Significant progress has been made over the past decade with pilot scale polyhydroxyalkanoate (PHA) production by direct accumulation using municipal waste activated sludge (WAS). However, industrial upscaling experiences are still lacking in the research literature. In this study, a demonstration scale (4 m³) PHA production process was operated using industrially relevant equipment and compared favourably to those from parallel pilot scale (200 L) production runs. WAS grab samples from a Dutch full scale municipal wastewater treatment plant (WWTP) was used as the biomass source. Final biomass PHA contents and production yields, that are critical for technology viability, were statistically the same between the experiments conducted at pilot scale (0.41 ± 0.02 gPHA/gVSS and 0.42 ± 0.02 gCOD/gCOD) and demonstration scale (0.45 ± 0.05 gPHA/gVSS and 0.39 ± 0.07 gCOD/gCOD). The results furthermore aligned with previous 1 m³ piloting experiences and five year old historical data that similarly used WAS sourced from the same WWTP. Scalability for the technology and a robustness of the applied PHA production methods using WAS were demonstrated. Temperature and foaming control were identified to be critical to upscaled process engineering and design towards successful industrial implementations. The results of the present study, combined with previously produced PHAs and those historical data, support that feedstock quality predictably determines both the average PHA co-monomer content, as well as the blend distribution. PHA solvent extraction from WAS is inherently a blending process. Extraction homogeneously mixes polymer contributions from collectively stored granules from all species of microorganisms in the biomass. Dried PHA-rich biomass batches can be stockpiled and batches can be blended in extraction processes for both recovery and formulation to reach consistent polymer qualities across production batches. More centralized extraction facilities are therefore anticipated to offer economic benefits due to scale and greater opportunities for product quality specification and control. Research findings are presented herein of the production scale comparative study along with practical perspectives of technological readiness for realizing WAS based industrial scale PHA production, quality control, and the supply chains that will be necessary for successful commercial implementation.

Past studies have repeatedly demonstrated the technical feasibility to produce polyhydroxyalkanoate (PHA) using bacterial biomass of mixed microbial cultures (MMCs). Commercial quality grades of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, can be produced with control of average monomer composition. However, demonstration of PHBV production and recovery with quality control of molecular weight (MW) distribution has been lacking in the research literature. Towards this goal, a workflow has been developed for characterizing molecular weight control by thermal treatment pre-processing of dried PHA-rich biomass before solvent extraction. Dimethyl carbonate (DMC) was a suitable solvent in this workflow in the routine evaluation of extractable PHA. From assessments of DMC extraction using differential scanning calorimetry, 125 °C was selected for nominally 100 percent extraction yield independent of polymer 3-hydroxyvalerate (3HV) content (2 to 41 wt.% 3HV) and molecular weight (100 to 1400 kDa). Intrinsic viscosity measurements of PHBV in DMC at 60 °C was used for molecular weight monitoring. Mark-Houwink constants, α (0.738 ± 0.010) and LogK (-2.016 ± 0.025), were estimated for a PHBV co-polymer blend having 36 wt.% 3HV. A model of random scission supported that weight average molecular weight (M_w) was a more robust metric, compared to number average molecular weight (M_n), for assessing the polymer scission rates. During isothermal heat treatment for a given biomass batch, interpreted scission rate was reproducible and commonly, but not always, constant in time. Scission rates between biomass batches were also variable. Measured properties of the polymer in the biomass (thermal stability, biomass PHA content, PHBV grade, initial moisture content) could not be correlated to this observed batch-to-batch variation of scission rate. Molecular weight loss before extraction did not influence the melting temperatures of the co-polymer blends of PHBV evaluated over a wide sub-eutectic range of average 3HV content. Molecular weight changes for these PHBV co-polymer blends were considered to have likely influenced the nature of blend 3HV distribution, and consequently, crystallization behaviour. Molecular weight loss effects on crystallization behaviour at constant PHBV average 3HV wt.% content could then have contributed to the observed variability for glass transition temperatures and melting enthalpies. However, a reproducible correlation between this variability and MW change was not observed.

Three novel xanthate-containing water-soluble triazine derivatives, 2,4-Di-(N,N-diethanolamine)-6-(ethyl xanthate ester-yl)-1,3,5-triazine (EXT), 2,4-Di-(N,N-diethanolamine)-6-(butyl xanthate ester-yl)-1,3,5-triazine (BXT) and 2,4-Di-(N, N-diethanolamine)-6-(hexyl xanthate ester-yl)-1,3,5-triazine (HXT), were synthesized and used as additives in water-glycol base fluid. It was found that the additive-containing samples had no corrosive effect on the cast iron and copper surface within 2.5 wt% additive. The tribological test results using a four-ball tribometer showed that the three additives greatly improved the P_B value, friction-reducing and antiwear performances of water-glycol. XPS results indicated that the additives had reacted with the contact metal surfaces and formed complex tribofilms composed of iron oxide, iron sulfide and iron sulfate, which may contribute to the reduction of friction coefficient and wear rate of the friction system.

Two triazine derivatives, 6-(diethanolamino)−2,4-bi-(sodium sulfanilate-yl)−1,3,5-triazine (STB) and 6-(ethyl xanthate)−2,4-bi-(sodium sulfanilate-yl)−1,3,5-triazine (STC) were synthesized and used as additives in water-glycol base fluid (mass ratio 1:1). Water solubility tests indicated that STB and STC met the solubility prerequisite for a water-soluble additive. The tribological tests by using a four-ball tribometer showed that, STB and STC both improved greatly the P_B value, antiwear and friction-reducing capacities of the base fluid. Based on friction test results and wear scars’ analysis, it was concluded that the differences in tribological performances of STB and STC samples were mainly due to the differences of the sulfur content and the sulfur activity in additives. XPS found that STB-tribofilm mainly contained sulfate, but STC-tribofilm additionally contained sulfide.

Graphene oxide (GO) was asymmetric chemically modified with myristyltrimethylammonium bromide (TTAB) to get modified graphene oxide (MGO). This MGO was used as an emulsifier and additive in oil-in-water emulsion. The emulsifying tests showed MGO greatly improved the stability of base emulsion and decreased its droplets size. Tribological test results showed that under the boundary lubrication condition with MGO-emulsion, the friction coefficient (COF) and the wear rate of the steel ball were decreased by about 18% and 48% respectively, comparing with base emulsion lubrication. The tribological mechanism of MGO-emulsion could be explained by the strong film-forming ability on the metal surface; the good lubricity of its small droplets; the formed adsorption film, transfer film and tribofilm between the contact surfaces.