Septic tank;A device For treatment of domestic sewage .

Septic tank. Apparatus used for wastewater treatment . In it, the physical-chemical separation and transformation of the organic matter contained in these waters is carried out. It is a simple and cheap way to treat wastewater and is indicated (preferably) for rural areas or residences located in isolated areas. However, the treatment is not as complete as in a sewage treatment plant.


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  • 1 Tank function
    • 1 Hydraulic and bacteriological treatment
  • 2 Forecasts of use
  • 3 Environmental protection
  • 4 Sources

Tank function

  • First section: The septic tank consists of two compartments, in the first, the effluents are degraded and solubilized by the action of anaerobic bacteria ( unicellular organisms), the diluted solids are separated from the liquids , with gas evolution , this process occurs with decantation and accumulation of organic matter .
  • Second section: The effluent comes into contact with the airand the aerobic bacteria act , after this process, it is assumed that the pathogenic germs are eliminated and the waters can be evacuated after about six to ten days, without danger to the environment .

An important element in these tanks, from the constructive point of view, lies in the need for the tubes to drain directly towards the bottom inside the liquid that accumulates, to prevent the mixture from beating. And so do not promote oxygenation, since at that stage the most important thing is the action of anaerobic bacteria.

Septic tanks may have bacteriological filters that help clean sewage. The dimensioning of the wells depends on the type of water to be treated and the contributions, which depend on the family nucleus.

Hydraulic and bacteriological treatment

  • Primary Treatment; In this process, the solidsare separated from the liquids by sedimentation and in the background the anaerobic bacteria act , which feed on organic materials , which are broken down through the enzymes , with release of ammonia (NH4 +), with penetrating odor , being able to affect the eyes ; then oxidized and nitrites (NO2-) are obtained , this gas in concentrations greater than 0.01 mg / l warns of the presence of biological activity that can be harmful; The action of bacteria allow the release of nitrates(NO3-) that with values ​​of about 45 mg / dm3 shows the existence of organic decomposition, at the end of the process the residues are mineralized and crystallized. The mud or silt, accumulates at the bottom of the well and decreases its volume considerably, this whole process usually occurs in a period of about three to five days.

The process of bacterial action is important and is required in stages as follows:

  1. In the first stage of putrefaction, the complex organic compounds are divided into simple compounds, for example in ammonia ( NH4-), carbon dioxide ( CO2 ), sulfuric acid ( H2SO3 ).
  2. In the second stage of oxidation, it is the one where oxygen fixation occurs , producing volatile gases and nitrates (NO-3), until the stabilization of the organic fuse. In these processes unpleasant odors occur.
  • Secondary Treatment; It occurs due to bacterial action and is intended, among others, to remove the biochemical demand for oxygen remaining in the well, where the water comes into contact with anaerobic and aerobic bacteria, clarifies, so the resulting effluent will be less contaminated and the protecting the environment. There are different criteria for these processes, but the most accepted is that in the pits the process should not be ventilated because that delays the process of stabilization of organic matter from domestic waste.

Forecasts of use

The operation of a pit is more effective depending on how long the water used in it remains , so it should be made as large as possible. There is the possibility of accelerating the process of oxidation of organic matter by bubbling air through the waters contained in the first chamber, by means of a pump, to accelerate aerobic digestion . This device is used in large installations, for several houses grouped and isolated from sewage systems , already forming a small treatment plant.

Other provisions should also be taken to help this end. Rainwater should never be poured into the pit, but directly into the ground, since they are clean waters. It is a good measure not to take to the pit more than the fecal waters themselves (those coming from the toilets) as well as those that drag organic waste (kitchen), and not the other domestic waters (soapy waters of baths and toilets or cleaning ), which must be taken directly to the trench or filter well, without the need to treat them in the pit, since it does not carry organic matter.

It is convenient to install a grease separator system at the outlet of the kitchen water and before the union of that duct with that coming from the toilets (better the closer it is to the house, to avoid the clogging of the drain pipes ) because the pit does not properly treat these products, unless it is a pit with oxygen bubbling . The separator must also be emptied periodically.

Environmental protection

According to environmental protection directives , these solutions are subject to regulation in the territory. Septic tanks should be checked and emptied with some periodicity (depending on their characteristics, location and design). This process must be carried out by specialized companies (poceros), equipped with the appropriate certifications and authorizations. The waste obtained must be processed in appropriate and specific facilities (such as sludge dryers and treatment plants), and the final waste must be disposed of in a manner regulated by the competent official bodies. There are currently adequately conditioned deposits; But this solution is not permanent, and may be modified by new municipal, autonomous or state ordinances.

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