How to make feed from flies

Have you ever noticed larvae in your compost bin (if you have not, watch this video)? Does their wriggling slimy appearance make you feel squeamish? Well, brace yourself as I take you on a tour of Sanergy`s waste treatment facility in Nairobi, Kenya. This story is about my work with Sanergy, a company that treats organic waste with a process that uses tens of millions of fly larvae. The larvae convert waste into larval biomass and, eventually, a valuable animal feed.

One way to offset the cost of waste management is to create a revenue stream from waste treatment products. Organic matter such as human faeces or kitchen waste include nutrients, energy, and water. These resources can be used to produce products such as compost, biogas, fuels, heat, or even electricity. However, it is a common misconception that treatment products are an easy way to cover all treatment efforts.

Sanergy’s black soldier fly larvae treatment facility, an award winning social enterprise, is among the largest in the world. While Sanergy takes advantage of the larvae’s big appetite for waste, it is not viable at the current scale. Operationally, it is important to take into account economies of scale. Sanergy needs to treat more waste and produce animal feed to be viable. Not just any waste will do; however, blindly accepting more waste has dramatic consequences on insect biomass production. Since larvae control their growth depending on available nutrients, a systematic approach for facility scale-up is necessary. Scaling up requires consideration of the waste nutrient composition and treatment performance, availability, and, of course, costs. (Read more here)

The collaboration also helps me to reflect on the current narratives regarding the hot topic of treating waste with fly larvae, and scenarios for identifying more sustainable production concepts via Life Cycle Assessments (LCAs) performed by an interdisciplinary team around the Sustainable Food Processing (SFP) Group at ETH Zurich. The case study of Nairobi demonstrates that sourcing waste for a black soldier treatment facility is actually challenging, despite the daunting waste management problem. In reality, high-quality wastes that have the highest potential for viable facility operations already have a use and price. Taking these waste out of existing resource recovery options may conflict with the frequently claimed environmental sustainability of insect-based feeds. For example, restaurant and hotel waste typically result in a high larval biomass production due to their high nutrient content, but come at a price due to their already existing use as animal feed. Animal manure and fruit waste might also already have a use as soil conditioner, are available at lower cost, but have a lower biomass production due to their lower overall nutrient content. While it is more sustainable to use waste products that are not already used for feed - such as animal manure and fruit waste - this process produces less larvae and changes the economic viability. The current aim is to strike a balance by creating animal feed from high-quality waste products that do not produce larvae more sustainable than the status quo.

Moritz Gold is an Engineering for Development (E4D) doctoral student in the group of Prof. Alexander Mathys at ETH Zurich’s Laboratory of Sustainable Food Processing, as well as Dr. Christian Zurbrügg, Eawag: Department of Water, Sanitation and Solid Waste for Development. His research is funded by the Sawiris Foundation for Social Development, Eawag, ETH Global, ETH Foundation and Bühler AG. Moritz holds an MSc. in Environmental Engineering from the University of Stuttgart. Since 2013, he has worked on waste management in India, Uganda, Senegal, Tanzania, and Kenya.