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.