German robot pig the star of sludge drying plants

Robot pig. Photo: www.thermo-system.com

What would a machine look like if it lived in the mud? Well, probably like a pig. Some 12 years ago, Tilo Conrad, together with two of his fellow students from the University of Hohenheim, built the first electrical pig, pioneering a device that is now being used as a solution to waste disposal problems throughout the world.

The stainless steel pigs, which in a sense resemble big beetles, are an important part of a larger solar drying process was patented by Thermo-System GmbH, a company Conrad founded in 1997 in Filderstadt.

Today, nearly 200 mechanical pigs do what normal pigs do: wallow in and shuffle through the mud — only these pigs do it to reduce sewer sludge disposal costs and protect the environment. Conventional drying processes use non-renewable energy, but Thermo-System’s process harvests solar power to dry the mud. It spreads the wet sewage sludge into sheds that are similar to greenhouses and puts the pigs to work.

In the sheds, the sludge absorbs heat from the solar rays and an innovative ventilation system keeps the air inside the shed warm and dry. The electrical pig, which is a fully automated robot complete with stainless steel mixing tools, tills and aerates the microbiologically active sludge, thereby accelerating the drying process. The whole system is fully automatic, uses very little energy and can be easily maintained.

Less weight, greater savings

“So what,” you say? Why dry sewage sludge at all? Well, because drying the sludge before disposing of it is better for the environment and easier on the pocketbook. Sewage sludge is primarily made of water, and 90 to 95 percent of its mass can be eliminated through Thermo-System’s drying process. The remaining 5 to 10 percent is much less expensive to transport and burn. The result: A saving of cash and the fossil fuels needed to transport and incinerate the waste.

"Germany alone produces roughly 60 million tons of sewage sludge per year," Conrad said in a recent interview. "Given the fact that it costs between 75 and 100 euros to get rid of 1 ton, communities can save a considerable amount of money."

Sewage sludge is the by-product of recycling sewage water. In the past, the sludge was dumped or spread over farmland as fertilizer. In recent years, both disposal systems have fallen out of favor because the sludge may contain harmful chemicals, germs, medications or even hormones.

"After the drying process, the sludge has lost its strong odor, it is virtually free of bacteria and its burning value has increased fourfold," Conrad said. "Imagine 600 tons of sludge that turn into 60 tons -- you need much less fossil fuels to transport that mud and you need much less fossil fuels to burn it."

The systems are sold in various sizes, depending on the clients’ needs. A small one sells for about €300 000, and the largest — which is able to service a mid-sized city — sells for about €3 million. Systems aren’t only sold in Germany — they have been installed in countries as diverse as Brazil, Australia and France.

On Mallorca, Spain’s largest island and a popular Mediterranean holiday destination, Thermo-System is currently building the world’s largest solar sludge drying plant. Some 24 electrical pigs will dry the sludge of 600,000 citizens on an area of 20,000 square meters.

Despite steady growth and sales of some $4 million in 2007, Thermo-System remains a mid-sized business: Only 25 people, roughly half of whom are engineers, work for Conrad.

Of course the market for the green pigs still is small, but as Europe extends eastward and outward, so do Conrad’s hopes of growing his business. “These countries have to bring their environmental technology up to EU standards,"he said.

Photos: www.thermo-system.com