Blog post by Heather Purshouse
If you have an interest in faecal sludge management, then you have probably heard of black soldier fly larvae (BSFL). These bugs have attracted the interest of WASH specialists due to their widespread distribution in the tropics, and emerging use in organic waste management. In theory, BSFL treatment of faecal sludge can offer faster processing times then composting, and lower energy requirements than technologies such as LaDePa, provided that the local climate is suitably warm. What’s more, spent biomass and insect frass can potentially be utilised as fertiliser or soil conditioner in agriculture, whilst larvae can be processed to make animal feed or biodiesel.
So, how are BSFL being used to treat faecal sludge, at present, around the world?
Scaling up: commercial and municipal operations
In terms of small-to-medium-scale operations treating faecal sludge, a number of organisations in South Africa and Kenya are making substantial progress with support from the continental leader in BSFL organic waste treatment – Agriprotein.
In South Africa, The BioCycle runs a community-level BSFL faecal sludge treatment plant in an informal settlement in Cape Town, and was also commissioned by eThekwini municipality to operate a new BSFL treatment plant to process faecal waste from the municipality’s urine diverting toilets (UDTs) (The BioCycle n.d., Sustainable Sanitation Alliance 2018). This plant is owned by the municipality and operated by The BioCycle, and is designed to process 20 tonnes of material per day (Alcock et al. 2016, Sustainable Sanitation Alliance 2018). UDT waste is mixed with primary sewage sludge and market waste, in order to increase the moisture levels and nutritional content for the larvae. Rearing of BSF does not take place on site, although there are plans to install a hatchery in the future. Instead, young larvae (3-4 days old) are received from the AgriProtein facilities in Cape Town, reared on food waste with a high nutrient content in an on-site ‘nursery,’ and then moved to the faecal sludge treatment bays. Sale of larvae as chicken/fish feed, larvae oil as biodiesel, and insect frass as soil conditioner and as biochar will take place in the near future, and is expected to provide a revenue stream to supplement the gate fee.
Outside of South Africa, the only other prominent example of BSFL being used to treat faecal sludge at scale is by Sanergy, who run a franchised network of public UDTs in the informal settlements of Nairobi, Kenya. Faecal sludge is removed from the toilets daily, co-processed with organic waste by BSFL at a centralised facility, and larvae are sold as animal feed (Sanergy 2015). A research partnership with Agriprotein has been established (Sanergy 2014), whilst experimentation is underway to improve the separation process for the larvae and residue (Ruto 2016).
On a smaller scale, Water for People (WfP) also tried feeding faecal sludge from pit latrines to BSFL as part of a trial in Kampala, Uganda (Sustainable Sanitation Alliance 2018). Whilst they saw that BSFL can eat and survive on faecal sludge, market waste is preferred, with jackfruit being particularly enjoyed by the larvae. The trial was discontinued after a few years in part due to concerns about the social acceptability of the products, however, a spin-off company called Natures Answer was created by WfP employees, which will use BSFL to process market waste and sell larvae as chicken feed.
All plants apply post-processing treatment steps to by-products, as pathogens can potentially be transmitted on larval or prepupal skin, inside larvae/prepupae, and in frass. The BioCycle community-level plant boils larvae for an hour, utilising frass as fuel for the process, whilst the eThekwini plant dries the larvae in the oven and then converts them into meal or oil, whilst residue is processed into biochar (The BioCycle 2013, Sustainable Sanitation Alliance 2018). Sanergy boil larvae, then dry them in the sun prior to selling (Sanergy 2015).
Scaling down: household-level facilities
What about using BSFL at the household level? A project in Mozambique has been attempting to design, create and implement the world’s first BSFL toilet. As of February 2018, field trials are being carried out in Maputo (Biological Urban Sanitation Project n.d.). The Biological Urban Sanitation (BUS) project pilot latrines are made up of a flushing toilet draining onto a permeable suspended bed, where BSFL live and feed on faecal material. Adult flies are expected to emerge from the latrine and remain nearby to mate and lay eggs in the toilet.
Other efforts to innovate and develop the application of BSFL in sanitation at a household level include the LSHTM BSF Toilet Design Challenge, held in 2012. Two designs emerged: the ‘kone’, and the ‘daisy chain’ (London School of Hygiene and Tropical Medicine n.d.). The ‘kone’ is a rubber cone, and the ‘daisy chain’ is a tube, both of which can be lowered through the latrine drop hole and placed on the surface of the pit. Larvae, which are seeded into the pit, consume faecal waste and then climb up the sides of the cone, or inside the tube, and accumulate in a collection pot once they reach the prepupal migratory stage. The cone or tube can be periodically removed and pupae harvested. LSHTM has expressed an intention to prototype and test both systems, but no further developments have been shared to date (Ibid.).
After several years of study and trials, there is some consensus that a semi-decentralised BSFL treatment plant could potentially offer the most robust model for municipalities looking to operate local organic and faecal sludge BSFL treatment plants (Sustainable Sanitation Alliance 2018, Lohri et al. 2017, Diener et al. 2015). Such a system would involve larvae being bred and reared in a centralised hatchery and then regularly distributed to decentralised waste processing sites. The benefits of a semi-decentralised system include centralisation of specialist expertise and resources on the delicate task of fly rearing, whilst keeping satellite faecal sludge and organics processing sites located close to where the material is being produced. This could be particularly useful where climatic conditions mean that additional heat sources are required to rear flies, and where sources of organic waste and faecal sludge are distributed across a large area. It also provides the opportunity to centralise more technical equipment for converting larvae/prepupae into meal, biodiesel, and chitin, as grown larvae can be returned from the waste treatment sites to the centralised site for processing.
In terms of research priorities, there is currently a knowledge gap as to how the effectiveness of the BSFL treatment process can be improved and optimised, especially in the context of highly contaminated feed stocks. Whilst insect frass by-products from the treatment process are promoted for agricultural use, their safety is not yet fully established and their marketability is unclear. My PhD seeks to fill these knowledge gaps by investigating the safety and socio-cultural acceptability of by-products from the treatment process intended for agricultural use.
Alcock, N., Wilson, D., Still, D., Mercer, S., Gounden, T., and Buckley, C. (2016) ‘Treating UD Faecal Waste Using Black Soldier Fly (BSF): A Municipal, Researcher and Contractor Partnership’. in 80th IMESA Conference. held 2016 at East London. Institute of Municipal Engineering of South Africa, 129–134
Biological Urban Sanitation Project (n.d.) Home [online] available from <https://www.youtube.com/channel/UCYXWm2uK4hSQG6_aQAFvt8g> [15 March 2018]
Diener, S., Lalander, C., Zurbruegg, C., and Binneras, B. (2015) ‘Opportunities and Constraints for Medium-Scale Organic Waste Treatment with Fly Larvae Composting.’ in 15th International Waste Management and Landfill Symposium [online] held 2015 at Santa Margherita di Pula. International Waste Working Group. available from <https://www.researchgate.net/publication/283072268_Opportunities_and_constraints_for_medium-scale_organic_waste_treatment_with_fly_larvae_composting>
Lohri, C.R., Diener, S., Zabaleta, I., Mertenat, A., and Zurbrugg, C. (2017) ‘Treatment Technologies for Urban Solid Biowaste to Create Value Products: A Review with Focus on Low-and Middle- Income Settings’. Reviews in Environmental Science and Bio/Technology 16, 81–130
London School of Hygiene and Tropical Medicine (n.d.) BSF Toilet Design Workshop [online] available from <http://blogs.lshtm.ac.uk/sanitationventures/innovation/bsf-toilet-design-workshop/> [6 March 2018]
Ruto, D. (2016) Engineering Solutions to Optimize Black Soldier Fly Production [online] available from <http://www.saner.gy/archives/5755>
Sanergy (2015) The Sanergy Model [online] available from <http://www.saner.gy/our-work/the-sanergy-model>
Sanergy (2014) Partnering across the Sanitation Value Chain – Animal Feed and Agriprotein [online] available from <http://www.saner.gy/archives/4534>
Sustainable Sanitation Alliance (2018) Webinar 17 Jan 30 2018. Black Solider Fly Larvae for Faecal Sludge Treatment. [online] available from <https://www.youtube.com/watch?v=XlKNx1xu27c> [15 March 2018]
The BioCycle (2013) Black Soldier Fly (BSF) Larvae for Faecal Sludge Reduction – Research in South Africa (with the Company Agriprotein) [online] available from <http://forum.susana.org/forum/categories/147-production-of-insect-biomass-from-excreta-or-organic-waste/4430-black-soldier-fly-bsf-larvae-for-faecal-sludge-reduction-research-in-south-africa-with-the-company-agriprotein?limitstart=0> [16 March 2018]
The BioCycle (n.d.) The BioCycle [online] available from <http://thebiocycle.com/> [15 March 2018]