Black soldier fly larvae mitigate greenhouse gas emissions from domestic biodegradable waste by recycling carbon and nitrogen and reconstructing microbial communities.

Black soldier fly larvae have been proven to reduce greenhouse gas emissions in the treatment of organic waste. However, the microbial mechanisms involved have not been fully understood. The current study mainly examined the dynamic changes of carbon and nitrogen, greenhouse gas emissions, the succession of microbial community structure, and changes in functional gene abundance in organic waste under larvae treatment and non-aeration composting. Thirty percent carbon and 55% nitrogen in the organic waste supplied were stored in larvae biomass. Compared to the non-aeration composting, the larvae bioreactor reduced the proportion of carbon and nitrogen converted into greenhouse gases (CO2, CH4, and N2O decreased by 62%, 87%, and 95%, respectively). 16S rRNA sequencing analysis indicated that the larvae bioreactor increased the relative abundance of Methanophaga, Marinobacter, and Campylobacter during the bioprocess, enhancing the consumption of CH4 and N2O. The metagenomic data showed that the intervention of larvae reduced the ratio of (nirK + nirS + nor)/nosZ in the residues, thereby reducing the emission of N2O. Larvae also increased the functional gene abundance of nirA, nirB, nirD, and nrfA in the residues, making nitrite more inclined to be reduced to ammonia instead of N2O. The larvae bioreactor mitigated greenhouse gas emissions by redistributing carbon and nitrogen and remodeling microbiomes during waste bioconversion, giving related enterprises a relative advantage in carbon trading.

Elastomeric Polymer Multilayer Thin Film with Sustainable Gas Barrier at High Strain.

Most gas barrier thin films suffer from cracking or plastic deformation when stretched, leading to significant loss of barrier. In an effort to make a stretchable gas barrier, which maintains low permeability when exposed to cyclic strain, we prepared layer-by-layer assemblies of tannic acid (TA) and poly(ethylene oxide) (PEO). A 40-bilayer (344 nm-thick) TA/PEO assembly maintained its oxygen transmission rate (6X lower than the 1.6 mm-thick rubber substrate) after being stretched 100%. This submicron coating maintains a barrier 4X lower than the thick rubber substrate even after being strained 20X at 100%. These highly elastomeric assemblies are potentially useful for light-weighting inflatable devices.

Structural tailoring of hydrogen-bonded poly(acrylic acid)/poly(ethylene oxide) multilayer thin films for reduced gas permeability.

Hydrogen bonded poly(acrylic acid) (PAA)/poly(ethylene oxide) (PEO) layer-by-layer assemblies are highly elastomeric, but more permeable than ionically bonded thin films. In order to expand the use of hydrogen-bonded assemblies to applications that require a better gas barrier, the effect of assembling pH on the oxygen permeability of PAA/PEO multilayer thin films was investigated. Altering the assembling pH leads to significant changes in phase morphology and bonding. The amount of intermolecular hydrogen bonding between PAA and PEO is found to increase with increasing pH due to reduction of COOH dimers between PAA chains. This improved bonding leads to smaller PEO domains and lower gas permeability. Further increasing the pH beyond 2.75 results in higher oxygen permeability due to partial deprotonation of PAA. By setting the assembling pH at 2.75, the negative impacts of COOH dimer formation and PAA ionization on intermolecular hydrogen bonding can be minimized, leading to a 50% reduction in the oxygen permeability of the PAA/PEO thin film. A 20 bilayer coating reduces the oxygen transmission rate of a 1.58 mm natural rubber substrate by 20 ×. These unique nanocoatings provide the opportunity to impart a gas barrier to elastomeric substrates without altering their mechanical behavior.

Improving the gas barrier property of clay-polymer multilayer thin films using shorter deposition times.

Relatively fast exposure times (5 s) to aqueous solutions were found to improve the gas barrier of clay-polymer thin films prepared using layer-by-layer (LbL) assembly. Contrary to the common belief about deposition time (i.e., the longer the better), oxygen transmission rates (OTRs) of these nano-brick-wall assemblies are improved by reducing exposure time (from 1 min to 5 s). Regardless of composition, LbL films fabricated using shorter deposition time are always thicker in the first few layers, which correspond to greater clay spacing and lower OTR. A quadlayer (QL) assembly consisting of three repeat units of branched polyethylenimine (PEI), poly(acrylic acid) (PAA), PEI and montmorillonite (MMT) clay is only 24 nm thick when deposited with 1 min exposure to each ingredient. Reducing the exposure time of polyelectrolytes to 5 s not only increases this film thickness to 55 nm but also reduces the oxygen transmission rate (OTR) to 0.05 cm3/(m2 day atm), which is 2 orders of magnitude lower than the same film made using 1 min exposures. A conceptual model is proposed to explain the differences in growth and barrier, which are linked to polyelectrolyte relaxation, desorption, and interdiffusion. The universality of these findings is further exemplified by depositing clays with varying aspect ratios. This ability to quickly deposit high-barrier nanocomposite thin films opens up a tremendous opportunity in terms of commercial-scale processing of LbL assemblies.

Super Stretchy Polymer Multilayer Thin Film with High Gas Barrier.

Unlike ionically bonded or clay-loaded gas barrier thin films, which easily crack when moderately stretched, hydrogen-bonded poly(acrylic acid) (PAA)/poly(ethylene oxide) (PEO) multilayer thin films remain crack-free. Even after 100% strain, these nanocoatings provide more than a 5× reduction in oxygen transmission rate. This study shows that the lowest modulus PAA/PEO thin film is obtained at pH 3, but maintains a high barrier. A total of 20 PAA/PEO bilayers (367 nm thick) on 1.58 mm rubber reduced the oxygen transmission rate by 1 order of magnitude. Stretching from 25-100% caused plastic deformation and reduced gas barrier, but the oxygen transmission rate remained at least 5× lower than the uncoated rubber. The ability to prevent cracking and preserve the gas barrier up to 100% strain provides a tremendous opportunity for reducing weight and improving the barrier of elastomeric materials.