You can do it by simultaneously adding methanol and a basic or acidic homogenous or heterogeneous catalyst with algae in the reactor. Selection of catalyst depends on type of lipid present in algae if high content of fatty acid than add acidic catalyst if high content of triglycerides in algae add basic catalyst. for more information read :In-situ processing of Nannochloropsisoculata algal biomass using a mixed-bed ion-exchange resin as a heterogeneous catalyst.