Wastewater treatment plant, Niederbrechen, DE

Municipal Sewage Plant Niederbrechen: Refurbishment with Specialised StoCretec Systems

The Niederbrechen municipal sewage treatment plant near Limburg Lahn in central Hesse, Germany, has been in operation for 38 years. The “Goldener Grund” Wastewater Association is refurbishing and expanding the sewage treatment plant in order to ensure a good ecological and economic basis for the coming years.

Large-scale investments are being made over a construction period of 4 years. The new requirements of the state of Hesse for phosphorus elimination are being implemented through additional basins, a precipitant dosing station and a digestion tower. New, efficient machine technology in conjunction with a combined heat and power plant that runs on the digester gas saves around 70 % of the energy required. This not only reduces costs, but also around 5,335 tons of CO2 over the next 30 years of operation. These measures will help to achieve the 2050 Climate Protection Plan.

The target of the refurbishment: Ensure the durability of the entire plant for the future decades. After preliminary structural investigations, the investor and the planning office DAR (Deutsche Abwasser Reinigungs-Gesellschaft mbH, Wiesbaden, DE) decided to repair the existing structures - the inlet pumping station, sand trap, sludge thickener and storm overflow basin - during this general refurbishment. Since the sewage treatment plant had to be kept in operation during the construction phase, a tight construction schedule was drawn up in advance.

In order to meet the requirements of the plant’s use, the chemical attacks from the wastewater and the strict construction schedule, the investor and planner are relying on the StoCretec product range: mortars specially formulated for sewage treatment plants that are characterised by excellent resistance to water containing sulphuric acid, ammonium and sulphate.

The preliminary investigations of the wall surfaces of the existing buildings mentioned did not show any sulphates at greater depths. Therefore, deeper breakouts were reprofiled with the statically active repair system StoConcrete Repair Prime TG 203 to ensure stability.

For permanent protection against wastewater, the existing concrete cover of the walls had to be increased with a wastewater-resistant mortar system. The StoConcrete Repair Resist system offers the optimal solution here. Based on a chemically highly resistant HS special cement and a special formulation, the products of this system are tested according to DIN 19573 up to exposition class XWW3. The mineral system is ideal for the permanent repair of concrete components in contact with the ground in municipal sewage treatment plants.

StoCrete TH 250 is a sulphate-resistant bonding agent. The repair mortar StoCrete TG 252 is certified as a concrete replacement mortar (PCC / RM) for highly aggressive, sulphatecontaminated wastewater for layer thicknesses of 6 - 30 mm. The wet-mix spray mortar StoCrete TS 250 also enables time- and cost-saving application on large surfaces. In order to ensure easy cleaning the basins, the coating system was given a finely structured surface finish with the fairing coat StoCrete TF 250 with a layer thickness of 2 - 5 mm.

In order to counteract a possible odour nuisance caused by the digested sludge in the sludge thickeners, it was decided to equip both structures with capping. As described in the DWA* data sheet M 211, the gas compartment of these structures can suffer strong chemical attack by thiobacilli and hydrogen sulphide from the sludge. Mineral materials cannot withstand this permanently. They must be coated with an additional surface protection system. The StoConcrete Protect Resist system was chosen for this purpose. It has been tested for exposure class XWW 4 (biogenic sulfuric acid attack) in accordance with DIN 19573 and this is proven by long-term references.

The StoPox 452 EP primer resin has a very good bond and, thanks to special additives, forms a very good capillary and pore sealing coat on the mineral substrate. Due to its formulation, it can also be used on damp substrates, which significantly speeds up the construction process. The EP sealing coat StoPox KU 180 is a chemically and mechanically highly resistant epoxy resin which can be used indoors and outdoors and which is ideally suited for wall surfaces due to its thixotropic properties.

The concrete cover also had to be increased in the flooring area. This was achieved using the StoConcrete Screed Resist System. In this system, too, the same binding agent as applied in the StoConcrete Repair Resist System ensures high chemical resistance. A modified formulation and a different grain size make this PCC I / RM mortar very robust and mechanically resistant. The system, consisting of the sulphate-resistant bonding agent StoCrete TH 250 and the PCC I / RM concrete replacement, StoCrete TG 154, is certified for highly aggressive sulphate-contaminated wastewater for layer thicknesses of 12 - 50 mm.

Download project report | PDF 2 MB