Methods for optimisation of the biogas yield in manure based biogas plants
The main objective of the project was to improve biogas production from manures. This objective was addressed by investigating: 1) the effect of different reactor configurations, 2) operational procedures, aiming to selectively retain/return degradable material in the reactor, and 3) different posttreatments to improve the degradability of the ungraded material.
The main objective with the project is to investigate and propose methods for optimization of the biogas yield of manure based biogas plants. The project is focusing in the following three areas: 1) To investigate different reactor configurations for biogas plants for achieving more effective biogas production and more stable operation. Serial operation of two methanogenic steps (one with long retention time and one with short retention time) will be investigated. Opposite to previous theories about dividing the biogas process in a hydrolytic and a methanogenic step, this project is focusing on the advantages of serial coupling two methanogenic steps in the plant for reduction of the short-cut between influent and effluent, which is a weakness of one-step processes. 2) To investigate operational procedures, aiming to selectively retain/return degradable material in the reactor. Stirring and pumping strategies will be investigated in order to maximize the part of degradable material that is retained in the reactor. 3) To investigate methods for degradation of undegraded material, by returning without/with after-treatment to the main reactor. The project will in addition to laboratory experiments analyze operational data and samples from relevant full scale biogas plants for verification of the laboratory and modeling results. Eventually economic evaluation of the investigated methods will be performed
In the first experiment, the effect of serial digestion on process performance and methane production was compared to a conventional single CSTR process at 55 deg. C. The total working volume (5 l) between the two methanogenic reactors of serial CSTR process was varied by distributing the volume between the first and second reactor at 90/10, 80/20, 70/30, 50/50, 30/70 or 13/87%. Results showed that serial CSTR process at 90/10, 80/20, 70/30, 50/50 or 30/70% volume distribution could produce 11-17.8% more biogas compared to single CSTR process under similar operating conditions. The increased biogas production was mainly from the second reactor of the serial process, which accounted for 16-18% of the total biogas production. Temperature was found to have a strong influence on the methane production and process performance of the second reactor of a serial CSTR process. The effect of continuous mixing (control), mixing for 10 min. per day (minimal mixing and withholding mixing for 2 hrs prior to feeding (intermittent mixing) on biogas production was evaluated in three lab-scale CSTRs. Results showed that minimal and intermittent mixing improved biogas productions by 12.5% and 1.3% respectively over continuous mixing. Intermittent mixing also resulted in stratification of solids with higher solids content in the top and bottom layers compared to middle layer. Similar result was also noticed in pilot-scale plant when intermittent mixing was sequenced with continuous mixing. Biogas yields improved from 2.5 to 14.6% when the reactor was operated under intermittent mixing compared to continuous mixing. In the third experiment, the effect of eight different post-treatments on improving the biogas production of fibres separated from thermophilically digested cow manure was studied in batches at 55 deg. C. Results showed that only partial aerobic treatment (air flow rate at 0.28 l/min g total solids) and grinding (mortar and pestle) improved methane yields while chemical treatments (NaOH or CaO at 40g/kgVS) resulted in more or less similar methane yields to that untreated fibres
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Contact
Bygningstorvet Byg. 113
DK-2800 Lyngby, Denmark
www.er.dtu.dk
Angelidaki, Irini , 45251429, ria@er.dtu.dk
Øvr. Partnere: BWSC
