Prof. Paul Péringer, Prof. Christof Holliger, Chantal Seignez
CTI The Innovation Promotion Agency, Berne, Switzerland
1996 – 2000
Rohner AG, Pratteln, Switzerland
Rohner AG produced textile dyes, dyazo-type chemicals, chemicals for the graphic industry and fine chemicals (substituted aromatics), a manufacture that involves the use of large quantities of solvents, part of which is emitted into the atmosphere as waste gas. In the gaseous emissions there are alcohols (methanol and ethanol), aromatic hydrocarbons (toluene and xylene) and chlorinated aromatics (monochlorobenzene and o-dichlorobenzene). In order to respect the environmental protection law of the Swiss and local authorities, Rohner was obliged to treat its gaseous effluents. The biofiltration was chosen because it is cheaper for treating air streams containing low concentration of pollutants than classical air-cleaning techniques such as combustion or adsorption. The goal was to develop a biotrickling filter system in collaboration with LBE to treat waste gas from this medium sized chemical industry located in Pratteln, Switzerland. The objectives were
- to develop a system to separate waste gas streams in order to avoid mixing of incompatible compounds for biodegradation,
- to establish microbial consortia able to degrade efficiently either a mixture of toluene and xylene or chlorobenezene and dichlorobenzene, and
- to develop an operation procedure for optimal performance of the biotrickling filter system.
The inocula were produced by a special technique where the substrate was supplied by pulses to allow the growth of bacteria with different degradation properties. It has been observed during the cultivation of the inocula as well as the operation of the biotrickling filter that intermediates formed during the degradation have a negative effect on the performance of the microbial consortia. Different bacterial strains have been isolated from the solvent degrading consortia, which led to the discovery of a new CB degrading bacterium.
The biotrickling filter technology was applied for the treatment of waste gas containing a mixture of chlorobenzene and 1,2-dichlorobenzene. The adapted microbial community was immobilized on a structured packing material. The strategy followed was to reach first high removal efficiencies at low mass loading rates followed by an increase of the latter. This procedure was successful and resulted in a short start-up period of only two weeks. Three months operation under steady-state conditions showed good performance with >95% removal efficiency at a mass loading rate of 1800 g m-3 d-1. Dimensionless concentration profiles showed that the chlorobenzenes were simultaneously degraded. Low dissolved organic carbon of 15 mg l-1 and stoichiometric chloride concentrations in the trickling liquid indicated complete mineralization of the pollutant. Transient-state experiments with five time higher mass loading rates caused a decrease in the removal efficiency that recovered fast once the mass loading rate was again at its original steady-state level. A progressive increase of the mass loading rate in a long-term performance experiment showed that the removal efficiency could be kept stable between 95 and 99% at loads up to 5200 g m-3 d-1 during several days. Above this mass loading rate, the elimination capacity did not increase any further. These results demonstrated that with a well-adapted inoculum and optimal operation parameters, a biotrickling filter system with excellent performance and stability can be obtained that efficiently removes a mixture of cholorobenzene vapors from air.
The developed technology has been successfully implemented at Rohner AG, Prattlen, Switzerland. This project has been honored with the first price in its category of the 1998 competition “Technologie Standort Schweiz”.