Aerobic treatment of piggery slurry can be used to tackle a range of slurry problems. Batch aeration (in particular at thermophilic temperatures) is well suited to reducing pathogen numbers, offering a cheap and simple process. For other duties, continuous treatments are more suitable. For odour control, short treatment times (1 to 2 d) are adequate if land spreading is intended within a few days. Longer treatment times (3 to 5 d) enable up to 6 weeks subsequent storage of slurry without offensive odour; removal of solids after treatment can extend this period. Nitrification can be encouraged by long treatments at a high level of aeration (i.e. dissolved oxygen concentration above 1% of saturation). The nitrogen lost to the atmosphere as ammonia is thereby reduced. Denitrification in anoxic storage will remove nitrate as nitrogen gas if nitrate leaching is a problem, but some nitrous oxide, which is a greenhouse gas, may also be produced. Depending on the extent of treatment, costs can vary between £1.60 and £10.50 per pig produced, thus representing a high proportion of the profit margin. There may be some benefits from slurry aeration resulting from the fertilizer value, possible heat extraction and easier disposal of the slurry but developments are likely to remain legislation-led, with minimum cost being the principal criterion.