The methane production in a full-scale biogas plant – a survey in two-time periods under different ammonia levels

S. Kalamaras, M.-L. Christou, Th. Sfetsas and T.A. Kotsopoulos*
Lab. of Agricultural Structures & Equipment. Department of Agriculture, Aristotle University of Thessaloniki, 54124, Greece
*Corresponding author: E-mail: mkotsop@agro.auth.gr, Tel +30 2310 991796

Abstract

Anaerobic digestion is the preferred choice to treat waste with a high concentration of organic matter, such as livestock waste. Anaerobic digestion is a complex process in which the organic matter is decomposed by the synergistic activity of different groups of bacteria and archaea in the absence of oxygen. Livestock waste are rich in protein and urea and during their anaerobic degradation ammonia is produced. Ammonia is a major inhibitor of anaerobic digestion that affects negatively on the biogas production. Methane, an energy carrier, is the main product of this process and is used mainly for electricity production. During the last decade significant investments have been made in the biogas sector of Greece and currently they are 28 operating biogas plants with a total power that exceeds 25 MWe. The main substrate used in these plants is livestock waste and therefore, they are often working under ammonia toxicity resulting in reduced methane production. In this study the effect of different ammonia levels on methane production in a full-scale biogas plant was examined in two different time-periods. A set of batch experiments were carried out in triplicate in order to measure the methane potential of all the substrates that were used in the biogas plant for each time period. The experiments were carried out in 300mL batch reactors at 37 °C. The concentrations of ΝΗ3-Νin the biogas plant were 3200ppm and 4400ppm for the 1stand 2ndperiod, respectively. The results of the batch experiments were compared with the methane production of the biogas plant in these two periods. During the 1stperiod the methane producedin the biogas plant was less by 9.9%, while in the 2ndperiod the reduction was 20.3%, compared with the measured methane potential in the batch reactors. The measured VFA concentration in the effluents of the biogas plant in the 2nd period was high, while in the 1st period was negligible. These combined results indicate that the biogas plant during the 1st study period did not operate under ammonia toxicity conditions, but the reduced methane production was due to other factors, while in the 2ndstudy period the reduced methane production was affected by the high ammonia concentrations.

Acknowledgment

This research has been co-financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH –CREATE –INNOVATE (project code:T1EDK-406), Project title: Innovative technologies to eliminate ammonia inhibition in anaerobic digestion in order to enhance methane production».

Keywords: ammonia toxicity, methane production, waste, anaerobic digestion

The effect of direct exposure at high ammonia levels of non-acclimated microorganisms on the methane potential

M-L. Christou, G. Vitoulis, S. Kalamaras, A. Totsidisand T.A. Kotsopoulos*
Lab. of Agricultural Structures & Equipment. Department of Agriculture, Aristotle University of Thessaloniki, 54124, Greece
*Corresponding author: E-mail: mkotsop@agro.auth.gr, Tel +30 2310 991796

Abstract

A set of co-digestion experiments in 300mL batch reactors at 37 °C were carried out in order to examine the effect of different high ammonia levels on the methane potential after direct exposure of non-acclimated microorganisms. Four different treatments with different ammonia levels by the addition of NH4Cl were performed in triplicate. Specifically, the initial ammonia levels werearound 2000, 3300, 4300 and 5300 ppm of Ν-ΝΗ4+and each treatment was designated as 2N, 3N, 4N and 5N, respectively. The methane production was measured daily during the first 30 days, and per three days afterwards. In the first 30 days of the experiment the methane production of the treatments 3N 4N and 5N was significantly reduced in comparison with the treatment 2N. The results showed a reduction on methane production of 14.02%, 20.56% and 35% for treatments 3N, 4N and 5N, respectively compared to 2N in this 30 days period. The reduction on the methane production remained significant high and after 60 days of operation of the batch reactors. This result strongly indicates that the direct exposure of the microorganisms at high ammonia levels did not allow them to acclimatize even after 60 days.

Acknowledgment

This research has been co‐financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH –CREATE–INNOVATE (project code:T1EDK-406), Project title: Innovative technologies to eliminate ammonia inhibition in anaerobic digestion in order to enhance methane production

Keywords: ammonia toxicity, methane production, waste, anaerobic digestion