Selective exchanger system, SAT system

A selective exchanger system, SAT system, is used as a so-called police filter in industrial wastewater plants (CP plants, chemical-physical wastewater plants) in the final filtration after precipitation/flocculation or, for example, in groundwater remediation in order to keep regulatory relevant residual heavy metal contents in the wastewater below the required monitoring value.

In industrial chemical-physical wastewater treatment plants, there is usually a batch or continuous treatment of the wastewater produced, in which substances relevant to monitoring are removed from the wastewater by precipitation and flocculation. However, due to the complex composition and discontinuity of industrial wastewater (partial) streams, this treatment alone may not be sufficient to meet the official requirements for wastewater treatment in accordance with the relevant annex of the Wastewater Ordinance or, in the case of indirect dischargers, the drainage statutes of the local municipal wastewater treatment plant. To ensure this in accordance with the state of the art, a selective exchanger system, SAT system, with an IDE exchanger resin (iminodiacetic acid exchanger), e.g. Lewatit TP 207, is used in these cases to remove the heavy metals not sufficiently reduced in the CP treatment, often nickel, copper, zinc or lead, and replace them with Na⁺, Ca²⁺or another cation with which the Ion exchanger was conditioned. Parameters that are not relevant for monitoring, such as alkaline earth metals (e.g. Mg), are not bound by the exchanger to a relevant extent in order not to unnecessarily exhaust the capacity of the exchanger. The order of binding is determined by the ion exchanger selectivity, i.e. the affinity of the individual heavy metals for the iminodiacetic acid group of Lewatit TP207.

The same process can also be used in groundwater remediation, depending on the parameters, possibly also with other resin types than the selective exchanger TP 207, e.g. a weakly or strongly basic anion exchanger for cyanide complexes.

Selective exchanger system use case:

A typical application of a selective exchanger system is the so-called police filter after chemical-physical wastewater treatment in metalworking companies that discharge indirectly into a municipal wastewater treatment plant. According to Annex 40 of the Wastewater Ordinance, the parameters subject to monitoring for indirect discharge are generally 0.5 mg/L nickel and 0.5 mg/L copper, for example. In the course of chemical-physical wastewater treatment, e.g. by means of hydroxide precipitation and flocculation via a polymer and/or a bentonite, the heavy metals are precipitated to a residual content of a few mg/L. In this area, it makes economic sense to use an IDE selective exchanger such as Purolite S930 Plus or Lewatit TP 207 to achieve the legal limits by means of ion exchange against sodium, for example. The use of an IDE selective exchanger may eliminate the need for sulphide-based complexing agents. A new selective exchanger system or significant changes to existing systems are subject to WHG approval.

Another application is the targeted removal of foreign substances from process solutions, e.g. the removal of foreign metal ions (Cu, Ni, possibly Fe(III)) from a process solution for chromium deposition based on Cr(III) salts.

Selective exchangers are also regularly used in groundwater remediation and the remediation of contaminated groundwater. When designed for external ion exchanger regeneration, no waste water is produced on site in this application.

Further process engineering expansion stages:

Furthermore, depending on the application of the selective ion exchanger system, a (physical) pre-filtration by means of a gravel filter or multi-layer filter and a pH adjustment in the inlet and outlet of the ion exchanger is carried out in order to optimize the feed parameters for the selective ion exchanger for heavy metal separation. In addition, any interfering biology can be denatured using UV light and separate post-filtration and/or apolar or non-ionic substances (in particular mineral oils) can be removed using activated carbon or a scavenger resin as an exchange unit. In rare cases, further filter stages with separate filter material may be required, e.g. a strongly basic anion exchanger to remove anionic complexes or anionic compounds (e.g. PFC) or a further ionogenic filter material.

Functionality of the selective exchanger system

Although an ion exchanger such as a selective exchanger system basically works like a filter, it is an ion exchanger. This means that it always requires a preload, usually sodium in the case of selective exchangers, which is released when loaded with another, usually divalent cation such as nickel. When the selective exchanger has reached the end of its capacity, i.e. sodium has been completely replaced by nickel and copper, for example, the selective exchanger enters a discharge phase if it is loaded further. This means that copper is now bound further in accordance with its selectivity series, but the less strongly bound nickel is released again due to the lack of further exchanger groups. In this case, the selective exchanger is overrun, the value in the outlet of the ion exchanger is higher than in the inlet and can also violate a monitoring value. SAT exchangers are therefore always operated as 2 cartridges in series to prevent unintentional overrunning of the ion exchanger.

The selectivity series of a selective exchanger system with the selective exchanger resin Lewatit TP 207 (iminodiacetic acid exchanger) corresponds to the ion exchanger selectivity:

Fe³⁺ > Cu²⁺ > TiO²⁺ > VO⁵⁺> UO²⁺ > VO²⁺ > Hg²⁺ > Pb²⁺ > Sc³⁺ > Ni²⁺ > Zn²⁺ > Co²⁺ > Co²⁺ > Cd²⁺ > Fe²⁺ > Be²⁺ > Al³⁺ > Mn²⁺ > Ca²⁺ > Mg²⁺ > Sr²⁺ > Ba²⁺ > Na⁺ > K⁺ > Cs⁺

Requirements for the residual heavy metal content of the wastewater treated by the selective ion exchanger system

As a rule, the wastewater treated by a selective exchanger system is monitored on the basis of the heavy metal content in the final pH control. Depending on the annex of the Wastewater Ordinance or the statutes of the municipal wastewater treatment plant, individual, regulatory heavy metal monitoring values apply to the discharger which can be complied with by means of a SAT, usually based on Part D of the respective annex of the Wastewater Ordinance:

Copper 0.5 mg/L, nickel 0.5 mg/L, lead 0.5 mg/L, zinc 2.0 mg/L

In addition, other municipal requirements for indirect dischargers based on DWA-M 115-2, such as pH, temperature, sulphate or requirements from Part C of the respective Annex to the Wastewater Ordinance, which are summarized in the individual indirect discharger permit, also regularly apply.

In special cases, a further or different ion exchanger or filter material may be required instead of or in addition to an iminodiacetic acid exchanger, e.g. a strongly basic anion exchanger for anionic complexes.

Nickel recovery systems using the example of compaction / anodizing

In principle, the selective exchanger can also be designed to recover valuable materials, so that the heavy metals recovered, e.g. nickel from the compaction in the anodizing process, are concentrated in the reclaimed material. The system consists of two ion exchanger columns through which water flows in series. After regeneration, the freshly regenerated column is connected downstream (operation I – II / II – I). The discharge limit for nickel is complied with at all times. The regeneration of the loaded column (450 L selective exchange resin Lewatit TP 207, loaded with approx. 17.4 – 22.5 kg nickel) is carried out with sulphuric acid. The regenerating acid is used several times for regeneration to produce a recyclable concentration of between 50 and 70 g/L nickel. The nickel concentrate is automatically removed proportionally during each regeneration and replenished with fresh acid. No rinsing water containing nickel is discharged during regeneration, but remains in the system for replenishment.

Products

Selective exchanger system

Selective exchanger systems

Selective exchanger plant-nickel recovery plant

Selective exchanger systems for external regeneration 3D

Depending on the design of the system for the customer process, a selective exchanger system has its own regeneration station for on-site regeneration. Due to the often long running times of SE systems, it often makes sense to have the ion exchanger regeneration service carried out externally at the central regeneration station in 92348 Berg.

For a flow rate of between 2.5 and 20 m³/h and for heavily contaminated wastewater, a selective exchanger system with its own regeneration station is advisable. The resins used in the system in the two columns connected in series are regenerated with an acid and activated with an alkali, usually with hydrochloric acid and caustic soda. The regenerates from the plant are then treated in the company’s own chemical and physical wastewater treatment plant. Please note that the system is at least subject to notification under water law.

With a flow rate of up to 5 m³/h, an externally regenerated ion exchanger system is often the more economical solution, in special applications up to 25 m³/h. This means that the ion exchanger cartridges are loaded at the customer’s premises during the customer process and then sent to the central regeneration station in 92348 Berg. After regeneration, the cartridges are returned to the customer. The cartridge size can vary depending on throughput and capacity and is typically between 30 – 1500L resin volume.

Customized adaptation of selective exchanger system:

Customer-specific design for the wastewater treatment process in existing or new CP wastewater plants (e.g. also wastewater containing Cr(VI) and cyanide) and degree of automation starting from a semi-automated, functional basic design with 2 columns up to an automated and remotely monitored 3-column design.
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
Preliminary investigations and optional provision of test facilities/technical center possible
Fulfillment of the legal requirements for divalent heavy metals acc. the annexes to the Wastewater Ordinance acc. the best available techniques (BAT) for IED installations in accordance with of the IE Directive 2010/75/EU or the 4th BImSchV.
Siemens PLC circuit with/without touch display and with the option of external access
Duplex version for uninterrupted 24/7 operation as standard, additional protection with a 3rd pillar possible
Stainless steel or plastic frame construction for corrosive environments
Pressure tanks in PE/GfK, PVDF/GfK or coated steel
Selective exchange resin from LANXESS, Lewatit TP 207 or Purolite S930 Plus
Piping and fittings in PVC, PP, PE or PVDF from the manufacturers GF, GEMÜ (pneumatic or electric) or according to customer requirements; otherwise design with standard industrial components without special elements where possible.
Temperature design up to 70°C possible, higher temperatures on request. However, please note the maximum soaking temperature of 35°C, which should only be used permanently with special denaturation measures.
System design for operation in compliance with occupational safety requirements, even in the event of typical misuse
Disinfection option for the resin bed
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. multi-layer filters, receiver tanks, chemical storage tanks as dosing stations or as AwSV LAU systems, drip pans, simple feeding to redundant FU duplex pressure booster stations, pressure difference display, actual consumption and production data recording, separate resin changeover connections, system access control, valve position feedback, additional filter stages.
Designed as an ion exchanger to be regenerated externally in a central regeneration station for ion exchangers with exchangeable cartridges in the system (without wastewater generation on site) or as a system with its own automatic regeneration station on site (with wastewater to be treated on site).

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