Utilization Of Polyhydroxyalkanoates Research Articles

PHA granule formation and degradation by Cupriavidus necator under different nutritional conditions.

Polyhydroxyalkanoates (PHA) are polymers produced by microorganisms with increasing commercialization potential; Cupriavidus necator has been the model microorganism to research PHA production. Despite many contributions concerning the formation and degradation of PHA granules, as well as the morphological changes in cells, these phenomena have not been univocally explained yet. Thus, this study aims to integrate the microscopic and analytical analysis to characterize changes in bacterial cell/PHA granules morphology, PHA content, and yield coefficients under different cultivation strategies of C. necator ATCC 17697. The cell size and morphology, granule size and amount, residual biomass, and PHA concentration along the fermentation and degradation depend greatly on nutritional conditions and cultivation time of C. necator. It was proposed to calculate a yield coefficient for the residual biomass production in the PHA utilization stage, related to the bacteria's ability to survive without a carbon source in the culture medium by utilizing the accumulated PHA previously. Maximum granule length reached 1.07 µm after 72 h of PHA accumulation stage under optimum nutritional conditions. This value is twice the values previously reported for C. necator. It is important since the larger PHA granules facilitate the recovery of PHA and different application development.

Optimal iron concentrations for growth-associated polyhydroxyalkanoate biosynthesis in the marine photosynthetic purple bacterium Rhodovulum sulfidophilum under photoheterotrophic condition.

Polyhydroxyalkanoates (PHAs) are a group of natural biopolyesters that resemble petroleum-derived plastics in terms of physical properties but are less harmful biologically to the environment and humans. Most of the current PHA producers are heterotrophs, which require expensive feeding materials and thus contribute to the high price of PHAs. Marine photosynthetic bacteria are promising alternative microbial cell factories for cost-effective, carbon neutral and sustainable production of PHAs. In this study, Rhodovulum sulfidophilum, a marine photosynthetic purple nonsulfur bacterium with a high metabolic versatility, was evaluated for cell growth and PHA production under the influence of various media components found in previous studies. We evaluated iron, using ferric citrate, as another essential factor for cell growth and efficient PHA production and confirmed that PHA production in R. sulfidophilum was growth-associated under microaerobic and photoheterotrophic conditions. In fact, a subtle amount of iron (1 to 2 μM) was sufficient to promote rapid cell growth and biomass accumulation, as well as a high PHA volumetric productivity during the logarithmic phase. However, an excess amount of iron did not enhance the growth rate or PHA productivity. Thus, we successfully confirmed that an optimum concentration of iron, an essential nutrient, promotes cell growth in R. sulfidophilum and also enhances PHA utilization.

Production of Sterilized Medium Chain Length Polyhydroxyalkanoates (Smcl- Pha) as a Biofilm to Tissue Engineering Application

The current increase in the utilization of polyhydroxyalkanoates (PHAs) in various industrial and biomedical applications is due to their biodegradability, compatibility, resorbability and piezoelectricity. In the present study, we developed a modified medium chain length PHAs (Mmcl-PHA) by sterilizing surfaces of PHAs extracted from bacterial isolate. FTIR analysis of the neat polymer confirmed the presence of functional groups corresponding to alkyl halide, alkyne, hydroxyl group, and alkane groups. Sterilization of PHA using ethylene oxide as a medium was resulted modification of minor band differences in the absorption spectrum of homopolymer of PHB (scl-PHA) in to the co polymer of P (HB-co-HV) medium chain (mcl-PHA). The variation on to carbonyl (C=O) ester groups modified without significant changes to physico-chemical properties of the polymer were noticed. Sterilization of PHA using ethylene oxide has been evident surface modification properties suited to tissue engineering application of scaffold fabrication.

Simultaneous storage and utilization of polyhydroxyalkanoates and glycogen under aerobic conditions

This study aims to investigate the storage response of an activated sludge system in the presence of two different substrates which are stored as two different polymers. The objective of the study was to determine the changes in the response of an activated sludge system when two different storage mechanisms could occur simultaneously. Acetic acid (HAc) and soluble starch (SolS) were selected as model substrates and three different feeding conditions, namely (i) when both HAc and SolS were initially present in the reactor, (ii) only HAc was present, and (iii) only SolS was present in the substrate solution. The batch reactors were monitored for acetic acid, polyhydroxyalkanoates (PHA), poly-glucose (glycogen like substances) and oxygen uptake rate (OUR). The experiments have shown that, while the main portion of hydrolyzed starch was stored as poly-glucose, which was further used for heterotrophic growth, the rest was utilized for direct growth. However, acetic acid was totally stored as PHA and the stored PHA was used for biomass growth under the presented experimental conditions. When the system was fed with the substrate mixture, the storage mechanism was not significantly affected. Both PHA and poly-glucose storage took place simultaneously with the same stoichiometry and kinetics defined for single substrate utilization.

Enhanced Biological Phosphorus Removal Driven by Short-Chain Fatty Acids Produced from Waste Activated Sludge Alkaline Fermentation

This paper examines the feasibility of using alkaline fermentative short-chain fatty acids (SCFAs) as the carbon sources of enhanced biological phosphorus removal (EBPR) microorganisms. First, the released phosphorus was recovered from the SCFA-containing alkaline fermentation liquid by the formation of struvite precipitation, and 92.8% of the soluble ortho-phosphorus (SOP) could be recovered under conditions of Mg/P = 1.8 (mol/mol), pH 10.0, and a reaction time of 2 min. One reason for a Mg addition required in this study that was higher than the theoretical value was thatthe organic compounds consumed Mg. Then, two sequencing batch reactors (SBRs) were operated, respectively, with acetic acid and alkaline fermentative SCFAs as the carbon source of EBPR. The transformations of SOP, polyhydroxyalkanoates (PHAs), and glycogen and the removal of phosphorus were compared between two SBRs. It was observed that the phosphorus removal efficiency was around 98% with the fermentative SCFAs, and about 71% with acetic acid, although the former showed much lower transformations of both PHAs and glycogen. The reasons that fermentative SCFAs caused much higher SOP removal than acetic acid were due to less PHAs used for glycogen synthesis and a higher PHA utilization efficiency for SOP uptake. Finally, the toxicity of fermentation liquid to EBPR microorganisms was examined, and no inhibitory effect was observed. It can be concluded from this studythatthe SCFAs from alkaline fermentation of waste activated sludge were a superior carbon source for EBPR microorganisms than pure acetic acid.

The efficiency of enhanced biological phosphorus removal from real wastewater affected by different ratios of acetic to propionic acid

The effect of different ratios of propionic to acetic acid on the efficiency of enhanced biological phosphorus removal (EBPR) from real wastewater supplemented with volatile fatty acids (VFAs) was investigated. Two sequencing batch reactors (SBRs) were used to acclimate two types (SBR1 and SBR2) of biomass. They were cultured and studied using real wastewater with an average propionic to acetic acid carbon molar ratio of 0.16 and 2.06, respectively. The laboratory results showed that for a given long-term cultured biomass the more the soluble ortho-phosphate (SOP) was released in the anaerobic stage, the higher the SOP was taken up in the aerobic phase. However, the SBR2 biomass had a much greater SOP uptake to release ratio than SBR1, which resulted in a higher SOP removal efficiency than SBR1 (average 87.3% versus 76.9% in SBRs experiments, and 93.5% against 68.1% in batch tests). The SBR2 biomass therefore had a higher SOP uptake ability than the SBR1 for a given amount of SOP release. In addition, the SBR1 had a higher secondary SOP release following VFAs uptake. It was found that the SBR2 biomass synthesized and utilized less observable polyhydroxyalkanoates (PHAs) during the anaerobic and aerobic stage respectively than SBR1. The apparent PHAs utilization efficiency for SOP uptake with the SBR2 biomass was much greater than with the SBR1, and the SBR2 biomass synthesized less glycogen during aerobiosis than SBR1, which might mean a higher PHAs fraction was used for SOP removal, resulting in the increased efficiency with the long-term cultured SBR2 biomass. Higher propionic acid content led to superior EBPR in long-term cultivation, but was transiently detrimental in the short term.

Phosphorus and polyhydroxyalkanoates variation in a combined process with activated sludge and biofilm

This study investigates variations of phosphorus and polyhydroxyalkanoates (PHAs) in a combined activated sludge - biofilm process, operating under various sludge retention times (5, 10 and 15 days) and different dissolved oxygen conditions (0.1, 0.5, 1.0 and 2.0 mg/l in aerobic stage). Experimental results indicate that phosphorus uptake closely corresponds to utilization of PHAs during anoxic and aerobic stages. Moreover, the sludge in the anoxic stage exhibits a higher PHAs utilization efficiency with respect to phosphorus uptake than sludge in the aerobic stage, when it is under low COD-SS loading conditions. The values of rP/PHAs, representing sludge capacity on phosphorus uptake, range from 0.1-1.0 mg P/mg PHAs. In addition, analyzing the distribution of 3-hydroxybutyrate (3HB), 3-hydroxy-2-methylbutyrate (3H2MB), 3-hydroxyvalerate (3HV) and 3-hydroxy-2-methylvalerate (3H2MV) reveals that 3HB and 3HV are the major components of PHAs. The values of 3HB/PHAs and 3HV/PHAs vary with COD-SS loading of the process. When F/M ratio increases, 3HV/PHAs value increases and 3HB/PHAs value decreases simultaneously. This phenomenon implies that more bacteria accumulated 3HV as storage matter under high COD-SS loading conditions. The kind of bacteria population shift would intensify the competition of “G bacteria” with polyphosphate accumulating organisms, possibly causing process deterioration during phosphorus removal.

Phosphorus and polyhydroxyalkanoates variation in a combined process with activated sludge and biofilm

This study investigates variations of phosphorus and polyhydroxyalkanoates (PHAs) in a combined activated sludge - biofilm process, operating under various sludge retention times (5, 10 and 15 days) and different dissolved oxygen conditions (0.1, 0.5, 1.0 and 2.0 mg/l in aerobic stage). Experimental results indicate that phosphorus uptake closely corresponds to utilization of PHAs during anoxic and aerobic stages. Moreover, the sludge in the anoxic stage exhibits a higher PHAs utilization efficiency with respect to phosphorus uptake than sludge in the aerobic stage, when it is under low COD-SS loading conditions. The values of rP/PHA, representing sludge capacity on phosphorus uptake, range from 0.1–1.0 mg P/mg PHAs. In addition, analyzing the distribution of 3-hydroxybutyrate (3HB), 3-hydroxy-2-methylbutyrate (3H2MB), 3hydroxyvalerate (3HV) and 3-hydroxy-2-methylvalerate (3H2MV) reveals that 3HB and 3HV are the major components of PHAs. The values of 3HB/PHAs and 3HV/PHAs vary with COD-SS loading of the process. When F/M ratio increases, 3HV/PHAs value increases and 3HB/PHAs value decreases simultaneously. This phenomenon implies that more bacteria accumulated 3HV as storage matter under high COD-SS loading conditions. The kind of bacteria population shift would intensify the competition of “G bacteria” with polyphosphate accumulating organisms, possibly causing process deterioration during phosphorus removal.

Effects of SRT and DO on nutrient removal in a combined AS-biofilm process

This study examines the effects of sludge retention time (SRT) and dissolved oxygen (DO) on COD, nitrogen and phosphorus removal in a combined activated sludge - biofilm process. Various SRT (5, 10, 12 and 15 days) and dissolved oxygen (0.1, 0.5, 1.0 and 2.0 mg/l in aerobic stage) conditions are performed during the hybrid process. Experimental results indicate that SRT significantly affects the behavior of nitrogen and phosphorus removal, although the variation of COD removal is only slight in different SRT experiments. The SRT should be controlled for longer than 10 days to achieve efficient nitrogen removal. However, a SRT less than 12 days is deemed necessary to complete the phosphorus removal. The process displays similar characteristics when dissolved oxygen is operated between 1.0 to 2.0 mg/l in the aerobic stage. Moreover, analyzing polyhydroxyalkanoates (PHAs) reveals that phosphorus release and uptake are closely related to PHAs accumulation and utilization, respectively, during anaerobic, anoxic and aerobic stages of the process. The ratio of phosphorus uptake and PHAs utilized, rP/PHAs, denotes a dissimilar trend during anoxic and aerobic stages. The sludge has a high efficiency in utilizing PHAs for phosphorus uptake in anoxic stage when it is under lower COD-SS loading conditions. The value of rP/PHAs ranges from approximately 0.1 to 1.0 mg P/mg PHAs. In addition, experimental results also demonstrate that anoxic phosphorus uptake can improve phosphorus removal in biological nutrient removal processes.

Effects of SRT and do on nutrient removal in a combined as-biofilm process

This study examines the effects of sludge retention time (SRT) and dissolved oxygen (DO) on COD, nitrogen and phosphorus removal in a combined activated sludge - biofilm process. Various SRT (5, 10, 12 and 15 days) and dissolved oxygen (0.1, 0.5, 1.0 and 2.0 mg/l in aerobic stage) conditions are performed during the hybrid process. Experimental results indicate that SRT significantly affects the behavior of nitrogen and phosphorus removal, although the variation of COD removal is only slight in different SRT experiments. The SRT should be controlled for longer than 10 days to achieve efficient nitrogen removal. However, a SRT less than 12 days is deemed necessary to complete the phosphorus removal. The process displays similar characteristics when dissolved oxygen is operated between 1.0 to 2.0 mg/l in the aerobic stage. Moreover, analyzing polyhydroxyalkanoates (PHAs) reveals that phosphorus release and uptake are closely related to PHAs accumulation and utilization, respectively, during anaerobic, anoxic and aerobic stages of the process. The ratio of phosphorus uptake and PHAs utilized, rP/PHAs, denotes a dissimilar trend during anoxic and aerobic stages. The sludge has a high efficiency in utilizing PHAs for phosphorus uptake in anoxic stage when it is under lower COD-SS loading conditions. The value of rP/PHAs ranges from approximately 0.1 to 1.0 mg P/mg PHAs. In addition, experimental results also demonstrate that anoxic phosphorus uptake can improve phosphorus removal in biological nutrient removal processes.