The writer has been involved in Municipal Composting since 1952. The Composting Company of Rhodesia, of which the writer was Managing Director, put up an enclosed Windrow Composting Plant at Mabelreign Town Management Board, Near Salisbury, Southern Rhodesia in 1957. Before, the Composting Company of Rhodesia obtained the contract for this Plant at the Salisbury Sewage Works. This plant consisted of one silo, 40ft. long and stood 4ft. apart and 3ft. 8ins. High; between and below the walls, we provided four plenum chambers, covered with grills, with ¼ in. mesh on them. These plenum chambers were provided with drainage by means of air seals so that air could be blown under pressure into the plenum chambers by a fan ...
The ends of the silo were provided with removable doors and a special turning machine was devised so it could run on top of the silo wall and could turn and aerate the composting refuse in the silo as often as was necessary. The material composted was raw household refuse wetted with raw sewage sludge. The pilot plant proved to be very satisfactory and it was found that on test the compost produced germinated seeds and grew seedlings better than control after 4 ½ days composting.
The full sized plant, at Mabelreign, on these lines was erected in 1957 and the writer was most fortunate in obtaining the help of Professor Jones, Microbiologist, from Hawaii University, USA. who was attached to the University of Rhodesia & Nyasaland at the time. Professor Jones, with his knowledge of fungi was particularly helpful to the writer. Temperature measurements were taken over some six months. The method of operation of the plant was that refuse was placed in one or other of the silos at one end thereof, the refuse being filled to the top of the silo which was 6ft. high and for the first 10ins. thereof. A special turning machine was devised so that it would come right through the silo, moving one way only, so that every time it passed, it moved the refuse 10ins. back. This meant that if the first 10ins of the silo was filled every day, it took the refuse ten days to reach the end of the silo. A point of fact, the silo did not have to be filled quite as often as this, and it is merely stated to avoid a full explanation of the system.
The important findings are shown in figure (1) and these are that if the refuse is turned daily, the temperature rise due to the first stage is that caused by the thermophilic aerobic bacteria breaking down sugars, amino acids and the more readily decomposed parts of the refuse.
The secondary rise is caused by fungal activity, which in the main break down the cellulose materials. It should be stated that the majority of the fungi, capable of breaking down cellulose materials are mesophyllic and do not thrive at a high temperature, however there are sufficient fungi that are able to function at high temperatures to cause a rise in temperature into the thermophillic stage. This is perhaps unfortunate because it does not encourage the more valuable mesophyllic fungi to thrive and this is why the secondary stage, that of breaking down the cellulose material and the making of the mature compost, takes a long time. We found that if the temperature was artificially kept in the mesophyllic range, we could obtain a much quicker breakdown of cellulose materials and make for quicker maturity in the compost. The artificial means employed were much more frequent aeration and turning and spraying with cold water, both to keep the temperature down and to keep moist conditions. It will be appreciated that if the temperature is allowed to rise, this does not only discourage fungi but also desiccates the compost which itself kills fungi.
The result of this finding is to encourage the writer to believe that there is no need to have a complicated composting plant because there is no real advantage in hastening the first bacterial - stage, since even if one does so, one does not get mature compost appreciably sooner, since the maturity of the compost is dependant on the second or fungal stage. However quick the finalising of the first bacterial stage, a second treatment by retention in stockpile is necessary and the economics of the plant depend upon the length of the total retention, both in the plant and in the stockpile. We, therefore, now recommend simple Windrow Composting. Our recommendation is supported by work done at the University of Savannah, Georgia and elsewhere in the States, as well as the much greater experience in Holland where the methods of composting are simple actions consisting of
The economies depend upon the efficiency of and low labour required in the primary treatment of separating and pulverisation and we believe that our ballistic/seperator/pulveriser which will accept all the refuse without pre-sorting and will automatically separate this into compostable and un-compostable parts is a very considerable advantage over any other method. What is required is a system, which will dispose of as much of the refuse as possible and certainly almost 100% of the household refuse. With other methods of mechanical treatment, items such as television sets, small perambulators, etc., have to be removed from the picking belt and dealt with separately. These are bulk items and are a fair percentage of the total refuse. In most methods of mechanical disposal these are not disposed of except by such separate treatment as the forgoing, whereas our machine will accept these items and will reduce them in bulk just as it reduces the bulk of the rest of the refuse, without extra hard work. It is because of these characteristics that we can say that our pulveriser will accept and dispose of almost 100% of the refuse. We have put a cylinder head in our machine and it was rejected through the reject shute without doing any damage whatsoever to the machinery. Our machines must have accepted hundreds of 7lb. weights, hammer-heads, old electric irons and items of this sort without damage.
This primary section of pulverising, receiving and sorting can be provided on its own and the pulverised refuse will rot down in heaps and become compost. To produce good compost from this, some turning and some further screening or pulverisation is desirable. Not all of the material will be rotted down because of the fermentation will stop due to lack of moisture. It will not stop due to lack of air that no smells are produced, but it is because of the lack of moisture that the fermentation is not complete. One can only add sufficient water or other liquid (sewage sludge) to complete the fermentation if one is willing to turn and aerate any refuse moistened sufficiently but complete fermentation will become anaerobic and produce H2S if it is not kept aerated sufficiently to avoid this.
The composting section can be elaborate or simple, but normally we would recommend that the pulverised refuse is mechanically fed into the Windrows and mechanically turned as necessary by an Athey Travel Loader, which is a well known and proven piece of standing equipment. This will certainly compost the refuse extremely well and is able to treat it by passing it through a secondary pulveriser carried on a trailer behind, so that it is ground as finely as is required by the demands of the particular town. An Athey Travel Loader has the further advantage offered by its ability to turn the refuse sideways, of automatically passing the refuse to a stockpile area or can feed it into lorries for transportation to farms to further long term stockpile areas or a bagging plant. The fact, it can deal with it as required with as little handling as possible.
The forgoing may well seem unorthodox but we would like to emphasise that far and away the greatest experience in the world is of V. A. M., The Dutch Composting Organisation, who have much more experience than anybody else and experience over many more years.
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