Photofermentative production of hydrogen and poly-β-hydroxybutyrate from dark fermentation products

Polyhydroxyalkanoates production in purple phototrophic bacteria ponds: A breakthrough in outdoor pilot-scale operation

The versatile capacity of purple phototrophic bacteria (PPB) for producing valuable bioproducts has gathered renewed interest in the field of resource recovery and waste valorisation. However, greater knowledge regarding the viability of applying PPB technologies in outdoor, large-scale systems is required. This study assessed, for the first time, the upscaling of the phototrophic polyhydroxyalkanoate (PHA) production technology in a pilot-scale system operated in outdoor conditions. An integrated system composed of two up-flow anaerobic sludge blanket (UASB) reactors (for fermentation of wastewater with molasses), and two high-rate algal ponds retrofitted into PPB ponds, was operated in a wastewater treatment plant under outdoor conditions. UASB's adaptation to the outdoor temperatures involved testing different operational settings, namely hydraulic retention times (HRT) of 48 and 72 h, and molasses fermentation in one or two UASBs. Results have shown that the fermentation of molasses in both UASBs with an increased HRT of 72 h was able to ensure a suitable operation during colder conditions, achieving 3.83 ± 0.63 g CODFermentative Products/L, compared to the 3.73 ± 0.85 g CODFermentative Products/L achieved during warmer conditions (molasses fermentation in one UASB; HRT 48 h). Furthermore, the PPB ponds were operated under a light-feast/dark-aerated-famine strategy and fed with the fermented wastewater and molasses from the two UASBs. The best PHA production was obtained during the summer of 2018 and spring of 2019, attaining 34.7 % gPHA/gVSS with a productivity of 0.11 gPHA L-1 day-1 and 36 % gPHA/gVSS with a productivity of 0.14 gPHA L-1 day-1, respectively. Overall, this study showcases the first translation of phototrophic PHA production technology from an artificially illuminated laboratory scale system into a naturally illuminated, outdoor, pilot-scale system. It also addresses relevant process integration aspects with UASBs for pre-fermenting wastewater with molasses, providing a novel operational strategy to achieve photosynthetic PHA production in outdoor full-scale systems.

Bioconversion of volatile fatty acids from organic wastes to produce high-value products by photosynthetic bacteria: A review

Anaerobic fermentation of organic waste to produce volatile fatty acids (VFAs) production is a relatively mature technology. VFAs can be used as a cheap and readily available carbon source by photosynthetic bacteria (PSB) to produce high value-added products, which are widely used in various applications. To better enhance the VFAs obtained from organic wastes for PSB to produce high value-added products, a comprehensive review is needed, which is currently not available. This review systematically summarizes the current status of microbial proteins, H2, poly-β-hydroxybutyrate (PHB), coenzyme Q10 (CoQ10), and 5-aminolevulinic acid (ALA) production by PSB utilizing VFAs as a carbon resource. Meanwhile, the metabolic pathways involved in the H2, PHB, CoQ10, and 5-ALA production by PSB were deeply explored. In addition, a systematic resource utilization pathway for PSB utilizing VFAs from anaerobic fermentation of organic wastes to produce high value-added products was proposed. Finally, the current challenges and priorities for future research were presented, such as the screening of efficient PSB strains, conducting large-scale experiments, high-value product separation, recovery, and purification, and the mining of metabolic pathways for the VFA utilization to generate high value-added products by PSB.

The phototrophic bacteria Rhodomicrobium spp. are novel chassis for bioplastic production

Polyhydroxybutyrate (PHB) is a bio-based, biodegradable alternative to petroleum-based plastics. PHB production at industrial scales remains infeasible, in part due to insufficient yields and high costs. Addressing these challenges requires identifying novel biological chassis for PHB production and modifying known biological chassis to enhance production using sustainable, renewable inputs. Here, we take the former approach and present the first description of PHB production by two prosthecate photosynthetic purple non-sulfur bacteria (PNSB), Rhodomicrobium vannielii and Rhodomicrobium udaipurense. We show that both species produce PHB across photoheterotrophic, photoautotrophic, photoferrotrophic, and photoelectrotrophic growth conditions. Both species show the greatest PHB titers during photoheterotrophic growth on butyrate with dinitrogen gas as a nitrogen source (up to 44.08 mg/L), while photoelectrotrophic growth demonstrated the lowest titers (up to 0.13 mg/L). These titers are both greater (photoheterotrophy) and less (photoelectrotrophy) than those observed previously in a related PNSB, Rhodopseudomonas palustris TIE-1. On the other hand, we observe the highest electron yields during photoautotrophic growth with hydrogen gas or ferrous iron electron donors, and these electron yields were generally greater than those observed previously in TIE-1. These data suggest that non model organisms like Rhodomicrobium should be explored for sustainable PHB production and highlights utility in exploring novel biological chassis.

Performance of production of polyhydroxyalkanoates from food waste fermentation with Rhodopseudomonas palustris

The use of waste as a carbon source can significantly reduce the cost of production of Polyhydroxyalkanoates (PHAs). In this study, an acidified hydrolysate solution derived from food waste (FW) was used as a carbon source for the synthesis of PHAs by Rhodopseudomonas palustris (R. palustris) and optimized the process parameters. The results showed that the PHAs yield reached 48.62% under optimal conditions (an incubation time of 30 days, volatile fatty acids (VFAs) in substrate concentration of 2202.21 mg⋅L^-1, an initial pH of 8.0, and inoculum concentration of 15%). The fraction of VFAs affects the composition of PHAs, R. palustris first uses VFAs with an even number of carbons to synthesize poly(3-hydroxybutyrate)(3HB), and later uses VFAs with an odd number of carbons to synthesize poly-3-hydroxyvalerate (3HV). Pathways for the synthesis of PHAs by R. palustris were inferred. R. palustris is a strain with the potential to synthesize PHAs.

Influences of specific surfactant structures on biohydrogen production from oily wastewater in batch and continuous anaerobic dark fermentation

Residual oil in palm oil mill effluent (POME) poses difficulties in its treatment chain. Non-ionic surfactants containing different hydrophobic tail structures and their optimal concentrations were evaluated for effectiveness in biohydrogen production. By adding the surfactants at their critical micelle concentration in synthetic oily wastewater, the maximal H₂ yield was increased by 2.2 and 3.5 times for Triton X-100 and Tergitol 15-S-9, respectively, compared to the control. Using real POME, the supplemental Tergitol 15-S-9 resulted in a 56.4 % improvement in H₂ production. For continuous digestion studies, pure POME and Tergitol 15-S-9 supplemented POME (sPOME) were fed to thermophilic anaerobic sequencing batch reactors (ASBRs) under hydraulic retention time (HRT) of 32-12.5 days. Optimally at HRT 19 days, H₂ content in the biogas from sPOME-fed ASBR was noticeably higher, which gave a superior yield of 203.4 mLH₂/gCOD_removed (+15 %).

Mathematical modeling of metal recovery from E-waste using a dark-fermentation-leaching process

In this work, an original mathematical model for metals leaching from electronic waste in a dark fermentation process is proposed. The kinetic model consists of a system of non-linear ordinary differential equations, accounting for the main biological, chemical, and physical processes occurring in the fermentation of soluble biodegradable substrates and in the dissolution process of metals. Ad-hoc experimental activities were carried out for model calibration purposes, and all experimental data were derived from specific lab-scale tests. The calibration was achieved by varying kinetic and stoichiometric parameters to match the simulation results to experimental data. Cumulative hydrogen production, glucose, organic acids, and leached metal concentrations were obtained from analytical procedures and used for the calibration. The results confirmed the high accuracy of the model in describing biohydrogen production, organic acids accumulation, and metals leaching during the biological degradation process. Thus, the mathematical model represents a useful and reliable tool for the design of strategies for valuable metals recovery from waste or mineral materials. Moreover, further numerical simulations were carried out to analyze the interactions between the fermentation and the leaching processes and to maximize the efficiency of metals recovery due to the fermentation by-products.

Research and economic perspectives on an integrated biorefinery approach for the simultaneous production of polyhydroxyalkanoates and biohydrogen

Alarming environmental impacts have been resulted across the globe due to the recovery and consumption of fossil fuels. The elevated global carbon footprint has paved the way to an alternative to combat the prevalent pollution. On the other hand, the fossil-based plastics produced from the byproducts of petroleum remain intact in the environment leading to pollution. Fossil abated bioproducts are in high demand due to the increase in pollution. This call to utilize feedstock for simultaneous production of biologically useful products through carbon capture utilisation where the leftover carbon-rich substrate is converted into usable chemicals like bioplastics, methanol, urea and various other industrially essential components. The present review extensively focuses on the research and economic perspectives of an integrated biorefinery and addresses technical breaches, bottlenecks, and efficient strategies for the simultaneous production of biohydrogen and polyhydroxyalkanoates.

Carbon catabolite repression occurrence in photo fermentation of ethanol-rich substrates

The paper investigates the phenomenon of Carbon Catabolite Repression occurring during photo fermentation of ethanol-rich effluents, which usually contain ethanol as main carbon source, and glycerol as secondary one. The study was conducted using mixed phototrophic cultures, adopting, as substrate, the effluent produced by the alcoholic fermentation of sugar cane bagasse. In order to elucidate the phenomenon, experimental tests were carried out using two different ethanol to glycerol ratios. Results were compared with those resulting from pure ethanol and glycerol conversion. According to the obtained data, as a result of Carbon Catabolite Repression occurrence, the presence of glycerol negatively affects hydrogen production. Indeed, part of the ethanol source is converted to biomass and polyhydroxybutyrate rather than to hydrogen. In more details, the presence of glycerol determines a drop of the hydrogen production, which goes from 12 % to 32 %, according to the ethanol/glycerol ratio, compared to the production obtained from fermentation of ethanol alone. Therefore, to promote the hydrogen production, it is advisable to apply strategies to produce low glycerol concentrations in the ethanol production stage.

Recent approaches for enhanced production of microbial polyhydroxybutyrate: Preparation of biocomposites and applications

In modern decades, an increase in environmental awareness has attracted the keen interest of researchers to investigate eco-sustainable, recyclable materials to minimize reliance on petroleum-based polymeric compounds. Poly (3-hydroxybutyrate) is amorphous, linear, and biodegradable bacterial polyesters that belong to the polyhydroxyalkanoates family with enormous applications in many fields. The present review provides comprehensive information on polyhydroxybutyrate production from different biomass feedstock. Various studies on PHB production by genetically engineered bacterial cells and optimization of parameters have been discussed. Recent technological innovation in processing polyhydroxybutyrate-based biocomposite through the different process has also been examined. Besides this, the potential applications of the derived competent biocomposites in the other fields have been depicted.

Polyhydroxyalkanoates from organic waste streams using purple non-sulfur bacteria

Many microorganisms can produce intracellular and extracellular biopolymers, such as polyhydroxyalkanoates (PHA). Despite PHA's benefits, their widespread at the industrial level has not occurred due mainly to high production costs. PHA production under a biorefinery scheme is proposed to improve its economic viability. In this context, purple non-sulfur bacteria (PNSB) are ideal candidates to produce PHA and other substances of economic interest. This review describes the PHA production by PNSB under different metabolic pathways, by using a wide range of wastes and under diverse operational conditions such as aerobic and anaerobic metabolism, irradiance level, light or dark conditions. Some strategies, such as controlling the feed regime, biofilm reactors, and open photobioreactors in outdoor conditions, were identified from the literature review as the approach needed to improve the process's economic viability when using mixed cultures of PNSB and wastes as substrates.

A comprehensive review of mathematical models of photo fermentation

This work aims at analyzing and comparing the different modeling approaches used to date to simulate, design and control photo fermentation processes for hydrogen production and/or wastewater treatment. The study is directed to researchers who approach the problem of photo fermentation mathematical modeling. It is a useful tool to address future research in this specific field in order to overcome the difficulty of modeling a complex, not totally elucidate process. We report a preliminary identification of the environmental and biological parameters, included in the models, which affect photo fermentation. Based on model features, we distinguish three different approaches, i.e. kinetic, parametric and non-ideal reactors. We explore the characteristics of each approach, reporting and comparing the obtained results and underlining the differences between models, together with the advantages and the limitations of each of them. The analysis of the approaches indicates that Kinetic models are useful to describe the process from a biochemical point of view, without considering bio-reactor hydrodynamics and the spatial variations that Parametric Models can be utilized to study the influence and the interactions between the operational conditions. They do not take into account the biochemical process mechanism and the influence of reactor hydrodynamics. Quite the opposite, non-ideal reactors models focus on the reactor configuration. Otherwise, the biochemical description of purple non-sulfur bacteria activities is usually simplified. This review indicates that there still is a lack of models that fully describe photo fermentation processes.

The transition of Rhodobacter sphaeroides into a microbial cell factory

Microbial cell factories are the workhorses of industrial biotechnology and improving their performances can significantly optimize industrial bioprocesses. Microbial strain engineering is often employed for increasing the competitiveness of bio‐based product synthesis over more classical petroleum‐based synthesis. Recently, efforts for strain optimization have been standardized within the iterative concept of “design‐build‐test‐learn” (DBTL). This approach has been successfully employed for the improvement of traditional cell factories like Escherichia coli and Saccharomyces cerevisiae. Within the past decade, several new‐to‐industry microorganisms have been investigated as novel cell factories, including the versatile α‐proteobacterium Rhodobacter sphaeroides. Despite its history as a laboratory strain for fundamental studies, there is a growing interest in this bacterium for its ability to synthesize relevant compounds for the bioeconomy, such as isoprenoids, poly‐β‐hydroxybutyrate, and hydrogen. In this study, we reflect on the reasons for establishing R. sphaeroides as a cell factory from the perspective of the DBTL concept. Moreover, we discuss current and future opportunities for extending the use of this microorganism for the bio‐based economy. We believe that applying the DBTL pipeline for R. sphaeroides will further strengthen its relevance as a microbial cell factory. Moreover, the proposed use of strain engineering via the DBTL approach may be extended to other microorganisms that have not been critically investigated yet for industrial applications.

Biohydrogen and poly-β-hydroxybutyrate production by winery wastewater photofermentation: Effect of substrate concentration and nitrogen source

The applicability and convenience of biohydrogen and poly-β-hydroxybutyrate production through single-stage photofermentation of winery wastewater is demonstrated in the present study. Experiments are conducted using a purple non-sulfur bacteria mixed consortium, subject to variable nutrient conditions, to analyze the effect of initial chemical oxygen demand and the available nitrogen source on the metabolic response. Results show that winery wastewater is a promising substrate for photofermentation processes, despite the presence of inhibiting compounds such as phenolics. Nonetheless, the initial chemical oxygen demand must be carefully controlled to maximize hydrogen production. Up to 468 mL L^-1 of hydrogen and 203 mg L^-1 of poly-β-hydroxybutyrate can be produced starting from an initial chemical oxygen demand of 1500 mg L^-1. The used nitrogen source may direct substrate transformation through different metabolic pathways. Interestingly, the maximum production of both hydrogen and poly-β-hydroxybutyrate occurred when glutamate was used as the nitrogen source.

Molecular biohydrogen production by dark and photo fermentation from wastes containing starch: recent advancement and future perspective

Changing lifestyle is increasing the energy demand. Fossil fuel is unable to deliver such huge energy. Clean energy from renewable source can solve this problem. Hydrogen is a clean and energy-efficient fuel and used for electricity generation by fuel cells or can be used in combustion engine. Easy availability of starch wastes from different industrial food processing wastes makes it a potential source for hydrogen (H₂) generation. Among various processes such as steam reforming, electrolysis, biophotolysis of water and anaerobic fermentation, anaerobic fermentation technique is environmentally friendly and requires less external energy, making it a preferred process for H₂ generation. Dark fermentation process can use wide range of substrates including agricultural and industrial starchy waste with low level of undesirable compounds. Application of both anaerobic dark and photofermentation can improve H₂ yield and production rate. H₂ production from wastes containing starch serves dual benefit of waste reduction and energy generation. As starch is a polymer and all hydrogen-producing bacteria cannot produce amylase to hydrolyze it, a pretreatment step is required to convert starch into glucose and maltose. In this present review paper, we have summarized: (i) potential of various types of starch-containing wastes as feedstock, (ii) various fermentation techniques, (iii) optimization of external process parameter, (iv) application of bioreactor and simulation in fermentation technique and (v) advancement in H₂ production from starchy wastes.

Purple phototrophic bacteria for resource recovery: Challenges and opportunities

Sustainable development is driving a rapid focus shift in the wastewater and organic waste treatment sectors, from a "removal and disposal" approach towards the recovery and reuse of water, energy and materials (e.g. carbon or nutrients). Purple phototrophic bacteria (PPB) are receiving increasing attention due to their capability of growing photoheterotrophically under anaerobic conditions. Using light as energy source, PPB can simultaneously assimilate carbon and nutrients at high efficiencies (with biomass yields close to unity (1 g COD_biomass·g COD_removed^-1)), facilitating the maximum recovery of these resources as different value-added products. The effective use of infrared light enables selective PPB enrichment in non-sterile conditions, without competition with other phototrophs such as microalgae if ultraviolet-visible wavelengths are filtered. This review reunites results systematically gathered from over 177 scientific articles, aiming at producing generalized conclusions. The most critical aspects of PPB-based production and valorisation processes are addressed, including: (i) the identification of the main challenges and potentials of different growth strategies, (ii) a critical analysis of the production of value-added compounds, (iii) a comparison of the different value-added products, (iv) insights into the general challenges and opportunities and (v) recommendations for future research and development towards practical implementation. To date, most of the work has not been executed under real-life conditions, relevant for full-scale application. With the savings in wastewater discharge due to removal of organics, nitrogen and phosphorus as an important economic driver, priorities must go to using PPB-enriched cultures and real waste matrices. The costs associated with artificial illumination, followed by centrifugal harvesting/dewatering and drying, are estimated to be 1.9_, 0.3-2.2 and 0.1-0.3 $·kg_{dry biomass}^-1. At present, these costs are likely to exceed revenues. Future research efforts must be carried out outdoors, using sunlight as energy source. The growth of bulk biomass on relatively clean wastewater streams (e.g. from food processing) and its utilization as a protein-rich feed (e.g. to replace fishmeal, 1.5-2.0 $·kg^-1) appears as a promising valorisation route.

Grid columnar flat panel photobioreactor with immobilized photosynthetic bacteria for continuous photofermentative hydrogen production

A biophotoreactor with a transparent glass flat panel with polymethyl methacrylate (PMMA) grid columnar for enhanced biofilm growth with Rhodopseudomonas palustris GCA009 was developed and tested at 590 nm incident light. Continuous photofermentative hydrogen production from glucose was tested using this novel reactor. At light intensity of 210 W/m², feed substrate concentration of 56.0 mmol/L, and crossflow velocity of 1.68 × 10^-6 m/s, a maximum hydrogen production rate of 32.6 mmol/L-d (3.56 mmol/m²-h), hydrogen yield of 1.15 mol H₂/mol glucose and light conversion efficiency of 5.34% can be achieved. Since the revised grid columnar effectively enlarged the surface area of reactor and enhanced cell attachment, the present reactor design led to higher hydrogen production rates than literature works.

Repeated-Batch Fermentation of Cheese Whey for Semi-Continuous Lactic Acid Production Using Mixed Cultures at Uncontrolled pH

The paper investigates mixed-culture lactate (LA) fermentation of cheese whey (CW) in order to verify the possibility of using waste materials as feedstock to produce a product with high economic potential. The fermentation performance of two reactors operating in repeated-batch mode under uncontrolled pH conditions and various hydraulic retention time and feeding conditions was evaluated in terms of LA production. Five experimental phases were conducted. The hydraulic retention time (HRT) was varied from 1 to 4 days to verify its effect on the process performance. The best results, corresponding to the maximum LA concentration (20.1 g LA/L) and the maximum LA yield (0.37 g chemical oxygen demand (COD)(LA)/g COD(CW)), were reached by feeding the reactors with cheese whey alone and setting the HRT to 2 days. The maximum productivity of lactic acid (10.6 g LA/L/day) was observed when the HRT was decreased to 1 day.

Disruption of poly (3-hydroxyalkanoate) depolymerase gene and overexpression of three poly (3-hydroxybutyrate) biosynthetic genes improve poly (3-hydroxybutyrate) production from nitrogen rich medium by Rhodobacter sphaeroides

BACKGROUND

Due to various environmental problems, biodegradable polymers such as poly (3-hydroxybutyrate) (PHB) have gained much attention in recent years. Purple non-sulfur (PNS) bacteria have various attractive characteristics useful for environmentally harmless PHB production. However, production of PHB by PNS bacteria using genetic engineering has never been reported. This study is the first report of a genetically engineered PNS bacterial strain with a high PHB production.

RESULTS

We constructed a poly (3-hydroxyalkanoate) depolymerase (phaZ) gene-disrupted Rhodobacter sphaeroides HJ strain. This R. sphaeroides HJΔphaZ (pLP-1.2) strain showed about 2.9-fold higher volumetric PHB production than that of the parent HJ (pLP-1.2) strain after 5 days of culture. The HJΔphaZ strain was further improved for PHB production by constructing strains overexpressing each of the eight genes including those newly found and annotated as PHB biosynthesis genes in the KEGG GENES Database. Among these constructed strains, all of gene products exhibited annotated enzyme activities in the recombinant strain cells, and HJΔphaZ (phaA3), HJΔphaZ (phaB2), and HJΔphaZ (phaC1) showed about 1.1-, 1.1-, and 1.2-fold higher volumetric PHB production than that of the parent HJΔphaZ (pLP-1.2) strain. Furthermore, we constructed a strain that simultaneously overexpresses all three phaA3, phaB2, and phaC1 genes; this HJΔphaZ (phaA3/phaB2/phaC1) strain showed about 1.7- to 3.9-fold higher volumetric PHB production (without ammonium sulfate; 1.88 ± 0.08 g l^-1 and with 100 mM ammonium sulfate; 0.99 ± 0.05 g l^-1) than those of the parent HJ (pLP-1.2) strain grown under nitrogen limited and rich conditions, respectively.

CONCLUSION

In this study, we identified eight different genes involved in PHB biosynthesis in the genome of R. sphaeroides 2.4.1, and revealed that their overexpression increased PHB accumulation in an R. sphaeroides HJ strain. In addition, we demonstrated the effectiveness of a phaZ disruption for high PHB accumulation, especially under nitrogen rich conditions. Furthermore, we showed that PNS bacteria may have some unidentified genes involved in poly (3-hydroxyalkanoates) (PHA) biosynthesis. Our findings could lead to further improvement of environmentally harmless PHA production techniques using PNS bacteria.

Biohydrogen production from food waste: Current status, limitations, and future perspectives

Among the various biological routes for H₂ production, dark fermentation is considered the most practically applicable owing to its capability to degrade organic wastes and high H₂ production rate. Food waste (FW) has high carbohydrate content and easily hydrolysable in nature, exhibiting higher H₂ production potential than that of other organic wastes. In this review article, first, the current status of H₂ production from FW by dark fermentation and the strategies applied for enhanced performance are briefly summarized. Then, the technical and economic limitations of dark fermentation of FW are thoroughly discussed. Economic assessment revealed that the economic feasibility of H₂ production from FW by dark fermentation is questionable. Current efforts to further increase H₂ yield and waste removal efficiency are also introduced. Finally, future perspectives along with possible routes converting dark fermentation effluent to valuable fuels and chemicals are discussed.

Integrated systems for biopolymers and bioenergy production from organic waste and by-products: a review of microbial processes

Recently, issues concerning the sustainable and harmless disposal of organic solid waste have generated interest in microbial biotechnologies aimed at converting waste materials into bioenergy and biomaterials, thus contributing to a reduction in economic dependence on fossil fuels. To valorize biomass, waste materials derived from agriculture, food processing factories, and municipal organic waste can be used to produce biopolymers, such as biohydrogen and biogas, through different microbial processes. In fact, different bacterial strains can synthesize biopolymers to convert waste materials into valuable intracellular (e.g., polyhydroxyalkanoates) and extracellular (e.g., exopolysaccharides) bioproducts, which are useful for biochemical production. In particular, large numbers of bacteria, including Alcaligenes eutrophus, Alcaligenes latus, Azotobacter vinelandii, Azotobacter chroococcum, Azotobacter beijerincki, methylotrophs, Pseudomonas spp., Bacillus spp., Rhizobium spp., Nocardia spp., and recombinant Escherichia coli, have been successfully used to produce polyhydroxyalkanoates on an industrial scale from different types of organic by-products. Therefore, the development of high-performance microbial strains and the use of by-products and waste as substrates could reasonably make the production costs of biodegradable polymers comparable to those required by petrochemical-derived plastics and promote their use. Many studies have reported use of the same organic substrates as alternative energy sources to produce biogas and biohydrogen through anaerobic digestion as well as dark and photofermentation processes under anaerobic conditions. Therefore, concurrently obtaining bioenergy and biopolymers at a reasonable cost through an integrated system is becoming feasible using by-products and waste as organic carbon sources. An overview of the suitable substrates and microbial strains used in low-cost polyhydroxyalkanoates for biohydrogen and biogas production is given. The possibility of creating a unique integrated system is discussed because it represents a new approach for simultaneously producing energy and biopolymers for the plastic industry using by-products and waste as organic carbon sources.