Effect of Granular Sizes on Nutrient Removal and Recovery in wastewater treatment processes

Abstract

High nitrogen and phosphorus loadings in wastewater treatment plant (WWTP) effluents are known to cause eutrophication damaging aquatic lives and habitats. However, many WWTP’s in the United States are not designed for nutrient removal. WWTP infrastructure renovations and upgrades using traditional technology are costly, energy-intensive, and require large footprints. Meanwhile, population growth in urban areas increases constraints on area available for WWTP improvements. As a result, innovative solutions are essential for transitioning WWTP’s to being more economical and eco-friendlier. This dissertation investigates means of upgrading existing WWTPs using three cutting edge technologies:a) Aerobic Granular Sludge (AGS) (at WestPoint WWTP, WA) b) Kenaf technology (at Edmonds WWTP, WA) c) Bioaugmentation of nitrifying sludge (Blue Plains WWTP, Washington DC) As we explored these solutions, we focused on increasing the treatment capacity of existing plants, adding nutrient removal capabilities at minimal cost with minor retrofits, and avoiding the need for decommissioning plants or extensive reconstruction. So far, the AGS technology research has been limited to sequencing batch systems even though most existing WWTPs are continuous flow systems. However, we found that small granules naturally exist in some continuous flow systems carrying out enhanced biological phosphorus removal (EBPR), opening the potential for integrating AGS into existing continuous flow infrastructure. Our studies were engineered to advance this aspect: (a) At WestPoint WWTP, to optimize the potential of AGS in continuous flow, we studied the optimal sizes of aerobic granules in a side-stream pilot plant for nitrogen and phosphorus removal prior to introducing AGS into the mainstream at Westpoint WWTP. The effect of aerobic granule size on N2O emission was also investigated to mitigate the greenhouse gases released from WWTPs. (b) At Edmonds WWTP, as an alternative to AGS, we used the Nuvoda® technology which uses a plant-based carrier (kenaf) as substratum for biofilm attachment. We studied the benefit of adding kenaf for bioaugmentation of nitrification and denitrification capacity. (c) Lastly, at Blue Plains WWTP in Washington DC, we evaluated bioaugmentation using Comammox enriched activated sludge which demonstrated considerable improvement in nitrification capacity with minor retrofit.