Modeling the Carbon Footprint of Various Biosolids Treatment Options

There are a wide variety of processes which are capable of treating biosolids to comply with the pathogen reduction requirements defined by US EPA 503 regulations. Choice of technology is complex and dependent on a number of project specific and economic influences. However, within Europe, long term sustainability and carbon impact are becoming more influential and this is being backed up by economic incentives in the form of taxes and levies. This paper presents results of a model developed to calculate the carbon footprints of a number biosolids treatment processes. Results showed that Class A systems were more carbon intensive than Class B equivalents due to additional power required to meet pasteurization temperatures. Generally, processes with anaerobic digestion had far smaller carbon impacts due to lower quantities of biosolids for downstream processing and transport and the production of renewable energy. The benefits of fertilizer displacement by composting were also significant.