Carbon Storage in an Artificial Soil

Abstract

As we strive to find new technologies to dispose of our municipal solid waste, compost-like outputs (CLOs) are becoming more widely created. As a product of both aerobic and anaerobic digestion, they provide a potentially important carbon store and some have proven to enhance existing carbon stores when added to brownfield sites and agricultural land. However, the CO2 flux from this artificial soil is relatively high when compared to natural soils. The aerobic digestion process under which it is produced lasts only 9 days, producing a material which is still comparatively unstable and yet to mature. The CLO is laid in windrows where it is hoped that it will stabilise and mature; if the humification process at this stage can be optimised, would an even greater carbon store be achieved?
This thesis seeks to answer this question, through the research into humification in both natural and artificial systems; through the measurement of CO2 flux to assess the stability of CLO over time; using adapted methodologies to gauge the maturity of this artificial soil by analysing the amount of humic acids present; by adding proposed catalysts to the material in fully factorial lysimeter studies; and by examining the affects of different physical environmental conditions under which CLO product humifies.
The results of a series of experimental trials, undertaken over a three year period, are presented. Manganese-coated sand and char, both currently ‘waste’ products were both used as potential catalysts for the humification process of CLO. Temporal trends were seen in most samples using infra-red gas analysis, an alkali extraction technique, UV photospectrometry, fluorescence and a novel pseudo-thermogravimetric analysis. The waterlogging of the samples appeared to have an effect on the humification process and a great deal of concurrent data was seen upon the addition of Mn-coated sand and char to the CLO. Both appeared to have a stabilising effect on the CLO, reducing flux rate and increasing humification as compared to a control.
An overriding theme present throughout this thesis is the heterogeneous and contaminated nature of the non-source-segregated CLO tested. It is therefore recommended that similar studies be undertaken on a purer, more homogenous CLO in order to assess whether promising results seen could be elucidated in order to gauge the efficacy of biochar and Mn in encouraging the production of humic substances. A field trial would allow the unified soil system to be considered, rather than the CLO alone.