The main goals for improving the ADP are increasing the conversion efficiency while simultaneously decreasing capital and operational costs.

5.1.2 Inoculum Source for Anaerobic Digestion of Algae

As discussed earlier, algal biomass has specific biochemical composition and con­tains unique compounds, such as algin, laminarin, and fucoidan. Moreover, marine algal biomass has a high salt concentration that can affect anaerobic microorgan­isms. Isolation and application of microorganisms adapted for digestion of specific algae is labor-intensive but has the potential to improve algal ADP.

Generally, anaerobic sludge from a domestic sewage plant or marine anaerobic sediment is used for startup of the algal ADP. Several authors reported that anaerobic organisms adapt readily to algal biomass as a sole substrate, and the inoculum source has a minor or no effect on the final methane yield and VS reduction [77,159, 368]. On the other hand, addition of an inoculum from marine sediments to anaerobic sewage sludge increased the initial methane production rate (Fig. 13) [77],

and addition of a rumen and sewage sludge inoculum adapted to algal substrate increased biogas production and methane concentration [369]. Application of an inoc­ulum adapted to high ammonia concentration is a possible solution to overcome the problem of ammonia inhibition. The inoculum from a piggery anaerobic pond yielded stable methane production from algae with an added ammonia-N concentration up to 3 g/L [370]. In contrast, a sewage mesophilic digester inoculum showed inhibition in methane production at an added ammonia-N concentration larger than 0.5 g/L.