Biowaste arises from a number of human activities, including agriculture, hor-ticulture and industry, broadly falling into one of the following three major categories: faeces/manures, raw plant matter or process waste. This fits neatly into the process-orientated approach mentioned above, since the general char-acteristics of each are such that biological breakdown proceeds in essentially the same manner within the group and, thus, the ease of their decomposition is closely similar. Although, at least chemically speaking, biowaste can be seen as being characterised by a high carbon content, this definition is so wide as to include the vast majority of the substances for which all environmental biotech-nologies are viable process options. Hence, in the present discussion, biowaste is limited to substances which have been derived from recently living matter, with the approaches available to deal with other carbon-rich materials having already been examined in the preceding on pollution control, contaminated land and effluent treatment.
Biowaste of animal origin such as that contained in sewage and soiled animal bedding contains unabsorbed fats, proteins and carbohydrates, resulting from incomplete digestion of ingested food of animal and plant origin. In addition, abattoir waste would include all of the above and a substantial proportion of fats and protein, derived from the slaughtered animal. In addition, materials excreted by the animal include metabolic breakdown products such as urea and other small nitrogen-containing materials, for example partially degraded bile pigments. Live and dead bacteria, normally resident in animal gut are also present in the biowaste and so contribute their own fats, proteins, carbohydrates and nucleic acids.