Nutrient Removal From Clarified Municipal Wastewater Using Microalgae Raceway Ponds

Abstract

Nutrient Removal From Clarified Municipal Wastewater Using Microalgae Raceway PondsJustin Andrew Kraetsch Shallow, mixed raceway ponds can be used to grow microalgae for the dual purposes of wastewater treatment and biofuel feedstock production. To improve the environmental sustainability of microalgae biofuels and to alleviate resource limitations, nutrients remaining after biofuel production should be recycled for additional cultivation. This thesis considers three topics: wastewater treatment by algae, nitrogen and phosphorus assimilation by algae, and algae cell disruption to facilitate nutrient recovery.The main experimental work was done in pilot raceway ponds growing polycultures of microalgae on clarified municipal wastewater. In addition, two lab-scale pretreatment technologies were tested for their ability to disrupt cells, as indicated by subsequent biomass organic nitrogen and particulate phosphorus degradation during sequential anaerobic and aerobic digestion. The two pretreatment technologies were sonication and high-pressure homogenization. in three sets of triplicates. One set was operated at a 2-day hydraulic residence time (HRT) on clarified wastewater throughout the study. A second set ("Round 1" of pondsin-series) was operated at a 3-day HRT, also on clarified wastewater. Its effluent was v clarified and then discharged into the third set ("Round 2" of ponds-in-series), which initially operated at a 4-day HRT but then later a 3-day HRT.The nutrient removal and assimilation data were compared seasonally-summer (MarchOctober) and winter (November-February). The triplicate raceways operating at a 2-day HRT achieved average total ammonia nitrogen (TAN) removal efficiencies of 11% in the winter and 71% in the summer, while dissolved reactive phosphorus (DRP) removal remained similar throughout seasonality. In the first ponds-in-series experiment (3-day HRT followed by 4-day), average summer TAN removal efficiencies for Round 1 and 2were 88% and nearly 100%, respectively. Round 1 and 2 average summer DRP removal efficiencies were 29% and 67%, respectively. The first ponds-in-series experiment was not conducted in the winter. In the second experiment, the Round 2 HRT was changed to 3 days. Average TAN removal efficiencies for Round 2 in the winter and summer were 88% and 100%, respectively. DRP removal for Round 2 increased from 38% in the winter to 66% in the summer.Total nitrogen (TN) mass balances on the raceway pond experiments were useful to illustrate the fate of influent nitrogen, including losses. In the first ponds-in-series experiment, 76% of the influent soluble nitrogen was converted to organic nitrogen by assimilation, while 6% of the influent ammonia was lost by volatilization. In the second ponds-in-series experiment, 81% of the influent soluble nitrogen was converted to organic nitrogen by assimilation and only 1% of the influent ammonia was lost by volatilization. The 2-day HRT raceway experiment achieved 41% conversion of influent soluble nitrogen to organic nitrogen by as...

Nutrient Transformations in Algae Raceway Ponds Fed Municipal Wastewater

“…As noted in Metcalf and Eddy, constituents like ammonia and inorganic phosphorus can typically vary between 14 to 41 mg/L-N and 1.6 to 4.7 mg/L-P, respectively (Metcalf and Eddy, Inc., 2003). The primary clarified effluent grab entering the algae raceway ponds in San Luis Obispo have an average ammonia concentration of 36.6 mg/L-N and inorganic phosphorus concentration of 3.7 mg/L-P (Kraetsch, 2015). These averages are from grab samples collected at the same time of the day on each individual sample day.…”

“…The Cal Poly Algae Field Station (AFS) facility is located at 35 Prado Road at the City of San Luis Obispo Water Resource Recovery Facility (WRRF), which has a treatment capacity of 5.2 million gallons of wastewater per day (MGD) (Kraetsch, 2015).…”

“…The ramp was closed at the bottom and this standpipe controlled the heights in Ponds 4 and 5. The standpipe sits in concrete that was poured into a cut off bottom from a 20-L bucket (Kraetsch, 2015). Side view of the tube settlers set up at a 60° angle to settle algae before the water flowed to the next process (Chang, 2014).…”

“…This thesis also looked into the results of the aerobic digestion of algae previously boiled prior to anaerobic digestion. The works of Hill (2014), Chang (2014), and Kraetsch (2015) regarding other pretreated algae digestion experiments were summarized to compare against each other. These findings can assist with future modeling and the potential to further scale up and implement into a functioning wastewater treatment and biofuel production facility.…”

“…xii LIST OF TABLES Table Page Table 3 Table 3-4: Anaerobic digestion incubation durations for the various anaerobic digestion experiments. The first three pretreatments listed all were tested by others (Hill, 2014;Chang, 2014;Kraetsch, 2015 Figure 2-1: Diagram of a high rate algae pond system used to grow algae for collection (Craggs, Sutherland, & Campbell, 2012). .............................................. 4 Figure 2-2: A simplified diagram of the relationship between algae and bacteria growing in algae ponds fed wastewater (Oswald, Gotass, Ludwig, & Lynch, 1953 the square containers.…”