The Oxygenic Photogranule Process for Aeration-Free Wastewater Treatment

Abstract

This study presents the oxygenic photogranule (OPG) process, a light-driven process for wastewater treatment, developed based on photogranulation of filamentous cyanobacteria, nonphototrophic bacteria, and microalgae. Unlike other biogranular processes requiring airlift or upflow-based mixing, the OPG process was operated in stirred-tank reactors without aeration. Reactors were seeded with hydrostatically grown photogranules and operated in a sequencing-batch mode for five months to treat wastewater. The new reactor biomass propagated with progression of photogranulation under periodic light/dark cycles. Due to effective biomass separation from water, the system was operated with short settling time (10 min) with effective decoupling of hydraulic and solids retention times (0.75 d vs 21-42 d). During quasi-steady state, the diameter of the OPGs ranged between 0.1 and 4.5 mm. The reactors produced effluents with average total chemical oxygen demand less than 30 mg/L. Nitrogen removal (28-71%) was achieved by bioassimilation and nitrification/denitrification pathways. Oxygen needed for the oxidation of organic matter and nitrification was produced by OPGs at a rate of 12.6 ± 2.4 mg O/g biomass-h. The OPG system presents a new biogranule process, which can potentially use simple mixing and natural light to treat wastewater.

Microalgal–bacterial aggregates with flue gas supply as a platform for the treatment of anaerobic digestion centrate

“…Previous studies recently reported microalgal enrichment under phototrophic conditions using activated sludge from wastewater treatment as inoculum. 22,23 Hence, it was not surprising to find out that the centrate herein used also contained microalgae.…”

Emerging biological processes for municipal wastewater treatment

“…Microalgal-bacterial granules can be obtained under aerated conditions and non-aerated conditions in the presence of light, and are called activated algal granules and photo-granules, respectively (Abouhend et al, 2018;Tiron et al, 2017). During the formation of photo-granules, extracellular polymeric substances secreted by microalgae play a key role, with a higher ratio of polysaccharides to proteins .…”

Mapping the biological activities of filamentous oxygenic photogranules

“…The production of oxygen by these cyanobacteria via photosynthesis is typically coupled to the oxygen consumption of heterotrophic bacteria that convert organic matter, for example, from wastewater, into CO 2 , which is immediately used by cyanobacteria for biomass synthesis. This syntrophic relationship between bacteria makes photogranules a promising candidate biomass for wastewater treatment (Abouhend et al, 2018, 2020). External aeration in conventional activated sludge is currently the major energy expenditure of wastewater treatment plants (Longo et al, 2016; Shoener et al, 2014).…”

“…External aeration in conventional activated sludge is currently the major energy expenditure of wastewater treatment plants (Longo et al, 2016; Shoener et al, 2014). In an OPG process, external aeration is not necessary (Abouhend et al, 2018) and therefore no energy for aeration is required. However, this energy may be off‐set in a bioprocess using OPGs by the energetic requirements of mixing and the potential supply of electric light for pollution removal.…”

“…photogranules a promising candidate biomass for wastewater treatment (Abouhend et al, 2018(Abouhend et al, , 2020. External aeration in conventional activated sludge is currently the major energy expenditure of wastewater treatment plants (Longo et al, 2016;Shoener et al, 2014).…”