T. Thamsiriroj

Modelling mono-digestion of grass silage in a 2-stage CSTR anaerobic digester using ADM1

This paper examines 174 days of experimental data and modelling of mono-digestion of grass silage in a two stage wet process with recirculation of liquor; the two vessels have an effective volume of 312 L each. The organic loading rate is initiated at 0.5 kg VS m(-3) d(-1) (first 74 days) and subsequently increased to 1 kg VS m(-3) d(-1). The experimental data was used to generate a mathematical model (ADM1) which was calibrated over the first 74 days of operation. Good accuracy with experimental data was found for the subsequent 100 days. Results of the model would suggest starting the process without recirculation and thus building up the solids content of the liquor. As the level of VFA increases, recirculation should be employed to control VFA. Recirculation also controls solids content and pH. Methane production was estimated at 88% of maximum theoretical production.

What will fuel transport systems of the future

This paper seeks to decry the notion of a single solution or “silver bullet” to replace petroleum products with renewable transport fuel. At different times, different technological developments have been in vogue as the panacea for future transport needs: for quite some time hydrogen has been perceived as a transport fuel that would be all encompassing when the technology was mature. Liquid biofuels have gone from exalted to unsustainable in the last ten years. The present flavor of the month is the electric vehicle. This paper examines renewable transport fuels through a review of the literature and attempts to place an analytical perspective on a number of technologies.

5 – Fundamental science and engineering of the anaerobic digestion process for biogas production

: The aim of this chapter is to explain, in a simplified manner, the complex microbiological process of anaerobic digestion and detail the relationship between feedstock, anaerobic digester and methane production. The chapter first reviews basic microbiology and explores the interplay between the different groups of bacteria, the conditions under which they prosper and potential sources of inhibition. Then, the chapter deals with engineering aspects – categorisation of feedstocks, methane production per unit of feedstock, reactor configurations, mass and energy balance of digestion systems, up-scaling laboratory systems to commercial reality and modelling. In the analysis, an emphasis is placed on high solid content feedstocks. Two different feedstocks are highlighted – the organic fraction of municipal solid waste and grass silage.

Use of modeling to aid design of a two-phase grass digestion system

A sequentially fed leach bed system coupled with a leachate holding tank and an Upflow Anaerobic Sludge Blanket (UASB) was modeled based on 310d of grass silage digestion with the goal of generating specific design instruction. The model suggests the hydrolysis rate is proportional to the sprinkling rate and retention time. It suggests that raising the sprinkling rate by a third (from 600L/d to 800L/d) increases the volatile solids destruction from 70% to 80% for a retention time of 30d yielding 370L CH(4)/kg VS. The volume of the leachate holding tank has a minimal influence on methane production (reducing its volume by a factor of 2 reduces methane yield by 1%). The model suggests that for a constant sprinkling rate, shorter retention time increases daily methane production, but lowers specific methane yield (L CH(4)/kg VS). Longer retention time increases methane content in the biogas.

Grass Biomethane for Agriculture and Energy

Many factors enforce the intensification of grassland utilization which is associated with significant environmental impacts subjected to various legislative constraints. Nevertheless, the need for diversification in agricultural production and the sustainability in energy within the European Union have advanced the role of grassland as a renewable source of energy in grass biomethane production with various environmental and socio-economic benefits. Here it is underlined that the essential question whether the gaseous biofuel meets the EU sustainability criteria of 60% greenhouse gas emission savings by 2020 can be met since savings up to 89.4% under various scenarios can be achieved. Grass biomethane production is very promising compared to other liquid biofuels either when these are produced by indigenous or imported feedstocks. Grass biomethane, given the mature and well known technology in agronomy and anaerobic digestion sectors and the need for rural development and sustainable energy production, is an attractive solution that fulfils many legislative, agronomic and environmental requirements.