With the world shifting towards renewable and sustainable resources, polyhydroxyalkanoates (PHAs) have attracted significant interest as an alternative to synthetic plastics. While possessing promising properties suitable for various applications, the production of PHAs has not yet reached a global commercial scale. The main reason is the high cost of production, which represents a major limitation. Sugarcane bagasse (SCB) is an abundant lignocellulosic waste around the world. Its use to produce PHA enhances the feasibility of producing PHAs at commercial scale. However, SCB requires pretreatment and hydrolysis steps to release the sugars prior to the microbial fermentation. The cost associated with these steps poses additional challenges for large-scale production. Another challenge is the release of inhibitors during the pretreatment process which can result in a low PHA yield. The development of a low cost, co-culture strategy for the bioconversion of SCB into PHAs, can represent a pivotal step towards the large-scale production of bioplastics. This review highlights the advancements made in recent years on the microbial production of PHA using SCB as potential feedstock, with a proposed biological strategy and circular economy model.

In this study, the efficacy of biochar to mitigate ammonia stress and improve methane production is investigated. Chicken manure (CM) was subjected to high-solid mesophilic anaerobic digestion (15% total solid content) with wood biochar (BC). Wood biochar was further treated using HNO₃ and NaOH to produce acid–alkali-treated wood biochar (TBC), with an improvement in its overall ammonium adsorption capacity and porosity. Three treatments were loaded in triplicate into the digesters, without biochar, with biochar and with acid–alkali-treated biochar and maintained at 37 °C for 110 days. The study found a significant improvement in CH₄ formation kinetics via enhanced substrate degradation, leading to CH₄ production of 74.7 mL g⁻¹ VS and 70.1 mL g⁻¹ VS by BC and TBC treatments, compared to 39.5 mL g⁻¹ VS by control treatments on the 28th day, respectively. However, only the use of TBC was able to prolong methane production during the semi-inhibition phase. The use of TBC also resulted in the highest removal of total ammonia nitrogen (TAN) of 86.3%. In addition, the treatment with TBC preserved the highest microbial biomass at day 110. The presence of TBC also resulted in an increase in electrical conductivity, possibly promoting DIET-mediated methanogenesis. Overall, the acid–alkali treatment of biochar can be a novel approach to improve biochar’s existing characteristics for its utilisation as an additive in anaerobic digestion.

The process of breaking down chicken manure through anaerobic digestion is an effective waste management technology. However, chicken manure can be a challenging feedstock, causing ammonia stress and digester instability. This study examined the impacts of adding wood biochar and acid-alkali-treated wood biochar to anaerobically digest chicken manure under conditions of ammonia inhibition. The results highlighted that only the addition of 5 % acid-alkali-treated wood biochar by volume can achieve cumulative methane production close to the typical methane potential range of chicken manure. The treated wood biochar also exhibited highest total ammonia nitrogen removal compared to the Control treatment. Scanning Electron Microscope revealed growing interactions between biochar and methanogens over time. Real-time polymerase chain reaction showed that treated wood biochar produced the highest number of bacterial biomass. In addition, 16S amplicon-based sequencing identified a more robust archaeal community from treated biochar addition. Overall, the acid-alkali treatment of biochar represents an effective method of modifying biochar to improve its performance in anaerobic digestion.

Anaerobic digestion has attracted great interest for use in the management of organic wastes and the production of biomethane. However, this process is facing challenges, such as a high concentration of ammonia nitrogen, which affects the methanogenesis process and, thus, the production of methane. This study investigates the use of biosolid-derived biochar for mitigating ammonia stress and improving methane production during the anaerobic digestion of chicken manure, using both pristine biochar and biochar modified with a potassium hydroxide (KOH) solution. Batch mesophilic anaerobic digestion (37 °C) was carried out over 18 days. When compared to chicken-manure-only controls, a significant increase in methane formation was observed in the digesters amended with biochar and KOH-modified biochar, producing 220 L kg⁻¹ volatile solids (VSs) and 262 L kg⁻¹ VSs of methane, respectively, compared to 139 L kg⁻¹ VSs from the control digesters. The use of biochar and KOH-modified biochar resulted in a significant reduction of 8 days in the lag phase. The total ammonia nitrogen (TAN) concentration was reduced in the digesters with biochar and KOH-modified biochar by 25% and 35.5%, respectively. The quantitative polymerase chain reaction (QPCR) data revealed that the number of 16S rRNA gene copies was around 50,000 and 41,000 times higher in the biochar and KOH-modified biochar digesters, respectively, compared to the control digesters on day 18. The taxonomic profiles indicated that the BC and KOH-BC digesters contained a mixture of methanogenic pathways, including acetoclastic (Methanosaetaceae), hydrogenotrophic (Methanosarcinaceae), and methylation (Methanofastidiosaceae). This mix of pathways suggests a more robust archaeal community and, hence, more efficient methanogenesis. The results show that the addition of biosolids biochar enhances anaerobic digestion, mitigates ammonia stress to methanogens, and significantly increases biogas production.