Kartik Chandran

Temperature swing solvent extraction (TSSE) has been shown to effectively desalinate hypersaline brines. However, the fate of organic contaminants during TSSE remains poorly understood. This study elucidates the key physicochemical phenomena governing the equilibrium distribution of organic contaminants in biphasic solvent-aqueous systems relevant to TSSE. Distribution coefficients of organic analytes spanning roughly five orders of magnitude of hydrophobicity were systematically evaluated across five thermomorphic hydrophilicity amine solvents, at extraction and disengagement temperatures, and in hypersaline environments. While hydrophobicity has a principal role in governing distribution, acid-base interactions between the solvent and the contaminant were also found to be significant. Temperature typically has a minimal effect on conventional partitioning behavior but exerts a substantial influence in TSSE due to the thermal sensitivity of solvent solubility in water. Brine salinity does not uniformly affect distribution until the aqueous phases approach saturation, at which point the analytes are salted-out of the brine. A multiple linear regression analysis using K_OW, pK_a's, and solvent solubility to model distribution achieved high accuracy (R² = 0.93), offering a practical framework for a priori determination of contaminant fate. These findings provide key mechanistic insights and design tools for TSSE solvent selection and process engineering.

This study focused on the development of machine-learning- (ML) based strategies for mitigating nitrous oxide (N ₂ O) emissions from various wastewater treatment systems in the United States measured using a benchmark USEPA-endorsed protocol. Results revealed that in general, poor process performance correlated with higher N ₂ O emissions. Specifically, local variables including zone-specific dissolved oxygen, ammonia, and nitrite concentrations and global variables including effluent nitrite and nitrate concentrations contributed positively towards N ₂ O emissions from both aerobic and anoxic zones of the process bioreactors. The optimal operational conditions identified for minimizing N ₂ O emissions included operation of aerobic and anoxic zones at DO < 4 mg O ₂ L ^-1 and < 1 mg O ₂ L ^-1 , respectively, coupled with appropriate solids retention times (SRTs) that maximize process performance. Accordingly, our results strongly underscore the utility of ML models in combination with bioprocess fundamentals for predicting and mitigating N ₂ O emissions, while concomitantly optimizing wastewater treatment operations.

This study explored the implementation of mainstream partial denitrification with anammox (PdNA) in the second anoxic zone of a wastewater treatment process in an integrated fixed film activated sludge (IFAS) configuration. A pilot study was conducted to compare the use of methanol and glycerol as external carbon sources for an IFAS PdNA startup, with a goal to optimize nitrogen removal while minimizing carbon usage. The study also investigated the establishment of anammox bacteria on virgin carriers in IFAS reactors without the use of seeding, and it is the first IFAS PdNA startup to use methanol as an external carbon source. The establishment of anammox bacteria was confirmed in both reactors 102 days after startup. Although the glycerol‐fed reactor achieved a higher steady‐state maximum ammonia removal rate because of anammox bacteria (1.6 ± 0.3 g/m²/day) in comparison with the methanol‐fed reactor (1.2 ± 0.2 g/m²/day), both the glycerol‐ and methanol‐fed reactors achieved similar average in situ ammonia removal rates of 0.39 ± 0.2 g/m²/day and 0.40 ± 0.2 g/m²/day, respectively. Additionally, when the upstream ammonia versus NOx (AvN) control system maintained an ideal ratio of 0.40–0.50 g/g, the methanol‐fed reactor attained a lower average effluent TIN concentration (3.50 ± 1.2 mg/L) than the glycerol‐fed reactor (4.43 ± 1.6 mg/L), which was prone to elevated nitrite concentrations in the effluent. Overall, this research highlights the potential for PdNA in IFAS configurations as an efficient and cost‐saving method for wastewater treatment, with methanol as a viable carbon source for the establishment of anammox bacteria.Practitioner Points: Methanol is an effective external carbon source for an anammox startup that avoids the need for costly alternative carbon sources. The methanol‐fed reactor demonstrated higher TIN removal compared with the glycerol‐fed reactor because of less overproduction of nitrite. Anammox bacteria was established in an IFAS reactor without seeding and used internally stored carbon to reduce external carbon addition. Controlling the influent ammonia versus NOx (AvN) ratio between 0.40 and 0.50 g/g allowed for low and stable TIN effluent conditions.