The identification and quantification of microorganisms in water samples is crucial to improve processes in organic waste treatment facilities. Most of the currently available tests are either labour-intense or costly, and they do not allow determination of the dynamics within microbial communities in digestate samples. This study is the first report on the use of thermal analysis, specifically the Heat Transfer Method (HTM), to monitor microbial load in aqueous systems and digestate samples. Staphylococcus aureus was used as a model organism and different concentrations in water were measured by HTM. It was demonstrated that there was a positive correlation between the thermal resistance and concentration of the bacterial cells. Subsequently, the influence of temperature on growth rates was studied and confirmed by plating experiments and Scanning Electron Microscopy (SEM). These results showed the possibility to monitor the temperature dependent growth of S. aureus using HTM. To determine if this technique can be applied for studying complex matrices, digestate samples were collected from a number of sources and plated on nutrient agar plates. The bacterial cultures derived from 2 single colonies were characterised and identified by sequencing of DNA regions for 16S ribosomal RNA. HTM measurements were performed in diluted or centrifuged digestate samples that were enriched with S. aureus. The results indicated that it is possible to evaluate microbial load even in samples containing other organic material. The thermal analysis method has the potential to provide a low-cost monitoring option, which is simple to use and provides real-time analysis, thus improving the existing monitoring procedures in organic waste treatment facilities.

This study examines the yields of solid residue and by-product from the microwave-assisted acid hydrolysis of lignocellulosic poplar wood for levulinic acid production. The aim of this study was to optimise levulinic acid production via response surface methodology (RSM) and also investigate the effect of reaction conditions on other products such as furfural, solid residue, formic acid and acetic acid yields. A maximum theoretical levulinic acid yield of 62.1% (21.0 wt %) was predicted when reaction conditions were 188 °C, 126 min and 1.93 M sulphuric acid, with a corresponding solid residue yield of 59.2 wt %. Furfural from the hydrolysis of hemicellulose was found to have significantly degraded at the optimum levulinic acid yield conditions. The investigation of formic acid yields revealed lower formic acid yields than stoichiometrically expected, indicating the organic acid reactions under microwave-assisted hydrolysis of lignocellulose. The solid residue yields were found to increase significantly with increasing reaction time and temperature. The solid residue yields under all conditions exceeded that of levulinic acid and, therefore, should be considered a significant product alongside the high-value compounds. The solid residue was further examined using IR spectra, elemental analysis and XRF for potential applications. The overall results show that poplar wood has great potential to produce renewable chemicals, but also highlight all by-products must be considered during optimization.

The synergistic conversion of Miscanthus xGiganteous with sulphated zirconia and dilute hydrochloric acid was investigated. The sulphated zirconia was prepared using H2SO4 impregnation and characterised using X-ray Diffraction (XRD), Energy-dispersive X-ray (EDX), Scanning Electron Miscroscope (SEM) spectroscopy and nitrogen adsorption–desorption measurements. The microwave-assisted reaction was evaluated at various temperatures, reaction times and catalyst-to-biomass ratios, with and without the presence of trace HCl in the solution medium for the conversion of Miscanthus xGiganteous to levulinic acid. The highest levulinic acid yield of 63.8% was achieved at 160 °C, 80 min and a 2:1 catalyst-to-biomass ratio, with 10 mM HCl. The catalyst recyclability was investigated with and without calcination, finding that significant humin deposition on the catalyst surface likely caused catalyst deactivation. The post-reaction solid residue was also characterised using SEM, EDX, XRD, elemental composition and nitrogen adsorption–desorption measurements. Findings indicate that this residue could potentially be used as a soil amendment or as a fuel source. The synergistic conversion of real lignocellulosic biomass with sulphated zirconia and trace hydrochloric acid showed remarkable promise and should be investigated further.

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