Post aerobic digestion (PAD) and anaerobic ammonium oxidation (Anammox) are sidestream treatment technologies which are both excellent options for the reduction of nitrogen recycled back to the liquid stream without the need for supplemental carbon or alkalinity. However, the achievement of this goal is where the similarities between the two technologies end. PAD is an advanced digestion process where aerobic digestion is designed to follow anaerobic digestion. Other benefits of PAD include volatile solids reduction, odor reduction, and struvite formation reduction. Anammox harnesses a specific species of autotrophic bacteria that can help achieve partial nitritation/deammonification. Other benefits of Anammox include lower energy consumption due to requiring less oxygen compared with conventional nitrification. This manuscript describes the unique benefits and challenges of each technology. Example installations are presented with a narrative of how and why the technology was selected. A whole plant simulator is used to compare and contrast the mass balances and net present value costs on an 'apples to apples' basis. The discussion includes descriptions of conditions under which each technology would potentially be the most beneficial and cost-effective against a baseline facility without sidestream treatment.

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Autothermal Thermophilic Aerobic Digestion (ATAD) is becoming more prevalent due to its advantages over conventional aerobic digestion, including the generation of a Class "A" product, a relatively small footprint, and reduced biosolids for end disposal.Both the Grand Chute-Menasha West Wastewater Treatment Facility (WWTF) in Neenah, Wisconsin and the Edwards Wastewater Treatment Plant (WWTP) operated by the Eagle River Water and Sanitation District located in Edwards, Colorado have "First Generation" ATAD systems and are in the process of converting the systems to "Second Generation" ATAD systems.The "Second Generation" ATAD systems include process modifications over the "First Generation" ATAD systems such as better mixing and process control that have resulted in higher volatile solids reduction, lower product volume, less odor generation and less sidestream impacts at several installations. This paper explores the advantages of the "Second Generation" ATAD systems over the original installations and the reasons why the two plants decided to convert their systems to the newer ATAD systems.

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