K. Grolle

Properties of acid casein gels made by acidification with glucono-δ-lactone. 1. Rheological properties

The effects of gelation temperature (20, 30 or 40 °C), assay temperature, concentration of glucono-δ-lactone (GDL) added, and NaCl concentration on the rheological properties of acid casein gels were studied at small and large deformations. Gels prepared at a high incubation temperature had very low storage moduli (G′), whereas those made at a low incubation temperature had extremely high G′ values. A higher concentration of GDL resulted in faster gelation but slightly lower G′ values of aged gels. Addition of NaCl resulted in longer gelation times and a slower rate of increase of G′. Cooling of gels prepared at 30 or 40 °C resulted in an increase in G′. However, for gels formed at 20 °C, G′ decreased initially on cooling but returned to its original value on holding at 5 °C. The loss tangent (tan δ) of gels formed at 20 or 30 °C was independent of frequency; however, for gels formed at 40 °C, tan δ was lower at low frequencies. As gels were cooled to 5 °C, tan δ increased. Fracture stress (σfr) of gels formed at 20 °C was much greater than that of the gels formed at higher temperatures. Heating gels to temperatures higher than the gelation temperature resulted in a decrease in σfr. At low gelation temperatures, young gels had very high (σfr values.

Properties of acid casein gels made by acidification with glucono-δ-lactone. 2. Syneresis, permeability and microstructural properties

Syneresis of casein gels made by acidification with glucono-δ-lactone (GDL) was studied in relation to gel structure as derived from permeametry and confocal scanning laser microscopy (CSLM). Gels made at 40 °C exhibited ‘spontaneous syneresis’ with wheying-off almost immediately after gelation, while those formed at 30 °C exhibited little syneresis and only after it was initiated by wetting the surface. Syneresis decreased with a reduction in the pH of gels (increasing amount of GDL added). Gels cooled to 5 °C (before initiating syneresis) and low pH gels exhibited ‘negative syneresis’, i.e. an increase in the height of the gel after wetting. Addition of NaCl had little effect on syneresis, except at pH values > 4.6, where gels with added NaCl exhibited stronger syneresis than those made without added NaCl. Higher gelation temperatures resulted in a far greater permeability coefficient (B), indicating the presence of large pores in these gels. Gels formed at low temperatures had a very low B. Addition of NaCl, at all gelation temperatures, markedly reduced B. Confocal scanning micrographs showed that gels made at high gelation temperatures had large pores, many > 20 μm. At low gelation temperatures, the pores were small, mostly < 5 μm. Fractal aggregation theory was used to explain some of the results, especially the rearrangement of aggregated particles at an early stage of the gelation process, i.e. over relatively short distances. It was concluded that gelation temperature had a large effect on this rearrangement. At low temperatures (e.g. 20 °C), rearrangement did not occur, whereas it was already extensive at 30 °C, implying that the ‘building blocks’ of the fractal gel consisted of dense aggregates of, say, 25 casein particles. This resulted in increased permeability. It was also concluded that the syneresis occurring at 30 °C is primarily due to consolidation of the gel network under its own weight, which is soon counteracted by the stress induced by the deformation of this network. Gels formed at higher temperatures may be unstable and show spontaneous syneresis, presumably because some of the strands in the gel network were weak enough to break. No conclusive explanation could be given for the effects of NaCl concentration and pH on the properties of acid casein gels.

Oil spill dispersants induce formation of marine snow by phytoplankton-associated bacteria

Unusually large amounts of marine snow, including Extracellular Polymeric Substances (EPS), were formed during the 2010 Deepwater Horizon oil spill. The marine snow settled with oil and clay minerals as an oily sludge layer on the deep sea floor. This study tested the hypothesis that the unprecedented amount of chemical dispersants applied during high phytoplankton densities in the Gulf of Mexico induced high EPS formation. Two marine phytoplankton species (Dunaliella tertiolecta and Phaeodactylum tricornutum) produced EPS within days when exposed to the dispersant Corexit 9500. Phytoplankton-associated bacteria were shown to be responsible for the formation. The EPS consisted of proteins and to lesser extent polysaccharides. This study reveals an unexpected consequence of the presence of phytoplankton. This emphasizes the need to test the action of dispersants under realistic field conditions, which may seriously alter the fate of oil in the environment via increased marine snow formation.

Fast anaerobic sludge granulation at elevated salinity

It is commonly accepted that high salt concentrations negatively affect microbial activity in biological wastewater treatment reactors such as upflow anaerobic sludge blanket (UASB) reactors. Microbial aggregation in such reactors is equally important. It is well documented that anaerobic granules, when exposed to high salinity become weak and disintegrate, causing wash-out, operational problems and decreasing process performance. In this research, the possibility of microbial granule formation from dispersed biomass was investigated at salinity levels of 5 and 20xa0g Na+/L. High removal efficiencies of soluble influent organics were achieved at both salinity levels and this was accompanied by fast and robust formation of microbial granules. The process was found to be stable for the entire operational period of 217 days. As far as we know this is the first time it has been demonstrated that stable granule formation is possible at a salinity level as high as 20xa0g Na+/L. Methanosaeta was identified as the dominant methanogen at both salinity levels. Streptococcus spp. and bacteria belonging to the family Lachnospiraceae were identified as the dominant microbial population at 5 and 20 and g Na+/L, respectively.

Efficiency of additives and internal physical chemical factors for pit latrine lifetime extension

Pit latrines are the most common form of on-site sanitation, but are blighted by the problem of pit fill-up. Little is known about what factors and conditions affect decomposition of pit content and thus govern pit filling, but the liquid–mass balance is the key factor. Under laboratory conditions the effect of inorganic and biological additives and the effect of physical chemical factors on solids hydrolysis of black water and human faeces were investigated to establish the potential of these to extend pit latrine lifetime. Additives did little or nothing to enhance net solids hydrolysis in batch tests or to reduce pit fill height in miniature simulated pit latrines. Physical chemical factors such as redox condition and initial pH increased solids hydrolysis, whereas temperature and substrate moisture did little. Since additives need contact with the substrate to act, measurements on faeces crust formation speed and strength were performed and showed that crusts formed within three hours and persisted af...

Removal of organic compounds from shale gas flowback water

Ozonation, sorption to granular activated carbon and aerobic degradation were compared as potential treatment methods for removal of dissolved organic carbon (DOC) fractions and selected organic compounds from shale gas flowback water after pre-treatment in dissolved air flotation unit. Flowback water was characterised by high chemical oxygen demand and DOC. Low molecular weight (LMW) acids and neutral compounds were the most abundant organic fractions, corresponding to 47% and 35% of DOC respectively. Ozonation did not change distribution of organic carbon fractions and concentrations of detected individual organic compounds significantly. Sorption to activated carbon targeted removal of individual organic compounds with molecular weight >115u202fDa, whereas LMW compounds remained largely unaffected. Aerobic degradation was responsible for removal of LMW compounds and partial ammonium removal, whereas formation of intermediates with molecular weight of 200-350u202fDa was observed. Combination of aerobic degradation for LMW organics removal with adsorption to activated carbon for removal of non-biodegradable organics is proposed to be implemented between pre-treatment (dissolved air floatation) and desalination (thermal or membrane desalination) steps.