SBO performance in Anaerobic Digestion

In ACEA, the data showed that the effect of CV SBO was lower than the effect observed during the CVD SBO addition. During the CV campaign, considering only the effectiveness at the highest concentration (0.08%), a 27% decrease in ammonia concentrations were evidenced in the liquid fraction of the digestate. The best results were obtained during the CVD SBO campaign in which the ammonia concentration decreased by 6% in the digestate downstream, 46% in the separated liquid of the digestate, and 30% in the filter-pressed sludge. Moreover, a residual reduction effect of ammonia reduction was found up to 20 days after the trial conclusion. This very important residual effect was presumably due to the modification of the bacterial flora, a modification that was still significant up to the end of the monitoring phase. These results were complemented with a lower methane content in the biogas (7-8%). Although not statistically relevant, these results need a further deeper investigation during the following experimental campaigns.

In OT, no distinctive differences were observed between the results of reactor A and reactor B when 0.05% SBO was used indicating that SBO is not critical at low concentrations. Decreased ammonia concentration of 19% was observed in the effluent and increased biogas production rate (17%) compared to the reference reactor when high CV SBO concentration (0.2%) was used. Finally, on the last pilot trial with a high CVD SBO (0.2%) concentration, a high decrease in the ammonia content was observed (27%) and a higher biogas rate (8.1%) compared to the control reactor.

In SBLA, the obtained data demonstrated that none of the applied SBO treatments had an effect on biogas production rate and composition. Thus, SBO did not affect methane production as compared to the control. Regarding the production of ammonia, a decrease of 70.1% and 54.4% in ammonia concentrations were found using 0.2% CV and CVD SBO, respectively, demonstrating that the highest SBO concentration could substantially reduce the ammonia content in digestate.

At the end, this action demonstrated that in all cases, an effective reduction in ammonia is obtained when CVD SBO is used. In Table 1 results are compared.

Table 1. CVD SBO experiment results obtained in ammonia reduction for each country.

ACEA and OT obtained lower values in ammonia reduction using CV SBO, instead SBLA obtained a decrease of 70.1% in ammonia concentration. Furthermore, all three partners showed that an increase in SBO concentration caused the decrease of the ammonia concentration.

The effects on biogas production are different for each partner: in ACEA, the results shows a lower methane content in the biogas, but they were not statistically relevant. In OT the biogas production rate increases when the concentration of SBO increases to 0.2% w/w and better results are obtained when CV SBO is used (an increase of about 17% of biogas production rate). In SBLA, the obtained data show that none of the applied SBO treatments have any effect on biogas production rate and composition.

The LIFECAB prototype located in ACEA can produce 15,8 ton/day for a total of 4170 ton/year. During ACEA experimental trials the injected volume in the reactor B was 2 m3/day (~2 ton/day), so the prototype can be actually used at large-scale and the SOS production is enough to feed both reactors (~4 ton/day) in the ACEA plant. The SOS production with LIFECAB prototype is enough to cover the need of an industrial plant bigger than ACEA: ACEA need could be 4 ton/day and the prototype can produce 15.8 ton/day, about 4 times more.

A potential scale-up of the unit to produce higher contents of SBO could be considered. In this case, the extra SBO produced could be considered as a product to be sold to MWM industries or to employ the SBO with other purposes. This will be assessed in Deliverables DC1-2, DE3-2 and DE3-3, through economic analysis, exploitation and business plan, and a transferability and replicability plan, respectively. This could be very encouraging, and the production of SBO could be increased by 10 times according to the local productivity of compost at the ACEA plant.

ACEA digestors

SBLA AD Prototype in Cyprus

 The two anaerobic digester prototypes operating at OT premises.