Use of Algae in a Landfill Leachate Treatment System

Landfill leachate, a high-strength liquid waste, is collected at landfills and then trucked to and treated at wastewater treatment facilities, where it is one of the largest contributors of nitrogen in the wastewater influent. This process costs each landfill hundreds of thousands to millions of dollars annually, mostly due to the high ammonia content. Nutrients released in effluent from wastewater treatment facilities have raised concerns over the resulting ecological and economic costs that eutrophication has on downstream water quality as well as commercial fishery and recreational uses. This issue may be addressed by combining leachate treatment, specifically nutrient removal, with commercial algae growth. The pairing of these systems has potential cost savings to biomass production, wastewater treatment, and solid waste disposal industries. The feasibility of such a remediation system was evaluated based on the biomass growth and removal of nitrogen from raw landfill leachate by a mixed algae-bacteria culture. This system was designed to treat leachate with minimal inputs and maintenance requirements, and was operated as an open semi-batch reactor in an urban greenhouse. The results, presented in Chapter 3, revealed that the average biomass growth rate was 5.6 ± 6.4 mg biomass/L/day and reached a maximum biomass density of 480 mg biomass/L. This maximum biomass density is comparable to the algae biomass industry goal of 500mg biomass/L. The maximum nitrogen removal rate measured from this system was 9.18 mgN/L/day. The ammonia removal rates of this culture increased with increasing initial ammonia concentration; maximum nitrogen removal occurred at an ammonia concentration of 80 mg N-NH3/L. At starting ammonia concentrations above 80 mg N-NH3/L a reduction in nitrogen removal was seen; this inhibition is hypothesized to be caused by ammonia toxicity. This inhibiting concentration is considerably higher than that of many other published studies. To determine if these productivity rates are feasible when the scale of the system is increased, a comparison of productivity at three significantly different scales was completed. The methodology of this comparison study, described in Chapter 4, used ammonia removal, nitrogen removal and algal growth rates as metrics of productivity. The treatment system evaluated utilized an algae-bacteria consortium to remediate raw landfill leachate and was monitored continuously for 52 weeks. The result of this comparison-of-scale study, presented in Chapter 5, determined that the rates observed in small-scale reactors (0.25L flasks) were significantly different from the rates observed in mid- (100L aquarium tanks) and large- (1000L raceway ponds) scale reactors. These results are of great significance since many predictive analyses, such as life cycle assessments (LCAs) and techno economic analyses (TEAs), use results from small scale studies as input values for large-scale predictions. This suggests that the results from small-scale experiments may not be appropriate as input data in predictive analyses of full scale algal processes. Throughout all of these studies it was observed that the amount of nitrogen removed from the liquid portion of the systems did not equal that amount of nitrogen in the biomass grown, calculated by the Redfield ratio. An evaluation of the potential nitrogen transformation pathways present in the yearlong study of the algae based leachate treatment systems, from Chapter 5, is presented in Chapter 6. The results of this evaluation concluded that while the nitrogen removal pathway of bio-assimilation was present, it was not the only nitrogen removal pathway in the treatment system. During a major part of the study (83.4% of the weeks), all nitrogen could not be accounted for in the dissolved inorganic nitrogen or biomass portions of the system. It is hypothesized that some of the unaccounted for nitrogen was lost due to volatilization of gaseous nitrogen species. Scenarios for the occurrence other nitrogen transformation pathways have been postulated based upon characteristic distribution of measured dissolved inorganic nitrogen and the nitrogen content of the biomass for each week and prior metagenomic analysis of the microbial community in the treatment system.Ph.D., Environmental Engineering -- Drexel University, 201