How Coatings Protect Wastewater Pretreatment Equipment in Food and Beverage Processing

Concrete assets with especially severe chemical exposures may require even more robust lining systems. For example, linings for MBR basins must be able to withstand the highly corrosive 2% citric acid used to backwash and clean filters. In this case, the basins may require a lining system embedded with fiberglass matting. Following surface preparation, applicators may first apply a base layer of Sherwin-Williams Dura-Plate® UHS Clear Laminate, top that with a 1.5-ounce fiberglass mat (Figures 1 and 2) and seal that mat with more of the clear laminate material. Next, they may spray-apply Dura-Plate UHS Epoxy White as a high-build topcoat to protect the layers below (Figure 3). This ultra-high-solids epoxy amine coatings system with fiberglass reinforcement provides superior protection with high-build, edge-retentive properties.

For steel tanks that may be used to store or process wastewater, products like Sherwin-Williams Nova-Plate® UHS Epoxy are recommended for added durability in areas subject to high-wear and abrasion. The ultra-high-solids epoxy novolac amine was developed for immersion service and offers superior protection compared to conventional epoxies due to its advanced high-build, edge-retentive properties.

Inside such tanks, applicators may first apply a stripe coat of Dura-Plate® UHS Primer (Figure 4) to critical areas such as weld seams, edges, angles, bolts and more to ensure complete coverage on these surfaces. This ultra-high-solids, two-component epoxy amine has exceptional surface wetting and adhesion properties and is recommended for immersion service.

As chemicals increase in quantity, acidity and/or corrosiveness, food and beverage plants may need to look at different formulations that offer even greater durability. Dura-Plate® 8200 is one such option. Developed to handle the rigors of storing high temperature crude oil/water mixes and aggressive acids for the oil and gas industry, the high-temperature and chemical-resistant novolac tank lining can readily handle the rigors of severe wastewater pretreatment service. It acts as an insulating material to reduce the effects of thermal shock as higher-temperature contents fill an ambient temperature tank. The product offers the ease of single-leg application and cures rapidly, allowing assets to return to service within 24 hours, saving the added expense of additional downtime.

Another common line of coating solutions for wastewater service are vinyl esters and novolac vinyl esters, as they are highly resistant to organics and chemicals, as well as extreme corrosion. For example, Magnalux™ 2100FF is an epoxy novolac vinyl ester that’s glass flake filled. Magnalux™ 2500WX is an acrylic co-polymer novolac vinyl ester that features wax in its formulation to improve chemical resistance and product purity. Both topcoat materials provide resistance to many aromatic and aliphatic solvents, organic and mineral acids, and strong oxidizers. They also offer excellent resistance to thermal degradation, making them suitable for use with heated contents.

Magnalux™ 1100 serves as a primer for the two topcoats. The polyester coating promotes adhesion to concrete and metal substrates and improves mechanical stresses such as impact, tensile and flexural stress, helping the topcoats last even longer.

Interestingly, vinyl esters are also used for resinous flooring installations for this same ability to resist acids. In fact, flooring is part of the wastewater treatment process that’s hardly top of mind for plant managers since it’s underfoot. But these surfaces will need to resist many of the same materials that tank linings and other coatings do, as wastewater may spill or splash onto floors. So, flooring also needs to be specified carefully.

How to Address Multi-Surface Combinations

Sometimes both steel and concrete are used in the same equipment – with the steel even embedded inside concrete in some situations. This particular combination creates a challenging situation for coatings, as steel and concrete expand and contract at different rates, creating multi-directional stresses on the materials.

Consider a small cheese plant that uses a 150-foot diameter, all-in-one tank unit to pretreat wastewater, removing FOGs, solids, acids and cleaning chemicals from the plant’s wastewater stream. Operators first add various coagulants to the tank, which destabilize suspended particles via chemical reactions so the waste solids begin to clump together. Next, a steel flocculation arm gently mixes the contents to allow larger clumps to form for easier separation of waste from the water. During this process, the tank and its related equipment are exposed directly to highly acidic and caustic contents, necessitating robust coatings to protect their integrity.

Interestingly, the tank is made from different materials, with steel walls embedded in a concrete foundation. This steel-to-concrete transition creates a unique challenge for protecting those different materials with coatings. As the tank contents are heated, the steel walls expand in one direction, while the concrete foundation expands in a more limited fashion. Therefore, the leading edge of the steel-to-concrete transition will experience significant stress that could potentially cause coatings to crack and peel, allowing tank contents to reach both the steel and concrete substrates.

In some cases, the solution would be to leave the concrete uncoated since it would be beneath the oxygen level and therefore wouldn’t have enough oxygen available to corrode. However, that foundation will likely need to be coated in most cases.

For this tank, applicators used a two-fold solution to coat the concrete and steel, while limiting the stress placed on the 90-degree transition from the steel walls to the concrete floor. They first installed a cant cove at the transition, adding flexible material at the base of the walls to create a 45-degree angle instead. That Resuflor™ Topfloor MER I (Mechanical Equipment Room) material offers flexible epoxy crack bridging capabilities to reduce stress at angles and allow movement as the steel and concrete expand and contract at different rates. They next added fiberglass mesh to the transition area, overlapping it a couple of inches each way to reinforce the transition. Finally, they applied a topcoat of Dura-Plate 8200, with Nova-Plate UHS also being an option for the durable, high-build protective topcoat.

Coatings Selection Support and Site Surveys Enable Success

Given the array of assets used in the food and beverage wastewater pretreatment process and the multitude of coating and lining solutions available to keep that equipment in peak operating condition, selecting the ideal protective solutions can be a challenge. To get those selections right, food and beverage plant managers are best served by consulting with coatings manufacturers to identify what exposures the equipment will face and what coating solutions can be considered to mitigate those corrosive threats. In many cases, a certified coatings professional will be able to provide an array of solutions that algin longevity of service with operating and maintenance budgets, giving plant managers a range of options to meet the needs at hand. While the most robust coatings solution will be desired in most cases, some situations will call for more budget-conscious or short-term fixes before the plant invests in a longer-term solution.

A certified coatings expert can help in other ways, as well, including engaging in site surveys to help plant managers identify any current deficiencies and prepare for future coatings maintenance needs. During a site survey, a certified coatings expert will look for areas of paint cracking, blistering or peeling that indicate an imminent coating failure, as well as observe all areas where coatings are used or could be used to maintain assets. They’ll then prepare a report listing recommended maintenance protocols for each asset and provide a list of vetted contractors that have been approved to install the suggested coating systems. This comprehensive report thereby readies facilities for any coating maintenance-related needs – from having a tiered selection of potential solutions at the ready to providing qualified leads for getting the job done.

With the right materials specified and the right contractors doing the work, food and beverage facilities can be poised to realize longer service lives for their operating assets, which in turn leads to reduce maintenance needs and unplanned shutdowns, as well as a healthier bottom line.

Figure 1. An especially robust protective coating system for MBR basis may include reinforcement with fiberglass matting. In this installation, applicators applied Sherwin-Williams Dura-Plate UHS Clear Laminate as a base layer and then tinted the material green to provide contrast when sealing in a 1.5-ounce fiberglass mat for reinforcement.

Figure 2. Using aluminum fiberglass rollers, the applicators worked the green-tinted laminate material into the matting to ensure full wetting and proper adhesion.

Figure 3. For the final layer of the MBR basin linings, applicators spray-applied Dura-Plate UHS Epoxy White, an ultra-high-solids epoxy amine coating engineered for immersion service that features high-build, edge-retentive properties for superior protection.

Figure 4. For added protection in steel tanks, applicators commonly apply stripe coats of Dura-Plate UHS Primer, using a combination of brushing and rolling techniques, to ensure full coverage on weld seams, bolts and edges.