Anaerobic membrane bioreactor (AnMBR) is a
promising sustainable alternative to common wastewater treatment technologies
(WWT) for producing high-quality effluent while recovering most of the energy
stored in wastewater as biogas. In addition, the nutrient-rich AnMBR effluent
provides a unique opportunity to recover both NH 4 + and PO 4 3- as a
sustainable alternative to energy-intensive production of inorganic
fertilizers. A promising technology for nutrients recovery is microalgae cultivation.
Moreover, sustainable WWT should include waste management. Lately, there has
been a growing interest in converting low-cost wastewater sludge into
hydrochar. The goal of this research was to develop, investigate, and analyze a
near-zero waste treatment of food-processing wastewater consisting of AnMBR
with outdoor PBR microalgae cultivation and hydrothermal carbonization under
realistic arid- desert climate conditions for the production of high-quality
effluent, recovery of nutrients, carbon, and energy.
The wastewater contained average values of 1.5
gr/L total organic carbon, 160 mg/L total nitrogen, and 9 mg/L total phosphate.
The AnMBR process reduced total organic carbon by 97%, which was partially
recovered as biogas and hydrochar. The AnMBR operated under constant
sub-critical flux and therefore, the fouling was kept relatively low throughout
the study. The AnMBR effluent was used as a growth medium for the cultivation
of microalgae under outdoor conditions during one year (four seasons). The TN
and TP were efficiently recovered and their concentration in the effluent
reached the required standards for discharge within 2-5 days in summer in
winter, respectively. Mass balance analysis demonstrated near-complete carbon
and nutrient recovery and high-water recovery.
Overall, we present an integrated process with a
near-zero waste discharge producing high-quality effluent, nutrient recovery
into microalgae biomass, and energy production as biogas and hydrochar.