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

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.

Automated summary

The MBGS process utilizes mutualism and symbiosis between microalgae and bacteria to efficiently remove soluble organics, ammonia, and phosphate from municipal wastewater, while also fixing wastewater nutrients into granular sludge for potential energy and resource recovery. Compared to traditional treatment processes, MBGS can significantly reduce energy consumption and carbon emissions, offering a promising alternative for energy-and carbon-neutral municipal wastewater treatment.