, Techno-economic assessment of poly-3-hydroxybutyrate (PHB) production from methane-The case for thermophilic bioprocessing, Journal of Environmental Chemical Engineering http://dx.doi.org/10.1016/j.jece. 2016.07.033 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractA major obstacle preventing the large scale production of polyhydroxyalkanoates (PHAs) has been the lack of a reliable, low cost, large volume feedstock. The abundance and relatively low price of methane therefore marks it as a substrate of interest. This paper presents a technoeconomic assessment of the production of poly-3-hydroxybutyrate (PHB) from methane.ASPEN Plus was used for process design and simulation. The design and economic evaluation is presented for production of 100,000 t/a PHB through methanotrophic fermentation and acetone-water solvent extraction. Production costs were estimated at $4.1-$6.8/kg PHA, which compares against a median price of $7.5/kg from other studies. Raw material costs are reduced from 30-50% of production for sugar feedstocks, to 22% of production for methane. A feature of the work is the revelation that heat removal from the two-stage bioreactor process contributes 28% of the operating cost. Thermophilic methanotrophs could allow the use of cooling water instead of refrigerant, reducing production costs to $3.2-5.4/kg PHA; it is noted that PHB producing thermophilic methanotrophs are yet to be isolated. Energy consumption for air compression and biomass drying were also identified as significant capital and operating costs and therefore optimisation of bioreactor height and pressure and biomass moisture content should be considered in future research.3

Dicyandiamide (DCD) has been studied as a stabilizer for nitrogen fertilizers for over 50 years. Its efficacy is limited at elevated temperatures, but this could be addressed by encapsulation to delay exposure. Here, poly­(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated as a biodegradable matrix for the encapsulation of DCD. Cylindrical ∼3 mm × 3 mm pellets were fabricated through extrusion processing with 23 wt % DCD. Release kinetics were monitored in water, sand, and both active and γ-irradiated agricultural clay loam soils. Raman maps showed a wide particle size distribution of DCD crystals and indicated that Hitachi’s classic moving front theory did not hold for this formulation. The inhibitor release kinetics were mediated by four distinct mechanisms: (i) initial rapid dissolution of surface DCD, (ii) channeling of water through voids and pores in the PHBV matrix, (iii) gradual diffusion of water and DCD through layers of PHBV, and (iv) biodegradation of the PHBV matrix. After ∼6 months, 45–100% release occurred, depending on the release media. PHBV is shown to be an effective, biodegradable matrix for the long-term slow release of nitrification inhibitors.

This work investigates the use of polyhydroxyalkanoate (PHA) films as moisture barriers for thermoplastic starch (TPS) films, to produce biodegradable, multi‐layer materials with high gas barrier properties. This is a necessary extension to the limited work available on this topic and confirms that PHAs are suitable coating materials for TPS films intended for use in food packaging. Under storage conditions of up to 75% relative humidity (RH) for 2 weeks, a PHA coating maintained the moisture content (MC) of the TPS below the point at which its barrier properties were detrimentally affected. Furthermore, for PHBV coating thicknesses of 91–115 μm, the MC of the TPS remains significantly lower than uncoated TPS for the duration of the experiment (>25 days). The flux of water into the coated TPS fit to a model based on Fick's law. However, when the multi‐layered films were stored at 95% RH delamination occurred within 24 h. Preliminary investigation into possible material design improvements showed that the addition of a small amount of PHA to the TPS layer prolonged the time to delamination. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46379.

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BACKGROUND Various active chemical agents, such as soil microbial inhibitors, are commonly applied to agricultural landscapes to optimize plant yields or minimize unwanted chemical transformations. Dicyandiamide (DCD) is a common nitrification inhibitor. However, it rapidly decomposes under warm and wet conditions, losing effectiveness in the process. Blending DCD with an encapsulating polymer matrix could help overcome this challenge and slow its release. Here, we encapsulated DCD in a biodegradable matrix of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and investigated the effects of DCD crystal size and loading rates on release rates. RESULTS Three DCD crystal size fractions (0–106, 106–250 and 250–420 μm) were blended with PHBV at 200, 400, 600 and 800 gkg−1 loadings through extrusion processing and release kinetics were studied in water over 8 weeks. For loadings ≥ 600 g kg−1, more than 95% release was reached within the first 7 days. By contrast, at 200 g kg−1 loading only 10%, 36% and 57% of the DCD was mobilized after 8 weeks in water for 0 to 106 μm, 106 to 250 μm and 250 to 420 μm crystal size fractions, respectively. CONCLUSION The lower percolation threshold for this combination of materials lies between 200 and 400 g kg−1 DCD loading. The grind size fraction of DCD significantly affects the quantity of burst release from the surface of the pellet, particularly below the lower percolation threshold. The results presented here are likely translatable to the encapsulation and release of other crystalline materials from hydrophobic polymer matrices used in controlled release formulations, such as fertilizers, herbicides and pesticides. © 2020 Society of Chemical Industry