Gel Strength Measurements Research Articles

Formulation and Evaluation of Gastroretentive In Situ Gelling System of Ketoprofen

Abstract A revolutionary concept for achieving long-term medication release is the gastroretentive in situ gelling system. The goal of this research was to formulate and test a gastroretentive in situ gel for ketoprofen delivery to targeted site to increase the residence and delivery time. Ketoprofen gastroretentive in situ gels were synthesized using a cation-driven gelation approach using various combinations and concentrations of polymers such as gellan gum, sodium alginate, and hydroxypropyl methylcellulose (HPMC) K100M. Visual appearance, pH, viscosity, in vitro gelation, in vitro buoyancy, drug content, density measurement, gel strength measurement, water uptake, and in vitro drug release were all evaluated. The total floating time was more than 12 h, with a floating lag time of less than 2 min. The formulations showed pH ranging from 6.89 to 7.61 and drug content ranging from 82.01% to 95.53%. For 11 h, the percent cumulative drug release of formulations F5 and F14, which contained a greater concentration of polymer sodium alginate (1.5%) and a combination of gellan gum and HPMC K100M (0.175% and 0.2%), was 84.10% and 85.49%, respectively. In vitro dissolution experiments and stability investigations both revealed no significant changes in drug content. The findings revealed that the formulated in situ gels aided in extending gastric residence duration, allowing the drug to be released in the stomach.

Fabrication of flavour oil high internal phase emulsions by casein/pectin hybrid particles: 3D printing performance

In this study, three-dimensional (3D) printable oil/water (O/W) high-internal-phase emulsions (HIPEs) (internal phase fraction = 75%) were fabricated using casein (3% w/v)/pectin (1–5% w/v) hybrid particles with flavour oil. The morphologies of the HIPEs, revealed by confocal laser scanning microscopy (CLSM) and cryo-scanning electron microscopy (cryo-SEM), indicated that the casein/pectin hybrid particles were mainly distributed on the interface of oil droplets. Additionally, the results of rheological and gel-strength measurements indicated that the viscosity (ranging from 1316.51–0.21 to 4301.84–0.79 Pa.s) of HIPEs increased with increasing pectin content (from 0% to 4% w/v), and the gel strength of printed HIPEs increased (from 10.37 to 21.19 g) with increasing pectin (from 1% to 5% w/v). The developed HIPEs were applied for 3D printing and the thus-printed objects could adequately maintain the designed shape and structure. The developed 3D printable HIPEs have excellent potential applications in the food, medical, and cosmetic industries.

A Brief Review of Gas Migration in Oilwell Cement Slurries

Gas migration in oil and gas wells is defined as gases and/or fluids from adjacent formations invading a freshly cemented annulus. During well completions, gas and/or fluids can migrate to zones with lower pressure or even to the surface. Static gel strength (SGS), related to the yield stress of the cement, is a widely accepted measurement used to predict and minimize gas migration. In this review article, we look at the mechanisms and some possible solutions to gas migration during oil and gas well cementing. The use of static gel strength (SGS) and experimental measurements for SGS and wellbore pressure reduction are discussed. Rheological properties, including the yield stress and the viscosity of cement slurries, are also briefly discussed. Understanding the rheological properties of cement is complex since its material properties depend on cement type, as well as the shape and size distribution of cement particles. From this brief review, it is evident that in order to reduce free water and settling of the cement particles, to lower fluid loss, and to develop compressive strength in the early stages of cementing, an optimal cement slurry design is needed. The SGS test is a standard method used in estimating the free water in the well and could be a reference for gas migration reduction for oilwell cement slurries.

Comparison of Gel Preparation Methods on Gel Strength Measurement of Carrageenan

This study aims to develop a carrageenan gel strength test method with an emphasis on the carrageenan gel preparation method for measurement. The gel was prepared by comparing the two heating temperatures (80 °C and 90 °C), heating devices (waterbath and hotplate) and measurement (with container and without container). The results showed that there were no difference between cooking temperatures of 80 °C and 90 °C, but heating at 80°C obtained a lower deviasi standard. The use of hotplate and waterbath were not significantly different resulted in gel strength, but the use of hotplate had a slightly larger variation than waterbath. Measuring the strength of the gel that was still in the crystal container and removed from the container were not significantly different, but measurements with the gel condition were still in the container obtained more accurate test results. Based on the results of this study it can be concluded that the carrageenan gel preparation technique by heating at a temperature of 80 °C using a waterbath or hotplate is the best preparation test method. Meanwhile, the gel does not need to be removed from the container before being measured using a texture analyser. The development of this method can be used as a standard gel preparation method for measuring the strength of carrageenan gel.

Experimental analysis of cassava starch as a fluid loss control agent on drilling mud

This study designed the effective fluid loss agents for controlling fluid loss. Various polymers have been used as additives using natural polymer from cassava starch. Bulky Cassava was cleaned with water and it was grounded, filtered, dried, and sieved to obtain suitable starch additive size. filtration loss and mud cake test was carried out under Low Pressure Low Temperature (LPLT) apparatus. The sample was separated to accommodate aqueous phase after 30 min and the thickness of mud cake on the filter paper that has been installed on the LPLT device. for plastic viscosity, yield point and gel strength measurement were completed using Fann VG Meter apparatus for measuring shear stress. the rotor speed was set by 600, 300, 200, 100, 6 and 3 RPM. The results showed that filtration loss obtained for 6.8–5.6 ml, the value of mud cake thickness was 0.155–0.135 cm, the value of plastic viscosity was 10–20 cp, the value of yield point was 5–15 lb/100 ft 2 and the value of gel strength was 0.4–0.6 lb/100 ft 2. Addition of cassava starch mass to the mud can reduce the filtration loss, mud cake and canincrease the plastic viscosity, yield point and gel strength.

Improving the rheological properties of alkali-activated geopolymers using non-aqueous fluids for well cementing and lost circulation control purposes

Typical alkali-activated low-calcium fly ash (AAF) geopolymer formulations are yet to deliver acceptable rheologies for applications such as oil and gas well cementing, where the cement slurry needs to be pumped, and few effective superplasticizers have been identified. The work reported here centers on the discovery that the rheological properties (mixability and pumpability) of AAFs can be significantly improved by incorporating an organic-based non-aqueous fluid (NAF). NAFs such as oil-based muds and synthetic-based muds are water/brine-in-oil invert emulsions that are widely used in the oil and gas industry for drilling and completion operations. Adding NAF can significantly improve the rheological properties of AAF geopolymers, to the point where the rheology of the mixture approaches that of a Portland cement slurry. Overcoming the poor pumpability issue of AAF opens up a large variety of well cementing applications for AAF slurries including primary cementation and plug cementing in severe lost circulation zones.To modify the gelation and setting characteristics multiple fly ash sources and activators were considered in this study. The alkali activators tested in this study were sodium hydroxide and sodium hydroxide with addition of liquid or solid form sodium silicates. Sodium hydroxide activated AAFs showed improved rheological properties with the addition of NAFs. The liquid sodium silicate activated AAFs resulted in unfavorable rheology readings, gel strength measurements and accelerated the pumping time in comparison to use of pure sodium hydroxide activator. The addition of NAF further accelerated the pumping time, increased the viscosity of the AAF, leading to an unpumpable slurry with a rapid setting behavior. In contrast, activation with solid sodium silicate did not negatively affect the rheological behavior of AAF in the presence or absence of NAF. The use of a solid activator showed an initial high consistency peak that broke down with continued shearing. This early high consistency behavior may be exploited to combat lost circulation problems on troublesome oil and gas wells.

PH‐responsive variation of biomineralization via collagen self‐assembly and the simultaneous formation of apatite minerals

ABSTRACTCollagen self‐assembly and simultaneous mineralization by incubating a mixture containing collagen, calcium, and phosphate ions under physiological conditions, is an effective method to prepare bone‐like biomimetic materials. The formation of fibrils and minerals is related to pH of system. In the present work, we evaluated the effect of pH (7.9–10.4) on biomineralization process and synthesized composites. Turbidity kinetics and X‐ray diffraction (XRD) measurements revealed that increasing pH delayed the crystallization process from nucleation phase to plateau phase because of promoting chelation of Ca2+ with collagen. Typical peaks of phosphate in Fourier transform infrared spectroscopy coupling with characteristic peaks of hydroxyapatite (HAp) in XRD spectra illustrated the formation of HAp after biomineralization. Scanning electron microscopy measurements indicated that the increase of pH promoted the deposition of spherical minerals in fibrils. Especially, the minerals tended to form cluster‐like structure at pH 10.4. The hyp content, Ca and P contents, and gel strength measurements suggested that higher pH promoted the formation of HAp with a Ca/P closed to 1.67 and the prolongation of crystallization gave the time for collagen self‐assembly leading to the increase of gel strength at higher pH (9.4–10.4). These results might provide some new ideas for designing biomimetic materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48876.

Strength, fracture and compression properties of gelatins by a new 3D printed tool

A new test has been developed to determine gel strength and, at the same time, fracture and compression parameters. By using an especially designed probe and standard gelatin gels, we have set up a method to assess gel strength, the cut resistance, simulating a teaspoon, as well as food consistency and chewiness, just in one experiment. In particular, hydrogels of different Bloom degrees, ranging from 90 to 300, were prepared. Gel strength, fracture and compression properties of gelatins were evaluated by a new 3D printed device. A cylindrical-shaped tool and a concentric piston were obtained by means of 3D-printing technology and combined for a fracture/compression test. A device for the classical Bloom test was 3D printed and used for gel strength measurements to find a correlation parameter. The cylindrical-shaped tool has been designed in order to expose to the gelatin surface the same contact area of the classical Bloom probe. Additionally, the optimized test was applied to commercial edible gelatins. The influence of temperature and flavors on gelatin properties was investigated.

An environmental friendly and biodegradable shale inhibitor based on chitosan quaternary ammonium salt

Abstract In this paper, the inhibition of chitosan quaternary ammonium salt (HTCC) in the drilling fluid was studied. The inhibition was evaluated by linear swelling test, mud making test and rolling recovery. The results indicated that the inhibition of HTCC was better than polyether amino, which be used widely in the oil flied as the excellent shale inhibitor. Especially HTCC is an environmental friendly and biodegradable. The inhibition mechanism of HTCC was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, Scanning electron microscopy, Zeta potential, Gel strength measurement analysis. The negative charge in the surface of montmorillonite (MMT) was neutralized by the positive charge. HTCC was absorbed and coated in the surface and intercalated in the interlayer of MMT, which reduced the hydration repulsion of diffuse electric double layer and leaded to the inhibiting hydration of clay. Hydrogen bonding between hydroxyl, amino groups in the HTCC and the surface of clay can be formed in the process. The coordination of electrostatic interaction and hydrogen bonding prevented the water molecules from the gallery of clay, which resulted from the absorption and intercalation of HTCC in the surface and interlayer of MMT. The high molecular weight of HTCC was coated in the surface of MMT, which further expelled the hydration swelling of clay. It kept the high inhibition even if the ether bond hydrolysis partly in high temperature, comparing to polyether amino which the inhibition be reduced.

Experimental Study of CO2-Sensitive Chemicals for Enhanced Sealing of Leakage Pathways in CO2 Geological Storage Process

Many demonstration projects conducted in recent years have proved that CO2 capture and geological storage (CCS) can be an effective technology to reduce the emission of the greenhouse gases. The prospective storage sites under investigation mainly include deep saline aquifers, depleted oil and gas reservoirs and unminable coal seams, which should have huge storage capacity to sequestrate CO2 safely and permanently. Technically, the CCS method is feasible and can be acceptable to the public, but the storage safety and the economics of the CCS projects are of the main concerns. There are mainly three types of leakage pathways, including the failure of injection or other wells in the storage sites, undiscovered faults or fractures and seepages of cap rocks, and newly formed fractures during CO2 injection process. For CO2 storage in depleted oil and gas reservoirs, poor well integrity can be the main reason for CO2 leaks, in which CO2 can be leaked through cracks generated in cement ring or at the interface between casing and cement to upper formations. It is proposed that chemical method can be used to enhance sealing in failed wellbore or to block the leakage in near wellbore formations, since chemicals (solution) can be readily injected into wellbore or to where they are needed to form sealing packs as measures of precaution or emergency remediation. In this study, an innovative method for blocking CO2 leakage is proposed, which is based on CO2-sensitive chemicals to formulate selective agents and can associate with other common technology such as cementing to enhance the sealing of leakage pathways. The CO2-sensitive chemicals are referred to that, when they encounter the leaked CO2 in the formation or in wellbore, reactions will be triggered by CO2 to form gel or solid structure inside the leakage pathways, because CO2 is an active chemical that can take part in reaction or generate acidic environment when it dissolves into the water. The selection and design of the chemicals are based on two mechanisms: (1) certain polymers and resins will take part in crosslink reactions when CO2 appears in their aqueous solution, resulting in gelation or solidification. (2) CO2 can react with certain compounds in aqueous solution, in which precipitation will occur or solid can be produced to form blocking substance. In the paper, the CO2-sensitivity of some selected chemicals have been demonstrated in terms of generation of gels and blocking structures through visualization experiments and gel strength measurements. The chemicals studied include polyacrylamide, sodium aluminate, and phenolic resin. Their blocking capability was evaluated via core and sandpack flooding experiments, and the effects of important influencing factors on the chemical reaction and gelation prevailed at reservoir conditions are investigated, including the formulation and concentration of the chemicals, temperature, pressure and the salinity of formation water. The experimental results show that polyacrylamide and CO2 can react via a cross-linking mechanism, in which gelation with a class H visual strength has been observed at 70°C and 1MPa. Good blocking performance was also achieved at sandpack flooding conditions. The solution of sodium aluminate can react with CO2 and generate solid Al(OH)3 under high pressure and temperature conditions, which can significantly reduce the permeability of sandpacks or form a blockage for the moving CO2. The reaction product of CO2-cured resol phenol-formaldehyde resin exhibited good blocking strength. These results can provide guidelines for the design and deployment of CO2 sensitive chemicals for blocking or enhancing the sealing of CO2 leakage pathways in geological formation and wellbores.

Influence of different pectins, process and storage conditions on anthocyanin and colour retention in strawberry jams and spreads

Strawberry jams and spreads were prepared under reduced pressure at various temperatures (70, 75 and 90 °C, respectively) using amidated, high and low esterified commercial pectins. For their full characterisation, dry matter, ash contents and amounts of selected metal ions were determined. Gel strength measurements were performed, and the products were stored in the dark (+20 ± 2 °C and +4 ± 2 °C, respectively) and under light exposure (+20 ± 2 °C/4500 lux) over a period of 24 weeks. Amounts of monomeric and polymeric anthocyanins were monitored spectrophotometrically, individual anthocyanins were assessed by HPLC-DAD-MSn, and colour measurements were carried out applying the CIE L*a*b* system.Pigments and colour were best retained immediately after processing, when jams were cooked at 70 °C under reduced pressure. Anthocyanin storage stability was generally higher in the jams than in the spreads strongly depending on pectin type and water activity. Storing the products at +4 °C in the dark was indispensable for sufficient colour and pigment retention, while illumination resulted in rapid discolouration.

Design and Evaluation of In-Situ Ophthalmic Gel Containing Carbopol and Methylcellulose as Viscosity Modifier

To increase the bioavailability of the drug in eye it is necessary to increase the residence time of the formulation with minimum solution drainage and untoward disposition of the instilled dose. The reliable method to overcome the above problem is in-situ ophthalmic gel. Combination of carbopol 940, a pH dependent polymer and methyl cellulose A4M, a thermo sensitive polymer were used for present research. The total six batches were prepared and subjected to the evaluation. Rheological studies, gel strength measurement, bioadhesion force measurement, drug content uniformity, in-vitro release study were carried out for all formulations. In-vitro study shows drug release up to 12 hrs. The in-vitro study data treated with various kinetic equations revealed that drug release follows first order diffusion controlled by Fickian diffusion mechanism. The optimized batch is subjected to eye safety evaluation, stability study and comparison with marketed preparation for in-vitro release. The present formulation shows the negligible difference in drug release as compare to the marketed preparation. Hence it is concluded that the present formulation will perform well in the eye upon instillation as in-situ gel.

Nonspecific Activity of Bacillus acidopullulyticus Pullulanase on Debranching of Guar Galactomannan

Pullulanase (EC 3.2.1.41) from Bacillus acidopullulyticus could preferentially remove galactose residues from guar galactomannan (GG), a heteropolymer consisting of polymannan backbone with alternating galactose as single-residue side-chain stubs. The enzyme showed maximum activity at pH 4.5 and 45 degrees C and exhibited Michaelis-Menten kinetics with a K(m) and V(max) of 6.0 mg mL(-1) and 1820 nmol min(-1) mg(-1), respectively. The native and modified GG had a viscosity of 4800 and 3800 cps, respectively. The molecular mass of the enzyme-treated GG varied between 152 +/- 0.5 kDa, and its GLC analysis revealed a significant change in galactose-mannose content of 1:3.8, respectively, similar to that of locust bean gum (LBG). FTIR and solid-state CP-MASS (13)C NMR analyses indicated subtle changes in the conformation of modified GG because of the removal of galactose residues. Gel-strength measurements with kappa-carrageenan showed an improvement in the gelling behavior, similar to that shown by LBG. Debranching of GG by pullulanase is an alternative and inexpensive route to produce modified GG with enhanced functional properties, as a cost-effective replacement for LBG.

Hydrocolloid from leaves of Corchorus olitorius and its synergistic effect on κ-carrageenan gel strength

Hydrocolloid from leaves of Corchorus olitorius was fractionated with ammonium sulfate (50%, w/v) and extracted with distilled water. The yield of the hydrocolloid was 6.0% (w/w) based on dry material. The contents of total carbohydrate, anhydrouronic acid, ash, protein, and moisture of the hydrocolloids were 62.2%, 35.3%, 13.3%, 5.5%, and 16.1% (w/w), respectively. Degree of esterification of 19.4% was calculated assuming that the methoxyl groups were attached to only anhydrouronic acid. When the molecular weight distribution was checked by size-exclusion chromatography on Sepharose CL-4B, the hydrocolloid gave a single peak with a molecular weight of 1860 kDa. The rheological behavior of mixed gels made from κ-carrageenan and the hydrocolloid at a total hydrocolloids concentration of 1% (w/w) was investigated by gel strength measurement. Then it was found that the hydrocolloid exhibited synergy with κ-carrageenan in relation to gel strength.

Comparative study of gelation and cross-link formation during enzymatic texturisation of leguminous proteins

Abstract Isopeptide bonds that resulted from protein cross-linking, catalysed by a microbial transglutaminase (MTG), substantially contributed to the physicochemical modification of leguminous proteins. For the development of texturised vegetable protein (TVP)-based foodstuffs using MTG, valid methods for an efficient control of the gelation process are a prerequisite. Formation of e-(γ-glutamyl)lysine cross-links in a simple food model system, containing proteins from soy [Glycine max (L.) Merr.] or pea (Pisum sativum L.), was monitored by quantification of the e-(γ-glutamyl)lysine bond via HPLC-MS and by determining the depletion of free amino groups during cross-linking spectrophotometrically after derivatisation with o-phthaldialdehyde (OPA). Increasing gel strengths during incubation with MTG were measured via texture analysis. The OPA method proved too unspecific for controlling the enzymatic gelation process of leguminous proteins. Specifically for each substrate, the levels of isopeptide cross-links, detected via HPLC-MS analysis, correlated well with the gel strength of the texturised proteins (R2 = 0.961–0.994). Rapidly measurable, gel strength was shown to be a reliable command variable for managing MTG-induced gelation. Its use also allowed indirect estimation of the degree of feasible cross-linking. Industrial relevance Leguminous proteins represent a valuable alternative to animal proteins for the manufacture of texturised foodstuffs. However, due to the poor gelling properties of the native proteins, their potential is still unexploited. For the development of TVP using MTG, simple gel strength measurements were shown to be a valid tool for the control of the gelation process. For this purpose, unlike OPA determination of free amino groups and LC-MS analysis of isopeptide bonds, tedious sample preparation is not required.

Radiation synthesis and characteristic of IPN hydrogels composed of poly(diallyldimethylammonium chloride) and Kappa-Carrageenan

A new system of IPN hydrogels composed of diallyldimethylammonium chloride (DADMAC) and natural macromolecule, Kappa-Carrageenan (KC) were prepared by γ-irradiation. Their gel fraction and swelling behavior were studied. Elemental analysis and gel strength measurement results showed that there was an amount of KC that remained in the gels and the gel strength was enhanced obviously.

New Method of Measuring Gel Strength of Clay-Based Drilling Fluids and the Determination of their Long-Term Gelation Behaviour

Abstract For avoiding environmental pollution, predominantly water based drilling fluids are employed in drilling operations. If these drilling fluids contain clays as structural agents, contamination by electrolytes or exposure to elevated temperature, or both, can result in more or less severe flocculation and thickening; this phenomenon can cause serious problems during the resumption of circulation, especially after long round trips, as well as swab and surge. For this reason, it is especially important in practice to be capable of predicting the long-term gelation behavior of the drilling fluid on the basis of short-term gel strength measurements. In the present study, it has been shown that reproducible gel data can be obtained only in exceptional cases on water-based clay drilling fluids exposed to electrolytes or elevated temperature, or both, with the use of measuring instruments standardized in conformance with API (such as the Fann V-G Meter, model 35). On the other hand, it has been shown that arbitrarily high gel strength values can be determined reproducibly with the ITE instrument for measuring gel strength of clay suspensions (GMT), because the apparent wall slip is eliminated. On the basis of short-term gel strength values measured with the ITE GMT, the long-term gelation behavior of water-based clay drilling fluids can be predicted with sufficient accuracy by means of the analytical method introduced by Garrison in 1938; this is of particular interest especially after lengthy round trips. Introduction For reasons of environmental protection, water-based drilling fluids are now being used to an increasing extent in drilling operations, even under difficult drilling conditions. As a rule, clays are employed as structural agents in these drilling fluids. For stabilizing the clay against electrolytes or elevated temperatures, or both, protective colloids are added. As a result, the polymers impose their flow behavior on the clay; that is, the differential (true) viscosity of the clay suspensions treated with polymers decreases as a function of the shear stress. Consequently, the clay is then responsible only for the value of the yield point in these systems. If water-based drilling fluids are exposed to electrolytes or elevated temperatures, or both, the protective action of the added polymers may be inhibited; as a result, the flow and gelation behavior of the clay may break through. Especially during long round trip times, the severely gelled drilling fluid can then cause problems with the pumping pressure necessary for resuming the circulation as well as with swab and surge. Hence, there is a need for reliable measuring methods and analytical techniques for predicting the long-term development of the gel strength. In the present study, the standardized API methods for measuring gel strength are first examined for reproducibility of the results. If appropriate measures prove necessary, suitable methods are developed and investigated for measuring the gel strength. Finally, the analytical method of Garrison(1) is examined for its applicability in calculating the long-term gel strength from the results of short-term measurements.

Rheological Properties of Sago Starch

The swelling characteristics and rheological properties of 11 sago starches have been studied and compared to a number of commonly used starches. The swelling power of the sago starches were all very similar except for two samples which were known to contain a lower molecular mass amylose component. The swelling and solubility for these two samples were higher than the rest. The values for sago starches were similar to that for potato and tapioca starch, but higher than maize and pea starch. The storage modulus, G‘, of the sago starches as studied by small deformation oscillation measurements showed a rapid initial increase in G‘ followed by the development of a pseudoplateau. The dependence of G‘ on the molecular mass of the amylose followed the relationship G‘ ∝ M-0.4. Gels were formed only at sago starch concentrations of >3.5%, corresponding to an amylose concentration of ∼ 1.0% and varied with concentration according to the relationship G‘ ∝ C1.8 and G‘ ∝ C2.5 for high and low amylose molecular mass samples, respectively. Gel strength (GS) measurements also confirmed that the minimum concentration for gelation was ∼3.5% and that GS ∝ C2.0. Sago starches showed good freeze−thaw stability compared to other starch types. Keywords: Sago starch; swelling; solubility; gelatinization; gelation; rheology; freeze−thaw stability

Functional stability of temperature-compensated nitrification in domestic wastewater treatment obtained with PVA-SbQ/alginate gel entrapment

Gel beads (3 mm) of PVA-SbQ were cast by entrapment in Ca-alginate beads prior to photo-induced crosslinking of the synthetic polymer. Such beads have maintained their physical integrity, being continuously exposed to domestic wastewater for more than 2 years. Gel strength measurements indicated that the alginate gel network had been degraded and lost. Gel entrapment of homogenized nitrifying sludge gave an immediate 30% loss of activity compared to that of the same sludge kept in suspension, but it reached the same level within 3 days in a sequenced batch reactor. A continuous 4-litre lab-scale reactor containing 25% (v/v) gel-entrapped nitrifying sludge was run successfully fed with ammonium-enriched domestic wastewater for a period of 300 days. At 30°C, the system reached a steady-state activity of 15 mgN pr litre and hour (/Lh) after a month. After reducing the temperature successively to 20 and 10°C, at least 75% of this activity was maintained. Even at 10°C, activities could be increased to 25 mgN/Lh by improving oxygen transfer by increased aeration or stirring, verifying that oxygen transfer should be considered the rate-limiting factor of the system. Despite an organic load of 10–50 mgCOD/Lh during the whole period, heterothropic overgrowth or grazing protozoa could not be detected attached to the beads, even though such organisms were abundant in the sludge leaving the reactor. The system presented may be suitable for specially designed full-scale reactors with short hydraulic retention times, as well as an additive to existing biofilm or activated sludge nitrification plants.

Description and validation of an apparatus for gel strength measurements

The increasing interest in gel-like dosage forms and in systems that undergo gelification upon contact with biological fluids (like hydrogels and hydrophilic swellable matrices) suggests the importance of gel strength measurements. For example, it has been suggested that the strength rather than the viscosity of the gel layer plays a major role in drug release from hydrophilic matrices. Nevertheless, probably due to the lack of a user-friendly and suitable apparatus, the gel strength parameter is not routinely investigated in preformulation and formulation studies of such dosage forms. In the present work, an apparatus, which had been previously designed for the characterisation of industrial polymers, was modified to make it suitable for measuring the gel strength of pharmaceutical systems and its performance was validated under differing experimental conditions. The results of gel strength measurements effected on hydroxypropylmethylcellulose solutions and on κ-carrageenan and carboxyvinyl polymer gels are reported herein.