A circular economy is the goal

Stefan Lengel is an industry pioneer. Inheriting an agricultural operation in 1988, he became one of the first in Austria to set up a plant for composting organic waste and green cuttings.


Today his family-owned company near Vienna has two state-of-the-art compost and soil plants plus an own biogas plant. Quality requirements for compost are high, so contaminants, especially plastics, are a big problem. In order to solve it, Lengel recently set up a new stationary fine compost prep line with the help of Komptech.

When Maria Lengel started producing grass sod in the late 1960s, nobody could anticipate that sustainability and climate protection would ever be such hot topics. But the company aligned itself early on with the cycles of nature, and designed its production processes accordingly. “We’re proud that with our business we contribute to conserving natural resources,” says her son Stefan Lengel. For him as the current owner the sustainability principle is a key part of the family company’s philosophy. It extends over three generations and includes his children, who bear responsibilities in company management. Daughter Stefanie runs Lengel GmbH, and son Alexander is director of Marchfelder BioEnergie GmbH and thus in charge of biogas production. “Green blood runs in our veins” says Lengel senior with a grin.

Organic soil in high quality

Both Lengel composting plants recycle regional biogenic waste and green cuttings. Every year they make around fifteen thousand tonnes of finished compost, various organic soils, plant substrates and bark mulches. Finished sod remains part of the portfolio. More than half of the annual compost production reaches quality class A+. “Our company stands for high product quality,” emphasizes Alexander Lengel. That makes the increasing contamination of organic waste with foreign matter a problem. Recently he contacted the Komptech Systems technology Office in Vienna. The goal: Better fine compost processing.


Compost virtually free of foreign matter

Instead of a drum screen, Lengel will now screen compost in a flip-flow screen (the BIVITEC® by Binder+Co) with eight or six-millimetre holes. The resulting fine fraction is almost contaminant-free. The final product is also nice and flaky, since waste cannot clump into little balls in a flip-flow screen. The screen overflow goes to a combination wind sifter and stone separator for further cleaning, and then on to composting. Thus, no valuable organic material is lost.

So that Lengel management would be able to estimate the achievable output quality before investing in the new system configuration, Komptech called in the Vienna University of Natural Resources and Life Sciences, and the Binder+Co Technical Centre. Together they evaluated a series of material samples from the processing sequence. The customer was very happy with this way of doing things.

Organic waste that doesn’t go to composting is used by Lengel to make green energy. Back in 2004 the current senior director took the company’s own biogas plant into operation, and since then it has been supplying the vehicle fleet with CO2-neutral energy. The plant feedstock is expired foodstuffs, food scraps and organic waste collected by regional disposal companies. Each year about 15,000 tonnes of biomass come together. Alexander Lengel: “Materials with higher energy content tend to go to the biogas plant. Also, we’re better able to even out seasonal fluctuations in compost production.”

The biogas plant makes about 220m3 (500 kWh) of raw gas, all of which is used for electricity generation. That gives 12 megawatts per day. For the future, Alexander Lengel plans to increase the capacity of the plant to 30,000 tonnes of processed biomass per year, and to output biogas in natural gas quality. A biogas filling station is also planned. That would let the company start selling green gas.

“The combination of composting and biogas generation gives us more control options.”

Alexander Lengel

Business associates and friends

The Lengel and Komptech companies didn’t start working together just yesterday. After Stefan Lengel founded his first composting plant, in the early 90s he met with Josef Heissenberger and bought a first-generation Komptech compost turner. It was a Topturn 300, serial number #3. Both founders shared the vision of returning organic waste to the natural cycle at large scale. The business relationship became a friendship.

Over the years, this compost and soil maker acquired not less than 24 Komptech machines, including shredders, screeners and eight Topturn compost turners. The relationship continues with the third Lengel generation and the current Komptech team. Alexander Lengel: “What sold us on Komptech was the overall package. This includes the secure availability of spare parts, and their fast and dependable service.” He adds that it is also important to him to work together for a greener world.