THE EFFECT OF FARM SCALE AEROBIC TREATMENT OF PIGGERY SLURRY ON ODOR CONCENTRATION, INTENSITY AND OFFENSIVENESS

Piggery slurry was aerobically treated in a farm scale treatment plant with mean residence times of between 1.7 and 6.3 d. The treated slurr y was analysed using standard laboratory methods including key paramet ers such as COD (chemical oxygen demand) and VFA (volatile fatty acids ) concentrations. Further samples were taken and analysed either fresh from treatment or after a period of storage, for odour using olfactom etric methods. These included the determination of odour concentration , by dynamic dilution, and offensiveness and intensity, by use of a pa nel score. Chemical analysis of the treated samples indicated a breakd own of organic material broadly in line with that expected, although, in the short treatment, insufficient aeration may have retarded the ex tent of the process. The olfactometry clearly demonstrated that reduct ion of odour in terms of concentration and offensiveness were achieved by aerobic treatment. The reduced level of odour was evident even aft er 28 d of subsequent anaerobic storage. Typically, the treatment redu ced the concentration by 50-75% although this was insufficient to redu ce the perceived intensity at source to below two, (equating to ''fain t odour'') from the high valve of over five (equating to ''very strong odour'') measured for the untreated slurry. The effect of the duratio n of treatment on odour abatement was mixed. Reductions of odour conce ntration were broadly similar in all treatments. However, in terms of odour offensiveness, the best result was clearly achieved by the longe st treatment of 6.3 d. In this case, the score of the odour quality of the freshly treated slurry was below two (equating to better than ''f aintly offensive odour''), compared with a score of four for the untre ated slurry (equating to ''strongly offensive odour'') (C) 1998 Silsoe Research Institute.