an aqueous mineral slurry, providing insights for solid–liquid separation in the presence of a mobile third phase.

The filterability of different types of minerals and the role of swelling clays in the filtration of oil sands tailings

The dewatering of oil sands tailings is one of the most challenging problems faced by the oil sands industry. Despite significant efforts in the past several decades, the industry still lacks viable technologies that can quickly dewater and reclaim the oil sands tailings and eliminate their environmental impacts. The poor dewatering of oil sands tailings has been categorially attributed to fine clays and/or residual bitumen, but has not been pinned to specific entities. In this work, the research is focused on investigating the filterability of different types of minerals with an objective to identify the ones that are responsible for the difficult filtration of oil sands tailings. Three different types of minerals, including non-clay minerals (rutile, quartz), non-swelling clays (kaolinite, illite), and swelling clays (illite–smectite, montmorillonite) were selected for the study. The fine mineral solids were characterized by particle size distribution, methylene blue index (or cation exchange capacity), and specific surface area measurements. The dewatering of each mineral was studied using vacuum filtration and capillary suction time measurements. Initial filtration rate and capillary suction time were used to assess the dewatering performance. It was found that particle size was not a primary factor affecting the filterability of the minerals, but the type of mineral is the deciding factor. Non-clay minerals and non-swelling clays were easier to filter than the swelling clays. The presence of the swelling clays, even in small quantities, significantly affected the filterability of other minerals, and it was thus deduced that swelling clays in the oil sands tailings were the main reason for the latter’s poor filterability. The swelling clays were characterized to correlate its composition and structure to filtration behavior using the effective volume fraction of the solids in an aqueous mineral slurry.

A rigid body dynamics model to predict the combined effects of particle size and shape on pressure filtration

• Developed a novel computational workflow for simulating pressure filtration. • Rigid body dynamics used to simulate cake formation with various particle shapes. • A “local” Ergun equation developed to capture spatial variations in cake structure. • Platelet-shaped particles predicted to generate low porosity and poor filterability. • Large and small particle mixtures predicted to generate spatial heterogeneities. Many theoretical studies have focused on the effects of spherical particle size on pressure filtration, a solid-liquid separation method commonly used in pharmaceutical manufacturing and other industries. While experimental studies have demonstrated the importance of particle shape as well as size on the filterability of non-spherical particles commonly produced from pharmaceutical crystallization, process models that mechanistically capture how particle morphology affects the microscopic properties of the particle cake are lacking. The objective of this study was to investigate the combined effects of particle shape and size on pressure filtration performance using rigid body dynamics simulation, a powerful method for predicting porous cake structure based on the properties of the constituent particles. Once a detailed cake structure was generated, the Ergun equation was used to predict the macroscopic flow behavior of the filtration process. This workflow was validated by comparing model predictions with filtrate flow measurements from a series of dead-end filtration experiments using spherical particles with heterogeneous size. By simulating cylindrical particles over a wide range of aspect ratios, we showed that particle shape can have a dramatic effect on cake porosity and filtrate flow with disk-shaped particles predicted to be particularly difficult to filter. Rigid body simulation allowed the prediction of local as well as average cake properties. We predicted that heterogeneously sized particles with small or large aspect ratios such as disks or needles could produce highly asymmetric cake structures characterized by densely packed and low porosities near the filter medium. A modified Ergun equation based on local particle size and porosity was developed and shown to predict substantially different filtrate flows than the standard Ergun equation based on spatially-averaged properties, especially for cylindrical particles with high aspect ratio.

Combined filtration and oxalic acid leaching for recovering phosphorus from hydrothermally carbonized sewage sludge

Hydrothermal carbonization is a promising pretreatment for the energetic utilization of municipal sewage sludge. However, the carbonized slurry must be dewatered and the valuable compound phosphate recovered. This article reveals a new approach of combined slurry filtration and subsequent phosphate leaching using oxalic acid (18–72 g l−1) in a single apparatus for the first time. A slurry of hydrothermally carbonized sludge was filtered, washed, leached twice with oxalic acid and washed again. A thorough characterization of the filtration performance and the process products was conducted. The suspension is difficult to filter, but the permeability of the filter cake increases during acidic leaching. The specific filter cake resistance of (4.5 ± 2.2) · 1015 m−2 indicates poor filterability of the hydrochar slurry. 41–83% of phosphate and sodium are leached from the hydrochar, while all other investigated inorganics are leached to a lower extent. 12–31% of iron, calcium and manganese are removed from the hydrochar. The relative contents of carbon, hydrogen and oxygen increase in the residual hydrochar after leaching. After leaching, oxalic acid accounts 10.5–16.9% of the dry hydrochar due to adsorption and poor cake washing. Co-leached calcium, bivalent iron and magnesium precipitate from the leachate as oxalate salts. In conclusion, combined filtration and phosphate leaching enables efficient phosphate removal and generates an ash-reduced hydrochar for energetic utilization. However, to enable its technical application, the filtration performance and system integration need to undergo further development.

Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding

The goethite process has gained renewed attention due to the generation of environmentally acceptable sludge in hydrometallurgical processing of nickel. Goethite precipitation at low pH (2.1 to 2.5) contributes to minimizing the loss of nickel, but results in iron precipitates with poor filterability. In this paper, crystallization induced by natural limonite seeds was used to improve the filterability of iron precipitates. The X-ray Diffraction, Scanning Electron Microscopy and Laser Particle Size Analysis show that limonite seeds could induce the growth of goethite crystals and reduce the generation of amorphous iron phases at low pH. The limonite particles of size range −74+37μm were the most suitable for inducing goethite crystallization. A smaller specific surface area of goethite particles by limonite seeding and hot acid washing contributed to a decrease in the adsorption on to the precipitates.

Fouling analysis and mitigation in a tertiary MBR operated under restricted aeration

Operation of tertiary membrane bioreactors at low dissolved oxygen concentration (DO) reduces energy consumption associated with biological aeration. However, low oxygen concentrations affect biological activity, sludge bioflocculation and fouling propensity. This study assesses the effectiveness of an alternative backwash initiation strategy for fouling control in a tertiary membrane bioreactor operated under restricted oxygenation. Long-term filtration tests were carried out at five DOs (0.09–1.23mg/L) in a pilot-scale unit operated in dead-end filtration mode (i.e. without air-scouring) under a broad-range of permeate fluxes (25–65L/h m2). Bioflocculation was negatively affected at low DO ([O2]≤0.25mg/L), resulting in relatively high values of biopolymeric clusters concentration (BPC ≥4.3mg DOC/L). This produced small floc sizes (D(v,0.5)≤49µm), poor filterability (TTF≥573s) and low critical fluxes (Jc≤20L/h m2). However, above moderate oxygen concentrations ([O2]≥0.38mg/L), sludge bioflocculation significantly increased, showing good filterability (TTF≤173s) and relatively high critical fluxes (Jc≥45L/h m2). The filtration tests showed that the controlled backwashing initiation was effective in limiting the residual fouling even at a very low oxygen concentration, since it automatically increased backwashing frequency as sludge bioflocculation decreased. The reversible fouling, it can be described by the compressible cake model, with a specific cake resistance at zero pressure governed by the bioflocculation state, while the compressibility is determined by the filtration flux. Optimal sustainable conditions were established at moderate DO ([O2]=0.38mg/L), which involves a low specific energy demand for the filtration process and biological aeration (SED=0.25 kWh/m3), and a high net permeate flux (J =42.2L/h m2).

Assessing the performance of an MBR operated at high biomass concentrations

Reducing the footprint requirements of membrane bioreactors (MBR)s can both decrease the surface area needs for new wastewater treatment plants (WWTP)s, and increase the treatment capacities of existing WWTPs at a given surface area. In addition, it may promote the development of movable/portable containerized MBRs for a diverse range of wastewater treatment applications. Applications may include the provision of municipal/industrial wastewater treatment in remote areas without sewerage, and the provision of sanitation services under challenging site-specific conditions such as after the occurrence of a human-made or a natural disaster. The reduction of the footprint requirements of MBRs is constrained by the maximum amount of biomass that can be accommodated in the aerobic basin. The biomass concentration is mainly limited by the extremely low oxygen transfer efficiency (OTE) experienced by conventional aeration bubble diffuser systems at mixed liquor total suspended solids (MLSS) concentrations higher than 20 g L−1. Another potential limitation for the operation of MBRs at such high MLSS concentrations is the reduction on the membrane permeability due to excessive fouling. A pilot MBR with a treatment capacity of one m3 d−1 was installed at the research hall facilities at the Harnaschpolder wastewater treatment plant in Delft, The Netherlands. The MBR was operated at MLSS concentrations of up to 28 g L−1 at sludge retention times (SRT)s ranging from 30 to 35 days. The MBR was provided with a Speece cone concentrated oxygen delivery system to overcome the oxygen transfer limitations of conventional bubble diffuser aeration systems at high MLSS concentrations. The MBR performance was evaluated by monitoring the influent and effluent water quality, the membrane permeability, the sludge filterability, the dissolved oxygen (DO) concentration, and the oxygen uptake rate (OUR). The Speece cone proved to be effective in delivering enough oxygen to maintain DO concentrations in the MBR of approximately 2 mg L−1 at MLSS concentrations of up to 22 g L−1. OUR values above 200 mg L−1 h−1 were observed at 14 g L−1 MLSS and higher than 300 mg L−1 h−1 at 22 g L−1 MLSS. The MBR exhibited chemical oxygen demand (COD) removal efficiencies of up to 99% even at a hydraulic retention time (HRT) as low as 3.7 h. A reduction in permeability from 33 to 11 lmh bar−1 was observed when the MLSS concentrations increased from 18.7 to 27.8 g L−1. Sludge filterability values expressed as the added resistance (ΔR20) fell in the range of “poor filterability” for all the evaluated operational conditions; however, a lower filtration resistance in the range of “moderate filterability” at approximately 23 g L−1 MLSS was noticed. The experimental results suggest that at the evaluated experimental conditions the existent limitations on poor oxygen transfer and low permeability when operating a MBR at high MLSS concentrations can be overcome; therefore, the footprint requirements of MBR systems may be further reduced.

Magnetic separation of iron precipitate from nickel sulfate solution by magnetic seeding

The application and development of goethite process were hindered by the poor filterability of the precipitate and the great loss of nickel in nickel hydrometallurgy. In this study, the effects of pH on the goethite precipitation and the mechanism of the nickel loss were investigated. The goethite precipitation at a lower pH (2.4 to 3.0) guaranteed a higher recovery of nickel at the cost of the filterability of the precipitate. Then a novel process, magnetic seeding and separation, was proposed to improve the filterability of iron residues and simplify the iron removal process. The iron precipitated on the surface of the magnetic seeds to form a large particle with core-shell structures and the magnetic core endowed the particles magnetism. Efficient magnetic separation offseted the poor settleability and filterability of the precipitate. After magnetic separation of iron residue, the nickel solution was qualified and the dried iron residue contained more than 52% Fe and less than 0.6% Ni, indicating a promising alternative process for treatment of bulky residues of iron precipitate. Further analyses with Environmental scanning electron microscopy (ESEM) and X-ray Diffraction (XRD) provided a fundamental understanding of the new process.

Improvement on filterability in the aerobic treatment of carboxymethyl cellulose (CMC) wastewater

CMC is chemically modified from natural cellulose and widely applied in various industries. CMC wastewater consists mainly of sodium glycolate, sodium chloride and water. With extremely high COD and salinity, high concentration CMC wastewater can?t be biologically treated, but with COD and salinity around 15000 mg/L and 30000 mg/L respectively, low concentration CMC wastewater can be aerobically treated. In a CMC factory, the treatment of low concentration wastewater with aerobic MBR was successful except for one serious problem: poor filterability. Two trial solutions: adding micronutrients and applying MBBR were expected to improve the filterability. In the experiment, adding micronutrients was achieved by mixing filtered natural water into the wastewater, rather than dosing chemicals into it. The treatment efficiency of both solutions was close, but adding micronutrients showed distinguished performance in improving filterability, which includes higher filtration flux and slighter membrane fouling. Adding micronutrients also effectively improved the filterability under severe salinity shock.

Influence of electrical field on COD removal and filterability of activated sludge

Three batch reactors were operated in order to investigate the effects of electrocoagulation and electrical field on chemical oxygen demand (COD) degradation rates, efficiencies, and filterability. The first reactor was operated with iron electrode, the second reactor was operated with relatively inert titanium electrode, and the last one was run as control without any electrical field. The electrical field application with iron electrodes increased the COD degradation rates at 0.5 and 2.5 V/cm with COD removals around 90%. However, the removal efficiencies decreased down to 70% at 5 V/cm. Increases in degradation rates were observed with titanium electrodes with time at all the three voltages. Activated sludge from the reactor with iron electrodes showed excellent filtration properties at 2.5 and 5 V/cm experiments. This was attributed to iron precipitates screening membrane foulants and preventing the formation of high resistive cake layer and pore structure rather than floc size increase. Electrocoagulation showed promising results in reducing membrane fouling. A critical voltage gradient should be maintained and the magnitude of iron electrode dissolution should be controlled in the reactor to obtain optimum COD degradation and to enhance filterability. Sludge samples from reactor with titanium electrodes showed poor filterability as voltage gradient increased (at 5 V/cm). This was attributed to the elevated soluble protein content (SMPp) concentration due to cell disruption.

Coagulation–Membrane Filtration of Chlorella vulgaris at Different Growth Phases

Coagulation and membrane filtration separation of Chlorella vulgaris, a species with excellent potential for CO2 capture and lipid production, was studied at different growth stages of algal cells using chitosan as the coagulant and a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane as the filter medium. Three samples were collected and tested: sample A in a logarithmic growth phase, sample B in a late stage of the growth phase, and sample C in a stationary phase. Sample A revealed efficient autocoagulation capability and samples B and C had poor settleability. The coagulation efficiency of algal suspension was increased with increasing chitosan dosage, reaching 99.7% removal rate at 200 mg L−1 chitosan for sample A, 99.5% removal rate at 50 mg L−1 chitosan for sample B, and 99.0% removal rate at 100 mg L−1 chitosan for sample C. Sample A, coagulated with 50 mg L−1 chitosan, had a membrane filtration flux of 10–14 m3/m2-min after a 5-min test. Samples B and C had poor filterability with membrane flux of less than 1.0 m3/m2-min after a 5-min test. Chitosan coagulation could incrementally enhance the filterability of samples B and C. Conversely, the solid contents in filtered cake from original samples A, B, and C were 26.8, 31.9, and 33.7%, respectively. That is, a long cultivation time led to a dry filtered cake after membrane filtration. Adding chitosan slightly decreased the solids content of the filtered cake from sample A, largely reduced the solids content from sample B, and first increased and then decreased the solids content of the filtered cake of sample C. Low water–solid binding energy corresponded to a dry cake after membrane filtration. Selection of the appropriate harvesting time and the required chitosan dose relies on the cost of membrane operation, coagulation operation, and subsequent drying steps. Supplemental materials are available for this article. Go to the publisher's online edition of Drying Technology to view the free supplemental file.

Optimization of the cooling profile to improve the filterability of crystals isolated during an optical resolution by diastereomeric salt formation

The crystallization of a diastereomeric salt during the optical resolution of a synthesized intermediate led to crystals showing poor filterability. With a view to decrease the duration of the filtration step, linear cooling profiles, including a preliminary stabilization step, and non-linear cooling profiles (quoted as controlled type) are tested. This latter type of profile enables a significant increase of mother liquors flowrate during filtration (from 50% to 300% according to crystallization duration). Scanning Electron Microscopy observations of crystals confirmed the trends deducted from the comparison of mean mother liquors flowrates: the promotion of crystal growth over nucleation leads to wider (and fewer small) crystals exhibiting an improved filterability.

Defining the Paragoethite process for iron removal in zinc hydrometallurgy

The previously ambiguous Paragoethite process and residue are defined, and the importance of a fundamental understanding of iron-phase precipitation in hydrometallurgical processing is demonstrated. A review of iron removal in zinc hydrometallurgy and in the Paragoethite process extends previous Paragoethite process studies and provides a brief overview of the iron-phase ferrihydrite, including recent experimental evidence. It is demonstrated that commonly referred to ‘amorphous iron phases’ are likely to be the nanoscale minerals ferrihydrite and/or schwertmannite. In the case of the Paragoethite process, 6-line ferrihydrite constitutes around 40–50% of the residue. Through further characterization and continuous crystallization studies the remaining precipitated components of Paragoethite process residues were found to be solid-solution jarosite phases (containing Pb), silica (containing iron), and at lower pH, poorly crystalline goethite. By using continuous crystallization, the effect of pH on phase formation and on the properties of the residue is documented; emphasizing filterability constraints and the role and reaction of residual calcine. Such studies have permitted a more fundamental understanding of the simultaneous precipitation of ferrihydrite, goethite, and jarosite from acidic hydrometallurgical liquors, including the interplay in this kinetically controlled system, where ferrihydrite is favoured. Reasons for poor filterability are suggested, indicating that the rate of crystallization, and hence, supersaturation, governs phase formation and residue properties. The aggregation-dominated and kinetically favoured nanoscale ferrihydrite particles dictate the physical properties of the residue.

Distinction between Electrostatic and Electrokinetic Effects on the Permeability of Colloidal Packed Beds

AbstractElectrostatic and electroviscous effects can significantly decrease the permeability of packed beds which consist of colloidal particles. This results in poor filterability of colloidal suspensions. Electrostatic effects refer to the dependency of the structure of the packed bed on the particles' tendency to agglomerate or disagglomerate. This tendency is influenced by the particle charge, and thus the pH and the ionic strength of the suspension. Electroviscous effects relate to the increased flow resistance of the pores due to a streaming potential being established when the electrochemical double layer of the particles is sheared off. It is difficult to distinguish electrostatic and electroviscous effects because they are interrelated. The comparison of permeability measurements of both TiO2 and Al2O3 with a classical permeability model demonstrates the influence of the two different effects on permeability.

Using seafood waste as sludge conditioners

In this study, three kinds of seafood wastes (shrimp shell particles, oyster shell particles, and internal bone particles of squid) were added to dewatered sludge preconditioned with chemical conditioner (alum or ferric chloride). The specific resistance of sludge dewatering was calculated to evaluate the effectiveness of sludge dewatering. The result showed that adding chemical conditioners alone caused noticeable pH decrease and resulted in a conditioned sludge with poor filterability. The addition of oyster shell or internal bone of squid to chemically preconditioned sludge efficiently improved sludge dewatering. This result was possibly due to both the availability of alkaline and the function as skeleton builder provided by these two waste solids. Particle sizes (0.59-2.0 mm) of oyster shell and internal bone of squid were found to have insignificant effect on sludge dewatering.

Sr/TRU REMOVAL FROM HANFORD HIGH LEVEL WASTE

The originally proposed removal process for strontium and transuranic species from 241-AN-102 and 241-AN-107 Hanford waste tank supernates was a co-precipitation method. In initial testing, the slurry formed during the strontium and ferric nitrate co-precipitant additions was not filterable. A series of statistically designed tests were performed to evaluate the variables responsible for this poor filterability. These tests also explored strategies to improve the associated decontamination efficiency of the treatment process. These tests revealed that filterability is negatively influenced by ferric ion added to co-precipitate actinide and lanthanide species. The concentrations of sodium and organic complexants were observed to influence decontamination of the supernate. Furthermore, the amount of at least one organic complexant was correlated to the poor filterability. The americium decontamination factors measured following the maximum iron nitrate addition were marginal at levels of precipitant addition that are of practical interest. Based on these results, alternative precipitation schemes were investigated. Reported here is the chosen replacement process, a permanganate precipitation process. A statistically designed series of experiments examined the relationship between three responses and five precipitation parameters. The three responses are precipitate filterability, strontium decontamination, and plutonium decontamination. The parameters varied were the initial sodium and hydroxide concentrations of the waste, and the amount of calcium, strontium, and permanganate introduced. The results reveal an optimum set of conditions for decontamination of strontium and plutonium as well as improved filterability.

Examples of the Selective Preparation of a Desired Crystal Modification by an Appropriate Choice of Operating Parameters

If a compound can crystallize in more than one structural modification, this will generally also be manifested as different morphologies. In a manufacturing process crystal morphology can have a decisive impact on product characteristics such as filterability, drying time, flowability, etc. In addition, it is usually one particular modification that undergoes registration. In this lecture transcript, two examples of the influence of operating parameters on the obtained crystal modification are presented. The first example comprises a food colorant for which four crystal modifications are known. The conventional operating procedure always yielded modification D, which is characterized by extremely poor filterability. Systematic investigations have shown that in suspension each crystal modification is stable within a narrow temperature range. After solid−liquid separation no interconversion of the crystal modifications occurs. Through an appropriate change to the manufacturing process it was possible to rel...

Characterization and treatment of lime sludge dewatering effluents

With ever increasing regulatory constraints on the disposal of residuals produced during water treatment, the cost of handling, treatment, transport, and disposal of these residuals has become a significant portion of overall water treatment costs. In plants practicing lime softening, a major source of residuals is lime sludge. Of the many options proposed for the management of lime sludges most include sludge dewatering. The dewatering process produces effluents that also must be disposed of. This paper presents the results of the characterization of dewatering effluents from a large water treatment plant. Also presented are treatment and management options which were evaluated through designed bench-scale experiements.The quality and quantity of supernatant effluents from the thickener and centrate from the centrifuge were determined. It was found that the supernatant is composed predominantly of calcium ions and caustic alkalinity which can be treated through pH adjustment. The centrate was found to be of much poorer quality with poor settling and filterability properties. These qualities were found to be mostly attributed to the high organic content of the centrate. Bench-scale tests found that polymer pretreatment could substantially improve both the settleability and filterability of the centrate. Key words: water treatment, sludge dewatering, softening, polymers, sludge conditioning.

The Sterile Filtration and Packaging of Beer into Polyethylene Terephthalate Containers

This paper describes the successful practical development of a system for the sterile filtration and aseptic packaging of beer into 2-L polyethylene terephthalate (PET) bottles. The major factors resulting in poor filterability were found to be colloidal carbohydrates and the use of coarse grades of kieselguhr in a single-pass filtration regime. The filterability of the beer through high-capacity prefilters followed by 0.45-μm Millipore membrane filters was greatly improved by addition of μ-glucanase in the mash tun and optimization of the single-pass kieselguhr filtration. Microbiological stability of the beer was achieved primarily by filtration through 0.45-μm Durapore membranes and secondly by adherence to stringent quality assurance procedures with regard to the filling operation. Although the specification of nil microorganisms in the bottle was not always achieved, no beer spoilage was observed. These microorganisms possibly found ingress through contaminated bottles and closures. Our experience supports the findings of similar operations showing that the success of sterile filtration and aseptic packaging lies in good “quality assurance” procedures.