Synergistic effect of nitrate on UV-chlorine photochemical degradation of carbamazepine.

We investigated the use of UV-chlorine advanced oxidation process for the removal and transformation of carbamazepine (CBZ), and its photochemical synergy with NO3- for the production of .OH towards enhancing CBZ removal in aqueous solution. Production of .OH by UV-chlorine system with/without NO3- was studied under different conditions, by using salicylic acid (SA) as the chemical probe for .OH. Initial concentration of 30 mg/L SA, 5 and 10 mg/L chlorine, and 0-10 mg/L NO3- under irradiation at 254 nm (3.026 W/L) in a photochemical reactor was used. Aqueous solutions containing 10 mg/L chlorine and spiked with 4 mg/L NO3- gave the highest reproducible generation of .OH. Using initial concentrations of 10 mg/L CBZ and 10 mg/L chlorine, 60 % CBZ was removed after 10 min of irradiation without NO3-, while 72 % CBZ was removed with 4 mg/L NO3- added. There was no noticeable CBZ removal after 10 min of irradiation in the presence of NO3- without chlorine. Corresponding dark reactions were also conducted, with no noticeable degradation of CBZ. Samples were analyzed via UHPLC, LC-MS, and TOC (total organic carbon) analyzer for CBZ and TOC concentrations respectively. Although, there was significant reduction in CBZ concentration during both photochemical degradation processes, the was low TOC removal (~10%) in each case. The two photochemical degradation processes also seem to generate similar degradation products indicating that the addition NO3- of the UV-chlorine process might not have changed the degradation mechanism. The results indicate that NO3- could act synergistically in a UV-chlorine system to increase CBZ removal and reduce the quantity of free chlorine required to achieve a target removal efficiency. This could facilitate reduction in the potential production of chlorinated byproducts in the system.

The use of recycled materials in a biofilter to polish anammox wastewater treatment plant effluent.

Anammox is gaining popularity for treating wastewater containing high-strength ammonia due to lower energy demand compared to conventional nitrification-denitrification processes; however, anammox is reported to increase nitrate loads in the effluent. The objective of this study was to assess the applicability of recycled materials [recycled concrete aggregate (RCA) and rice husks (RH)] as a polishing step to improve anammox reactor effluent quality. Anammox effluents were separately passed through two single-stage columns containing RCA and RH, and one two-stage column (50% RCA, 50% RH) to quantify total N, ammonia, nitrate, nitrite, and phosphate removal efficiencies. Langmuir isotherm experiments were conducted to quantify nitrate, nitrite, and phosphate sorption capacities in the columns. The RCA column exhibited the highest phosphate sorption capacity (0.074 mg/g), while the RH column exhibited higher nitrite and nitrate adsorption (0.063 mg/g and 0.023 mg/g respectively). We created a Hydrus-1D model to estimate pseudo-first-order reaction rates in the columns. Because RCA media can form metal-phosphate precipitates, the fastest phosphate reaction rate (1.58 min-1) occurred in the RCA column. The two-stage column demonstrated the greatest overall removals for all nutrients, and removal rates were consistent throughout the experimental period. The two-stage column achieved 15% total N, 94% ammonia-N, 38% nitrate-N, 75% nitrite-N, and 27% phosphate removal. The maximum nitrite, nitrate, and phosphate adsorption capacities in the two-stage column were 0.030 mg/g, 0.017 mg/g, and 0.014 mg/g respectively. This is the first study to demonstrate that recycled materials can successfully be integrated into a biofilter as an effluent polishing step to remove nutrients from anammox wastewater.

Modeling transport, fate, and removal kinetics of nitrate and orthophosphate using recycled adsorbents for high and low-flow stormwater runoff treatment.

Excessive nitrate and orthophosphate carried by the stormwater runoff potentially lead to eutrophication in surface water bodies. Various green infrastructures are used that commonly consider the biological treatment of nutrients from the runoff. Due to the leaching and clogging complexities in biological mechanisms, the selection of high-flow, eco-friendly, and recycled adsorbents has been advocated to promote the physiochemical treatment of nutrients as an alternative. In this study, column experiments were conducted to investigate the transport, fate, adsorption equilibria, and reaction kinetics of nitrate (NO3-N) and orthophosphate (PO4-P) onto three recycled adsorbents - recycled concrete aggregate (RCA), recycled crushed glass (RCG), rice husks (RH), and a layered media (LM), under high and low-flow conditions. The non-reactive solute transport in columns was investigated through the bromide tracer test. The HYDRUS-1D model was used to estimate adsorption coefficients and reaction kinetics of pollutants in unsaturated media columns. Our results indicated the maximum superficial pore velocity (v = 4.40 cm/s) and dispersion (α = 2.50 cm) in RCA at the low-flow condition. Overall, NO3-N removal at the exhaustion was low in all columns, ranging between 1 and 25%. Conversely, orthophosphate removal was significant (p < 0.05) in RCA (≤94%) under low flow conditions with increased reaction kinetics (kr,d = 3.45 min-1, kr,s = 0.55 min-1) and enhanced adsorption capacity at saturation (qmax = 1.87E+05-2.33E+05 mg/kg). In conclusion, the dissolved-phase reaction kinetics (kr,d) played a significant role apart from the physisorption for the satisfactory removal of orthophosphate in RCA.

Nutrients and solids removal in bioretention columns using recycled materials under intermittent and frequent flow operations.

This research investigated the fate and removal of nitrite (NO2-N), nitrate (NO3-N), orthophosphate (PO4-P), and total suspended solids (TSS) in two bioretention columns, which were designed with three recycled materials. The first column was packed with Recycled Concrete Aggregate (RCA). The second column was a Layered Media (LM), which has layers of RCA with crushed glass and rice husks. The columns were tested under intermittent and frequent operations of synthetic runoff with low and high feed concentrations. The effect of inflow concentration, antecedent dry days (ADD), column age, and the anticipated number of events (EN) was also statistically analyzed on the performance of columns. Depending on column types, nutrient removal was significantly (p < 0.05) increased under frequent flow operations by 26-53% over intermittent. However, TSS removal was notably (p < 0.05) increased by 23-35% under intermittent operations over frequent. Overall, LM showed an increased NO2-N (92 ± 2%) and NO3-N (88% ± 2%) removal under low feed frequent operations and TSS removal (97% ± 2%) under initial intermittent operations. On the contrary, RCA showed a maximum of 99% PO4-P removal under high feed frequent operations. Results showed that the nutrient outflow concentration was found to have a negative correlation with EN and column age and a positive correlation with ADDs throughout the experiments.

Hydrogen peroxide-assisted UV photodegradation of Lindane.

Aqueous solutions of gamma-hexachlorocyclohexane (Lindane) were photolyzed (lambda=254 nm) under a variety of solution conditions. The initial concentrations of hydrogen peroxide (H(2)O(2)) and Lindane varied from 0 to 20 mM and 0.21 to 0.22 microM, respectively, the pH ranged from 3 to 11, and several concentration ratios of Suwannee River humic acid and fulvic acid were dissolved in the irradiated solutions. Lindane rapidly reacted, and the maximum reaction rate constant (9.7 x 10(-3) s(-1)) was observed at pH 7 and initial [H(2)O(2)]=1 mM. Thus, 90% of the Lindane is destroyed in approximately 4 min under these conditions. In addition, within 15 min, all chlorine atoms were converted to chloride ion, indicating that chlorinated organic by-products do not accumulate. The reactor was characterized by measuring the photon flux (7.04 x 10(-6) E s(-1)) and the cumulative production of *OH during irradiation. The cumulative *OH production during irradiation was fastest at an initial [H(2)O(2)]=5 mM (k=0.77 micro M s(-1)).

Photodegradation of decabromodiphenyl ether adsorbed onto clay minerals, metal oxides, and sediment.

The photodebromination of decabromodiphenyl ether (BDE-209) adsorbed onto six different solid matrixes was investigated in sunlight and by irradiation with 350 +/- 50 nm lamps (four lamps at 24 W each). After 14 days of lamp irradiation, BDE-209 degraded with a half-life of 36 and 44 days, respectively, on montmorillonite or kaolinite, with much slower degradation occurring when sorbed on organic carbon-rich natural sediment (t1/2 = 150 days). In late summer and fall sunlight (40.5 degrees N, elevation 600 ft), the half-lives of BDE-209 sorbed on montmorillonite and kaolinite were 261 and 408 days, respectively. Under both irradiation schemes, no significant loss of BDE-209 occurred when sorbed to aluminum hydroxide, iron oxide (ferrihydrite), or manganese dioxide (birnessite). Upon exposure to both lamp and solar light and in the presence of montmorillonite and kaolinite, numerous lesser brominated congeners (tri- to nonabromodiphenyl ethers) were produced. Nearly identical product distribution was evident on montmorillonite and kaolinite. Dark control experiments for each mineral showed no disappearance of BDE-209 or appearance of degradation products. These results suggest that photodegradation of BDE-209 on mineral aerosols during long-range atmospheric transport may be an important fate process for BDE-209 in the environment.

Solar photodecomposition of decabromodiphenyl ether: products and quantum yield.

Decabromodiphenyl ether (BDE209) is a widely used flame retardant, yet information regarding its environmental transformation rates and pathways are largely unknown. Because photochemical transformation is often suggested as a potentially important fate process for BDE209, the reaction rate and products of the solar degradation under favorable solvent conditions were determined in this study. Decabromodiphenyl ether (BDE209), dissolved in hexane, reacts in minutes via direct solar irradiation, at midlatitude (40 degrees 29' N, 86 degrees 59.5' W) in afternoon July and October sunlight. Observed first-order reaction rate constants, kobs, at the different exposure times were kobs = 1.86 x 10(-3) s(-1) (July) and kobs = 1.11 x 10(-3) s(-1) (October). The photodecomposition quantum yield was calculated from these data and from the solar irradiance data measured at 300, 305.5, 311.4, 317.6, 325.4, 332.4, and 368 nm reported at a USGS UVB monitoring station located nearby. The range of wavelengths where both the molar absorptivity of BDE209 and the solar irradiance flux are significant occurs between 300 and 350 nm. For this range, the wavelength average quantum yield for BDE209 photoreaction, phiave, was calculated to be 0.47. The difference between kobs values at the two exposure times is explained fully by the difference between the solar irradiation fluxes. Upon solar irradiation, BDE209 reductively dehalogenated to other polybrominated diphenyl ethers (PBDEs). During 34 h of irradiation, PBDEs ranging from nona- to tri-bromodiphenyl ethers were observed. In total, 43 PBDEs were detected, and the GC retention times and mass spectral fragment patterns of 21 products matched those of available congener standards, including congeners 2,2',4,4',5-pentabromodiphenyl ether and 2,2',4,4'-tetrabromodiphenyl ether.