SINGAPORE - Murky wastewater from washing uncooked staples like rice or soya beans may eventually become “microbial factories” to grow food for fish at an industrial scale.
Scientists from Nanyang Technological University (NTU) and the Singapore Centre for Environmental Life Sciences Engineering (SCELSE) have found that various microbial organisms in used water from soya processing plants can become a “substantial” amount of protein.
These microbes multiply even when simply stirred at room temperature in bioreactors – making it a cheap, convenient and sustainable way to synthesise protein.
The proof-of-concept study, which will be published in the journal Science Of The Total Environment in May, shows that such wastewater itself is nutrient rich, and can support the growth of microbial communities containing many types of beneficial bacteria that can produce vitamins or probiotics.
Once the nutrients in the water are exhausted, the microbes can be dried and harvested as protein.
Around 40 per cent of the dried biomass extracted from exhausted soya processing wastewater is viable protein, with essential amino acids needed for fish aquaculture.
Professor Stefan Wuertz, who led the study, said the new finding has the potential to create a local sustainable source of aquaculture feed, which is typically made of ground-up fish – a finite, imported resource.
According to a report by non-governmental organisations Changing Markets Foundation and Compassion in World Farming, over 69 per cent of fishmeal is used to feed farmed fish, which can lead to overfishing and depletion of wild fish populations.
The local soya processing market is valued at around $200 million, while the market for beer production is valued at around $1.36 billion, noted Prof Wuertz, who is deputy director of SCELSE.
He said 4.9 litres of nutrient-rich wastewater are produced for every litre of soya sauce produced in Singapore, while 4 litres of wastewater are produced for every litre of beer made here.
“With aquaculture producing around 10 per cent of Singapore’s local food consumption, we thought that connecting the waste stream of the food processing industry to the growing needs of the aquaculture industry would help create a local circular economy.”
Additionally, used water from food processing plants is also particularly viable compared with wastewater from other sources such as sewage, because it must already meet the Singapore Food Agency’s standards for cleanliness and the absence of dangerous pathogens.
A further study is currently under way to quantify how protein yields from food processing wastewater can be improved to make them viable as a replacement for aquaculture feed.
The study will be out later in 2023.
Prof Wuertz said the best way to operate such a microbial protein farming facility would be for food processing companies to build the facility close to their premises, as this would avoid the logistical difficulties and cost of transporting large amounts of wastewater to a central plant.
The microbial protein harvested can be sold to aquaculture farms, creating a new revenue stream for food processing companies, he added.
Prof Wuertz said that while the proof-of-concept study was done specifically on wastewater from soya processing plants, he expects the findings to be applicable to wastewater from any type of food processing plant.
“What we are trying to do is build a blueprint that can inform those who would like to apply such technology towards contributing to the circular economy in a commercially viable way.”