A technique for turning sewage sludge into compost, proposed by Hensby
Biotech of Huntingdon, uses up straw that farmers would otherwise burn and
has an added benefit: the compost smells sweet (British patent 2 224 021).
Sewage sludge is currently dumped at sea or used as landfill. Although
dried sludge makes good fertiliser, it smells foul. The inventors propose
piling up straw into a loose heap, and pumping in sludge over a period of
at least three days. Microorganisms to break down the sludge are provided
by adding compost from a previous batch. The wet heap is left for at least
a week while air is pumped in to encourage aerobic composting. This raises
the temperature to at least 75 °C, killing any pathogens.
The heap is then left for a month to dry out and for its pH level to
fall. The result is a sweet-smelling compost containing a very high proportion
of organic material.
