Trends and challenges in the valorization of kitchen waste to polyhydroxyalkanoates.

Kitchen waste (KW) is frequently available for free or with a negative cost due to its huge production. It contains a large proportion of organic substances, especially fermentable sugars, which can be used for bioplastic (polyhydroxyalkanoates or PHA) synthesis. Nevertheless, due to the difficulties in processing, various pre-treatments of KW are being investigated to enhance the concentration of simple sugars released during its hydrolysis. The effective use of KW will help in minimizing the issues of its inappropriate disposal. However, the review on KW to bioplastic synthesis is rarely reported in the literature. Hence, this particular review provides a comprehensive summary of the updated research developments in KW valorization and its potency as a feedstock for PHAs synthesis. Additionally, the impacts of KW, its availability, the necessary pre-treatments for the biopolymerization process, as well as the prospects and challenges for industrially generating sustainable PHAs, are critically discussed.

Bioconversion of organic wastes into value-added products: A review.

Rapid urbanization has increased the demand for food, feed, and chemicals that have in turn augmented the use of fossil-based resources and generation of organic waste. Owning to the characteristics like high abundance, renewability, and ease of accessibility, valorization of organic wastes serves as a potential solution for waste management issues. Several industrial wastes, due to their organic and nutrient-rich composition, have been utilized as a resource for the production of value-added products such as biofuels, biopesticides, biohydrogen, enzymes, and bioplastics via microbial fermentation processes. The process consists of pre-treatment of the waste biomass, production of value-added product in reactors and downstream processing for product's recovery. The integration of new comprehensive technologies for organic waste utilization will also stimulate the transition towards a circular economy. Therefore, the feasibility and sustainability of the production of various value-added products from biowastes and byproduct streams will be discussed in the present review.

A review on production of polyhydroxyalkanoate (PHA) biopolyesters by thermophilic microbes using waste feedstocks.

Polyhydroxyalkanoates (PHAs) are produced by numerous microbes as a subcellular energy source. Despite of their diverse applications, exorbitant production cost limits their commercial synthesis. Apart from various cost determining factors such as cost-effective feedstocks or economic recovery methods, the use of appropriate bacteria holds the key to reduce the fermentation economics. Extremophiles, especially thermophilic PHA producers, could make the bioprocess economically viable by reducing the production cost in several aspects. Using variety of waste feedstocks as carbon substrates could open the way for the valorisation of industrial waste streams and cost-effective PHA production. Therefore, the article critically reviews the current knowledge of the synthesis of PHA polyesters in thermophilic conditions. Additionally, it summarises several studies on thermophilic PHA producing bacteria grown on various waste substrates. To conclude, the paper focuses on screening and recovery methods as well as technical challenges in thermophilic PHA production.

Concomitant production of value-added products with polyhydroxyalkanoate (PHA) synthesis: A review.

The concern over the damaging effects of petrochemical plastics has inspired innumerable researchers to synthesize green plastics. Polyhydroxyalkanoates (PHAs) are promising candidates as they are biodegradable and possess characteristics similar to conventional plastics. However, their large-scale production and market application still have a long way to go due to the high production cost associated. Approaches like using industrial wastes as substrates and developing green strategies for PHA extraction during downstream processing have been investigated to make the process more economical. Recently, PHA production cost was minimized by concomitant synthesis of other valuable bioproducts with PHA. Investigating these co-products and recovering them can also make the process circular bioeconomic. Therefore, the paper attempts to review the recent strategies for the simultaneous synthesis of value-added bioproducts with PHA together with the challenges and opportunities for their large-scale production and applications.

Food waste valorization: Energy production using novel integrated systems.

Management of food waste (FW) is a global challenge due to increasing population and economic activities. Presently, landfill and incineration are the keyways of FW management, while economical and environmental sustainability have been an issue. Therefore, the biological processes have been investigated for resource and energy recovery from FW. However, these biological approaches have certain drawbacks and cannot be a complete solution for FW management. Therefore, this review aims to offer a detailed and complete analysis of current available technologies to achieve environmental and economical sustainability. In this context, zero solid waste discharge for resource and energy recovery has been put into view. Corresponding to which several innovative technologies using integrated biological methods for resource and energy recovery from FW have been elucidated.

A review on recovery of proteins from industrial wastewaters with special emphasis on PHA production process: Sustainable circular bioeconomy process development.

The economy of the polyhydroxyalkanoate (PHA) production process could be supported by utilising the different by-products released simultaneously during its production. Among these, proteins are present in high concentrations in liquid stream which are released after the cell disruption along with PHA granules. These microbial proteins can be used as animal feed, adhesive material and in manufacturing of bioplastics. The recycling of the protein containing liquid stream also serves as a promising approach to maintain circular bioeconomy in the route. For this aim, it is important to obtain good yield and limit the drawbacks of protein recovery processes and associated costs. The review focuses on recycling of the liquid stream generated during acid/thermal-alkali treatment for PHA production that would close the gap in linear economy and attain circularity in the process. Examples to recover proteins from other industrial waste streams along with their applications have also been discussed.

Bioconversion of waste (water)/residues to bioplastics- A circular bioeconomy approach.

Research insight into the technical challenges of bioplastics production has revealed their confoundedness in their niche markets and struggles to enter the mainstream. There is an increasing problem of waste disposal and high cost of pure substrates in polyhydroxyalkanoates (PHA) production. This has led to the future need of upgrading the waste streams from different industries into the role of feedstocks for production of PHA. The review covers the latest developments in using wastes and surplus materials for PHA production. In addition to inexpensive carbon sources, efficient upstream and downstream processes and recycling of waste streams within the process are required to maintain the circularity in the entire process. A view on the link between circular bioeconomy and PHA production process covering the techno-economic, life cycle assessment and environmental aspects has also been provided. Furthermore, the future perspectives related to the topic have also been discussed.

Assessment of the Role of Wastewater Treatment Plant in Spread of Antibiotic Resistance and Bacterial Pathogens.

In current study, we performed a comparative study on bacterial load, total coliform counts and type of organisms present in pre- and post-treated wastewater samples from municipal wastewater treatment plant of Pune, India. In addition, we also studied the antibiotic resistance profiling and role of the selected treatment plant in spread of antibiotic resistance in the environment. Data showed that total 30 different bacterial species from 18-different genera were present in untreated wastewater while only 9 species from 6-different genera were present in post-treated effluent. Furthermore, pre-treated wastewater sample contains wide range of organisms with high levels of antibiotic resistance while bacterial load reduced drastically and pathogens were absent from post-treated effluent.