Greenhouse gases emissions during open pit storage and composting of swine slurry in Brazil

Greenhouse gases (GHG) emissions were monitored fro m swine slurry (SL) stored in an open pit and treated by composting. Methane (CH 4), carbon dioxide (CO2) and nitrous oxide (N 2O) emissions were measured through 40 days using dynamic chambers cov ering the whole emitting surfaces and equipped with fans to control the ventilation rate in order to provide a constant laminar flow above t h emission sources. Air samples from chambers’ inlet and outlet airflow were continuously analysed by infrared photoacoustic monitor. Results have shown that CH4 was the main GHG emitted from the slurry deposit being responsible for 97.6% of the g lobal warming potential (GWP) whereas the CO 2 responded for the remaining 2.4%. No N 2O emission was observed which confirms the anaerobi c character of the biodegradation in open pits. The a erobic process prevailed during SL composting, and the CO2 was responsible for 55.7% of GWP and CH 4 and N2O for 20.3% and 24%, respectively. Introduction Swine manure is recognized as an important source o f greenhouse gases (GHG) to atmosphere however its proper management can mitigate the cont ribution of livestock production on global warming [1]. Although the usual practice in Brazil consists in open pit storage followed by crop application, manure composting with sawdust is an a lternative treatment that could reduce risks of soi l and water pollution by decreasing the mobility of n itrogen and organic matter in the environment and also enabling economically the exportation of the e xcess of nutrient as compost. Nevertheless such modification on usual manure management could resul t in an increase on N 2O emission [1, 2] as slurry storages are principally anaerobic and the opportun ity to NH4 + nitrification is negligible. There is lack of information about GHG emissions fr om storage and treatment systems under tropical conditions. Most part of available data an d i ventories are supported by mathematical models whose emissions factors were generated from data ob tained under temperate climate conditions, which increase the uncertainties about the estimations ma de for livestock production located in warmer regions. Recent studies have demonstrated that the productio n and emission of CH 4 from swine slurry is strongly affected by temperature [3] as well as the usual water management in production facilities adopted by each country, such as frequency of washi ng and sludge removal [1]. Therefore the aim of this study was to compare the CH 4 and N2O emissions during the initial forty days of swine slurry composting and pit storage in pilot scale under Bra zilian climate conditions. This period (initial 40 days) is characterized by higher GHG emissions in b oth systems due to manure incorporation and revolving of biomass (composting) and loads that di s urb the surface of fresh manure stored (pit). Proper O2 supply is essential for composting as its limitati on can increase N 2O and CH4 emission [2], therefore CO2 emission was also analysed to evaluate the aerobic activity in both systems. Material and Methods Experiments were conducted in Concórdia-SC, Souther n Brazil (2718’46” S, 5159’16” W) in a 30 m open concrete circular pit and a 3 m 3 composting bin of during approximately 40 days fro m June-July/2012 (winter). The pit was daily fed with 1 m 3 of fresh swine manure (5 days a week) during the wh ole period of the experiment and composting material wa s obtained by mixing fresh swine slurry (SL) with 300 kg of wood shavings (WS) in a total of six applications/turning as follows: at day 1 (727 L) , day 8 (724 L), day 16 (217 L), day 17 (215 L), day 22 (247 L), and day 30 (252 L) in order to achieve a final ratio of 7.94 L of SL for 1 kg of WS. Emissions of CO2, CH4 and N2O were measured using dynamic chambers made of tran sparent PVC film with 10.6 m (Figure 1a) and 12 m 3 (Figure 1b) of volume to cover the whole emitting surfaces of 19.8 m 2 and 3.2 m respectively. The fixed ventilation rate of chambe rs was controlled using fans equipped with dimmer in order to obtain constant laminar flow (< 1 m.s ) above the emission surfaces.