Monofermentation of Nutritional Waste in Biogas Plants - Laboratory Investigations

Abstract

In the following publication a joint project with the partners Ing. Frie- drich Bauer GmbH from Kemmelbach, Austria, Enersys GmbH, Donaueschingen, the Institute of Agricultural Engineering and the Insti- tute of Environmental and Animal Hygiene and Veterinary Medicine (with Animal Clinic), (head: Prof. Dr. R. Böhm), both University of Hohenheim will be presented. In the project a process engineering tech- nique was developed for the anaerobic monofermentation of low - fibre and high - energy material. For a period of 126 days systematic labora- tory investigations have been accomplished in twelve horizontal lab - fermenters with 16 litre net volume. After a starting period of 29 days to adapt the microorganisms to the substrate, the influence of different tem- peratures (mesophilic operation with 40 °C and thermophilic operation with 55 °C) and different organic loading rates (high organic loading with 5.1 kg odm/m³ reactor volume per day and low organic loading with 3.5 kg odm/m³ reactor volume per day) were tested in three experiments. Moreover a two - stage treatment with a doubled organic loading rate of 10.1 kg odm/m³ reactor volume per day was monitored in the methanisa- tion - stage. In this experiment hydrolysis und methanisation were sepa- rated in back to - back reactors. Because of the high energy content of up to 18.3 MJ ME / kg odm the used nutritional waste are predestined for monofermentation in biogas plants with anticipated high gas yields. Comparing the different tempera- ture levels the reactor specific methane yields were equal with approxi- mately 2.12 l CH4 /l reactor volume per day. In the last third the perform- ance of the mesophilic variant decreased down to 50 % of the thermo- philic reactors. Varying the loading rate in interaction with the tempera- ture range the thermophilic variant with high loading rate showed the highest reactor specific methane yields with 2.25 l CH4 /l reactor vol- ume per day in comparison to only 0.86 l CH4 /l reactor volume per day in the mesophilic variant with a low organic loading rate. By dividing the fermentation into a hydrolysis- and a methanogenic step it was possible to stabilise the process.