The kinetics of the polyacrylic superabsorbent polymers swelling in microalgae suspension to concentrate cells density

Construction of injectable starch-based superabsorbent resin with wet adhesion for agricultural application

Superabsorbent resins (SARs) have been developed to improve water management in agriculture. Injectable SARs offer significant potential for enhancing plant growth by penetrating deeply into the soil prior to gelation; however, relevant research remains scarce. In this study, injectable starch-based SARs were synthesised via a straightforward two-step process. Initially, hydrophilic polar groups were grafted onto the starch backbone, followed by crosslinking with pentaerythritol tris [3-(1-aziridinyl) propionate] (PTAP). This approach conferred both injectability and underwater gelation capabilities to the system. By adjusting the starch content, the time required for the gelation precursor to reach clogging and gelation points was significantly extended. Additionally, the effective injection ratio was enhanced, and macromolecular diffusion into water was inhibited, resulting in excellent injectability. The equilibrium swelling ratio of the resin reached 517.62 g/g with high water retention ratio. Because the contact angles of the gelation precursor on wood, glass, and aluminium surfaces were lower than those of water, it effectively displaced interfacial water, enabling strong underwater adhesion to the substrates. The gelation precursor effectively penetrated the crevices of wet sandstone and adhered the fragments without dispersal, highlighting its potential for applications in agricultural water retention and sandstone stabilisation.

Poly (sodium acrylate-acrylamide) hydrogels for enrichment and purification of microalgal biomass in an open system: performance optimization and mechanistic analysis

Super adsorbent polymer gels can be utilized in microalgal culture systems to concentrate and harvest microalgal biomass through water absorption. In open microalgal culture systems, however, bacteria and other non-algal impurities may affect the water absorption efficiency of the hydrogels and the quality of harvested microalgae. This study prepared and tested hydrogels synthesized with varying sodium acrylate (SA) and acrylamide (AM) ratios in open systems to evaluate their biomass harvesting efficacy. Results showed that when WSA:WAM = 10:0, the chlorophyll a (Chl-a) concentration in the harvested microalgal biomass increased by 417.9 %, the Chl-a/VSS ratio increased by 3.7 %, and the concentration of extracellular polymeric substances (EPS) decreased by 9.5 % compared to the pre-harvest period. Additionally, the number of bacteria adsorbed in the hydrogel particles also significantly increased. It indicates that the poly (sodium acrylate-acrylamide) (PSA-AM) hydrogel absorbed both water and non-algal impurities, achieving both concentration and purification of microalgal biomass. Mechanistic analysis revealed that the pore size and ratio of the PSA-AM hydrogel acted as a sieve, separating microalgal cells from other substances such as water, EPS, and bacterial cells. Given that EPS and bacterial cells are more hydrophilic compared to microalgal cells, it may explain that the hydrogel particles absorbed water while also capturing EPS and bacterial cells. Moreover, the PSA-AM hydrogel exhibited superior reusability. In conclusion, this study provides valuable data and a theoretical basis for the application of PSA-AM hydrogel in open microalgal culture systems, which could further promote the purification of PSA-AM in microalgal biomass utilization by optimizing the preparation of hydrogels.

Carboxymethyl chitosan-capped nanoparticles for the preparation of epoxidized rubber dipped products with chemical resistance, barrier and antibacterial properties

Epoxidized natural rubber (ENR), a kind of bio-elastomer, exhibits favorable elasticity, gas tightness and solvent resistance, thereby demonstrating considerable potential for utilization in the rubber industry. However, producing ENR latex products poses significant challenges due to the low dry rubber content and high surfactant concentration in ENR latex. This study addresses these challenges by employing superabsorbent polymer beads as concentration agents to prepare concentrated ENR latex. Additionally, carboxymethyl chitosan is utilized as a bridging agent to securely bind ENR with manganese silicate nanoparticles through the formation of hydrogen bonds. The resulting composite material-based dipped film retains the inherent properties of ENR while exhibiting stable mechanical performance, even exposure to various disinfectants. Notably, the composites exhibit remarkable barrier capabilities and antibacterial properties, effectively disrupting the cellular structures of diverse bacterial species and promoting the healing of infected wounds. Furthermore, this research provides a set of standardized testing methods for rubber-based antibacterial products. These advancements underscore the distinct advantages of the ENR latex production process, highlighting its simplicity, cost-effectiveness, and potential for commercialization due to the affordability of the raw materials.

Performance and feasibility analysis of an integrated airlift microalgae photobioreactor for cultivation and pre-harvesting

Microalgae technology is highly attractive in the realm of wastewater treatment and CO2 removal. However, during the cultivation of microalgae, the phenomenon of light attenuation intensifies with the increasing cell concentration, resulting in a decrement in microalgal growth rate. To maintain high light transmittance and growth rate of microalgae, this study introduces a two-step pre-harvesting process involving flocculation and filtration within an airlift photobioreactor. In this way, the growth performance of microalgae was bolstered by an improvement in light availability, which was increased 1.59 times by harvesting 30% of the microalgae biomass. Additionally, the microalgae productivity was increased 12.3%. By diluting the cationic starch concentration to 3 g L-1, the harvesting efficiency approached levels comparable to those achieved through magnetic stirring, while filtration resulted in a 1.9-fold increase in final biomass concentration. Moreover, a comparative life-cycle assessment of three harvesting methods revealed that the flocculation-filtration method exhibited the lowest global warming potential of -0.09 CO2 eq, positioning it as a viable and low-carbon alternative for microalgae harvesting.

Microalgae harvesting techniques: updates and recent technological interventions

Microalgal biomass has garnered attention as a renewable and sustainable resource for producing biodiesel. The harvesting of microalgal biomass is a significant bottleneck being faced by the industries as it is the crucial cost driver in the downstream processing of biomass. Bioharvesting of microalgal biomass mediated by: microbial, animal, and plant-based polymeric flocculants has gained a higher probability of utility in accumulation due to: its higher dewatering potential, less toxicity, and ecofriendly properties. The present review summarizes the key challenges and the technological advancements associated with various such harvesting techniques. The economic and technical aspects of different microalgal harvesting techniques, particularly the cationic polymeric flocculant-based harvesting of microalgal biomass, are also discussed. Furthermore, interactions of flocculants with microalgal biomass and the effects of these interactions on metabolite and lipid extractions are discussed to offer a promising solution for suitability in selecting the most efficient and economical method of microalgal biomass harvesting for cost-effective biodiesel production.

Hydrothermal hydrolysis of algal biomass for biofuels production: A review

Hydrothermal hydrolysis is an energy-efficient and economical pretreatment technology to disrupt the algal cells and hydrolyze the intracellular compounds, thereby promoting the biofuels production of fermentation. However, complex reaction mechanisms, unpredictable rheological properties of algal slurry, and immature continuous reactors still constrain the commercialization of such a process. To systematically understand the existing status and lay a foundation for promoting the technology, the chemical mechanism of hydrothermal hydrolysis of algal biomass is elaborated in this paper, and the influences of temperature, residence time, total solid content, and pH, on the biomethane production of hydrolyzed algal biomass are summarized. Besides, a comprehensive overview of the rheological behavior of algal slurries is discussed at various operational factors. The recent advances in flow, heat and mass transfer model coupling with the generic kinetics model in continuous reactors and the application of energy-saving strategies for efficient algal biomass pretreatment are detailed reviewed.

Microalgae Harvesting by Self-Driven 3D Microfiltration with Rationally Designed Porous Superabsorbent Polymer (PSAP) Beads

Microalgae are emerging as next-generation renewable resources for production of sustainable biofuels and high-value bioproducts. Conventional microalgae harvesting methods including centrifugation, filtration, flocculation, and flotation are limited by intensive energy consumption, high capital cost, long treatment time, or the requirement of chemical addition. In this study, we design and fabricate porous superabsorbent polymer (PSAP) beads for self-driven 3D microfiltration of microalgal cultures. The PSAP beads can swell fast in a microalgal suspension with high water absorption capacity. During this process, microalgal cells are excluded outside the beads and successfully concentrated in the residual medium. After treatment, the beads can be easily separated from the microalgal concentrate and reused after dewatering. In one PSAP treatment, a high concentration factor for microalgal cultures up to 13 times can be achieved in 30 min with a harvesting efficiency higher than 90%. Furthermore, microalgal cultures could be concentrated from 0.2 g L^-1 to higher than 120 g L^-1 with minimal biomass loss through multistage PSAP treatments. Therefore, the use of PSAP beads for microalgae harvesting is fast, effective, and scalable. It does not require any complex instrument or chemical addition. This technique potentially provides an efficient and feasible alternative to obtain high concentrations of functional biomass at a very low cost.

Self-Driven Pretreatment and Room-Temperature Storage of Water Samples for Virus Detection Using Enhanced Porous Superabsorbent Polymer Beads

The continuous emergence of infectious viral diseases has become a major threat to public health. To quantify viruses, proper handling of water samples is required to ensure the accuracy and reliability of the testing results. In this study, we develop enhanced porous superabsorbent polymer (PSAP) beads to pretreat and store water samples for virus detection. By applying PSAP beads to collect water samples, the viruses are captured and encapsulated inside the beads while undesired components are excluded. We have successfully demonstrated that the shelf life of the model virus can be effectively extended at room temperature (22 °C) and an elevated temperature (35 °C). Both the infectivity level and genome abundance of the viruses are preserved even in a complex medium such as untreated wastewater. Under the tested conditions, the viral degradation rate constant can be reduced to more than 10 times using the PSAP beads. Therefore, the enhanced PSAP beads provide a low-cost and efficient sample pretreatment and storage method that is feasible and practical for large-scale surveillance of viral pathogens in water samples.

Adsorption Properties of Comb-Shaped Polycarboxylate Dispersant onto Different Crystal Pyraclostrobin Particle Surfaces

The stability of the suspension system of the two crystal forms of pyraclostrobin is evaluated using multiple light technology, and the adsorption performance of polycarboxylate dispersant on the surface of two different crystalline pyraclostrobin particles is compared in combination with XRD, FTIR, XPS, and SEM from the microscopic view. The adsorption kinetics and thermodynamics studies of 2700 on the surfaces of different crystalline forms of pyraclostrobin particles show that the adsorption process of 2700 on the surfaces of pyraclostrobin crystal forms II and IV conform to pseudo-second-order kinetic adsorption model. The Ea values for crystal forms II and IV are 12.93 and 14.39 kJ∙mol⁻¹, respectively, which indicates that both adsorption processes are physical adsorption. The adsorption models of 2700 on the surfaces of pyraclostrobin crystal forms II and IV are in accordance with Langmuir adsorption isotherms. The ∆G_ad values of crystal forms II and IV are negative and the ∆S_ad values are positive at different temperatures. Therefore, the adsorption processes are spontaneous and accompanied by entropy increase. The results of this study provide an important theoretical basis for the selection of polycarboxylate dispersants in the suspension of pyraclostrobin. This study also provides a reference for the research of polycrystalline pesticide suspension concentrate.

Adsorption thermodynamic characteristics of Chlorella vulgaris with organic polymer adsorbent cationic starch: Effect of temperature on adsorption capacity and rate

Aiming at optimizing the adsorption process of Chlorella vulgaris and cationic starch, the adsorption thermodynamic characteristics were evaluated. Different from inorganic calcium salt adsorbent, the adsorption nature of organic polymer cationic starch is exothermic (ΔH° < 0) and spontaneous (ΔG° < 0). Besides, the adsorption capacity and rate can be well described by Langmiur isotherm and pseudo second kinetic models. As results of exothermic nature and great driving force of lower temperature, the adsorption capacity and rate declined with the rising temperature. The maximal values of them were obtained at 278.15 K, which were 9148.14 mg microalgae (g cationic starch)^-1 and 8.74 × 10^-6 mg g^-1 min^-1. Additionally, with insufficient adsorbent, the highest adsorption efficiency (96.37%) was achieved at 278.15 K for stirring 150 min. For 288.15, 298.15, 308.15 and 318.15 K, the adsorption efficiency decreased to 93.77%, 86.75%, 83.32% and 81.57% and the time consumed were at least 40 min longer.

Removal of methylene blue via bioinspired catecholamine/starch superadsorbent and the efficiency prediction by response surface methodology and artificial neural network-particle swarm optimization

This paper demonstrates coupling of the artificial neural network (ANN) technique with the particle swarm optimization (PSO) method and compares the performance of ANN-PSO with response surface methodology (RSM) in prediction of the adsorption of methylene blue (MB) by a novel bio-superadsorbent. To this, a starch-based superadsorbent was synthesized using acrylic acid and acryl amid polymers and then catecholamine functional groups were combined onto the surface with oxidative polymerization of dopamine. The adsorption of MB was considered as a function of pH, dye concentration, and contact time. The best topology of the ANN was found to be 3-7-1, and prediction model of the adsorption capacity was demonstrated as a matrix of explicit equations. ANN-PSO is more accurate than RSM. The results revealed that the root-mean-square error, correlation coefficient, and normalized standard deviation for the ANN-PSO are 22.46, 0.99, and 16.83, respectively, while for RSM are 82.89, 0.98, and 65.41, respectively.

Rheokinetics of microalgae slurry during hydrothermal pretreatment processes

Hydrothermal pretreatment is an efficient process for improving the productivity of biofuels from wet microalgae biomass. The rheological behavior of microalgae slurry is a significant parameter affecting the performance of hydrothermal pretreatment reactors. Herein, the dynamic rheological behavior of microalgae slurry during hydrothermal pretreatment was investigated for the first time. The results revealed that the insoluble organics released from microalgae cells was the main factor affecting the rheological behavior of microalgae slurry. The denaturation and hydrolysis of starch and protein in liquid phase at different temperature regions caused the increasing and decreasing of viscosity of the microalgae slurry, respectively. The rheokinetics equations were established based on four-parameter cross-linking rheokinetics equation to describe the variation of viscosity with reaction time in different temperature. The variation of the rheokinetics model parameters with temperature revealed that the temperature has an obviously positive influence on the hydrothermal pretreatment process of the microalgae slurry.

Salt-Tolerant Superabsorbent Polymer with High Capacity of Water-Nutrient Retention Derived from Sulfamic Acid-Modified Starch

The application of superabsorbent polymers (SAPs) is hindered because their absorption capability is greatly affected by the electrolytes in a solution. A novel modified water-absorbent polymer was fabricated by solution polymerization of sulfamic acid-modified starch and acrylic acid; the swelling ratios of this absorbent polymer were 1026 g/g in deionized water and 145 g/g in 0.9% sodium chloride solution and increased by 99.5 and 13.4%, respectively, when compared with ordinary starch-grafted acrylic SAPs. The water absorption capacity was measured in water at different pH values, salt concentrations, and temperatures. In addition, water and fertilizer retentions were studied by simulated leaching tests in a soil column. The results showed that water absorption capacities of the modified SAP in salt solutions were improved due to the adsorption and transfer of water molecules by the sulfonic acid groups. Compared to the losses when there was no superabsorbent treatment, the water, nitrate, ammonium nitrogen, and water-soluble potassium losses during the salt-tolerant superabsorbent treatment were significantly reduced by 18.5, 22.8, 88.0, and 63.8%, respectively. The method introduced in this study could guide the development and wide application of salt-tolerant SAPs in agriculture and horticulture.

Bioinspired catecholamine/starch composites as superadsorbent for the environmental remediation

Focusing on the encouraging properties of starch-based composite materials, starch‑g‑(acrylic acid‑co‑acrylamide) superabsorbent was synthesized using solution polymerization method, and then the catecholamine functional groups were introduced on to pore surface of the absorbent via oxidative polymerization of dopamine (DA). The adsorbent was optimized in terms of the monomers' mass ratio and synthesis conditions, and characterized by different characterization techniques. The polydopamine (PDA) coating thickness was estimated using transmission electron microscopy (TEM) image and it was found to be 83 nm. The bimodal mesoporous adsorbent with 5914.66% swelling ratio bearing micropores with a specific surface area of 2.8031 m² g^-1 was used for the adsorption of methylene blue (MB) as a model water pollutant dye. The maximum adsorption capacity was obtained 2276 mg g^-1 at pH 9 and within 100 min. The adsorbent with unprecedented super high adsorption capacity can be encouraging from different environmental remediation points of view.

Biodegradable branched cationic starch with high C/N ratio for Chlorella vulgaris cells concentration: Regulating microalgae flocculation performance by pH

To improve the carbon to nitrogen (C/N) ratio of harvested microalgae biomass for better producing biogas by fermentation, biodegradable cationic starch with high C/N ratio were synthesized to harvest Chlorella vulgaris. The impact of pH was also studied as the zeta potential of both microalgae and cationic starch would change with pH. Results indicated the cationic starch can harvest above 99% of the microalgae and the C/N ratio can rise from 7.50 to 7.90. The zeta potential of microalgae always kept negative and presented a trend of descending firstly and then upgrade. The maximum microalgae biomass flocculation capacity of 1 g cationic starch was 8.62 g with the help of self-flocculation at pH 3. The concentration of flocs formed at pH 11 was 25.74 g L^-1 and the diameter was 0.553 mm which was much larger than the flocs formed at pH 3 (0.208 mm).

A novel non-starch based cationic polymer as flocculant for harvesting microalgae

This work intends towards the preparation of different grades of cationic locust bean gum biopolymer (CLBG) through the incorporation of 2,3-epoxypropyltrimethylammonium chloride (GTMAC) on to the pristine locust bean gum (LBG) biopolymer. Among them the best grade was further selected, characterized and their flocculation efficacy was evaluated towards harvesting of three different indigenous isolated green microalgae viz. Chlorella sp. NCQ, Micractinium sp. NCS2 and Scenedesmus sp. CBIIT(ISM). Flocculation efficiency of 96.68%, 96.64%, and 97.42% were obtained for Chlorella sp. NCQ, Micractinium sp. NCS2 and Scenedesmus sp. CBIIT(ISM) at an optimum dosage of 55, 40, and 30 ppm respectively. Thus CLBG was proven to be an efficient flocculant towards harvesting of green microalgae than its natural form.

Optimizing culture conditions for heterotrophic-assisted photoautotrophic biofilm growth of Chlorella vulgaris to simultaneously improve microalgae biomass and lipid productivity

In order to solve the technical bottleneck that the biomass yield and lipid accumulation cannot be increased simultaneously during microalgae growth, a heterotrophic-assisted photoautotrophic biofilm (HAPB) growth mode of Chlorella vulgaris was constructed. The light penetration capability of the microalgae biofilm formed through heterotrophic-assisted photoautotrophic growth was 64% stronger than that formed by photoautotrophic growth. Due to the different demands of autotrophic and heterotrophic growth of microalgae, the nutrient environment and growth conditions were optimized to fully utilize the advantages and potentials of the HAPB culture model. An optimized molar ratio of total inorganic carbon (CO₂) to total organic carbon (glucose) (20:1) and a molar ratio of total carbon to total nitrogen (72:1) were obtained. The maximum specific growth rate of Chlorella vulgaris increased by 78% compared to that before optimization. Meanwhile, the lipid content and yield increased by 120% and 147%, respectively, up to 47.53% and 41.95 g m^-2.