Removal efficiency of organic micropollutants in successive wastewater treatment steps in a full-scale wastewater treatment plant: Bench-scale application of tertiary treatment processes to improve removal of organic micropollutants persisting after secondary treatment.

The goal of this study was to investigate the occurrence and removal of 52 organic micropollutants (OMPs) during each wastewater treatment step in a full-scale wastewater treatment plant (WWTP). Pharmaceuticals such as metformin, acetaminophen, caffeine, ibuprofen, cimetidine and naproxen were found with high average concentrations in the influent. Most OMPs were not affected by the primary treatment (removal <10%), while secondary biological treatment contributed the most to overall removal of the OMPs. Among the three lanes of the secondary treatment of the WWTP, a combined anaerobic-anoxic-oxic process followed by a membrane bioreactor (A2O-MBR) process effectively facilitated removal of the OMPs (96%) using a different redox: a conventional activated sludge (CAS) process exhibited removal of approximately 85% of total concentrations of the OMPs, while a Modified Ludzack-Ettinger (MLE) process achieved approximately 92.1% removal. Removal of more than 50% of the concentrations of 13 targeted OMPs was observed in the secondary effluent (except for metformin showing only 3.8% removal) via adsorption with powdered activated carbon (PAC) as additional tertiary treatment. Metformin, inadequately removed by additional tertiary treatments, was effectively removed by a biological activated carbon (BAC) process, reaching a removal efficiency of 90.5%. To increase the removal of the amounts and types of OMPs with various physico-chemical properties, hybrid processes through a combination of diverse advanced treatment should be tailored to WWTPs.

Occurrence and transformation of gabapentin in urban water quality engineering: Rapid formation of nitrile from amine during drinking water chlorination.

The occurrence and fate of the popular pharmaceutical gabapentin (GBP) in the urban water cycle were investigated with a focus on its transformation during water chlorination. GBP was detected in all samples with average concentrations of 1285 ng/L (n = 24) for wastewater effluent, 304 ng/L for river water (n = 22), and 180 ng/L for drinking water treatment plant (DWTP) influent (n = 4). The monitoring sites were located in the Nakdong River watershed, Korea. GBP was rapidly (within 20 min) transformed into 1-cyanocyclohexylacetic acid (GBP-nitrile) under typical chlorination conditions (1.4 mgCl2/L). When there was a molar excess of chlorine to GBP, the primary amine of GBP was double-chlorinated to form N-Cl2 GBP with a second-order rate constant of >103 M-1 s-1. Decomposition of N-Cl2 GBP had a first-order rate constant of (0.5-1.0) × 10-2 s-1 and produced GBP-nitrile with a yield of 87%-100%. We propose that N-Cl2 GBP is transformed into N-Cl GBP imine and then to GBP-nitrile via two consecutive dehydrochlorinations with the former as the rate-limiting step. N-Cl2 GBP had a much higher decomposition rate than N-Cl2 produced from other simple aliphatic amines, which could be related to the structural features of GBP such as its carboxyl group and quaternary ß-carbon. The wastewater effluent samples did not contain GBP-nitrile even in the chlorinated effluent because of the relatively low chlorine dose or high ammonia level. In a full-scale DWTP employing a pre-chlorination unit, GBP present in the influent river water was fully transformed into GBP-nitrile. The formed GBP-nitrile was degraded in subsequent ozonation (•OH oxidation) and biological activated carbon filtration (biodegradation) processes. The toxicity of GBP-nitrile is thought to be low but further studies are warranted to assess the toxicological relevance of nitrile formation during water chlorination.

Transformation of an Amine Moiety of Atenolol during Water Treatment with Chlorine/UV: Reaction Kinetics, Products, and Mechanisms.

Transformation of atenolol (ATN), a micropollutant containing a secondary (2°) amine moiety, can be significantly enhanced in water treatment with sequential and combined use of chlorine and UV (chlorine/UV) through photolysis of the N-Cl bond. This study investigated the transformation kinetics, products, and mechanisms of the amine moiety of ATN in chlorine/UV (254 nm). The fluence-based, photolysis rate constant for N-Cl ATN was 2.0 × 10-3 cm2/mJ. Transformation products (TPs) with primary (1°) amines were mainly produced, but TPs with 2° and 3° amines were also formed, on the basis of liquid chromatography (LC)/quadrupole-time-of-flight/mass spectrometry and LC/UV analyses. The amine-containing TPs could be further transformed in chlorine/UV (with residual chlorine in post UV) via formation and photolysis of new N-Cl bonds. Photolysis of N-Cl 1° amine TPs produced ammonia as a major product. These data could be explained by a reaction mechanism in which the N-Cl bond was cleaved by UV, forming aminyl radicals that were transformed via 1,2-hydrogen shift, ß-scission, intramolecular addition, and 1,2-alkyl shift. Among these, the 1,2-alkyl shift is newly discovered in this study. Despite enhanced transformation, only partial mineralization of the ATN's amine moiety was expected, even under chlorine/UV advanced oxidation process conditions. Overall, the kinetic and mechanistic information from this study can be useful for predicting the transformation of amine moieties by chlorine/UV water treatment.

Elimination efficiency of organic UV filters during ozonation and UV/H2O2 treatment of drinking water and wastewater effluent.

The efficiency of elimination of organic UV filters by ozonation and UV254nm/H2O2 processes was assessed and predicted in simulated treatments of sewage-impaired drinking water and wastewater effluent in bench-scale experiments. Second-order rate constants (k) for the reactions of the eight UV filters with ozone and OH were determined by quantum chemical calculations and competition kinetics methods, respectively. The UV filters containing phenolic (ethylhexyl-salicylate, homosalate, and benzophenone-3) and olefinic moieties (4-methylbenzylidene-camphor, benzyl-cinnamate, and 2-ethylhexyl-4-methoxycinnamate) showed high ozone reactivity (k ≥ 8 × 104 M-1s-1 at pH 7), while those without such electron-rich moieties (isoamyl-benzoate and benzophenone) were ozone-refractory. All the UV filters showed high OH reactivity (k ≥ 6.2 × 109 M-1s-1). In concordance with the rate constant information, the phenolic and olefinic UV filters were efficiently eliminated by ozone treatment, requiring specific ozone doses of <0.5 mgO3/mgDOC for ∼100% elimination. The UV filters were eliminated by ≤ 38% at a UV fluence of 1500 mJ/cm2 in the UV254nm-only treatment. Rapid photoisomerisation between the E and Z geometric isomers was observed for the olefinic UV filter, benzyl-cinnamate. The addition of H2O2 (10 mg/L) greatly enhanced the elimination of all UV filters, indicating that OH was the main contributor to their elimination in the UV254nm/H2O2 treatment. A chemical kinetics approach developed previously for ozonation and UV/H2O2 processes was shown to predict the elimination of the UV filters in the tested water matrices reasonably well, demonstrating that the chemical kinetics method can be used for a priori prediction of micropollutant elimination in oxidative treatment processes for potable reuse of municipal wastewater effluents.

Transformation of methylparaben during water chlorination: Effects of bromide and dissolved organic matter on reaction kinetics and transformation pathways.

The reaction kinetics, products, and pathways of methylparaben (MeP) during water chlorination with and without bromide (Br-) were investigated to better understand the fate of parabens in chlorinated waters. During the chlorination of MeP-spiked waters without Br-, MeP was transformed into mono-Cl-MeP and di-Cl-MeP with apparent second-order rate constants (kapp) of 64M-1s-1 and 243M-1s-1 at pH7, respectively, while further chlorination of di-Cl-MeP was relatively slower (kapp=1.3M-1s-1 at pH7). With increasing Br- concentration, brominated MePs, such as mono-Br-MeP, Br-Cl-MeP, and di-Br-MeP, became major transformation products. The di-halogenated MePs (di-Cl-MeP, Br,Cl-MeP, and di-Br-MeP) showed relatively low reactivity to chlorine at pH7 (kapp=1.3-4.6M-1s-1) and bromine (kapp=32-71M-1s-1), which explains the observed high stability of di-halogenated MePs in chlorinated waters. With increasing pH from 7 to 8.5, the transformation of di-halogenated MePs was further slowed due to the decreasing reactivity of di-MePs to chlorine. The formation of the di-halogenated MePs and their further transformation become considerably faster at Br- concentrations higher than 0.5µM (40µg/L). Nonetheless, the accelerating effect of Br- diminishes in the presence of dissolved organic matter (DOM) extract (Suwannee River humic acid (SRHA)) due to a more rapid consumption of bromine by DOM than chlorine. The effect of Br- on the fate of MeP was less in the tested real water matrices, possibly due to a more rapid bromine consumption by the real water DOM compared to SRHA. A kinetic model was developed based on the determined species-specific second-order rate constants for chlorination/bromination of MeP and its chlorinated and brominated MePs and the transformation pathway information, which could reasonably simulate the transformation of MePs during the chlorination of water in the presence of Br- and selected DOM.