Resource recovery, preferably as high value products, is becoming an integral part of modern wastewater treatment, with conversion to heterotrophic or phototrophic/photosynthetic microbes a key option to minimise dissipation, and maximise recovery. This study compares the treatment capacities of purple phototrophic bacteria (PPB) and microalgae of five agri-industrial wastewaters (pork, poultry, red meat, dairy and sugar) to recover carbon, nitrogen, and phosphorous as a microbial product. The mediators have different advantages, with PPB offering moderate removals (up to 74% COD, 80% NH-N, 55% PO-P) but higher yields (>0.75 gCOD gCOD) and a more consistent, PPB dominated (>50%) product, with a higher crude protein product (>0.6 gCP gVSS). The microalgae tests achieved a better removal outcome (up to 91%COD, 91% NH-N, 73%PO-P), but with poorer quality product, and <30% abundance as algae.

Concentrated wastewaters from agricultural industries represent a key opportunity for the upcycling of organics, nitrogen and phosphorus to higher value products such as microbial protein. Phototrophic or photosynthetic microbes very effectively capture input organics and nutrients as microbial protein. This study compares purple phototrophic bacteria (PPB) and microalgae (photosynthesis) for this purpose, treating real, high strength poultry processing wastewater in continuous photo bioreactors utilising infrared (IR) and white light (WL) respectively. Both reactors could effectively treat the wastewaters, and at similar loading rates (4 kgCOD md). The infrared reactor (IRR) was irradiated at 18 W m and the white light reactor (WLR) reactor at 1.5-2 times this. The IRR could remove up to 90% total chemical oxygen demand (TCOD), 90% total nitrogen (TN) and 45% total phosphorus (TP) at 1.0 d hydraulic retention time (HRT) and recover around 190 kg of crude protein per tonne of influent COD at 7.0 kWh per dry tonne light input, with PPB dominating all samples. In comparison, the WLR removed up to 98% COD, 94% TN and 44% TP at 43-90% higher irradiance compared to the PPB reactor. Microalgae did not dominate the WLR and the community was instead a mix of microbes (algae, bacteria, zooplankton and detritus - ALBAZOD) with a production of approximately 140 kg crude protein per tonne influent COD.

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