Current advances in microalgae-based treatment of high-strength wastewaters: challenges and opportunities to enhance wastewater treatment performance

Abstract

Microalgae-based technologies, usually configured as high rate algal ponds (HRAP), are efficient, sustainable, and cost-effective alternatives for wastewater treatment due to their high removal efficiencies at low energy demand, ability to recover nutrients and ease of operation. HRAPs and other photobioreactors have been intensively studied in recent years for the treatment of highstrength wastewaters, which are mainly characterised by high and unbalanced (in terms of microalgae requirements) concentrations of organic carbon and nutrients. This review critically evaluated research papers that used microalgae-based systems for the removal of carbon and nitrogen from high-strength wastewaters. These systems can provide removal efficiencies up to 100% for organic matter and ammonium nitrogen. Relatively large area requirements, high evaporative losses, ammonia inhibition, poor light penetration and scattering, carbon dioxide limitation, and unbalanced nutrient ratios rank among the main current limitations of these technologies. Optimisation strategies, including modifications in bioreactor design and operation, can broaden their full-scale application for the treatment of high strength wastewaters.

Anaerobic co‐digestion of food waste and microalgae in an integrated treatment plant

“…Experimental data from the demonstration‐scale system were used to determine food waste fed to the anaerobic reactor and the microalgal biomass produced in the HRAP (Table 5). 32,56 According to literature, HRAPs have been used for treating diverse sorts of anaerobic supernatants, such as domestic sewage, animal manure, agricultural wastes, and food waste, among others 57 . Research has shown that, since food waste supernatants have a high concentration of organic matter, ammonia, and solids, its low C/N ratio, high N/P ratio, and high turbidity may hinder microalgae growth 57,58 …”

“…32,56 According to literature, HRAPs have been used for treating diverse sorts of anaerobic supernatants, such as domestic sewage, animal manure, agricultural wastes, and food waste, among others. 57 Research has shown that, since food waste supernatants have a high concentration of organic matter, ammonia, and solids, its low C/N ratio, high N/P ratio, and high turbidity may hinder microalgae growth. 57,58 Based on the results obtained in this scenario, a proportion of 99:1 (%VS FW :%VS MA ) of food waste and microalgal biomass would be fed to the anaerobic reactor, if all the microalgae produced with the current food waste fed to the digester were considered.…”

“…57 Research has shown that, since food waste supernatants have a high concentration of organic matter, ammonia, and solids, its low C/N ratio, high N/P ratio, and high turbidity may hinder microalgae growth. 57,58 Based on the results obtained in this scenario, a proportion of 99:1 (%VS FW :%VS MA ) of food waste and microalgal biomass would be fed to the anaerobic reactor, if all the microalgae produced with the current food waste fed to the digester were considered. As may be observed, the amount of food waste used is much higher than that of microalgae.…”

Algal biorefinery: a potential solution to the food–energy–water–environment nexus

“…Thus, there is a preference to use the appropriate wastewater effluents to obtain efficient nutrient uptake and remove the barriers in the way of microalgae-based wastewater treatment. 206…”

Balancing Microalgae and Nitrifiers for Wastewater Treatment: Can Inorganic Carbon Limitation Cause an Environmental Threat?

“…By providing oxygen to nitrifiers, algae substantially increase the overall ammonium removal capacity of the system, while nitrifiers reduce the oxygen level below the inhibition thresholds for algae . Nitrification, in turn, helps by keeping the ammonium concentration low, thus reducing the risk of free ammonia inhibition on algae, especially when high strength wastewaters are to be treated. , Nitrifiers convert ammonium into nitrate that can be uptaken by the algae. The combination between algae and nitrifying bacteria has also some drawbacks, inducing negative interactions like the competition for CO 2 or micronutrients or the inhibition of bacterial growth when the photosynthesis increases the pH level .…”