Jun Wang

Biogenic Nanoscale Colloids in Wastewater Effluents

The size, surface area, metal complexation capacity, organic pollutant sorption potential, reactivity with disinfectants, and elevated nitrogen content of biogenic organic nanoscale material (BONM) can potentially affect aquatic environments. BONM in effluents from 11 full-scale wastewater treatment plants (WWTPs), which use a range of biological processes, were characterized in two ways. First, BONM was measured by hydrodynamic size-exclusion chromatography coupled with an online organic carbon and UV detector. Second, BONM was isolated from the wastewater using rotary evaporation and dialysis and then characterized by elemental analysis, transmission electron microscopy, and Fourier transform infrared spectroscopy. The wastewaters contained 6-10 mg/L of dissolved organic carbon (DOC). BONM accounted for 5%-50% of the DOC in wastewater effluent organic matter, and the largest size fraction (>10 kDa) of organic carbon correlated with the organic carbon content determined after rotary evaporation and dialysis. Membrane bioreactor WWTPs had the lowest fraction of BONM (<10% of the DOC), followed by conventional activated sludge (10% to 30% of the DOC), with other processes (e.g., trickling filters, aerated lagoons) containing larger BONM percentages. BONM had a lower carbon to nitrogen ratio (6.2 ± 1.7) compared with the literature values for humic or fulvic acids, exhibited chemical bonds that were indicative of amides and polysaccharides, and contained fibril entangled networks. This work has important implications for operations efficiency of WWTPs, including controlling membrane fouling and release of organic nitrogen into sensitive environments.

Effects of organic fractions on the formation and control of N-nitrosamine precursors during conventional drinking water treatment processes

Knowledge of N-nitrosamine precursors from dissolved organic matter (DOM) is important for water professionals to better control N-nitrosamine formation. The characterization of DOM from the Luan River in Northern China was conducted using Amberlite XAD resins and ultra-filtration methods. N-nitrosamine formation potentials were investigated for various DOM fractions. The removal of the DOM during water treatment were evaluated using dissolved organic carbon (DOC) and ultraviolet absorbance at 254 nm (UV254) bulk parameters as well as size exclusion chromatography and fluorescence spectroscopy. The results indicated that the XAD-4 hydrophilic fraction, with normalized yields of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR), and N-nitrosopiperidine (NPIP) of 27.2, 5.2, 5.9, and 6.1 ng/mg-DOC, respectively, tended to form more N-nitrosamines than the hydrophobic and the transphilic fractions. The DOM fraction with a molecular weight (MW) below 1 kDa, with normalized yields of NDMA, NPYR, NMOR, and NPIP of 39.6, 8.1, 14.7, and 3.3 ng/mg-DOC, respectively, tended to form more N-nitrosamines than those with a higher MW. The limited removal of the hydrophilic fraction and the lower MW DOM faction during conventional water treatment processes suggests that the process may not effectively remove the nitrosamine precursors.

Transformation in Bulk and Trace Organics during Ozonation of Wastewater

The aim of this paper is to determine the ozone dosages needed to oxidize bulk and trace organics. Treated effluent from eight full-scale wastewater treatment plants was collected and subjected to lab-scale ozonation. Because both organics and inorganics exert ozone demand, an approach was developed to calculate only the ozone demand associated with organics. This method allowed normalization of dosing parameters to correlate with removal of color, UV absorbance, plus oxidation of trace organics and nitrosamine precursors. We also showed that ozonation effectively reduces the fraction of organic matter characterized as “colloidal organic matter,” thereby reducing the potential for membrane fouling.

Detecting N-nitrosamines in water treatment plants and distribution systems in China using ultra-performance liquid chromatography-tandem mass spectrometry

N-nitrosodimethylamine (NDMA) and several other N-nitrosamines have been detected as disinfection by-products in drinking waters in many countries around the world. An ultra-performance liquid chromatographytandem mass spectrometry method with solid phase extraction sample preparation was developed to study the occurrence of N-nitrosamines in several water treatment plants and distribution systems in China. Isotope labeled N-nitrosodi-n-propylamine-d14 (NDPA-d14) was selected as the internal standard for quantification. The solid phase extraction procedures including pH, enrichment process and MS/MS parameters including capillary voltage, cone gas flow, cone voltage, collision energy were optimized to give average recoveries of 26% to 112% for nine N-nitrosamine species. The instrument detection limits were estimated to range from 0.5 to 5 μg·L−1 for the nine N-nitrosamine species. NDMA and several other N-nitrosamines were found at fairly high concentrations in several water treatment plants and distribution systems. NDMA was found in all locations, and the highest concentrations in cities B, G, T, and W were 3.0, 35.7, 21.3, and 19.7 ng·L−1, respectively. A wide range of N-nitrosamines concentrations and species were observed in different locations. Higher concentrations of N-nitrosamines were detected in distribution systems that were further away from the treatment plants, suggesting that the contact time between the residual disinfectant and natural organic matter may play an important role in the formation of these compounds.

Applying the polarity rapid assessment method to characterize nitrosamine precursors and to understand their removal by drinking water treatment processes.

Some N-nitrosamines (NAs) have been identified as emerging disinfection by-products during water treatment. Thus, it is essential to understand the characteristics of the NA precursors. In this study, the polarity rapid assessment method (PRAM) and the classical resin fractionation method were studied as methods to fractionate the NA precursors during drinking water treatment. The results showed that PRAM has much higher selectivity for NA precursors than the resin approach. The normalized N-nitrosodimethylamine formation potential (NDMA FP) and N-nitrosodiethylamine (NDEA) FP of four resin fractions was at the same level as the average yield of the bulk organic matter whereas that of the cationic fraction by PRAM showed 50 times the average. Thus, the cationic fraction was shown to be the most important NDMA precursor contributor. The PRAM method also helped understand which portions of the NA precursor were removed by different water treatment processes. Activated carbon (AC) adsorption removed over 90% of the non-polar PRAM fraction (that sorbs onto the C18 solid phase extraction [SPE] cartridge) of NDMA and NDEA precursors. Bio-treatment removed 80-90% of the cationic fraction of PRAM (that is retained on the cation exchange SPE cartridge) and 40-60% of the non-cationic fractions. Ozonation removed 50-60% of the non-polar PRAM fraction of NA precursors and transformed part of them into the polar fraction. Coagulation and sedimentation had very limited removal of various PRAM fractions of NA precursors.

Activated carbon adsorption of quinolone antibiotics in water: Performance, mechanism, and modeling

The extensive use of antibiotics has led to their presence in the aquatic environment, and introduces potential impacts on human and ecological health. The capability of powdered activated carbon (PAC) to remove six frequently used quinolone (QN) antibiotics during water treatment was evaluated to improve drinking water safety. The kinetics of QN adsorption by PAC was best described by a pseudo second-order equation, and the adsorption capacity was well described by the Freundlich isotherm equation. Isotherms measured at different pH showed that hydrophobic interaction, electrostatic interaction, and π-π dispersion force were the main mechanisms for adsorption of QNs by PAC. A pH-dependent isotherm model based on the Freundlich equation was developed to predict the adsorption capacity of QNs by PAC at different pH values. This model had excellent prediction capabilities under different laboratory scenarios. Small relative standard derivations (RSDs), i.e., 0.59%-0.92% for ciprofloxacin and 0.09%-3.89% for enrofloxacin, were observed for equilibrium concentrations above the 0.3mg/L level. The RSDs increased to 11.9% for ciprofloxacin and 32.1% for enrofloxacin at μg/L equilibrium levels, which is still acceptable. This model could be applied to predict the adsorption of other chemicals having different ionized forms.

Characterization of dissolved organic matter as N-nitrosamine precursors based on hydrophobicity, molecular weight and fluorescence

It is very important to identify the dominant precursors for N-nitrosamine formation from bulk organic matter, to enhance the understanding of N-nitrosamine formation pathways in water treatment plants and allow the development of practical treatment technologies. In this study, dissolved organic matter (DOM) from two source waters was fractionated with XAD resins and ultrafiltration membranes. The N-nitrosamine formation potential (FP) (ng of N-nitrosamines formed per mg of dissolved organic carbon (DOC)) from raw water and each fraction were measured and correlated with the fluorescence excitation-emission matrix (EEM), molecular weight (MW) and other assays. The results showed that the hydrophilic fraction had N-nitrosamine FP 1.3 to 3.5 times higher than the hydrophobic fraction from both source waters. The DOM fraction with low MW was the dominant fraction in these two source waters and contributed more precursors for N-nitrosamine formation than the larger MW fraction. The EEM spectra indicated there were notable amounts of soluble microbial products (SMPs) and aromatic proteins in the two studied rivers, which probably originated from wastewater discharge. The SMPs tended to be more closely correlated with N-nitrosodimethylamine formation potential than the other DOM components. Higher N-nitrosamine FP were also related to fractions with lower DOC/DON ratios and lower SUVA254 values.

Factors controlling N-nitrosodimethylamine (NDMA) formation from dissolved organic matter

The formation of cancinogenic nitrosamines, esp. N-nitrosodimethylamine (NDMA) in water and wastewater treatment plants has drawn much attention in recent years. Dissolved organic matter from the transported Luan River water as water source of Tianjin was fractionated with different XAD resins and a series of ultra-filtration membranes with molecular weight (MW) cut-offs of 5k Da, 3k Da, and 1k Da, respectively. The NDMA yields from the raw water and each fraction were measured to investigate their role in NDMAyield. Results indicated that the hydrophilic fraction had a higher NDMA yield than those of hydrophobic fraction and transphilic fraction. The fraction with MW below 1k Da had a higher NDMAyield than that with larger MW. NDMA formation increased as the dissolved organic carbon (DOC) to dissolved organic nitrogen (DON) ratio decreased, which indicated that DON might serve as the real important precursor for NDMA. The correlation between NDMA yield and specific ultraviolet absorbance at 254 nm (SUVA254) suggested that the latter might not represent the specific precursors for NDMA in the water. Besides the water quality, the influences of pH, disinfectant dosage, and disinfection contact time on the formation of NDMA were also examined. These results will help water treatment plants establish measures to control this harmful disinfection by-product.

Capability of cation exchange technology to remove proven N-nitrosodimethylamine precursors

N-nitrosodimethylamine (NDMA) precursors consist of a positively charged dimethylamine group and a non-polar moiety, which inspired us to develop a targeted cation exchange technology to remove NDMA precursors. In this study, we tested the removal of two representative NDMA precursors, dimethylamine (DMA) and ranitidine (RNTD), by strong acidic cation exchange resin. The results showed that pH greatly affected the exchange efficiency, with high removal (DMA>78% and RNTD>94%) observed at pHMg2+>RNTD+>K+>DMA+>NH4+>Na+. The partition coefficient of DMA+ to Na+ was 1.41±0.26, while that of RNTD+ to Na+ was 12.1±1.9. The pseudo second-order equation fitted the cation exchange kinetics well. Bivalent inorganic cations such as Ca2+ were found to have a notable effect on NA precursor removal in softening column test. Besides DMA and RNTD, cation exchange process also worked well for removing other 7 model NDMA precursors. Overall, NDMA precursor removal can be an added benefit of making use of cation exchange water softening processes.

Monthly survey of N-nitrosamine yield in a conventional water treatment plant in North China

A sampling campaign was conducted monthly to investigate the occurrence of N-nitrosamines at a conventional water treatment plant in one city in North China. The yield of N-nitrosamines in the treated water indicated precursors changed greatly after the source water switching. Average concentrations of N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMOR), and N-nitrosopyrrolidine (NPYR) in the finished water were 6.9, 3.3, and 3.1ng/L, respectively, from June to October when the Luan River water was used as source water, while those of NDMA, N-nitrosomethylethylamine (NMEA), and NPYR in the finished water were 10.1, 4.9, and 4.7ng/L, respectively, from November to next April when the Yellow River was used. NDMA concentration in the finished water was frequently over the 10ng/L, i.e., the notification level of California, USA, which indicated a considerable threat to public health. Weak correlations were observed between N-nitrosamine yield and typical water quality parameters except for the dissolved organic nitrogen.