Mitigation of variable seasonal productivity in algae biomass through blending and ensiling: An assessment of compositional changes in storage

Utilization of microalgal-bacterial energy nexus improves CO2 sequestration and remediation of wastewater pollutants for beneficial environmental services

Carbon dioxide (CO2) emissions from the combustion of fossil fuels and coal are primary contributors of greenhouse gases leading to global climate change and warming. The toxicity of heavy metals and metalloids in the environment threatens ecological functionality, diversity and global human life. The ability of microalgae to thrive in harsh environments such as industrial wastewater, polluted lakes, and contaminated seawaters presents new, environmentally friendly, and less expensive CO2 remediation solutions. Numerous microalgal species grown in wastewater for industrial purposes may absorb and convert nitrogen, phosphorus, and organic matter into proteins, oil, and carbohydrates. In any multi-faceted micro-ecological system, the role of bacteria and their interactions with microalgae can be harnessed appropriately to enhance microalgae performance in either wastewater treatment or algal production systems. This algal-bacterial energy nexus review focuses on examining the processes used in the capture, storage, and biological fixation of CO2 by various microalgal species, as well as the optimized production of microalgae in open and closed cultivation systems. Microalgal production depends on different biotic and abiotic variables to ultimately deliver a high yield of microalgal biomass.

Biohydrogen production using algae: Potentiality, economics and challenges

The biohydrogen production from algal biomass could ensure hydrogen's sustainability as a fuel option at the industrial level. However, some bottlenecks still need to be overcome to achieve the process's economic feasibility. This review article highlights the potential of algal biomasses for producing hydrogen with a detailed explanation of various mechanisms and enzymes involved in the production processes. Further, it discusses the impact of various experimental parameters on biohydrogen production. This article also analyses the significant challenges confronted during the overall biohydrogen production process and comprehends the recent strategies adopted to enhance hydrogen productivity. Furthermore, it gives a perception of the economic sustenance of the process. Moreover, this review elucidates the future scope of this technology and delineates the approaches to ensure the viability of hydrogen production.

Effect of solid-state fermentation and ultrasonication processes on antimicrobial and antioxidant properties of algae extracts

Algal biomass (AB) is prospective source of valuable compounds, however, Baltic Sea macroalgae have some challenges, because of their high microbial and chemical contamination. These problems can be solved, by using appropriate technologies for AG pre-treatment. The aim of this study was to evaluate the influence of two pre-treatments, solid-state fermentation with the Lactiplantibacillus plantarum LUHS135 and ultrasonication, on the antioxidant and antimicrobial characteristics of macro- (Cladophora rupestris, Cladophora glomerata, Furcellaria lumbricalis, Ulva intestinalis) and Spirulina (Arthrospira platensis) extracts. Also, combinations of extracts and LUHS135 were developed and their characteristics were evaluated. The total phenolic compound content was determined from the calibration curve and expressed in mg of gallic acid equivalents; antioxidant activity was measured by a Trolox equivalent antioxidant capacity assay using the DPPH^• (1,1-diphenyl-2-picrylhydrazyl), ABTS^•+ 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid), FRAP (Ferric Reducing Ability of Plasma) discoloration methods. Antimicrobial activity was measured by using agar well diffusion assay and in a liquid medium. The highest DPPH^• and ABTS^•+ was shown by C.rupestris and F.lumbricalis extract × LUHS135 combinations, the highest FRAP - by non-pretreated C.rupestris and F.lumbricalis extract × LUHS135 combinations. Ultrasonicated samples inhibited four out of seven tested pathogens. Finally, the tested pre-treatments showed good perspectives and can be recommended for AB valorization.

Optimization Study on Microwave-Assisted Hydrothermal Liquefaction of Malaysian Macroalgae Chaetomorpha sp. for Phenolic-Rich Bio-Oil Production

There are several methods of biomass conversion, including hydrothermal liquefaction (HTL). The implementation of microwave technology in the HTL process is still new, especially on the conversion of marine biomass into bio-crude. In this work, the macroalgae Chaetomorpha sp. was used as the biomass feedstock to produce phenolic-rich bio-oil through microwave-assisted HTL. Chaetomorpha sp. was abundantly found in Malaysia, creating a green tides issue. By utilizing these algae, the green tide issue can be solved and value-added bio-oil is obtained. However, bio-oil from macroalgae has a relatively low heating value, restricting its fuel application. Therefore, it is suggested to be used for bio-polymer synthesis, including bio-based phenol formaldehyde. In this study, the effect of different parameters, such as reaction temperature, preloaded pressure, water-to-algal biomass ratio, and holding time, on both the bio-oil yield and phenolic yield was evaluated. Folin–Ciocalteu method was introduced as the phenolic determination method and the optimal conditions were located by using Response Surface Methodology (RSM). As a results, an optimal biodiesel yield and phenolic yield of 21.47 wt% and 19.22 wt% Gallic Acid Equivalent was obtained at a reaction temperature of 226 °C, 42 bar preloaded pressure and 30:1 water-to-algal biomass ratio after 79 min. Sensitivity analysis also concluded that the water-to-algal biomass ratio is the most influential factor, followed by the preloaded pressure. The FTIR spectrum of the bio-oil produced indicated the presence of different functional group of compounds. In short, Chaetomorpha sp. has been successfully converted into valuable bio-oil through microwave-assisted HTL.

Effects of Inoculation with Lactic Acid Bacteria on the Preservation of Nannochloropsis gaditana Biomass in Wet Anaerobic Storage and Its Impact on Biomass Quality

Wet anaerobic storage of algal biomass is a promising preservation approach that can ensure a continuous supply of these feedstocks to biorefineries year-round. An effective solution to preservation must ensure minimal dry matter loss and a change in biochemical composition during storage. Therefore, the objective of this study is to investigate the preservation of Nannochloropsis gaditana biomass through wet anaerobic storage and its impact on biomass quality. Prior to storage, the algae sample is inoculated with two different strains of lactic acid bacteria and thereafter stored for 30 and 180 days. Each inoculant limited the dry matter loss to <10% (dry basis) after the storage duration. Final pH values (4.3–4.8) indicate that the biomass samples are properly ensiled, achieving the acidic conditions necessary for preservation. Compositional analysis of the biomass after storage shows a reduction in carbohydrate content, a relative increase in lipid content, and no significant change in the protein fraction. Glucose and galactose were the most prevalent sugar monomers. The low dry matter loss and minimal compositional change indicate that wet anaerobic storage is an effective means of preserving algal biomass and ensuring a constant supply of algal biomass feedstock to a biorefinery.

Effects of different simulated seasonal temperatures on the fermentation characteristics and microbial community diversities of the maize straw and cabbage waste co-ensiling system

Ensiling is considered as a suitable method to preserve seasonal agricultural residues to enable long-term supply for wastes valorization. In this study, the effects of simulated seasonal temperatures (-3, 18 and 34 °C) on the organic compositions, ensiling fermentation characteristics, and microbial community evolution during 120 days co-ensiling of maize straw and cabbage wastes were investigated. Successful storage performance was obtained at all these three temperatures. Comparatively, silages at 18 and 34 °C showed lower ammonia nitrogen, lower pH and more intensive lactic acid bacteria fermentation than that at -3 °C. Both silages at -3 and18 °C were well-preserved for 120 days with higher biodegradation potential (BDP), accompanied by lower content of acid detergent lignin (ADL). However, the silages at 34 °C could only preserved for 90 days due to low carbohydrate, low BDP and higher ADL content than that at -3 or18 °C. The storage temperature is a critical parameter that significantly affected the silage quality by influencing the microbial community diversity in silages. Proteobacteria and Firmicutes were dominant bacteria at phylum level for all silages while the dominant lactic acid bacteria at genus level were Lactobacillus and Leuconostoc, which restrained the undesirable microbes such as Enterobacteriaceae, Pseudomonas, Flavobacterium, and Pantoea during co-ensiling. Co-ensiling of maize straw with vegetable wastes may provide a promising strategy for long-term preservation of air-dried crop straw while using vegetable wastes as regulatable supplement to achieve silages of desired quality. This study could provide valuable information for conservation and management of agricultural wastes.