The Use of Biochar and Pyrolysed Materials to Improve Water Quality through Microcystin Sorption Separation

Coupling physiochemical adsorption with biodegradation for enhanced removal of microcystin-LR in water

To innovate the design of water treatment technology for algal toxin removal, this research investigated the mechanisms of cyanotoxin microcystin-LR (MC-LR) removal by a coupled adsorption-biodegradation. Eight types of woody carbonaceous adsorbents with and without Sphingopyxis sp. m6, a MC-LR degrading bacterium, were tested for MC-LR removal in water. All adsorbents showed good adsorption capability, removing 40 % to almost 100 % of the MC-LR (4.5 mg/L) within 48 h in batch experiments. Adding Sphingopyxis sp. m6 continuously promoted MC-LR biological removal, and successfully broke the barrier of adsorption capacity of tested adsorbents, removing >90 % of the MC-LR in most of the coupled adsorption-biodegradation tests, especially for those adsorbents had low physiochemical adsorption capacity. Variance partitioning analysis indicated that mesopore was the dominant contributor to adsorption capacity of MC-LR in pure adsorption treatments, which acted synergistically with electrical conductivity, polarity and total functional groups on the absorbent. Pore structure was the key factor beneficial for the growth of Sphingopyxis sp. m6 (51% contribution) and subsequent MC-LR biological removal rate (80 % contribution). Overall, pinewood-based carbonaceous adsorbents (especially pinewood activated carbon) exhibited the highest adsorption capacity towards MC-LR and provided the most favorable conditions for biological removal of MC-LR, largely because of their high mesopore volume, total functional groups and electric conductivity. The research outcomes not only deepened the quantitative understanding of mechanisms for MC-LR removal by the coupled process, but also provided theoretical basis for future materials' selection and modification during the practical application of coupled process.

Influence of biochar on the removal of Microcystin-LR and Saxitoxin from aqueous solutions

The present study assessed the effective use of biochar for the adsorption of two potent HAB toxins namely, Microcystin-LR (MCLR) and Saxitoxin (STX) through a combination of dosage, kinetic, equilibrium, initial pH, and competitive adsorption experiments. The adsorption results suggest that biochar has excellent capabilities for removing MCLR and STX, with STX reporting higher adsorption capacities (622.53-3507.46 µg/g). STX removal required a minimal dosage of 0.02 g/L, while MCLR removal needed 0.4 g/L for > 90%. Similarly, a shorter contact time was required for STX removal compared to MCLR for > 90% of toxin removed from water. Initial pH study revealed that for MCLR acidic conditions favored higher uptake while STX favored basic conditions. Kinetic studies revealed that the Elovich model to be most suitable for both toxins, while STX also showed suitable fittings for Pseudo-First Order and Pseudo-Second Order in individual toxin systems. Similarly, for the Elovich model the most suited kinetic model for both toxins in presence of each other. Isotherm studies confirmed the Langmuir-Freundlich model as the best fit for both toxins. These results suggest adsorption mechanisms including pore filling, hydrogen bonding, π-π interactions, hydrophobic interactions, electrostatic attraction, and dispersive interactions.

Carbon dioxide-assisted thermochemical conversion of magnetically harvested harmful algae into syngas and metal biochar

With rising of harmful algae blooming and toxin exposure, practical utilization of harmful algae has been developed. This work aimed to magnetically harvest Microcystis aeruginosa (MA) using iron oxides and investigate the feasibility of algae/iron oxides mixture as feedstock in pyrolytic platform to produce syngas and metal biochar. Carbon dioxide (CO2) was used as a feeding gas to enhance the production efficiency of syngas and also functioned pH controller for better MA harvesting and toxin removal. CO2 support brought multiple benefits: magnetite (Fe3O4) and maghemite (γ-Fe2O3) recovered MA in a relatively short period of time (∼1 min), the recovered biomass generated 34-fold increased carbon monoxide, and metal biochar adsorbed higher amount of toxin from MA (2.8-fold). Pyrolytic utilization of harmful algae supported by CO2 and iron oxides could be one of promising techniques for evolution of metal biochar to remove toxin, while efficiently recover biomass and enhance syngas production.

Nature-Based Solution to Eliminate Cyanotoxins in Water Using Biologically Enhanced Biochar

Climate change and high eutrophication levels of freshwater sources are increasing the occurrence and intensity of toxic cyanobacterial blooms in drinking water supplies. Conventional water treatment struggles to eliminate cyanobacteria/cyanotoxins, and expensive tertiary treatments are needed. To address this, we have designed a sustainable, nature-based solution using biochar derived from waste coconut shells. This biochar provides a low-cost porous support for immobilizing microbial communities, forming biologically enhanced biochar (BEB). Highly toxic microcystin-LR (MC-LR) was used to influence microbial colonization of the biochar by the natural lake-water microbiome. Over 11 months, BEBs were exposed to microcystins, cyanobacterial extracts, and live cyanobacterial cells, always resulting in rapid elimination of toxins and even a 1.6-1.9 log reduction in cyanobacterial cell numbers. After 48 h of incubation with our BEBs, the MC-LR concentrations dropped below the detection limit of 0.1 ng/mL. The accelerated degradation of cyanotoxins was attributed to enhanced species diversity and microcystin-degrading microbes colonizing the biochar. To ensure scalability, we evaluated BEBs produced through batch-scale and continuous-scale pyrolysis, while also guaranteeing safety by maintaining toxic impurities in biochar within acceptable limits and monitoring degradation byproducts. This study serves as a proof-of-concept for a sustainable, scalable, and safe nature-based solution for combating toxic algal blooms.

Graphene as a rational interface for enhanced adsorption of microcystin-LR from water

Cyanotoxins such as microcystin-LR (MC-LR) represent a global environmental threat to ecosystems and drinking water supplies. The study investigated the direct use of graphene as a rational interface for removal of MC-LR via interactions with the aromatic ring of the ADDA1 chain of MC-LR and the sp2 hybridized carbon network of graphene. Intra-particle diffusion model fit indicated the high mesoporosity of graphene provided significant enhancements to both adsorption capacities and kinetics when benchmarked against microporous granular activated carbon (GAC). Graphene showed superior MC-LR adsorption capacity of 75.4 mg/g (Freundlich model) compared to 0.982 mg/g (Langmuir model) for GAC. Sorption kinetic studies showed graphene adsorbs 99% of MC-LR in 30 min, compared to zero removal for GAC after 24 hr using the same MC-LR concentration. Density functional theory (DFT), calculations showed that postulated π-based interactions align well with the NMR-based experimental work used to probe primary interactions between graphene and MC-LR adduct. This study proved that π-interactions between the aromatic ring on MC-LR and graphene sp2 orbitals are a dominant interaction. With rapid kinetics and adsorption capacities much higher than GAC, it is anticipated that graphene will offer a novel molecular approach for removal of toxins and emerging contaminants with aromatic systems.

Immobilization of Microcystin by the Hydrogel-Biochar Composite to Enhance Biodegradation during Drinking Water Treatment

Microcystin-LR (MC-LR), the most common algal toxin in freshwater, poses an escalating threat to safe drinking water. This study aims to develop an engineered biofiltration system for water treatment, employing a composite of poly(diallyldimethylammonium chloride)-biochar (PDDA-BC) as a filtration medium. The objective is to capture MC-LR selectively and quickly from water, enabling subsequent biodegradation of toxin by bacteria embedded on the composite. The results showed that PDDA-BC exhibited a high selectivity in adsorbing MC-LR, even in the presence of competing natural organic matter and anions. The adsorption kinetics of MC-LR was faster, and capacity was greater compared to traditional adsorbents, achieving a capture rate of 98% for MC-LR (200 μg/L) within minutes to tens of minutes. Notably, the efficient adsorption of MC-LR was also observed in natural lake waters, underscoring the substantial potential of PDDA-BC for immobilizing MC-LR during biofiltration. Density functional theory calculations revealed that the synergetic effects of electrostatic interaction and π-π stacking predominantly contribute to the adsorption selectivity of MC-LR. Furthermore, experimental results validated that the combination of PDDA-BC with MC-degrading bacteria offered a promising and effective approach to achieve a sustainable removal of MC-LR through an "adsorption-biodegradation" process.

Biocrude Production Using a Novel Cyanobacterium: Pilot-Scale Cultivation and Lipid Extraction via Hydrothermal Liquefaction

The use of renewable energy to reduce fossil fuel consumption is a key strategy to mitigate pollution and climate change, resulting in the growing demand for new sources. Fast-growing proprietary cyanobacterial strains of Fremyella diplosiphon with an average life cycle of 7-10 days, and a proven capacity to generate lipids for biofuel production are currently being studied. In this study, we investigated the growth and photosynthetic pigmentation of a cyanobacterial strain (SF33) in both greenhouse and outdoor bioreactors, and produced biocrude via hydrothermal liquefaction. The cultivation of F. diplosiphon did not significantly differ under suboptimal conditions (p < 0.05), including in outdoor bioreactors with growth differences of less than 0.04 (p = 0.035) among various batches. An analysis of the biocrude's components revealed the presence of fatty acid biodiesel precursors such as palmitic acid and behenic acid, and alkanes such as hexadecane and heptadecane, used as biofuel additives. In addition, the quantification of value-added photosynthetic pigments revealed chlorophyll a and phycocyanin concentrations of 0.0011 ± 5.83 × 10^-5 μg/μL and 7.051 ± 0.067 μg/μg chlorophyll a. Our results suggest the potential of F. diplosiphon as a robust species that can grow at varying temperatures ranging from 13 °C to 32 °C, while producing compounds for applications ranging from biofuel to nutritional supplements. The outcomes of this study pave the way for production-level scale-up and processing of F. diplosiphon-derived biofuels and marketable bioproducts. Fuel produced using this technology will be eco-friendly and cost-effective, and will make full use of the geographical location of regions with access to brackish waters.

Multi-Soil-Layering Technology: A New Approach to Remove Microcystis aeruginosa and Microcystins from Water

Eutrophication of surface waters caused by toxic cyanobacteria such as Microcystis aeruginosa leads to the release of secondary metabolites called Microcystins (MCs), which are heptapeptides with adverse effects on soil microbiota, plants, animals, and human health. Therefore, to avoid succumbing to the negative effects of these cyanotoxins, various remediation approaches have been considered. These techniques involve expensive physico-chemical processes because of the specialized equipment and facilities required. Thus, implementing eco-technologies capable of handling this problem has become necessary. Indeed, multi-soil-layering (MSL) technology can essentially meet this requirement. This system requires little space, needs simple maintenance, and has energy-free operation and high durability (20 years). The performance of the system is such that it can remove 1.16 to 4.47 log10 units of fecal contamination from the water, 98% of suspended solids (SS), 92% of biological oxygen demand (BOD), 98% of chemical oxygen demand (COD), 92% of total nitrogen (TN), and 100% of total phosphorus (TP). The only reported use of the system to remove cyanotoxins has shown a 99% removal rate of MC-LR. However, the mechanisms involved in removing this toxin from the water are not fully understood. This paper proposes reviewing the principal methods employed in conventional water treatment and other technologies to eliminate MCs from the water. We also describe the principles of operation of MSL systems and compare the performance of this technology with others, highlighting some advantages of this technology in removing MCs. Overall, the combination of multiple processes (physico-chemical and biological) makes MSL technology a good choice of cyanobacterial contamination treatment system that is applicable in real-life conditions, especially in rural areas.