Calcium enhances polyhydroxyalkanoate production and promotes selective growth of the polyhydroxyalkanoate-storing biomass in municipal activated sludge

Demonstrating performance in scaled-up production and quality control of polyhydroxyalkanoates using municipal waste activated sludge

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.

Bioplastic production by harnessing cyanobacteria-rich microbiomes for long-term synthesis

Departing from the conventional axenic and heterotrophic cultures, our research ventures into unexplored territory by investigating the potential of photosynthetic microbiomes for polyhydroxybutyrate (PHB) synthesis, a biodegradable polyester that presents a sustainable alternative to conventional plastics. Our investigation focused on a cyanobacteria-enriched microbiome, dominated by Synechocystis sp. and Synechococcus sp., cultivated in a 3 L photobioreactor under non-sterile conditions, achieving significant PHB production-up to 28 % dry cell weight (dcw) over a span of 108 days through alternating cycles of biomass growth and PHB accumulation. Nile Blue staining and Transmission Electron Microscope visualization allowed to successfully confirm the presence of PHB granules within cyanobacteria cells. Furthermore, the overexpression of PHA synthase during the accumulation phase directly correlated with the increased PHB production. Also, gene expression changes revealed glycogen as the primary storage compound, but under prolonged macronutrient stress, there was a shift of the carbon flux towards favoring PHB synthesis. Finally, analysis through Raman, Fourier- transform infrared spectroscopy and proton Nuclear Magnetic Resonance further validated the extracted polymer as PHB. Overall, it was demonstrated for the first time the feasibility of using phototrophic microbiomes to continuous production of PHB in a non-sterile system. This study also offers valuable insights into the metabolic pathways involved.

Bio-Based and Biodegradable Polymeric Materials for a Circular Economy

Nowadays, plastic contamination worldwide is a concerning reality that can be addressed with appropriate society education as well as looking for innovative polymeric alternatives based on the reuse of waste and recycling with a circular economy point of view, thus taking into consideration that a future world without plastic is quite impossible to conceive. In this regard, in this review, we focus on sustainable polymeric materials, biodegradable and bio-based polymers, additives, and micro/nanoparticles to be used to obtain new environmentally friendly polymeric-based materials. Although biodegradable polymers possess poorer overall properties than traditional ones, they have gained a huge interest in many industrial sectors due to their inherent biodegradability in natural environments. Therefore, several strategies have been proposed to improve their properties and extend their industrial applications. Blending strategies, as well as the development of composites and nanocomposites, have shown promising perspectives for improving their performances, emphasizing biopolymeric blend formulations and bio-based micro and nanoparticles to produce fully sustainable polymeric-based materials. The Review also summarizes recent developments in polymeric blends, composites, and nanocomposite plasticization, with a particular focus on naturally derived plasticizers and their chemical modifications to increase their compatibility with the polymeric matrices. The current state of the art of the most important bio-based and biodegradable polymers is also reviewed, mainly focusing on their synthesis and processing methods scalable to the industrial sector, such as melt and solution blending approaches like melt-extrusion, injection molding, film forming as well as solution electrospinning, among others, without neglecting their degradation processes.

Acclimation of microbial communities to low and moderate salinities in anaerobic digestion

In recent years anaerobic digestion (AD) has been investigated as suitable biotechnology to treat wastewater at elevated salinities. However, when starting up AD reactors with inocula that are not adapted to salinity, low concentrations of sodium (Na+) in the influent can already cause disintegration of microbial aggregates and wash-out. This study investigated biomass acclimation to 5 g Na+/L of two different non-adapted inocula in two lab-scale hybrid expanded granular sludge bed (EGSB)-anaerobic filter (AF) reactors fed with synthetic wastewater. After an initial biomass disintegration, new aggregates were formed relatively fast (i.e., after 95 days of operation), indicating microbial community adaptation. The newly formed microbial aggregates accumulated Na+ at the expense of calcium (Ca2+), but this did not hamper biomass retention or process performance. The hybrid reactor configuration, including a pumice stone filter in the upper section, and the low up-flow velocities applied, were key features for retaining the biomass within the system. This reactor configuration can be easily applied and represents a low-cost alternative for acclimating biomass to saline effluents, even in existing digesters. When the acclimated biomass was transferred from EGSB to an up-flow anaerobic sludge blanket (UASB) reactor configuration also fed with saline synthetic wastewater, more dense aggregates in the form of granules were obtained. The performances of the UASB inoculated with the acclimated biomass were comparable to another reactor seeded with saline-adapted granular sludge from a full-scale plant. Regardless of the inoculum origin, a defined core microbiome of Bacteria (Thermovirga, Bacteroidetes vadinHA17, Blvii28 wastewater-sludge group, Mesotoga, and Synergistaceae) and Archaea (Methanosaeta and Methanobacterium) was detected, highlighting the importance of these microbial groups in developing halotolerance and maintaining AD process stability.