EVALUATION OF DIFFERENT BIOLOGICAL WASTE TREATMENT STRATEGIES

Biological treatment of organic waste by aerobic composting and anaerobic digestion (biogas production) was compared with respect to a number of environmental effects and sustainability criterias including energy balance, nutrient recycling, global warming mitigation potential, emission of xenobiotic compounds and economy. The parameters were assessed based on case studies in the literature as well as our own research. Assessment of energy balance, nutrient recycling and global warming came out in favour of biogas production, but especially the results regarding estimation of global warming mitigation differ according to the assumptions made. Our calculations showed that a fugitive loss of approx. 14% of the biogas produced by anaerobic digestion will turn the scale in favour of composting regarding global warming mitigation. In Europe actual biogas losses from 3.5 to 8.4% are reported but this may be exceeded in developing countries. Regarding emission of xenobiotic compounds composting is much in favour, as recent experiments show that a number of organic micro-pollutants are rapidly degraded during composting as opposed to anaerobic treatment. In most cases, composting is more cost-effective compared to biogas production but estimations of actual costs differ considerably. Published results of Life Cycle Assessment of organic waste management using the ORWARE model generally showed biogas production to have less environmental impact than composting, but it was demonstrated that changes in, e.g. system boundaries or functional units can result in substantial differences on the conclusions as well. In conclusion, the optimum waste planning strategy may be the implementation of an integrated waste treatment system operating with different scales of composting and anaerobic treatment, depending on local conditions.