Poly(3-hydroxybutyrate)
(PHB)—a renewable and biodegradable
polymer—is a promising alternative to nonbiodegradable synthetic
plastics that are derived from petrochemicals. The methods currently
employed for PHB production are costly, in part, due to the expensive
cultivation feedstocks and the need to sterilize the culture medium,
which is energy-intensive. This study investigates the feasibility
of nonsterile PHB production from several saline organic wastes using
a salt-tolerant strain,
Zobellella denitrificans
ZD1 (referred to as strain ZD1). Factors such as the pH, salinity,
carbon/nitrogen (C/N) ratio, nitrogen source, and electron acceptor
that might affect the growth of strain ZD1 and its PHB production
were determined. Our results showed successful nonsterile PHB production
by growing the strain ZD1 on nonsterile synthetic crude glycerol,
high-strength saline wastewater, and real municipal wastewater-activated
sludge under saline conditions. The PHB production was significantly
enhanced when the levels of salts and nitrate-nitrogen in the culture
medium were increased. This study suggested a promising low-cost nonsterile
PHB production strategy from organic wastes using strain ZD1.
Recirculation aquaculture system (RAS) is a unique indoor fish farming method. Yet, the RAS system needs to address challenges such as effective wastewater/waste management, reduction of feed cost, and usage of antibiotics during farming to become a sustainable aquaculture system. Here, we report a novel RAS-polyhydroxybutyrate (PHB) system to overcome these challenges simultaneously. The RAS-PHB enables effective aquaculture wastewater (AW) treatment for reuse while producing and harvesting PHB-rich biomass as a protein-rich, immune-stimulating fish feed without the need for antibiotics. The feasibility of nitrogen recovery from AW for nonsterile cultivation of a salt-tolerant PHB-producing strain (Zobellella denitrificans ZD1) with or without supplementing agro-industrial wastes/wastewaters (e.g., glycerol, cheese whey wastewater, and aquaculture solid waste) was examined. Glycerol-grown Z. denitrificans ZD1 showed high contents of PHB (48%) and proteins (45.5%). High harvest efficiency of PHB-rich Z. denitrificans ZD1 (97%) was achieved by using small amounts of medium-molecular-weight chitosan. A simple economic analysis showed that the production costs were 0.6−0.7 $/kg of fish produced for the RAS-PHB and 1.2−1.6 $/kg for the conventional RAS, suggesting a reduction of 56% of the total cost by using a RAS-PHB. Overall, this proof-of-concept study showed that the RAS-PHB system is promising for future sustainable aquaculture practice.
In this study, the properties of virgin linear low-density polyethylene (LLDPE) and its blends with reclaimed plastic solid waste (PSW) are investigated by thermogravimetry, differential scanning calorimetry (DSC), infrared spectroscopy and scanning electron microscopy (SEM). The PSW constituted polyolefin (PO) polymers recycled mechanically via extrusion/blown-film and exposed to accelerated weathering tests to determine the change in their degradation behaviour. The oxidation products determined using the FTIR analysis and thermal stability studies points toward the blend constituting 25% of waste by weight as the most stable. Changes in crystallinity of the polymers were attributed to the crystal size change as a consequence of the weathering mechanism. The DSC results revealed that both oxidation induction temperature (OIT) and crystallinity were affected by the PO waste content. This points towards the impact of polymers immiscibility and polydispersity within the matrix of the blends due to chain scission reaction and oxidation with the UV exposure.
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