Responsible scientist; Paula R. Westerman

In this study, the probability that weed seeds enter and survive the biogas-chain was investigated, using 1) a literature review to identify high-risk weed species and seed survival mechanisms, 2) a field survey to estimate the probability that ripe weed seeds are harvested together with crop biomass and 3) experiments in batch and continuous biogas reactors to estimate seed survival chances. Experiments in batch reactors were preceded by exposure of seeds to silage.

Weed species with hard seeds (physical dormancy) or seeds adapted to endozoochory were identified as potential high-risk species. Mechanisms of seed inactivation could be classified as thermal, biological and chemical inactivation. Evidence for all mechanisms except chemical inactivation was found.

Chenopodium album and Echinochloa crus-galli had the highest probability of being harvested together with maize; they produced the highest number of ripe seeds above cutting height (approx. 20 cm) at maize harvest, of all weeds encountered.

Weed species clearly differed in their ability to survive silage and anaerobic digestion. Differences were also found between populations of one weed species, between batch and continuous biogas reactors and even between two subsequent runs of one reactor. Among the best surviving species were Abutilon theophrasti (Samtpappel; silage and batch reactor), Malva neglecta (Weg-Malve; continuous reactor) and C. album (continuous reactor).

The combination of high seed production and survival probability in commercial biogas reactors makes it likely that especially seeds of C. album will survive the biogas chain, although in low numbers. However, the possibility exists that seeds of other species, in particular those with hardseededness, will adapt to the survival in anaerobic digesters.

Project leader; Bärbel Gerowitt
Funding agency; BMELV, FNR
Partners: Humboldt Universität Berlin, JKI, ATB Potsdam, KTBL
Project duration; 2009-2011

MSc Student
Christoph Lück MSc 2012 - Überlebensfähigkeit von Gräsersamen in der Biogasprozesskette

Links
Carmen Büttner
Bernd Rodemann
Monika Heiermann
www.ktbl.de  (u.schultheiss(at)ktbl.de)