Filtrate Clarity Research Articles

Depth filter material process interaction in the harvest of mammalian cells.

Upstream advances have led to increased mAb titers above 5g/L in 14-day fed-batch cultures. This is accompanied by higher cell densities and process-related impurities such as DNA and Host Cell Protein (HCP), which have caused challenges for downstream operations. Depth filtration remains a popular choice for harvesting CHO cell culture, and there is interest in utilizing these to remove process-related impurities at the harvest stage. Operation of the harvest stage has also been shown to affect the performance of the Protein A chromatography step. In addition, manufacturers are looking to move away from natural materials such as cellulose and Diatomaceous Earth (DE) for better filter consistency and security of supply. Therefore, there is an increased need for further understanding and knowledge of depth filtration. This study investigates the effect of depth filter material and loading on the Protein A resin lifetime with an industrially relevant high cell density feed material (40 million cells/ml). It focuses on the retention of process-related impurities such as DNA and HCP through breakthrough studies and a novel confocal microscopy method for imaging foulant in-situ. An increase in loading of the primary-synthetic filter by a third, led to earlier DNA breakthrough in the secondary filter, with DNA concentration at a throughput of 50 L/m2 being more than double. Confocal imaging of the depth filters showed that the foulant was pushed forward into the filter structure with higher loading. The additional two layers in the primary-synthetic filter led to better pressure profiles in both primary and secondary filters but did not help to retain HCP or DNA. Reduced filtrate clarity, as measured by OD600, was 1.6 fold lower in the final filtrate where a synthetic filter train was used. This was also associated with precipitation in the Protein A column feed. Confocal imaging of resin after 100 cycles showed that DNA build-up around the outside of the bead was associated with synthetic filter trains, leading to potential mass transfer problems.

A Novel Flux That Determines the Physico-Chemical Properties of Calcined Diatomite in Its Industrial Use as a Filler and Filter Aid: Thenardite (Na2SO4)

Diatomite needs to go through the flux-calcination process in order to increase its functionality in some specific applications such as filter aids. In this study, the effects of the thenardite, which was used for the first time as a flux in the calcination of diatomite, and widely used soda ash on the industrially important physico-chemical properties of diatomite were investigated. Samples taken from two diatomite deposits in the Aegean region of Turkey (Seydiler diatomite from Afyon and Sarayköy diatomite from Denizli) were used in this study. In raw and calcined diatomite samples, geochemical and mineralogical composition and parameters such as colour, grain size, morphology, specific surface area, permeability and wet cake density were characterized. It was found that thenardite was more effective than traditionally used soda ash in improving whiteness (L* = 98.20) and filtrate clarity (wet cake density = 0.378 g/cm3). However, higher permeability (k), i.e., higher filtration rate, was obtained in diatomite calcined with soda ash (k = 0.97 µm2). Fluxes had different effects on different diatomite species. The necessity of choosing flux type depending on the application area and the desired properties from diatomite was demonstrated.

Influence of Particle Size and Pressure Drop in Cake Filtration Process on Removal of Suspended Solids in Anaerobically Digested Palm Oil Mill Effluent

Palm oil mill effluent (POME) poses a great threat to the environment. However, it contains valuable resources such as energy, water and nutrients that could be recovered for sustainable development. Currently, anaerobic digester has been employed to recover the energy potential in POME. However, the presence of suspended solids in the digestate hinders the downstream nutrients recovery process. In that light, cake filtration process appears to be an attractive option for the removal of suspended solids in the digestate. Hence, this paper studied the performance of cake filtration in removing suspended solids at different pressure condition and particle size of perlite. The effectiveness of cake filtration process was evaluated based on the quality of filtrate (turbidity and total suspended solids (TSS)) and filtration flux. In this study, perlites of different particle size distribution (FP3, FW6, FW20, and FW50) were used as both precoat and body feed. The amount of precoat and body feed were chosen as 1 g each. The filtration process was carried out at different pressure condition (2 – 5 bar). It was found that perlite with the finest particle size (FP3) achieved up to 90% of turbidity and TSS removal due to the formation of more compact cake filtration layer. On the other hand, larger perlite FW50 recorded lowest removal efficiency due to its porous cake layer, though this resulted in higher filtration flux. Generally, the increase in pressure drop resulted in higher flux but at the same time led to drastic initial flux decline due to the quick cover up of filtration voids. The outcomes from this study show that it is wise to consider the effect of particle size distribution and pressure drop in order to achieve high clarity of filtrate as well as high filtration flux.

Permeability distribution for filter media characterization in solid liquid filtration

In solid liquid filtration, textiles represent a key element of the setup where it represents the barrier between disperse solid particles and the filtrate. Among other characteristic textile data, the specific flow at standard test conditions is relevant information of filter performance. Nevertheless filter media with comparable characteristic data may exhibit quite different filter performance in terms of filtration rate and filtrate clarity. For a better description of the interaction between filter media and suspension the determination of the permeability distribution (PD) is proposed. This characteristic function is derived from filtration tests where the filtrate is obtained cumulatively over time at constant pressure. Experimental data show that for the same suspension different filter media with different mean permeability show different permeability distributions but also result in different specific cake resistance.

Effects of fluxes on the structure and filtration properties of diatomite filter aids

Diatomite filter aids were prepared using raw diatomite and various fluxes. The effects of composition, amount and granularity of the flux on the micro-structure and filtration performance of the diatomite filter aids were studied. Filter aids with high flow rate and filtrate clarity were successfully obtained when 7wt. % of Na2CO3 flux was employed. It was shown that opal in the diatomite was converted to cristobalite in the presence of flux at 1000°C, being similar to the formative process of silicate glass. The additive alkali ions from the flux are believed to partially break SiOSi chains of the opal at a high temperature and then recombine the broken structure to a hexatomic ring mesh structure during the cooling process, which is significative to control the phase composition for preparation of diatomite filter aids.

Wastewater filtration performance of multilayer glassy microporous filters

The glassy composition (quartz, clinoptilolite and frit glass mixture) provides a filter having glassy pore wall microstructure and thus enables easily cleaning through the filter recovery by back flushing. The filter was obtained as multilayer compaction by one step slip cast-processing where a cylindrical filter, consisting of filtration layer on granular assemblies with specific interlayer was shaped by a fine particle migration phenomenon. The multilayer compaction has low resistance to liquid flow and thus the filter great potential to use for wastewater filtration. It is known that high capacity filtration also requires correct pore size/interval with respect to filtered particles. In this study, a wastewater overflow from marble factory (0.035 wt.% of solid with a size distribution of 0.58–1.46 μm) was filtered by different pore sizes of the glassy filters (pore size intervals: 0.4–10 μm, 0.2–4 μm, 0.1–1.5 μm and 0.04–2 μm) and significantly different filtering capacities was obtained; the irreversible fouling capacities were determined between 2.9 and 8.5 m 3 of filtrate per m 2 of the filter area through the filtration produced 5 min intervals. The filtration pressure was 5 bar and backflushing was achieved at 1 bar. The high filterability (8.1 m 3/m 2 in 5 min) with high filtrate clarity (∼0.5 nephelometric turbidity units) could be obtained using finer pore sized filters. The large size filter was seriously clogged during the filtration.

Improvement in filtration characteristics of diatomite by calcination

This paper examines the calcination and filtration characteristics of diatomite. For this purpose, diatomite ore was calcined at 1000°C in order to improve the material characteristics for use in filtration. The physical, chemical, thermal and micro-structural features of the raw and the calcined diatomites were then determined to compare them with those of the commercial filter aids currently used. In order to determine filtration efficiency of the diatomite samples, several filtration tests were carried out together with the beer samples and the commercial filter aids taken from a leading beer factory in Turkey. It is shown that the calcined diatomite could successfully be used for beer filtration after suitable arrangement of the particle size distribution, such that the highest possible flow rate and filtrate clarity are obtained.

Fabrication of glassy ceramic membrane filters for filtration of spring water with clogging phenomena

Ceramic membrane filters consisting of a filtration layer of varying thickness coated on a tubular porous support made of quartz-based materials and with a pore size of about 10 μm were fabricated. The filtration performance for spring water clarity was examined. The coatings were prepared by a filtration process with a dilute particle suspension of quartz-natural zeolite–lead borosilicate glass mixture. The filter matrix was of quartz type and the additives (frit glass and zeolite) made the filters with glassy pore walls as the sintering temperature applied was above their fusion temperature. The pores of the filtration layer have a relatively coarse size distribution and thus lead to clogging phenomena within the glassy pores during filtration operation. The pore clogging is a benefit for producing clear filtrate and the glassy pore walls favour the filter cleaning and recovery. It was observed that a sufficiently thick coating (>62 μm) was required for good enough filtrate clarity (0.2 NTU turbidity) and cleaning of the filter was possible by filtrate backflushing and air blowing.

Separation technologies for sludge dewatering

Particles in sludge feeds interact strongly one with another to prevent settling and offer a significant resistance to filtration and compression. This leads to the need for dewatering forces to be compressive ones applied directly to the networked solid phase; sometimes shear forces can be an assist dewatering. Designs of filtration equipment most suitable for sludge dewatering have evolved to meet the intrinsic characteristics of sludges, the most important of which are their compressibility and fine particle sizes, which lead to cakes with extraordinarily high solids contents close to the filter medium. Hence, the membrane plate press, the belt filter and the decanter centrifuge have become most widely accepted machines for sludge dewatering. Filter presses tend to yield a drier solids discharge, but the level of dryness depends on the sludge properties. The same feed properties dictate the need for chemical pre-treatment to ensure the highest rates of dewatering and best clarity of filtrate, and correct choice of filter cloth is also crucial in these respects.

Effect of calendering of filter cloth on transient characteristics of cake filtration

In this article, the effects of a filter fabric calendering treatment and the permeability of filaments with regards to the particle deposition phenomena onto or into filter fabrics at the initial stage of filtration are conducted quantitatively using a microscopical forces analysis. The flow pattern and the resistance to fluid flow in the calendered interstice were obtained numerically by using the fluid-flow software FLUENT™. Based upon the numerical data of continuous phase, a program is devised to simulate the transient behaviours of pore clogging and cake formation by ways of the Lagrangian approach and this estimates the change of filtrate clarity at the initial stage of filtration for various calendered fabrics porosities and various filament permeabilities. Results show that in the case of tightly woven filter cloths, the flow is predominantly through the yarns of the cloth; while flow will generally be directed around the yarns of a loosely woven cloth, especially if the yarn is twisted tightly. Therefore, filtrations with tightly woven but loosely twisted yarn can increase the unfavourable but inevitable clogging problem. The simulated results further show that although the filtration resistance of woven filter fabric increases after calendering, the permeability is rectified and the clogging of the filter pores is also improved. After the calendering finishing of the filter fabric has taken place, only the cake formation mode in accordance with the law of blocking for all types of pore is evident shown. The critical concentration proposed by previous investigators is not observed for the calendered filter fabrics.

Relating quality, capacity and energy consumption of oil filters

In the theoretical part of the paper a simple theory is presented relating filtrate clarity, filter capacity and energy consumption. The particle size distribution is subdivided in coarse, intermediate and fine particles. The key role play the intermediate particles who can enter and clog the filter medium. This combined with a layered cake model selects complete blocking as the filtration mechanism for the intermediate particles. In the experimental part results are given on the Multipass flat cell filtration of SAE 5–80 test dust in oil, monitoring upstream and downstream pressure and particle concentration as a function of time. For the chosen filter media and within the experimental range of flow and concentration the simple theory can be applied successfully to these SAE oil filtration experiments.

Methods of enhancing the recovery of plasmid genes from neutralised cell lysate

In this study we have investigated the use of flotation and filtration, singly and combined, to enhance the separation of plasmid containing liquors from neutralised lysates with very different levels of solids. Filtration of crude neutralised lysates, containing roughly 100 g l−1 solids, through various diatomaceous earth and cellulose precoat materials was invariably accompanied by severe loss of plasmid through adsorption and/or absorption. The use of more refined and inert filter aids did not alleviate these problems. The finest filter aid, Celatom FP-1SL, gave the best compromise of filtrate clarity (solids content of 0.05 g l−1) and plasmid purity (71%) and was selected for further studies involving combined use of flotation and filtration. Removing the vast bulk of solids prior to filtration by flotation of the floc and draining of the plasmid liquor beneath, impacted dramatically on the filtration performance. Though systematic reductions in the solids challenge per unit filter area were accompanied by increased flux, elevated levels of solids extrusion, chromosomal DNA and protein contamination were also observed, and losses of plasmid to filter aids were still high. We have observed that increasing the scale of operation during lysis and neutralisation from 0.3 or 0.6 l to 15 l is accompanied by significant improvements in separation of cell debris solids from the plasmid and increased recoveries of the plasmid containing liquor. At the latter scale, the drained liquor contained ∼80% of the plasmid and the solids content was only 0.2 g l−1.

Effects of filter additives on cake filtration performance

Effects of various additives, such as diatomaceous earth, inorganic adsorbent, and polymeric flocculant, on cake filtration performance were evaluated. By performing the standard vacuum filtration experiments under a constant pressure condition, we quantified their ability to reduce cake compressibility and to remove fine particulate matters. From the flux decline curves obtained, we used modified Ruth equation to determine the cake compressibility index. The filtrate clarity was quantified by measuring its turbidity spectrophotometrically. Diatomaceous earth filter aid was very effective in reducing the compressibility thereby improving filtrate flux. Calcium phosphate adsorbent was more effective in clarity improvement than in flux enhancement, whereas an anionic flocculant was effective in both aspects. When these additives were used together, the expected additive, synergic effect was not realized. However, about 3.5 times higher initial flux and 6-fold improved clarity were obtained as compared to the control experiment. Experimentally obtained flux decline curves were perfectly fitted into one of the Hermia’s blocking filtration law equations. Also, it was experimentally observed that the compressibility reduction improved filtrate clarity in a linear fashion. This type of approach is useful to quantitatively determine each additive’s characteristics and thus to maximize the performance of cake filtration operations.

Effect of woven structure on transient characteristics of cake filtration

Three-dimensional particles deposition on four basic woven structures was studied numerically by analyzing forces acting on the depositing particles and was applied to estimate the change of clarity of filtrate at the initial stage of filtration. The effects of woven structures, feed concentration and particle/pore size ratio on the transient behavior of cake filtration and the variation of medium resistances at the beginning stage of cake filtration were analyzed quantitatively. The simulated results show that the filtration period at the initial stage can be divided into the three modes of standard pore blocking, intermediate blocking and cake formation in accordance with the law of blocking for all types of pores. Furthermore, the critical concentration proposed by previous investigators is also confirmed quantitatively in this study.

Crossflow microfiltration of beer: Laboratory-scale studies on the effect of pore size

For a given type of crossflow microfiltration membrane, increasing the pore size leads to improved filtration rates and declining clarity. With Ceramem ceramic 0.5 μm filters, very bright filtrate and near-sterility (99.99% removal of Acetobacter BS011) are achieved, with no loss of beer components. Non-sterilising filtration can be achieved using membranes of pore size between 0.5 and 1 μm, with slightly poorer filtrate clarity. Conditioning tank bottoms can be filtered using the 1.3 μm membrane. An economic assessment indicates that the replacement of powder filtration with crossflow systems using ceramic membranes is attractive.

Clarification and Decontamination of Poultry Chiller Water for Recycling

The chilling operation in poultry processing involves dipping birds in slush ice for rapid removal of body heat. The United States Department of Agriculture Food Safety and Inspection Service (USDA/FSIS) permits recycling of reconditioned chiller water to meet fresh water intake requirements, thereby reducing refrigeration, water use, and liquid waste effluent. Laboratory scale filtration experiments used four types of perlite filter aids applied as a precoat and as body feed (filter aid mixed with the water entering the filter). Results showed that rate of filtrate flow dropped rapidly regardless of type used. Rapid filtrate flow lasted only 20 min from the start of a cycle, suggesting that the frequent cycling and application of a fresh filter aid precoat with each cycle would use large quantities of filter aid. Mean filtration rate defined as the ratio of filtrate volume to length of filtration cycle at a cycle time of 20 min was 24.1 L/min (m2 filter area) when the finest filter aid was used. Use of this filter aid also resulted in filtrate clarity and total aerobic count reduction, which were consistently within the range specified under FSIS guidelines for recycling. Mean filtrate flow during a 20-min cycle was 39.8 L/min (m2 filter area) when a slightly coarser filter aid was used; filtrate clarification was adequate. However, total microbial reduction sometimes fell below 60%, suggesting possible use only when microbicides are added to the reconditioned water prior to recycling.