Evaluation of the Odorous Compounds Emitted in a Full- Scale Sewage Sludge Composting Plant and Its Relationship with the Biological Stability

摘要

Volatile organic compounds (VOCs) and ammonia are some of the compounds present in gaseous emissionsfrom waste treatment installations that contribute to odour pollution. In the present work, a characterisation ofthe VOCs emitted during the biological treatment of raw sludge (RS) by composting in dynamic windrowsfollowed by a curing phase in a full-scale sewage sludge composting plant was conducted, aiming to provide aspecific inventory of the odorous compounds emitted. In addition, the biological stability evolution during thewhole process was monitored in order to ensure the proper stabilisation of the material. Waste stability andodorous compound analysis considered both a first phase where a mixture of RS and vegetal fraction (RS –VF) was actively composted in continuous dynamic windrows and a second standard curing phase intrapezoidal turned piles, where material reached maturation. The dynamic windrows were operated at 4 daysof composting time, each one of 86 Mg approximately. From an initial biological activity –defined by theDynamic Respiration Index (DRI)– of the RS – VF mixture of 2.2 ± 0.3 g O_2·kg~（-1） OM·h~（-1）, the reductionachieved at the end of the first composting phase was about a 48 %, and finally at the end of the curing phasewas about a 79 %, ensuring the biological stabilisation of the material. Different VOC families were identifiedand up to 20 specific compounds were also quantified in the gaseous emissions generated throughout theentire process. Terpenes such as α-pinene or limonene were found during the whole process, sulphurcompounds such as dimethyl sulphide (DMS) or dimethyl disulphide (DMDS) where emitted during the firststages of the composting process and decreased as the material was stabilised while carboxylic acids such asbutanoic acid were normally found at higher concentrations in the middle of the composting process.