Sewage Treatment Plants

Sewage Treatment Plants

 

1) Biological Sewage Treatment and Recycled Water Production Plant at Moni

The Biological Sewage Treatment and Recycled Water Production Plant at Moni began operations in 1995. It can handle up to 40,000m³ of wastewater per day and has the capacity to treat an organic load of around 16,000kg per day. The Plant produces treated water of excellent quality. Tertiary treated water is suitable for use in agriculture and industry and it is provided to the Water Development Department, which is responsible for its distribution.

The sewerage system contributes to saving water for use in agriculture since the water, which is disinfected at the end of the tertiary treatment stage, is suitable for agricultural and other uses. Through the re-use of the treated water, we conserve water in the reservoirs and aquifers.

Today, the Plant produces around 10 million m³ of treated water per year. This is expected to increase as new areas are connected.

Using Renewable Energy Sources

BIOGAS 

In addition to the re-use of water and biosludge, biogas is also produced for use in generating electricity and heat, thereby contributing to energy-saving.

Since 1 September 2008, the Board has operated two 311kV biogas generators for electricity and heating.

Biogas, resulting from the anaerobic digestion of biosludge, is collected in a 2,000m³ capacity gas holder. Τhe biogas produced in the sludge digesters is used as a renewable energy source, i.e. as ‘green’, environmentally friendly energy, to operate electricity generators. The heat created by the generators is used for heating the digesters, while the generated electricity, which today amounts to some 5,000kWh per day, is used to operate the Biological Sewage Treatment and Recycled Water Production Plant at Moni, reducing by 35%-40% the daily consumption of electricity provided by the Electricity Authority of Cyprus that is required to operate the Plant.

At the same time, the generated thermal energy, which today amounts to around 4,000kWh per day, is used to heat sludge as an alternative source heating. Due to the controlled production of biogas, the level of pollutant emissions is extremely low.  

In this way, a significant amount of energy is saved and, at the same time, any additional environmental impact is reduced. On the basis of the Plant’s current operating levels, the amount of electricity produced by the biogas generators is approximately 4,500kWh per day, while with the expansion of the networks, this is expected to increase to 5,000kWh daily.

The Board secured the funding of the initial capital expenditure from the Ministry of Energy, Commerce & Industry’s Energy Department’s funding programme the use of RES. The cost of the investment was around €2 million and the funding €320,000.

BIOSLUDGE

Treated sludge (biosludge) produced through sewage treatment is suitable for use in agriculture, forestry, gardening, landscaping and mining (improving the soil to reintroduce vegetation and revitalize greenery).

 

 

 

 

2) West Limassol Biological Sewage Treatment and Recycled Water Production Plant

The Plant stands on agricultural land within the administrative boundaries of the Municipality of Kato Polemidia inside the Sovereign Base Areas, away from populated areas and adjacent to the Rainwater Retention Lake. It is located some 500 metres from the 1st Limassol Industrial Zone and 1,200 metres from the nearest residential area in the Municipality of Kato Polemidia.

The contract for its construction was signed on 30 November 2018 with the Kruger A/S – Cybarco Limited JV consortium. Work began in January 2019 and construction work was completed in September 2022. The Project was included in the Programming Period 2014-2020 for European Projects co-financed by the EU Cohesion Fund. The approximately €30 million Project was co-funded by the Government and the SBLA.

On 7 March 2020, the foundation stone of the West Limassol Biological Sewage Treatment and Recycled Water Production Plant was laid by the then President, Nicos Anastasiades.

The Plant, with a capacity of 13,000 cubic metres per day, serves Polemidia, Zakaki, Agios Spyridon and other areas of West Limassol. It also serves Limassol General Hospital, Limassol New Port, the 1st Limassol Industrial Zone and two major commercial developments: the City of Dreams Mediterranean integrated resort and the My Mall shopping centre. The Plant will eventually be capable of serving 65,000 residents.

The Plant is one of the most important infrastructure projects undertaken in the city and district of Limassol. It involves state-of-the-art technology and is of major environmental significance. Its design took into consideration the need to reduce noise and odour to a minimum or even zero and was based on the membrane technology used in tertiary treatment.

On 4 November 2023, the SBLA’s West Limassol Biological Sewage Treatment and Recycled Water Production Plant was officially inaugurated by President Nikos Christodoulides.

BUILDINGS

 

STAGES OF TREATMENT

Wastewater inflow (K.01):

Wastewater flows by gravity into the Plant from the highest areas and is pumped from the lower areas via the SBLA pumping station No. 6 which is located in the Lady’s Mile area.

Pre-treatment (K.02):

On arrival at the Plant, the wastewater undergoes pre-treatment, passing through two 6mm diameter filters and three 1.5mm diameter filters. Everything collected is compressed and placed in closed crates and transported to authorised areas. The wastewater is then transferred by gravity into two adjacent tanks for the removal of fat, grease and grit. These tanks are enclosed to avoid the leaking of any odours into the environment. The collected grease and fat are channelled into the digester (B.12).

Next, sand, grit and other heavier-than-water solids that settle are pumped into a sand-collecting channel, separated from the liquid area and transported in a closed lorry to an authorized treatment unit.

Lagooning (K.03):

The wastewater is passed by gravity from the pre-treatment stage to two adjacent tanks, enclosed to avoid the leaking of any odours. At this stage, the organic load is reduced by 20%-40% and that of suspended solids by 40%-60%. 

Biological Treatment (K.05):

The wastewater then overflows into two circular aeration basins through the separation drain, where two lines of sludge recycling also terminate. During the biological treament process, wastewater and micro-organisms are mixed together and remain in the two tanks with a controlled air and agitation rate. The degradation of the organic load is achieved through the correct conditions of temperature, oxygen and contact time. The tanks operate in aerobic cycles (with the presence of oxygen – nitrification) and anoxic cycles (absence of oxygen – denitrification).

Membrane Bioreactor Treatment (K.07):

From the aeration basins, the mixture of water and biosludge is passed by gravity through the separation drain into tanks where it is filtered by passing through the membrane bioreactor. There are three filtration lines via membranes within an enclosed system to prevent the leaking of any odours into the environment. These lines are used as a final filter in the production of tertiary treated water.

UV Disinfection (K.09):

The tertiary treated water from the membrane bioreactor is disinfected through the use of ultraviolet radiation, so as to fully inactivate any traces of micro-organisms.

Pumping Station for Irrigation and Emergencies (K.23):

The tertiary treated water, having been disinfected by ultraviolet radiation, is channelled into the reservoir of the Water Development Department (WDD), which undertakes its distribution for the irrigation of agricultural areas and the enrichment of the aquifer.

Sludge Treatment (K. 10, 11, 12):

The resultant sludge is thickened and treated by anaerobic digestion and dehydration. Dehydrated sludge, with a minimum moisture content of 25% after treatment, is placed in a 70m3 storage space and loaded onto a lorry, which transports it to an authorized unit.

Biogas (K.13, 15):

Biogas resulting from the anaerobic digestion of biosludge is fed into units that generate electricity and heat. The electricity is used to meet the Plant’s own needs while the heat is used to warm the sludge in the digester.

Chemicals Building (K.16):

This building stores ferric chloride, which is used to reduce phosphorus levels when needed.

Deodourisation System (K.17):

Deodourisation systems have been installed at every stage of the treatment process where there is a possibility of odours leaking, resulting in the minimum emission into the environment.

Renewable Energy Sources:

The Plant is equipped with 200kW photovoltaic systems, with a provision for this capacity to be increased by a further 100kW. Furthermore, the biogas produced is used to generate electricity and heat as mentioned above.

Electrical Equipment Building (K.20):

This building stores electronic panels, the backup generator and other electrical equipment.

Administration Building (K. 19)

The Administration Building contains the personnel offices and a control room from which the entire Plant is fully monitored. The Plant operates an advanced SCADA system, noise monitoring systems, an ultramodern laboratory and other cutting-edge technology.

The West Limassol Biological Sewage Treatment and Recycled Water Production Plant is one of the most important infrastructure projects undertaken in our city. It is undoubtedly a project that improves our quality of life, contributes to economic activity and promotes environmental protection.

Biological Treatment

The effluent from the Primary settling tanks overflows towards the secondary treatment system which consists of two aeration tanks and four circular secondary settling tanks.

The biological treatment is provided in an activated sludge plant where nitrogen, organic matter and part of the phosphorus are removed using the Bio-Denitro process. This process involves two interconnected aeration tanks where nitrogen is removed biologically in two stages – Nitrification and Denitrification. In the aerobic (oxygen present) phase ammonia is converted to nitrate. In the anoxic (oxygen absent, but nitrates present) phase the nitrate is converted to nitrogen which is released to the atmosphere.

Operation of the plant

The WWTP is a modern plant, which is fully automated and operated by only twelve persons: Plant Manager, Chemist - Assistant Plant Manager, Chemist Assistant, Electrical Engineer, three technicians, two workers and three guards on a 8-hours shift.

All operations are controlled via a computer-based SCADA system (supervisory control and data acquisition system).

The SCADA system provides a central overview of all the treatment plant’s functions and makes it possible to change process variables either locally or centrally from the control room or even remotely via a link through the internet.

Primary Water treatment

At the inlet to the treatment plant the sewage passes through mechanical (coarse) screens with a bar spacing of 10 mm. The screens retain large particles such as paper, plastic, pieces of wood and stones that may cause clogging, wear and tear of the pipes and pumps, or other problems in the following processes. The screens are automatically cleaned, the screenings passed through a compactor and conveyed to a container for disposal. From the screen all flows pass to the aerated grit and grease chamber. The sand and grit which settles here is pumped to a sand dewatering unit and from there to a container for disposal. Grease and oils that inhibit the biological process and cause obnoxious smells, clogging of the pipes, accumulation of sludge and foams in the aeration tanks, are scraped off and collected in a grease pit.

After the grit and grease chamber flows pass through fine screens with 5 mm bar spacing and then on to primary settling tanks. Screenings from the fine screens are handled in a similar way to those from the coarse screens.

In the primary settling tanks, the settlement of large particles is achieved in order to reduce the sewage load on following stages. The organic load can be reduced by up to 20-40 % and the suspended solids by 40-60 %. The settled sludge is pumped to the gravity thickener and subsequently to the digester.

Secondary Settling

Mixed liquor which flows from the aeration tanks is equally distributed into the secondary settling tanks where the water is separated from the biological sludge. The velocity is controlled to allow the activated sludge floc to settle out to the bottom of the tanks, whilst the surface liquor passes over the tank outlet weirs to tertiary treatment. Most of the sludge removed is returned to the inlet of the aeration tanks in order to maintain a sufficient quantity of sludge in the tanks for the biological process to operate effectively. A small percentage of the sludge is removed as excess sludge to the mechanical thickeners for further sludge treatment.

Sludge Treatment

Sludge is accumulated in the primary and secondary settling tanks as well as in the aeration tanks and the filter plant. It is removed and thickening takes place in the thickeners to increase the concentration of solid materials in the sludge.

From the thickeners the sludge is pumped to the anaerobic digesters. The digestion process of the sludge is achieved at a temperature of 35 oC over a minimum period of 18 days resulting in a further reduction of the organic load. The water is then removed from the digested sludge in special centrifuges and the dewatered sludge is collected and transferred for sun drying.

The proper management and disposal of the sludge produced at the sewage treatment plant of Limassol is under the administration of SBLA. The main concern of the Board is to ensure the optimum management in order to safeguard public health and the environment. 

SBLA has examined the potential use of the sludge produced at the Limassol sewage treatment plant by assigning experts to prepare a report about the applicability, capital and operating costs and environmental impact of a wide range of options for its treatment and disposal. This report concluded that the best way to utilise the sludge is either to use it as a fertilizer in agriculture or as a green fuel at the nearby cement factory. The produced sludge contains nutrients including nitrogen N, phosphorous P, and organic matter; which, when added into the soil creates favourable agronomic conditions for plant growth. 

The application of the sludge on agricultural land improves the physical, chemical and biological properties of soils which may enhance crop growth. The sludge used as a fertilizer in agriculture conforms with Directive 86/278/ EEC, the provisions for the control of water pollution and soil legislation no. 106(I)/2002 and the disposal licence no. 60/2008 of treated sludge disposal issued by the Ministry of Agriculture, Natural Resources and Environment of the Republic of Cyprus (MARNE). These rules and regulations are designated to avoid and restrict the pollution of the environment by setting a Code of Practice, specifying the sampling and analysis of the sludge and soil for heavy metals. The Code of Practice sets out requirements for keeping detailed records of the type of treatment, of the quantities of sludge produced, the composition and properties of the sludge, the quantities used in agriculture and the application areas. 

The use of the sludge as an alternative renewable, green energy source has been a very attractive solution for the cement factory. The use of sludge as a substitute of fuel results in the reduction of carbon dioxide emissions and reducing the foreign currency required for conventional fuels.

Biogas –Photovoltaics – Production of Green Energy

The Sewerage Board of Limassol- Amathus (SBLA) is a leader in the use of renewable green energy sources. Moni - Limassol wastewater treatment plant is the only plant in Cyprus which, in addition of the reuse of the treated water and biosolids, has, since October 2008, utilised the produced biogas as a renewable green energy source for the production of heat and electricity. This contributes to meeting the targets set by an EU Directive on energy production and in the reduction of greenhouse emissions whilst providing substantial benefits related to energy savings, environmental benefits, economical matters and social merits.

Biogas is generated from the anaerobic digestion of sludge. The annual quantities of gas produced are about 800,000 m3. The gas is collected in a gasholder of capacity 2000 m³. The Sewerage Board of Limassol - Amathus has installed and operates two biogas generators, each of 311kW capacity for the production of heat and electricity.  The electricity currently produced is about 4500 kWh and is used for the operation of the Moni wastewater treatment plant. This reduces by 40%, the daily electricity power requirement supplied from the Cyprus Electricity Authority.

The generators also produce 300 kWh of heat energy which is presently used to heat the digesters as an alternative heat resource. Due to the controlled production of biogas, the emission levels of pollutants (CO2) remain very low. In this manner, a considerable amount of energy is saved resulting in less damage to the environment.  At current plant operation level and current electricity rates, energy saving amounts to €20.000 per month, and as the sewerage system networks are expanded , savings will exceed €30.000 per month. The investment was also approved for a subsidy for the provision of renewable resources of energy by the Ministry of Commerce, Industry and Tourism. The cost of the investment amounts to approximately €1,800,000 plus the subsidy to €320.000.

An additional green power source is the production of energy from the photovoltaics installed at the roof of the chemical storage shed at Moni WWTP. The power produced is about 44kW and is connected to the grid.

Tertiary treatment

In the tertiary unit secondary treated effluent passes through layers of sand and gravel. In this way very small particles (suspended solids) that may still exist in the secondary effluent are trapped in the sand. All tertiary treated effluent is disinfected using sodium hypochlorite produced by on-site electrolytic chlorination (OSEC) from salt and water. The treated wastewater passes through the contact tank where it has a minimum of 30-minute contact time with the sodium hypochlorite.

Utilization of Treated Wastewater in Agriculture

The treated wastewater is delivered to Water Development Department and is mainly used for irrigation in agriculture, industry, hotels and green areas.

The use of treated wastewater for agricultural purposes is the most beneficial alternative for Cyprus. The main criteria used for establishing the quality standards are the protection of public health and the environment, the effects on soil and crops and public acceptance. Cyprus quality standards are divided in two parts: The Guidelines and the Code of Practice. The Guidelines are set in the form of a table where limits of four biological and microbiological parameters are defined, namely biochemical oxygen demand (BOD5), suspended solids (SS), faecal coliforms and intestinal worms. The guidelines specify the required and the maximum permissible concentrations of these parameters according to the five different categories of crops to be irrigated. Furthermore, in order to ensure the quality parameters, the methods of treatment and disinfection are also specified under the heading ‘‘treatment required’’. The Code of Practice are regulations complementing the Guidelines, given in the form of text. It is an inseparable part of the guidelines in order to ensure proper operation of the treatment facilities and for the control of the methods used for irrigation.

Wastewater Treatment Plant

The wastewater treatment plant is located 22 km east of Limassol at Moni village area. The construction works of the first phase started in 1993 and was finalised in 1995. It was carried out by the joint venture Kruger A/S and Zachariades construction company. Originally the plant was designed to receive flows up to 20,000 m3 /d at a BOD5 load of 4,567 kg/d and it was able to serve a population equivalent of 72,000. In 2006 the extension and upgrading of the plant was started by Kruger A/S and Cybarco Plc consortium and was finalized by the end of 2008. It can now treat 40,000 m3/d at a BOD5 load of 16,320 kg/d and a population equivalent of 272,000. Since then the operation and maintenance of the plant with the extensions has been performed by the same consortium. The plant treats the sewage in primary, secondary and tertiary stages.

Επεξεργασία Λάσπης

H λάσπη η οποία παράγεται υποβάλλεται στην πλέον προηγμένη επεξεργασία (αναερόβια και φυγοκέντρηση) η οποία υπάρχει σήμερα στην Κύπρο με τη χρήση τελευταίου τύπου μηχανημάτων. Περαιτέρω, το βιοαέριο που παράγεται κατά την επεξεργασία της λάσπης χρησιμοποιείται για παραγωγή ηλεκτρικής ενέργειας η οποία καλύπτει ήδη το 40% των αναγκών του σταθμού σε ενέργεια.

Τα διάφορα στάδια επεξεργασίας της λάσπης, η οποία παράγεται στο Σταθμό του Συμβουλίου στην περιοχή Μονής αναλύονται πιο κάτω. 

Στις δεξαμενές πρωτοβάθμιας και δευτεροβάθμιας καθίζησης συσσωρεύεται λάσπη η οποία απομακρύνεται στην μεν πρώτη περίπτωση στον παχυντή βαρύτητας στη δε δεύτερη στους μηχανικούς παχυντές. 

Από τους παχυντές η λάσπη αντλείται στους αναερόβιους χωνευτές. 

Γίνεται δηλαδή χώνευση (μεσοφιλική 35 oC) της λάσπης όπου επιτυγχάνεται περαιτέρω μείωση του οργανικού και παράλληλα μικροβιολογικού φορτίου με αποτέλεσμα την παραγωγή σταθεροποιημένης λάσπης. 

Ακολούθως η χωνευμένη λάσπη αφυδατώνεται σε ειδικές μηχανές φυγοκέντρισης απ’ όπου συλλέγεται και μεταφέρεται για περαιτέρω αποξήρανση στον ήλιο σε ειδικά διαμορφωμένες πλατείες από μπετόν. 

Η αποξηραμένη λάσπη ελέγχεται στο χημείο για περιεκτικότητα βαρέων μετάλλων και εφόσον πληρούνται οι προδιαγραφές, διατίθεται σαν εδαφοβελτιωτικό για χρήση στη γεωργία. Η λάσπη χρησιμοποιείται και σαν καύσιμη ύλη από το Τσιμεντοποιείο Βασιλικού. 

Κατά τη λειτουργία των χωνευτών παράγεται βιοαέριο το οποίο χρησιμοποιείται για εσωτερική χρήση για τη θέρμανση της λάσπης στους χωνευτές και για την παραγωγή ηλεκτρικής ενέργειας για τις ανάγκες της μονάδας. 

Στάδια Επεξεργασίας

Στο σταθμό γίνεται προεπεξεργασία λυμάτων, πρωτοβάθμια καθίζηση, βιολογική επεξεργασία δευτεροβάθμια καθίζηση, τριτοβάθμια επεξεργασία, απολύμανση με χλώριο, επεξεργασία λάσπης. (πάχυνση, χώνευση, αφυδάτωση, αποξήρανση)

Προεπεξεργασία

Τα λύματα με την είσοδο τους στην εγκατάσταση υφίστανται την προκαταρκτική επεξεργασία.

Σ’ αυτή τη φάση συγκρατούνται όλα τα στερεά σωματίδια όπως πέτρες, ξύλα, πλαστικά τα οποία έχουν μέγεθος μεγαλύτερο από 1 εκατοστό. Με την επέκταση έχει εγκατασταθεί επιπρόσθετο σύστημα απομάκρυνσης στερεών μέχρι και 5 χιλιοστά.

Η λειτουργία είναι αυτόματη και τα στερεά που συλλέγονται, συμπιέζονται και απομακρύνονται σε σκυβαλλοδοχεία.

Στη συνέχεια τα λύματα καταλήγουν σε δύο επιμήκεις αεριζόμενες δεξαμενές. Στο κεντρικό τμήμα της δεξαμενής διαχέεται αέρας. Ο άμμος, τα χαλίκια και άλλα βαρύτερα του νερού στερεά καθιζάνουν, αντλούνται σε κανάλι αμμοσυλλογής, διαχωρίζονται από το νερό και διατίθενται σε αδειοδοτημένους χώρους απόρριψης.

Στο πλαϊνό τμήμα της δεξαμενής πάλι με τη βοήθεια του αέρα περισυλλέγονται τα αιωρούμενα λίπη και έλαια τα οποία και απομακρύνονται.

Πρωτοβάθμια Καθίζηση

Τα λύματα οδηγούνται στις δεξαμενές πρώτης καθίζησης όπου έχουμε και την πρωτοβάθμια επεξεργασία κατά την οποία είτε με φυσικά ή χημικά μέσα επιτυγχάνεται η μείωση του οργανικού φορτίου κατά 30-40% και των αιωρούμενων στερεών κατά 40-60%.

Βιολογική επεξεργασία – Δευτεροβάθμια καθίζηση

Στη συνέχεια τα λύματα υπερχειλίζουν προς τις δεξαμενές αερισμού όπου χρησιμοποιείται η πιο κοινή μέθοδος επεξεργασίας, αυτή της ενεργούς λάσπης με ταυτόχρονη απονιτροποίηση (μέθοδος ΒΙΟ-DENITRO).

Σύμφωνα με την επεξεργασία αυτή, λύματα και μικροοργανισμοί αναμειγνύονται, έρχονται και παραμένουν σε επαφή μερικές ώρες σε δύο μεγάλες δεξαμενές με ελεγχόμενη παροχή αέρα και ρυθμό ανάδευσης.

Απαιτείται φροντίδα ώστε παράγοντες όπως θερμοκρασία οξυγόνο και χρόνος επαφής να κυμαίνονται στα επίπεδα εκείνα, που διασφαλίζουν την βιοαποδόμηση του οργανικού φορτίου. 

Οι δεξαμενές λειτουργούν εναλλάξ βάση προγράμματος σε κύκλους αεροβίων συνθηκών (παρουσία οξυγόνου-νιτροποίηση) και σε κύκλους ανοξικών συνθηκών (απουσία οξυγόνου – απονιτροποίηση).

Οταν τα λύματα βρίσκονται στην αερόβια δεξαμενή η αμμωνία που υπάρχει σ’ αυτά ενώνεται με το οξυγόνο το οποίο διοχετεύεται στις δεξαμενές με τη λειτουργία τεραστίων επιφανειακών αναδευτήρων και μετατρέπεται σε νιτρικά.

Εδώ γίνεται και η μερική μείωση του φωσφόρου.

Οταν τα λύματα βρίσκονται στη δεξαμενή όπου έχουμε αναερόβιες συνθήκες τα νιτρικά στην απουσία οξυγόνου μετατρέπονται σε αέριο άζωτο το οποίο φεύγει στην ατμόσφαιρα. 

Από τις δεξαμενές αερισμού με βαρύτητα το μείγμα νερού και βιολογικής λάσπης οδηγείται στις δεξαμενές δευτεροβάθμιας καθίζησης. Στις δεξαμενές αυτές η λάσπη καθιζάνει και το επεξεργασμένο νερό υπερχειλίζει και συνεχίζει την πορεία του προς την τριτοβάθμια επεξεργασία.

Το μεγαλύτερο ποσοστό της ενεργούς λάσπης που έχει καθιζήσει στις δεξαμενές δευτεροβάθμιας καθίζησης επιστρέφει στις δεξαμενές αερισμού έτσι ώστε να διατηρείται μια σταθερή ποσότητα σ’ αυτές.

Ενα ποσοστό της λάσπης απομακρύνεται ως πλεονάζουσα λάσπη και αντλείται στους μηχανικούς παχυντές.

Τριτοβάθμια Επεξεργασία

Στη μονάδα αυτή τα δευτεροβάθμια επεξεργασμένα νερά περνούν διά μέσου στρωμάτων άμμου και χαλικιών και με τον τρόπο αυτό συγκρατούνται στην άμμο μικρού μεγέθους σωματίδια, που τυχόν να περιέχονται ακόμη σε αυτά. Το οργανικό φορτίο BOD5, τα αιωρούμενα στερεά και το ολικό άζωτο των τριτοβάθμια επεξεργασμένων λυμάτων έχουν τιμές που δεν ξεπερνούν τα 10mg/l.

Απολύμανση

Ακολούθως γίνεται απολύμανση των τριτοβάθμια επεξεργασμένων λυμάτων με διάλυμα υποχλωριώδους νατρίου το οποίο δοσολογείται αναλόγως της ροής των επεξεργασμένων λυμάτων στην είσοδο της δεξαμενής επαφής χλωρίου. Το διάλυμα υποχλωριώδους νατρίου παράγεται με την Ηλεκτρολυτική μέθοδο από το άλας, το νερό και το ηλεκτρικό ρεύμα.

Το τελικό προϊόν, οδηγείται στις αποθηκευτικές δεξαμενές του Τ.Α.Υ και διατίθενται κυρίως στη γεωργία για άρδευση.