Consumer Energy Report is now Energy Trends Insider -- Read More »

By Robert Rapier on Dec 19, 2009 with no responses

German Robot Pigs

“What I need for this project”, I explained to my young son, “is an army of German robot pigs.” His eyes went wide. “And I know just where to get them…”

I have a project on my desk right now to look at avenues of disposal for sewage sludge in a specific location. There are lots of things you can do with sewage sludge, but it is obviously dependent on a number of factors. There are places where farmers spread it on their fields, there are places where it is incinerated, and there are places that it is land-filled. And there are other options beyond that.

In order to utilize sludge for energy, the water content is obviously critical. Too much water, and any energy you create from the sludge is lost due to the need to dry the sludge. So what I really needed in this specific case was a method of drying that could help generate net energy from the project.

Obviously you could just spread the sludge out in a sunny location, but there are many problems with that. One good rainstorm can ruin a week’s worth of drying and create a brown river to the nearest waterway. Further, as the outside layers dry, the drying slows down unless the sludge is constantly mixed.

I thought that this particular situation could benefit from a solar dryer. I am familiar with solar kilns and solar ovens, so why not a solar sludge dryer? I envisioned a system like a greenhouse that allows the sludge to dry, but also ventilates and removes the moisture. Several of the functions would need to be automated if this has any hope of being economical.

So I thought “Hmm, I wonder if anyone has invented such a system.” Since about 98% of anything that I ever think of has already been invented, I Googled it. Turns out that there are lots of solar sludge dryers to choose from, but one in particular caught my eye. Enter the German robot pig:

German robot pig the star of sludge drying plants

A group of young, up-and-coming German scientists in the late 1990s founded a company that today is the world leader in solar sludge drying. The star of the environmentally friendly drying process is an unusual pig that works all day without food or complaint.

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.

Alas, another invention that someone thought of 10 years before I did. But this system really has many of the characteristics that I am looking for. Whether the economics pan out is still entirely unclear. The company does have an impressive project portfolio, though, having already built over 100 sludge-drying plants worldwide.

But one doesn’t get a chance to work with an army of German robot pigs every day, so I will continue to investigate and maybe this works out. Besides, that sounds so much more interesting than “I am working on sewage sludge.”