Increased salinity improves the thermotolerance of mesophilic nitrification

Abstract

Nitrification is a well-studied and established process to treat ammonia in wastewater. Although thermophilic nitrification could avoid cooling costs for the treatment of warm wastewaters, applications above 40°C remain a significant challenge. This study tested the effect of salinity on the thermotolerance of mesophilic nitrifying sludge (34°C). In batch tests, 5 g NaCl L −1 increased the activity of aerobic ammonia-oxidizing bacteria (AerAOB) by 20-21 % at 40 and 45°C. For nitrite-oxidizing bacteria (NOB), the activity remained unaltered at 40°C, yet decreased by 83 % at 45°C. In a subsequent long-term continuous reactor test, temperature was increased from 34 to 40, 42.5, 45, 47.5 and 50°C. The AerAOB activity showed 65 and 37 % higher immediate resilience in the salt reactor (7.5 g NaCl L −1) for the first two temperature transitions and lost activity from 45°C onwards. NOB activity, in contrast to the batch tests, was 37 and 21 % more resilient in the salt reactor for the first two transitions, while no difference was observed for the third temperature transition. The control reactor lost NOB activity at 47.5°C, while the salt reactor only lost activity at 50°C. Overall, this study demonstrates salt amendment as a tool for a more efficient temperature transition for mesophilic sludge (34°C) and eventually higher nitrification temperatures.

A robust nitrifying community in a bioreactor at 50 °C opens up the path for thermophilic nitrogen removal

“…These advantages apply not only to warm wastewaters but also to wastewaters on sites with excess heat available. A few lab-scale studies have explored the potential of thermophilic nitrification for wastewater treatment, but achieved no more than 40-42.5°C (Shore et al, 2012;Courtens et al, 2014a). Thus far, this is the first study describing a thermophilic nitrifying bioreactor at 50°C.…”

“…Lopez-Vazquez et al (2014) recently reported nitrifying activity up to 50°C in mesophilic sludge from an industrial wastewater treatment plant after temperature shocking of mesophilic biomass (34°C) in short-term batch activity assays. However, the observations by Courtens et al (2014a) pointed out that prolonged exposure (48 h) of mesophilic biomass to a temperature shock can lead to a complete loss of nitrifying activity. To our knowledge, there is no description of nitrification at 50°C or above for an extended period of time.…”

“…As neither nitrite nor nitrate was ever measured in these bioreactors at 45-60°C, there is no evidence that nitrification took place in these thermophilic systems. Until now, only a few bioreactor studies focused on the long-term establishment of coupled thermophilic ammonia and nitrite oxidation, yet reaching no more than 42°C (Shore et al, 2012;Courtens et al, 2014a).…”

Lettuce production in hydroponic and fish-farming aquaponic under different channel slopes and nutrient solutions in the NFT system

“…The pH of the residual water in the aquaponic systems presented an average value of 7.5 after passing through the tilapia tanks. After the biofilter, the pH was reduced to average values of 6.0 to 6.5, depending on the nitrification process, as described by Courtens et al (2014). During periodic samplings, the pH oscillated between 5.5 and 6.9, controlled and similar to those used by Van Rijn (2013).…”

Lab‐scale data and microbial community structure suggest shortcut nitrogen removal as the predominant nitrogen removal mechanism in post‐aerobic digestion (PAD)

“…Traditional denitritation/denitritation with removal of NO 2 À and/or NO 3 À and heterotrophic production of nitrogen gas can also affect TIN mass balance (Daigger, As mentioned earlier in Section 3.1.1, this is possible when high solids concentration and coarse bubble diffusion create a favorable environment for the formation of anoxic pockets where production of nitrogen gas occurs (McNamara et al, 2022). Finally, the TIN mass balance (Figure S3) could also be impacted by biological uptake of nitrogen through bacterial growth and likely accounts for a small portion (<5%) (Courtens et al, 2014). In our study, we focused on the fate of nitrogen at constant saturated DO, while future work should look at TN and other nitrogen species, such as N 2 O.…”