Combustion Temperature and Molecular Weight Fractionation Provide Insights into Soil-Derived Wildfire-impacted Disinfection Byproduct Precursors

Coagulation behavior of aluminum chloride and polyaluminum chloride (PACl) for removing corresponding disinfection byproduct (DBP) precursors was discussed in this paper. CHCl3, bromine trihalomethanes (THM-Br), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) formation potential yields were correlated with specific ultraviolet absorbance (SUVA) values in different molecular weight (MW) fractions of humic substances (HS), respectively. Correlation analyses and principal component analysis were performed to examine the relationships between SUVA and different DBP precursors. To acquire more structural characters of DBP precursors and aluminum speciation, freeze-dried precipitates were analyzed by fourier transform infrared (FTIR) and C 1s, Al 2p X-ray photoelectron spectroscopy (XPS). The results indicated that TCAA precursors (no MW limits), DCAA and CHCl3 precursors in low MW fractions (MW<30 kDa) had a relatively good relations with SUVA values. These DBP precursors were coagulated more easily by in situ Al13 of AlCl3 at pH 5.0. Due to relatively low aromatic content and more aliphatic structures, THM-Br precursors (no MW limits) and CHCl3 precursors in high MW fractions (MW>30 kDa) were preferentially removed by PACl coagulation with preformed Al13 species at pH 5.0. Additionally, for DCAA precursors in high MW fractions (MW>30 kDa) with relatively low aromatic content and more carboxylic structures, the greatest removal occurred at pH 6.0 through PACl coagulation with aggregated Al13 species.

Carbonaceous and nitrogenous disinfection byproduct precursor variation during the reversed anaerobic–anoxic–oxic process of a sewage treatment plant

Humic acid (HA) was extracted and separated into different molecular weight (MW) fractions, then coagulated by aluminum chloride and polyaluminum chloride (PACl). The removal of disinfection byproduct (DBP) precursors and the aluminum speciation variation of the coagulants were investigated in detail. In particular, the role of aluminum speciation in the removal of DBP precursors was discussed. During the coagulation process, AlCl3 hydrolyzed into dominating in situ Al13 species at pH 5.5. The in situ Al13 species exhibited better removal ability for haloacetic acid (HAA) precursors than PACl. At pH 7.5, in situ hydrolyzed Al13 species of AlCl3 decomposed into dimeric Al species. In this case, preformed Al13 of PACl had a high removal ability of HAA precursors. Specially, the greatest reduction of HAA precursors with a low MW (<30 kDa) was through charge neutralization at pH 5.5, and that of HAA precursors in high MW (> 30 kDa) fractions was through adsorption at pH 7.5. Different from HAA precursors, the in situ Al13 species did not have a high removal ability of trihalomethane (THM) precursors. Therefore, PACl exhibited a better removal ability of THM precursors than AlCl3 at different pH values. In the different MW fractions, the greatest reduction of THM precursors was through charge neutralization at pH 5.5.

Periodic membrane fractionation of freshwater organic matter reveals various reactivity patterns during chlorine/chloramine disinfection

Application of fluorescence spectra and molecular weight analysis in the identification of algal organic matter-based disinfection by-product precursors

Response of dissolved organic matter and disinfection by-product precursors to algal blooms and thermal stratification in deep reservoirs.

Disinfection Byproducts and Their Precursors in Drinking Water Sources: Origins, Influencing Factors, and Environmental Insights

Extracellular organic matter (EOM) is an important precursor of disinfection by-products (DBPs). Nowadays, little is known about changes in molecular weight (MW) and hydrophilic (HPI)/hydrophobic (HPO) fractions of EOM during the entire algal growth phase. In this study, a combined approach of fractionation procedure and parallel factor (PARAFAC) analysis was applied to characterize the EOM during the entire growth phase of two algal species (M. aeruginosa and Synedra sp.), and investigated the relationships between fluorescent component and the DBP formation potential (FP) in MW and HPI/HPO fractions. Thereinto, three components (including one protein-like component (C1), one humic-like component (C2), and one fulvic acid-like component (C3)) were identified by the PARAFAC model. For two algae, the HPI and high MW (> 100 kDa) fractions were both the main components of algal EOM in the three growth phases in terms of the dissolved organic carbon. The high MW fraction had more C1 compared with other MW fractions, especially for M. aeruginosa. Besides, the formation risk of EOM-derived DBPs from M. aeruginosa was lower than that from Synedra sp. The result of this study showed the FP of DBPs varied with fluorescent components of algal EOM fractions and also indicated that the humic-like substances were tended to form trichloromethane and the tryptophan-like substances were associated with dichloroacetic acid by canonical correspondence analysis for both two algae.

Combustion synthesis of intermetallic−ceramic composite materials usually involves high combustion temperature as well as high temperature gradient. Gravity may play an important role in such systems when the liquid phase is present, and the intermetallic and ceramic phases have different densities. The combustion characteristics and microstructure may both be affected by gravity. Combustion synthesis of (1 − x)Ni3Al + xTiB2 composites, with the weight fraction x varying from 0.05 to 0.8, was carried out under normal gravity conditions. Both the combustion temperature and wave propagation velocity increased, and the propagation mode changed from unstable (x ≤ 0.2) to stable (x ≥ 0.4), as the TiB2 content increased. The combustion temperatures were higher than the melting point of Ni3Al for samples with x ≥ 0.4, resulting in a composite material consisting of ceramic TiB2 particles dispersed in a Ni3Al matrix. Owing to buoyancy of TiB2 particles in the denser molten Ni3Al phase, gravity was found to affect the microstructure of the composite, yielding a nonuniform distribution of phases. The phase separation distance calculated by using Stokes' law compared well with measurements.

Comparative investigation of known and unknown disinfection by-product precursor removal and microbial community from biological biochar and activated carbon filters

Ultraviolet absorbance monitoring for removal of DBP-precursor in waters with variable quality: Enhanced coagulation revisited

Nanotechnologies such as TiO2 photocatalysis (UV/TiO2 or solar/TiO2), silver nanoparticles, carbon nanotubes, and chitosan are currently being evaluated for use in drinking water and wastewater treatment applications. TiO2 photocatalysis, in particular, is an attractive option for drinking water treatment because it can provide concurrent disinfection, disinfection by-product (DBP) precursor reduction, and degradation of recalcitrant compounds. Like any oxidation-based process, however, it has the potential to contribute to the formation of by-products, whether by directly oxidizing precursor compounds to form degradation products with potential health effects or indirectly by breaking down innocuous water constituents to form DBP precursors that can later be converted to DBPs when chemicals such as chlorine and chloramines are applied for disinfection. Research into DBP formation in water treatment processes employing TiO2 photocatalysis is limited, but the studies that have been conducted to date suggest that these technologies create few DBPs directly and have site-specific effects on DBP precursor formation. The latter are also highly dependent on system design parameters, in particular UV dose and TiO2 configuration or concentration. UV/TiO2 compares favorably to existing disinfection and DBP precursor removal technologies in terms of both DBP formation and DBP precursor removal. Hybrid systems incorporating UV/TiO2 along with another DBP precursor removal technology such as coagulation, adsorption, or membrane filtration are also promising for both applications.

Transforming dissolved organic matter (DOM) is a crucial approach to alleviating the formation of disinfection byproducts (DBPs) in water treatment. Although catalytic ozonation effectively transforms DOM, increases in DBP formation potential are often observed due to the accumulation of aldehydes, ketones, and nitro compound intermediates during DOM transformation. In this study, we propose a novel strategy for the sequential oxidation of DOM, effectively reducing the levels of accumulation of these intermediates. This is achieved through the development of a catalyst with a tailored surface and nanoconfined active sites for catalytic ozonation. The catalyst features a unique confinement structure, wherein Mn-N4 moieties are uniformly anchored on the catalyst surface and within nanopores (5-20 Å). This design enables the degradation of the large molecular weight fraction of DOM on the catalyst surface, while the transformed smaller molecular weight fraction enters the nanopores and undergoes rapid degradation due to the confinement effect. The generation of *Oad as the dominant reactive species is essential for effectively reducing these ozone refractory intermediates. This resulted in over 70% removal of carbonaceous and nitrogenous DBP precursors as well as brominated DBP precursors. This study highlights the importance of the nanoscale sequential reactor design and provides new insights into eliminating DBP precursors by the catalytic ozonation process.

This study is a mathematical model to obtain the characteristics performance of magnesium metal (powder) and carbon on a potassium nitrate-sucrose (KNSU) solid propellant formulation. Characterization of propellant is, as a general rule, important to determine its performance before it can be suitable for use for a rocket flight or any mission. Method of ballistic load cell evaluation was used to validate results and a mathematical model using the combustion exhaust products was solved to obtain the characteristics performance parameters of the propellant. The carbon constituent which acts as an opacifier and coolant was kept constant at 2% in order to arrest some of the heat during the combustion process and helped to lower the combustion temperature, because high combustion temperature could lead to combustion chamber rupture or failure. The effect of addition of magnesium which was optimized for 3% in the formulation contributed significantly in improving the overall performance of the propellant. The utilization of magnesium in KNSU propellant provided higher values parameters and better performance compared to when not included. This was confirmed with the model equations. The propellant combustion products equation was used to model and obtain the characteristics performance parameters. This gave propellant specific impulse (122.9s), combustion temperature (1821K), heat ratio (1.1592), molecular weight (36.89g/mole), propellant density (1912.5kg/m3) and characteristics velocity (1000m/s) result while maintaining the same chamber pressure.

Characteristics of C-, N-DBPs formation from algal organic matter: Role of molecular weight fractions and impacts of pre-ozonation