The ever-increasing contamination of soil and water through sewage systems poses a number of serious problems. Soils and wells are being contaminated by wastes reaching the soil and through open cesspools and leaking sewers. More and more lakes, rivers and coastal waters are being similarly contaminated. The absence of effective treatment plants results in enormous increases in contamination.

Sufficient treatment based on present methods requires extensive and costly transportation and treatment, including utilities, vehicles, equipment, buildings, land, and labor. High capital and operating costs required for this process indicate to some degree why it is impossible to solve the problem of public cleansing even in cities.

In most common waste disposal plants, wastes are mixed with water. This requires relatively large quantities of clean water just to serve as a transportation medium for the wastes. In sewers the wastes are transported after mixing with about 100 times their volume in water. This system is not practical, especially in areas with a restricted fresh water supply. Yet it has been considered as the only seemingly usable system as far as cities are concerned.

Simple treatment plants do not provide adequate sewage treatment but merely separate the solid wastes from the liquid. Efficient treatment plants, such as sludge and refuse incinerators, are being built in cities but are too costly for use in all areas where effective treatment plants are necessary. In certain communities it is difficult or impossible to provide sewer systems and central treatment plants due to the elevation of houses or the type of terrain, such as in very hilly terrain.

There is great need for simpler, yet effective, processes and plants which do not require transportation or complicated treatment. Because sewage with large quantities of water is difficult to treat, excreta, animal wastes, and other unsanitary materials should be prevented from entering sewers. An experimentally-tested process to achieve an aerobic biological change in organic wastes is described here. The key to the process is that wastes are deposited into a naturally-ventilated chamber. They then move by gravity from this chamber into a second chamber. The speed of movement is chosen so that the wastes are substantially decomposed as they reach the second chamber.

A tank (1) (see figure 1) of impervious material such as concrete or plastic is divided by vertical partitions (5,6) into two or more chambers (a,b,c).

The chambers are connected through ventilation holes in the partitions (17) and to the outside air through air vents (16) and a vent pipe (18) which extends above the roof of the building. The partitions do not reach the bottom of the tank but leave open flow passages so sized that, with the slope of the bottom, a suitable downward movement of the wastes occurs.

It is possible to achieve with this arrangement an aerobic biological change in wastes of all kinds, such as excrement and refuse, with a first?class manure as an end-product. This is all done without mechanism and without the addition of chemicals or water.

Depending on the desired capacity, this arrangement can be built in small or large units connected directly to the house or building from which the wastes originate, such as homes and auxiliary buildings. It serves as the toilet, as garbage container, as the apparatus for biological conversion, and as collection and storage place for the converted wastes (compost) (see Figure 2).

Because this system is completely independent of transportation or other auxiliary equipment, the only costs are for the initial construction. These costs are very minute compared to high-performance treatment plants connected to tight sewer systems.

The invention is primarily used in areas where no sewage treatment plant is available but also in areas where leaking sewers exist that contaminate the soil. The system is further usable in all cases where transportation and disposal of wastes, refuse, and excreta pose practical or economic problems.

Most of the tank is below ground level in a firm, well drained sub-soil. When the tank adjoins a building, it will be placed near an outer wall of the building and entirely or partially beneath the floor. If used in a house or auxiliary building, it will usually have two receiving chambers, one of which is connected to the toilet.

The air entrance (16) and vent pipe (18) are covered with fine wire screens to keep out insects or other vermin. The illustration also shows several inverted U?shaped conduits (19) in the bottom of the refuse chamber. These conduits, which connect partitions 5 and 6, run essentially parallel to the bottom of the tank in its longitudinal direction. They permit a larger amount of air to reach the refuse in the lower portion of the center chamber. This is particularly important in installations with deep refuse chambers in which the wastes are heavily compressed. As previously mentioned no chemicals such as chlorinated lime should be added to the tank because the bacteria needed for aerobic decomposition would thereby be destroyed. No water should be added as it has been shown that normal moisture of the wastes is suitable for the conversion process. Wastes of highest moisture content are added in the excrement chamber. Urine, which represents the major part of moisture in excreta, is spread on the dry mass in the refuse chamber. There is no free moisture in the storage chamber. Rich bacterial cultures developing in the mixture of excrement and refuse provide extremely rapid decomposition, considerably faster than with refuse alone. Decomposition occurs mainly in the refuse chamber. Many factors are involved in planning an installation as discussed below.

The volume of excrement is a small part of the total waste volume from a household. The first chamber should be large enough so that the contents use only a small part of the tank depth. This keeps air passages between the excrement and refuse chambers open. In initial use, it is recommended that first a layer of garden wastes or soil and kitchen wastes be added as this will absorb the moisture from the feces.

Garden refuse or soil add the important nitrate bacteria. These increase slowly but must be present in adequate numbers later so that a complete change of the ammonium carbonate into ammonium nitrate occurs.

The vent pipe must be fairly high (comparable to a chimney) especially in hemmed-in locations.

The tank can be advantageously built entirely in the house (cellar). When located in the cellar there is no extreme cooling in winter. If the installation permits, the vent pipe can be led into the chimney.

In the illustration of a tank for a normal household, the length of excrement chamber can be so chosen that it may be connected to the building. The inside width can be about 1 m for a tank of smallest practical size.

The top of the refuse chamber should be close to the ground level to permit easy access to the interior. The refuse chamber volume is about 1.5 m3. Dimensions of the chamber may be varied - the primary requirement being a good air flow to the refuse mass. If the refuse chamber is deep, too much pressure exists and insufficient air is provided through the U-shaped conduits. These are inserted to form a grating running parallel to or slightly less inclined than the tank bottom (see figure 1). The inner depth and width of the conduits should not be over 5 cm and the distance between them should be about 15 cm. Screens over the conduit openings should prevent clogging when the layer of excrement reaches them.

The storage chamber should have a relatively shallow depth and large surface area which is exposed to the air. Also, the volume of this chamber should be sufficiently large to permit long-time storage, such as a year. The compartment length should be at least 1.5 m for ease in removing the contents.

Vent holes in partitions should be distributed over the entire surface area of the partitions. The upper vent holes should be relatively large for adequate air circulation in the tank and aeration of the upper layer of refuse. Yet the length of air passages should be no larger than necessary to prevent stoppage by wastes. The partitions can be formed by perforated plates or screens. The one between the excreta and refuse compartments should be only far enough above the bottom to prevent the refuse from taking up too much room in the excrement compartment. Yet there should be a certain mixing of the various wastes which has a favorable influence on moisture distribution, porosity and aeration.

The partition between the refuse and storage compartments is designed to prevent non-decomposed wastes from falling into the storage chamber. The opening at the bottom is of such height that only the refuse that has been converted can enter the storage compartment. In figure 1 this height is about 30 cm. The height of opening can be adapted to the volume and depth of the refuse compartment and the length of the storage compartment.

Aeration of the wastes is of primary importance in the decomposition and determines the planning of the tank and compartments to a great degree. Sufficient care must be taken so that the area in contact with the flow of air is large enough ? achieved best with shallow depths and large surface area of the contents. This is especially critical in the excrement and storage compartment. If desired, the refuse chamber can be relatively short and deep because aeration is provided through vent holes in the partitions and through the air conduits.

The tank can be compared to a furnace. The excrement and refuse chambers are equivalent to the combustion chambers; the storage compartment is equivalent to the ash chamber; and the vent stack is equivalent to the chimney. When parts of the tank walls and cover are of translucent material, the heat from the sun's radiation increases the conversion process.

The slope of the tank bottom provides continual movement of decomposed refuse to the storage chamber as additional wastes are added to the other two compartments. When more refuse is added, the lower layer is compressed and decays. The waste volume is reduced to a fraction of the original during this process. When the depth of garbage in the refuse chamber is great, the material is then pressed through the opening into the storage compartment independently of the bottom slope. Even if the bottom slope is insufficient, there occurs a state of balance. Excess slope results in inadequately decomposed wastes entering the storage compartment and accumulating in the lower part. This is obviously difficult to remove. A further disadvantage is that the moisture content easily becomes excessive and the oxygen content too low such that anaerobic processes occur in the lower layer. Experiments showed that the bottom slope must be between 1:4 and 1:3 (i.e., 14° and 18.5°). Even minor deviations from this range causes improper operation.

The bottom slope need not be uniform lengthwise nor is it necessary that the floor run evenly. The profile can be curved or stepped. In one example the upper part can be sloped 1:3, the middle 1:3.5, and the lower 1:4.

When the total tank length is about 3.5 m and the slope is about 16°, the elevation difference of the bottom is about 1 m. The depth of the excrement chamber is then at least 1-1.5 m.

The tank cross-section need not be rectangular but can be made of cyclindrical elements. It is also possible to build the unit in one piece using a single concrete pouring or prefabricated parts. These changes permit variations in form and size. As the layout of the tank is considered, the various parts can be changed to conditions and type of usage. It is possible to build more than the three compartments illustrated. If only two are provided, one serves as the receiving chamber and the other for storage.

If the plant is at a central point for biological conversion of organic wastes, then it will not be directly connected with a toilet. A major advantage is that the process is fully automatic and the end product contains large amounts of humus-forming substances.

This composting process and its plans (patent pending) were successfully tried and improved by the author over several years. It has created interest among Swedish authorities and will be closely studied soon.