The ADP is widely used for processing a variety of organic residues and wastes. The AD can be integrated into many potential pathways for algal biofuels production as shown in Fig. 19 [433]. Coupling biodiesel and green diesel production processes with the ADP (Fig. 20) can improve the overall efficiency of energy recovery and reduce the final cost of biofuel [434]. Based on the theoretical calculations, the ADP can recover approximately 55-85% of the biomass energy content in a coupled biodiesel-ADP, depending on algal lipid content [263]. Similar results were achieved by the calculation of theoretical energy output from conversion of T. suecica [435].

Chlorella residue from the biodiesel production process is a feasible substrate for methane production [436, 437]. Either 1-butanol as a solvent for lipid extraction or acid catalyzed in situ transesterification was recommended because application of the normal chloroform/methanol mixture inhibited methane production. The observed methane yield from algal residues was approximately 52-63% from fresh algae. Addition of glycerol as a co-substrate slightly increased the methane yield by

4- 7% possibly due to a more favorable N to C balance [437].