Nitrate residual as a key parameter to efficiently control partial denitrification coupling with anammox

Abstract

Despite the increased research efforts, full-scale implementation of shortcut nitrogen removal strategies has been challenged by the lack of consistent nitrite-oxidizing bacteria out-selection. This paper proposes an alternative path using partial denitrification (PdN) selection coupled with anaerobic ammonium-oxidizing bacteria (AnAOB). A nitrate residual concentration (>2 mg N/L) was identified as the crucial factor for metabolic PdN selection using acetate as a carbon source, unlike the COD/N ratio which was often suggested. Therefore, a novel and simple acetate dosing control strategy based on maintaining a nitrate concentration was tested in the absence and presence of AnAOB, achieving PdN efficiencies above 80%. The metabolic-based PdN selection allowed for flexibility to move between PdN and full denitrification when required to meet effluent nitrate levels. Due to the independence of this strategy on species selection and management of nitrite competition, this novel approach will guarantee nitrite availability for AnAOB under mainstream conditions unlike shortcut nitrogen removal approaches based on NOB out-selection. Overall, a COD addition of only 2.2 g COD/g TIN removed was needed for the PdN-AnAOB concept showing its potential for significant savings in external carbon source needs to meet low TIN effluent concentrations making this concept a competitive alternative. • Practitioner points• Nitrate residual is the key control parameter for partial denitrification selection. • Metabolic selection allowed for flexibility of moving from partial to full denitrification. • 2.2 g COD/g TIN removed was needed for partial denitrification-anammox process.

Enhancing biological nitrogen removal for a retrofit project using wastewater with a low C/N ratio—a model-based study

“…However, under the 0.5 mg/L DO scenario, the AMX activities increase over the process train before each influent feeding, and each influent feeding noticeably reduces the AMX activities. This is because in the model framework, can only be conserved for anammox if organic carbon is not enough for further denitrification of , and the simulation outcome conforms to experimental observations that PdN requires delicate controls of organic carbon addition (Cao et al 2013 ; Du et al 2019b ; Le et al 2019 ). The contrast between the 0.1 and 0.5 mg/L DO scenarios also demonstrates that availability (pre-ready versus immediate generation among competitive environment) has a pronounced impact on AMX activities (Le et al 2019 ; Jia et al 2020 ).…”

“…In reality, PdN is more controllable than PN, but maintaining PdN might also require proper types of organic carbon, e.g., acetate or glycerol (Cao et al 2013 ). In a PdNA study carried by the District of Columbia Water and Sewer Authority (DC Water), it is demonstrated that the organic carbon from raw wastewater should be depleted before PdN can occur in a controllable manner, and a delicate control of organic carbon addition should also be implemented depending on the level in the PdNA unit (Le et al 2019 ). In this current model-based study, the depressed AMX activities by each influent feeding under the 0.5 mg/L DO scenario suggest the need for an even more distributed organic carbon dosage to lower the negative effect from organic loading shocks, e.g., use intermittent carbon source addition to prevent thorough denitrification (Du et al 2019a ), similarly like intermittent aeration is often used to promote PN by preventing full nitrification (Corbalá-Robles et al 2015 ).…”

“…Therefore, this study together with some other recent literature indicates a strong need for implementing advanced process controls to achieve higher wastewater treatment purposes, e.g., cultivating AMX, enhancing the system's resilience to influent fluctuations, etc. (Le et al 2019;Du et al 2019aDu et al , 2019bJia et al 2020). It becomes evident that the ongoing campaign of evolving from energy-intensive to more energy-efficient or even energyneutral processes cannot be accomplished without the help of more in-depth studies on process control strategies.…”

“…In reality, maintaining PN is delicate due to the difficulty of out-select nitrite-oxidizing bacteria (NOB) (Ali and Okabe 2015 ), while PdN can be more reliably controlled by limiting the availability of organic carbon (Du et al 2019a ). With increased interests in PdNA, the US EPA recently launched a project to evaluate mainstream PdNA (USEPA 2020 ), and it is generally agreed that achieving mainstream anammox requires advanced control strategies to provide intensive care of PdN for AMX to thrive (Le et al 2019 ).…”

Modeling, instrumentation, automation, and optimization of water resource recovery facilities (2019) DIRECT

“…A pilot-scale application of ammonia vs. nitrate-nitrite DO control algorithm using dynamic alpha adjustment based on influent inorganic nitrogen demonstrated the potential for ANNUAL LITERATURE REVIEW reducing aeration and carbon requirements and meeting an effluent total inorganic nitrogen of 4 mg/L based on a partial denitrification-anoxic ammonia-oxidizing bacteria shortcut-nitrogen removal process (Le, Fofana, et al, 2019). Le, Peng, et al (2019) reported the potential for more than 50% reduction in supplemental carbon during operation of a partial denitrification-anoxic ammonia oxidation pilot process controlled by ammonia vs. nitrate-nitrite DO control.…”