BIOLOGICAL CONVERSION OF FUEL SYNTHESIS PROCESS WATER TO SINGLE CELL PROTEIN AND OTHER VALUE BIOPRODUCTS FOR AQUACULTURE FEED USING PURPLE NON-SULFUR BACTERIA (PNSB)

Abstract

The global water and food security crisis has invoked the need for audacious approaches to achieve sustainable development. This project aims to bridge this gap by facilitating the production of single-cell protein (SCP) via the treatment of fuel synthesis process water (FSPW) – a high-strength industrial wastewater notably abundant in the Gulf Cooperation Council region. Resource recovery of SCP from organic waste by microbes like yeast and microalgae is commonly documented. However, in recent times, the phototrophic Purple Non-Sulfur Bacteria (PNSB) have emerged as a favourable option for both wastewater treatment and resource recovery due to their bioproduct-rich biomass and ability to withstand diverse culture/environmental conditions. The broad objectives of this research were to optimise culturing conditions for PNSB in FSPW, with pollutant removal rate, biomass yield, and biomass protein content as key metrics indicators. Other objectives of this project were to optimise cellular disruption methods of PNSB mixed culture biomass for accurate protein quantification, evaluate PNSB’s resilience in the FSPW feedstock under extreme culture conditions and validate the biotechnology’s feasibility via a naturally-illuminated pilot-scale setup (155L flat-panel photobioreactor). Results revealed that commonly employed cellular disruption methods (chemical, thermal, sonication, and alkaline-assisted thermal treatment) proved ineffective due to PNSB’s distinct cellular features, with NaOH-assisted sonication emerging as the preferred method. Moreover, PNSB proved its resilience and metabolic versatility by thriving in diluted (5X) and undiluted FSPW (COD =10.1 g/L), achieving COD and NH4-N removal rates between 78% and 100%. In addition, comprehensive experimentation on upstream conditions revealed that even when cultured at unconventional C:N ratios (19:1 to 38:1), PNSB adapted to low light intensity (9.6 W/m2), visible light, diurnal light cycles, fluctuating pH and temperature, extreme pH and iv temperature, excess ammonium, increased conductivity, and anaerobic/microaerobic conditions resulting in significant pollutant removal rates (as high as 2,100 mgCOD∙L-1∙d-1, 86 mgNH4-N∙L-1∙d-1, and 16 mgPO4-P) and substantial biomass protein- up to 63% dry weight (DW). Oxygen availability was the most integral factor, with anaerobic conditions resulting in higher PNSB selectivity and biomass yield, while microaerobic conditions resulted in higher pollutant removal rate and biomass productivity. Furthermore, PNSB’s diazotrophic metabolism was exploited to efficiently treat zero-nitrogen FSPW (COD= 3.0-6.0g/L) at small (150 mL) and large scale (65 L), producing substantial quantities of protein-rich biomass (43% DW) for aquaculture testing. In addition, biotechnology’s feasibility was validated via the naturally-illuminated pilot testing, resulting in protein-rich biomass (>50% DW), and substantial biomass areal productivity (6.8 to 13.9 g VSS∙L-1∙d-1) and yields (0.64 to 0.82 gvss/gCOD consumed). Further biomass characterisation revealed that its amino acid content surpassed that of plant-based proteins (e.g. soybean), satisfying the nutritional needs of aquaculture species and poultry. Additionally, the analysis confirmed significant quantities of other value bioproducts (e.g. lipids and pigments) and the absence of metals of public health concern. Overall, this biotechnology demonstrates promising potential as a circular economy and environmental sustainability driver, effectively merging greener treatment methods for high-strength industrial wastewater with the upcycling of protein-rich biomass. This approach presents a holistic solution, potentially alleviating energy, food, and water scarcity challenges.

Date of Award	2024
Original language	American English
Awarding Institution	HBKU College of Science and Engineering