Biological break-down of harmful substances in waste gas and waste water

Bacteria on activated carbon-doped PU carrier break down harmful substances from waste gas and waste water

Solvents are used in many industrial sectors, such as the production and processing of paints and lacquers, the chemical and pharmaceutical industries, semiconductor industry and the production and processing of synthetic materials. The solvents often enter the environment as volatile organic compounds (VOCs) together with processed exhaust air flows. However, many companies are putting extracted air purification measures far behind other investments, as they rarely contribute to direct value creation. However, increased governmental requirements regarding environmental protection as well as residents' complaints about unpleasant odours have increased the pressure on companies to make more provisions for reducing VOC emissions or to improve existing treatment concepts.
This is why Centrotherm clean solutions GmbH & Co. KG has expanded its product portfolio to include plants for biological treatment of VOC containing extracted air or wastewater flows. Based on the CT Eco method, pollutants are eliminated by taking advantage of the fact that most organic compounds are biodegradable if special microorganisms are used. A modular plant concept makes it possible to customise the process to the specific application.
“Both the investment costs and the need to comply with legal emission limits play important roles when selecting a suitable extracted air purification concept,” says Dr. Angela Bayler, head of business development at centrotherm clean solutions GmbH & Co. KG. “Factors such as operating and maintenance costs, energy and other operating costs as well as the flexibility of the process to adapt to different processing conditions must also be taken into consideration.” Whereas the biological decomposition of organic pollutants is a long-established process, e.g. the treatment of municipal wastewater in sewage plants, biological processes for extracted air and wastewater purification have still to become established in industry. The reasons for this are, amongst others, the large space requirement for conventional biofilters as well as the, at times, poor long-term stability of the degradation process. Biological processes are also often difficult to adapt to fluctuating operating conditions such as fluctuating pollutant concentrations and compositions.
Therefore, extracted air flows that contain VOCs are usually treated in the processing industry through the use of thermal processes, such as thermal post-combustion (TPC). Since many of the extracted air flows that contain VOCs have a comparatively low pollutant load, this can sometimes become an extremely high energy and operating cost-intensive process.
By using a solution from centrotherm clean solutions, it is possible to ensure comprehensive biological break-down of organic pollutants from waste gases and wastewater in a multitude of applications, whilst also taking into consideration the different system requirements. Examples of the possible applications are the treatment of VOC contaminated extracted air flows from paint shops or the semiconductor or chemical industries as well as the reduction of the chemical oxygen demand (COD) of organic wastewater from the food or cellulose industries. The CT Eco process can also be used for the removal of odour-intensive substances during ground or process water treatment. As most of the organic substances are biodegradable when special microorganisms are used, this process is used mainly without the need of chemicals and is distinguished by a broad range of applications as well as low operating costs.
The CT Eco process uses a carrier material made from highly-porous polyurethane foam bodies and it is additionally doped with active carbon to further enlarge the surface. The carrier is covered with a film of bacteria that is able to absorb the pollutants and to metabolise carbon dioxide and water. The microorganisms use the pollutants as a food source. Other nutrients essential for bacterial growth are dosed in if required. During operation, a bacterial culture adapted to the relevant conditions is formed, by which a large number of organic pollutants can be degraded. “The active carbon coating on the PU carrier material provides optimal living conditions for the bacteria to fully develop their biological activities. High degradation rates in a small space are made possible by this”, continues Bayler. “The activated carbon also has a sort of buffer function: Pollutant peaks are first adsorbed on the activated carbon surface and they are then degraded by the microorganisms in situ over an extended period of time. At the same time, this buffer also causes the bacteria to survive without external pollutants over a long period of time.” The CT-Eco method solves previous biological plant problems where microorganisms are suspended in a solution or immobilised on non-porous carrier materials. Decisive advantages are the high space/time yield and the resulting compact design of the plants as well as the plant's huge tolerance against process fluctuations and downtimes.
The plant's modular design also makes it possible to customise the process to the specific application. “The CT-Eco is not an off-the-shelf but a custom-made product. Thus, we can always adapt the plant to the local requires”, says Bayler. By combining different modules, the plant can be designed both as a bioscrubber for extracted air purification and as a biofilter for treating organically polluted wastewater.
By using the most extensive circulation possible, the media consumption of the plants is restricted to small amounts of fresh water, which are needed to compensate for evaporation losses, as well as electricity for driving the air extraction fans or wastewater pumps. A nutrient solution for the bacteria normally has to be added only to bridge longer downtimes. Each project starts with a customer requirements assessment, whereby a material balance will be prepared, if necessary through additional analysis, and the application as well as the local conditions are discussed. Only then can the project planning and design of the plant, the selection of the appropriate bacterial culture as well as the planning and definition of the structural measures be undertaken. Finally, a demand report will be drawn up and a mobile test plant with all previously clarified conditions will be put into operation for a few weeks in order to ensure that the planned implementation meets the requirements and the required wastewater and extracted air purification can be achieved under real processing conditions. The trial operation can simultaneously be used to adapt the design and operating parameters for the later construction of the large plant in a process-specific and customer-specific manner. Once this has been satisfactorily completed, the detailed planning and construction of the coordinated CT Eco plant at the customer's site can start. Centrotherm clean solutions has a worldwide network of highly-trained service staff and process specialists for commissioning as well as any maintenance or repair work that might be needed.
A high degree of automation as well as intelligent communications between the plants with customers' on-site process or factory control systems have already implemented as standard components. This ensures that the plants always work at their optimum operating points and that the operating and maintenance effort is minimised. Further improvements regarding energy efficiency, e.g. through energy recovery measures as well as processes for recovering valuable components from extracted gases and wastewater flows, are the focus of future developments.