Biochar and gypsum amendment of agroindustrial waste for enhanced black soldier fly larval biomass and quality frass fertilizer

Open Access Journal; Published online: 27 Aug 2020Black soldier fly (BSF) (Hermetia illucens L.) is one of the most efficient bio-waste recyclers. Although, waste substrate amendments with biochar or gypsum during composting process are known to enhance nutrient retention, their impact on agro-industrial waste have not been documented. Hence, this study focuses on a comparative effect of agro-industrial waste amended with biochar and gypsum on BSF larval performance, waste degradation, and nitrogen (N) and potassium retention in frass fertilizer. Brewery spent grain was amended with biochar or gypsum at 0, 5, 10, 15 and 20% to determine the most effective rates of inclusion. Amending feedstock with 20% biochar significantly increased wet (89%) and dried (86%) larval yields than the control (unamended feedstock). However, amendment with 15% gypsum caused decrease in wet (34%) and dried (30%) larval yields but conserved the highest amount of N in frass. Furthermore, the inclusion of 20% biochar recorded the highest frass fertilizer yield and gave a 21% increase in N retention in frass fertilizer, while biomass conversion rate was increased by 195% compared to the control. Feedstock amendment with 5% biochar had the highest waste degradation efficiency. Potassium content in frass fertilizer was also significantly enhanced with biochar amendment. At maturity, frass compost with more than 10% inclusion rate of biochar had the highest cabbage seed germination indices (>100%). The findings of this study revealed that initial composting of biochar amended feedstocks using BSF larvae can significantly shorten compost maturity time to 5 weeks with enhanced nutrient recycling compared to the conventional composting methods

Low-cost technology for recycling agro-industrial waste into nutrient-rich organic fertilizer using black soldier fly

Open Access Article; Published online: 15 Oct 2020Efforts to recycle organic waste using black soldier fly (BSF) larvae into high-quality alternative protein ingredients in animal feeds and organic fertilizers have gained momentum worldwide. However, there is limited information on waste manipulation to increase nutrient retention for enhanced larval performance and frass fertilizer quality. In the present study, brewer’s spent grain with a carbon to nitrogen (C/N) ratio of 11 (control) was amended with sawdust to obtain substrates with C/N ratios of 15, 20, 25 and 30. The effects of substrate C/N ratios on BSF larval yield, waste degradation, biomass conversion efficiency, compost maturity and nutrient levels of frass fertilizer were evaluated. Substrates amended with sawdust did not significantly affect waste degradation efficiency and biomass conversion rates of BSF larvae. The wet and dried larval yields were significantly higher for substrates with C/N ratio of 15 compared to the other amended substrates. An amended substrate with C/N ratio of 15 enhanced nutrients uptake by BSF larvae, and increased nitrogen (N) and phosphorus retention in frass compost by 21 and 15%, respectively. Compost maturation time was shortened to five weeks, as indicated by the stable C/N ratios and high seed germination indices. This study has demonstrated that the amendment of the substrate with sawdust to C/N ratio of 15 could generate compost with desirable nutrients for use as high-quality fertilizer for organic farming

Insights in the global genetics and gut microbiome of black soldier fly, Hermetia illucens: implications for animal feed safety control

Open Access Journal; Published online: 07 July 2020The utilization of the black soldier fly (BSF) Hermetia illucens L. for recycling organic waste into high-quality protein and fat biomass for animal feeds has gained momentum worldwide. However, information on the genetic diversity and environmental implications on safety of the larvae is limited. This study delineates genetic variability and unravels gut microbiome complex of wild-collected and domesticated BSF populations from six continents using mitochondrial COI gene and 16S metagenomics. All sequences generated from the study linked to H. illucens accessions KM967419.1, FJ794355.1, FJ794361.1, FJ794367.1, KC192965.1, and KY817115.1 from GenBank. Phylogenetic analyses of the sequences generated from the study and rooted by GenBank accessions of Hermetia albitarsis Fabricius and Hermetia sexmaculata Macquart separated all samples into three branches, with H. illucens and H. sexmaculata being closely related. Genetic distances between H. illucens samples from the study and GenBank accessions of H. illucens ranged between 0.0091 and 0.0407 while H. sexmaculata and H. albitarsis samples clearly separated from all H. illucens by distances of 0.1745 and 0.1903, respectively. Genetic distance matrix was used to generate a principal coordinate plot that further confirmed the phylogenetic clustering. Haplotype network map demonstrated that Australia, United States 1 (Rhode Island), United States 2 (Colorado), Kenya, and China shared a haplotype, while Uganda shared a haplotype with GenBank accession KC192965 BSF from United States. All other samples analyzed had individual haplotypes. Out of 481,695 reads analyzed from 16S metagenomics, four bacterial families (Enterobactereaceae, Dysgonomonadaceae, Wohlfahrtiimonadaceae, and Enterococcaceae) were most abundant in the BSF samples. Alpha-diversity, as assessed by Shannon index, showed that the Kenyan and Thailand populations had the highest and lowest microbe diversity, respectively; while microbial diversity assessed through Bray Curtis distance showed United States 3 (Maysville) and Netherlands populations to be the most dissimilar. Our findings on genetic diversity revealed slight phylogeographic variation between BSF populations across the globe. The 16S data depicted larval gut bacterial families with economically important genera that might pose health risks to both animals and humans. This study recommends pre-treatment of feedstocks and postharvest measures of the harvested BSF larvae to minimize risk of pathogen contamination along the insect-based feed value chain

Spin coating of Silver Nanoparticles and Silicon quantum dots for enhanced down conversion efficiency

The commercial efficiency of a c-Si solar cell is ~18% although the thermodynamic limit is ~95%. This indicates a good scope for improvements. The major loss mechanism in a solar cell is spectral mismatch which is contributed to by non-absorption of low energy photons and thermalization of high energy photons. In this thesis, it is sought to reduce the loss that occurs through thermalization of high energy photons. For this purpose, the concept of down conversion is used. Silicon being relevant to the semiconductor industry, being abundant in nature and having been proved to exhibit down conversion in the form of spherical particles in the nm size range through space separated quantum cutting is opted. However, the down conversion efficiency of these is low owing to their indirect bandgap which leads to higher absorption within the material than enhancement in the number of photons through down conversion. In order to reduce the absorption within the material, it is sought to enhance the rate of radiative decay through the use of plasmonics exhibited by metal nanoparticles. Silver nanoparticles are used for our purpose as they exhibit resonance in the visible region of the spectrum and have the lowest absorption among different plasmonic materials. The silicon nanoparticles (quantum dots) powders are fabricated through the expanding thermal plasma chemical vapor deposition route while the silver nanoparticles fabricated through wet chemical synthesis are purchased from the market as powders. The silver nanoparticles are also deposited as metal island films in-house. Optimal deposition parameters for the deposition of quantum dots are arrived upon by depositing samples using different parameters and analyzing the results. A configuration for the down conversion layer is arrived upon based on simulations and analysis of design. The powders are then dispersed in ethanol for the purpose of spin coating. The dispersions are then spin coated on glass substrates. The quantum dot dispersion is also spin coated onto the metal island film substrate as per the chosen configuration. The silver nanoparticle samples are analyzed for plasmonic behavior, quantum dots for their absorption characteristics and the combination for enhancement in transmission through down conversion from their reflection and transmission spectra. To confirm the interaction between the silver nanoparticles and quantum dots, the enhancement in the photoluminescence spectra is checked. From the results, it is observed that there is agglomeration in the spin coated silver nanoparticles resulting in a loss of plasmonic behavior. The quantum dots are also agglomerated due to which an enhancement in the transmission spectra was not observed. However, the interaction between the quantum dots and the silver nanoparticles could be observed through the enhanced photoluminescence of the quantum dots. The enhancement is found to vary from 9 folds to about 50 folds which are high compared to similar results in the literature. Keeping in mind that this down conversion layer has not yet been optimized, even higher enhancements may be possible. This indicates the potential for the combination of silicon quantum dots and silver nanoparticles for application in solar cell down conversion layers.Sustainable Energy TechnologyElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc