Thesis (M.S.)--University of California, Davis, 2011
Algae have been discussed as a biofuel feedstock but recent economic assessments have determined that algal biofuels are not cost effective in current energy markets. Likewise, several life cycle assessments have shown that algae cultivated exclusively for fuel production can result in net GHG emissions and energy consumption. Some researchers suggest that using algae to treat wastewater and produce energy products simultaneously could overcome these challenges. Little research has been published, however, on the environmental impacts of algal wastewater treatment systems
The purpose of the research reported in this thesis was to determine the life cycle energy, greenhouse gas emissions, eutrophication potential, and cost impacts of incorporating an algal turf scrubber (ATS) into a treatment process for dairy wastewater. The ATS is a shallow flow-way which supports a biofilm of algae and other microorganisms. A life cycle model was developed for a conceptual treatment facility in order to assess system impacts. The system utilizes two anaerobic digesters: one for secondary wastewater treatment and one for algae digestion. Biogas from these digesters is used to generate electricity and process heat; no liquid fuels are produced by the system. The results show that utilization of an ATS significantly reduces eutrophication impacts by reducing chemical oxygen demand (COD) and removing nitrogen and phosphorous from the wastewater. With low water recirculation rates and good algae productivity, inclusion of the ATS in the treatment system results in net displacement of grid electricity and GHG emissions. High water recirculation rates through the ATS and drying of the algae biosolids results in net energy consumption and GHG emissions. The cost of wastewater treatment using the ATS was estimated to be $1.42 per m3 influent wastewater in the baseline scenario. This was found to be cost-effective if dairies can receive monetary credit through nutrient trading programs on the order of $3.83 kg-1 nitrogen and $9.57 kg-1 phosphorous
