Hurricane resulted in releasing more nitrogenous than carbonaceous disinfection byproduct precursors in coastal watersheds

Release of biochar-derived dissolved organic matter and the formation of chlorination disinfection by-products: Effects of pH and chlorine dosage

Transformation, fragmentation, dissolution, and oxidation of biochar are inevitable in the environment, which will undoubtedly accelerate the release of biochar-derived dissolved organic matter (BDOM) into various water bodies. In addition, biochar may affect disinfection by-products (DBPs) during water treatment and subsequent disinfection. In this study, biochars were derived at three selected pyrolysis temperatures (350 °C, 500 °C, and 650 °C) from rice husk, wheat straw, and shrimp shell, and BDOM was extracted from biochar-derived in artificial seawater and ultrapure water. The TOC analyzer results showed that the concentrations of three BDOM decreased with increasing pyrolysis temperature. The BDOM derived from rice husk biochar and wheat straw biochar in seawater was lower than that in ultrapure water, while that of shrimp shell biochar showed an opposite trend, being released in seawater at nearly twice the extent of that in ultrapure water at 350 °C. Moreover, BDOM showed a catalytic effect on chlorination, and GC analysis showed that the concentrations of its DBPs were affected by pH. The concentration of halogenated acetic acid reached the highest value (54.51 μg/L) in weak acidic environment, while the concentrations of trihalomethane and halogenated acetonitrile had the highest values (23.63 and 47.53 μg/L, respectively) in alkaline conditions. The concentrations of all the three DBPs were lowest under neutral pH conditions. In addition, the volatile halogenated DBPs such as dichloroacetone and trichloroacetone were easily hydrolyzed under alkaline conditions. Therefore, it is something be aware of the release of BDOM and the effects of chlorination DBPs when biochar is used for water treatment or water purification.

Impact of climate change on formation of nitrogenous disinfection by products. Part I: Sea level rise and flooding events

Climate change causes heavy rainfall incidents and sea level rise, which have serious impact on the availability and quality of water resources. These extreme phenomena lead to the rise of external and internal precursors in water reservoirs, and consequently affect the formation of disinfection by-products (DBPs). The aim of this study was to investigate the formation of nitrogenous_DBPs (N-DBPs) under extreme conditions caused by climate change. For this reason, two scenarios were adapted: a) sea level rise leading to increase of water salinity and b) heavy rainfall incidents leading to flooding events. The target-compounds were haloacetonitriles (HANs), haloacetamides (HAcAms) and halonitromethane (TCNM). Chlorination and chloramination were employed as disinfection processes under different doses (5 and 10 mg/L) and contact times (24 and 72 h). The results showed enhancement on the formation of N-DBPs and changes in their profile. Sea level rise scenario led to elevated concentrations of brominated species (maximum concentration of dibromoacetonitrile 23 μg/L and maximum concentration of bromoacetamide 57 μg/L), while flooding events scenario led to extended formation of chloroacetamide and bromochloroacetonitrile up to 58 μg/L and 40 μg/L, respectively. At the same time, changes in cytotoxicity and genotoxicity of the samples were observed.

Water quality and periphyton functional response to input of dissolved manure-derived hydrochars (DHCs)

Dissolved organic matter (DOM) plays a critical role in the global carbon cycle and provides food and energy for aquatic organisms. Recently, hydrochar, as a solid carbonaceous substance derived from hydrothermal carbonization, has been increasingly used as a soil amendment. Upon entering the soil, dissolved components (DHCs) were released from hydrochar as exogenous DOM, finally entering the aquatic ecosystems by runoff, which participates in environmental geochemical processes. However, relevant reports revealing the response of the aquatic ecosystem to the input of DHCs remain insufficiently elucidated. For the first time, the fundamental features of DHCs and their influence on water quality and aquatic biological function were investigated in this study. DHCs at 260 °C (DHC260) had lower yields, a greater [C/N], worse biodegradability, and larger humic acid relative amounts than did DHCs at 180 °C (DHC180). The DHC structural alterations in periphyton-incubated aquatic ecosystems suggested that protein substances were more easily degraded or assimilated by periphyton, especially for DHC180, with rates of decrease of 34.5-63.5%. The increased chemical oxygen demand (COD) degradation in the DHC260 treatments was most likely due to humic acid substances with higher COD equivalents. Furthermore, DHC260 caused phosphorus to accumulate in periphyton, reducing aquatic phosphorus concentration. Notably, the abundances of Flavobacteria and Cyanobacteria associated with water blooms increased 12.7-25.5- and 1.3-8.3-fold, respectively; consequently, the promotional impact of DHCs on algal blooms should be considered. This result extends the nonnegligible role of DHCs in aquatic ecosystems and underlines the need to regulate the hydrochar application process.

Challenges in quantifying and characterizing dissolved organic carbon: Sampling, isolation, storage, and analysis

Despite the advancements in analytical techniques, there are still great challenges and difficulties in accurately and effectively quantifying and characterizing dissolved organic carbon (DOC) in environmental samples. The objectives of this review paper are (a) to understand the roles and variability of DOC along the water continuum; (b) to identify the constraints, inconsistences, limitations, and artifacts in DOC characterization; and (c) to provide recommendations and remarks to improve the analytical accuracy. For the first objective, we summarize the four ecological and engineering roles of DOC along the water continuum from source water to municipal utility, including nutrients and energy sources, controlling the fates of micropollutants, buffering capacity, and treatability and precursors of disinfection byproducts. We also discuss three major challenges in DOC analysis, including spatial and temporal variations, degradability and stability, and unknown structures and formulas. For the second objective, we review the procedures and steps in DOC analysis, including sampling in diverse environmental matrices, isolation of DOC fraction, storage and preservation techniques, and analyses on bulk chemical characteristics. We list and discuss the available options and evaluate the advantages and disadvantages of each choice. Last, we provide recommendations and remarks for each stage: sampling, isolation, storage, and analysis.

Characteristics and chlorine reactivity of biochar-derived dissolved organic matter: Effects of feedstock type and pyrolysis temperature

Increasing biochar application worldwide may release more biochar-derived dissolved organic matter (BDOM) to the source water for drinking water supply. However, it is unclear how feedstock types and pyrolysis temperatures for biochar production would affect the characteristics and chlorine reactivity of BDOM. Here, we studied the spectroscopic characteristics of BDOM pyrolyzed from pine needle, wheat straw, walnut shells, alfalfa, pig manure, and sludge derived biochars at 300, 500, and 700 °C, as well as the formation potential of disinfection byproducts (DBPs) and their bulk toxicity after BDOM chlorination. The N/C ratio of biochar was higher for N-rich than C-rich feedstocks. Optical analyses indicated that BDOM aromaticity was highest at 700 °C, while the impact of pyrolysis temperature on the molecular weight of BDOM varied greatly among feedstocks. Increasing pyrolysis temperature caused consistently decreased BDOM reactivity toward haloketone formation but did not show consistent impacts on the other DBPs. Among feedstocks, the N-rich sludge showed the highest specific haloacetonitrile formation potential of BDOM at any given pyrolysis temperature. The DBP formation potential from biochar was consistently highest at 300 °C and was higher for N-rich than C-rich feedstocks. The microtoxicity of DBP mixture was highest for the BDOM derived from sludge produced at 300 °C. This study highlights the high variations in characteristics and chlorination reactivity of BDOM with varying feedstocks and pyrolysis temperatures, which implies that more attention should be paid to the environmental impacts of the intensive application of low-temperature biochar from N-rich feedstock such as sludge.

Long-term biochar addition alters the characteristics but not the chlorine reactivity of soil-derived dissolved organic matter

Biochar is widely and increasingly applied to farmlands. However, it remains unclear how long-term biochar addition alters the characteristics and chlorine reactivity of soil-derived dissolved organic matter (DOM), an important terrestrial disinfection byproduct (DBP) precursor in watersheds. Here, we analyzed the spectroscopic and molecular-level characteristics of soil-derived DOM and the formation and toxicity of DBP mixtures from DOM chlorination for two long-term (5 and 11 years) biochar addition experimental farmlands. As indicated by spectroscopic indices and Fourier transform ion cyclotron resonance mass spectrometry analyses, 11 years of biochar addition could increase the humic-like and aromatic and condensed aromatic DOM and decrease the microbial-derived DOM, while 5 years of biochar addition at the other site did not. The response of condensed aromatic dissolved black carbon did not increase with increasing cumulative biochar dose but appeared to be affected by biochar aging time. Despite the possible increase in aromatic DOM, biochar addition neither increased the reactivity of DOM in forming trihalomethanes, haloacetonitriles, chloral hydrates, or haloketones nor significantly increased the microtoxicity or genotoxicity of the DBP mixture. This study indicates that biochar addition in watersheds may not deteriorate the drinking water quality via the export of terrestrial DBP precursors like wildfire events.

Two years of post-wildfire impacts on dissolved organic matter, nitrogen, and precursors of disinfection by-products in California stream waters

We investigated the effects of two California wildfires (Rocky and Wragg Fires, 2015) compared to an unburned reference watershed on water quality, dissolved organic matter (DOM), and precursors of disinfection by-products (DBPs) for two years' post-fire. The two burned watersheds both experienced wildfires but differed in the proportion of burned watershed areas. Burned watersheds showed rapid water quality degradation from elevated levels of turbidity, color, and suspended solids, with greater degradation in the more extensively burned watershed. During the first year's initial flushes, concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium (NH₄⁺/NH₃), and specific ultraviolet absorbance (SUVA₂₅₄) were significantly higher (67 ± 40%, 418 ± 125%, 192 ± 120%, and 31 ± 17%, respectively) in the more extensively burned watershed compared to the reference watershed. These elevated values gradually declined and finally returned to levels like the reference watershed in the second year. Nitrate concentrations were near detection limits (0.01 mg-N/L) in the first year but showed a large increase in fire-impacted streams during the second rainy season, possibly due to delayed nitrification. Changes in DOM composition, especially during the initial storm events, indicated that fires can attenuate humic-like and soluble microbial by-product-like (SMP) DOM while increasing the proportion of fulvic-like, tryptophan-like, and tyrosine-like compounds. Elevated bromide (Br^-) concentrations (up to 8.7 μM]) caused a shift in speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) to brominated species for extended periods (up to 2 years). Wildfire also resulted in elevated concentrations of N-nitrosodimethylamine (NDMA) precursors. Such changes in THM, HAA, and NDMA precursors following wildfires pose a potential treatability challenge for drinking water treatment, but the effects are relatively short-term (≤1 year).