Reverse osmosis system industry, RO system

A reverse osmosis system (RO system) is used in the same way as a demineralized water system to produce demineralized water. The input water, often city water, is softened or hardness-stabilized and applied to a membrane under high pressure to produce consistently pure demineralized water for industrial purposes, known as permeate, and saline wastewater, so-called concentrate.

High-purity water is often required in many industrial processes, e.g. when cleaning parts after metalworking. The use of city water “from the tap” is prohibited due to the formation of stains caused e.g. by hardness formers such as calcium and magnesium. The core element of the reverse osmosis system is a high-pressure pump that presses the inlet water onto a semi-permeable membrane at with around 14 to 16 bar. Depending on the membrane and process used, an average salt retention of 97 to 99% of the input water is achieved, typically with a conductance of 5 – 15 µS/cm at 15°C water temperature, related to the salt content. Depending on the process, there is also a continuous concentrate discharge, i.e. wastewater, of around 10% – 25% of the input water, which can or must be discharged into the operational wastewater stream at various points. This requires a permit from a discharge volume of 10 m³/week,a separate wastewater treatment system for the treatment of the wastewater flow, however, is generally not required (exception e.g. excessive copper values in drinking water, as up to 2.0 mg/l are permitted according to the Drinking Water Ordinance, but the monitoring values for Cu in wastewater are 0.5 mg/l or often 1.0 mg/l for less than 10 m³/week of concentrate according to the respective drainage statutes, as well as other parameters). The reverse osmosis system industry generally requires a pre-treatment unit for the hardness formers, usually a (duplex) softening system based on ion exchangers, which is regenerated with common salt, or an anti-scalant dosing, which ensures temporary masking of the hardness formers through complex formation.

A common application for a reverse osmosis system Industry is the production of demineralized water in a surface treatment company with a conductance of < 20 µS/cm salt load. The RO system consists of a system separator, a 100 µm pre-filter, a duplex softening system each with one strongly acidic cation exchanger in the Na form, so-called SAC (sulphonic acid exchanger on styrene-divinylbenzene copolymer) and NaCl regeneration. The high-pressure pump increases the pressure from at least 2 bar to 14 bar on the 120 µm thick polyethersulfone layer of the semi-permeable membrane and thus performs a temperature-dependent separation of the feed into permeate and concentrate. However, the demineralized water produced differs from the demineralized water from a demineralization system in that the ion retention on the anion side depends on the respective ion: ammonium ~92%, nitrate ~85%, fluoride ~95%, silicate ~90%, sulphate ~97%.

An industrial reverse osmosis system can be expanded with additional filtration stages depending on requirements. The typically installed softening system can be replaced with an antiscalant dosing system for larger volume flows. Gases dissolved in the feed stream (CO2) may be converted into HCO3 in advance by pH adjustment and separated at the membrane or by means of a downstream membrane degassing. A further reduction of the conductance down to the technically lowest achievable conductance of 0.056 µS/cm or 18.2 MΩ-(at 25°C) cm as ultrapure water can be achieved without a wastewater system, e.g. by a downstream demineralized water cartridge with a mixed bed ion exchanger as exchange cartridges or by electrodeionization (EDI system) for continuous purification. The membranes installed in the system can be chemically and thermally cleaned using an optional cleaning system (for larger systems). The RO system can also be designed as permeate-staged, i.e. two reverse osmosis membranes in series in the permeate for a special purification of the demineralized water up to 99.5% of the input water or concentrate-staged, i.e. two reverse osmosis membranes in series in the concentrate for a particularly small amount of wastewater. In the event of changing inlet pressure or fluctuating delivery quantities, storage tanks with pumping stations may be required.

Fully demineralized water (VE-water) or deionized water (DM water) is not defined separately as such, but its parameters are derived from the customer-specific process.

Demineralized water from a reverse osmosis system (RO system) differs from demineralized water from an ion exchanger-based demineralized water system in terms of its composition, even if the conductance is comparable, due to the different production processes. Therefore, pay attention to the requirements for your process. Typically, however, the water from a reverse osmosis system is suitable for most processes such as forklift water or battery water or for use in electroplating, for example.

As a rule, the VE-water produced by reverse osmosis systems, known as permeate, is monitored using the conductance in [µS/cm] at the outlet of the reverse osmosis systems. Typical conductance values at the outlet of the RO system are values between 10 – 20 µS/cm in relation to the total conductance value, depending on the input water, system and expansion stage.

If a lower conductance is required, this can be achieved by further expansion stages, e.g. a permeate-staged RO system or downstream electrodeionization and/or a demineralization cartridge in order to produce conductance values between 1 – 0.1 µS/cm, so-called pure water, or even lower of 0.1 – 0.056 µS/cm, so-called ultra pure water.

A typical question for system operators in industry with a desired conductivity of around 20 µS/cm is whether to purchase a reverse osmosis system or a demineralization system (resp. only a demineralization cartridge or VE-cartridge for small quantities of< 4 m³/week which is to be regenerated externally via the ion exchanger regeneration service). Both typically achieve this conductance value, but differ in the process and the composition of the demineralized water produced. If only the conductance value is required as a sum parameter, the main differences can be summarized as follows: A wastewater treatment system is required for the demineralized water system, but generally notfor the reverse osmosis system. Both systems do not require a WHG permit on their own up to 10m³/week of wastewater production (however, the municipal monitoring values still apply, especially copper can be problematic here due to the Drinking Water Ordinance, as this can be present up to 2.0 mg/l, but the Wastewater Ordinance regularly provides a monitoring value of 0.5 mg/l or 1.0 mg/l for small discharges of < 10 m³/week). The industrial reverse osmosis system constantly produces waste water via the concentrate ejector, whereas the ion exchanger system does not. Cost considerations can be made over the period of use, in which the generally higher acquisition costs for the VE system can be weighed up against the lower operating costs, see here as an example.

Products

Reverse osmosis system 300 with pure water tank
Reverse osmosis system 10000
Reverse osmosis system 10000 3D

If a water softener is installed upstream of a reverse osmosis system, it is always equipped with its own regeneration station with common salt (NaCl).

The separator modules installed in the reverse osmosis system, so-called RO membranes, have a typical service life of ~5-7 years, depending on the load from the input water. Please note that the system must at least be notified in accordance with Annex 31 of the Wastewater Ordinance if more than 10 m³/week of wastewater is produced. The wastewater is usually made up of the backwash from the pre-filtration, the regenerate from the softening system and the continuously occurring concentrate from the reverse osmosis system. The local drainage regulations with their monitoring values also apply to every discharge, i.e. limit values can also be violated below the limit of 10 m³/week.

Customized design of the reverse osmosis system:

  • Customized design to suit the process (city water/well water constituents), regulatory requirements and budget, starting from an all-in-one complete and rack-mounted “plug-and-play” basic version (with system separator, prefilter, simplex softening and reverse osmosis) to self-cleaning, permeate- or concentrate-staged RO with softening duplex design or antiscalant dosing.
  • Adaptation to any existing control technology and connection to a process control system and the existing structural conditions at the site or the entry to the site
  • Meeting customer requirements for industrial processes when planning a reverse osmosis system Industry
  • Use of high-quality ion exchangers for pre-softening, e.g. from Lanxess Lewatit or Purolite.
  • Siemens PLC circuit with/without touch display and with the option of external access or microprocessor control
  • Duplex version on the softener for uninterrupted 24/7 operation optional
  • “Plug-and-play” design for the user. Only connection to electricity, city water, permeate (pure water for further use) and concentrate/regenerate pipes (waste water) required.
  • Stainless steel frame
  • Pipes and fittings in PVC or PP or stainless steel
  • Internal flushing processes to preserve the membranes
  • Possibility of pre-acceptance and trial operation in our own workshop
  • Modular, maintenance-friendly design according to customer requirements with various optional expansion options, e.g. UV-irradiated storage tanks with sterile filtration, chemical storage tanks as dosing stations or as AwSV LAU systems, collecting basins, simple feeding to redundant FU duplex pressure booster stations, membrane degassing systems, electrodeionization, a demineralization cartridge or VE- as a mixed bed polisher.

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