Optimization of the anaerobic digestion process by substrate pretreatment and the application of NIRS

Abstract

Biogas production is a complex process depending on many factors and is an area that is being researched intensively. This thesis is based on studies that were aimed at optimizing the biogas production process by:

• Reducing the time taken to assess the biochemical methane potentials (BMP) of substrates (specifically meadow grasses) by rapid analytical methods such as near infra-red spectroscopy (NIRS), in-vitro organic matter digestibility assay and the neutral detergent fibre assay
• Applying NIRS as a monitoring tool to assess the concentrations of ammonia (which is inhibitory to the process) in the contents of anaerobic digesters.
• Improving the BMP of materials such as cattle manure and dewatered pig manure and chicken manure by thermal pre-treatment at various temperatures between 100°C and 225°C

Results show that the NIRS method can be used to discriminate between meadow grasses with high or low BMP. In detecting the ammonia content, NIRS was shown to have the potential to be a process monitoring tool. Thermal pre-treatment proved to be most effective on dewatered pig manure which showed improvements at lower pretreatment temperatures. Cattle manure required pre-treatment temperatures higher than 175°C to show improvement. Chicken manure did not show any improvements but instead showed a decrease in BMP at 225°C.