An agitated in vessel composting means that the composting material is mixed mechanically
An agitated in vessel composting means that the composting material is mixed mechanically (either by turning, tumbling or other methods of agitation) during the compost cycle.
There are two stages in in-vessel composting system, one is the high rate phase and the other one is the curing phase. .The physical and biological changes in composting process mainly depends on temperature, aeration, moisture are directly related to the surface to volume ratio (Burile et al., 2017). Both designs are less subjected to variations in weather conditions since they are closed designs.
In the circular agitated in vessel composting bioreactor, the composting material is fed from the top. Oxygen is supplied to the microorganisms by forced aeration through the augers which rotate around the centre of the reaction vessel. The set of augers (as shown in Fig 1) is connected to a bridge which is attached to a central pivoting system. The bridge is rotated slowly to move the augers. As the augers are hollow and perforated on the edges, oxygen is forced into the composting material. High temperatures are used to ensure that the limit of pathogens is controlled. If the retention time is less than three weeks, then the discharged material must be windrowed until stability is reached i.e. the curing phase. (Tchobanoglous et al., 2002)
In the rectangular agitated in vessel composting bioreactor, the prepared waste is placed in the bin. Oxygen is supplied by forced aeration through the perforated plates at the bottom of the bin. Tumbling is achieved via the extraction conveyer (as shown in Fig. 2). The extraction conveyer either mixes the compost in the reactor periodically or discharges it in the outfeed conveyer. After a retention time of 6-12 days in the bin, the material is windrowed for 1-2 months until stability is reached. The horizontal rectangular tank is well suited for sewage sludge, MSW and mixtures of MSW and sludge (Tchobanoglous et al., 2002).