Effect of sulfamethazine on surface characteristics of biochar colloids and its implications for transport in porous media

Insight into the wheat residues-derived adsorbents for the remediation of organic and inorganic aquatic contaminants: A review

Wheat is a major grain crop of the world that provides a stable food for human consumption. Large amounts of by-products/waste materials are produced after the harvesting and processing of wheat crop. Such materials can cause an environmental issue if not disposed of properly. Several studies have shown that wheat residues can be efficient precursors for adsorbents because of their availability, renewability, lignocellulosic composition, and surface active groups enriched structure. In the literature, there are few review articles that address wheat residues-based adsorbents. However, these reviews were specific in terms of adsorbate or adsorbent and did not provide detailed information about the modification, properties, and regeneration of these adsorbents. This article extensively reviews the utilization of wheat biomass/waste including straw, bran, husk, and stalk as precursors for raw or untreated, chemically treated, carbonaceous, and composite adsorbents against various environmental pollutants. The influences of inlet pollutant amount, adsorbent dose, pH, temperature, and time on the performance of adsorbents against pollutants were considered. The maximum uptakes, equilibrium time, and adsorption nature were identified from isotherms, kinetic, and thermodynamic studies. The highest adsorbed amounts of most tested contaminants were 448.20, 322.58, and 578.13 mg/g for lead, chromium, and copper, 1374.6 and 1449.4 mg/g for methylene blue and malachite green, and 854.75, 179.21, and 107.77 mg/g for tetracycline, phosphate, and nitrate, respectively. For the studied adsorbate/adsorbent systems the adsorption mechanism and regeneration were also discussed. Significant results and future directions are finally presented.

Effect of coupled physical and chemical heterogeneity on the transport of pristine and aged pyrogenic carbon colloids in unsaturated porous media

Due to extensive application and recurrent wildfires, an increasing number of pyrogenic carbon (PyC) colloids are present in the environment, experiencing processes of environmental aging. Subsurface environments are typically heterogeneous in unsaturated conditions, which may affect the transport of PyC colloids. This study focused on the transport of both pristine and aged PyC colloids in physically (clean coarse and fine sand) and physicochemically (iron oxides-coated coarse and clean fine sand) heterogeneous porous media at three different water saturations (100 %, 70 %, and 40 %). In physically heterogeneous porous media, the decrease in water saturation from 100 % to 40 % led to a shift in the main water flow from the clean coarse sand to the clean fine sand domain, resulting in a continuous decrease in the transport of PyC colloids. In physicochemically heterogeneous porous media, the primary water flow shifted from the iron oxides-coated coarse sand to the clean fine sand domain, resulting in an initial increase and subsequent decrease in PyC colloid transport. Aging enhanced the transport of PyC colloids, attributed to the increasingly negative and hydrophilic surface. Retention profiles revealed substantial PyC colloid retention at the interface between coarse and fine sand domains. The release of retained PyC colloids exhibited two peaks at 100 % and 70 % water saturations, along with a single peak at 40 % water saturation. Additionally, the increased irreversible retention was observed at lower water saturation. This study underscores the significance of water content, environmental aging, and heterogeneity in PyC colloid transport. It provides essential insights into the environmental fate of PyC colloids in natural field conditions.

Differential photodegradation processes of adsorbed polychlorinated biphenyls on biochar colloids with various pyrolysis temperatures

Despite the crucial role of photodegradation in the environmental transformation of organic pollutants, the photodegradation process of organic pollutants irreversibly absorbed on biochar colloids (BCCs) remains poorly understood. This study investigated the photodegradation processes and mechanisms of 2,4,4'-trichlorobiphenyl (PCB28) adsorbed on BCCs released from bulk biochars derived from bamboo chips at pyrolysis temperatures of 300, 500, and 700 °C. Results show that BCCs-adsorbed PCB28 could be degraded under simulated solar illumination (95-105 mW·cm-2) but at decreased photodegradation rates compared to the dissolved PCB28. The inhibition effect of BCCs on the PCB28 photodegradation increased with increasing pyrolysis temperature. After adsorptive binding to BCCs, the half-life of PCB28 (0.1 mg/L) was prolonged from 2.65 h for the dissolved PCB28 alone in deionized water to 7.48, 40.67, and 81.82 h in the presence of BCC300, BCC500, and BCC700 (5.0 mg/L), respectively. Mechanistically, the photodegradation of adsorbed pollutants was regulated by the photogenerated free radicals and surface functional groups of the low-temperature BCCs, as well as the defects and direct electron transfer capabilities of the high-temperature BCCs; PCB28 adsorbed on the low-temperature BCCs accepted electrons from persistent free radicals under light illumination, which led to PCB28 dechlorination, followed by ring-opening oxidation through hydroxyl radical attack, ultimately resulting in progressive mineralization; singlet oxygen caused preferential ring opening of adsorbed PCB28 on the high-temperature BCCs, preceding dechlorination. The photodegradation of BCCs-adsorbed PCB28 remained significant though more or less being inhibited under the effects of water pH, ionic strength, dissolved organic matters (humic acid and fulvic acid), and in natural water samples. These findings contribute to a better understanding of the structural properties of BCCs that impact phototransformation processes of adsorbed pollutants and facilitate an accurate assessment of the environmental risk associated with biochar application.

Oxygen-limited pyrolysis and incineration impact on biochar transport

At present, studies on biochar transport have focused on biochar obtained by oxygen-limited pyrolysis, which may differ from conventional biochar produced by incineration in nature. This work investigated the transport and retention mechanisms of three types of oxygen-limited pyrolytic biochar and three types of traditional biochar in saturated porous media. The results showed that the specific surface area of the three oxygen-limited pyrolysis biochar (180-200 m2·g-1) was higher than that of the traditional biochar (50-60 m2·g-1). Therefore, the retention capacity of pyrolytic biochar is strong and the permeability is less than 0.1. The absolute value of the zeta potential of traditional biochar is greater than 30 mV, and the electrostatic repulsion generated is stronger, with a peak penetration rate of 0.16. Moreover, the zeta potential of biochar and traditional biochar is regulated by pH value and ionic strength. In acidic conditions or solutions with high ionic strength, the zeta potentials of the six types of biochar changed to about - 15 mV, and the second minimum value was less than 0, indicating that there was a tendency for sedimentation. This study provides a new perspective for assessing the transport and environmental risks of biochar in the environment.

Effects of Antibiotic Resistance Genes and Antibiotics on the Transport and Deposition Behaviors of Bacteria in Porous Media

Antibiotics present in the natural environment would induce the generation of antibiotic-resistant bacteria (ARB), causing great environmental risks. The effects of antibiotic resistance genes (ARGs) and antibiotics on bacterial transport/deposition in porous media yet are unclear. By using E. coli without ARGs as antibiotic-susceptible bacteria (ASB) and their corresponding isogenic mutants with ARGs in plasmids as ARB, the effects of ARGs and antibiotics on bacterial transport in porous media were examined under different conditions (1-4 m/d flow rates and 5-100 mM NaCl solutions). The transport behaviors of ARB were comparable with those of ASB under antibiotic-free conditions, indicating that ARGs present within cells had negligible influence on bacterial transport in antibiotic-free solutions. Interestingly, antibiotics (5-1000 μg/L gentamicin) present in solutions increased the transport of both ARB and ASB with more significant enhancement for ASB. This changed bacterial transport induced by antibiotics held true in solution with humic acid, in river water and groundwater samples. Antibiotics enhanced the transport of ARB and ASB in porous media via different mechanisms (ARB: competition of deposition sites; ASB: enhanced motility and chemotaxis effects). Clearly, since ASB are likely to escape sites containing antibiotics, these locations are more likely to accumulate ARB and their environmental risks would increase.

Adsorption and desorption of polychlorinated biphenyls on biochar colloids with different pyrolysis temperatures: the effect of solution chemistry

Biochar releases colloidal particles into the environment during applications and aging which can become carriers of pollutants and influence on the environmental risk of pollutants due to the excellent adsorption and migration properties of biochar colloids (BCCs). The adsorption and desorption behaviors of BCCs can be different from their bulk ones due to the colloidal size, which merits specific studies. Herein, the adsorption and desorption of 2,4,4'-trichlorobiphenyl (PCB28) as a representative on BCCs released from bulk biochars prepared from bamboo chips at 300, 500, and 700 C and the effects of solution properties were specifically investigated. Results show that the adsorption was dominated by pore filling and π-π interaction, and thus, BCCs prepared at higher temperature with greater pore volume and aromaticity had higher adsorption of PCB28. Results show that the adsorption was dominated by pore filling and π-π interaction, and thus, BCCs prepared at higher temperature with greater pore volume and aromaticity had higher adsorption of PCB28. The saturation adsorption amounts of PCB28 on BCC300, BCC500, and BCC700 were 21.9, 40.3, and 62.4 mg/g, respectively. It is noteworthy that PCB28 possessed a significant desorption hysteresis from BCCs, with the hysteresis index (Ce = 80 μg/L) increased from 0.380 to 0.661 as the preparation temperature of BCCs rising from 300 to 700 ℃. High concentration of NaCl (100 mmol/L) was unfavorable for the adsorption and desorption. The presence of humic acid or fulvic acid (FA), especially the smaller FA, could inhibit the adsorption and desorption of PCB28 on BCCs due to micropore blocking. In seawater, groundwater, surface water, and soil solution samples, the PCB28 adsorption of BCCs was inhibited to varying degrees in comparison with that in deionized water, and the desorption was noticeably inhibited in the groundwater sample. These findings provide valuable information for the understanding of interactions between BCCs and organic contaminants in natural waters and for the environmental application of biochars as well.

Transport of biochar colloids under unsaturated flow condition: Roles of chemical aging and cation type

Biochar colloids released from biochar materials are ubiquitous in the environment and undergo environmental transformation processes that may alter their properties. Natural subsurface environments are usually under unsaturated conditions, which could affect the transport of biochar colloids. This study investigated the transport of pristine and aged biochar colloids under unsaturated conditions by aggregation test, bubble column experiment, and sand column experiment. After aging, the biochar showed a more negative, hydrophilic, and rougher surface. Compared with pristine biochar colloids, aged biochar colloids in NaCl solution were not retained at the air-water interface (AWI) due to their more hydrophilic and rougher surface. In CaCl₂ solution, more pristine and aged biochar colloids were retained at the AWI because Ca²⁺ weakened the electrostatic repulsion between biochar colloids and the AWI. With the decrease in saturation, the transport of pristine and aged biochar colloids decreased by 17 %‑67 % through the retention at AWI and air-water-solid (AWS) interface. The transport of biochar colloids in NaCl solution was increased by 10 %‑20 % after aging as the aged biochar was not retained at the AWI. The difference of transport between pristine and aged biochar colloids in CaCl₂ solution (<8 %) was lower than that in NaCl solution due to the enhanced retention of aggregated biochar colloids at the AWI and AWS interfaces. These results highlight the importance of the surface structure of biochar on its behavior in the environment, which is essential for assessing the potential of biochar application for carbon sequestration and environmental protection.

Insights on ball milling enhanced iron magnesium layered double oxides bagasse biochar composite for ciprofloxacin adsorptive removal from water

Both ciprofloxacin (CIP) and sugarcane bagasse have brought enormous pressure on environmental safety. Here, an innovative technique combining Fe-Mg-layered double oxides and ball milling was presented for the first time to convert bagasse-waste into a new biochar adsorbent (BM-LDOs-BC) for aqueous CIP removal. The maximum theoretical adsorption capacity of BM-LDOs-BC reached up to 213.1 mg g^-1 due to abundant adsorption sites provided by well-developed pores characteristics and enhanced functional groups. The results of characterization, data fitting and environmental parameter revealed that pore filling, electrostatic interactions, H-bonding, complexation and π-π conjugation were the key mechanisms for CIP adsorptive removal. BM-LDOs-BC exhibited satisfactory environmental safety and outstanding adsorption capacity under various environmental situations (pH, inorganic salts, humic acid). Moreover, BM-LDOs-BC possessed excellent reusability. These superiorities illustrated that BM-LDOs-BC was a promising adsorbent and created a new avenue for rational placement of biowaste and high-efficiency synthesis of biochar for antibiotic removal.

Aggregation kinetics of biochar nanoparticles in aqueous environment: Interplays of anion type and bovine serum albumin

The colloidal particles, especially those at the nanoscale, are the most active part of the pyrogenic carbon (biochar). Increasingly applied biochar has resulted in a large number of biochar nanoparticles (NPs) being released into the environment. The aggregation of biochar NPs affects their environmental behavior and fate. The complex effects of anion type (Cl^-, SO₄^2-) and protein (bovine serum albumin, BSA) on the aggregation of wheat straw biochar (WB) and pinewood biochar (PB) NPs in solutions were investigated by the time-resolved dynamic light scattering method. The critical coagulation concentration (CCC) of WB and PB NPs in Na₂SO₄ solution was higher than their CCCs in NaCl solution, which was consistent with the Hofmeister series that SO₄^2-, a kosmotrope anion, increased the interaction between water molecules, thus enhancing the hydrophobic interactions between biochar NPs in solution and promoting their aggregation, while Cl^-, a chaotropic agent, exhibited the opposite effect. When BSA was added into the solution, BSA was adsorbed on the surface of biochar NPs and BSA corona was formed, which inhibited the aggregation of biochar NPs by inducing steric force. The enhanced stability of biochar NPs by BSA was more significant in NaCl than in Na₂SO₄ solution because BSA corona had a more negatively charged surface and a more steric structure in NaCl solution, thus generating stronger electrical repulsion and steric hindrance. The classical DLVO theory and the XDLVO theory incorporating the steric repulsion (in the presence of BSA) were used to interpret the aggregation and dispersion of biochar NPs. Through this study, we found that anion type indirectly affected the aggregation of biochar NPs by influencing the interaction between water molecules, while the aggregation of BSA-biochar NPs conjugates is mainly influenced by the surface charge and structure of BSA corona.

Pyrolyzed biomass-derived nanoparticles: a review of surface chemistry, contaminant mobility, and future research avenues to fill the gaps

Nanoparticles are abundant in the subsurface, soil, streams, and water bodies, and are often a critical control on elemental speciation, transport and cycling in the natural environment. This review provides an overview of pyrolyzed biomass-derived nanoparticles (PBNPs), their surface properties and reactivity towards aqueous species. We focus specifically on biochar-derived nanoparticles and activated carbon-derived nanoparticles which fall under our classification of PBNPs. Activated carbon-iron (nano)composites are included in some instances where there are significant gaps in literature because of their environmental relevance. Increased use of activated carbon, along with a resurgence in the manufacture and application of biochar for water treatment and soil amendment, has generated significant concerns about the mobility and toxicity of PBNPs derived from the bulk material in environmental applications. Recent examples are discussed to highlight current progress in understanding the influence of PBNPs on contaminant transport, followed by a critical discussion of gaps and future research directions.

Preparation of carbonyl, hydroxyl, and amino-functionalized microporous carbonaceous nanospheres from syrup-based waste to remove sulfamethazine

Sulfadiazine (SDZ) was a persistent sulfonamide antibiotic with a potential risk to human health. The waste dipping syrup was considered useless and environmentally unfriendly solution. In this work, carbonyl-, hydroxyl-, and amino-functionalized microporous carbonaceous nanospheres were synthesized using waste dipping syrup with glucose, fructose, and nitrogen, which was used as precursor for hydrothermal and pyrolysis process. The products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), the point of zero charge (PZC), Xray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET). The carbonaceous nanospheres with large BET surface area (924.528 m²/g), micropores (2.127 nm), and high micro-porosity (89.54 %) allowed the rapid diffusion of SDZ (0.512nm×0.738 nm) into micropores of nanospheres. The majority SDZ (initial concentration = 20 mg/L) was removed (>96.8%) in the presence of 1.0 g/L nanoparticles after 40-min reaction at pH = 6.0. The adsorption capacity of SDZ onto nanospheres was 96.6 mg/g. The adsorption kinetic and equilibrium followed pseudo-first-order model and Langmuir isotherm, respectively. The intra-particle diffusion model indicated a three-step adsorption process. In addition, the regenerated nanospheres could be reused over four recycles. The optimal fabrication was realized at lower hydrothermal and pyrolysis temperature of 180 °C and 400 °C, respectively, which involved no additional chemical activating agent and had a high yield (70.8 %). Collectively, hydroxylation, carboxylation, amination, large specific surface area, and multi-microporosity may be responsible for improved adsorption performance of SDZ onto nanospheres. The findings provided a novel pathway for SDZ-loading wastewater treatment using waste syrup.

Impact of biochar-induced vertical mobilization of dissolved organic matter, sulfamethazine and antibiotic resistance genes variation in a soil-plant system

The migration risk of antibiotic and antibiotic resistance genes (ARGs) have attracted lots of attentions due to their potential threaten to public health. Strategies to reduce their vertical mobilization risk are urgently required for groundwater safety and human health. Biochar enjoys numerous interests due to its excellent sorption affinity. However, little was known about the efficacy of biochar amendment in impeding the vertical mobilization of antibiotic and ARGs. To fill this gap, a column study was carried out to investigate biochar-induced variations in the leaching behavior of dissolved organic matter (DOM), sulfamethazine (SMZ) and ARGs. Results showed that biochar addition enhanced DOM export from soil, changed its composition and impeded the vertical transport of SMZ. Biochar amendment could effectively decrease the occurrence of extracellular and intracellular sul2 in soil and impede its vertical transportation, however, it did not work out with sul1 gene. Structural equation modeling analysis demonstrated that the abundance of sul2 was significantly controlled by SMZ concentration, while the primary drivers of sul1 were SMZ concentration and DOM content. These results indicated the failure in inhibiting the vertical transfer of sul1 under biochar amendment and highlighted the important role of DOM in the leaching of soil ARGs.

Accumulation of sulfamethazine and ciprofloxacin on grain surface decreases the transport of biochar colloids in saturated porous media

The increasing amount of antibiotics entering the environment through manure usage and sludge application from wastewater treatment plants (WWTP) attracts much concern due to their potential threat to ecological security and human health. When biochar, a soil and water amendment, is introduced into the soil for remediation, the antibiotics are usually co-present with the biochar colloids (BC) or pre-accumulated in soils. However, little is known about the effect of antibiotics on the behavior of BC. Column experiments were conducted at three different pH values to study the effect of sulfamethazine (SMT) or ciprofloxacin (CIP) on BC transport. Under certain conditions (co-present in the influent and pre-sorbed on quartz sand), large numbers of cation and zwitterion forms of the less mobile CIP at pH 5 and 7 led to less negatively-charged surface of BC and quartz sand, resulted in higher BC retention compared to the highly mobile SMT. The decrease in BC transport became more significant with a higher amount of SMT or CIP pre-sorption. Therefore, when biochar is applied into soils polluted by antibiotics, the pH-dependency and the loading amount of antibiotics in soil matrix should be paid attention to as they might affect the transport of BC and the related facilitated-contaminants transport.

Transport of nanoparticles in porous media and its effects on the co-existing pollutants

Nanomaterials are widely used in daily life owing to their superior characteristics. The release and transport of nanoparticles (NPs) in the environment is inevitable during their entire life cycle, posing a risk to the aquatic environment. Thus, considerable attention has been focused on the fate and behavior of NPs in porous media, as well as the co-transport of NPs with other pollutants. In this review, current knowledge about the retention and transport behavior of NPs in porous media is summarized. NP transport in porous media is dominated by various internal and external factors, including the characteristics of NPs, porous media, and water flow. Generally, NPs with high density, small particle size, and surface coating are easily transported in porous media with the characteristics of large size, smooth surface, and low water saturation. Meanwhile, high pH and velocity, low temperature, and natural organic matter-containing fluids are also conducive to NP transport. Aggregation, adsorption, straining, and blocking are the primary mechanisms by which NPs affect the transport of co-existing pollutants in porous media. Current research on NP transport has been performed predominantly using modal porous media (e.g., sand and glass beads); however, there is a large gap between simulated and natural porous media. Further studies should focus on the transport, fate, and interaction of NPs and coexistent pollutants in natural porous media, as well as the coupling mechanisms under actual environmental conditions.

Co-transport of ball-milled biochar and Cd2+ in saturated porous media

The combination of ball milling technology and biochar materials provides new prospects for environmentally friendly and sustainable environmental pollution control technologies, but comes with opportunities and risks. In this study, column experiments were used to evaluate the environmental behavior of ball‑milled biochar (BMBC). The results of the column experiments showed that BMBC transport increased with a high flow velocity, large medium size, high pH, and low ionic strength. Owing to the strong adsorption of Cd²⁺ by BMBC, the presence of BMBC in the medium led to a decrease in effluent Cd²⁺. The presence of Cd²⁺ in the solution slightly inhibited the transport of BMBC. The transport of Cd²⁺ was facilitated by BMBC due to the high affinity. Therefore, attention should be paid to favorable conditions for BMBC transport. This study provides a perspective to assess the behavior of BMBC in the environment and whether its interaction with Cd²⁺ will introduce new environmental hazards.

Co-transport and retention of zwitterionic ciprofloxacin with nano-biochar in saturated porous media: Impact of oxidized aging

While biochar (BC) is used for contaminant remediation (i.e. antibiotics) in the field, geochemical aging can alter its chemical structure, releasing nano-sized BC (NBC, sizes ranging from approximately 200 nm to 500 nm), and further influence the environmental behaviour of antibiotics affiliated with BC. In this study, we comprehensively examined the sorption behaviour of NBCs with and without aging toward ciprofloxacin (CIP), their aggregation performance, and transport behaviour in porous media. The results showed that aging improved the oxygen-containing groups within the NBCs and made their surfaces more negatively charged. The thermodynamic enhancements of specific interactions (i.e. π-π interaction or Coulombic force) with CIP resulted in the enhancement of slow sorption (from 60-64% to 40-58%) and a higher normalised sorption capacity (Q_e). The aggregation of NBCs was affected by changes in individual specific interactions and interfacial forces between the NBCs before and after CIP sorption. Further, aging could enhance the transport of NBCs both in the absence and presence of CIP. In addition to the interaction with the quartz sand surface, the contributions of aggregation and chemical heterogeneity caused by rebalanced specific interactions with CIP, may explain the observed transport behaviours of the aged NBCs in porous media. Additionally, the presence of NBCs, regardless of aging, suppressed the transport of CIP. Thus, mechanisms such as increased sorption sites due to aggregation and competitive sorption between NBCs and CIP, rather than the contribution of co-transport from NBCs, might play an important role in determining the fate of CIP in the natural environment.

Impact of rice straw biochar addition on the sorption and leaching of phenylurea herbicides in saturated sand column

The application of phenylurea herbicides (PUHs) may lead to the extensive distribution in soils, while the role of straw biochar as a soil amendment on the transport and sorption of PUHs are still unclear. Thus, the transport and sorption behavior of three typical PUHs with rice straw biochar (RSB) was studied in both adsorption simulation experiments of aqueous solution and packed column experiments. The sorption mechanism of RSB to herbicides was investigated through batch sorption studies with three influencing factors including dosage of RSB, pH, and ionic strength (IS) with orthogonal test. The sorption coefficients were improved significantly by increasing the dosage of RSB, while there was no obvious influence by enhancing the pH and IS value. The optimal sorption conditions (pH value at 3, IS at 0.1 M, and RSB dosage at 60 mg) of three herbicides were set and the maximum removal rates of Monuron, Diuron, and Linuron were 41.9%, 25%, and 56.8%, respectively. The co-transport process of RSB and PUHs were investigated under different RSB dosage, pH value, and IS value. The retention effect increased greatly with enhancing the RSB dosage and pH value. However, IS did not have a significant influence on the retention of RSB, and therefore it had little effect on the adsorption capacity, which was consistent with the results of sorption experiments. The breakthrough curves (BTCs) for co-transport were well simulated by the two-site non-equilibrium convection-dispersion equation (CDE). Most of the regression coefficients (R²) were above 0.99, which uncovered the co-transport in packed column were affected by physical absorption and chemical forces. According to the fitting parameters analysis, the RSB particles and PUHs were subjected to a greater resistance and a stronger stability by reducing pH value in porous media. The presence of RSB increased the amount of dynamic sorption sites in the entire co-transport system, which led to a significant promotion of the PUHs' sorption and interception.

Co-transport of biochar colloids with organic contaminants in soil column

Co-transport of biochar (BC) colloids with coexisting organic contaminants (OCs) in soil involves complex interactions among BC colloids, OCs, and soil particles, which is significant for the environmental application and risk assessment of BC and yet has not been well addressed. This study explored co-transports of three typical OCs (i.e., phenanthrene (PHN), atrazine (ATZ), and oxytetracycline (OTC)) and BC colloids obtained from bulk BCs with different charring temperatures (200-700 °C) and particle sizes (250 nm, 500 nm, and 1 μm) in a soil column of 9 cm in height. Considerable transport of BC colloids alone was observed and the maximum breakthrough concentration (C/C_o) increased from 0.08 to 0.77 as the charring temperature decreased from 700 to 200 °C. The mobilities of PHN, OTC, and ATZ alone were very low but were greatly increased by co-transports with BC colloids, and their maximum C/C_o values were within 0.05-0.33, 0.03-0.44, and 0.05-0.62, respectively, in the absence and presence of various BC colloids. The enhancement effect of BC colloids on the OC transport decreased with increasing charring temperature or particle size of BC colloids. BC colloids mainly acted as a vehicle to facilitate the transport of OCs, and dissolved organic carbon from BC colloids also contributed to the increased mobility of OCs in dissolved form. These findings provide new insights into co-transport of BC colloids and contaminants in soil.

Indirect photodegradation of sulfadiazine in the presence of DOM: Effects of DOM components and main seawater constituents

The presence of pharmaceuticals and personal care products in coastal waters has caused concern over the past decade. Sulfadiazine (SD) is a very common antibiotic widely used as human and fishery medicine, and dissolved organic matter (DOM) plays a significant role in the indirect photodegradation of SD; however, the influence of DOM compositions on SD indirect photodegradation is poorly understood. The roles of reactive intermediates (RIs) in the indirect photolysis of SD were assessed in this study. The reactive triplet states of DOM (³DOM∗) played a major role, whereas HO· and ¹O₂ played insignificant roles. DOM was divided into four components using excitation-emission matrix spectroscopy combined with parallel factor analysis. The components included three allochthonous humic-like components and one autochthonous humic-like component. The allochthonous humic-like components contributed more to RIs generation and SD indirect photolysis than the autochthonous humic-like component. A significant relationship between the indirect photodegradation of SD and the decay of DOM fluorescent components was found (correlation coefficient, 0.99), and the different indirect photodegradation of SD in various DOM solutions might be ascribed to the different components of DOM. The indirect photolysis rate of SD first increased and then decreased with increasing pH. SD photolysis was enhanced by low salinity but remained stable at high salinity. The increased carbonate concentration inhibited SD photolysis, whereas nitrate showed almost no effect in this study.