FRP (Fiber Reinforced Polymer): The Ideal Solution for Chemical Resistance and Durability in Water Treatment Plants | P-TREX
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FRP (Fiber Reinforced Polymer): The Ideal Solution for Chemical Resistance and Durability in Water Treatment Plants


Irisacqua S.r.l., a public entity representing 25 municipalities in the former province of Gorizia, has sought the expertise of P-TREX, the industry division of Fibre Net Group, to secure a specific part of the Grado wastewater treatment plant. The plant had suffered severe chemical degradation due to the ingress of brackish water through the drainage pipes of road manholes, leading to progressive chemical reactions and rapid overall deterioration. The corrosion affecting the concrete also compromised structures used for control and inspection activities, raising concerns about the safety of operators and the overall security of the plant. In response, the focus of the RSPP (Person Responsible for Prevention and Protection) and Managers was to preserve personnel safety by seeking a solution to guarantee it. Hence, the expertise of P-TREX was enlisted to secure access structures through the total replacement of existing walkways and stairs.

In the overall plant redevelopment, the collaboration between Irisacqua’s technical office and P-TREX proved decisive in addressing the issues plaguing the treatment plant. Grado, known as the “Island of the Sun” and the “First Venice” due to its unique history, is a significant tourist and thermal center in Friuli-Venezia Giulia. Its tourist appeal imposes a substantial intermittent load on the treatment plant, compounded by the lagoon environment and strong influences of external chemical agents.

The solutions proposed by P-TREX, leveraging advanced materials and innovative technologies, were crucial in ensuring undeniable resistance to corrosion, durability, and efficiency. Among the materials that emerged as an improvement for support and access structures to the plant, FRP proved to be the sought-after enhancing solution.

Initially commissioned in 1980 with a capacity of 40,000 population equivalent (a.e.) in compliance with Law No. 319 of 10/05/76, the plant featured a chemical-physical section and a biological section. In the 1990s, following an expansion to 80,000 a.e., the chemical/physical technology was abandoned in favor of biological technology. Upon the subsequent renewal of the discharge authorization, the plant was downgraded to a hydraulic capacity just above 40,000 a.e.

In the current configuration, wastewater entering the plant is divided into two pretreatment lines passing through a self-cleaning grid with a filtration clearance of 3 mm. This prevents the passage of coarse materials to subsequent purification phases. One line consists of a specially shaped concrete structure called a sand and oil separator, designed to separate inert solids (sand, gravel, etc.) from the liquid stream and float and retain oils and fats.

The second line comprises a compact stainless steel plant capable of performing all pretreatments of screening, sand removal, and oil separation with the same capabilities as the concrete line.

Downstream of the sand and oil separator, the wastewater undergoes biological phosphorus removal, where bacteria in anoxic conditions absorb the phosphorus present in the wastewater. The subsequent treatment is denitrification, where the wastewater is kept without oxygen to facilitate the conversion of nitrogen from liquid to gaseous state and its removal.

The wastewater, supplemented with aluminum polychloride to further promote phosphorus removal, is then introduced into nitrification tanks, where a bottom layer of air diffusers agitates the wastewater to dissolve atmospheric oxygen and feed aerobic bacteria, promoting the reduction of organic pollutants in the wastewater.

In the next phase, known as secondary clarification, the slow flow velocity allows the water to rid itself of settleable substances by depositing them at the bottom. Clean water exits at the top and is directed to discharge after disinfection with peracetic acid, pumped into the sea through a submarine pipeline.

The plant is equipped with two units of aerobic digestion operating in parallel, aimed at digesting and stabilizing excess sludge through prolonged oxidation, after which the sludge passes through a static thickener.

Almost all the sludge extracted from the thickener is sent to mechanical dehydration, where, after conditioning with polyelectrolyte, it goes through a centrifuge that removes part of the water before being sent for appropriate disposal. The residual part of the unsold sludge returns to the two digesters to nourish the biological culture.

Composite Materials Engineering P-TREX designs and manufactures customized solutions in FRP composite material to meet the needs of different users in various stages of the process. Choosing P-TREX products means minimizing environmental impact and contributing to ecological transition, as they are 100% reusable and recyclable.

The value of the proposal arises from a detailed feasibility study, project analysis, and preliminary assessments of the indicated context. Defining methods, costs, and intervention times in line with the progress of the construction is facilitated by the possibility of prefabricating some components in the company. Therefore, there is a dedicated area for metalwork, where specialized teams work on the pre-assembly of structures. The priority remains attention to detail and verification of design criteria for a product that must maintain reliability and durability throughout its operational life.

The synergy between the technical office of Irisacqua and P-TREX’s technical office has resulted in an improved solution for the structures near the concrete tank dedicated to dual oxidation and sedimentation processes.

The intervention was divided into two lots. The first part includes:

  • Design, development, and installation of FRP walkways on the tank edge, divided into modules with a length of 8.2 meters each, fixed to the tank’s supporting partition, complete with protective railing on both sides.
  • Design, development, and installation of a sloping ramp with an arrival platform and protective railing on both sides, and open grating steps with a yellow visual fringe element. Additionally, a vertical ladder with a protective cage for safe access to the tank’s movable bridge was provided.

The second part includes the design, development, and installation of:

  • Four FRP walkways totaling 20 meters, installed by cantilever using reinforcing struts.
  • Protective railing fixed laterally on the walkway and a second one fixed on the tank’s supporting partition.
  • In the central part, between the two longer walkways of 6.4 meters each, P-TREX’s technical office created an additional FRP structure, covering an intermediate tank.

Special attention was given to choosing A4 stainless steel anchor bolts to ensure maximum strength and durability over time, considering the aggressive environment that heavily degraded previously used anchors.

The operational efficiency of the wastewater treatment plant has significantly improved thanks to the design flexibility offered by FRP. This composite material allowed engineers to design and implement tailor-made solutions, ensuring the specific needs of the plant were fully met. The lightness of FRP significantly simplified the installation process, reducing plant downtime and minimizing associated costs.

Furthermore, the electrical insulation of FRP proved crucial for ensuring safety in an environment containing hazardous chemicals. This aspect helped prevent electrical risk from stray currents, protecting both personnel and the surrounding environment.

Corrosion Resistance One of the main advantages of FRP in a wastewater treatment plant is its exceptional resistance to corrosion and UV radiation. Treatment plants often deal with water loaded with corrosive agents, such as acids, bases, and aggressive chemicals. FRP withstands these corrosive agents much better than other materials, such as metal, which, as in this case, may deteriorate over time and require costly repairs or replacements.

Durability and Longevity FRP is known for its exceptional durability, meaning structures servicing treatment plants require less maintenance and have a significantly longer lifespan than other options. This extended lifespan translates into considerable long-term cost savings, in addition to minimizing plant downtime due to repairs and replacements.

Lightweight and Ease of Installation FRP is a lightweight yet highly durable material. This feature makes it ideal for constructing service structures, as it is easier to handle and install compared to heavier materials like metal. The ease of installation can reduce overall construction times and associated costs, including transportation and handling costs of the component.

Design Flexibility and Environmental Integration FRP offers greater design flexibility than other materials. This allows engineers to design custom components to meet the specific requirements of a particular treatment plant. Additionally, FRP is easily moldable, allowing for the creation of complex and detailed shapes.

The linearity of FRP structure geometries has a positive impact on the surrounding environment, seamlessly integrating with the protected green area, surrounded by a golf course and overlooking the lagoon landscape.

These technical advantages not only improve the operational efficiency of wastewater treatment plants but also contribute to long-term cost reduction. Therefore, it is evident that this material represents an ideal solution for modern treatment plants seeking to maximize efficiency and longevity. The absence of corrosion eliminates the risk of accidental injuries to operators due to contact with deteriorated ferrous materials, contributing to increased safety for all activities within the site.


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