Current and Future Perspective of Microalgae for Simultaneous Wastewater Treatment and Feedstock for Biofuels Production

Algae-based approaches for Holistic wastewater management: A low-cost paradigm

Aquatic algal communities demonstrated their appeal for diverse industrial applications due to their vast availability, ease of harvest, lower production costs, and ability to biosynthesize valuable molecules. Algal biomass is promising because it can multiply in water and on land. Integrated algal systems have a significant advantage in wastewater treatment due to their ability to use phosphorus and nitrogen, simultaneously accumulating heavy metals and toxic substances. Several species of microalgae have adapted to thrive in these harsh environmental circumstances. The potential of algal communities contributes to achieving the United Nations' sustainable development goals in improving aquaculture, combating climate change, reducing carbon dioxide (CO2) emissions, and providing biomass as a biofuel feedstock. Algal-based biomass processing technology facilitates the development of a circular bio-economy that is both commercially and ecologically viable. An integrated bio-refinery process featuring zero waste discharge could be a sustainable solution. In the current review, we will highlight wastewater management by algal species. In addition, designing and optimizing algal bioreactors for wastewater treatment have also been incorporated.

A review on the sustainable procurement of microalgal biomass from wastewaters for the production of biofuels

The feasibility of microalgal biomass as one of the most promising and renewable sources for the production of biofuels is being studied extensively. Microalgal biomass can be cultivated under photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic cultivation conditions. Photoautotrophic cultivation is the most common way of microalgal biomass production. Under mixotrophic cultivation, microalgae can utilize both organic carbon and CO2 simultaneously. Mixotrophic cultivation depicts higher biomass productivity as compared to photoautotrophic cultivation. It is evident from the literature that mixotrophic cultivation yields higher quantities of polyunsaturated fatty acids as compared to that photoautotrophic cultivation. In this context, for economical biomass production, the organic carbon of industrial wastewaters can be valorized for the mixotrophic cultivation of microalgae. Following the way, contaminants' load of wastewaters can be reduced while concomitantly producing highly productive microalgal biomass. This review focuses on different aspects covering the sustainable cultivation of different microalgal species in different types of wastewaters.

Microalgae bioreactor for nutrient removal and resource recovery from wastewater in the paradigm of circular economy

Every day, large quantities of wastewater are discharged from various sources that could be reused. Wastewater contains nutrients such as nitrogen or phosphorus, which can be recovered. Microalgae-based technologies have attracted attention in this sector, as they are able to bioremediate wastewater, harnessing its nutrients and generating algal biomass useful for different downstream uses, as well as having other advantages. There are multiple species of microalgae capable of growing in wastewater, achieving nutrient removal efficiencies surpassing 70%. On the other hand, microalgae contain lipids that can be extracted for energy recovery in biodiesel. Currently, there are several methods of lipid extraction from microalgae. Other biofuels can also be obtained from microalgae biomass, such as bioethanol, biohydrogen or biogas. This review also provides information on bioenergy products and products in the agri-food industry as well as in the field of human health based on microalgae biomass within the concept of circular bioeconomy.

Biotechnology of Microorganisms from Coal Environments: From Environmental Remediation to Energy Production

Simple Summary

Despite the wide perception that coal environments are extreme habitats, they harbor resident microbial communities. Coal-associated habitats, such as coal mine areas/drainages, spoil heaps, and coalbeds, are defined as complex ecosystems with indigenous microbial groups and native microecological networks. Resident microorganisms possess rich functional potentials and profoundly shape a range of biotechnological processes in the coal industry, from production to remediation.

Abstract

It was generally believed that coal sources are not favorable as live-in habitats for microorganisms due to their recalcitrant chemical nature and negligible decomposition. However, accumulating evidence has revealed the presence of diverse microbial groups in coal environments and their significant metabolic role in coal biogeochemical dynamics and ecosystem functioning. The high oxygen content, organic fractions, and lignin-like structures of lower-rank coals may provide effective means for microbial attack, still representing a greatly unexplored frontier in microbiology. Coal degradation/conversion technology by native bacterial and fungal species has great potential in agricultural development, chemical industry production, and environmental rehabilitation. Furthermore, native microalgal species can offer a sustainable energy source and an excellent bioremediation strategy applicable to coal spill/seam waters. Additionally, the measures of the fate of the microbial community would serve as an indicator of restoration progress on post-coal-mining sites. This review puts forward a comprehensive vision of coal biodegradation and bioprocessing by microorganisms native to coal environments for determining their biotechnological potential and possible applications.