Experimental investigation of wastewater microalgae in a pilot-scale downdraft gasifier

Abstract

Microalgae are potential feedstock for biofuels due to higher heating value and rapid growth rate. It can be cultivated in sewage, avoiding costs associated with clean water and nutrients, making the possibility of energy generation from wastewater treatment plants appealing. Compact microgeneration systems involving biomass gasifiers are already commercialized for small-scale projects and could be adapted for use with microalgae in wastewater. In this study, an experimental investigation of a commercial downdraft gasifier was conducted using microalgae produced in a wastewater treatment plants. The effects of the air-fuel equivalence ratio on syngas composition, higher heating value, and production rates were evaluated. An increasing and then decreasing trend in equivalence ratio with a peak was observed, indicating that the optimum equivalence ratio for the best performance is 0.23. The cold gas efficiency was 87%, higher heating value was 6.2 MJ/Nm3, and the production rate was 2.8 Nm3/kg dry biomass. The syngas composition was 11.9% H2, 19.5% CO, 8.5% CxHy, and 9.8% CO2. The H2/CO ratio observed in the syngas was 0.61, which is very close to the 0.60 recommended for synthetic fuel production (Fischer-Tropsch gasoline and diesel).