Storage management influences greenhouse gas emissions from biosolids Ramaprasad Majumder a , Stephen J. Livesley a , David Gregory b , Stefan K. Arndt a, c, * a School of Ecosystem and Forest Sciences, The University of Melbourne, 500 Yarra Boulevard, Richmond, VIC 3121, Australia b Technology and Marine Research, Melbourne Water, 990 Latrobe Street, Docklands, VIC 3008, Australia c Terrestrial Ecosystem Research, Department of Microbiology and Ecosystem Science, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria article info Article history: Received 8 September 2014 Received in revised form 2 January 2015 Accepted 4 January 2015 Available online Keywords: Sewage sludge Respiration Biomass Carbon offset Sequestration Nitrous oxide Methane abstract Biosolids produced by wastewater treatment plants are often stored in stockpiles and can be a significant source of greenhouse gases (GHG). Growing trees in shallow stockpiled biosolids may remove nutrients, keep the biosolids drier and offset GHG emissions through C sequestration. We directly measured methane (CH 4 ), carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) flux from a large biosolid stockpile and two shallow stockpiles, one planted with Salix reichardtii (willow) trees, from December 2009 to January 2011. All stockpiles emitted large annual amounts of GHG ranging from 38 kg CO 2 -e Mg 1 dry biosolid for the large stockpile, to 65 kg CO 2 -e Mg 1 for the unplanted shallow stockpile, probably due to the greater surface area to volume ratio. GHG emissions were dominated by N 2 O and CO 2 whilst CH 4 emissions were negligible (<2%) from the large stockpile and the shallow stockpiles were actually a CH 4 sink. Annual willow tree growth was 12 Mg dry biomass ha 1 , but this only offset 8% of the GHG emissions from the shallow planted stockpile. Our data highlight that biosolid stockpiles are significant sources for GHG emissions but alternate management options such as shallow stockpiles or planting for biomass pro- duction will not lead to GHG emission reductions. © 2015 Published by Elsevier Ltd. 1. Introduction Biosolids are an end product of the sewage treatment processes and their production gradually increases every year due to sewage production from an increasing human population (Wang et al., 2008). For example, in Australia there is an approximate 3% in- crease in biosolid production from wastewater treatment plants (WTPs) annually (Australian Water Association, 2014The storage of biosolids within WTPs is necessary either temporarily, or long- term, depending upon whether an ultimate end-use is available. Desirable end uses have a low environmental impact or even an environmental and economic benefit, such as biosolid application to agricultural or production forestry systems (Pritchard et al., 2010). Biosolids are often stored in large stockpiles to minimize the use of space, but this can present a fire risk (spontaneous combustion), pollution risks (leachate and particulate) and increased GHG emission risks as they are rich in organic matter and nutrients (Fernandes et al., 2005). In fact, biosolid stockpiles can emit large amounts of greenhouse gases, especially in young stockpiles (Majumder et al., 2014). A potential alternative end use, or long term storage option for biosolids are shallow stockpiles (e.g. 0.5 m deep) over larger areas and within which woody vegetation can be planted for carbon offset gains, biosolid stabilization and pollutant/nutrient removal (Laidlaw et al., 2012). In such a system, the high labile carbon and nitrogen content of the biosolid, in combination with rainfall and/ or supplementary irrigation, could lead to high plant biomass production and therefore a value adding product for bioenergy or biochar production and/or carbon offset potential of related GHG emissions from the WTP. However, microbial decomposition and transformations of labile carbon and nitrogen in these stockpiles may still lead to significant production of methane (CH 4 ), carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) under aerobic and anaerobic conditions. In WTPs, GHG emissions are generally estimated using emission factors based on the initial chemical properties of the wastewater or sewage sludge (Brown et al., 2010) and as such there is substantial uncertainty in these GHG emissions estimates (Bogner et al., 2008). This also relates to the storage and manage- ment of dried biosolids as direct measurements of GHG emissions from biosolids in stockpiles or other interim storage options are * Corresponding author. School of Ecosystem and Forest Sciences, The University of Melbourne, 500 Yarra Boulevard, Richmond, VIC 3121, Australia. E-mail address: sarndt@unimelb.edu.au (S.K. Arndt). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2015.01.007 0301-4797/© 2015 Published by Elsevier Ltd. Journal of Environmental Management 151 (2015) 361e368