Assessment of Microalgal-Bacterial Granular Sludge Process for Environmentally Sustainable Municipal Wastewater Treatment

Abstract

The conventional municipal wastewater treatment processes are facing increasing pressures due to their huge energy consumption, significant emissions of greenhouse gases, and low resource recovery potential. As such, the microalgal–bacterial granular sludge (MBGS) process has recently been explored with the aim for concurrent high-efficiency water, energy, and resource recovery from municipal wastewater in an environmentally sustainable manner. This review attempts to offer a holistic view of the state of the art techniques of MBGS process for municipal wastewater treatment. It was shown that mutualism and symbiosis between microalgae and bacteria could determine the physical structure and microbial community of MBGS. Microbial assimilation instead of dissimilation was identified to be the main mechanisms for removing soluble organics, ammonia, and phosphate in municipal wastewater under both light and dark conditions. Different from the conventional biological nutrients removal processes, wastewater nutrients were effectively fixed into MBGS which could be regarded as a potential source for further energy and resource recovery. Compared to the conventional activated sludge process, the energy consumption and carbon emissions would be reduced, respectively, by 100% and 63% by adopting MBGS. It is apparent that MBGS could offer an alternative toward energy- and carbon-neutral municipal wastewater treatment.

Phosphorus Recovery from Eutrophic Lake Water Using Al/Fe Micro-Electrolysis

“…In eutrophic lake water, P generally exists in particulate form and it can be easily uptaken by microalgae or absorbed by suspended particles. ,, For example, PP accounts for 67.4% of TP in eutrophic Taihu Lake water on average . Charge neutralization is an essential step in flocculation, which can eliminate the energy barrier for particle aggregation .…”

“…Therefore, P recovery has been considered as a promising strategy for combating the P crisis. 1,4,5 In the food system, only approximately 16.0% of the P applied as fertilizer enters the food chain, and even less is finally assimilated. 6,7 Large fractions are lost to water bodies through soil erosion, animal wastes, and crop residues, eventually leading to eutrophication in rivers, lakes, reservoirs, estuaries, and coastal oceans.…”

“…Moreover, it has implications for transboundary disputes because almost all existing sources of P are located in only a few countries. Therefore, P recovery has been considered as a promising strategy for combating the P crisis. ,, …”

“…Iron/aluminum (Fe/Al) micro-electrolysis can generate Fe/Al ions and positively charged colloidal hydroxides, which can precipitate, adsorb, or flocculate dissolved and particulate matters. − With its advantages of low cost, high efficiency, and easy operation, Fe/Al micro-electrolysis has been widely applied to concentrate and harvest high-value resources from wastewater. − For instance, Fe micro-electrolysis was used to recover rare-earth elements from wastewater . In eutrophic lake water, P exists in both dissolved and particulate forms after uptaking by microalgae or absorption by particles . With the application of Fe/Al micro-electrolysis, dissolved P may be concentrated by Fe/Al ion precipitation and Fe/Al hydroxide adsorption, and particulate P (PP) may be concentrated by Fe/Al hydroxide flocculation, facilitating the co-harvesting of dissolved P and PP from eutrophic lake water.…”

Cultivation of algal‐bacterial granular sludge and degradation characteristics of tetracycline

“…Different from CAS process with energy‐intensive aeration, the algal‐bacterial granular sludge process can operate without aeration (Abouhend et al, 2018), and the net energy consumption is zero, while the net energy consumption of the CAS technology is 0.32 kwh/m 3 (Ji & Liu, 2021). On the other hand, microalgae photosynthesis can use the carbon dioxide released in the bacterial degradation process of organic matters; therefore, algal‐bacterial granular sludge process emits less greenhouse gases, that is, only 0.30‐kg CO 2 e/m 3 , while the CAS technology emits 0.81‐kg CO 2 e/m 3 (Ji & Liu, 2021). In addition, the algal‐bacterial granular sludge is compact and conducive to the separation of sludge and water.…”