Somnath Basu, PhD, PE, Fellow AIChE
Abstract:
Nitrogen (N), phosphorus (P) and potassium (K) are essential nutrients for the growth and sustenance of microbial population carrying out wastewater treatment. Effective biological wastewater treatment is mediated by a healthy microbiological population which is supported by the presence of nutrients N, P and K in the ratio of 100:5:1. However, excessive discharge of nutrients from treatment plants into the receiving bodies of lakes, rivers, etc. render the quality of their waters poor and unsuitable for beneficial uses, a phenomenon termed ‘Eutrophication’. Regulations around the globe are becoming increasingly stringent demanding low levels of nutrients in wastewater discharges. To achieve the goal of nitrogen control, plant operators are adopting technologies for biochemical nitrification of ammonia to nitrate ions, followed by denitrification of nitrate to nitrogen gas. Details of the eutrophication phenomenon and the biochemical processes for effective nutrient control were presented by this author as “Impact of Nutrients on Water Environment: Control Technologies and Policy” at the 2019 Spring Conference of the American Institute of Chemical Engineers (AIChE), New Orleans, LA. This was later published in the April 2020 issue of the journal Chemical Engineering Progress with the title “Controlling Nitrogen and Phosphorus in Wastewater”.
Nitrogen removal from wastewater is quite expensive from both capital and operating viewpoints due to the facts that – (a) nitrification of ammonia to nitrate is kinetically a very slow process requiring large reactor volume compared to that for carbon (COD) removal alone, and (b) denitrification of nitrate to nitrogen gas requires addition of methanol, which is expensive and a flammable chemical raising safety concerns.
Anammox (Anaerobic Ammonia Oxidation) is a new advancement in technology which only partially oxidizes a part of ammonia to nitrite (not nitrate) ions, followed by the oxidation of remaining part of ammonia by the nitrate ions resulting in nitrogen gas. This is a short cut nitrogen removal process which bypasses total nitrification denitrification cycle. It results in - a) the savings in oxygen requirement for nitrification, and hence reduction in energy consumption and greenhouse gas emissions by ~ 55% by anammox over traditional nite-denite process, b) elimination of methanol addition for denitrification, resulting in chemical cost and reduction in greenhouse gas emission.
This presentation will describe the details of the microbiology, biochemistry, stoichiometry and kinetics of anammox process and its differences with the traditional nitrification-denitrification for nitrogen removal from wastewater. Several case studies with cost savings data by adoption of anammox process at operating wastewater treatment plants will be presented.
While the focus of this presentation will primarily be biochemical nitrogen control, treatment processes for integrated nitrogen and phosphorus control will also be presented.