Biosolid stockpiles are a significant point source for greenhouse gas emissions.
The wastewater treatment process generates large amounts of sewage sludge that are dried and then often stored in biosolid stockpiles in treatment plants. Because the biosolids are rich in decomposable organic matter they could be a significant source for greenhouse gas (GHG) emissions, yet there are no direct measurements of GHG from stockpiles. We therefore measured the direct emissions of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) on a monthly basis from three different age classes of biosolid stockpiles at the Western Treatment Plant (WTP), Melbourne, Australia, from December 2009 to November 2011 using manual static chambers. All biosolid stockpiles were a significant point source for CH4 and N2O emissions. The youngest biosolids (<1 year old) had the greatest CH4 and N2O emissions of 60.2 kg of CO2-e per Mg of biosolid per year. Stockpiles that were between 1 and 3 years old emitted less overall GHG (∼29 kg CO2-e Mg(-1) yr(-1)) and the oldest stockpiles emitted the least GHG (∼10 kg CO2-e Mg(-1) yr(-1)). Methane emissions were negligible in all stockpiles but the relative contribution of N2O and CO2 changed with stockpile age. The youngest stockpile emitted two thirds of the GHG emission as N2O, while the 1-3 year old stockpile emitted an equal amount of N2O and CO2 and in the oldest stockpile CO2 emissions dominated. We did not detect any seasonal variability of GHG emissions and did not observe a correlation between GHG flux and environmental variables such as biosolid temperature, moisture content or nitrate and ammonium concentration. We also modeled CH4 emissions based on a first order decay model and the model based estimated annual CH4 emissions were higher as compared to the direct field based estimated annual CH4 emissions. Our results indicate that labile organic material in stockpiles is decomposed over time and that nitrogen decomposition processes lead to significant N2O emissions. Carbon decomposition favors CO2 over CH4 production probably because of aerobic stockpile conditions or CH4 oxidation in the outer stockpile layers. Although the GHG emission rate decreased with biosolid age, managers of biosolid stockpiles should assess alternate storage or uses for biosolids to avoid nutrient losses and GHG emissions.
Department of Forest and Ecosystem Science, The University of Melbourne, 500, Yarra Boulevard, Richmond, VIC 3121, Australia.
Ramaprasad
R
Majumder
Department of Resource Management and Geography, The University of Melbourne, 500, Yarra Boulevard, Richmond, VIC 3121, Australia.
Stephen J
SJ
Livesley
Technology and Marine Research, Melbourne Water, 990 Latrobe Street, Docklands, VIC 3008, Australia.
David
D
Gregory
Department of Forest and Ecosystem Science, The University of Melbourne, 500, Yarra Boulevard, Richmond, VIC 3121, Australia. Electronic address: sarndt@unimelb.edu.au.
Stefan K
SK
Arndt
D000393:Air Pollutants / Q000032:analysis; D001315:Australia; D002245:Carbon Dioxide / Q000032:analysis*; D017752:Greenhouse Effect; D008697:Methane / Q000032:analysis*; D009566:Nitrates / Q000032:analysis; D009584:Nitrogen / Q000378:metabolism; D009609:Nitrous Oxide / Q000032:analysis*; D010100:Oxygen / Q000032:analysis; D012621:Seasons; D012722:Sewage; D014865:Waste Disposal, Fluid / Q000379:methods; D062065:Wastewater
D000393:Air Pollutants; D002245:Carbon Dioxide; D008697:Methane; D009566:Nitrates; D009584:Nitrogen; D009609:Nitrous Oxide; D010100:Oxygen; D012722:Sewage; D062065:Wastewater
Biosolids; Greenhouse gases; Labile carbon; Sewage sludge; Waste management; Water treatment