the system consequently air taken from the ambient environment will normally serve as the source for additional oxygen fig1 illustrates this air inlet at valve 2 however one or more inlets may be provided throughout the system for example introduction of ambient air into the gas stream between compost vessel co and curing bin cu 2 will serve to lower the temperature and relative humidity of the gas stream thereby lowering the load upon the heat exchanger sensors will also most preferably be provided in the system and at least some of these will most desirably be provided in the gas stream coming from the output of curing bin cu 2 these sensors can monitor the concentration of various contaminants and also the gas flow rate in the event the gas is vented to ambient it is possible to monitor and track continuously if desired the concentrations of contaminants emitted and also the total mass over a given time interval these sensors can be used in conjunction with an electronic control system to only release through a particular output device when the contaminants are within a particular range for example should the compost within compost vessel co have an unusually high ammonia emission that overloads the biofiltration function of curing bin cu 2 then valve 1 can be controlled to prevent the release of any gas into the ambient environment and instead recirculate the entire gas stream should this situation not be resolved.