Fly larvae composting of fibrous food industry waste : impact of pre-treatment
Sammanfattning: With increasing population worldwide comes higher demands of food and greater waste generation. Effective ways for safe nutrient recycling and waste treatment are thus needed to minimize the human impact on the environment. Utilizing techniques in which waste is turned into valuable products could be a driving force for making biodegradable waste treatment more applicable and attractive on a commercial scale. For biodegradable waste, one method is to use insect larvae that feed and grow on the biodegradable material. The larvae can subsequently be used as feedstuff in animal feed. An additional product generated in the process is the treatment residue, a compost-like material that can be used as soil enhancement. The black soldier fly (BSF, Hermetia illucens (L.) Diptera: Stratiomyidae) larvae (BSFL) can be reared on biodegradable waste, however nutrient and physical composition of the biodegradable waste affects the larvae growth. Peels from fruit, from the fruit industry, are not optimal for fly larvae treatment in terms of nutritional composition and thus methods to alter the biodegradable waste before BSFL treatment of this particular substrate is of interest. Pre-treatment of the peels is a possible method to increase BSFL composting efficiency by altering the biochemical composition and/or structure. To address this, two pre-treatment methods were used in this study, Rhizopus oligosporus and ammonia. In this study, the impact of pre-treatment on black soldier fly larvae treatment efficiency were evaluated based on biomass conversion of banana and orange peel into larval biomass. In the orange peel study, two larval densities (1.9 and 4.0 larvae cm-2) were evaluated. The impact of pre-treatment on amino acid content and fiber content were evaluated in the banana peel study. For the banana peel study, the Biomass conversion rate (BCR) decreased in both pre-treatments. The untreated peels (Control) had the highest BCR with a mean 7.1±0.6 % on a total solids (TS) basis. The protein conversion rate was highest in the Control at 49.1±7.1 % and there was no significant difference in concentration of the essential amino acids lysine and methionine in the larvae in terms of pre-treatment method. The fiber components in the banana peels were to some extent degraded by the pre-treatments, but there was no significant difference in fiber decomposition by the BSFL in terms of pre-treatment method, as fiber decomposition were only observed in the Control. However, the Control was regarded as inaccurate so fiber degradation by BSFL could not be verified for any setup. For the orange peel trial, the Control had the highest BCR, 8.5±0.8 % on TS basis, in the 1.9 larvae cm-2 density setup. For the 4.0 larvae cm-2 density setup, the ammonia pre-treatment had the highest BCR with 9.2±0.3 % on TS basis. Rhizopus oligosporus pre-treatment generated poor results regarding BCR in the orange peel study (0.9±0.1 & 1.3±0.4 % TS) contrary to the banana peel study (6.4±0.2 % TS). Higher larval density increased BSFL composting efficiency for all treatments. Further studies could explore the impact of ammonia pre-treatment further, larval density and other possible pre-treatments.
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