DOMESTIC WASTEWATER TREATMENT USING ALGAE

Abstract

Bioenergy system is very complex and sustainability assessment of bioenergy requires reference system to understand pros and cons of bioenergy system. Bioenergy system requires nutrients for growth of biomass, and nutrient additions in bioenergy system make it complicated to understand the greenhouse gas emission from bloenergy system. This study explores carbon sequestration from land and water discharge of nutrients which alternatively can be used in bioenergy production. The carbon sequestration values obtained from this study would work as a reference value for bioenergy. This reference system considers the application of wastewater to a water body, and application of sewage sludge to land. Microalgae and Bermuda grass were considered to be the sole biomass producing species in water and land system respectively. Daily application of the nutrient was made for both the systems. For simulation of biomass production and carbon sequestration, governing differential equations of nutrient loading, biomass production, and carbon sequestration were solved simultaneously using a numerical scheme. Matlab was used as a computation tool. An effort is made to compare reference system's biomass production and carbon sequestration to that of the algal biorefinery for the same loading of nutrients. Running time of both the systems was 100 years. Biomass production in case of the water body was 148, 532, 1178 tonnes, in the case of land biomass production per year was between 50 to 60 tonnes for nitrogen loading of 0.13 ton/day. Carbon sequestration in CO2 equivalent was 47, 102 and 890 tonnes for a water body, and 0.2, 5.6 and 13.2 tonnes for land. C/N ratio for sequestered carbon ranges between 0.0005 to 0.003 and I to 25 for water body and land respectively. In an algal biorefinery, biomass production ranges between 31-49 ton/year, and sequestered carbon produced ranges between 3.62-7 ton/year for a nitrogen loading of 0.13 ton/day.