In this present paper we give results of investigation of the performance of single-stage leach-bed reactor for treatment of solid cattle manure, concentrating on the biogas production and composition. Experiments were conducted in bioreactor with a working volume of 50 L which had been constructed by modifying leach-bed reactor and fixed-bed reactor for anaerobic digestion of cattle manure. Full characteristics of the experimentdl set-up are given in Korazbekova et al. (2013) [1]. Fresh material (FM) as received and inoculum samples were analyzed in triplicate according to standard methods of APHA (1995) [2]. Accordance with results of tested substrate analysis, DM content of cattle manure was 25.93% and 84.07% of solids were oDM.
Results of cumulative biogas production are shown in Fig. 1. The rapid initial biogas production was due to readily biodegradable organic matter and presence of high content of the methanogens. The biogas generation started after inoculating, kept increasing until reaching the peak, and then began to decline (Li et al., 2011) [3]. Run 1 showed the maximum biogas production on day 4 in the amount of 0.032 Nm3(kg oDM)-1 and daily biogas generation was observed more than 0.018 Nm3(kg oDM)-1 between days 2 and 10, reduced to less than 0.005 Nm3(kg oDM)-1 after day 19. The cumulative biogas yield was indicated as 0.327 Nm3(kg oDM)-1 at the end of Run 1. Biogas production started faster in Run 2, i.e. peak biogas generation (0.047 Nm3(kg oDM)-1) was achieved up to day 3 of the experiment demonstrating the maximum degree of biogas formation till days 9 (daily production more 0.02 Nm3(kg oDM)-1) and intensive metabolism of microorganisms, since reactor was enriched with methanogens because of biofilm formation and use of fermented leachate from previous run. The cumulative biogas production was 0.328 Nm3(kg oDM)-1 at the end of 21-day of HRT. There were not observed several peaks during the digestion process in both two runs as reported by Li et al. (2011) [3; 4].
Fig. 1: Cumulative biogas production
Final data of biogas production showed that, (0.331±0.005) Nm3(kg oDM)-1 biogas (standard error = 0.003) with an average percentage of methane (47.13±1.40)% was obtained during the anaerobic fermentation of cattle manure in the reactor with immobilization device.
In conclusion, dry fermentation of cattle manure with dry matter content of 25.93% in leach-bed reactor without anaerobic pretreatment and mixing is feasible and stable process for production of biogas from agricultural wastes. Immobilization of methanogens on the supporting materials (polyethylene packing rings) in leach-bed reactor improved biogas production.
References
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