Biological treatment technology is good for the recovery of resources and energy from municipal solid waste (MSW) and cutting down biodegradable components in landfill waste. Recently, the aerobic biological treatment of MSW has increased in rural areas of China. These facilities are usually close to nearby residents, and complaints tend to be received regarding odorous gases. Ammonia is the predominant gaseous pollutant with emissions of around 18 − 1150 g/t waste [1]. The concentration of ammonia in the exhaust gas from sludge composting facilities can be as high as can be as high as 700 mg/m3 [2]. Volatile organic compounds (VOCs) are also one of typical air pollutants, with concentrations in the air around MSW composting facilities ranging from 8 mg/m3 to 16 mg/m3 [3]. Rodriguez et al. [4] researched the influence of the operating technology to VOC release, such as moisture, oxygen, and C:N ratios. They found that the most important factor was the C:N ratio, then was the internal oxygen and moisture contents of the windrow.
The emission patterns of gaseous pollutants during mechanical processes, such as waste sorting and shredding, differ significantly from those in aerobic biological treatment processes. Stirring and crushing processes can strip some compounds, especially xenobiotic organics, from the surface of the waste and make them readily volatilized [5]. Toluene and xylene are the dominant VOCs in the shredding, mixing, and sorting areas of composting facilities. Some studies reported that these aromatics originated from the decomposition of polymer and solvents [6], whereas others have shown that these aromatics compounds are released from raw materials rather than intermediate products of waste biodegradation. Volatile fatty acids (VFAs) can be produced by the hydrolysis and anaerobic digestion of carbohydrates [7–8], fats, and proteins in waste, and they can accumulate when inadequate oxygen is supplied during aerobic biodegradation [9]. The olfactory threshold of VFAs is low, which has a great impact on the environment.
Sulfur compounds, nitrogen-containing compounds and terpenes have strong pungent odor also, so the emission of these gas pollutants will have odor impact on nearby communities. In the process of refuse composting, incomplete or inadequate ventilation will lead to the release of hydrogen sulfide and other malodorous substances [10–11]. Fang et al. [12] found that limonene, dimethyl sulfide, dimethyl disulfide and α - pinene are the main odorants in municipal solid waste composting facilities. Tsai et al. [13] studied the kitchen waste composting facilities and found that the concentrations of ammonia, dimethyl sulfide and hydrogen sulfide had a logarithmic relationship with odor intensity, while the concentrations of ethylbenzene, acetic acid and p-toluene had a linear relationship with odor intensity. This result tells us that reducing odor intensity of ammonia, dimethyl sulfide and hydrogen sulfide is much more difficult than other pollutants. It is reported that the odor of trimethylamine has high persistence and low odor threshold. Therefore, if the odor source contains trimethylamine, the influence range and distance of the source are larger than others [14].
The present study investigated the odor compounds emitted from a small-scale MSW aerobic biological treatment facility as well as assessing the odor impact and carcinogenic risk for the operators. Based on calculations of the theoretical odor concentrations, the main odor compounds were identified in various treatment processes and the environmental quality was evaluated.