High waste-to-biomass conversion and efficient Salmonella spp. reduction using black soldier fly for waste recycling

Cecilia H. Lalander 0 Jrgen Fidjeland 0 Stefan Diener 0 Sara Eriksson 0 Bjrn Vinners 0 0 S. Diener Eawag: Swiss Federal Institute of Aquatic Science and Technology , Dbendorf, Switzerland The recycling of organic waste worldwide is not effective, which leads to water pollution and loss of potential crop fertilizers. Available resources have to be used more efficiently as the world population increases. An innovative solution is to use insects for the management of organic waste. Here, we used black soldier fly to convert organic waste into animal feed protein, as fly larvae, and plant fertilizer, as compost residue. A continuous fly reactor was monitored for 9 weeks. We analyzed physicochemical and microbial parameters, and we evaluated the sanitary risk. Results show 55.1 % of material degradation and 11.8 % of biomass conversion based upon total solids. We observed higher levels of N and P in the treatment residue than in the inflow material. Results also show a lower concentration of Salmonella spp. and viruses. Compost treatment with black soldier fly is therefore an efficient system for nutrient recycling. - organic material, e.g., food waste, animal manure, and market waste. If left untreated, the valuable energy and nutrients contained in the waste can contribute to an increase in annual greenhouse gas emissions (UNEP 2010) and a leaching of nutrients into water bodies, causing eutrophication (Sharpley et al. 1994). Over and above this, there is a risk of spreading the pathogens contained in the organic waste. The waste management coverage in high-income countries is considerably higher, but at the same time the waste generated per person is up to three times greater and still increasing (Hoornweg and Bhada-Tata 2012). The proportion of organic waste is around 30 % and only a small proportion of the nutrients returns into the food cycle (Cordell et al. 2009). This is a growing concern, since the nitrogen and phosphate cycle has been identified as key factors that has to be maintained within certain levels for the planet to be able to support human existence in the future (Rockstrm et al. 2009). One way of securing human well-being is, according to Griggs et al. (2013), sustainable production systems. In a report by the United Nations Food and Agricultural Organization, it was stated that the consumption of insects in the food sector, as animal feed and directly for human consumption, is one such solution (van Huis et al. 2013). The black soldier fly, encountered between 46N and 42S (Martnez-Snchez et al. 2011), is of particular interest. Their ability to consume prodigious amounts of organic waste has long been known. Black soldier fly larvae have been reported to consume and degrade a number of organic materials with material degradation up to 70 % (Diener et al. 2011). The larvae in the final larval stage, the prepupae, crawl out of the feeding material to find a dry and dark place to pupate (Sheppard et al. 2002) and are thus self-harvesting. The prepupae contain around 40 % protein and 30 % fat and have been demonstrated to be a good alternative feed in fish (St-Hilaire et al. 2007) and pig (Newton et al. 1977) production, with the potential to replace fish meal and fish oil as source of animal feed protein. Replacing fish meal would alleviate the pressure on the wild fish population (Tacon and Metian 2008). With the increasing consumption of fish and meat, the demand for animal feed protein has increased greatly, while its availability is limited. As a consequence, the price of fish meal has reached new heights valued USD 1,820 per tons (World Bank, May 2014) making the production of compatible alternative animal feed protein a lucrative business. By producing an economically valuable product, organic waste management could become a financially sustainable system that would increase resource reuse efficiency and reduce negative environmental impacts (Fig. 1). Hygiene aspects play an important role when dealing with organic waste and animal feed (Sidhu and Toze 2009). In several studies, black solider fly larvae waste treatment systems have been shown to remove bacteria in the Enterobacteriaceae family: the concentration of Salmonella spp. was reduced by 7 log10 in 8 days in a small batchoperated fly larvae system treating fecal sludge (Lalander et al. 2013); Erickson et al. (2004) observed the reduction of Salmonella enterica Serovar Enteritidis and Escherichia coli O157:H7 in cattle manure, while Liu et al. (2008) have reported on the reduction of E. coli in poultry manure. However, a l t h o u g h a h i g h r e d u c t i o n i n b a c t e r i a o f t h e Enterobacteriaceae family occur, reduction of other organisms has not been observed. All these systems were operated in batch mode. The question is whether the same results would be obtained in a continuous flow reactor. In a large-scale fly Fig. 1 A graphical representation of the concept of fly larvae composting: organic waste is consumed by fly larvae, in the sixths and final larval stage, the prepupae migrate out of the compost. The prepupae can be used as animal feed and the treatment residue used as organic fertilizer. The loop is closed when the animal manure and food waste is diverted as substrate into the fly larvae compost larvae waste management system, it is likely that a continuous flow reactor would be implemented, as it would be too timeconsuming to operate in batch mode. One hypothesis is that the operation over a long period would support the buildup of a microbial community, helping to break down the waste material and thus improve the hygienic quality of the treatment residue. The objective of this study was to establish a continuous flow fly larvae reactor and to analyze important process and hygiene parameters in order to evaluate material degradation, waste-to-biomass conversion rate, nutrient flow, and average weekly reduction of evaluated pathogens and indicator organisms. 2 Materials and methods 2.1 Materials Pig manure (21.11.7 % total solids) was collected on a pig farm in Uppsala municipality, Sweden. Dog food (Puppy Original, Pro Plan, Purina) mixed with water (21.9 0.2 % total solids) was used as the model substrate for organic waste (Vinners et al. 2003). Human feces were collected fresh in plastic bags and stored at 20 C immediately upon collection. A mixture of pig manure, dog food, and human feces was prepared (4:4:2; 28.71.2 % total solids), divided into feeding portions, and kept at 20 C until use. Ascaris suum, which infects pigs, is often used as model for Ascaris lumbricoides, which infects humans (Johnson et al. 1998). A. suum extracted from the feces of infected pigs were purchased from Excelsior Entinel, Inc. and received in aqueous solution at a concentration of 100,000 eggs mL1. The bacterial inoculate solutions consisted of 108 colony forming units (CFU) mL1 Enterococcus faecalis (ATCC 29212) and 109 CFU mL1 Salmonella enterica subspecies ~ 1 s (...truncated)