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.

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.

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters that are considered as alternatives to petroleum derived plastics. To reduce the production cost, many studies have focused on the use of sugarcane bagasse (SCB) as a cheap substrate for the biosynthesis of PHAs. Many microorganisms have been reported as PHA producers, but only a few can utilise xylose as a carbon source for their production. In this study, five xylose-utilising PHA producing bacteria (two mesophilic and three thermophilic) were isolated from decomposing SCB and assessed. Among the five isolates, Mycolicibacterium smegmatis, reported for the first time as a PHA producer, accumulated the highest amount of PHA using xylose (22% cell dry weight). M. smegmatis was then tested for its ability to utilise a mixture of simple sugars (2 glucose: 1 xylose) and alkaline pretreated SCB hydrolysate without any detoxification step. The results showed bacterial growth in both media; however, growth was lower in the media supplied with the hydrolysate (0.63 g L⁻¹) compared with a mixture of glucose and xylose (1.11 g L⁻¹), presumably due to the presence of inhibitors in the hydrolysate. PHA accumulation was similar in media supplied with hydrolysate or mixture, with 27% and 28% cell dry weight, respectively. The extracted biopolymer was studied by Fourier Transform Infrared (FTIR) spectroscopy, Gas Chromatography Mass Spectrometry (GC-MS) and Scanning Electron Microscopy (SEM) and identified as polyhydroxybutyrate (PHB). These findings highlighted the potential use of M. smegmatis for PHB production after further optimisation steps.

This is the first study that specifically investigated biosolid-derived biochar for mitigating ammonia stress and methane production during the anaerobic digestion of chicken manure, using both pristine and modified biochar with potassium hydroxide (KOH) solution. Batch mesophilic anaerobic digestion (37 ℃) was carried out over 18 days. Compared to chicken-manure-only controls, a significant increase in methane formation was observed in digesters amended with biochar and KOH-modified biochar, producing 220 L kg^-1-VS and 262L kg^-1-VS of methane, respectively, compared to 139 L kg^-1 VS from control digesters. Moreover, the use of biochar and KOH-modified biochar resulted in a significant reduction of 8 days in the lag phase. Total Ammonia Nitrogen (TAN) concentration was reduced in digesters with biochar and KOH-modified biochar by 25% and 35.5%. respectively. QPCR data revealed that the number of 16S rRNA gene copies was around 50,000 and 41,000 times higher in biochar and KOH-modified biochar digesters, respectively, compared to control digesters on day 18. In addition, adding biochar and alkali-modified biochar to digesters created a mixture of pathways (acetoclastic, hydrogenotrophic and methylation), leading to a robust archaeal community. The results showed that biosolids biochar additives enhance the anaerobic