Effect of temperature and shear on the microstructure of a microbial polysaccharide secreted by Sphingomonas species in aqueous solution

Recent advancement on water filtration membranes: Navigating biofouling challenges

This study investigates the field of antifouling membranes for water filtration and desalination applications, specifically focusing on two-dimensional materials. The study examines the importance of these membranes in the context of climate change and its effects on coastal ecosystems. The occurrence of biofouling in seawater desalination membranes is closely connected to intricate processes influenced by factors such as water quality, microbial communities, hydrodynamics, and membrane properties. Microorganism adhesion initiates the process, which then advances into irreversible attachment and the creation of biofilm. Detached pieces contribute to the perpetuation of fouling. Biofouling is caused by a variety of biomaterials and organics, including bacteria, extracellular polymeric substances (EPS), proteins, and humic compounds. Innovative methods such as surface alterations using two-dimensional materials like graphene and graphene oxide, as well as the use of biofouling-resistant materials, provide promising possibilities. These materials have antifouling characteristics, making them environmentally beneficial options that reduce the need for chemical cleaning. Their application improves the water treatment process by preventing fouling and enhancing membrane performance. Real-world research applications can enhance and optimize these tactics to effectively reduce biofouling in seawater desalination systems, hence improving efficiency and sustainability. This is particularly important in light of climate change and its impact on coastal ecosystems. The findings obtained from the literature review emphasise the utmost significance of tackling biofouling in the face of a changing environment, particularly with regard to microorganisms. Important factors to consider are the selection of coating materials, the implementation of environmentally friendly cleaning solutions made from natural chemicals, and the improvement of pretreatment systems. Green cleaning agents are important eco-friendly alternatives to typical biocides, as they possess antibacterial, antifungal, and antifouling capabilities. Given the existence of climate change, these observations serve as a basis for promoting environmentally friendly methods in water treatment technology.

Evaluation of Viscosity Changes and Rheological Properties of Diutan Gum, Xanthan Gum, and Scleroglucan in Extreme Reservoirs

The chemically synthesized polymer polyacrylamide (HPAM) has achieved excellent oil displacement in conventional reservoirs, but its oil displacement is poor in extreme reservoir environments. To develop a biopolymer oil flooding agent suitable for extreme reservoir conditions, the viscosity changes and rheological properties of three biopolymers, diutan gum, xanthan gum, and scleroglucan, were studied under extreme reservoir conditions (high salt, high temperature, strong acid, and alkali), and the effects of temperature, mineralization, pH, and other factors on their viscosities and long-term stability were analyzed and compared. The results show that the three biopolymers had the best viscosity-increasing ability at temperatures of 90 °C and below. The viscosity of the three biopolymers was 80.94 mPa·s, 11.57 mPa·s, and 59.83 mPa·s, respectively, when the concentration was 1500 mg/L and the salinity 220 g/L. At the shear rate of 250 s-1, 100 °C~140 °C, scleroglucan had the best viscosification. At 140 °C, the solution viscosity was 19.74 mPa·s, and the retention rate could reach 118.27%. The results of the long-term stability study showed that the solution viscosity of scleroglucan with a mineralization level of 220 mg/L was 89.54% viscosity retention in 40 days, and the diutan gum could be stabilized for 10 days, with the viscosity maintained at 90 mPa·s. All three biopolymers were highly acid- and alkali-resistant, with viscosity variations of less than 15% in the pH3~10 range. Rheological tests showed that the unique double-helix structure of diutan gum and the rigid triple-helix structure of scleroglucan caused them to have better viscoelastic properties than xanthan gum. Therefore, these two biopolymers, diutan gum, and scleroglucan, have the potential for extreme reservoir oil displacement applications. It is recommended to use diutan gum for oil displacement in reservoirs up to 90 °C and scleroglucan for oil displacement in reservoirs between 100 °C and 140 °C.

A polysaccharide from Lignosus rhinocerotis sclerotia: Self-healing properties and the effect of temperature on its rheological behavior

This work investigated the self-healing properties of Lignosus rhinocerotis polysaccharide (LRP) and the effect of temperature on its rheological behavior. Dynamic sweep tests (strain sweep, frequency sweep, and time sweep) showed that the LRP/water system possessed self-healing properties due to the entangled network formed by hyperbranched LRP molecular chains. The flow activation energy of LRP solution calculated by Arrhenius equation was shown to decrease with increasing LRP concentration, indicating that LRP solution at higher concentration was less sensitive to temperature. Temperature ramp test exhibited that LRP had a glass transition temperature (T_g) determined as 49.35 °C and the temperature effect was irreversible. Microrheological test revealed that the LRP aqueous solution can form a gel at room temperature with the concentration ≥ 20 mg/mL. This work provided a theoretical basis for the development of LRP-based self-healing materials and facilitated a deep understanding of the temperature effect on rheological behavior of LRP.

Biodiversity and ecology of microorganisms in high pressure membrane filtration systems

High-pressure membrane filtration (reverse osmosis and nanofiltration) is used to purify different water sources, including wastewater, surface water, groundwater and seawater. A major concern in membrane filtration is the accumulation and growth of micro-organisms and their secreted polymeric substances, leading to reduced membrane performance and membrane biofouling. The fundamental understanding of membrane biofouling is limited despite years of research, as the means of microbial interactions and response to the conditions on the membrane surface are complicated. Here, we discuss studies that investigated the microbial diversity of fouled high-pressure membranes. High-throughput amplicon sequencing of the 16S rRNA gene have shown that Burkholderiales, Pseudomonadales, Rhizobiales, Sphingomonadales and Xanthomonadales frequently obtain a high relative abundance on fouled membranes. The bacterial communities present in the diverse feed water types and in pre-treatment compartments are different from the communities on the membrane, because high-pressure membrane filtration provides a selective environment for certain bacterial groups. The biofilms that form within the pre-treatment compartments do not commonly serve as an inoculum for the subsequent high-pressure membranes. Besides bacteria also fungi are detected in the water treatment compartments. In contrast to bacteria, the fungal community does not change much throughout membrane cleaning. The stable fungal diversity indicates that they are more significant in membrane biofouling than previously thought. By reviewing the biodiversity and ecology of microbes in the whole high pressure membrane filtration water chain, we have been able to identify potentials to improve biofouling control. These include modulation of hydrodynamic conditions, nutrient limitation and the combination of cleaning agents to target the entire membrane microbiome.

Flow, dynamic viscoelastic and creep properties of a biological polymer produced by Sphingomonas sp. as affected by concentration

In this work, the influence of the concentration on the flow behaviour, dynamic viscoelastic and creep properties of diutan gum in aqueous solution was investigated. Diutan gum is a biopolymer which belongs to the sphingans group. To know its rheological properties and its microstructure as a function of the concentration is directly related to the current and future applications of this biological polymer. Mechanical spectra showed a crossover point between G' and G″ which changed as a function of diutan gum concentration. A master curve for the frequency dependence on the η* was obtained. The creep compliance results made it possible to deduce the yield stress value and they were fitted to Burgers model. A shear-thinning behaviour was exhibited by diutan gum aqueous solutions, which was fitted to the Carreau-Yasuda model. Higher G', G″, τ₀ and η₀ values and lower ω_c, J_e⁰, γ̇_c and n values were obtained by increasing the gum concentration, it is being possible to modulate the viscoelasticity, viscosity and shear resistance as a function of concentration. A more complex structure with stronger entanglements between macromolecules of diutan was obtained when the concentration of diutan increases.