Treatment of industrial waste water

Essen, 2 September 2024 – Water is needed for a wide range of industrial applications. It is used as a coolant, heat transfer medium, steam, raw material, solvent, washing water, etc. The possibilities are as diverse as our industry itself.

According to the Federal Statistical Office, businesses (excluding public water utilities) consumed a total of 15.3 billion cubic metres of fresh water in 2019. By far the largest share (84.7%) is used for cooling production and power generation plants. Since the majority of the cooling water is either recirculated or can be returned to nature without being polluted, it usually does not require any separate cleaning as waste water. Only in water-poor waters is it important to ensure that the temperature of the water into which the water is discharged is not increased to an impermissible level.

According to the Federal Statistical Office, the next largest share of water used in the economy goes to production and other purposes (10.7%). Unless the water is incorporated into the products (1.4 %), sooner or later this water will end up as industrial wastewater. A distinction is made here between indirect and direct dischargers.

Indirect discharge

Industrial and commercial enterprises, but also most private households, are understood to be indirect dischargers if they discharge wastewater via a public or private sewer system to a municipal or private wastewater treatment plant before it is returned to the water cycle.

In the case of indirect discharge, it should be noted that only those substances that cannot be removed, or cannot be sufficiently removed, by the corresponding treatment plant must be removed beforehand by means of pre-treatment. Since the equipment and ability to break down different substances varies in the individual municipal treatment plants, the requirements for the water to be discharged are regulated in the corresponding drainage statutes of the cities and municipalities.

Direct discharge

In the case of direct discharge, the wastewater is treated directly on site and discharged into a body of water. The minimum requirements for water are regulated here both for municipal sewage treatment plants and for industrial wastewater treatment plants in the German Federal Wastewater Ordinance (AbwV). It is not differentiated regionally, but according to so-called wastewater source areas or industries.

The AbwV is supplemented by the Water Framework Directive (WFD), depending on local conditions. The WFD in turn differentiates regionally, as it aims to achieve ‘good status’ for all rivers, lakes, groundwater and coastal waters at the European level by 2027.

Wastewater treatment in industry

In principle, the same wastewater treatment processes are available to industry as are available to municipal sewage treatment plants.

The advantage for industry is that it can be very targeted, since in most cases the target substances are known and the composition of the wastewater does not fluctuate or vary as much as in municipal wastewater. If the wastewater contains oil, for example, grease traps are used. If sand, shavings or similar solids get into the wastewater through production processes, the wastewater is filtered. However, a full or partial biological stage is also possible. This allows carbon, phosphorus and nitrogen to be broken down biologically. Some substances, such as phosphorus, can also be chemically separated from the water by precipitation.

In a sewage treatment plant, the degradation processes take place under optimal conditions and are identical to the processes that occur more slowly in nature.

Substances that cannot be removed, or cannot be sufficiently removed, by these processes pose a problem. Bioaccumulation and persistence lead to an accumulation of toxic substances in water and in nature. Sooner or later, this can lead to drinking water sources becoming contaminated. It is therefore better if these substances do not enter the environment and the water cycle. These substances are also referred to as trace substances or micropollutants. These include, among others: pharmaceutical residues, organic chlorine compounds, disinfectants, corrosion inhibitors, pesticides, polycyclic aromatic hydrocarbons (PAHs), plasticisers and other persistent compounds.

If we take a closer look at these substances, it quickly becomes clear that some of them are indispensable in industrial processes. One possible solution for removing these micro-pollutants from the wastewater stream is to adsorb them onto activated carbon. There are a number of different methods available for doing this.

Adsorption on powdered activated carbon (PAC)

The wastewater is fed into a contact reactor into which the powdered activated carbon is dosed. In the contact reactor, the activated carbon and the wastewater are intensively mixed. During this process, the micro-pollutants adsorb to the activated carbon and can then be removed from the wastewater stream together with the activated carbon. At present, the powdered activated carbon cannot be reprocessed after use and is disposed of.

Adsorption on granulated activated carbon (GAC)

In this process, the wastewater flows through a filter that is equipped with a bed of activated carbon. As the wastewater passes through the activated carbon bed, the micropollutants adsorb onto the activated carbon and the treated wastewater exits the filter (adsorber).

When the activated carbon has reached the end of its capacity, either the activated carbon filling can be replaced or the entire adsorber can be replaced when working with GAC filters.

In many cases, the granulated activated carbon used can be reprocessed afterwards and thus fed back into the value chain. In this process, known as reactivation, the micro-pollutants are desorbed from the activated carbon at high temperatures, and the pores of the activated carbon are opened up again for a new or further use. This increases the lifespan of the activated carbon used and thus reduces the carbon footprint.

We will be happy to advise you on any questions you may have about activated carbon and reactivation.