Effect of some parameters on the formation of chloroform during chloramination of aqueous solutions of resorcinol

The effects of various factors (N/Cl ratio used to prepare monochloramine, monochloramine doses, pH and contact time) on the monochloramine demand and on the chloroform yield during chloramination of resorcinol have been investigated. Chloramination experiments were carried out at 24 ± 1 °C, at pH values ranging from 6.5 to 12 using a bicarbonate/carbonate buffer and preformed monochloramine solutions prepared at pH 8.5 with N/Cl ratios ([NH₄Cl]₀/[Total free Cl₂]₀ ranging from 1.0 to 150 mol/mol). Kinetic experiments ([Resorcinol]₀ = 5 or 100 μM, [NH₂Cl]₀/[Resorcinol]₀ = 20 mol/mol, pH = 8.5 ± 0.1) showed a slow increase of the monochloramine consumption with reaction time. The monochloramine demands after reaction times of 7 days ([Resorcinol]₀ = 100 μM) and 14 days ([Resorcinol]₀ = 5 μM) were equal to 8.5 mol of NH₂Cl/mole of resorcinol and were higher than the chlorine demands (≈7.3 mol/mol). Chloroform yields from monochloramination of resorcinol were lower than 8% (<80 mmol of CHCl₃/mole of resorcinol) and were less than the yields obtained by chlorination (0.9-0.95 mol/mol). Chloroform productions increased with increasing monochloramine dose and reaction time and decreased with increasing pH values within the pH range 6.5-10. Chloroform formation markedly decreased when the N/Cl ratio increased from 1 to 1.5 mol/mol and was suppressed at N/Cl > 100 mol/mol. The data obtained in the present work suggest that free chlorine released from monochloramine hydrolysis plays a significant role on the formation of chloroform during chloramination of resorcinol at N/Cl ratios close to unity (1.0 < N/Cl < 1.5).     

Mechanism of Cu(II)-catalyzed monochloramine decomposition in aqueous solution

The decomposition of monochloramine, which is commonly used as a secondary disinfectant at water treatment plants to reduce the formation of disinfection byproducts, always occurs in water and can be accelerated by certain catalytic substances. This work was to investigate the mechanism of monochloramine decomposition catalyzed by Cu(II) in aqueous solution. Ultraviolet (UV) spectral results showed that either Cu(II) addition or pH decrease would significantly promote the transformation of monochloramine to dichloramine. A copper intermediate, Cu(I), was extracted from the NH₂Cl-Cu(II) solution by solid-phase extraction and identified by X-ray photoelectron spectroscopy (XPS). Electron spin resonance (ESR) results showed that hydroxyl radical (·OH) and amidogen radical (·NH₂) were generated in the reaction between monochloramine and Cu(II). These radical intermediates also contributed to monochloramine decomposition. Based on the experimental results, the reaction mechanism for Cu(II)-catalyzed monochloramine decomposition was proposed which consisted of two pathways: 1) direct catalysis in which Cu(II) acts as a Lewis acid to accelerate monochloramine decomposition to dichloramine (major pathway); and 2) indirect catalysis in which the active radical intermediates (·OH and ·NH₂) react with monochloramine and lead to its decomposition (minor pathway).     

Comparison of chlorine and chloramine in the release of mercury from dental amalgam

The purpose of this project was to compare the ability of chlorine (HOCl/OCl⁻) and monochloramine (NH₂Cl) to mobilize mercury from dental amalgam. Two types of amalgam were used in this investigation: laboratory-prepared amalgam and samples obtained from dental-unit wastewater. For disinfectant exposure simulations, 0.5 g of either the laboratory-generated or clinically obtained amalgam waste was added to 250 mL amber bottles. The amalgam samples were agitated by end-over-end rotation at 30 rpm in the presence of 1 mg/L chlorine, 10 mg/L chlorine, 1 mg/L monochloramine, 10 mg/L monochloramine, or deionized water for intervals of 0 h, 2 h, 4 h, 8 h, and 24 h for the clinically obtained amalgam waste samples and 4 h and 24 h for the laboratory-prepared samples. Chlorine and monochloramine concentrations were measured with a spectrophotometer. Samples were filtered through a 0.45 µm membrane filter and analyzed for mercury with USEPA standard method 245.7. When the two sample types were combined, the mean mercury level in the 1 mg/L chlorine group was 0.020 mg/L (n = 25, SD = 0.008). The 10 mg/L chlorine group had a mean mercury concentration of 0.59 mg/L (n = 25, SD = 1.06). The 1 mg/L chloramine group had a mean mercury level of 0.023 mg/L (n = 25, SD = 0.010). The 10 mg/L chloramine group had a mean mercury level of 0.024 mg/L (n = 25, SD = 0.011). Independent samples t-tests showed that there was a significant difference between the natural log mercury measurements of 10 mg/L chlorine compared to those of 1 mg/L and 10 mg/L chloramine. Changing from chlorine to chloramine disinfection at water treatment plants would not be expected to produce substantial increases in dissolved mercury levels in dental-unit wastewater.     

Modeling monochloramine loss in the presence of natural organic matter

A comprehensive model describing monochloramine loss in the presence of natural organic matter (NOM) is presented. The model incorporates simultaneous monochloramine autodecomposition and reaction pathways resulting in NOM oxidation. These competing pathways were resolved numerically using an iterative process evaluating hypothesized reactions describing NOM oxidation by monochloramine under various experimental conditions. The reaction of monochloramine with NOM was described as biphasic using four NOM specific reaction parameters. NOM pathway 1 involves a direct reaction of monochloramine with NOM (k_doc1=1.05×10⁴-3.45×10⁴ M⁻¹ h⁻¹). NOM pathway 2 is slower in terms of monochloramine loss and attributable to free chorine (HOCl) derived from monochloramine hydrolysis (k_doc2=5.72×10⁵-6.98×10⁵ M⁻¹ h⁻¹), which accounted for the majority of monochloramine loss. Also, the free chlorine reactive site fraction in the NOM structure was found to correlate to specific ultraviolet absorbance at 280 nm (SUVA₂₈₀). Modeling monochloramine loss allowed for insight into disinfectant reaction pathways involving NOM oxidation. This knowledge is of value in assessing monochloramine stability in distribution systems and reaction pathways leading to disinfection by-product (DBP) formation.     

Electrochemical oxidation of trace organic contaminants in reverse osmosis concentrate using RuO2/IrO2-coated titanium anodes

During membrane treatment of secondary effluent from wastewater treatment plants, a reverse osmosis concentrate (ROC) containing trace organic contaminants is generated. As the latter are of concern, effective and economic treatment methods are required. Here, we investigated electrochemical oxidation of ROC using Ti/Ru_0.7Ir_0.3O₂ electrodes, focussing on the removal of dissolved organic carbon (DOC), specific ultra-violet absorbance at 254 nm (SUVA₂₅₄), and 28 pharmaceuticals and pesticides frequently encountered in secondary treated effluents. The experiments were conducted in a continuously fed reactor at current densities (J) ranging from 1 to 250 A m⁻² anode, and a batch reactor at J = 250 A m⁻². Higher mineralization efficiency was observed during batch oxidation (e.g. 25.1 ± 2.7% DOC removal vs 0% removal in the continuous reactor after applying specific electrical charge, Q = 437.0 A h m⁻³ ROC), indicating that DOC removal is depending on indirect oxidation by electrogenerated oxidants that accumulate in the bulk liquid. An initial increase and subsequent slow decrease in SUVA₂₅₄ during batch mode suggests the introduction of auxochrome substituents (e.g. -Cl, NH₂Cl, -Br, and -OH) into the aromatic compounds. Contrarily, in the continuous reactor ring-cleaving oxidation products were generated, and SUVA₂₅₄ removal correlated with applied charge. Furthermore, 20 of the target pharmaceuticals and pesticides completely disappeared in both the continuous and batch experiments when applying J ≥ 150 A m⁻² (i.e. Q ≥ 461.5 A h m⁻³) and 437.0 A h m⁻³ (J = 250 A m⁻²), respectively. Compounds that were more persistent during continuous oxidation were characterized by the presence of electrophilic groups on the aromatic ring (e.g. triclopyr) or by the absence of stronger nucleophilic substituents (e.g. ibuprofen). These pollutants were oxidized when applying higher specific electrical charge in batch mode (i.e. 1.45 kA h m⁻³ ROC). However, baseline toxicity as determined by Vibrio fischeri bioluminescence inhibition tests (Microtox) was increasing with higher applied charge during batch and continuous oxidation, indicating the formation of toxic oxidation products, possibly chlorinated and brominated organic compounds.     

The effects of selected preoxidation strategies on I-THM formation and speciation

In this study, the impacts of three preoxidation strategies [i.e., using potassium permanganate (KMnO₄), chlorine dioxide (ClO₂), or hydrogen peroxide (H₂O₂)] before preformed monochloramine (NH₂Cl) addition on the formation and speciation of iodinated trihalomethanes (I-THMs) were evaluated at the Br⁻/I⁻ mass ratio of 10 in two natural waters. The effects of preoxidant dose, Br⁻/DOC, and I⁻/DOC ratio were investigated. Preoxidation with KMnO₄ increased I-THM formation due to an increase in iodoform (CHI₃) and brominated I-THM (CHBrClI, CHBrI₂, CHBr₂I) formation. In contrast, preoxidation with ClO₂ sometimes reduced I-THM formation, primarily due to a reduction in CHI₃ formation. Preoxidation with H₂O₂ had no effect on I-THM formation or speciation. I-THM formation from each preoxidant alone was considerably less than the formation from NH₂Cl. Overall, preoxidant type, preoxidant/DOC, preoxidant/I⁻, and I⁻/DOC ratios are the important factors that water utilities should evaluate when assessing the impact of preoxidation for controlling I-THM formation.     

Chloramination of organophosphorus pesticides found in drinking water sources

The degradation of commonly detected organophosphorus (OP) pesticides, in drinking water sources, was investigated under simulated chloramination conditions. Due to monochloramine autodecomposition, it is difficult to observe the direct reaction of monochloramine with each OP pesticide. Therefore, a model was developed to examine the reaction of monochloramine (NH₂Cl) and dichloramine (NHCl₂) with chlorpyrifos (CP), diazinon (DZ), and malathion (MA). Monochloramine was found not to be very reactive with each OP pesticides, . While, dichloramine (NHCl₂) was found to be 2 orders of magnitude more reactive with each of the OP pesticides than monochloramine, , which is still three orders of magnitude less than the hypochlorous acid reaction rate coefficient with each OP pesticide. For each pesticide, the reactivity of the three chlorinated oxidants was then found to correlate with half-wave potentials (E_1/2) of each oxidant. With reaction rate coefficients for the three chlorinated oxidations as well as neutral and alkaline hydrolysis rate coefficients for the pesticides, the model was used to determine the dominant reaction pathways as a function of pH. At pH 6.5, OP pesticide transformation was mostly due to the reaction of hypochlorous acid and dichloramine. Above pH 8, alkaline hydrolysis or the direct reaction with monochloramine was the primary degradation pathway responsible for the transformation of OP pesticides. This demonstrates the ability of models to be used as tools to elucidate degradation pathways and parameterize critical reaction parameters when used with select yet comprehensive data sets.     

Optimized aeration strategies for nitrogen and phosphorus removal with aerobic granular sludge

Biological wastewater treatment by aerobic granular sludge biofilms offers the possibility to combine carbon (COD), nitrogen (N) and phosphorus (P) removal in a single reactor. Since denitrification can be affected by suboptimal dissolved oxygen concentrations (DO) and limited availability of COD, different aeration strategies and COD loads were tested to improve N- and P-removal in granular sludge systems. Aeration strategies promoting alternating nitrification and denitrification (AND) were studied to improve reactor efficiencies in comparison with more classical simultaneous nitrification–denitrification (SND) strategies. With nutrient loading rates of 1.6 gCOD L⁻¹ d⁻¹, 0.2 gN L⁻¹ d⁻¹, and 0.08 gP L⁻¹ d⁻¹, and SND aeration strategies, N-removal was limited to 62.3 ± 3.4%. Higher COD loads markedly improved N-removal showing that denitrification was limited by COD. AND strategies were more efficient than SND strategies. Alternating high and low DO phases during the aeration phase increased N-removal to 71.2 ± 5.6% with a COD loading rate of 1.6 gCOD L⁻¹ d⁻¹. Periods of low DO were presumably favorable to denitrifying P-removal saving COD necessary for heterotrophic N-removal. Intermittent aeration with anoxic periods without mixing between the aeration pulses was even more favorable to N-removal, resulting in 78.3 ± 2.9% N-removal with the lowest COD loading rate tested. P-removal was under all tested conditions between 88 and 98%, and was negatively correlated with the concentration of nitrite and nitrate in the effluent (r = −0.74, p < 0.01). With low COD loading rates, important emissions of undesired N₂O gas were observed and a total of 7–9% of N left the reactor as N₂O. However, N₂O emissions significantly decreased with higher COD loads under AND conditions.     

Temporal analysis of net fluvial methylmercury loading in a dystrophic and a clear water lake

The concentration of methylmercury (MeHg) in aquatic ecosystems is the net result of the highly dynamic abiotic and biotic processes of mercury methylation and demethylation. In this study, we conduct an examination of the net fluvial loading of methylmercury (MeHg_Net = MeHg_Watershed − MeHg_{Lake outflow}) across a 3 year time frame in both a dystrophic lake and an oligotrophic lake. A significant portion of MeHg_Net variance in both lakes could be attributed to a seasonal pattern (11.4%, p = 0.009; oligotrophic, and 27.0%, p < 0.0001; dystrophic) which in both cases, was most correlated with air temperature. The dystrophic lake appeared to be a net source of methylmercury (MeHg_Net = − 1.9 ± 0.3 mg MeHg d^− 1) while the oligotrophic lake appeared to be a net sink (MeHg_Net = 0.4 ± 0.2 mg MeHg d^− 1), indicating that there was net methylation in the dystrophic lake and net demethylation in the oligotrophic lake. Higher MeHg loading to the lakes occurred during the summer and between seasons there was a difference in MeHg_Net of 1.1 ±0.3 mg MeHg d^− 1 and 3.1 ± 0.6 mg MeHg d^− 1. Seasonal patterns of MeHg_Net in the oligotrophic lake lagged behind the dystrophic lake by 39 days. The short term variation in MeHg_Net was dominated by precipitation (t = 2.73, p = 0.008; dystrophic, t = 2.53, p = 0.017; oligotrophic).     

The impact of bromide/iodide concentration and ratio on iodinated trihalomethane formation and speciation

The objective of this study was to evaluate the formation and speciation of iodinated trihalomethanes (I-THMs) from preformed chloramination of waters containing bromide (Br⁻) and iodide (I⁻) at a Br⁻/I⁻ weight ratio of 10:1. The factors investigated were pH, iodide to dissolved organic carbon (I⁻/DOC) ratio, and NOM characteristics, specifically SUVA₂₅₄. A Br⁻/I⁻ ratio of 1:2 was also evaluated to determine the importance of Br⁻ and I⁻ concentrations and ratio on I-THM formation and speciation. Regulated triholamethanes (THMs) were measured alongside I-THMs for a more complete understanding of trihalomethane formation. The results showed that, in general, both I-THM and THM formation increased with decreased pH. Greater formation at lower pH was likely attributed to monochloramine decomposition and the formation of additional oxidants and substituting agents, most notably chlorine. For pH ≥ 7.5, I-THM yield increased with increasing I⁻/DOC ratio and decreasing specific ultraviolet absorbance (SUVA₂₅₄) of the water. The Br⁻/I⁻, Br⁻/DOC and I⁻/DOC ratios were important factors for I-THM and THM speciation. At pH 6, dichloroiodomethane (CHCl₂I) and bromochloroiodomethane (CHBrClI) were the dominant species at the common bromide and iodide levels. For pH ≥ 7.5 and for elevated bromide and iodide levels, iodoform (CHI₃) was always the dominant specie regardless of the Br⁻/I⁻ ratio. The results demonstrated that it is important to examine I-THM formation and speciation at typical Br⁻/I⁻ ratios (∼10) of natural waters, which have often been overlooked in previous investigations, in order to obtain practical and relevant results.     

Microbial community distribution and activity dynamics of granular biomass in a CANON reactor

The application of microelectrodes to measure oxygen and nitrite concentrations inside granules operated at 20 °C in a CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) reactor and the application of the FISH (Fluorescent In Situ Hybridization) technique to cryosectioned slices of these granules showed the presence of two differentiated zones inside of them: an external nitrification zone and an internal anammox zone. The FISH analysis of these layers allowed the identification of Nitrosomonas spp. and Candidatus Kuenenia Stutgartiensis as the main populations carrying out aerobic and anaerobic ammonia oxidation, respectively.Concentration microprofiles measured at different oxygen concentrations in the bulk liquid (from 1.5 to 35.2 mg O₂ L⁻¹) revealed that oxygen was consumed in a surface layer of 100-350 μm width. The obtained consumption rate of the most active layers was of 80 g O₂ (L_granule)⁻¹ d⁻¹. Anammox activity was registered between 400 and 1000 μm depth inside the granules. The nitrogen removal capacity of the studied sequencing batch reactor containing the granular biomass was of 0.5 g N L⁻¹ d⁻¹. This value is similar to the mean nitrogen removal rate obtained from calculations based on in- and outflow concentrations.Information obtained in the present work allowed the establishment of a simple control strategy based on the measurements of NH₄⁺ and NO₂⁻ in the bulk liquid and acting over the dissolved oxygen concentration in the bulk liquid and the hydraulic retention time of the reactor.     

Oxidation of sulfhydryl groups by monochloramine

In recent years there has been an increased used of monochloramine (NH₂Cl) for water disinfection because of its low trihalomethane formation potential. Monochloramine is also the predominant disinfectant upon chlorination of wastewater effluents. In an effort to more clearly understand the disinfectant's mode of action in inactivating microorganisms, a study was undertaken to evaluate the compound's reactions with sulfhydryl (−SH) groups. The extent of oxidation of these groups was dependent upon the molar ratio of −SH to NH₂Cl. When this ratio was >2:1, the reaction was reversible and ceased at disulfide formation. However, at a ratio of < 2:1, the reaction proceeded irreversibly beyond the disulfide; this reaction continued in the presence of a monochloramine residual. Not all −SH groups in Escherichia coli B were available for reaction. Masking of these groups within bacterial proteins prevented their complete oxidation at monochloramine doses as high as 100 mg 1⁻¹. The extent to which sulfhydryls are oxidized in bacteria may play an important role in further research on microbial reactivation.     

Effects of water parameters on the degradation of microcystin-LR under visible light-activated TiO2 photocatalyst

A study was performed to determine the effect of pH, alkalinity, natural organic matter (NOM) and dissolved oxygen in the performance of nitrogen and fluorine doped TiO₂ (NF-TiO₂) for the degradation of hepatotoxin microcystin-LR (MC-LR) in synthetic and natural water under visible light irradiation. The initial degradation rate of MC-LR was fastest under acidic conditions (3.50 ± 0.02 × 10⁻³ μM min⁻¹ at pH 3.0) and decreased to 2.29 ± 0.07 × 10⁻³ and 0.54 ± 0.02 × 10⁻³ μM min⁻¹ at pH 5.7 and 7.1, respectively. Attractive forces between the opposite charged MC-LR and NF-TiO₂ are likely responsible for the enhancement in the photocatalytic decomposition of MC-LR resulting from increased interfacial adsorption. For carbonate buffered solutions, the photocatalytic activity of NF-TiO₂ was reduced when increasing the carbonate concentration up to 150 mg CaCO₃ L⁻¹. The scavenging of radical species by the bicarbonate ion at pH 7.1 is discussed. In the presence of NOM, the degradation rates decreased as pH and initial concentration of the NOM increased. The inhibition was higher with fulvic acid than humic acid under alkaline conditions. Oxygenated solution yields higher NF-TiO₂ photocatalytic degradation of MC-LR compared to nitrogen sparged solution at pH 5.7. The involvement of specific reactive oxygen species implicated in the photodegradation is proposed. Finally, no significant degradation is observed with various natural waters spiked with MC-LR under visible light (λ > 420 nm) but high removal was achieved with simulated solar light. This study provides a better understanding of the interactions and photocatalytic processes initiated by NF-TiO₂ under visible and solar light. The results indicate solar photocatalytic oxidation is a promising technology for the treatment of water contaminated with cyanotoxins.     

Implications of organic matter on arsenic mobilization into groundwater: Evidence from northwestern (Chapai-Nawabganj), central (Manikganj) and southeastern (Chandpur) Bangladesh

Boreholes (50 m depth) and piezometers (50 m depth) were drilled and installed for collecting As-rich sediments and groundwater in the Ganges, Brahmaputra, and Meghna flood plains for geochemical analyses. Forty-one groundwater samples were collected from the three areas for the analyses of cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), anions (Cl⁻, NO₃⁻, SO₄²⁻), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) were performed to characterize the major mineral and chemical contents of aquifer sediments. In all three study areas, results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescent intensity of humic substances in groundwater samples ranges from 30 to 102 (mean 58 ± 20, n = 20), 54-195 (mean 105 ± 48, n = 10), and 27-243 (mean 79 ± 71, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Arsenic concentration in groundwater (20-50 m of depth) ranges from 3 to 315 μg/L (mean 62.4 ± 93.1 μg/L, n = 20), 16.4-73.7 μg/L (mean 28.5 ± 22.4 μg/L, n = 10) and 4.6-215.4 μg/L (mean 30.7 ± 62.1 μg/L, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Specific ultra violet adsorption (SUVA) values (less than 3 m⁻¹ mg⁻¹ L) indicate that the groundwater in the Ganges flood plain has relatively low percentage of aromatic organic carbon compared to those in the Brahmaputra and Meghna flood plains. Arsenic content in sediments ranges from 1 to 11 mg/kg (mean 3.5 ± 2.7 mg/kg, n = 17) in the three flood plains. Total organic carbon content is 0.5-3.7 g/kg (mean 1.9 ± 1.1 g/kg) in the Ganges flood plain, 0.5-2.1 g/kg (mean: 1.1 ± 0.7 g/kg) in the Brahmaputra flood plain and 0.3-4.4 g/kg (mean 1.9 ± 1.9 g/kg) in the Meghna flood plain. Arsenic is positively correlated with TOC (R² = 0.50, 0.87, and 0.85) in sediments from the three areas. Fourier transform infrared (FT-IR) analysis of the sediments revealed that the functional groups of humic substances in three areas include amines, phenol, alkanes, and aromatic carbon. Arsenic and Fe speciation in sediments were determined using XANES and the results imply that As(V) and Fe(III) are the dominant species in most sediments. The results also imply that As (V) and Fe (III) in most of the sediment samples of the three areas are the dominant species. X-ray absorption fine structure (EXAFS) analysis shows that FeOOH is the main carrier of As in the sediments of three areas. In sediments, As is well correlated with Fe and Mn. However, there is no such correlation observed between As and Fe as well as As and Mn in groundwater, implying that mobilizations of Fe, Mn, and As are decoupled or their concentrations in groundwater have been affected by other geochemical processes following reductive dissolution of Fe or Mn-hydroxides. For example, dissolved Fe and Mn levels may be affected by precipitation of Fe- and Mn-carbonate minerals such as siderite, while liberated As remains in groundwater. The groundwaters of the Brahmaputra and Meghna flood plains contain higher humic substances in relative fluorescence intensity (or fluorescence index) and lower redox potential compared to the groundwater of Ganges flood plain. This leads to the release of arsenic and iron to groundwater of these three plains in considerable amounts, but their concentrations are distributed in spatial variations.     

Biochemical oxygen demand and nutrient processing in a novel multi-stage raw municipal wastewater and acid mine drainage passive co-treatment system

A laboratory-scale, four-stage continuous flow reactor system was constructed to test the viability of high-strength acid mine drainage (AMD) and municipal wastewater (MWW) passive co-treatment. The synthetic AMD had pH 2.60 and 1860 mg/L acidity as CaCO₃ equivalent with 46, 0.25, 2, 290, 55, 1.2 and 390 mg/L of Al, As, Cd, Fe, Mn, Pb and Zn, respectively. The AMD was introduced to the system at a 1:2 ratio with raw MWW from the City of Norman, Oklahoma USA containing 265 ± 94 mg/L BOD₅, 11.5 ± 5.3 mg/L PO₄⁻³, and 20.8 ± 1.8 mg/L NH₄⁺-N. During the 135 d experiment, PO₄⁻³ and NH₄⁺-N were decreased to <0.75 and 7.4 ± 1.8 mg/L, respectively. BOD₅ was generally decreased to below detection limits. Nitrification increased NO₃⁻ to 4.9 ± 3.5 mg/L NO₃⁻-N, however relatively little denitrification occurred. Results suggest that the nitrogen processing community may require an extended period to mature and reach full efficiency. Overall, results indicate that passive AMD and MWW co-treatment is a viable ecological engineering approach for the developed and developing world that can be optimized and applied to improve water quality with minimal use of fossil fuels and refined materials.     

Influence of manganese and ammonium oxidation on the removal of 17 alpha-ethinylestradiol (EE2)

Flow-through reactors with manganese oxides were examined for their capacity to remove 17α-ethinylestradiol (EE2) at μg L⁻¹ and ng L⁻¹ range from synthetic wastewater treatment plant (WWTP) effluent. The mineral MnO₂ reactors removed 93% at a volumetric loading rate (B_V) of 5 μg EE2 L⁻¹ d⁻¹ and from a B_V of 40 μg EE2 L⁻¹ d⁻¹ on, these reactors showed 75% EE2 removal. With the biologically produced manganese oxides, only 57% EE2 was removed at 40 μg EE2 L⁻¹ d⁻¹. EE2 removal in the ng L⁻¹ range was 84%. The ammonium present in the influent (10 mg N L⁻¹) was nitrified and ammonia-oxidizing bacteria (AOB) were found to be of prime importance for the degradation of EE2. Remarkably, EE2 removal by AOB continued for a period of 4 months after depleting NH₄⁺ in the influent. EE2 removal by manganese-oxidizing bacteria was inhibited by NH₄⁺. These results indicate that the metabolic properties of nitrifiers can be employed to polish water containing EE2 based estrogenic activity.     

Source identification of nitrous oxide on autotrophic partial nitrification in a granular sludge reactor

Emission of nitrous oxide (N₂O) during biological wastewater treatment is of growing concern since N₂O is a major stratospheric ozone-depleting substance and an important greenhouse gas. The emission of N₂O from a lab-scale granular sequencing batch reactor (SBR) for partial nitrification (PN) treating synthetic wastewater without organic carbon was therefore determined in this study, because PN process is known to produce more N₂O than conventional nitrification processes. The average N₂O emission rate from the SBR was 0.32 ± 0.17 mg-N L⁻¹ h⁻¹, corresponding to the average emission of N₂O of 0.8 ± 0.4% of the incoming nitrogen load (1.5 ± 0.8% of the converted NH₄⁺). Analysis of dynamic concentration profiles during one cycle of the SBR operation demonstrated that N₂O concentration in off-gas was the highest just after starting aeration whereas N₂O concentration in effluent was gradually increased in the initial 40 min of the aeration period and was decreased thereafter. Isotopomer analysis was conducted to identify the main N₂O production pathway in the reactor during one cycle. The hydroxylamine (NH₂OH) oxidation pathway accounted for 65% of the total N₂O production in the initial phase during one cycle, whereas contribution of the NO₂⁻ reduction pathway to N₂O production was comparable with that of the NH₂OH oxidation pathway in the latter phase. In addition, spatial distributions of bacteria and their activities in single microbial granules taken from the reactor were determined with microsensors and by in situ hybridization. Partial nitrification occurred mainly in the oxic surface layer of the granules and ammonia-oxidizing bacteria were abundant in this layer. N₂O production was also found mainly in the oxic surface layer. Based on these results, although N₂O was produced mainly via NH₂OH oxidation pathway in the autotrophic partial nitrification reactor, N₂O production mechanisms were complex and could involve multiple N₂O production pathways.