The tunnel concept has major processing concept flaws. It was originally designed for compacting garbage for trucking. The natural bio reaction developed heat within the biomass and the decision to use it as a composting system was made. The system pushes and compresses what ever is in the tunnel to move it through the system. Fresh mix is loaded on one end and pushed out the other end with a hydraulic ram which pushes the product a couple of feet.

The concept of compressing the compost into a dense mass to push it through the system and the need to maintain porosity and aerate the mixture are directly opposing concepts. The dense mixture was very difficult to aerate. To compensate it required large amounts of dry coarse amendment to build porosity and high pressure blowers to attempt to aerate. This reduces production rates and makes it more costly to operate if it worked. It did not.

The aeration system is built into the reactor floor. Fines and wet material are forced into small aeration slots as the compost is pushed through the tunnel. The slots quickly plug and bind. In actual operation mud has been forced through the air piping all the way back to the blowers. As the compost mixture inside the tunnel dries, it cracks and shrinks. The air flow path from bottom to top is then short circuited. The center of the compost bin is poorly aerated. The result is that much larger plants are required to handle the increased amount of mixture. Actual plant throughput and compost retention time in existing plants have been greatly reduced because of this and all plants have required extended outdoor static piles to complete the composting processing.

Maintenance of a tunnel was not easy. In order to expose the bottom aeration slots to clean them, all the compost inside has to be removed manually, using front end loaders, which is a dirty difficult task.

Because of poor aeration, the compost discharged was not well stabilized. The product has to be piled outside to complete the composting process which didn't take place in the tunnel. To reduce the stigma of this inefficiency, the process is called curing. Odors from these cure piles are a very real problem.

Like other simple composting designs, people are often caught up in its apparent simplicity of operation, and not concerned with performance. It is not a good composting system design. Major installations have been shut down and sold for scrap.

There is also a non-automated tunnel, requiring front end loaders to fill and empty being marketed by the Dutch. The tunnel then simply becomes a very compact enclosed static pile, with many weaknesses. It does not mix, aerates poorly, and all compost has to loaded/unloaded manually with a frontend loader. Simply picture all the compost shown in one of the first pictures on windrow in a box, not very efficient. It is used in the mushroom growing industry in Holland where relatively small volumes of compost are processed.

Now that you've been educated to the real world issues surrounding composting, please feel free to download our technical documents or contact us for detailed information.