Abstract
Volatile organic compounds (VOCs) and ammonia are some of the compounds present in gaseous emissions from waste treatment installations that contribute to odour pollution. In the present work, a characterisation of the VOCs emitted during the biological treatment of raw sludge (RS) by composting in dynamic windrows followed by a curing phase in a full-scale sewage sludge composting plant was conducted, aiming to provide a specific inventory of the odorous compounds emitted. In addition, the biological stability evolution during the whole process was monitored in order to ensure the proper stabilisation of the material. Waste stability and odorous 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 in trapezoidal turned piles, where material reached maturation. The dynamic windrows were operated at 4 days of composting time, each one of 86 Mg approximately. From an initial biological activity –defined by the Dynamic Respiration Index (DRI)– of the RS – VF mixture of 2.2 ± 0.3 g O2·kg-1 OM·h-1, the reduction achieved at the end of the first composting phase was about a 48 %, and finally at the end of the curing phase was about a 79 %, ensuring the biological stabilisation of the material. Different VOC families were identified and up to 20 specific compounds were also quantified in the gaseous emissions generated throughout the entire process. Terpenes such as a-pinene or limonene were found during the whole process, sulphur compounds such as dimethyl sulphide (DMS) or dimethyl disulphide (DMDS) where emitted during the first stages of the composting process and decreased as the material was stabilised while carboxylic acids such as butanoic acid were normally found at higher concentrations in the middle of the composting process.
