Enhanced bioenergy recovery from oil-extracted microalgae residues via two-step H2/CH4or H2/butanol anaerobic fermentation

Microalgae to bioenergy production: Recent advances, influencing parameters, utilization of wastewater - A critical review

Fossil fuel limitations and their influence on climate change through atmospheric greenhouse gas emissions have made the excessive use of fossil fuels widely recognized as unsustainable. The high lipid content, carbon-neutral nature and potential as a biofuel source have made microalgae a subject of global study. Microalgae are a promising supply of biomass for third-generation biofuels production since they are renewable. They have the potential to produce significant amounts of biofuel and are considered a sustainable alternative to non-renewable energy sources. Microalgae are currently incapable to synthesize algal biofuel on an extensive basis in a sustainable manner, despite their significance in the global production of biofuels. Wastewater contains nutrients (both organic and inorganic) which is essential for the development of microalgae. Microalgae and wastewater can be combined to remediate waste effectively. Wastewater of various kinds such as industrial, agricultural, domestic, and municipal can be used as a substrate for microalgal growth. This process helps reduce carbon dioxide emissions and makes the production of biofuels more cost-effective. This critical review provides a detailed analysis of the utilization of wastewater as a growth medium for microalgal - biofuel production. The review also highlights potential future strategies to improve the commercial production of biofuels from microalgae.

Valorization of microalgae biomass into bioproducts promoting circular bioeconomy: a holistic approach of bioremediation and biorefinery

The need for alternative source of fuel has demanded the cultivation of 3rd generation feedstock which includes microalgae, seaweed and cyanobacteria. These phototrophic organisms are unique in a sense that they utilise natural sources like sunlight, water and CO₂ for their growth and metabolism thereby producing diverse products that can be processed to produce biofuel, biochemical, nutraceuticals, feed, biofertilizer and other value added products. But due to low biomass productivity and high harvesting cost, microalgae-based production have not received much attention. Therefore, this review provides the state of the art of the microalgae based biorefinery approach to define an economical and sustainable process. The three major segments that need to be considered for economic microalgae biorefinery is low cost nutrient source, efficient harvesting methods and production of by-products with high market value. This review has outlined the use of various wastewater as nutrient source for simultaneous biomass production and bioremediation. Further, it has highlighted the common harvesting methods used for microalgae and also described various products from both raw biomass and delipidified microalgae residues in order to establish a sustainable, economical microalgae biorefinery with a touch of circular bioeconomy. This review has also discussed various challenges to be considered followed by a techno-economic analysis of the microalgae based biorefinery model.

A review on the factors influencing biohydrogen production from lactate: The key to unlocking enhanced dark fermentative processes

Dark fermentation (DF) is one of the most promising biological methods to produce bio-hydrogen and other value added bio-products from carbohydrate-rich wastes and wastewater. However, process instability and low hydrogen production yields and rates have been highlighted as the major bottlenecks preventing further development. Numerous studies have associated such concerns with the inhibitory activity of lactate-producing bacteria (LAB) against hydrogen producers. However, an increasing number of studies have also shown lactate-based metabolic pathways as the prevailing platform for hydrogen production. This opens a vast potential to develop new strategies to deal with the "Achilles heel" of DF - LAB overgrowth - while untapping high-performance DF. This review discusses the key factors influencing the lactate-driven hydrogen production, paying particular attention to substrate composition, the operating conditions, as well as the microbiota involved in the process and its potential functionality and related biochemical routes. The current limitations and future perspectives in the field are also presented.

Recent advancement on biological technologies and strategies for resource recovery from swine wastewater

Swine wastewater is categorized as one of the agricultural wastewater with high contents of organics and nutrients including nitrogen and phosphorus, which may lead to eutrophication in the environment. Insufficient technologies to remove those nutrients could lead to environmental problems after discharge. Several physical and chemical methods have been applied to treat the swine wastewater, but biological treatments are considered as the promising methods due to the cost effectiveness and performance efficiency along with the production of valuable products and bioenergies. This review summarizes the characteristics of swine wastewaters in the beginning, and briefly describes the current issues on the treatments of swine wastewaters. Several biological techniques, such as anaerobic digestion, A/O process, microbial fuel cells, and microalgae cultivations, and their future aspects will be addressed. Finally, the potentials to reutilize biomass produced during the treatment processes are also presented under the consideration of circular economy.

Pilot study of cold-rolling wastewater treatment using single-stage anaerobic fluidized membrane bioreactor

A pilot-scale single-stage anaerobic fluidized membrane bioreactor (AFMBR) was firstly used in this study to treat cold-rolling emulsion wastewater from steel industry. It was continuously operated for 302 days with influent COD concentration of 860-1120 mg/L. Under a hydraulic retention time of 1.5 d, the average effluent COD concentration of 72 mg/L achieved corresponding 90% of COD removal. The permeate flux was varied between 1.7 and 2.9 L/m²/h during operation which decreased with increased biomass concentration inside AFMBR. The trans-membrane pressure (TMP) was generally around 35-40 kPa, however, it increased up to 60 kPa when volatile suspended solid increased to above 2.5 g/L. Both flux and TMP data reveal the importance of biomass control for AFMBR operation. Results from terminal restriction fragment length polymorphism (T-RFLP) show the genus Methanosaeta was dominant on GAC and it shared dominance with the genera Methanomethylovorans and Methanosarcina in suspended sludge.

Applications of de-oiled microalgal biomass towards development of sustainable biorefinery

In view of commercialization of microalgal biofuel, the de-oiled microalgal biomass (DMB) is a surplus by-product in the biorefinery process that needs to be exploited to make the process economically attractive and feasible. This DMB, rich in carbohydrates, proteins, and minerals, can be used as feed, fertilizer, and substrate for the production of bioethanol/bio-methane. Further, thermo-chemical conversion of DMB results into fuels and industrially important chemicals. Future prospects of DMB also lie with its conversion into novel biomaterials like nanoparticles and carbon-dot which have biomedical importance. The lowest valued application of DMB is to use it for adsorption of dyes and heavy metals from industrial effluents. This study reviews how DMB can be utilized for different applications and in the generation of valuable co-products. The value addition of DMB would thereby improve the overall cost economics of the microalgal bio-refinery.