Biopolymers are revolutionizing the materials landscape, driven by a growing demand for sustainable alternatives to traditional petroleum-based materials. Sourced from biological origins, these polymers are not only environment friendly but also present exciting solutions in healthcare, packaging, biosensors, high performance, and durable materials as alternatives to crude oil-based products. Recently, biopolymers derived from plants, such as lignin and cellulose, alongside those produced by bacteria, like polyhydroxyalkanoates (PHAs), have captured the spotlight, drawing significant interest for their industrial and eco-friendly applications. The growing interest in biopolymers stems from their potential as sustainable, renewable materials across diverse applications. This review provides an in-depth analysis of the current advancements in plant-based and bacterial biopolymers, covering aspects of bioproduction, downstream processing, and their integration into high-performance next-generation materials. Additionally, we delve into the technical challenges of cost-effectiveness, processing, and scalability, which are critical barriers to widespread adoption. By highlighting these issues, this review aims to equip researchers in the bio-based domain with a comprehensive understanding of how plant-based and bacterial biopolymers can serve as viable alternatives to petroleum-derived materials. Ultimately, we envision a transformative shift from a linear, fossil fuel-based economy to a circular, bio-based economy, fostering more sustainable and environmentally conscious material solutions using novel biopolymers aligning with the framework of the United Nations Sustainable Development Goals (SDGs), including clean water and sanitation (SDG 6), industry, innovation, and infrastructure (SDG 9), affordable and clean energy (SDG 7), sustainable cities and communities (SDG 11), responsible production and consumption (SDG 12), and climate action (SDG 13).

The production of polyhydroxyalkanoate (PHA) using CO2 through hydrogen-oxidizing bacteria under safe, non-explosive conditions is making impressive strides. The present study aimed to evaluate and demonstrate the growth and productivity of PHA by Cupriavidus sp. CY-1 under different non-explosive conditions, thereby providing critical data for practical applications. The experimental results highlighted the efficiency of the CY-1 strain in PHA biosynthesis, achieving a production rate of 11.87 g L−1, which corresponds to a 90.6% yield when fermenting a gaseous substrate composed of H2 (70%), O2 (20%), and CO2 (10%). The study also examined PHA production under different non-explosive conditions, including H2 concentrations of 3.8% (v/v) and O2 at 6.5% (v/v). Furthermore, the impact of CO (30% and higher) was assessed, revealing a detrimental effect on growth and PHA production. Notably, the addition of Tween 80 significantly enhanced PHA productivity. The effective utilization of CO2 has confirmed poly[(R)-3-hydroxybutyrate] (PHB) as a valuable derived form of PHA. By implementing a two-step treatment with valeric acid, we successfully produced P(3HB-co-3HV) (PHBV) at a concentration of 1.47 g L−1. This achievement highlights the potential to enhance PHA production through innovative strategies. Furthermore, the examination of phaC gene expression levels has facilitated accurate predictions of PHA productivity. The use of CO2 from trichloroethylene (TCE) biodegradation faced concentration-related challenges; however, the higher CO2 levels achieved from phenol biodegradation, at 1200 mg L−1, indicate substantial potential for efficient PHA production.

The inert nature, durability, low cost, and wide applicability of plastics have made this material indispensable in our lives. This dependency has resulted in a growing number of plastic items, of which a substantial part is disposed in landfills or dumped in the environment, thereby affecting terrestrial and aquatic ecosystems. Among plastic materials, polyolefins are the most abundant and are impervious to biodegradation, owing to the presence of strong C C and C H bonds. Nevertheless, naturally occurring biodegradation of polyolefins, albeit limited, has been reported. This observation has sparked research on microbial polyolefin degradation. More efficient and targeted versions of this process could be developed also in the laboratory by designing synthetic microbial consortia with engineered enzymes. In this review, we discuss strategies for the development of such microbial consortia and identification of novel polyolefin-degrading microorganisms, as well as the engineering of polyethylene-oxidizing enzymes with greater catalytic efficacy. Finally, different techniques for the design of synthetic microbial consortia capable of successful polyolefin bioremediation will be outlined.

Advancements in biological wastewater treatment with sustainable and circularity approaches have a wide scope of application. Biological wastewater treatment is widely used to remove/recover organic pollutants and nutrients from a diverse wastewater spectrum. However, conventional biological processes face challenges, such as low efficiency, high energy consumption, and the generation of excess sludge. To overcome these limitations, integrated strategies that combine biological treatment with other physical, chemical, or biological methods have been developed and applied in recent years. This review emphasizes the recent advances in integrated strategies for biological wastewater treatment, focusing on their mechanisms, benefits, challenges, and prospects. The review also discusses the potential applications of integrated strategies for diverse wastewater treatment towards green energy and resource recovery, along with low-carbon fuel production. Biological treatment methods, viz., bioremediation, electro-coagulation, electro-flocculation, electro-Fenton, advanced oxidation, electro-oxidation, bioelectrochemical systems, and photo-remediation, are summarized with respect to non-genetically modified metabolic reactions. Different conducting materials (CMs) play a significant role in mass/charge transfer metabolic processes and aid in enhancing fermentation rates. Carbon, metal, and nano-based CMs hybridization in different processes provide favorable conditions to the fermentative biocatalyst and trigger their activity towards overcoming the limitations of the conventional process. The emerging field of nanotechnology provides novel additional opportunities to surmount the constraints of conventional process for enhanced waste remediation and resource valorization. Holistically, integrated strategies are promising alternatives for improving the efficiency and effectiveness of biological wastewater treatment while also contributing to the circular economy and environmental protection.

Anaerobic digestion (AD) technology can potentially address the gap between energy demand and supply playing a crucial role in the production of sustainable energy from utilization of biogenic waste materials as feedstock. The biogas production from anaerobic digestion is primarily influenced by the chemical compositions and biodegradability of the feedstock. Organosolv-steam explosion offers a constructive approach as a promising pretreatment method for the fractionation of lignocellulosic biomasses delivering high cellulose content.This study showed how synergetic co-digestion serves to overcome the challenges of mono-digestion's low efficiency. Particularly, the study evaluated the digestibility of organosolv-steam pretreated wheat straw (WSOSOL) in mono as well as co-digesting substrate with cheese whey (CW) and brewery spent grains (BSG). The highest methane yield was attained with co-digestion of WSOSOL + CW (338 mL/gVS) representing an enhanced biogas output of 1–1.15 times greater than its mono digestion. An ammonium production was favored under co-digestion strategy accounting for 921 mg/L from WSOSOL + BSG. Metagenomic study was conducted to determine the predominant bacteria and archaea, as well as its variations in their populations and their functional contributions during the AD process. The Firmicutes have been identified as playing a significant role in the hydrolysis process and the initial stages of AD. An enrichment of the most prevalent archaea genera enriched were Methanobacterium, Methanothrix, and Methanosarsina. Reactors digesting simpler substrate CW followed the acetoclastic, while digesting more complex substrates like BSG and WSOSOL followed the hydrogenotrophic pathway for biomethane production. To regulate the process for an enhanced AD process to maximize CH4, a comprehensive understanding of microbial communities is beneficial.

Carbonic anhydrase (CA) is considered an efficient enzyme for fermentation systems exhibiting a wide range of applications, enhancing both the efficacy and output of the fermentation process. The present study aimed to evaluate the production of acidogenic biohydrogen (bioH2) and volatile fatty acids (VFA) using forest residues as a renewable feedstock. Specifically, the study examined the integration of CA derived from Desulfovibrio vulgaris into the acidogenic fermentation (AF) process. The experimental procedure involved a cascade design conducted in two distinct phases. In phase I, the concentration of CA in the AF was systematically optimized, with glucose serving as the substrate. In phase II, three influential parameters (pH, pressurization with in situ generated gas and organic load) were evaluated on AF in association with optimized CA concentration from phase I. In phase II, glucose was replaced with renewable sugars obtained from forest residues after steam explosion pretreatment followed by enzymatic saccharification. The incorporation of CA in AF was found to be beneficial in steering acidogenic metabolites. Alkaline conditions (pH 8) promoted bioH2, yielding 210.9 mLH2 gCOD−1, while introducing CA further increased output to 266.6 mLH2 gCOD−1. This enzymatic intervention improved the production of bioH2 conversion efficiency (HCE) from 45.3% to 57.2%. Pressurizing the system accelerated VFA production with complete utilization of in situ produced H2 + CO2 compared to non-pressurized systems. Particularly, caproic acid production was improved under pressurized conditions which was accomplished by the targeted enrichment of chain-elongating bacteria in the mixed culture. The microbial diversity analysis showed the dominance of Firmicutes suggesting a significant degree of adaptation to the experimental contexts, leading to an enhanced production of acidogenic metabolites.

Three tubular bioreactors with a varied substrate flow rate of (2 mL/min, 5 mL/min, and 8 mL/min) were examined for 75 days. At 8 mL/min flow rate, the biohydrogen evolution was higher (3.88 mL H2/h), while its conversion efficiency was lower compared to 5 and 2 mL/min flow rate. The formation of volatile fatty acids and ammonium was also influenced by substrate flow rates. The volatile fatty acids production was slightly higher at 2 mL/min (12.74 ± 2.42 gCOD/L) and 5 mL/min (18.09 ± 2.01 gCOD/L) while, decreasing at 8 mL/min (11.85 ± 0.78 gCOD/L). Substrate flow rate significantly affected the pattern and composition of volatile fatty acids showing higher acetic acid, butyric and propionic acid production of 4.72 ± 1.46 gCOD/L (2 mL/min) 10.41 ± 0.91 gCOD/L (5 mL/min) and 1.78 ± 0.13 gCOD/L (5 mL/min). Continuous substrate input maintained the pH in the reactor due to replacement with fresh substrate, thereby controlling feedback inhibition and boosting metabolite production. Hydrogen-producing Firmicutes on the biofilm confirmed the pivotal role of the microbial community's significant contribution to converting waste to bioenergy. Overall, the present results support the use of a continuous operation mode for large-scale biohydrogen production. However, to ensure the efficacy of the system using waste or wastewater, low substrate flow rates are recommended.

The world’s rising energy needs, and the depletion of fossil resources demand a shift from fossil-based feedstocks to organic waste to develop a competitive, resource-efficient, and low-carbon sustainable economy in the long run. It is well known that the production of fuels and chemicals via chemical routes is advantageous because it is a well-established technology with low production costs. However, the use of toxic/environmentally harmful and expensive catalysts generates toxic intermediates, making the process unsustainable. Alternatively, utilization of renewable resources for bioprocessing with a multi-product approach that aligns novel integration improves resource utilization and contributes to the “green economy”. The present review discusses organic waste bioprocessing through the anaerobic fermentation (AF) process to produce biohydrogen (H2), biomethane (CH4), volatile fatty acids (VFAs) and medium chain fatty acids (MCFA). Furthermore, the roles of photosynthetic bacteria and microalgae for biofuel production are discussed. In addition, a roadmap to create a fermentative biorefinery approach in the framework of an AF-integrated bioprocessing format is deliberated, along with limitations and future scope. This novel bioprocessing approach significantly contributes to promoting the circular bioeconomy by launching complete carbon turnover practices in accordance with sustainable development goals.

Globally, food waste (FW) is found to be one of the major constituents creating several hurdles in waste management. On the other hand, the energy crisis is increasing and the limited fossil fuel resources available are not sufficient for energy needed for emerging population. In this context, biohydrogen production approach through valorization of FW is emerging as one of the sustainable and eco-friendly options. The present review explores FW sources, characteristics, and dark fermentative production of hydrogen along with its efficiency. FW are highly biodegradable and rich in carbohydrates which can be efficiently utilized by anaerobic bacteria. Based on the composition of FW, several pretreatment methods can be adapted to improve the bioavailability of the organics. By-products of dark fermentation are organic acids that can be integrated with several secondary bioprocesses. The versatility of secondary products is ranging from energy generation to biochemicals production. Integrated approaches facilitate in enhanced energy harvesting along with extended wastewater treatment. The review also discusses various parameters like pH, temperature, hydraulic retention time and nutrient supplementation to enhance the process efficiency of biohydrogen production. The application of solid-state fermentation (SSF) in dark fermentation improves the process efficiency. Dark fermentation as the key process for valorization and additional energy generating process can make FW the most suitable substrate for circular economy and waste based biorefinery.