Anaerobic digester feed stream conditioning for increasing biogas production (Technnical report 3)

Anaerobic digester feed stream conditioning for increasing biogas production (Technnical report 3)

In this third report we are presenting additional results on the combined ultrasonication and enzymatic pre-treatment. We have shown that when treating 5% of WAS by ultrasound (3500J for 30 sec) and then incubating the sludge at 65°C for 24 hours a final SCOD concentration of up to 14,000 mg/L could be obtained, and the methane production increased by 19% compared to the non-treated WAS.
Various fraction of WAS were ultrasonicated followed by the thermal treatment at 65°C and the final SCOD after 1 and 24 hours incubation at 0, 5 ,10 and 20% ULS were all similar within 400 mg/L. With 100% ULS, however, the SCOD after 1 hour (+4,000 mg/L) and 24 hours (+2,300 mg/L) were higher. In terms of SCOD, 100%ULS (3,500J) was equivalent to 1 hr thermal treatment. Moreover, 100%ULS (3,500J) combined with 1hr thermal was equivalent to 24 hr thermal treatment, therefore ULS allowed to shorten significantly the thermal treatment, the effect is accentuated when the % of ULS increases. At 65°C there was little effect when the percentage was below 20%.
In the second section, we completed the characterisation of ozone treated WAS samples and it was found that 30 minutes (0.123 g O3/g TS) ozone treatment resulted in an increase of SCOD from 1,200 mg/L to 5,000 mg/L and there was a decrease in suspended solids concentration. We carried out a BMP test on 2 samples (15 and 30 minutes ozone treatment) that resulted in 25 % and 32 % increase in methane production compared to the non-treated WAS.
Finally, in the third section we are presenting results on the combined ultrasonication and NaOH treatment. This is a work that we are doing in parallel with the PUB project that focuses on the combination of ultrasonication and ozone. We found that there was a synergistic effect resulting in high SCOD concentrations (~9,000 mg/L) in less than 10 minutes using low NaOH dosage (0.02 M). Two successive addition of 0.02 M NaOH resulted in better results than one single addition of 0.05M, suggesting that the generation of hydroxyl radicals in a key aspect of the combination.

Unpublished report.