Abstract

The treatment of different types of wastewater by physicochemical or biological (non-microalgal) methods could often be either inefficient or energy-intensive. Microalgae are ubiquitous microscopic organisms, which thrive in water bodies that contain the necessary nutrients. Wastewaters are typically contaminated with nitrogen, phosphorus, and other trace elements, which microalgae require for their cell growth. In addition, most of the microalgae are photosynthetic in nature, and these organisms do not require an organic source for their proliferation, although some strains could utilize organics both in the presence and absence of light. Therefore, microalgal bioremediation could be integrated with existing treatment methods or adopted as the single biological method for efficiently treating wastewater. This review paper summarized the mechanisms of pollutants removal by microalgae, microalgal bioremediation potential of different types of wastewaters, the potential application of wastewater-grown microalgal biomass, existing challenges, and the future direction of microalgal application in wastewater treatment.

Highlights

  • Global economic and societal development has led to increased water demand along with a water deficit

  • In the floatation of microalgae harvesting, often with coagulants’ addition, microscopic bubbles are introduced to the bottom of the floatation tank, where the cells are attached to the surface of the bubbles and get destabilized; the cells rise to the top and get concentrated [187,188]

  • A prolific growth rate, ability to adapt in different wastewaters and uptake nutrients or remove pollutants from wastewater, coupled with the assimilation of carbon dioxide, could make microalgal bioremediation of wastewaters very promising

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Summary

Introduction

Global economic and societal development has led to increased water demand along with a water deficit. Other drawbacks of conventional wastewater treatment processes are high energy consumption, greenhouse gas emissions, recyclable resource wastage, and excessive solid landfilling Several technologies such as hydrothermal carbonization, anaerobic digestion, and pyrolysis are being developed and applied to maximize energy recovery from waste biosolids to phase out from excessive solid landfilling [1,5]. There is a need for alternative wastewater treatment methods that would be low carbon-emitting and high on resource recycling and consume less energy and promote biorefinery and circular economy concepts. One such alternative option could be the use of microalgae to treat industrial, agricultural, and domestic wastewaters. The major challenges in microalgal bioremediation of wastewaters were pointed out, and recommendations were made to overcome these challenges

Selection of Strains
The Necessity of Pretreatment of Wastewater
Nutrient Uptake
Organic Removal
Symbiotic Relationship
Passive Removal of Contaminants at Elevated pH
Microalgal Cultivation in Different Wastewaters
Municipal Wastewater
Industrial Wastewater
Produced Water
The Aqueous Phase of Biomass to Energy Generation Process
Pharmaceuticals Wastewater
Agro-Industry Wastewater
Wastewater Derived from Mining Activity
Landfill Leachate
Aquaculture Wastewater
Suspended Growth
Attached Growth
Harvesting of Microalgae Biomass
Sedimentation
Auto-Flocculation
Bio Flocculation
Coagulation–Flocculation
Electrocoagulation
Flotation of Microalgae
Filtration
Application of the Produced Biomass
Composition
The Necessity of Pretreatment
Biofertilizer
Energy Production and Nutrients Recycling
Bulk Chemicals
Animal Feed Production
Ingredients for the Cosmetic Industry
Challenges of Microalgal Wastewater Treatment and Future Research Direction
Findings
Conclusions

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