Biodigester Septic Tank

The Biodigester Septic Tank is an anaerobic digestion system that treats sanitary sewage (feces and urine) from a rural residence where up to 5 people live. The treated liquid effluent that leaves the Biodigester Septic Tank can be used in agriculture as biofertilizer (soil application).

One of the advantages of the Biodigester Septic Tank is the use of effluents (treated sewage) in agriculture as a means to recycle water and organic and inorganic compounds (nitrogen, phosphotus, potassium, etc), which are absorbed by plants in their process of growth. From an environmental point of view, this is an excellent solution as it prevents the excessive use of commercial chemical fertilizers and also protects the environment (rivers, lakes, watersheds and soils). In a house with 5 people, the Septic Tank will produce around 90 liters of biofertilizers a day.

Embrapa recommends the following criteria to choose a place for installation:

- water in the property
- bathrooms with toilets and plumbed water
the rural estate has to be of permanent use (it cannot be a weekend or holiday property)
- the estate cannot be in flooded areas
- bovine manure available in the proximities (for monthly use)
- enough area for the use of the effluent: orchards, coconut groves, pastures, etc.

The recommendation is that fibercement or fiberglass boxes are used. As fibercement boxes are increasingly difficult to find in the market, other materials can be used. The boxes can be made of bricks provided that they are very well sealed and waterproofed. There are specific products in the market for such waterproofing.
In that case, consult a civil engineer. Polyethylene water tanks are not recommended because they are very fragile, deforming easily with the soil pressure and under high temperatures, which prevents them from being perfectly sealed. In fact, the manufacturers do not recommend them to be buried.

All the necessary materials (water tanks, pipes, valves, etc.) are easily found in construction material stores.

The Biodigester Septic Tank was projected to treat sewage from toilets with the application of bovine manure, which works as an inoculant (additive) in the biological process. The use of sheep manure was tested; however, it did not present the same efficiency as cow manure. Thus, in view of the current stage of research, we recommend the application of bovine manure once a month. Future studies could be made with other types, to expand possibilities.

If the maintenance of the Biodigester Tank is done correctly, that is, if a mix of 10 liters of water and bovine manure is added every thirty days, and if products such as soaps and detergents that kill the bacteria are not added in excess, unpleasant odors will not be emitted. Unpleasant odors are a sign of malfunctioning, and their cause has to be verified.

No, a system in good operation does not proliferate cockroaches, scorpions, or rodents that can transmit diseases. It is important that the last tank, where treated effluents are stored, is well closed, in order to prevent the proliferation of mosquitoes within.

No. The effluent must only be used on the soil, in crops in which the liquid does not come into contact with the food.

Filter Garden

The Filter Garden is a technology adapted by Embrapa Instrumentation whose purpose is the treatment of domestic sewage characterized as gray water, that is, liquids from sinks, tanks, showers, washing machines, kitchens and others that are rich in soaps, detergents and fats. The sewage from toilets are treated by the Biodigester Septic Tank, which are biological reactors that can be easily built and that generate organic fertilizer at the end of the process.

Experiments led by Embrapa pointed to an efficient removal of organic substances through the interface between microorganisms with the roots of aquatic plants (macrophytes), which are fully adapted to saturated aquatic environments. These elements are attracted to the organic compounds present in the graywater, ensuring efficiency in the treatment.

The most recommendable use of the effluents (graywater treated in the Filter Garden) is the irrigation of gardens and plants in the rural property, as a complement and not an exclusive source of irrigation water. Until the present moment, Embrapa has not conducted any kind of research regarding the reuse of such water for fish farming or residential use. 

It is possible to use the Filter Garden jointly with the Biodigester Septic Tank, receiving the sewer treat to this last one. However, the best use of the biofertilizer generated by the Septic Tank is in farming, as it is a compost with high nutritional properties (nitrogen, phosphorus, potassium, organic matter) that will improve the performance of agriculture in the place it is applied.

Embrapa Chlorinator

The Embrapa Chlorinator is a very cheap, easily installable and simple technology to chlorinate the water from reservoirs (water tanks) in rural residences. It can be assembled by the residents themselves, with materials found in construction material stores. Its main benefit is that it disinfects the water used in the house, promoting health.

Applying chlorine in the recommended frequency (1x day) and dosage (1 spoon of granular chlorine) is essential. The chlorine concentration in the water decreases with time, hence the need to add it to the reservoir every day, even if the whole tank volume is not used. In that case, even if a small overload in the water tank's chlorine concentration occurs, there are no consumption-related health issues. Occasionally, there can be alterations to the water taste, which can be eliminated with small commercial activated carbon water filters, if that is the case. The benefits from the ingestion of chlorinated water, even with a slight chlorine taste, far exceed the health problems related to contamination.

No, it does not, because the chlorine concentration stipulated for domestic consumption (0.2 to 2.0 mg/L) does not interfere with the microbial activity in the septic tank.

The microorganisms that cause diarrhea, verminoses, and other diseases are microscopical, that is, they are not visible to the naked eye. Even thought the water does not taste or smell bad, it can still be contaminated, a common situation in rural wells.

The advantage of the chlorinator is the disinfection of all the water consumed in the residence, which includes water for showers, toothbrushing, and other uses. By using it, the risk of residents' forgetting to put the hypochlorite in their water is eliminated, and all the water in the residence will be germfree.