Odor pollutants analyzing during municipal solid waste (MSW) composting

Odor pollution caused by municipal solid waste (MSW) treatment plants has become a growing public concern. The 15-80 mm MSW fraction used in this study was collected from the Xiaowuji MSW pre-sorting station of Beijing. The 15-80 mm MSW consisted of 67% kitchen waste, 18% paper, 6% plastic, and 9% other wastes. The treatments were analyzed using a 60 L heat insulated composting vessel with forced aeration systems. The vessel was loaded with about 29 kg of 15-80 mm MSW, and controlled by the C-LGX program, which enables aeration to be controlled automatically by time or inside temperature. Aeration consisted of pumping ambient air into the reactor continuously at a rate of 0.2 L/kg.min dry matter. Odors were analyzed using a Model 5975N Gas Chromatography-Mass Selective Detector (Agilent Technologies, USA) coupled with an Entech 7890 Preconcentrator (Entech Instruments Inc., CA, USA). An SOC-01 sampling device (Tianjin Dylan Auto Environmental Protection Sci-tech Company, Ltd. China) was used to collect the gas sample. Three-stage cryo-trapping was used to concentrate VCS's in air samples before GC-MSD analysis. In the first stage, 50 mL air samples were drawn through a liquid nitrogen trap with glass beads at -150°C at a flow rate of 100 mL/min. After this, the first-stage trap was heated to 10°C and the trapped gases were transferred by 40 mL helium at a flow of 1.5 mL/min to a second-stage trap at -40°C. The second stage trap was then heated to 180°C, after which the thermally desorbed gases were transferred to a third-stage cryo-focusing capillary trap at -170°C by 30 mL helium at a rate of 1.5 mL/min. The cryo-focusing trap was then rapidly heated to 100°C and the VSC's were finally transferred to the GC-MSD system for determination. For analysis, an HP-1 capillary column (60 m×0.32 mm×1.0 mm, Agilent Technologies, USA) was used with helium as the carrier gas. The GC oven temperature was initially set at -50°C, where it was held for 3 min, after which it was increased to 35°C at 15°C/min, then to 150°C at 5°C/min, and then to 220°C at 15°C/min, where it was held for 7 min. The oxygen and H2S content was analyzed daily using a portable biogas analyzer. Composting gas samples were extracted using a suction pump (built-in biogas analyzer, gas flow: 550 mL/min) and then transferred to the inlet port of the biogas analyzer via a Teflon hose that contained a filter element (2.0 μm PTFE) installed in the middle of the pipe. Measurements were taken for about 90 seconds, and measured values of O2 and H2S were read directly from the screen. The results from this study indicate that there are 50 kinds of volatile organic compounds (VOC's) with particle size of 15-80 mm during MSW composting, including 5 kinds of sulfur odor compounds, 25 kinds of hydrocarbon compounds, 14 kinds of aromatic compounds and 6 kinds of other odor compounds. The correlation analysis show that the odor concentration is significantly correlated with the emissions of sulfurated hydrogen, dimethyl sulfide, carbon disulfide, methyl disulfide, 1,3-dimethyl and o-xylene (p<0.01). Considering of the detection olfactory threshold of all odor compounds, priority control sequence of the odors were sulfureted hydrogen>dimethyl sulfide>methyl disulfide>carbon disulfide>1,3-dimethyl> o-xylene. With the low olfactory threshold of methanthio, even if the emission concentration was very low, it would produce serious odor pollution. Furthermore, NH3 contribution to odor concentration was relatively small, but its emissions were relatively high. It should also focuse on monitoring and control of the methanthio and NH3 during the particle size of 15-80 mm MSW composting. This study can provide a reference for monitoring of odor substances and making control strategy.