Clarifier & Settlement Tank Maintenance: 3 Examples In Action
Water Management is an essential part of many industries, for which clarifier and settlement tanks play a crucial role. Whether it is for a pharmaceutical site, a mine or a wastewater treatment plant, ensuring correct and effective processing is the cornerstone of this sector and any damage to these pieces of equipment can have significant consequences.
Settling on a clear solution
By their very nature, clarifier and settlement tanks are susceptible to three main issues: corrosion, erosion and chemical attack. Of course, steps are taken to reduce the impact these issues have, simply by controlling their operation. For instance, the flow speed from inlet pipes is kept low. This minimises the amount of turbulence and disruption of the settled and coagulated solids. However, effective operation still cannot completely eliminate these problems.
Whether these problems arise in the form of deteriorated concrete; eroded and corroded metalwork, or failed expansion joints, the appropriate solutions must be able to withstand the operating conditions and demonstrate long-term resistance to the aforementioned effects. Belzona has been involved with maintenance for clarifier and settlement tanks for over 65 years and therefore, has significant experience in providing long-lasting repair and protective materials.
Below are a selection of three case studies which highlight a variety of different applications and solutions that have proved particularly successful:
This clarifier had been operating without any form of protective coating since its installation and as a result, had suffered from erosion damage to the concrete structure. Accentuating this even further were the rigorous cleaning processes. The customer was looking for a long-term repair in lieu of repairing it every 2-3 years as they have done in the past. Furthermore, the asset owner required any solution to accomodate for the cleaning procedures. With damaged concrete and no coating, the trough was hard to keep clean. In fact, it was taking 2-3 times longer than when new.
Notably, the Maintenance Manager for the facility was already familiar with Belzona systems. Having specified their use elsewhere in the plant and having a great deal of experience with the local Distributor, provided assurance that the proposed solution would work well.
During the designated downtime, scaffolding was erected around the circumference of the clarifier, allowing easy access for the maintenance crew. Using Belzona 4131 (Magma-Screed), which is easy to apply over large areas, the damaged concrete was returned to its original profile. Far stronger than concrete, this actually enhanced the erosion resistance of the clarifier. However, as a further protective measure and to facilitate easier cleaning, Belzona 5811 (Immersion Grade) was applied within the trough.
The application window available for the maintenance was simply three days. In comparison to competitor systems, which would have required shutdown for over a week, the Belzona repair was able to be carried out the long weekend specified by the facility. In addition to the quick turn-around, these materials have a proven track record within other areas of the treatment plant. Altogether, the Maintenance Manager was very satisfied with the repair as it saved both time and money, whilst also still faring well in service to this day.
Following particularly cold periods, clarifier and settlement tank concrete walls are under significant threat from freeze thaw damage. This can lead to hairline cracks appearing, as well as spalled concrete, which can affect the smooth running of the surface skimmer. Coupled with the wheels causing further abrasion and impact damage, the concrete wall can quickly deteriorate.
In this instance, the expansion joints located around the settlement tank had failed. The asset owner had used a cementitious material to repair them, but it was unable to account for the movement present at the joint. As a result, it quickly cracked leading to failure. Not only was this in one instance, but actually 82 locations around the tank!
Fundamental to the expansion joints were the concrete nosings either side. Initially, all loose and damaged concrete was removed, leaving a firm surface for application. Using Belzona 4111, the deteriorated concrete was repaired quickly and the inclusion of a former kept the adequate space in between. Belzona 2211 was then incorporated to restore the much-needed flexibility, missing with the cementitious alternative.
The primary settlement tanks’ original concrete design had failed within four years due to water ingress. This highlighted a significant issue and area for improvement with any future developments or maintenance. Belzona concrete repair materials made for the ideal solution due to their non-porous nature, ensuring a long-term repair and the elimination of further damage.
Belzona Dresses Clarifier with New Skirt
Application Date: March 2007
Location: Oklahoma, USA
Solution: Belzona 5811
As the skimmer travels around the clarifier, the scum layer is deposited in the outer trough. To prevent this rejected layer re-entering the clarifier basin, a shield or skirt is generally in place, enclosing the scum in the trough. If left unprotected, this barrier can suffer from erosion and corrosion over time, especially since they are located in a semi-immersed environment.
At a wastewater treatment plant in Oklahoma, 50% of the aluminum skirt on a clarifier had eroded away at the waterline. Extending 16 inches below the surface, this was in such a bad state that it no longer was fulfilling its function. Plus, as the only one serving a small city, it needed immediate maintenance or replacement.
A new skirt from the manufacturer would cost over $15,000 and take unduly long to install. As an alternative, the local Belzona representative for the plant suggested using a protective coating in conjunction with a cheaper material, alleviating the high costs and long lead times. Opting for this repair method, new aluminum panels were subsequently abraded, conditioned and finally coated with Belzona 5811 (Immersion Grade). The existing skirt was also sufficiently cleaned and taken back to a sound profile. The panels were then bolted to the remaining skirt, eliminating need for complete replacement.
In total, this application used $500 worth of Belzona and $1,000 in metal and supplies – a significantly cheaper and faster way of rectifying the issue. In fact, the application only took one day to complete, versus more than a week to replace the whole shield. Furthermore, this option offered a long-term resolution, with Belzona 5811 designed for immersed operation whilst providing outstanding corrosion and chemical resistance.