Clean water is becoming a scarce resource. There is an increasing need to treat waste water, both in developed countries and emerging countries alike. New, large waste water treatment plants are continually being built in Latin America, Asia and Africa.
However, in all those countries many waste water treatment plants have now severely aged and suffered various degrees of degradation – mostly due to biogenic corrosion in areal parts of confined pits in the plant or within the sewer network.
Count on Sika’s expertise to help solve this and related problems in waste water treatment plants.
Typical Exposures for Sewers
Heavy abrasion and erosion of the concrete and prefabricated elements are often found at the bottom of the sewers. In general rules, these elements shall be replaced and reassembled properly by bonding them in place with an epoxy adhesive. In the case of the concrete substrate, the erosion can be repaired with a high abrasion resistant mortar that will increase the service life of the substrate
Lateral walls and the crown often show localized defects of the concrete and some- times defects due to the corrosion of the reinforcement. After appropriate preparation, these defects can be repaired using sulfate resistant repair mortars.
The resistance of tamped concrete against a strong water current is generally not enough and often the full surface of the concrete is eroded. It is recommended in these zones to proceed with a full resurfacing.
Due to shrinkage or settlements, concrete in sewers often cracks. These cracks need
to be fi lled in order to prevent leakage of pollutant to surrounding ground water. It is often necessary to use expanding materials to fi ll these cracks.
Exposed tamped concrete surfaces show very low resistance against carbonation and the aggressive substances contained in the waste water. Therefore, these surfaces can be protected using EpoCem® technologies which are extremely resistant and watertight against urban waste water.
At the crown area, the structure can be protected against condensation water using a hydrophobic impregnation. Additionally, the aerial part of the sewer can suffer from biogenic corrosion or microbial induced corrosion (MIC). To repair and protect these areas a 100% Calcium Aluminate Mortar must be used.
General Refurbishment Considerations
Before defining the repair and protection strategy, the specific sewage treatment plant requirements on refurbishment must be considered. These requirements can have an important influence in determining the correct design, planning and construction procedures, together with the future maintenance works necessary for the sewage treatment plant.
Examples of such project related requirements include:
Durability
Duration of closure / Downtime
System compatibility
Total life cycle costing
Exposures / Site Conditions
Ecology
Systems Plus Knowhow
For many decades, Sika has been a reliable partner with waste water treatment plant contractors supplying products and systems on all continents. Sika has shown the industry we are a partner in whom they can trust.
The products and systems used in new waste water treatment plants, sewage facilities and retrofitted structures are thoroughly tested in Sika laboratories before being independently checked. Sika materials are further proven by long term site testing to withstand harsh conditions in the real environment.
The proposed solutions below are typical and may not be available in all countries. Check with your local Sika expert to find the best locally available solution.
1. Screening Channel
In a large treatment plant, the removal of large objects is automatically performed in the screening channel.
Problem
In waste water treatment plants, erosion is mainly due to abrasion or by chemical attack. Erosion damage results from the abrasive effect of waterborne silt, sand, gravel, and other debris being circulated over a concrete surface during operation. The compounds present in hardened Portland cement are attacked by the aggressiveness (low pH) of the waste water.
Sika Solution
Sika MonoTop®-3400 Abraroc
Problem
Chemical attacks, depending on the aggressiveness of the waste or industrial water.
Sika Solution
Sikagard®-75 EpoCem/Sikafloor®-81 EpoCem
Sikagard®-62/Sikagard®-63 N
SikaCor®-950 F
Problem
Leakage and risk of pollution due to cracks, untight joints or damaged concrete.
Sika Solution
Sikadur-Combiflex® SG System
Sikaflex® PRO-3 SL
2. Grit, Fat and Grease Removal Chamber
In some plants, pre-treatment may include a grit channel where the waste water velocity is adjusted to allow settlement of the sands/grits or other hard particles. Sands/grits must be removed as they may damage pumps or other equipment. Fat and grease removal is generally done in a large plant in the primary settlement tank using mechanical surface skimmers.
Problem
Abrasion and erosion due to sand, grit or other particles.
Sika Solution
Sika MonoTop®-3400 Abraroc
Problem
Chemical attacks depending on the aggressiveness of the waste or industrial water.
Sika Solution
Sikagard®-75 EpoCem/Sikafloor®-81 EpoCem
Sikagard®-62/Sikagard®-63 N
SikaCor®-950 F
Problem
Leakage and risk of pollution due to cracks, untight joints or damaged concrete. Very often in waste water treatment, joints sealed with average sealant fails due to the lack of chemical resistance to these products. Instead of proceeding to the full removal of the failed joint, Sika has developed a joint system that can be applied over the original failed material.
The Sikadur-Combiflex® SG system is the second generation development of the globally proven Sikadur-Combiflex® with even improved performance such as advanced adhesion properties. The unique system consists of the Sikadur Combiflex® SG tape and the Sikadur® adhesives. It is widely used as joint waterproofing in watertight concrete structures.
Sika Solution
Sikadur-Combiflex® SG System
Sikaflex® PRO-3 SL
3. Primary Sedimentation Tanks
In the primary sedimentation tank, sewage flows through large tanks, commonly named “primary clarifiers” or “primary sedimentation tanks”. These tanks are equipped with mechanically driven scrappers that drive the collected sludge towards a hopper. Some primary sedimentation tanks can be covered to control odor. In such conditions, they can be subjected to biogenic corrosion.
Problem
Chemical attacks depending on the aggressiveness of the waste or industrial water.
Sika Solution
Sikagard®-75 EpoCem/Sikafloor®-81 EpoCem
Sikagard®-62/Sikagard®-63 N
SikaCor®-950 F
Problem
Leakage and risk of pollution due to cracks, untight joints or damaged concrete
Sika Solution
Sikadur-Combiflex® SG System
Sikaflex® PRO-3 SL
Problem
Abrasion and erosion due to sand, grit or other particles at the bottom of the concrete floor.
Concrete spalling due to sulfate attack or other aggressors on the wall of the tank.
Sika Solution
SikaTop® Armatec®-110 EpoCem®
Sika MonoTop®-3400 Abraroc
Problem
Heavy abrasion on the rolling pad of the scrapper.
Sika Solution
Sikadur®-42 TH
4. Aerated and anoxic biological tanks
Biological tanks are designed to substantially degrade the biological content of the sewage. These biological contents are originated from human waste, soap, and detergents.
Problem
Chemical attacks depending on the aggressiveness of the waste or industrial water.
Sika Solution
Sikagard®-75 EpoCem/Sikafloor®-81 EpoCem
SikaCor®-950 F
Problem
Leakage and risk of pollution due to cracks, untight joints or damaged concrete.
Sika Solution
Sikadur-Combiflex® SG System
Sikaflex® PRO-3 SL
Problem
Concrete spalling due to reinforcement steel corrosion.
Sika Solution
SikaTop® Armatec®-110 EpoCem®
5. Secondary Sedimentation Plant
Secondary treatment is intended to degrade further the organic content of sewage water originating from human waste, soap, detergent, etc. Most of the plants treat the sewage using aerobic biological processes.
Problem
Erosion due to water flow
Sika Solution
Sikagard®-75 EpoCem/Sikafloor®-81 EpoCem
Problem
The water has already received some treatment, hence the level of chemical aggressiveness in this sedimentation tank is reduced.
Sika Solution
Sikagard®-75 EpoCem/Sikafloor®-81 EpoCem
SikaCor®-950 F
Problem
Leakage and risk of pollution due to cracks, untight joints or damaged concrete
Sika Solution
Sikadur-Combiflex® SG System
Sikaflex® PRO-3 SL
Problem
Steel reinforcement corrosion due to reduced concrete cover.
Sika Solution
SikaTop® Armatec®-110 EpoCem®
6. Filtration Beds
In the filtration bed, the treated water flows through various layers of sand beds for final filtration before being discharged in the environment. Filters are periodically cleaned using air and clean water at the counter stream. The cleansing water is then pumped back to the aeration basin for retreatment.
Problem
Abrasion and erosion due to sand, grit or other particles.
Sika Solution
Sika MonoTop®-3400 Abraroc
Problem
Chemical attacks depending on the aggressiveness of the waste or industrial water.
Sika Solution
Sikagard®-75 EpoCem/Sikafloor®-81 EpoCem
Problem
Leakage and risk of pollution due to cracks, untight joints or damaged concrete.
Sika Solution
Sikadur-Combiflex® SG System
Sikaflex® PRO-3 SL
7. Digestion Tanks
The sewage sludge digestion tank is where the sludge is stabilized, reduced in volume, made innocuous through the process of dissolving organic substance with the help of anaerobic bacteria and finally, where energy is recovered.
Problem
Abrasion and erosion due to sand, grit or other particles.
Sika Solution
Sika MonoTop®-3400 Abraroc
Problem
Leakage and risk of pollution due to cracks, untight joints or damaged concrete.
Sika Solution
Sikadur-Combiflex® SG System
8. Gasometers
Within the process of biological deterioration in the biological tank or the digestion tank, biogas (methane, CO²) will be produced and be stored in gasometers. These gasometers are generally built-in steel. Biogenic sulfuric acid is highly aggressive to steel. Additional stresses are caused by the elevated temperature.
Problem
Leakage and risk of pollution due to cracks, untight joints or damaged concrete.
Sika Solution
Sikadur-Combiflex® SG System
9. External Waterproofing
To keep drinking water in below-ground storage tanks clean, it has to be protected from groundwater entering the structure.
Sika Solutions
SikaProof®-612
Sika Solutions
SikaShield® W159 ED 1..5 mm
10. Service Buildings, Concrete & Masonry Exterior
Most waste water treatment plants have a technical service building. External surfaces of the building as well as of the above-ground tanks are exposed to weathering and therefore often need protection.
Problem
In these technical buildings, chemicals are handled. Therefore, the floors in the chemical storage area also need protection.
Sika Solution
Sikafloor®-20 PurCem® LP/Sikafloor®-21 PurCem® LP
Problem
Roofs in the buildings (technical and office) of the sewage treatment plants may require waterproofing.
Sika Solution
Sarnafil® PVC membranes
Sikalastic® liquid applied membranes
SikaShield® bitumen membranes
Problem
External concrete surfaces may undergo natural weathering due to carbonation. When the plant is located close to the sea, they may also suffer chloride attack.
Sika Solution
Hydrophobic impregnations: Sikagard®-705 L
