Complex processes concerning declining concentration of organic matter within pig wastes have been investigated using deuterated phenol and acetic acid over a ten day (d 5 ) ( d 4 ) period. Decomposition rates of products responsible for odours and pollution were also quantiΓΌed. These products included the volatile fatty acids, phenols and indoles as well as gaseous methane and carbon dioxide. The last two were quantiΓΌed in the headspace Γ½ow to assess methanogenesis and the activity of bacteria. The relative rates of emission, production and bio-decay were calculated as exponential curves showing that acetic acid was lost through emission and bio-decay with half lives of 158 h and 95 h, respectively. Bio-production of acetic acid was very low. The emission rate of methane was 4.0 g m-3 d-1. The ratio of methane generated to the bio-decay of acetic acid concentration was 1 : 66. The decline of acetic acid in slurry was shown to be a concentration-dependent process. Other volatile fatty acids demonstrated similar declining concentration characteristics but at a lesser rate. This was also the case for 4-methyl phenol with a half life of 495 h. However phenol demonstrated diΓΎ erent declining concentration and production characteristics with a maximum concentration of 85 mg l-1 at 175 h. Carbon dioxide was produced at a greater rate than acetic acid was lost from the slurry (a ratio of 1.88 : 1.0). Ammonia was emitted at a rate of 4.7 g m-2 d-1.
1999 Society of Chemical Industry