Heavy metal removal from wastewater: what changes in foundries
In foundries and, more broadly, in metallurgical industries, heavy metal removal from wastewater is one of the most critical issues for discharge compliance and site sustainability. The most problematic metals are often zinc, nickel, chromium, and copper, and in certain production processes or raw materials, lead and cadmium as well. These contaminants may be present in dissolved form, complexed with additives or surfactants, or bound to fine particulate matter, making a “multi-barrier” treatment approach necessary.
In practice, an effective strategy combines the separation of the most contaminated streams, targeted physico-chemical treatment for metal removal, and a polishing stage when very low residual concentrations are required. From a regulatory perspective, discharge limits depend on the receiving body (discharge to the public sewer system or to a surface water body) and on the site's permit conditions, with national references such as Italian Legislative Decree 152/2006 and often more restrictive local requirements.
If you need to verify compliance or size a custom treatment system, contact IDRO Group: we can support you from wastewater characterisation through to a turnkey solution.
Heavy metal contamination in water: where it originates and why it is difficult to manage
Water contaminated by heavy metals in foundries does not originate from a single source; it is typically the result of multiple streams combined together. The main sources include washing operations in production departments and outdoor yards, contact water exposed to dust and process residues, surface treatment or finishing lines (where present), and washing or recirculation systems associated with fume abatement or humidification processes.
Furthermore, different metals can behave in different ways. Chromium and nickel may remain more stable in solution, zinc may also be present in particulate form, while the presence of complexing agents can prevent simple precipitation.
For this reason, the most important preliminary step is almost always wastewater characterisation (metals, pH, solids, COD, surfactants, and any complexing agents), along with determining which streams should be segregated and treated separately.
Heavy metal treatment: precipitation, resins, filters and membranes
The basic technology for removing heavy metals from water is physico-chemical treatment, because it allows dissolved metals to be converted into separable solids.
In practice, the process involves pH adjustment and precipitation (typically as hydroxides, and in some cases as sulphides when lower residual concentrations are required), followed by coagulation/flocculation and solid-liquid separation (sedimentation, flotation, or filtration), together with sludge management.
When discharge limits are more stringent, or when complexing agents reduce precipitation efficiency, an additional polishing stage is introduced:
- Ion exchange or selective/chelating resins used as a polishing step, helping to further reduce specific metals and stabilise effluent quality.
- Specialised filters and membrane systems: advanced filtration, ultrafiltration, and nanofiltration can be employed to improve water quality and, in water reuse scenarios, to produce reusable process water.
In this field, IDRO Group also supplies compact and modular systems for process water recovery and reuse, where a membrane line (for example, ultrafiltration combined with nanofiltration) can be integrated with a dedicated physico-chemical treatment system for concentrate management, designed to ensure operational stability and adaptability to load variations.
Regulatory limits and compliance strategy: what to monitor and how to structure the project
Achieving compliance requires more than simply installing a treatment plant; it is necessary to establish a control strategy that combines permit limits, process variability, and operational continuity.
Applicable parameters and discharge limits derive from the regulatory framework governing wastewater discharges, particularly Italian Legislative Decree 152/2006, as well as the specific requirements of the site's discharge permit.
In general, an effective project includes defining the receiving body and applicable limits, whether discharge is to the sewer network or a surface water body, segregating critical streams, selecting the appropriate physico-chemical treatment based on the actual metal speciation, and sizing the polishing stage to handle peak loads.
From an operational perspective, it is useful to define sampling points and establish a monitoring plan using rapid indicators such as pH, conductivity, and turbidity, alongside periodic metal analyses and structured management of the generated sludge.
If you are considering a heavy metal wastewater treatment solution for a foundry or metallurgical plant, IDRO Group can support you from wastewater characterisation and system design through to turnkey implementation and operational management, in compliance with the limits and requirements applicable to your facility.
