Biosolids recycling to agricultural land: greenhouse gas emissions
Thorman, R.E., Williams, J.R., and Chambers, B.J., ADAS, UK
(free)
Nitrous oxide (N2O) and methane (CH4) are strong greenhouse gases (GHGs), which are c.300 and c.20 times more powerful than carbon dioxide (CO2), respectively. The recycling of biosolids and other organic materials to agricultural land is generally regarded as the Best Practicable Environmental Option in most circumstances, utilising the beneficial properties of these materials. Biosolids provide a valuable source of plant available nutrients which can reduce the need for inorganic fertiliser additions (particularly nitrogen and phosphate), and organic matter which acts as a soil conditioner and increases soil carbon storage (SOC). However, biosolids additions to land can result in N2O and to a much lesser extent CH4 emissions.
Using the most recent Intergovernmental Panel on Climate Change (IPCC) 2006 methodology and two alternative methods (i.e. IPCC 1996 & a ‘smart inventory’ approach), we estimated N2O and CH4 emissions, and SOC storage following the land spreading of a range of biosolids products at a field application rate of 250 kg/ha total nitrogen (i.e. the maximum field rate permitted in Nitrate Vulnerable Zones).
Following the land spreading of biosolids, the IPCC 2006 methodology estimates that 1% of the total nitrogen (N) applied is directly emitted as N2O. However, mean data from the limited number of field experimental studies undertaken to date in the UK indicate that only 0.2-0.4% of the total N applied is directly emitted as N2O. The IPCC methodology does not include a direct CH4 emission from soil, recognising that in most circumstances emissions are likely to minimal. The available UK field experimental evidence supports the IPCC view. Notably, increases in SOC storage following the land application of biosolids were estimated to be in the range 1.7 t/ha to 4.8 t/ha (c.720 kg CO2e/ha/t dry solids).
