Tackling odour nuisance in air emissions from wastewater treatment plants

WWTPs often produce emissions from multiple sources: for example, from sludge storage silos or buffer tanks; during the process of dewatering sludge for transportation; and from hall ventilation.

The chemicals responsible include organosulfur compounds such as mercaptans including dimethyl sulfide (DMS) or dimethyl disulfide (DMDS); aromatic hydrocarbons; hydrogen sulfide (H₂S); and ammonia (NH₄).

Odour limits depend on the country, the WWTP’s environmental permit, and how close the WWTP is to residential areas. The problem is exacerbated by the expansion of cities, with more housing being built closer to existing WWTPs.

One WWTP in the Netherlands needed to treat both emissions from hall ventilation and also point emissions from sludge mixing and storage.

The hall ventilation produced a very high flow rate with a low concentration of pollutants, typically sulfuric compounds.

The point extraction from sludge mixing and storage, however, produced a low flow rate of around 1 000 to 2 000 m3 per hour with a high concentration of pollutants, including inorganic compounds.

DESOTEC engineers have drawn on their extensive expertise to design the optimal filling for the activated carbon filters, focusing on ammonia and organosulfur compounds. The result is that the odour has been completely removed, and cannot be detected by those living nearby.

Odour removal was just one part of the client’s requirements. It is also aiming to be CO₂ neutral by 2025, and is therefore placing its sludge into an anaerobic digester on site to produce biogas for energy. An additional advantage is that transportation of sludge is no longer necessary.

Many WWTPs and sewage treatment plants are following similar models, with some bringing sludge from other plants to their own sites for mixing to create biogas.

This is a further potential application where DESOTEC solutions can help – filters which treat the pollutants in biogas or biomethane are also available.

While these are all long-term applications, DESOTEC can also provide emergency and short-term solutions. We work 24/7, and can install our mobile filters swiftly, for example when bacteria in a biofilter die off unexpectedly.

Our engineers can advise on the best types of carbon, including impregnated carbon, for different applications. Whatever the situation, we work with clients to find the optimal solutions for their site and its neighbours.