Sewage sludge represents an important energy- and material resource for the agricultural economy specifically, and for the economy in general as well: it has a fuel value of 10 to 12 MJ/kg and a phosphorus content of 2 to 8% in dry mass. Its exploitation-efficiency, however, is still inadequate, mainly because its energy-efficient use and its material exploitation through fertilization or phosphorous recycling are, to a great extent, mutually incompatible. To date there have been no viable concepts for enabling sewage sludge exploitation in sewage treatment plants.
With the newly-developed metallurgic phosphorous recycling “Mephrec® Process“ from the ingitec Foundry Engineering Firm GmbH (ingitec Ingenieurbüro für Gießereitechnik GmbH) of Leipzig, a one-stage technology which combines both is available for the first time: phosphorous recycling and energy extraction from sewage sludge are carried out in a single procedural step. The material is compressed into briquettes and subjected to melt-shaft gasification at temperatures of up to 2000 °C. Through this process a phosphorous slag low in heavy metals, a metal alloy which works as a heavy metals drain in the melting gasification system, and a high-fuel-value combustible gas are produced.
In order to guarantee the broadest possible application of the process, it is of crucial importance to continue the transformation of sludge into briquettes despite variable sludge quality. The energy-efficient and economical briquette-manufacturing technology developed by ingitec (ingitec Bürogemeinschaft für Gießereitechnik GbR, Leipzig) ensures that this is feasible.
