Algal biofuels present a promising future alternative to petroleum based fuels. Water nutrient recycling is a key step to increase the sustainability of algae biofuel production facilities. This thesis discusses the process of nutrient and water recycling in high rate algae raceway ponds (HRAP) fed primary treated municipal wastewater. Research was conducted primarily at the San Luis Obispo Water Resource Reclamation Facility (SLOWRRF). Nine 30 m2, 0.3 m deep HRAP’s were operated continuously from June 1, 2013 to April 17, 2014. The ponds were arranged in three sets of triplicate ponds, with two pond sets run on 3-day hydraulic residence time (HRT), and the third on a 2-day HRT. The biomass productivity of the 2-day HRT and 3-day HRT were compared. The two sets of 3-day HRT ponds were run in series to determine the effect on productivity associated with recycling growth media without supplemental nutrient addition. The first pond in series was referred to as round 1 and the second as round 2. Due to solids accumulation in the 2-day HRT ponds in summer proper biomass productivity values could not be determined. 4-inch standpipes were determined to cause the solids accumulation when large flocs were present in ponds. As a possible solution to the solids accumulation issue, a ramped standpipe was designed and installed in one pond per triplicate set. In winter the 2-day HRT pond was roughly 37% more productive than the 3-day HRT. In summer the round 1 (3-day HRT) ponds were roughly 33% more productive than the round 2 (3-day HRT) ponds. In winter the round 1 (3-day HRT) ponds were roughly 19% more productive than the round 2 (3-day HRT) ponds. The type of standpipe (ramped or 4-inch) did not cause a significant amount of solids accumulation in either of the 3-day HRT ponds. The type of standpipe did make a difference in the 2-day HRT ponds. On average the 4-inch standpipe pond had 35% higher TSS than the ramped standpipe ponds. In addition to these field experiments, laboratory aerobic degradation experiments were conducted to determine the nutrient release of previously digested sludge in aerobic ponds. Pretreatment of algae sludge did not have a significant effect on nutrient release of previously anaerobically digested algae sludge in aerobic conditions. The maximum soluble nitrogen generated in the aeration reactors was between 56% for the treated sludge, and 66% for the untreated sludge.

Although high rate algae ponds (HRAPs) are a proven wastewater treatment technology with numerous environmental, social, and economic benefits, their widespread use has been hindered by inconsistent and unreliable settling performance. Hence, the goal of this thesis is to investigate how specific operational parameters affect the settling performance of HRAPs. Nine HRAPs (30 m2 surface area, 0.3 m depth) were operated as three triplicate sets, with each set run on either a 2, 3, or 4 day HRT continuously from January 25, 2012 through April 11, 2013. Settling performance was determined (i) by measuring the TSS of Imhoff cone supernatant after 2 and 24 hours of settling and (ii) by measuring the TSS of tube settler effluent. Ponds operating on 2 - 3 day HRTs (loading rate was 24 - 36 g/m3-day csBOD5 and food to microorganism (F/M) ratio was 0.13 - 0.21 day-1) were able to settle consistently with residual TSS averaging less than 40 mg/L after 2 hours of settling time. Tube settlers showed potential as effective harvesting devices; ponds operating on a 2-day HRT averaged 27.9 ± 9.2 mg/L TSS in tube settler effluent at an overflow rate (OFR) of 9.4 L/min-m2. Microscopy analysis was performed and relationships were made between settling performance and algae dominance and floc structure.