Temperature-controlled partial nitrification for mainstream wastewater deammonification using batch, semi-batch and continuous systems
Abstract
Aeration is a critical component of the two-step nitrification, the biological conversion of ammonia (NH3) to nitrite (NO2-) and then to nitrate (NO3-), in municipal wastewater treatment plants. Aeration provides the necessary dissolved oxygen for the growth and activity of nitrifying bacteria to Partial nitrification-Anammox (PN-Anammox) is a two-step biological wastewater treatment process, used to remove nitrogen compounds from wastewater efficiently without the need for external carbon. It combines partial nitrification, where ammonia is partially oxidized to nitrite, with anaerobic ammonium oxidation (Anammox) to remove both ammonia and nitrite. About a 60% to 80% of the nitrification energy and 100% of the carbon sources can be saved by PN-Annamox process.
Mainstream partial nitrification, which relies on the inhibition of nitrite oxidizing bacteria (NOB) has drawn considerable attention from researchers and wastewater treatment professionals for several compelling reasons: energy efficiency, enhanced nitrogen removal, reduced carbon footprint and cost savings. 60-80℃ to achieve mainstream partial nitrification. In this study, heat treatment was explored as a new approach in continuous and intermittent for achieving mainstream PN.
Sustained continuous heating of 100% MLSS and offline heating of 20% of biomass at 37℃-42℃ at solids retention time (SRT) of 7 days, DO of 4 mg/L did not achieve any stable nitrite accumulation. In intermittent heating in sequencing batch reactors (SBR), heating once every 10 days at 45℃-2hr, 50℃-1hr and 55℃-0.5 hr with SRT of 7 days, DO of 4 mg/L showed 12% to 17% of nitrification energy savings with stable nitrite accumulation ratio (NAR) of 60%-80%. Similar NAR of 79% was found in continuous-flow systems using membrane bioreactors (MBRs), however with heating once in 4 days. A modified model, incorporating two Arrhenius temperature correction factors for positive and negative growths of nitrifiers: θ1=1.05 and 1.03, and θ2=1.02 and 1.01 respectively for ammonia oxidizing bacteria AOBs and NOBs as a pose to θ=1.072 and θ=1.065 for (AOBs) and NOBs respectively was developed for intermittent heating. This model, which deviated only 6%-20% from experimental data, is an impactful scientific contribution in PN modeling.
Optimization of temperature and contact time for NOB suppression using batches is not appropriate as NOBs are revived in 10-12 days in long-term studies. The impact of heating on the increase of COD of 45-90 mg/L at 45℃-60℃ compared to control ( 30 mg/L) and the reduced NOx of 17 mg/L compared to control ( 25 mg/L) which potentially occurred due to the lysis of heterotrophs and reduced ammonification, needs to be explored further. Any heat treatment higher than 45℃-2hr will solubilize microbial community and any heating higher than 60℃, will need external reactivation of AOBs before application for PN.