Disinfection of exhaust air from a wastewater treatment plant

Cause

Deutsche Extrakt Kaffee GmbH Berlin (hereafter DEK) has installed a biological wastewater treatment plant for the pre-treatment of its wastewater. Aerosols containing germs escape from the open aeration basins into the environment. An initial measurement showed a germ load of approx. 3,200 cfu/m³. A risk assessment carried out could not exclude the presence of pathogenic germs, especially legionella. [This prompted DEK to supplement the biological wastewater treatment plant with a treatment of the exhaust air stream. The disinfection performance should be at least 90%.

The disinfection of exhaust air has long been one of the standard applications of photo-oxidation technology. By irradiating with UVC light at 254 nm, bacteria (e.g. Escherichia coli, Pseudomonas, pneumococci, streptococci) are inactivated in such a way that proteins, DNA and other cell components are irreversibly damaged. In this way, the dreaded exponential growth processes are prevented. The sensitivity of the various microorganisms to UV-C radiation varies greatly and must be taken into account.

Disinfection of exhaust air from a wastewater treatment plant

For the application at hand, two processes - aerosol separation and disinfection - have been combined. The duct separator used is capable of separating aerosols up to a separation efficiency of 99.999%. Aerosol separation and the associated reduction of relative humidity are of decisive importance for the effectiveness of the disinfection unit. In addition, this separator is equipped with an automatic cleaning system that enables continuous cleaning of the separator. Wash water and condensates are fed into the aeration tank via a siphon.

In this way, the exhaust air is optimally pre-treated before it enters the downstream disinfection unit. This unit consists of a horizontally arranged irradiation chamber in which horizontally arranged UV-C low-pressure lamps are installed. The open aeration tanks are fitted with a bonnet made of galvanised steel/stainless steel. The disinfection unit with a nominal capacity of 1,800 Nm³/h is connected to the bonnet via a pipe/duct.