Synthesis and optimization of bio-based polyhydroxyalkanoates (PHAs) from waste agro-industrial residues via integrated fermentation and catalytic depolymerization for sustainable bioplastics production

Project Abstract

This study presents an integrated bioprocess strategy to convert waste agro-industrial residues into high-value polyhydroxyalkanoates (PHAs), addressing the critical need for sustainable bioplastics and circular economy practices. The work combines optimized microbial synthesis with catalytic depolymerization to maximize PHA yield, tailor polymer composition, and enable efficient material recovery from heterogeneous feedstocks. First, acid- or enzyme-pretreated residues rich in carbohydrates and lipids are evaluated to identify the most suitable feedstock blends for microbial growth and PHA accumulation. A systematic screening of indigenous and engineered microbial strains, including Pseudomonas, Cupriavidus, and Halomonas species, is conducted under varying carbon-to-nitrogen ratios, dissolved oxygen levels, and nutrient pulses to induce high intracellular PHA contents while maintaining robust growth. Kinetic models are developed to elucidate biomass formation, substrate uptake, and PHA accumulation dynamics, guiding fermentation parameter optimization such as pH control, feeding strategies, and reactor configuration (batch, fed-batch, and continuous modes). To address polymer diversity and agree with downstream valorization goals, the study explores copolymerization potential by modulating feedstock composition and precursor availability to produce polyhydroxybutyrate-co-hydroxyvalerate (PHB-HV) and related copolymers with desirable mechanical properties. A novel downstream integration step employs catalytic depolymerization of accumulated PHAs under catalytic hydrolysis and cracking conditions to recover monomeric or oligomeric building blocks, enabling closed-loop recycling and compatibility with existing chemical recycling streams. The catalytic stage is optimized via screening of heterogeneous catalysts, such as zeolites and metal-supported catalysts, under various temperatures, pressures, and solvent systems to minimize energy input while preserving product quality. Recovered monomers are characterized by GC-MS and NMR to assess purity and potential for repolymerization, enabling feedback into the fermentation design to improve overall material yield. Material properties of the produced PHAs, including molecular weight distribution, crystallinity, thermal transitions (melting and glass transition temperatures), and mechanical performance (tensile strength, elongation at break, and modulus), are comprehensively analyzed to align with target applications in packaging, agriculture, and specialty materials. Life cycle assessment and tech-economic analyses quantify environmental benefits and economic viability, comparing baseline petrochemical plastics with the integrated bioprocess route. The study also investigates process intensification strategies, such as one-pot fermentation and in-line depolymerization integration, to reduce capital and operating costs. Finally, the research identifies critical bottlenecks—feedstock variability, microbial tolerance to inhibitors, and catalyst deactivation—along with actionable mitigation strategies to scale the technology from laboratory to pilot plant stages. Overall, the project advances a holistically sustainable pathway from waste to value-added bioplastics, bridging biological synthesis with catalytic valorization to realize circular bioeconomy objectives.

Project Overview

What This Project Is About

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A straightforward study of making biodegradable plastics (PHAs) from waste materials from farming and food processing. It combines growing microbes to collect PHAs and breaking down the plastics into useful monomers, with the goal of using less waste and creating sustainable plastics.

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The Problem It Addresses

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Waste from farms and food industries often ends up unused or polluting. Traditional plastics rely on non-renewable resources and persist in the environment. This project seeks to turn waste into a renewable plastic alternative, reducing waste and reliance on fossil fuels.

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Objectives of the Project

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1. Identify suitable waste streams that can feed microbial growth.
2. Develop a simple, low-cost fermentation process to produce PHAs.
3. Optimize conditions to maximize PHA yield and quality.
4. Implement a catalytic method to break down PHAs into recyclable building blocks.
5. Assess the environmental and economic viability of the process.

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What You Will Do Step by Step

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1) Survey local waste sources and preprocess them for use. 2) Cultivate microbes under controlled conditions to accumulate PHAs. 3) Extract and quantify PHAs to measure yield. 4) Test a catalytic depolymerization step to recover useful chemicals. 5) Compare different waste inputs and process conditions. 6) Analyze energy use and costs to estimate practicality. 7) Compile results and discuss sustainability implications.

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Expected Outcome

Demonstration of a feasible pathway to produce PHAs from waste with improved sustainability metrics, including a basic process flow, yield data, and a preliminary assessment of environmental and cost benefits. This could guide future scale-up and policy discussions.