Polyhydroxyalkanoate accumulation ability and associated microbial community in activated sludge-derived acetate-fed microbial cultures enriched under different temperature and pH conditions

Molecular insight into the allocation of organic carbon to heterotrophic bacteria: Carbon metabolism and the involvement in nitrogen and phosphorus removal

Carbon metabolism and nutrient removal are crucial for biological wastewater treatment. This study focuses on analyzing carbon allocation and utilization by heterotrophic bacteria in response to increasing COD concentration in the influent. The study also assesses the effect of denitrification and biological phosphorus removal, particularly in combination with anaerobic ammonia oxidation (anammox). The experiment was conducted in a SBR operating under anaerobic/anoxic/oxic conditions. As COD concentration in the influent increased from 100 to 275 mg/L, intracellular COD accounted for 95.72 % of the COD removed. By regulating the NO3- concentration in the anoxic stage from 10 to 30 mg/L, the nitrite accumulation rate reached 69.46 %, which could serve as an electron acceptor for anammox. Most genes related to the tricarboxylic acid (TCA) cycle declined, while the genes involved in the glyoxylate cycle, gluconeogenesis, PHA synthesis increased. This suggests that glycogen accumulation and carbon storage, rather than direct carbon oxidation, was the dominant pathway for carbon metabolism. However, the genes responsible for the reduction of NO2--N (nirK) and NO (nosB) decreased, contributing to NO2- accumulation. The study also employed metagenomic analysis to reveal microbial interactions. The enrichment of specific bacterial species, including Dechloromonas sp. (D2.bin.10), Ca. Competibacteraceae bacterium (D9.bin.8), Ca. Desulfobacillus denitrificans (D6.bin.17), and Ignavibacteriae bacterium (D3.bin.9), played a collaborative role in facilitating nutrient removal and promoting the combination with anammox.

A review on microbes mediated resource recovery and bioplastic (polyhydroxyalkanoates) production from wastewater

BACKGROUND

Plastic is widely utilized in packaging, frameworks, and as coverings material. Its overconsumption and slow degradation, pose threats to ecosystems due to its toxic effects. While polyhydroxyalkanoates (PHA) offer a sustainable alternative to petroleum-based plastics, their production costs present significant obstacles to global adoption. On the other side, a multitude of household and industrial activities generate substantial volumes of wastewater containing both organic and inorganic contaminants. This not only poses a threat to ecosystems but also presents opportunities to get benefits from the circular economy. Production of bioplastics may be improved by using the nutrients and minerals in wastewater as a feedstock for microbial fermentation. Strategies like feast-famine culture, mixed-consortia culture, and integrated processes have been developed for PHA production from highly polluted wastewater with high organic loads. Various process parameters like organic loading rate, organic content (volatile fatty acids), dissolved oxygen, operating pH, and temperature also have critical roles in PHA accumulation in microbial biomass. Research advances are also going on in downstream and recovery of PHA utilizing a combination of physical and chemical (halogenated solvents, surfactants, green solvents) methods. This review highlights recent developments in upcycling wastewater resources into PHA, encompassing various production strategies, downstream processing methodologies, and techno-economic analyses.

SHORT CONCLUSION

Organic carbon and nitrogen present in wastewater offer a promising, cost-effective source for producing bioplastic. Previous attempts have focused on enhancing productivity through optimizing culture systems and growth conditions. However, despite technological progress, significant challenges persist, such as low productivity, intricate downstream processing, scalability issues, and the properties of resulting PHA.

Flow cytometry: a tool for understanding the behaviour of polyhydroxyalkanoate accumulators

The use of mixed microbial cultures (MMCs) is seen as an attractive strategy for polyhydroxyalkanoate (PHA) production. In order to optimize the MMC-PHA production process, tools are required to improve our understanding of the physiological state of the PHA-storing microorganisms within the MMC. In the present study, we explored the use of flow cytometry to analyse the metabolic state and polyhydroxybutyrate (PHB) content of the microorganisms from an MMC-PHA production process. A sequencing batch reactor under a feast and famine regime was used to enrich an MMC with PHB-storing microorganisms. Interestingly, once the PHB-storing microorganisms are selected, the level of PHB accumulation depends largely on the metabolic state of these microorganisms and not exclusively on the consortium composition. These results demonstrate that flow cytometry is a powerful tool to help to understand the PHA storage response of an MMC-PHA production process. KEY POINTS: • Flow cytometry allows to measure PHB content and metabolic activity over time. • Microorganisms showing high PHB content also have high metabolic activity. • PHB producers with low metabolic activity show low PHB content.

Polyhydroxybutyrate blends: A solution for biodegradable packaging?

Poly (3-hydroxybutyrate) (PHB) is a valuable bio-based and biodegradable polymer that may substitute common polymers in packaging and biomedical applications provided that the production cost is reduced and some properties improved. Blending PHB with other biodegradable polymers is the most simple and accessible route to reduce costs and to improve properties. This review provides a comprehensive overview on the preparation, properties and application of the PHB blends with other biodegradable polyesters such as medium-chain-length polyhydroxyalkanoates, poly(ε-caprolactone), poly(lactic acid), poly(butylene succinate), poly(propylene carbonate) and poly (butylene adipate-co-terephthalate) or polysaccharides and their derivatives. A special attention has been paid to the miscibility of PHB with these polymers and the compatibilizing methods used to improve the dispersion and interface. The changes in the PHB morphology, thermal, mechanical and barrier properties induced by the second polymer have been critically analyzed in view of industrial application. The biodegradability and recyclability strategies of the PHB blends were summarized along with the processing techniques adapted to the intended application. This review provides the tools for a better understanding of the relation between the micro/nanostructure of PHB blends and their properties for the further development of PHB blends as solutions for biodegradable packaging.

The impact of carbon to nitrogen ratios and pH on the microbial prevalence and polyhydroxybutyrate production levels using a mixed microbial starter culture

Growth conditions have been frequently studied in optimizing polyhydroxybutyrate (PHB) production, while few studies were performed to unravel the dynamic mixed microbial consortia (MMCs) in the process. In this study, the relationship between growth conditions (C/N ratios and pH) and the corresponding key-microbes were identified and monitored during PHB accumulation. The highest PHB level (70 wt% of dry cell mass) was obtained at pH 9, C/N 40, and acetic acid 10 g/L. Linking the dominant genera with the highest point of PHB accumulation, Thauera was the most prevalent species in all MMCs of pH 9, except when a C/N ratio of 1 was applied. Notably, dominant bacteria shifted at pH 7 (C/N 10) from Thauera (0 h) to Paracoccus, and subsequently to Alcaligenes following the process of PHB accumulation and consumption. Further understanding of the relationship between the structure of the microbial community and the performance will be beneficial for regulating and obtaining high PHB accumulation within an MMC. Our study illustrates the impact of C/N ratios and pH on microbial prevalence and PHB production levels using a mixed microbial starter culture. This knowledge will broaden industrial perspectives for regulating high PHB production and timely harvesting.

Exploring the feasibility of nitrous oxide reduction and polyhydroxyalkanoates production simultaneously by mixed microbial cultures

Nitrous oxide (N₂O), as a powerful greenhouse gas, has drawn increasing attention in recent years and different strategies for N₂O reduction were explored. In this study, a novel strategy for valuable polyhydroxyalkanoates (PHA) production coupling with N₂O reduction by mixed microbial cultures (MMC) using different substrates was evaluated. Results revealed that N₂O was an effective electron acceptor for PHA production. The highest PHA yield (0.35 Cmmol PHA/Cmmol S) and PHA synthesis rate (227.47 mg PHA/L/h) were obtained with acetic acid as substrate. Low temperature (15℃) and pH of 8.0 were beneficial for PHA accumulation. Results of the thermogravimetric analysis showed that PHA produced with N₂O as electron acceptor has better thermal stability (melting temperature of 99.4℃ and loss 5% weight temperature of 211.4℃). Our work opens up new avenues for simultaneously N₂O reduction and valuable bioplastic production, which is conducive to resource recovery and climate protection.

Beyond PHA: Stimulating intracellular accumulation of added-value compounds in mixed microbial cultures

This review compiled and analyzed the operational conditions (dissolved oxygen, feast and famine ratio, sequential batch reactor cycle length, organic loading rate (OLR), pH, C/N, and temperature) established during the feast and famine culture strategy for the mixed microbial cultures (MMC) selection to understand how these variables could affect the synthesis of polyhydroxyalkanoates, polyglucose, triacylglycerides, levulinic acid and adipic acid from non-fermented substrates. According to the reported information, the dissolved oxygen has a greater impact on the type and amount of produced compound. In a lesser extent, the OLR and the cycle length were identified to have an impact on the accumulation of polyhydroxyalkanoates, whose accumulation was favored at lower OLR and longer cycle lengths. Thereby, the information of this work will allow the design of future strategies for the simultaneous accumulation of compounds of interest other than the polyhydroxyalkanoates or understand the operational conditions that would optimize the polyhydroxyalkanoates production.

Optimization of aerobic dynamic discharge process for very rapid enrichment of polyhydroxyalkanoates-accumulating bacteria from activated sludge

The aerobic dynamic discharge (ADD) process has the potential to reduce the enrichment period of polyhydroxyalkanoates (PHA)-accumulating bacteria in PHA production using mixed microbial cultures (MMCs). This study aimed to efficiently enrich PHA-accumulating bacteria from activated sludge within a fixed period of 2 d by optimizing operating conditions of the ADD process. Based on the results, enrichment with separate feeding of carbon and nutrients in the feast and famine phases, respectively, and a settling duration of 10 min after the feast phase in the sequencing batch cycle for 12 h was found to be optimal. The MMC enriched at optimum conditions could store as much as 68.4 wt% of PHA. Dechloromonas and Zoogloea were identified as potential PHA-accumulating bacteria responsible for enhancing PHA accumulation ability in the enriched MMC. The optimized ADD process will facilitate the consecutive use of daily generated waste activated sludge for PHA production.

Metagenomic Insights Into Functional and Taxonomic Compositions of an Activated Sludge Microbial Community Treating Leachate of a Completed Landfill: A Pathway-Based Analysis

Upcycling wastes into valuable products by mixed microbial communities has recently received considerable attention. Sustainable production of high-value substances from one-carbon (C1) compounds, e.g., methanol supplemented as an external electron donor in bioreactors for wastewater treatment, is a promising application of upcycling. This study undertook a gene-centric approach to screen valuable production potentials from mixed culture biomass, removing organic carbon and nitrogen from landfill leachate. To this end, the microbial community of the activated sludge from a landfill leachate treatment plant and its metabolic potential for the production of seven valuable products were investigated. The DNA extracted from the activated sludge was subjected to shotgun metagenome sequencing to analyze the microbial taxonomy and functions associated with producing the seven products. The functional analysis confirmed that the activated sludge could produce six of the valuable products, ectoine, polyhydroxybutyrate (PHB), zeaxanthin, astaxanthin, acetoin, and 2,3-butanediol. Quantification of the detected functional gene hit numbers for these valuable products as a primary trial identified a potential rate-limiting metabolic pathway, e.g., conversion of L-2,4-diaminobutyrate into N-γ-acetyl-L2,4,-diaminobutyrate during the ectoine biosynthesis. Overall, this study demonstrated that primary screening by the proposed gene-centric approach can be used to evaluate the potential for the production of valuable products using mixed culture or single microbe in engineered systems. The proposed approach can be expanded to sites where water purification is highly required, but resource recovery, or upcycling has not been implemented.

Waste to bioplastics: How close are we to sustainable polyhydroxyalkanoates production?

Increased awareness of environmental sustainability with associated strict environmental regulations has incentivized the pursuit of novel materials to replace conventional petroleum-derived plastics. Polyhydroxyalkanoates (PHAs) are appealing intracellular biopolymers and have drawn significant attention as a viable alternative to petrochemical based plastics not only due to their comparable physiochemical properties but also, their outstanding characteristics such as biodegradability and biocompatibility. This review provides a comprehensive overview of the recent developments on the involved PHA producer microorganisms, production process from different waste streams by both pure and mixed microbial cultures (MMCs). Bio-based PHA production, particularly using cheap carbon sources with MMCs, is getting more attention. The main bottlenecks are the low production yield and the inconsistency of the biopolymers. Bioaugmentation and metabolic engineering together with cost effective downstream processing are promising approaches to overcome the hurdles of commercial PHA production from waste streams.

Recent developments in Polyhydroxyalkanoates (PHAs) production - A review

Polyhydroxyalkanoates (PHAs) are inevitably a key biopolymer that has the potential to replace the conventional petrochemical based plastics that pose jeopardy to the environment globally. Even then the reach of PHA in the common market is so restricted. The economy of PHA is such that, even after several attempts the overall production cost seems to be high and this very factor surpasses PHAs usage when compared to the conventional polymers. The major focus of the review relies on the synthesis of PHA from Mixed Microbial Cultures (MMCs), through a 3-stage process most probably utilizing feedstocks from waste streams or models that mimic them. Emphasis was given to the works carried out in the past decade and their coherence with each and every individual criteria (Aeration, Substrate and bioprocess parameters) such that to understand their effect in enhancing the overall production of PHA.

Potential of waste activated sludge to accumulate polyhydroxyalkanoates and glycogen using industrial wastewater/liquid wastes as substrates

Recovery of the organics in industrial wastewaters/liquid wastes as polyhydroxyalkanoate (PHA) and/or glycogen (GLG) in waste activated sludge is a useful strategy to not only improve the resource value of waste activated sludge but also reduce the energy and cost of waste disposal and wastewater treatment. This study aimed to evaluate the potential of activated sludge to accumulate PHA and GLG using complex substrates (actual and simulated industrial wastewaters/liquid wastes) in addition to various simple organic substrates (organic acids, saccharides, and glycerol). The 24 h PHA and GLG accumulation experiments resulted in the accumulation of up to 25.5%, 6.0% and 14.1% of polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and GLG, respectively, from simple substrates, and up to 9.8%, 0.1% and 14.6%, respectively, from complex substrates. The results indicated that activated sludge can accumulate PHA and GLG even from complex wastewater substrates, although the accumulated PHA and GLG levels were not sufficiently high. The results also indicated that the PHA and GLG accumulation abilities of activated sludge from complex substrates can be drastically enhanced by a short-term acclimation to the corresponding substrate. This study will present the practical implications for value-added resource production through the combined use of waste activated sludge and industrial wastewaters.

Composition of bacterial communities in municipal wastewater treatment plant

Efforts to understand the environmental and biological factors that influence the dynamics of microbial communities have received substantial attention in microbial ecology. In this study, Illumina MiSeq high-throughput sequencing technology was used to examine the microbial community structure of activated sludge in municipal wastewater treatment systems (Chuzhou city, China). Overall, Proteobacteria, Chloroflexi, Actinobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, and Firmicutes were the most dominant phyla in the five activated sludge samples. However, the community structure of nitrifying bacteria was relatively simple, and diversity was low; only AOB (Nitrosomonas) and NOB (Nitrospira) were detected. The dominant bacteria in the anaerobic sludge, anoxic sludge and oxic sludge were the same, and each bacterial species was relatively uniform, with differences only in proportions. Redundancy analysis indicated that pH, TP and COD were strong environmental factors influencing the bacterial community distribution. PICRUSt was used to describe the metabolic and functional abilities of the activated sludge bacterial communities. The results emphasized the vast genetic diversity of these organisms, which are involved in various essential processes such as amino acid transport and metabolism, energy production and conversion, cell wall/membrane/envelope/biogenesis, signal transduction mechanisms, and carbohydrate transport and metabolism. Activated sludge of municipal wastewater treatment systems can be ranked in the following order based on the 16S rRNA gene copy numbers of the detected phylotypes: S1 > S2 > S4 > S5 > S3. This study provides basic data and a theoretical analysis of the optimal design and operation in wastewater treatment plants.

Pretreatment of lignocellulosic feedstock to produce fermentable sugars for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production using activated sludge

The goal of this research was to release fermentable reducing sugar from lignocellulose (poplar) by hot water pretreatment, and then employed to synthesize poly(3-hydroxybutyrate-co-3-hydroxy-valerate) (PHBV) using activated sludge to replace traditional petroleum-based polymers. The orthogonal experiment was used to optimize the conditions of different pretreatment temperature, pretreatment time, enzymatic hydrolysis temperature and enzymatic hydrolysis time and the optimal condition for producing sugars was pretreated at 200 °C for 30 min and enzymatic hydrolysis at 45 °C for 3d. A maximum yield was 530.3 mg/g of reduced sugar, while the furfural and 5-HMF produced in the optimum conditions were 512.61 mg/L and 239.34 mg/L. Moreover, the effects of increasing concentration of hot water pretreated poplar hydrolysates (500-1700 mg/L) on PHBV production were investigated. Poplar hydrolysate (1700 mg/L) exhibited maximum PHBV concentration of 637.556 mg/L.

Effect of sodium chloride on polyhydroxyalkanoate production from food waste fermentation leachate under different organic loading rate

Polyhydroxyalkanoate (PHA) production integrated with anaerobic digestion is promising for food waste recycle. However, effect of salinity and high organic load in waste fermentation leachate (FWFL) on PHA production is unknown. Effects of sodium chloride (NaCl, 0, 5.0, 10.0 and 15.0 g/L) and organic loading rate (OLR, 1350 and 8433 mg COD/(L·d)) on the enrichment of PHA-accumulating microorganisms and PHA accumulation using FWFL were investigated in this research. Stable operation and obvious effect were observed under lower OLR with increasing NaCl concentration, but effect of NaCl was concealed by the inhibition caused by high OLR. Paracoccus was the dominant bacteria in all treatments with NaCl. Microbial community at low OLR and 5.0 g/L NaCl had the best performance reflected by kinetic parameters. Real FWFL with different NaCl concentrations was used in batch assays to verify the optimized enrichment strategy, reaching the maximum PHA content of 33.4% at 2.5 g/L NaCl.