Modelling shortcut nitrogen removal from wastewater using an algal–bacterial consortium

Abstract

A shortcut nitrogen removal process was investigated for treatment of high ammonium strength wastewater using an algal-bacterial consortium in photo-sequencing batch reactors (PSBRs). In this process, algae provide oxygen for nitritation during the light period, while denitritation takes place during the dark (anoxic) period, reducing overall energy and chemical requirements. Two PSBRs were operated at different solids retention times (SRTs) and fed with a high ammonium concentration wastewater (264 mg NH-N L), with a '12 hour on, 12 hour off' light cycle, and an average surface light intensity of 84 μmol m s. High total inorganic nitrogen removal efficiencies (∼95%) and good biomass settleability (sludge volume index 53-58 mL g) were observed in both PSBRs. Higher biomass density was observed at higher SRT, resulting in greater light attenuation and less oxygen production. A mathematical model was developed to describe the algal-bacterial interactions, which was based on Activated Sludge Model No. 3, modified to include algal processes. Model predictions fit the experimental data well. This research also proposes an innovative holistic approach to water and energy recovery. Wastewater can be effectively treated in an anaerobic digester, generating energy from biogas, and later post-treated using an algal-bacterial PSBR, which produces biomass for additional biogas production by co-digestion.

A comprehensive review on the use of algal-bacterial systems for wastewater treatment with emphasis on nutrient and micropollutant removal

“…Modeling of the algal-bacterial systems has to consider several factors such as light, carbon limitation, ammonia stripping along with biological and hydrodynamic processes. Arashiro et al [ 289 ] modeled nitrogen removal by modifying ASM3 by including two processes pertaining to algal growth and endogenous respiration. Ariza [ 201 ][] extended the model developed by Arashiro et al [ 289 ] by incorporating two additional processes: nitrogen storage by algal biomass and phototrophic growth on stored nitrogen.…”

“…Arashiro et al [ 289 ] modeled nitrogen removal by modifying ASM3 by including two processes pertaining to algal growth and endogenous respiration. Ariza [ 201 ][] extended the model developed by Arashiro et al [ 289 ] by incorporating two additional processes: nitrogen storage by algal biomass and phototrophic growth on stored nitrogen. These process parameters were estimated by performing respirometer tests on the photo-activated sludge.…”

Photo-oxygenation for nitritation and the effect of dissolved oxygen concentrations on anaerobic ammonium oxidation

“…Oxygen concentrations are also affected by the ratio between algae in the reactor that photosynthesise and respire in the illuminated zone, versus the algae in the dark zone that only carry out respiration. Arashiro et al (2017) tested the effect of solids retention time (SRT) in a photo-bioreactor (perfectly mixed sequencing batch reactor (SBR)) fed with reject water from an anaerobic digester treating swine manure.…”

“…Control-test-2 determined the potential ammonium removal by other mechanisms than anammox by incubating biomass harvested from the photo-bioreactor under dark and anoxic conditions without nitrite. concentrations or too high SRT (Arashiro et al, 2017). Nitrogen removal efficiency could be further improved by replacing nitritationdenitritation by nitritation-anammox (Manser et al, 2016).…”

A novel mechanistic model for nitrogen removal in algal-bacterial photo sequencing batch reactors

“…Furthermore, algal-bacterial models were developed to simulate algal-bacterial growth in photobioreactor (Zambrano et al, 2016;Arashiro et al, 2017;Shriwastav et al, 2018). However, complex interaction between microalgae and bacteria and the impact of operational conditions on nitrogen removal in the algal-bacterial systems are yet to be further studied.…”