Photochemical degradation of atenolol, carbamazepine, meprobamate, phenytoin and primidone in wastewater effluents.

The photochemical degradation of five pharmaceuticals was examined in two secondary wastewater effluents. The compounds, which included atenolol, carbamazepine, meprobamate, phenytoin and primidone, were evaluated for both direct and sensitized photolysis. In the two wastewaters, direct photolysis did not lead to significant compound degradation; however, sensitized photolysis was an important removal pathway for the five pharmaceuticals. Upon solar irradiation, hydroxyl radical (HO) was quantified using the hydroxylation of benzene and singlet oxygen ((1)O2) formation was monitored following the degradation of furfuryl alcohol. Degradation via sensitized photolysis was observed following five-day exposures for atenolol (69-91%), carbamazepine (67-98%), meprobamate (16-52%), phenytoin (44-85%), and primidone (34-88%). Varying removal is likely a result of the differences in reactivity with transient oxidants. Averaged steady state HO concentrations ranged from 1.2 to 4.0×10(-16)M, whereas the concentrations of (1)O2 were 6.0-7.6×10(-14)M. Partial removal due to presence of HO indicates it was not the major sink for most compounds examined. Other transient oxidants, such as (1)O2 and triplet state effluent organic matter, are likely to play important roles in fates of these compounds.

Using digital flow cytometry to assess the degradation of three cyanobacteria species after oxidation processes.

Depending on drinking water treatment conditions, oxidation processes may result in the degradation of cyanobacteria cells causing the release of toxic metabolites (microcystin), odorous metabolites (MIB, geosmin), or disinfection byproduct precursors. In this study, a digital flow cytometer (FlowCAM(®)) in combination with chlorophyll-a analysis was used to evaluate the ability of ozone, chlorine, chlorine dioxide, and chloramine to damage or lyse cyanobacteria cells added to Colorado River water. Microcystis aeruginosa (MA), Oscillatoria sp. (OSC) and Lyngbya sp. (LYN) were selected for the study due to their occurrence in surface water supplies, metabolite production, and morphology. Results showed that cell damage was observed without complete lysis or fragmentation of the cell membrane under many of the conditions tested. During ozone and chlorine experiments, the unicellular MA was more susceptible to oxidation than the filamentous OSC and LYN. Rate constants were developed based on the loss of chlorophyll-a and oxidant exposure, which showed the oxidants degraded MA, OSC, and LYN according to the order of ozone > chlorine ~ chlorine dioxide > chloramine. Digital and binary images taken by the digital flow cytometer provided qualitative insight regarding cell damage. When applying this information, drinking water utilities can better understand the risk of cell damage or lysis during oxidation processes.

Photochemical formation of hydroxyl radical from effluent organic matter.

The photochemical formation of hydroxyl radical (HO•) from effluent organic matter (EfOM) was evaluated using three bulk wastewater samples collected at different treatment facilities under simulated sunlight. For the samples studied, the formation rates of HO•(R(HO•)) were obtained from the formation rate of phenol following the hydroxylation of benzene. The values of R(HO•) ranged from 2.3 to 3.8 × 10(-10) M s(-1) for the samples studied. The formation rate of HO• from nitrate photolysis (R(NO3)(HO•)) was determined to be 3.0 × 10(-7) M(HO)• M(NO3)(-1) s(-1). The HO• production rate from EfOM (R(EfOM)(HO•)) ranged from 0.76 to 1.3 × 10(-10) M s(-1). For the wastewater samples studied, R(EfOM)(HO•) varied from 1.5 to 2.4 × 10(-7) M(HO)• M(C)(-1) (s-1) on molarcarbon basis, which was close to HO• production from nitrate photolysis. The apparent quantum yield for the formation of HO• from nitrate (Φ(NO3-HO•)(a)) was determined as 0.010 ± 0.001 for the wavelength range 290-400 nm in ultrapure water. The apparent quantum yield for HO• formation in EfOM (Φ(EfOM-HO•)(a)) ranged from 6.1 to 9.8 × 10(-5), compared to 2.99 to 4.56 × 10(-5) for organic matter (OM) isolates. The results indicate that wastewater effluents could produce significant concentrations of HO•, as shown by potential higher nitrate levels and relatively higher quantum yields of HO• formation from EfOM.

Evaluation of enhanced coagulation pretreatment to improve ozone oxidation efficiency in wastewater.

Enhanced coagulation (EC) using ferric chloride was evaluated as a pretreatment process to improve the efficiency of ozone (O3) for the oxidation of trace organic contaminants in wastewater. At the applied dosages (10-30 mg/L as Fe), EC pretreatment removed between 10 and 47% of the dissolved organic carbon (DOC) from the three wastewaters studied. Size exclusion chromatography (SEC) showed that EC preferentially removed higher apparent molecular weight (AMW) compounds. Subsequent O3 testing was performed using an O3:DOC ratio of 1. Results showed that O3 exposures were similar even though the required doses were reduced by 10-47% by the EC pretreatment process. Hydroxyl radical (HO·) exposure, measured by parachlorobenzoic acid (pCBA), showed 10% reduction when using a FeCl3 dose of 30 mg/L, likely due to the lower O3 dose and decreased production of HO· during the initial phase of O3 decomposition (t<30 s). The oxidation of 13 trace organic contaminants (including atenolol, carbamazepine, DEET, diclofenac, dilantin, gemfibrozil, ibuprofen, meprobamate, naproxen, primidone, sulfamethoxazole, triclosan, and trimethoprim) was evaluated after EC and O3 treatment. EC was ineffective at removing any of the contaminants, while O3 oxidation reduced the concentration of compounds according to their reaction rate constants with O3 and HO·.

Temperature dependence of the reaction between the hydroxyl radical and organic matter.

The temperature-dependent bimolecular rate constants for the reaction of the hydroxyl radical (HO(•)) with organic matter (OM) (k(OM-HO(•))) have been measured for three natural organic matter (NOM) isolates and three bulk effluent organic matter (EfOM) samples using electron pulse radiolysis and thiocyanate competition kinetics. The range of values for the room temperature k(OM-HO(•)) was 1.21-9.37 × 10(8) M(C)(-1)s(-1), with NOM isolates generally reacting slower than EfOM samples. The NOM isolates had an average apparent activation energy of 19.8 kJ mol(-1), while the EfOM samples had an average value slightly lower (14.3 kJ mol(-1)), although one NOM isolate (Elliot Soil Humic Acid, 29.9 kJ mol(-1)) was a factor of 2 times greater than other samples studied. These apparent activation energies are the first determined for OM and HO(•), and the Arrhenius plots obtained for NOM isolates (lowest R(2) > 0.993) suggest that no significant structural changes are occurring over the temperature range 8-41 °C. In contrast, the greater scatter (lowest R(2) > 0.903) observed for the EfOM samples suggests that some structural changes may be occurring. These results provide a deeper fundamental understanding of the reaction between OM and HO(•) and will be useful in quantifying HO(•) reactions in natural and engineered systems.

Reactivity of effluent organic matter (EfOM) with hydroxyl radical as a function of molecular weight.

The application of advanced oxidation processes (AOPs) for the treatment of wastewater is hindered by scavenging of the hydroxyl radical (HO*) by effluent organic matter (EfOM). This scavenging is directly proportional to the second-order reaction rate constant between EfOM and HO* (kEfOM-HO*). To understand the kinetics of this reaction as a function of the subcomponents of EfOM, four wastewater samples were fractionated by ultrafiltration into distinct apparent molecular weight (AMW) fractions (<1, <3, <5, and <10 kDa), and their kEfOM-HO* values were quantified. In general, the values for k(EfOM-HO*) decreased as the AMW increased. The values of k(EfOM-HO*) for the bulk waters varied between 6.32 and 14.1x10(8) MC(-1)s(-1) (units of per molar carbon concentration per second). In the case of the <1 kDa fraction, the values of kEfOM-HO* varied from 14.3 to 35.0x10(8) MC(-1)s(-1), or approximately 2.31(+/-0.24) times that of the corresponding bulk waters. For the <3 kDa, <5 kDa, and <10 kDa fractions, the k(EfOM-HO*) values were 1.83(+/-0.25), 1.32(+/-0.23), and 1.26(+/-0.35) times that of the bulk waters, respectively. Based on the obtained results, the variability and general magnitude of the kEfOM-HO* values were attributed to the production and reactivity of soluble microbial products (SMP), a major component of EfOM. Two samples collected at a wastewater treatment facility with different treatment variables had different kEfOM-HO* values, indicating that wastewater treatment processes will impact overall HO* scavenging by EfOM and should be considered during the implementation of AOPs.