Nematode biomass production from sewage sludge as a novel method for circular economy

Sludge generated in urban wastewater treatment plants is a huge environmental and economic challenge of sustainability. Sludge recovery is an environmental necessity and is a requirement for wastewater treatment plants. Predators have been proposed as a biological solution and simultaneously obtaining by-product of interest. Nematodes are predators that are found naturally in sludge but have never been proposed for sludge reduction. In this work, Caenorhabditis elegans, a nematode broadly used for biomedical studies, was used to grow on urban sludge, reaching a remarkable average population up to 92,668 nematodes/mL, 50.6% of sludge was converted into nematode biomass and up to 21.0% of organic matter removed. To demonstrate the viability of this nematode to grow and reduce urban sludges, different experiments in solid and liquid culture media were performed. The physio-chemical composition of the different types of sludges generated in the urban wastewater treatment plants was determined. The total lipids (4.52%, w/w) and fatty acid profiles obtained in the nematode biomass were determined. This work presents a new method to valorise urban sludge and opens the possibility to obtain by-products with high added value.