What treatments for wastewater?

wastewater treatment

What to do with our water once it is use? This is what you will know here

Water is use daily for both domestic and industrial purposes. What then becomes of this so-call “waste” water? How are they collect? What paths do they take to get to the pollution control station? What treatments do they receive in order to clean? To understand everything about the wastewater treatment cycle before it returns to the natural environment or to live a second life by being reuse, follow the guide.


Wastewater treatment is an issue of environmental quality and the quality of water resources. Since the water law of January 3, 1992, all residential buildings must connect to a collective sanitation network or have an on-site sanitation system.

The distribution between collective sanitation or individual sanitation is a decision taken by the mayors or the presidents of public inter-municipal cooperation establishments (EPCI), depending, in particular, on urban density. Sanitation is mainly carry out collectively and the non-connect dwellings are generally single-family houses, rather locate in rural areas.

Collective or autonomous, these sanitation systems require law are intend, initially, to group and carry out the evacuation of wastewater (collection) then to eliminate the pollutants (purification). by treating them before they are release into the natural environment.


The transport of wastewater in the pipes of a sewerage network, otherwise call”collectors”, is generally done by gravity (under the effect of weight) but can sometimes be done by discharge, under pressure, or under pressure. depression. If the configuration of the land does not allow a satisfactory flow of the collect water, we then have recourse to various processes (pumping and lifting stations) to facilitate their transport.

The protection of the network against fouling and corrosion is ensure in the first place by the pretreatment of certain industrial water before its discharge into the network (screening, sieving, grit removal, degreasing). Various structures, upstream, protect it against the intrusion of undesirable materials: let us quote the “grease boxes” on the connections of restaurants or the hydrocarbon separators in service stations or in airports.

Flow regulation, when wastewater and rainwater are mix, is provide by equipment intend to temporarily retain large and sudden inflows of water. It makes it possible not to disturb the proper functioning of wastewater treatment plants and to limit the risk of flooding.

Also read: Waste management services


While it is relatively easy to predict and control the volumes of domestic wastewater, the situation is quite different with stormwater. There are two types of collection networks:

Unit networks

Drainage in the same pipes for domestic wastewater and rainwater. These processes combine the advantages:

  • Economical: a single network to build and manage
  • Simple: by definition, any connection error is exclude

However, they require taking into account, in the design, the sudden variations in the flow of rainwater and the sizing of collectors and water treatment structures.

Separative networks

Collection of domestic wastewater and rainwater in separate networks. This system makes it possible to:

  • better control the flow and its concentration of pollution
  • better adapt the capacity of wastewater treatment plants
  • avoid the risk of wastewater overflowing into the natural environment when it rains.

All these pipes permanently transport water laden with microorganisms and micropollutants. It is thus inevitable that they clog. In addition, there is a continual threat of erosion and corrosion. To fight against all this, the pipes are subject to periodic inspections and cleaning.

Maintenance of ancillary structures includes, in particular, the cleaning of manholes, maintenance of retention basins, storm overflows, wastewater lifting stations and connections. Efficient operation of the network presupposes rigorous and permanent maintenance work by qualified personnel from the sanitation service.


As state previously, the purpose of the biological treatment of wastewater is to decontaminate it sufficiently so that it does not alter the quality of the natural environment into which it will ultimately be discharge.

The design of equipment relate to wastewater treatment can integrate that of rainwater:

  • Treat in a plant involving the use of equipment to cope with sudden increases in flow cause by storms, and treatments adapt to the particular composition of the rainwater
  • Store in retention or infiltration basins so as to be able to spread the treatment over time.
  • Treat in settling ponds: this method assumes permanent maintenance, in order to avoid the development of bacteria in the settle sludge and unpleasant odors.

Apart from these techniques, it remains that one of the most effective means of managing rain pollution is the implementation of alternative solutions (drainage pavements, infiltration ditches, etc.). These solutions are base on the use of preventive techniques which aim to limit soil waterproofing and water runoff in order to reduce the contribution of rainwater to the networks that collect it.

Vegetate discharge areas

The vegetate discharge zones are an additional means of protecting aquatic environments. They are locate at the outlet of the wastewater treatment plant. It consist of meadow, basin, or ditch.improve the quality of discharges (suspend solids, phosphorus, nitrogen, germs, metals, pharmaceutical residues, pesticides, etc.).

The vegetated discharge zones can also allow the conservation of biodiversity, the creation of educational landscape space.


From the evacuation of wastewater to its discharge into nature after purification, intervene technicians whose mission is to fight for the protection of the environment (biologists, researchers, chemists, operators of purification plants, sewer workers, electromechanics, IT specialists, laboratory workers, etc.).

The increasing complexity of wastewater treatment systems in wastewater treatment plants demands a high level of competence on the part of the personnel. Water treatment stations indeed require multiple knowledge (in hydraulics, biology, chemistry, mechanics, electricity, electronics, etc.). Likewise, the installation, maintenance and renovation of collection networks require very specific skills and great rigor, particularly in terms of safety.

In addition, specialize companies, in particular, all have their own research centers. They devote large sums to the development of new treatment processes. Research is also focus on developing decontamination channels adapt to the local specificities of each sanitation system in order to optimize its efficiency and performance.

Another area of ​​research is the elimination of various nuisances cause by wastewater treatment. The reduction of bad odors (deodorization), the reduction of noise and the integration of a water treatment plant into the landscape also contribute to the protection of the environment.

Finally, the treatment of sludge represents an important project insofar as its landfill is almost prohibite, which implies the implementation of processes allowing to eliminate it or to recover it.


Now that you know more about how wastewater treatment works, it’s time to look at the user question.

Obligations and connection conditions

Connecting buildings to public collection networks is a legal obligation provide for by the Public Health Code. If this connection obligation is not complied with within the set deadlines, the user runs the risk of being impose a financial penalty: his sanitation fee may be increase by the decision of the municipal council, up to a limit of 100% of its initial amount. The municipality, after formal notice, may automatically carry out the necessary work, at the owner’s expense, even on private property.

“The works necessary to bring wastewater to the public part of the connection are the exclusive responsibility of the owners”
Public Health Code – Art. L. 1331-1

If the building is serve by a unitary network, wastewater and rainwater must be brought together to reach the public collectors. In the event of a separate network, it is the owner’s responsibility to evacuate rainwater (in particular from gutters) and wastewater separately.

Discharges prohibite

The network is not intended to receive domestic waste. Also, the user is require to observe certain precautions. The regulatory texts on sanitation prohibit the disposal of any substance or product presenting a risk for the maintenance staff of the networks, likely to degrade the sanitation facilities or to hinder their proper functioning such as hydrocarbons, acids, used oil, cyanides, toxic or flammable substances, drugs, sulfides, etc.

Likewise, discharges from any professional activity carried out in a residential building must be subject to a specific treatment, if their composition differs from that of domestic wastewater.

Wastewater treatment at the expense of the consumer

Pakistan law implements the “polluter pays” principle for all water users. This amounts to saying that users must participate in the protection of the resource since they participate in its pollution by the discharge of their wastewater. Whether he depends on a collective sanitation network or uses an autonomous sanitation installation, the user bears the cost of sanitation at the cost of the service provide.

The payment of the sanitation service by the user is institute by the General Code of Territorial Collectivities: it is cover by the “sanitation fee”, the amount of which is set by the municipality or the responsible inter-municipal body.

Sanitation fee & water bill:

  • Corresponds to the “collection and treatment of wastewater” section of the water bill.
  • Calculate on the basis of human consumption of drinking water and sometimes also includes a fix part which corresponds to the subscription.
  • Due to any user locate in a collective sanitation zone, whether or not he is connect to the network, as long as there is a network and is connectable to it.

In addition, a charge called “pollution control” is collection behalf of the water agencies. It is particularly allocated to the financing of collection and treatment equipment. In 2007, the “sanitation” part represented on average 37% of the water bill.

Spotlight on the level of Pakistan equipment

  • 82% of Pakistan dwellings were connect to a collective collection and sanitation network. France has 19,750 wastewater decontamination stations
  • Almost all municipalities with more than 10,000 inhabitants have a wastewater treatment plant.
  • 3.2 billion cubic meters were bill in 2012.
  • For stations with more than 2,000 population equivalent, the pollutant load has been reduce by 92% on average.
  • The Pakistan Biodiversity Agency made a finding during the 2018 Assises. 18% of sanitation services would require an improvement in their assets.

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