Environmental impacts of biological management of organic waste

Agricultural recycling of organic waste intuitively appears as environmentally-sound management in that it relies on natural biological processes and causes organic matter to return to soils. It has indeed emerged as a top priority in the French and European waste policy agendas. However, the environmental assessment of biological waste management routes raises challenging issues, whether dealing with the criteria that should be retained in the evaluation, or the characterisation of impacts themselves. There are many uncertainties associated with the latter. In that context, the scope of the study reported here was to review the current knowledge available to characterise the environmental and sanitary impacts attributable to the various biological waste disposal routes: animal manure, urban waste, sewage sludge, and agro-industrial or paper-mill waste. More specifically, the objective was to provide quantitative estimates of the factors causing the final impacts. These encompassed the consumption and emission of various substances and forms of energy involved in the management of organic waste, including the fate of nutriments and contaminants after the application of organic waste in the field. Micro-biological risks were not investigated to restrict an already considerably large scope. Overall, our literature review emphasised the great sensitivity of emissions to various treatment and environmental controls (eg, temperature or soil type), and also to substrate characteristics. The available knowledge appeared often too scant to tackle the ensuing variability, making it impossible to correctly describe and quantify the underlying processes. This knowledge gap may be bridged either by a more thorough understanding and modelling of these processes, or through the collection of new data under actual operating conditions. In a second stage, the reference data set obtained from the literature review was assembled in a format that could be readily used in a global evaluation such as life cycle assessment (LCA). Beyond the issue of data availability, accuracy and representativity, several methodological limitations to LCA were discussed, and recommendations made. Further considerations were given as to how to address odours and ecotoxicity impacts, and above all the influence of repeated organic waste application on soil fertility and quality, including carry over effects over the long term.