Sulphate waste water
Sulphate in the wastewater of an industrial Indirect discharger with a chemical-physical wastewater treatment system is a typical problem when non-substitutable processes with sulphate are present in the plant (e.g. sulphuric acid in anodizing), as the monitoring values of 600 mg/L sulphate or 3000 mg/L with HS concrete cannot usually be complied with, even with an appropriate calcium pre-treatment.
By the way, the problem can already occur due to the operation of an industrial reverse osmosis system as part of process water treatment if the sulphate value from the municipal water already reaches the limit of 250 mg/L set out in the Drinking Water Ordinance and the monitoring value is then exceeded in the concentrate. Incidentally, the exemption limit of 10 m³/week does not apply in this particular case of sulphate in wastewater of the process water treatment.
The basic limit values for the discharger are also determined based on the parameters of which substances are used in the plant. Two legal systems apply in parallel: state system monitoring (usually by the district office) with the limit values (monitoring values) from the Wastewater Ordinance (AbwV) and municipal monitoring at the transfer point to the municipal sewerage system (usually by the municipality/city), whereby the stricter limit value is decisive in each case. The state limits are usually the decisive values, as they are twice as strict as the municipal limits and are linked to a different monitoring point, however with the exception of pH, temperature and sulphate. Special rules apply to these municipal monitoring values. In particular, the sulphate limit value for wastewater, even after pre-treatment, is a frequent problem for industrial indirect dischargers for which there are now largely established legal standard solutions:
The wastewater sulphate problem usually arises due to the monitoring value of the municipal drainage statutes or of the association’s model statutes. This includes a monitoring value for sulphate to protect the sewerage system. An excessively high sulphate value – together with other marginal parameters, which must also be present – can lead to various types of concrete corrosion, among others via sulphuric acid-producing bacteria in the air phase. The damage to the concrete channel can go so far that it collapses completely. In this case, the polluter is usually responsible for the costs.
Although there are basic options for treating sulphate in wastewater chemically and physically, e.g. by precipitation using Ca or by ion exchangers, both processes also have their disadvantages or do not solve the problem, but rather move it to another location at great expense. In many cases, this is so serious that the chemical-physical treatment options in the wastewater treatment plant also become legally inadmissible.
A consensus is therefore required with the supervision authorities as to which legally permissible technical measures should apply to the monitoring value sulphate in wastewater and which measures the polluter should take in return. This view has now also found its way into various drafts of the generally recognized rules of technology. Publication is expected in 2025.
The highest known and approved sulphate load is 14,000 mg/L or (2024) 36,000 mg/L.
Do you need support with sulphate in wastewater as an industrial company in your chemical-physical wastewater treatment system? Please do not hesitate to contact us.