Abstract: This study investigates the effect of trace element supplementation (TES) on mesophilic anaerobic digestion treating Laminaria digitata (LD) in both batch and continuous (CSTR) reactors. Two set of Experiment 1 and 2 (batch and continuous) reactors were carried out with and without trace element addition, and their performance compared. In Experiment 1, five (batch 500 ml and 1L CSTR) reactors were operated with the addition of metals mixtures in Reactors (TES 1–4) and Reactor (TES 0) as control without addition. The results of first batch test (BT 1) show that TES 1-4 reactors achieved an increase in methane yield of between 17-26 % compared to the control reactor without TES after 22 days of incubation. In CSTR reactors, the results show that daily trace elements addition with an HRT of 25 days allowed for a stable anaerobic digestion in three different combinations TES 2- 4 at an organic loading rate of 2 gVS.L-1.d-1 used throughout the experiment, but did not give any advantage over the reactor without TES 0. In Experiment 2, two (batch 500 ml and 1L CSTR) reactors were operated with and without TES 4 mix. Results of (BT 2), the TES 4 reactor achieved an increase in methane yield of 50 % compared to the control reactor without TES 0 after 40 days of incubation. The second CSTR run, with an OLR from 2 - 5 gVS.L-1.d-1, and weekly addition of the TES 4 mix, showed stable performance compared to the reactor TES 0 without metal addition.
Keywords: Anaerobic digestion, algae, batch, biogas, continuous reactors, trace element