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.