Chemical reduction of odour in fresh sewage sludge in the presence of ferric hydroxide

To assess the potential of ferric hydroxide (FH) to reduce odour emission from dewatered sewage sludge with a moisture of approximately 86%, odour reduction was evaluated using an electronic nose and measurements of odorous compounds (hydrogen sulphide, ammonia and volatile fatty acids (VFAs)). The sulphur species including sulphate, acid-volatile sulphide (AVS), Cr(II)-reducible sulphide (CRS) and elemental sulphur (ES), were analysed by a modified cold diffusion sequential extraction method before and after anaerobic incubation. Within 32 days, 69.3, 83.8 and 88.6% of the odour (or 81.3, 93.7 and 97.5% of hydrogen sulphide) were eliminated, respectively, at the rates of 0.05, 0.10 and 0.25% (wt) of FH. The sulphur species analysis indicated that FeS, FeS2 and a small portion of S0 were formed by FH-sulphide reaction. This study also found that the relationship between odour and H2S concentrations could be well expressed by Steven's law. We believe that FH can be a cost-effective reagent for sludge odour control in sewage treatment processes.