After five years of practical experience the time has come for Imtech, one of the leading companies for technical building equipment in Germany, to offer a promising procedure for the treatment of residual household waste to the international market: At the exhibition area "Metropolitan Solutions" at the Hanover Fair, Imtech presented its Maximum Yield Technology (MYT), which gains quality-assured fuels, biogas, minerals and metals from household waste.

The MYT has been developed by the Zweckverband Abfallbehandlung Kahlenberg (ZAK). Since 1996, the public company has been working on mechanical biological treatment technologies with the aim of breaking waste down into usable components, as opposed to landfill or incineration solutions. After a number of large-scale technical pilot projects, the patented „ZAK process" was developed in 2003 and went operational for the first time with the „Kahlenberg (ZAK) MBT Plant" project in 2006. Since then, the plant ? located at the village Ringsheim in the South-West of Germany ? treats over 100,000 tons of residual household waste a year.

The Imtech Germany GmbH has acquired the license of the method in the year 2010. "The MYT gives us the opportunity to offer to clients a well developed and working process which is extremely environmentally friendly and beneficial to the end user", said Dr. Jaroslaw Turek, who is responsible for the waste processing department at the Imtech group.

The MVT process consists of the following steps:

Waste acceptance ? A first inspection selects large unwanted materials and potential recyclables hidden in the waste, which are subsequently recycled or disposed. The inspected waste is continually fed to the mechanical processing step.

Mechanical pre-treatment ? A combination of different aggregates gains metals, minerals and fuels. Non-recyclable residual materials are sorted out.

Biological step ? In the Defined Aerobic Mixing Process (DAMP) the waste is selectively reduced in size and homogenized. Added process water ensures an uniform consistency. After a short retention time in the mixer, presses dewater the solid material. The water, which is rich of organic substances, is mechanically and physically treated to separate coarse and fibrous materials. Afterwards a mesophilic operated reactor ferments the organic ingredients of the water to biogas. The biogas is utilized for electricity and heat in a CHP. The gained energy covers the energy consumption of the process. Surplus heat is fed into an existing district heating system.

Biological drying ? In tightly-closed concrete tunnels, air flows through the solid waste material of the DAMP evenly and provides the microorganisms with oxygen. The micro-organisms feed on organic components and produce thermal energy. This thermal energy evaporates the water contained in the solid material. A homogenous, dry and free-flowing solid material is produced.

Mechanical material separation ? Sieving and classification systems break down the material into various sub-fractions. With differentiated materials handling, the energy-rich fuels, minerals and the few remaining metals flow into the loading stations.

Depending on national and regional requirements the minerals can either be re-used or land filled.

The refuse derived fuel (RDF) has defined standards in grade size range, chemical composition, heating value and biomass share. It replaces fossil-based resources.

Dr. Jaroslaw Turek's calculations: "Usually the process converts the household waste into about 35 to 40 percent of quality RDF. Out of 120.000 tons of household waste with an energy potential of 230.000 MWh/year the MYT extracts 165.000 MWh/year as solid fuels and 40.000 MWh/year as biogas. The own requirements of the process are 25.000 MWh/year."

The RDF can be used to replace fossil fuels in power plants or cement factories. According to Dr. Turek, for example a power plant in the German town of Pforzheim is substituting 25 percent of brown coal with fuels from the MYT process.

"For power plants involved in permit trading, the use of MYT fuels offers many ecological and economical benefits", stated Dr. Turek. Half of the RDF consists of biomass. If a power plant replaces a portion of its primary fossil fuels with renewable materials, there is a corresponding reduction in the overall emission of CO2. The power plant thus emits less CO2 than it is entitled to – based on the number of emission permits it has. The power plant operators can then sell the surplus emission permits for their own gain.

According to Imtech, the MYT can be easily operated near residential areas. "The main reason for this is the elaborate emission concept and treatment", said Turek. Polluted discharged air and process air streams are captured and recycled again. Discharged air with low-level pollution is fed through humidifiers and bio-filters. Air washers and a regenerative thermal oxidation system clean more severely polluted process air streams.

For the treatment of one ton of waste in the MYT plant the citizens currently have to pay around 80 Euro.