Abstract
Wastewater is not a liability, instead considered as a resource for microbial fermentation and value-added products. Most of the wastewater contains various nutrients like nitrates and phosphates apart from the organic constituents that favor microbial growth. Microalgae are unicellular aquatic organisms and are widely used for wastewater treatment. Various cultivation methods such as open, closed, and integrated have been reported for microalgal cultivation to treat wastewater and resource recovery simultaneously. Microalgal growth is affected by various factors such as sunlight, temperature, pH, and nutrients that affect the growth rate of microalgae. Microalgae can consume urea, phosphates, and metals such as magnesium, zinc, lead, cadmium, arsenic, etc. for their growth and reduces the biochemical oxygen demand (BOD). The microalgal biomass produced during the wastewater treatment can be further used to produce carbon-neutral products such as biofuel, feed, bio-fertilizer, bioplastic, and exopolysaccharides. Integration of wastewater treatment with microalgal bio-refinery not only solves the wastewater treatment problem but also generates revenue and supports a sustainable and circular bio-economy. The present review will highlight the current and advanced methods used to integrate microalgae for the complete reclamation of nutrients from industrial wastewater sources and their utilization for value-added compound production. Furthermore, pertaining challenges are briefly discussed along with the techno-economic analysis of current pilot-scale projects worldwide.
Highlights
Water is a natural resource and considered the most essential component of all living creatures
It is observed that C. vulgaris efficiently utilized and removed the high concentration of both nitrate and nitrite from the culture medium and simultaneously produces algal biomass for several wastewater treatments (Taziki et al, 2015)
Use of membrane-based harvesting method has been reported for the recovery of Scenedesmus almeriensis biomass using polyvinylidene fluoride (PVDF) membrane which helps in separation by retaining biomass and growth media is passed through the membrane filter (Marino et al, 2019)
Summary
Water is a natural resource and considered the most essential component of all living creatures. A recent study reported faster growth rates and higher biomass production with successful nutrient removal capacity in C. vulgaris when grown in the alginate-chitosan matrix (Castro and Ballesteros, 2020) Such porous bead structures provide a protected environment for the selected species to thrive in a wastewater setting. It is observed that C. vulgaris efficiently utilized and removed the high concentration of both nitrate and nitrite from the culture medium and simultaneously produces algal biomass for several wastewater treatments (Taziki et al, 2015). For the production of oils and biofuels, it is economical to starve the culture for nitrogen content and will shorten production cycles and the waste content produced (Chen et al, 2011) Micronutrients such as iron, manganese are required in small amounts (2.5–30 ppm) and trace elements, such as cobalt, zinc, and molybdenum, are essential in very low concentrations (2.5–4.5 ppm) for efficient growth of microalgae. The major disadvantage of this method is the presence of harmful chemicals that pose environmental risks
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