The electrical pig burrows in the sludge, ploughs huge areas - and still does not need to be fed

Solar sewage sludge drying systems from world market leader Thermo-System GmbH from the Stuttgart region help to reduce disposal costs and protect the environment
Filderstadt, 02.03.2006 | 

The world market leader for solar sludge drying is located in the Stuttgart Region: Thermo-System GmbH, founded in 1997 by scientists from the University of Hohenheim, has filed the patent for a cost-effective and environment-friendly solar drying process that can solve the waste disposal problems of sewage treatment plant operators all over the world. The company"s innovative solution has already proven itself at more than 60 locations in Germany, France, Brazil, Australia and Austria. In the USA, operators of sewage treatment plants in Rogue River (Oregon), Riovista (Tennessee), Discovery Bay (California) and Keowee Key (South Carolina) are already betting on the environment-friendly drying process. And it has already won several prizes, including the coveted "WEFTEC 2004 Innovative Technology Award", awarded annually by the Water Environment Federation.

The heart of the solar slurry drying plant is an "electrical pig’. It does not grunt, nor does it need to be fed. It churns its way tirelessly through the slurry and ploughs huge areas in a short time. The little robot vehicle used in solar slurry drying plants does its job in greenhouse-like sheds where the wet sewage sludge is spread for drying. Sunlight and a clever ventilation system ensure that water is removed from the brown mass. In this process, the little vehicle, which reminds one of a VW Beetle without a roof, has an important job to do. Using its mixing tools, it turns over and aerates the microbiologically highly active sludge, thus accelerating the drying process and helping to prevent rot. Drying is an important preparatory step for processing the liquid "treated sludge’; after all, untreated sludge consists to more than 95 percent of water. This thermal recycling is now considered to be the ideal method of sewage sludge disposal.

The main idea of the inventive founders was the following: instead of natural gas or oil, the sun should provide the energy required for the drying process. "In all conventional approaches, removing water from the slurry involves high energy and personnel costs," Dr. Tilo Conrad, one of the two managing directors, explains with regard to working the drying systems in conjunction with the "electrical pig’. "It"s much better to let the sun do our work for us, free of cost."

Of course, there is some sophisticated technical know-how in the plants from the Thermo think tank. The core of the system is a lightweight construction shed of weather-resistant galvanized steel. Of the simplest design, it is covered by a transparent polyethylene bubble-wrap foil. Through this transparent foil, sunlight penetrates unhindered into the insides of the shed; the moist slurry absorbs the heat of the radiation; and a sort of greenhouse phenomenon occurs. To support these natural effects, there is some clever engineering that comes into play. At one gable end, an exhaust fan ensures that the inside air -- and with it, the moisture separated from the slurry -- is driven out, and a ventilating valve on the opposite side lets fresh air in. Sensors and microprocessors regulate the exchange of air. The electrical pig additionally facilitates the ventilation by turning over the slurry.

This process offers a number of economic and ecological advantages. The low investment cost of about 150,000 Euro for a small plant is an important argument for the operators of sewage treatment plants. But the environment also benefits from this patented development: the solar drying reduces the transport volume of the slurry, making many truck trips superfluous. In addition, no fossil fuels are burnt, and bad odors are avoided. Due to their international success, Dr. Tilo Conrad is counting on further rapid growth for his company. Already, the electrical pig has more than 100 "successors’ all over the world - and its family is growing rapidly.

The Stuttgart Region
The Stuttgart Region has long been known as the center of Europe’s automotive and industrial machinery industry. More recently, Eurostat, the European Statistical Office, has labeled it "the high-tech capital of Europe". It is the home of global companies including DaimlerChrysler, Porsche and Bosch and also leading universities and private research institutes. It is a region of 2.6 million people and has Germany’s lowest unemployment rate, highest export ratio and the highest number of patents per capita.

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