Ivã Guidini Lopes

Frass produced from biowaste treatment with black soldier fly (BSF) larvae is a promising fertilizer, but its short bioconversion time can lead to phytotoxicity. A recently proposed method called ‘frass recirculation’ was found to improve frass quality by reintroducing fresh frass into subsequent rearing cycles. This study evaluated the effects of frass produced through different levels of recirculation on soil nitrogen (N) dynamics and plant performance. Five frass types were tested: fresh frass and frass recirculated once, twice, three, or four times. In the first experiment, the fertilizers were applied to the soil, and N mineralization was monitored over 84 days. The same treatments were then used to cultivated pak choi, where plant growth and photosynthetic activity were assessed. Frass recirculated four times had a higher intrinsic concentration of N-NH ₄ ⁺ and produced significantly higher soil mineral N after 84 days compared to fresh frass. This increased N availability allowed for lower application rates while still providing sufficient nutrients for supporting plant growth. Pak choi fertilized with highly recirculated frass achieved biomass comparable to that of plants supplied mineral fertilizer. In addition, nutrient concentrations and accumulation in plant tissues were similar between the highly recirculated frass and mineral fertilizer treatments. Notably, frass-fertilized plants exhibited higher chlorophyll content and greater CO ₂ assimilation rates, indicating an enhanced photosynthetic performance. Overall, frass recirculation enhanced N mineralization and improved the fertilization efficiency of BSF frass. These results demonstrate that recirculated frass have fertiliser potential comparable to that of mineral fertilizers, highlighting its potential as a sustainable organic alternative for greenhouse crop production.

This is the first and extensive study investigating the bioactive composition of black soldier fly larvae (BSFL) frass through liquid chromatography tandem mass spectrometry (LC-MS/MS), with specific focus on phytohormones and their links to frass microbial composition. Two types of frass were evaluated: fresh frass (Fr-Cycle 1), obtained after one larval bioconversion cycle of food waste; and recirculated frass (Fr-Cycle 2), produced by reintroducing fresh frass into a subsequent bioconversion cycle. Frass recirculation did not affect overall nutrient composition but resulted in marked reductions in humic (80%) and fulvic (65%) acid concentrations, likely due to further decomposition of organic matter during recirculation. In parallel, recirculation significantly altered the bacterial community, decreasing the relative abundance of Actinobacteria while increasing Proteobacteria. Saliently, this is the first mass spectrometric evidence for the presence of cytokinins (both cZ and tZ, as well as their precursors) in BSFL frass, but several other phytohormones were identified in frass at nanomolar levels, including auxins (IAA, PAA, IAM, among others), abscisic acid, salicylates, indoleamines and an ethylene precursor. Interestingly, specific microbial genera were found to be positively correlated with phytohormones, including Proteus , Providencia and Morganella . The potential connections between microorganisms, phytohormones and physico-chemical characteristics of frass might help explain the results reported in the current literature exploring frass as a biofertilizer or soil amendment. The results presented herein open possibilities for approaching BSFL frass research from a new perspective, paving the way for future studies aiming at a more mechanistic understanding of its interactions with soil, plants and microorganisms.

Olive pomace (OP) is a sludge arising from the production of olive oil, generated in increasing amounts in Portugal. The management of this toxic waste stream is complex and the number of processing plants is limited. In this study, OP was incorporated as a feed component for rearing black soldier fly larvae (BSFL) under industrial conditions. Larvae were reared inside a climate‐controlled room with regulated temperature and humidity. The rearing cycle lasted 13 days, after which larvae were harvested. In addition to assessing bioconversion efficiency and larval proximate composition, the resulting frass was examined for its fertilizer potential. Frass was analyzed for plant nutrient content and microbial profile in three forms: fresh, heat‐treated (70°C for 1 h), and pelletized. The inclusion of OP in the diets reduced waste‐to‐biomass conversion efficiency (21.5% _DM to approximately 13.3% _DM ) but did not affect the proximate composition of the larval biomass, which consistently contained around 43% _DM crude protein and 20% _DM crude fat. Neither the presence of OP nor the applied post‐treatments altered the nutrient composition of frass, which contained on average 3.5% total N, 2.6% P ₂ O ₅ , and 5.9% K ₂ O. However, at the highest inclusion level (84%), the abundance of bacterial and fungal groups was significantly reduced. The predominant phyla in the frass were Actinobacteria, Bacteroidota, Firmicutes, Proteobacteria, Ascomycota and Basidiomycota, and the dynamics of microbial communities were influenced by specific micronutrients. The presence of OP led to a significant reduction of potentially pathogenic bacteria and fungi in the frass, indicating a sanitizing effect attributable to this material.

Olive mill wastewaters (OMWWs) are an environmental problem in the Mediterranean region, and it is crucial to explore strategies for their treatment and repurposing. The chemical precipitation technique (CPT) has been presented as a cost-effective wastewater treatment solution that might be applied to OMWW. The CPT-resulting precipitant subproducts (sludge) may be reprocessed (e.g., agricultural fertilizer and/or soil amendment), while the treated wastewater may be repurposed or reused (e.g., irrigation, aquaponic, or industrial processes). This study aimed to evaluate the efficacy of CPT in treating wastewater from the olive oil industry from an ecotoxicological perspective. Additionally, to assess the safe use of the obtained sludge in CPT treatment, its effects on soil biota were assessed. For this, a set of ecotoxicological assays using freshwater (Raphidocelis subcapitata, Daphnia magna and Danio rerio), terrestrial invertebrates (Folsomia candida and Enchytraeus crypticus), and plants (Brassica oleracea and Lolium perenne) were used as model organisms. Results demonstrated that CPT reduced OMWW toxicity to freshwater organisms, offering a favorable outlook on CPT’s potential as a wastewater treatment method. Increasing application rates of sludge in soil reduced the shoot biomass and the hydric content of both plants compared to the control. Survival of F. candida and E. crypticus was not affected by sludge in soil at any tested application rate, yet sludge application negatively affected the reproduction of both species, even at relevant sludge application rates (2%) of sludge in soils. Overall, the applicability of this sludge obtained by the CPT treatment in soils should be carefully evaluated due to the observed adverse effects on soil biota. Although the results of CPT were promising in reducing the toxicity of OMWW for these aquatic species, some adjustments/improvements should be performed to improve this technique and use all the obtained resources (treated water and sludge) in a fully circular perspective.

Insect frass is one of the most abundant products in the insect industry, regardless of the farmed species. Rich in organic matter and plant nutrients, frass is a promising organic amendment that can be used in agriculture. While many benefits and challenges have been reported, several knowledge gaps remain unanswered, regarding the specific characteristics and mechanisms of its effects on soils and plants, particularly in terms of the processes driving these effects and interactions. This article aims to discuss recent research on frass and identify existing knowledge gaps, and propose strategies to improve research methodologies, increase comparability across studies, and generate more robust results. The topics covered include the evaluation of frass effects on soil physical properties, microbiological dynamics and fertility, as well as its effects on plant growth, development, and metabolism. The article also explores the potential of frass as an antimicrobial agent and highlights the need for stabilising and improving its quality and safety before it is used in agricultural activities. Looking forward, insect frass holds great promise as a sustainable input for agriculture, food production, and feed systems.

In 2013, the United Nations Food and Agriculture Organization identified insects as a promising solution for sustainably feeding the world’s growing population. However, despite a decade of development and innovation, the insect industry has yet to fully realize its environmental and economic potential. This review takes an evidence-based approach to addressing key challenges in the sector, including integrating circular production systems within existing regulatory frameworks in the Global North, ensuring product safety in circular systems, assessing allergen risks associated with insect-based products, mitigating biosecurity risks linked to non-native insect species, evaluating the environmental safety of insect by-products, and promoting animal welfare in insect production. While significant challenges remain, the evidence presented highlights how further research can help unlock opportunities for the industry to achieve its full potential globally. Ultimately, we argue that overcoming challenges – ‘working out the bugs’ – is a fundamental step in the evolution of any emerging industry. Furthermore, greater support for the transition to circular economies will accelerate the sector’s ability to generate meaningful environmental, ethical, and economic benefits.

Cropping systems are strongly dependent on mineral fertilisers, which are effective in achieving high crop productivities. However, these chemical inputs end up compromising soil quality in the long-term. Frass from black soldier fly (BSF) larvae is a novel organic fertiliser that is rich in organic matter and advocated as a material that can sustain crop productivity while increasing soil quality. This study aimed at evaluating distinct fertilisation regimes in the cultivation of ryegrass ( Lolium multiflorum Lam. or annual ryegrass) in soils of different types (sandy, loamy and clay) and fertility levels. In a 7-month pot experiment conducted in a glass greenhouse, plants were cultivated with exclusive mineral (MT) or organic (OT) fertilisation, in addition to combinations between both (mineral and organic, MOTs) in different proportions (25:50; 50:50 and 75:25), considering a 140 kg per hectare N demand. Crop yield was favoured by the combination of organic and mineral fertilisers in all soils, which also had its fertility increased, especially regarding organic matter build-up and nutrient accumulation. In addition, the presence of frass in the sandy soil stimulated microbial activity, which was measured by the enzyme dehydrogenase. Frass derived from BSF larvae can be considered an adequate organic fertiliser in the cultivation of ryegrass in distinct soil types, when applied in partial (25% to 75%) replacement of mineral fertilisers, enabling high crop productivity and nutritional quality of the crop, while increasing soil fertility.