Hot-Rot is a New Zealand technology that processes small to medium scale quantities of organic waste in highly controlled, continuous flow, agitated composting units. The technology consists of enclosed drums in which rotating paddles mixed and move organic waste placed in one end to the other end where it is removed as compost. Quantities as little as 400 kg (two or three 240 litre wheelie bins per day up to 8-11 tonnes per day of material can be processed through off the shelf units. Large quantities require a tailored solution. Typical applications includeuniversities (a unit is in operation at the Australian National University in Canberra), shopping centres and sewage treatment works.
Vermiculture or vermicomposting refers to the breakdown of organic material that, in contrast to microbial composting, involves the joint action of different species of earthworms and micro-organisms and does not involve a thermophilic (that is, high heat) stage. As the agents of turning, fragmentation and aeration, the worms consume organic wastes such as food waste, animal waste, greens and sewage sludge to produce a soil conditioner. Vermiculture systems are a simple technology, particularly when compared with in-vessel composting technologies, and are suitable for processing a much smaller range of food organic material (primarily fruit and vegetable scraps). They also require specialised management to achieve successful and consistent processing performance. The ‘mid-scale’ technologies and systems have processing capacities between 20 and 250 kg (fresh weight) per day (over a seven day week). Batch-flow (or box systems) units are a simple design and suitable for small-scale vermiculture applications. They require very little initial capital expenditure and can be popular for this reason. Continuous flow systems are considered to be the high-tech options for vermiculture. More sophisticated mid-scale vermiculture systems recirculate leachate back on top of the bedding. Figure 3 shows an example of a continuous-flow vermiculture unit.
Figure 3 Examples of continuous-flow vermiculture unit