Trattamenti Secondari Acque Reflue

Secondary Wastewater Treatment

Water purification, "managed" by microorganisms

COD, BOD, nitrogen and phosphorus undergo a net removal process through secondary treatments. Aerobic and anaerobic bacteria are the active player in this biodegradation, which returns an effluent ready for finishing tertiary systems. Biodiscs and other compact plants show great ease of operation at this stage.

Framing: the secondary treatments

Secondary wastewater treatments follow mechanical scouring operated by processes such as screening, de-oiling and desanding. They can also be called biological treatments, since they involve microorganisms such as bacteria to degrade organic pollutants. In fact, at this stage, a simple physical process would not be sufficient to remove COD, BOD, nitrogen and phosphorus: the goal, precisely, of biological degradation in this section of civil sewage treatment plants (maintaining the “minimum” ratio of 100:5:1 of C:N:P).

And we speak of civil water purification precisely because it is in this area that we find the now established sequence of primary, secondary and tertiary treatments in the plants: this in compliance with national and European regulations. In the industrial sphere, it is better, however, to use the definition of “biological treatments.”

It is, however, a decisive stage of water purification, since it aims to greatly reduce the pollutant load of the effluent by removing substances that are particularly harmful to health and the environment. This, on the other hand, is also the phase that prepares tertiary treatments and is responsible, therefore, for taking advantage of high-performance and reliable technologies so as not to “stress” downstream systems with an excessive load of pollutants.

These are the most common types of secondary treatment.

  • Anaerobic digestion processes. Here the action of bacteria that feed on organic matter and live in the absence of oxygen is exploited: this is typical of Imhoff pits and anaerobic digesters.
  • Aerobic digestion processes. As in the previous case, it relies on the degradative action of bacteria, but they are stimulated precisely by oxygen (lacking in anaerobic digestion): thus they feed on organic matter and metabolize pollutants. This is therefore referred to as “aerobic bio-stimulation”.
  • Phytodepuration. This is a decidedly peculiar process that mimics not only biological, but also physical and chemical treatments typical of aquatic environments: in fact, it involves specific plants, with high capacity to absorb effluent.
Trattamenti Primari Acque Reflue

MITA Water Technologies solutions for secondary treatments

We mainly propose three technologies for this key stage of wastewater treatment-all of which are easy to use and have very low installation and operating costs.

  • Lamella-pack decanters. This technology can be included in this range as it is often useful immediately upstream of true biological treatment (such as biodiscs): in fact, decanters treat most non-emulsified oils and ease the task for downstream solutions.
  • Biorulli® rotating biological contactors or biodiscs. Extremely simple machines for biological oxidation, composed of a large number of plastic discs on which bacteria can grow, and operated by an aerobic process precisely because of these microorganisms.
  • Biocombi compact plants. This is the synthesis of secondary (i.e., biological) treatments and the tertiary treatments allowed by MITA free-fiber cloth filters. A very compact and extremely efficient solution for small communities or in the absence of large installation spaces.

Benefits with MITA's secondary treatment solutions

  • Compact and modular solutions, with little ancillary work required for their containment.
  • Extreme simplicity of construction and use.
  • Low maintenance, low operating costs.
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Case studies of secondary treatments