Evaluation of different nutrient limitation strategies for the efficient production of poly(hydroxybutyrate-co-hydroxyvalerate) from waste frying oil and propionic acid in high cell density fermentations of Cupriavidus necator H16.

Because of its application potential and biodegradability, poly(3-hydroxybutyrate-co-3-hydroxyvalerate;PHBV), a member of the polyhydroxyalkanoates (PHA) biopolymer family, is one of the most extensively studied PHA. High PHBV productivity with a significant amount of hydroxyvalerate (HV) content is very appealing for commercial scale production. The goal of this study was to investigate the efficiency of various defined limitation strategies, namely nitrogen, phosphorus, and oxygen-limitation, for high yield PHBV production by Cupriavidus necator H16 with increased HV unit using waste frying vegetable oil (WFO) and propionic acid (PA) in a high cell density culture (5 L bioreactor). With optimized WFO and PA feeding, highest PHBV harvest (121.7 ± 2.59 g/L; HV 13.9 ± 0.44% (w/w)) and volumetric productivity (2.03 ± 0.04 gPHBV/L·h) were obtained in oxygen-limited operation, while highest HV content (19.8 ± 0.28 wt%) and yield coefficient (0.43 ± 0.017 gHV/gPA) were observed during phosphorus-limited cultivation. Although nitrogen limitation is widely applied in the production of PHA, nitrogen-limited cultivation had the lowest cell dry matter, PHBV production, volumetric productivity, oil-to-HB and PA-to-HV yield coefficients for the given conditions. The results of the present study demonstrate the highest PHBV yield together with the highest HV content using WFO as main carbon source and PA as the HV precursor ever reported in the literature.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate;PHBV), a member of the polyhydroxyalkanoates (PHA) biopolymer family, is one of the most extensively studied PHA due to its high application potential and biodegradability properties. High PHBV productivity with substantial amount of hydroxyvalerate (HV) content is of great interest for commercial scale PHA production to compete with conventional plastic costs.In this study, we investigated the effectiveness of different nutrient limitation strategies in optimizing the production of PHBV from waste frying vegetable oil and propionic acid. Although there are individual studies investigating the performance of operational PHBV production strategies such as nitrogen, phosphorus, or oxygen limitation, none of them have comprehensively compared the effect of different limitation strategies on PHA production parameters using waste frying vegetable oil as the main carbon source and propionic acid as the cheapest HV precursor. To our knowledge, this is the first study that evaluates the impact of these three limitation strategies on the efficient production of PHBV from waste frying oil and propionic acid in high cell density fermentations of Cupriavidus necator H16. The results demonstrate the highest PHBV yield together with the highest HV content using waste frying oil as main carbon source and propionic acid as the cheapest HV precursor ever reported in the literature. In addition, it is shown that the PHBV yield and its HV content could be intercorrelated by switching between oxygen and phosphorus-limited strategies for desired material specifications.

Polyhydroxyalkanoate production using waste vegetable oil and filtered digestate liquor of chicken manure.

The production of polyhydroxyalkanoates (PHA) using digestate of chicken manure combined with waste sunflower oil as no-cost feedstocks in a multi-stage process was investigated. Using Cupriavidus necator H16 in combined culture media, a maximum PHA accumulation of 4.6 ± 0.2 g/L at 75.1 ± 1.4% of cell dry matter and a residual cell matter yield of 1.5 ± 0.1 g/L were obtained after 96 hr of cultivation (30 °C, 160 rpm, pH 7.0) in flask-based experiments. Manure was acidogenically fermented in a continuous stirring tank reactor in fed-batch mode. The bioreactor was operated at varying organic loading rates (OLR) and hydraulic retention times (HRT) ranging from 1-4 g volatile solids (VS)/L/d and 4-8 days, respectively. Optimal operation was observed at an OLR of 4 g VS/L/d and an HRT of 4 days. Analysis showed the presence of significant amounts of ammonia, potassium, magnesium, calcium, and trace elements, i.e. Fe, Cu, Ni, Mn, Co, Zn, Cr in the digestate. The micro-filtered digestate was utilized as a complex culture media base while waste oil served as an additional carbon source and supplemented for effective PHA production. The total volatile fatty acid content of digestate greatly affected the growth performance of the PHA-producing microorganism Cupriavidus necator H16.

Cyanophycin production from feather hydrolysate using biotechnological methods.

Cyanophycin is a bacterial storage polymer for carbon, nitrogen and energy with emerging industrial applications. As efficient cyanophycin production is enhanced by peptone, but commercial peptones are very expensive, thereby increasing the overall production cost, an enzymatically produced feather hydrolysate (FH) is assessed as a cheap replacement of peptone to lower the costs and make cyanophycin production more economically feasible. Keratinase production using feather as the sole carbon/nitrogen source by S.pactum 40530 at 30-L fermentation scale was achieved within 93 h with degradation rate of 96.5%. A concentration of 60 g/L of FH, generated by keratinolytic activity (8 × 103 U g-1L-1d-1) within 24 h, was used as the main carbon/peptone source to produce cyanophycin. The growth performances of E. coli DapE/L using FH was compared to that of casamino acids (CA) and up to 7.1 ± 0.4 and 5.3 ± 0.3 g/L of cell mass were obtained after 72 h from FH and CA, respectively. Cyanophycin production yielded 1.4 ± 0.1g/L for FH with average molecular mass of 28.8 and 1.4 ± 0.2 for CA with average molecular mass of 35.3, after 60 h. For the first time, FH generated by biotechnological methods from environmentally problematic, abundant and renewable feather bioresource was successfully used for cyanophycin biopolymer production.

Arsenic removal in a sulfidogenic fixed-bed column bioreactor.

In the present study, the bioremoval of arsenic from synthetic acidic wastewater containing arsenate (As(5+)) (0.5-20mg/L), ferrous iron (Fe(2+)) (100-200mg/L) and sulfate (2,000 mg/L) was investigated in an ethanol fed (780-1,560 mg/L chemical oxygen demand (COD)) anaerobic up-flow fixed bed column bioreactor at constant hydraulic retention time (HRT) of 9.6h. Arsenic removal efficiency was low and averaged 8% in case iron was not supplemented to the synthetic wastewater. Neutral to slightly alkaline pH and high sulfide concentration in the bioreactor retarded the precipitation of arsenic. Addition of 100mg/L Fe(2+) increased arsenic removal efficiency to 63%. Further increase of influent Fe(2+) concentration to 200mg/L improved arsenic removal to 85%. Decrease of influent COD concentration to its half, 780 mg/L, resulted in further increase of As removal to 96% when Fe(2+) and As(5+) concentrations remained at 200mg/L and 20mg/L, respectively. As a result of the sulfidogenic activity in the bioreactor the effluent pH and alkalinity concentration averaged 7.4 ± 0.2 and 1,736 ± 239 mg CaCO3/L respectively. Electron flow from ethanol to sulfate averaged 72 ± 10%. X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses were carried out to identify the nature of the precipitate generated by sulfate reducing bacteria (SRB) activity. Precipitation of arsenic in the form of As2S3 (orpiment) and co-precipitation with ferrous sulfide (FeS), pyrite (FeS2) or arsenopyrite (FeAsS) were the main arsenic removal mechanisms.

Hexavalent chromium reduction in a sulfur reducing packed-bed bioreactor.

The most commonly used approach for the detoxification of hazardous industrial effluents and wastewaters containing Cr(VI) is its reduction to the much less toxic and immobile form of Cr(III). This study investigates the cleanup of Cr(VI) containing wastewaters using elemental sulfur as electron acceptor, for the production of hydrogen sulfide that induces Cr(VI) reduction. An elemental sulfur reducing packed-bed bioreactor was operated at 28-30°C for more than 250 days under varying influent Cr(VI) concentrations (5.0-50.0 mg/L) and hydraulic retention times (HRTs, 0.36-1.0 day). Ethanol or acetate (1000 mg/L COD) was used as carbon source and electron donor. The degree of COD oxidation varied between 30% and 85%, depending on the operating conditions and the type of organic carbon source. The oxidation of organic matter was coupled with the production of hydrogen sulfide, which reached a maximum concentration of 750 mg/L. The biologically produced hydrogen sulfide reduced Cr(VI) chemically to Cr(III) that precipitated in the reactor. Reduction of Cr(VI) and removal efficiency of total chromium always exceeded 97% and 85%, respectively, implying that the reduced chromium was retained in the bioreactor. This study showed that sulfur can be used as an electron acceptor to produce hydrogen sulfide that induces efficient reduction and immobilization of Cr(VI), thus enabling decontamination of Cr(VI) polluted wastewaters.