**7. Scaling up the AcoD process**

**Table 5** summarizes all the results obtained by semi-continuous or continuous assays at lab or pilot scale results up to date complying with the following prerequisites:


Semi-continuous or continuous processes could overpass some drawbacks from batch assays as reported by several authors [71, 77, 84]. This could be due to the acclimation of the inoculum during the experiments. To this sense, these processes had shown successful results in the co-digestion of substrates with low C/N ratios, low pH, and higher ammonium content, allowing a higher concentration of microalgae in the influent. However, some studies had shown negative results when compared with the AD of sole substrates [32, 46, 77]. This low methane production had been related to the difficulty of microalgae cell-wall digestion, accumulation over time of ammonium, or high OLR [32, 46, 77].

Regarding operational parameters, the most common used temperature was within the mesophilic range due to its low energy cost and good performance. OLR ranged from 0.5 to 4 g COD L−1 d−1, although, most studies showed a higher methane


*Anaerobic Co-Digestion of Microalgae and Industrial Wastes: A Critical and Bibliometric Review DOI: http://dx.doi.org/10.5772/intechopen.104378*



**Table 5.**

*Methane yield of co-digested microalgae with different substrates at different ratios in semi-continuous or continuous assays.*
