Membrane Processes for Industrial Water and Wastewater Treatment

The appropriate membrane process depends on the constituents of the water and the desired quality of the treated water. Microfiltration or ultrafiltration are often used to remove solids and colloids. Nanofiltration may be suitable for partial desalination and selective ion separation, while reverse osmosis is used when extensive desalination is required.

To make a reliable selection, the following factors are particularly important: water analysis, flow rate, desired yield, and target quality.

Nanofiltration may be useful when complete desalination is not required and the goal is to specifically reduce polyvalent ions, hardness components, or certain larger dissolved organic substances.

Typical applications include water softening, partial desalination, and sulfate reduction. However, reverse osmosis is generally more suitable for significantly reducing the total salt load.

Yes. Membrane stages can often be integrated into existing water and wastewater treatment plants. Typical examples include ultrafiltration upstream of an existing reverse osmosis system, an additional RO stage to improve permeate quality, or an NF stage for selective partial desalination.

The key factors are the existing pretreatment, hydraulic reserves, and the quality of the influent water.

The achievable yield varies by project and depends, among other factors, on salinity, hardness components, silicates, scaling potential, temperature, and system configuration. Therefore, it is not practical to provide a general value for industrial plants.

During the design phase, the technically and economically feasible recovery rate is selected so that membrane load, concentrate volume, and operational stability are balanced.

Fouling is primarily minimized through proper pretreatment, appropriate membrane selection, and controlled operating conditions. Depending on the water, filtration, ultrafiltration, activated carbon, biological treatment, or chemico-physical pretreatment may be necessary, for example.

In addition, it is important to monitor pressure, flow rate, and permeate quality, as well as to clean the membranes as needed.

Scaling occurs when sparingly soluble salts in the concentrate exceed their solubility limit. The risk is assessed during the design phase based on water analysis and the expected yield.

Possible measures include water softening, pH adjustment, antiscalant dosing, an adjusted recovery rate, and, if necessary, additional pretreatment steps.

The concentrate produced during RO or NF contains the retained salts and water constituents in higher concentrations. Depending on the location and composition, it can be discharged, further treated, or fed into an additional concentrate stage.

Concentrate treatment should be taken into account as early as the plant design phase, as it can significantly impact the overall economic viability of a water reuse concept.

Yes. Reverse osmosis is a commonly used process in industrial water reuse systems, particularly when dissolved salts and ions need to be reduced after pretreatment.

Depending on the required quality, the permeate produced can be used, for example, as process water, cleaning water, cooling water, or boiler feedwater.

Ultrafiltration is particularly useful when the feedwater contains particles, colloids, or elevated levels of microorganisms. It stabilizes water quality before the RO process and can thereby reduce the risk of fouling in the reverse osmosis system.

For industrial water reuse plants, the combination of UF and RO is therefore often a technically sound solution.

For deionized water, reverse osmosis is often used first to significantly reduce the concentration of dissolved salts. If an even lower conductivity is required, an additional polishing stage may follow.

Depending on the quality requirements, ion exchangers or EDI, for example, can be used for this purpose.