With help from hungry Black Soldier Fly larvae, our expert Ian Banks has been researching how to turn latrine sludge into valuable prepupae.
Based in Cambodia during autumn 2011, Ian explains what he’s hoping to learn and how he’s doing it.
What are you trying to find out?
We want to know how much ‘food’ (latrine sludge) can be transformed into a valuable product, namely the Black Soldier Fly (BSF) prepupae. These can be processed into high-protein animal feed or biofuel. I’m feeding different rates of sludge into the colony to see which produces the most larvae. I’m also looking into how the larvae change the chemical makeup of the pit sludge as time goes by, which can affect its decomposition rates.
Where are you working?
I’m based with Sanitation Ventures’ partner WaterSHED (Water, Sanitation and Hygiene Enterprise Development), a public-private partnership led by the University of North Carolina and supported by USAID. It works to bring effective, affordable water and sanitation products to market in Cambodia, Laos and Vietnam, which is very much in line with Sanitation Ventures’ market-based approach. I’m conducting the experiments in the lab at WaterSHED’s office in Cambodia’s capital, Phnom Penh.
Where do the BSF larvae live?
I designed a BSF colony which was built by a local carpenter. It’s located behind the WaterSHED building, where the temperature stays around 30°C all day. The wooden structure is surrounded by netting to prevent flies escaping and other flies entering. It also protects the colony from lizards. The roof of transparent corrugated plastic allows in sunlight, which the adults need for breeding, and they have plants to rest on.
How did you start the colony?
I collected 30 late-stage BSF larvae and prepupae from around the chicken coops and pig pens at a self-sustaining orphanage here. The adults emerged and laid their eggs next to some chicken feed, and these hatched into small larvae. The sludge they now feed on is supplied by WaterSHED contacts among local pit emptiers who own pumping trucks for de-sludging pit latrines. The BSF lifecycle depends on ambient temperature and available food. From egg to adult, it should take 30-45 days: eggs to larvae, prepupae (the stage we’re interested in), pupae and finally adults laying eggs.
How will you get your results?
Each day I weigh the larvae, prepupae and the ‘food’ they’re eating. At the end I’ll be able to calculate which feeding ratio produces the most valuable amount of prepupae. I’m also doing experiments to determine different chemical properties of the sludge, including heavy metals such as lead and cadmium, so we can see whether the BSF larvae change these properties as they feed on the pit material. We’ll also heat sludge samples to 550°C in a high-temperature oven at the Royal University of Agriculture in Cambodia. This reduces them to ash, which we weigh to determine the total volatile solids.
Developing a BSF toilet
When we have the results in early 2012, we’ll feed these into our innovation process to explore how we can harness the power of BSF larvae in improving sanitation. The open innovation and crowdsourcing platform InnoCentive is running an online challenge for people worldwide to help us find a way to use BSF larvae in latrines to prevent them filling. Anyone can join in, so why not find out more and see if you can help?