Microalgae for municipal wastewater nutrient remediation: mechanisms, reactors and outlook for tertiary treatment

Abstract

This review explores the use of microalgae for nutrient removal in municipal wastewater treatment, considering recent improvements in the understanding of removal mechanisms and developments of both suspended and non-suspended systems. Nutrient removal is associated to both direct and indirect uptake, with the former associated to the biomass concentration and growth environment (reactor). Importantly, direct uptake is influenced by the Nitrogen:Phosphorus content in both the cells and the surrounding wastewater, with opposite trends observed for N and P. Comparison of suspended and non-suspended systems revealed that whilst all were capable of achieving high levels of nutrient removal, only nonsuspended immobilized systems could do so with reduced hydraulic retention times of less than 1 day. As microalgae are photosynthetic organisms, the metabolic processes associated with nutrient assimilation are driven by light. Optimization of light delivery remains a key area of development with examples of improved mixing in suspended systems and the use of pulsating lights to enhance light utilization and reduce costs. Recent data provide increased confidence in the use of microalgae for nutrient removal in municipal wastewater treatment, enabling effluent discharges below 1 mg L −1 to be met whilst generating added value in terms of bioproducts for energy production or nutrient recovery. Ultimately, the review suggests that future research should focus on non-suspended systems and the determination of the added value potential. In so doing, it is predicted that microalgae systems will be significant in the delivery of the circular economy.

Nutrient removal by alginate‐immobilized Chlorella vulgaris: response to different wastewater matrices

“…The application of suspended algal systems can be limited by the difficulty of removing algae from wastewater after the treatment, and low concentrations of algae in the reactor, which results in low treatment rates with typical hydraulic retention times (HRTs) of 4 to 10 days . Immobilization of algal cells by entrapment in alginate beads facilitates the initiation and maintenance of higher concentrations of algae in the reactor, enabling rapid nutrient removal (HRT < 12 h) .…”

Using agro-industrial wastes for the cultivation of microalgae and duckweeds: Contamination risks and biomass safety concerns

“…), as well gaseous waste streams such as flue gases. The aptitude of microalgae and duckweed to grow on a range of waste streams has been extensively reviewed (Abinandan and Shanthakumar, 2015;Cai et al, 2013;de la Noüe and de Pauw, 1988;Iqbal, 1999;Journey et al, 1991;Markou and Georgakakis, 2011;Markou et al, 2014;Van Den Hende et al, 2012Whitton et al, 2015).…”

Use of Artificial Aquatic Food-Web for Post-Treatment of Domestic Wastewater in Cold Climate: A Review

“…Nutrients are consumed and further transformed through a series of biochemical processes taking place in the algal cell. They can be assimilated into nucleic acids and proteins for algae biomass growth or stored in the algae cells (Cai et al, 2013;Whitton et al, 2015). In wastewater, nutrients are mostly found in the organic form and as inorganic compounds such as ammonium, nitrate and orthophosphate.…”