Padma Priya Ravi has completed her Bachelor of Engineering in Biotechnology from VMKV University, India and obtained her Master’s degree in the field of environmental protection and agricultural food production from University of Hohenheim, Stuttgart, Germany. Presently she is pursuing PhD at State Institute of Agricultural Engineering and Bioenergy, University of Hohenheim, Stuttgart, Germany
Two-stage biogas systems consisting of a CSTR-acidification reactor and a subsequent anaerobic filter for methane production were frequently described in the newer literature for the microbial conversion of food and agricultural wastes to biogas. To use the hydrolysate from acidification step in the anaerobic filter, the solids particles have to be removed to prevent blockage. The purpose of this study is to integrate a membrane filtration process in a two-stage AD system to remove particles and inert COD-components from the hydrolysate. The hypothesis is that the removal of the inert COD leads to a more effective performance of anaerobic filter and higher degradation rates there so that the volume of the AF is used more efficiently. A cross flow ceramic membrane filtration plant with 0.2 µm pore size in membrane was used to treat the hydrolysate produced in acidification reactor, which was maintained at target pH-value 5.75. For this experiment, two different substrates (grass-maize silage and vegetable waste) were investigated. For the determination of organic acids, sugars and alcohols of hydrolysate, permeate and concentrate during filtration process, HPLC and GC analysis were performed. Additionally, the COD concentrations were detected. For the carbon balance, TC, TOC and IC and the gases produced in acidification reactor were measured quantitatively and qualitatively. Furthermore, the permeability of the ceramic membrane was determined. To evaluate the specific methane yield the Hohenheim Biogas Yield Test (HBT) was conducted for permeate, hydrolysate and concentrate. The preliminary results show that there were no significant differences in organic acid concentration of the hydrolysate permeate and concentrate, even though the COD concentrations had significant differences. During the experiment, the permeability of the membrane was stable, although there was no physical or chemical cleaning. The organic dry matter (oDM) degradation rate in acidification reactor was 36.01%.
Joerg Steinbrenner has completed his Bachelor of Science and Master’s degree in Biobased Products and Bioenergy from University of Hohenheim, Stuttgart, Germany. Presently he is pursuing his PhD at State Institute of Agricultural Engineering and Bioenergy, University of Hohenheim, Stuttgart, Germany.
In a green biorefinery system, the production of organic acids, fibers and biogas is in focus. The ensiling process and anaerobic digestion of different silages is well described in literature. During ensiling, different organic acids like lactic acid, acetic acid and butyric acid can occur, depending on the used substrate and ensiling treatment. The idea of this research is to increase contents of organic acids in the silage, separate the silage into press juice and press cake and determine the biogas yields of the different fractions. Fresh grass was ensiled in 1.5 liter glass jars and treated with carbonated lime, water, manure and ethanol. Every treatment was done in triplicates and stored for 3, 14, 30 and 90 days at mesophilic and psychrophilic conditions (20 °C, 37°C). Samples were taken from every glass and analyzed for organic acids, alcohols and sugars with GC and HPLC. Furthermore the dry matter and organic dry matter content was determined. The ingredients of the original fresh grass were measured with Weender van Soest analysis. The ensiling experiment was performed according to the standard of the German Agricultural Society (DLG) for ensiling experiments. After 90 days of storage, the most promising variations for organic acid production was selected and the material separated with a tincture press at 200 bar into a press juice with high contents of organic acids and a presscake with high fiber contents. The specific methane yield potential of the press cake was determined with Hohenheimer Biogas Yield Test (HBT).