How the wastewater purification process takes place

01 February 2023

What are waste waters? 

"Waste water" or "wastewater" is water used in human, domestic, industrial or agricultural activities, which for this reason contains organic and inorganic substances that can be harmful to health and the environment. Therefore, after use, this type of water cannot be discharged directly into the environment (soil, rivers, lakes and seas) without first undergoing a constantly monitored purification process.
The wastewater treatment process must be carried out in accordance with Italian and EU regulations, which provide for the measures necessary to achieve or maintain the good quality status of surface or deep waters, protecting them from pollution.

What is a water treatment plant?

"Wastewater treatment plants" are facilities designed to treat wastewater, that is, the specific process through which the various processes of decontamination of water from civil and industrial discharges take place. 
The purification of waste water takes place in several stages, during which toxic substances are removed from the liquid waste, transforming it into sludge. The sludge, which is still not completely free of harmful substances, undergoes further special treatments. Only then can the sludge be disposed of in special landfills, used in agriculture, or sent to composting plants. 

What are the wastewater treatment processes?


Wastewater treatment processes include:

Fine screening or screening systems

Initially, the dirty water is mechanically filtered through automatic or manual fine screening or sieving systems to rid it of large and small solid debris: from pieces of wood to the garbage that is produced every day (plastic, Q-tips, butts) and that should never be thrown into the water or toilet. 


Process of sedimentation or desanding

At a later stage, smaller debris, such as sand, soil, oils and grease, must be filtered out and removed by a process of sedimentation, or desanding, which involves bringing sedimentable bodies to settle to the bottom of the sedimentation tank or come in flotation in the case of oils and grease.


 Oxidative process

Only at this point does the actual water treatment and purification take place, that is, the cleaning of pollutants through an oxidative process. Biological oxidative treatment consists of the biodegradation by microorganisms of all organic substances in the water to be purified into simpler, environmentally harmless substances. This treatment is nothing more than an extension of the self-purification that takes place spontaneously in waterways, operated in the case of the treatment plant, in an environment in which certain optimal conditions are artificially maintained for the purpose of concentrating and accelerating the process taking place.

Several techniques can be used for biological oxidation, of which the most traditional ones are:

  • Active mud systems, currently the most widely used systems due to their high efficiency (>90% BOD removal). They are suspended biomass systems as they are characterized by the presence of free moving flocs within the liquid mass


  • Percolator filter systems: a biomass adhesive systems, in which the bacterial biomass grows by remaining ashesive to a surface, in particular, percolator filters are fixed support systems through which the slurry flows


  • Biodisc purification plants are also biomass-adhered systems on mobile supports, where the support moves semi-immersed in the slurry


  • MBBR (Moving Bed Biofilm Reactor): this innovative technology is an evolution and improvement of the traditional activated slurry plant. Basically, it is a suspended-mass biological plant in which the fill material (carrier), consisting of rigid plastic material with high specific surface area (up to 500-600 sq m/mc), is placed inside the MBBR reactor and acts as a support for the development of microorganisms. This type of plant can operate at much higher loads than the conventional Activated Sludge plant and is therefore particularly suitable for the treatment of highly polluting industrial wastewater.


  • MBR (Membrane Biological Reactor): it's a biological water purification system and consists of a combination of the traditional activated sludge purification process and a membrane filter separation system that replaces the normal secondary sedimenter. This process allows for a higher concentration of activated sludge in the biological reactors than conventional plants. Working at a high concentration of biomass therefore allows for a very high purification yield.


  • SBRs (Sequencing Batch Reactor) represent discontinuous-flow biological treatment systems, consisting of a basin in which you and actuators connected to a microprocessor that also manages the feed pumps, sludge purge and eventual emptying pump.


Process of secondary sedimentation

The last stage of the wastewater purification process is Secondary Sedimentation, which follows the oxidative stage and is responsible for separating the biological sludge from the rest of the clarified or treated effluent. At the bottom of the secondary sedimenter, the settled biological sludge accumulates, while the clarified effluent skims from the surface.


Process of Disinfection

The clarified or treated effluent will be sent for further treatment such as Disinfection to kill all pathogens present in the purified effluent (bacteria, funges, viruses) or discharged directly. The sedimented biological sludge (sludge line) can take various paths. It can be pumped back to the oxidation tank. It can be partially pumped to the first sedimenter to improve the characteristics of the primary sludge. It can be sent to sludge treatment aimed at disposal according to law.


The domestic and industrial wastewater treatment plants of IDRO Group

Both civil wastewater treatment plants and industrial wastewater treatment plants are systems that collect large quantities of water and, through treatment the biological systems outlined above are able to return water that is clean and has organoleptic, chemical, physical and biological characteristics that comply with legal standards and allow its reuse for multiple uses.
Plants can be designed in response to specific industry needs and for specific contamination problems.  There are also compact, mobile container plants for wastewater treatment designed by Idro to purify water from conventional and unconventional sources where the quality of the raw water is unknown.

Idro Group can design and build various water purification, potabilization, recovery and reuse plants for each specific need. If you need more specific information regarding water purification plants or would like to schedule a meeting for a consultation, please fill out the form in the contact section. We will get back to you as soon as possible! 

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