Re-vitalizing wastewater: Nutrient recovery and carbon capture through microbe-algae synergy using omics-biology.

Increasing amounts of wastewater is the most pervasive and challenging environmental problem globally. Conventional treatment methods are costly and entail huge energy, carbon consumption and greenhouse gas emissions. Owing to their unique ability of carbon capturing and resource recovery, microalgae-microbiome based treatment is a potential approach and is widely used for carbon-neutral wastewater treatment. Microalgae-bacteria synergy (i.e., the functionally beneficial microbial synthetic communities) performs better and enhances carbon-sequestration and nutrient recovery from wastewater treatment plants. This review presents a comprehensive information regarding the potential of microalgae-microbiome as a sustainable agent for wastewater and discusses synergistic approaches for effective nutrient removal. Moreover, this review discusses, the role of omics-biology and Insilco approaches in unravelling and understanding the algae-microbe synergism and their response toward wastewater treatment. Finally, it discusses various microbiome engineering approaches for developing the effective microalgae-bacteria partners for carbon sequestration and nutrient recovery from wastewater, and summarizes future research perspectives on microalgae-microbiome based bioremediation.

Improving the feasibility of aquaculture feed by using microalgae.

The aquaculture industry is an efficient edible protein producer and grows faster than any other food sector. Therefore, it requires enormous amounts of fish feed. Fish feed directly affects the quality of produced fish, potential health benefits, and cost. Fish meal (FM), fis oil (FO), and plant-based supplements, predominantly used in fish feed, face challenges of low availability, low nutritional value, and high cost. The cost associated with aquaculture feed represents 40-75% of aquaculture production cost and one of the key market drivers for the thriving aquaculture industry. Microalgae are a primary producer in aquatic food chains. Microalgae are expanding continuously in renewable energy, pharmaceutical pigment, wastewater treatment, food, and feed industries. Major components of microalgal biomass are proteins with essential amino acids, lipids with polyunsaturated fatty acids (PUFA), carbohydrates, pigments, and other bioactive compounds. Thus, microalgae can be used as an essential, viable, and alternative feed ingredient in aquaculture feed. In recent times, live algae culture, whole algae, and lipid-extracted algae (LEA) have been tested in fish feed for growth, physiological activity, and nutritional value. The present review discusses the potential application of microalgae in aquaculture feed, its mode of application, nutritional value, and possible replacement of conventional feed ingredients, and disadvantages of plant-based feed. The review also focuses on integrated processes such as algae cultivation in aquaculture wastewater, aquaponics systems, challenges, and future prospects of using microalgae in the aquafeed industry.

Techno-economic estimation of wastewater phycoremediation and environmental benefits using Scenedesmus obliquus microalgae.

This study investigated the dual application of Scenedesmus obliquus for wastewater phycoremediation and biochemical component accumulation in microalgal cells. The microalgae grown in wastewater showed micro-elements uptake and removal efficiencies of 71.2 ±â€¯3.5% COD, 81.9 ±â€¯3.8% NH4+, ∼100.0% NO3-, and 94.1 ±â€¯4.7% PO43-. The growth profile of Scenedesmus obliquus indicated a specific growth rate of 0.42 ±â€¯0.02 1·d-1 and carrying capacity of 0.88 ±â€¯0.04 g L-1. The lipid, protein, and carbohydrate yields (w·w-1 of dry weight) were 26.5 ±â€¯1.5%, 28.5 ±â€¯1.5%, and 27.5 ±â€¯1.6%, respectively. The de-oiled biomass was subjected to biochemical extraction, achieving protein and carbohydrate yields of 25.3 ±â€¯1.4% and 21.4 ±â€¯1.2%, respectively. Fourier transform infrared spectroscopy showed several functional groups (e.g., NH, CH3, CH2, CO, CN, PO, and SiO) on the biomass surface, confirming the accumulation of biochemical elements in microalgae. The thermal analysis of microalgal biomass depicted sequential stages of dehydration (60-190 °C), devolatilization (200-490 °C), and solid residue decomposition (490-600 °C). The cost-benefit analysis of microalgae cultivated in wastewater was derived regarding amortization and operating costs and energy and environmental benefits. The net profit of phycoremediation was 16885 US$·y-1, resulting in a payback period of 14.8 years (i.e., shorter than the project lifetime). Accordingly, the proposed phycoremediation process was economically viable.

Evaluation of various solvent systems for lipid extraction from wet microalgal biomass and its effects on primary metabolites of lipid-extracted biomass.

Microalgae have tremendous potential to grow rapidly, synthesize, and accumulate lipids, proteins, and carbohydrates. The effects of solvent extraction of lipids on other metabolites such as proteins and carbohydrates in lipid-extracted algal (LEA) biomass are crucial aspects of algal biorefinery approach. An effective and economically feasible algae-based oil industry will depend on the selection of suitable solvent/s for lipid extraction, which has minimal effect on metabolites in lipid-extracted algae. In current study, six solvent systems were employed to extract lipids from dry and wet biomass of Scenedesmus obliquus. To explore the biorefinery concept, dichloromethane/methanol (2:1 v/v) was a suitable solvent for dry biomass; it gave 18.75% lipids (dry cell weight) in whole algal biomass, 32.79% proteins, and 24.73% carbohydrates in LEA biomass. In the case of wet biomass, in order to exploit all three metabolites, isopropanol/hexane (2:1 v/v) is an appropriate solvent system which gave 7.8% lipids (dry cell weight) in whole algal biomass, 20.97% proteins, and 22.87% carbohydrates in LEA biomass. Graphical abstract: Lipid extraction from wet microalgal biomass and biorefianry approach.

A comparative study on biochemical methane potential of algal substrates: Implications of biomass pre-treatment and product extraction.

Dried powdered algae (SDPA), heat treated algae (MHTA), lipid extracted algae (LEA) and protein extracted algae (PEA) were digested to determine biomethane potential. The average CH4 production rate was ∼2.5-times higher for protein and lipid extracted algae than for whole algae (SDPA and MHTA) whilst the cumulative CH4 production was higher for pre-treated algae. Highest cumulative CH4 production (318.7mlCH4g-1VS) was observed for MHTA followed by SDPA (307.4mlCH4g-1VS). CH4/CO2 ratios of 1.5 and 0.7 were observed for MHTA and LEA respectively. Pre-treatment processes disrupted the algal cell wall, exposing intracellular material which remained intact as opposed to product extraction processes which broke down the intracellular compounds resulting in changes in elemental composition and decreases the cumulative gas yield and CH4/CO2 ratio. Comparative analysis determined that the most profitable route of biomass utilisation was protein extraction followed by biogas production giving ∼2.5-times higher return on investment.

Lipid extracted algae as a source for protein and reduced sugar: a step closer to the biorefinery.

The objective of this study was to investigate the feasibility of using lipid extracted algae (LEA) as a source for protein and reduced sugar, and the effects of various procedural treatments on their yields. LEA provided comparable yields of protein and reduced sugars to those from total algae. Oven drying provided highest yields of all products followed by freeze drying, while sun drying significantly lowered their yields. Effective cell disruption by microwave and autoclave increased the lipid yields from algae, but resulted in increased loss of other compounds with lipid extracting solvents lowering their yields during sequential extraction. Relatively inefficient cell disruption by ultrasonication and osmotic shock lowered the amount of cell protein lost to the lipid extracting solvents. These results highlight the complexity of concurrent extraction of all value added products from algae, and the need for proper selection of the processes to achieve the objectives of integrated biorefinery.

Adaptability of growth and nutrient uptake potential of Chlorella sorokiniana with variable nutrient loading.

Chlorella sorokiniana can sustain growth in conditions hostile to other species, and possesses good nutrient removal and lipid accumulation potentials. However, the effects of variable nutrient levels (N and P) in wastewaters on growth, productivity, and nutrient uptake by C. sorokiniana have not been studied in detail. This study demonstrates the ability of this alga to sustain uniform growth and productivity, while regulating the relative nutrient uptake in accordance to their availability in the bulk medium. These results highlight the potential of C. sorokiniana as a suitable candidate for fulfilling the coupled objectives of nutrient removal and biomass production for bio-fuel with wastewaters having great variability in nutrient levels.