Anaerobic digester feed stream conditioning for increasing biogas production (Technical report 5)

Anaerobic digester feed stream conditioning for increasing biogas production (Technical report 5)

In this fifth report we are presenting results of ULS and ozone at low energy inputs. No synergistic effect was observed on the TSS and VSS removals as well as on the methane production. In fact, there was no significant increase in methane production compared to the control. It was found that about 10-12 % TSS and VSS removals can be obtained at an ozone dosage of 4 mg O3/g TS (60 seconds). The combination with ULS did not result in higher removals.

Size Exclusion Chromatography (SEC) was used to shed more light on the hydrolysis of soluble compounds treated by ULS and ozone. It was found that ULS increased the concentration of high MW compounds (elution time 4-6 min) through the disruption of biological flocks, but was relatively inefficient to hydrolyze them. In contrast, ozone was very efficient to hydrolyze these high MW compounds as well as low MW compounds.

It was also found that the sequence ULS-ozone was more efficient than ozone-ULS. Ozone was able to hydrolyze further the high MW compounds generated by ULS whereas the opposite was not true. ULS was also not able to hydrolyze further the low MW compounds obtained after ozone, whereas ozone could further degrade the low MW generated by ULS. For the same conditions, ULS-ozone was able to produce lower MW compounds then ozone-ULS. However, significant foaming was observed during the ULS-ozone treatment and this issue increased as the time of treatment was longer because of the solubilization of proteins during ULS treatment.

Tests were carried out on the colloidal COD (>0.45 μm) and preliminary results indicated that it follows the same trend as Soluble COD (<0.45 μm), i.e. the ULS-ozone treatment did not provide synergistic effect on colloidal COD.

Unpublished report.