Dissolved Organic Carbon Reduction Research Articles

One-electron oxidant-induced transformation of dissolved organic matter: Optical and antioxidation properties and molecules

Dissolved organic matter (DOM) is a major sink of radicals in advanced oxidation processes (AOPs) and the radical-induced DOM transformation influences the subsequent water treatment processes or receiving waters. In this study, we quantified and compared DOM transformation by tracking the changes of dissolved organic carbon (DOC), UVA254, and electron donating capacity (EDC) as functions of four one-electron oxidants (SO4•−, Cl2•−, Br2•−, and CO3•−) exposures as well as the changes of functional groups and molecule distribution. SO4•− had the highest DOC reduction while Cl2•− had the highest EDC reduction, which could be due to their preferential reaction pathways of decarboxylation and converting phenols to quinones, respectively. Br2•− and CO3•− induced less changes in DOC, UVA254, and EDC than SO4•− and Cl2•−. Additionally, DOM enriched with high aromatic contents tended to have higher DOC, UVA254, and EDC reductions. Decreases in hydroxyl and carboxyl groups and increases in carbonyl groups were observed in these four types of radicals treated DOM using Fourier transform infrared spectroscopy. High resolution mass spectrometry using FTICR-MS showed that one-electron oxidants preferred to attack unsaturated carbon skeletons and transformed into molecules featuring high saturation and low aromaticity. Moreover, SO4•− was inclined to decrease oxidation state of carbon and O/C of DOM due to its strong decarboxylation capacity. This study highlights the distinct DOM transformation by four one-electron oxidants and provides comprehensive insights into the reactions of one-electron oxidants with DOM.

Fates of selected pharmaceuticals in a large recirculated mesocosm with a pond and bank filtration

Pharmaceuticals such as carbamazepine (CBZ), sulfamethoxazole (SMX) and diclofenac (DCF) are detected at a high frequency in the aquatic environment. The fates of these compounds in bank filtration (BF), a nature-based water treatment system, have been extensively studied, mainly in batch and laboratory column studies. This study, for the first time, investigated the fates of CBZ, SMX and DCF in a large recirculated mesocosm with a pond and subsequent BF. Changes in dissolved organic carbon (DOC) in the pond and bank filtrate were also observed. The averaged spiking concentration of CBZ, SMX and DCF was 1 μg/L at the pond influent and the hydraulic retention time of surface water in the pond was 15 days to reach at the bank. The infiltrated surface water travelled through two parallel subsurface layers and a combined effluent (from both layers) was collected (35 m from the bank) and recirculated as an influent of the pond. The redox conditions in both layers were significantly different (p < 0.05) and correlated with temperature (R2 = 0.91, p < 0.05). The results revealed that CBZ was persistent in the surface water and groundwater passage, SMX was persistent in surface water and removed entirely through BF within 50 days of operation. DCF was completely removed after infiltration and groundwater passage (within 2 m). The DOC in the surface water showed insignificant variations between the influent and the bank. A significant reduction of DOC was observed within the first 5 m after infiltration, and the reduction was associated with the removal of biopolymers. This work shows that the selected organic micropollutants in surface water were not affected by sunlight intensity, water chemistry and water depth. In addition, recirculation mesocosm BF confirms the potential environmental risk and predictive concentrations of organic micropollutants in the aquatic environment.

Enhanced coagulation process for removing dissolved organic matter, microplastics, and silver nanoparticles

Dissolved organic carbon (DOC), microplastics (MPs), and silver nanoparticles (AgNPs) in water are of major concern because of their direct and indirect toxic effects on aquatic organisms and human exposure via water. This work investigated the effect of poly aluminum chloride (PACl) coagulation for reducing DOC, MPs, and AgNPs. This work used water from a canal in Thailand with a DOC of 5.2 mg/L in the experiment. AgNPs of 5–20 mg/L were added to canal water to create synthetic water for the PACl coagulation. Polyethylene and polypropylene (PP) type MPs were identified in the raw water with Fourier transform infrared spectroscopy. Coagulation with 15 mg/L of PACl performed better in the PP removal. The PACl coagulation at dosages of 15, 40, and 70 mg/L removed DOC by 16–20%, 44–52%, and 46–63% and AgNPs by 34–90%, 53–93%, and 81–95%, respectively. The presence of AgNPs at high levels could inhibit the efficiency of DOC reduction by the PACl coagulation. The FESEM identified the adsorption of silver-containing nanoparticles onto the flocs with increased dosages of PACl. So, PACl is a coagulant in the removal of AgNPs that can reduce health hazards and eco-toxicological risks in water sources due to the release of silver.

Mixed coagulant-flocculant optimization for pharmaceutical effluent pretreatment using response surface methodology and Gaussian process regression

Wastewater from the Antibiotical-Saidal pharmaceutical plant (Medéa) was pretreated by coagulation-flocculation using copper sulfate (CuSO4), iron chloride (FeCl3), and mixture of the two salts combined in a 1:1 (v/v) ratio in the present study. Response surface methodology (RSM) was used to optimize pH and coagulant dosage as independent variables, while dissolved organic carbon (DOC), absorbance at 254 nm (UV 254), and turbidity were provided as dependent variables in the central composite design (CCD). Then, the databases of the three treatments were combined in a single database to create a general model valid for the three treatments at the same time, and to predict the reduction rates of DOC, UV254, and turbidity, using the Gaussian process regression coupled with the dragonfly optimization algorithm (GPR-DA). To have the best model obtained between RMS and GPR-DA, an experimental validation was carried out after having had the optimal conditions of each type of coagulant, using the multi-objective optimization technique. The results of the experimental validation show the superiority of the GPR-DA model compared to the RSM model. Also, the results show that the mixed coagulant (CuSO4 + FeCl3) obtain better results than CuSO4 or FeCl3 alone with a treatment efficiency equal to 92.68% at pH = 5 and dosage = 600 mg/L, and the reductions in DOC, UV 254 and turbidity are 97.32%, 82.90% and 96.47%, respectively.

The Fouling Effect on Commercial Ceramic Membranes during Filtration of Microalgae Chlorella vulgaris and Monoraphidium contortum

Although interest in the use of membranes for the concentration of microalgal biomass has steadily been growing, little is known regarding the phenomena of membrane fouling. In addition, more attention has been given to polymeric membranes compared to ceramic membranes, which have a longer life that is associated with a higher resistance to aggressive chemical cleaning. In this study, microfiltration (MF) and ultrafiltration (UF) of two microalgae species, Chlorella vulgaris and Monoraphidium contortum, were carried out using tubular crossflow ceramic membranes. Permeate flux was measured, resistance was calculated, and dissolved organic carbon (DOC) was determined. The flux reduction during the first 10 min of filtration was higher for MF than UF (&gt;70% and &lt;50%), and steady-state permeate fluxes were &lt;5% (for MF) and &lt;25% (for UF) of initial (in m3 m−2 s−1) 6.2 × 10−4 (for MF) and 1.7 × 10−4 (for UF). Total resistances (in m−1) were in the ranges of 4.2–5.4 × 1012 (UF) and 2.6–3.1 × 1012 (MF) for M. contortum and C. vulgaris, respectively. DOC reduction was higher for UF membrane (&gt;80%) than for MF (&lt;66%) and DOC concentrations (mg C L−1) in permeates following MF and UF were about five and two, respectively. In conclusion, we demonstrated: (i) higher irreversible resistance for UF and reversible resistance for MF; (ii) permeate flux higher for UF and for M. contortum; (iii) the significant role of dissolved organic compounds in the formation of reversible resistance for MF and irreversible resistance for UF.

Forest defoliator outbreaks alter nutrient cycling in northern waters

Insect defoliators alter biogeochemical cycles from land into receiving waters by consuming terrestrial biomass and releasing biolabile frass. Here, we related insect outbreaks to water chemistry across 12 boreal lake catchments over 32-years. We report, on average, 27% lower dissolved organic carbon (DOC) and 112% higher dissolved inorganic nitrogen (DIN) concentrations in lake waters when defoliators covered entire catchments and reduced leaf area. DOC reductions reached 32% when deciduous stands dominated. Within-year changes in DOC from insect outbreaks exceeded 86% of between-year trends across a larger dataset of 266 boreal and north temperate lakes from 1990 to 2016. Similarly, within-year increases in DIN from insect outbreaks exceeded local, between-year changes in DIN by 12-times, on average. As insect defoliator outbreaks occur at least every 5 years across a wider 439,661 km2 boreal ecozone of Ontario, we suggest they are an underappreciated driver of biogeochemical cycles in forest catchments of this region.

Evaluation of enzyme activity for monitoring biofiltration performance in drinking water treatment

Many water providers monitor adenosine triphosphate (ATP) as an indicator of biological acclimation of their biofilters; however, strong correlations between ATP concentration and filter performance (e.g., organic matter or disinfection by-product precursor removal) are not typically observed. As an alternative, this study evaluated the use of enzyme activity for monitoring biological processes within filters. Recent studies have proposed that enzyme activity may be used as an indicator of biofilter function as it provides a means to quantify biodegradation which may allow for a more accurate measure of degradation potential and to gain a better understanding of biofilter performance. Sampling was completed from full- and pilot-scale biofilters to assess impacts associated with pre-treatments, varying sources waters, as well as pre-treatment and operating conditions. Enzyme activity (carboxylic esterase, phosphatase, ß-glucosidase, α-glucosidase, ß-xylosidase, chitinase, and cellulase) and ATP were measured from the top 5 cm of biofilter media representative of typical full-scale sampling; water quality parameters included dissolved organic carbon (DOC) and disinfection by-products (DBPs): trihalomethane (THM) formation potential (FP), and haloacetic acid FP (HAA FP). Results confirmed that ATP was not a reliable monitoring tool for DOC and DBP FP reduction in biofilters. A strong relationship was observed between esterase activity and DOC reduction; chitinase activity significantly correlated to THM FP reduction for filters treating three different source waters and HAA FP reduction achieved by filters treating the same source water with a range of pre-treatment and backwash conditions. This study showed that enzyme activity may be appropriate for monitoring biological processes within drinking water filters and may act as a surrogate for the removal of organic compounds.

A vessel-inside-vessel microwave-assisted digestion method based on SO3 generation in situ for the mineral determination of fatty samples

Vessel-inside-vessel microwave-assisted acid digestion was developed for the analysis of samples with high-unsaturated fat content. For the first time, thermal decomposition of (NH4)2S2O8 solutions was evidenced for SO3 generation in situ and gas-phase modification in pressurized digestion flasks. NMR analysis demonstrated the oxidative effect of SO3 on olefin double bonds despite incomplete mineralization of oil samples. In this context, (NH4)2S2O8 decomposition was used in association with HNO3 solutions for sample digestion and mineral determination in edible oils (safflower, coconut, flaxseed, and chia). For all oils, dissolved organic carbon (DOC) contents lower than 5% m m-1 were obtained under optimum conditions: 210 °C with an irradiation time of 40 min, 7.0 mol L-1 HNO3 and 2.0 mol L-1 (NH4)2S2O8 in 0.9 mol L-1 H2SO4. Thus, a DOC reduction of about 70% was reached compared to digestions using only HNO3 at the same conditions. Additionally, a time reduction of up to three-fold was achieved compared to typically demanding edible oil digestions. The proposed method allowed the determination of As, Cd, Cr, Mn, Ni, and Pb in edible vegetable oil samples by ICP-MS. Accuracy was evaluated against the reference method, and no significant difference was observed (p = 0.05), with wide linear ranges and good linearity (r ≥ 0.999) and LOD ranging from 0.48 (As) to 2.41 (Cd) μg L-1.

Quantification of low molecular weight oxidation byproducts produced from real filtered water after catalytic ozonation with different pathways

Catalytic ozonation was suggested to be effective for micropollutant removal during water treatment. However, research on organic byproduct formation from catalytic ozonation of real filtered water in water treatment plants was lacking. In this work, two synthesized catalysts, α-FeOOH and CeO2, were applied to catalyze ozonation of real filtered water at different ozone dosages, and the byproducts were quantified. Results showed that the α-FeOOH enhanced hydroxyl radical production, while the CeO2 did not. Both catalysts further reduced dissolved organic carbon (DOC) and UV254 of the filtered water during the catalytic oxidation processes. The O3/CeO2 improved the removal of low molecular weight compounds, especially the refractory compounds such as ketoacids and carboxylic acids, compared to ozonation alone. While the O3/α-FeOOH generated higher concentrations of carboxylic acids than that of ozonation. Thus, in light of DOC and low molecular weight compound reductions, CeO2 was the superior catalyst for micropollutant removal in real filtered water.

Bacterioplankton response to nitrogen and dissolved organic matter produced from salmon mucus.

Aquaculture releases organic matter to the water column through excretion, fecal pellets, and uneaten food, but also by the continuous release of fish epithelium mucus. The effect of the latter on natural bacterial assemblages was determined using ammonium amended experiments at Puyuhuapi fjord in Chilean Patagonia. Mucus was added to seawater coming from 2 and 100 m depth and ammonium, nitrite and nitrate, dissolved organic carbon (DOC), picoplankton abundance, and active composition (i‐tag 16S rRNA) were followed for 24 h. The results showed a significant response from the microbial community but only at surface depth after 2 and 6 h of incubation. A reduction of DOC and ammonium concentration and accumulation of nitrite and nitrate over time was observed, mainly at 100 m. Changes in the composition of active bacteria between treatments were observed at different taxonomic levels, associated with Alphaproteobacteria (Clade SAR11), Bacteroidetes (Polaribacter) and Gammaproteobacteria (Colwellia, Oceaniserpentilla) and other bacteria such as Nitrospina sp, a nitrite‐oxidizing bacteria at some hours during the incubation. Fish pathogens, such as Vibrio and Piscirickettsia were rare (<0.02%). Overall, our study suggests that fish mucus can cause rapid modifications in microbial assemblages and stimulate organic matter and nutrient cycling, including heterotrophic and autotrophic (nitrification) in areas influenced by aquaculture.

Removal of disinfection by-product precursors by ion exchange resins

The removal of dissolved organic carbon (DOC) is a key factor in the control of disinfection by-product (DBP) formation in drinking water. Ion exchange process deals with the removal of naturally negatively charged organic matter. A fluidized bed column test has been chosen to test in parallel the efficiency of 4 different anionic exchange resins (Purolite PPA860S, Dowex TAN-1, Amberlite IRA-958 and IRA-410) in terms of DOC fraction removal and related DBP formation reduction. IRA-410 was shown to be the best performing resin in terms of DOC and DBP formation potential reduction followed by PPA860S. These resins removed respectively 41 and 37 % of DOC, with humic substances as the main target of the two resins (68 and 72 % reduction, respectively, based on size exclusion chromatography with an organic carbon detector). The UV absorbance was reduced in a higher proportion than the DOC demonstrating a preference of the resins for the relatively hydrophobic compounds. The reduction in trihalomethane and haloacetic acid formation was higher than the DOC removal for IRA-410 and PPA860S (53 and 59 %, respectively); whereas IRA-958 on the other hand showed a lower reduction in DBP formation potential than its DOC removal. All the resins showed a much higher reduction of iodinated trihalomethanes formation potential (66–96% reduction compared to raw water) due to the removals of iodide in addition of organic precursors. However, in a context of increasing halide concentrations, the different resins showed a reduction of their efficiency to control the formation of DBPs.

Comparison of O3-BAC, UV/H2O2-BAC, and O3/H2O2-BAC treatments for limiting the formation of disinfection byproducts during drinking water treatment in India

Natural organic matter (NOM) acts as a precursor to toxic disinfection byproducts (DBPs). Recently it has been established that a mixture of natural and effluent derived organic matter (NefOM) leads to very high concentration of DBPs. Both conventional and non-conventional/advanced ways of drinking water treatment do not remove NefOM sufficiently. Advanced oxidation processes (AOPs) have been shown to oxidize dissolved organic carbon (DOC) effectively but entail high energy inputs. Therefore, combining AOP as a pre-oxidation step with an economical system like biological activated carbon (BAC) filtration is a more economical solution. In this study, BAC was developed from virgin granular activated carbon (GAC) with river Yamuna water, which has the highest levels of DOC in the world, as influent water. Two columns were used, with one of them as a control. For the development of BAC from GAC, Empty bed contact time (EBCT) of 12 min was found to be effective. Steady-state was achieved after 90 days of continuous operation of the columns. After the steady-state was achieved, EBCT of 16 min was found to be optimum for the diffusion of organic molecules inside the biofilm and mineralization by the attached biomass on the surface of BAC.The percentage DO consumption and, DOC/UV254 reduction was found to be constant from t = 90 to t = 120 days, after which the column was assumed to be acting as a BAC column. To optimize the AOP dose for AOP-BAC experiments, biodegradable DOC (BDOC) was measured after various doses of individual AOP treatments. The maximum increase in biodegradability was observed in case of O3/H2O2 with BDOC of 3.43 mg/L at an ozone dose of 5.44 mg/L and 0.5 mM H2O2. All three AOP treated water were passed through BAC columns and change in BDOC, DOC, hydrophobic fraction of DOC and UV254 were observed. The maximum DOC, hydrophobic fraction of DOC and UV254 reduction was observed with O3/H2O2-BAC, as expected from BDOC results. The primary reason is enhanced biodegradability after optimum O3/H2O2 treatment and thus better utilization of simpler organic molecules by microbes in the BAC column. Maximum trihalomethane formation potential (THMFP) reduction was also observed in the case of O3/H2O2-BAC treatment.

Effective enzyme activity: A proposed monitoring methodology for biofiltration systems with or without ozone

“Effective Enzyme Activity”, or simply “Effective Activity”, is proposed as a biofiltration monitoring tool which combines enzyme activity with empty bed contact time (EBCT) to quantify biodegradation potential. The primary objective of this study was to evaluate the applicability of the Effective Activity concept for predicting water quality in biofiltration systems. This pilot-scale study evaluated eight different biofilter configurations in order to quantify impacts associated with filter media (anthracite/sand or granular activated carbon), pre-treatment (settled water with or without ozonation) and operating conditions (15- and 30-min EBCT, and backwash with or without chlorine). Microbial characterization included biomass concentration, as measured by adenosine triphosphate (ATP), in addition to esterase and phosphatase activity. Water quality parameters included dissolved organic carbon (DOC), trihalomethane (THM) formation potential (FP), haloacetic acid (HAA) FP, haloacetonitrile (HAN) FP, iodinated DBP FP (THMs and HAAs) and inorganic nutrients (phosphorus and nitrogen). Results confirmed the benefits to treated water quality associated with the application of an ozone residual of 0.5 mg/L, utilization of GAC filter media, eliminating chlorinated backwash, and extending EBCT. This study demonstrated a good relationship between effective esterase activity and reductions in DOC and THM FP, including those systems which incorporate pre-ozonation. As such, this study showed that Effective Activity may be appropriate for relating biomass characterization to treated water quality and highlights the importance of quantifying biomass activity in addition to quantity.

An Investigation of a Conventional Water Treatment Plant in Reducing Dissolved Organic Matter and Trihalomethane Formation Potential from a Tropical River Water Source

The characteristics and composition of dissolved organic matter (DOM) and trihalomethane (THM) generation during water treatment are important for producing safe drinking water. However, little information is available on this topic within the context of Indonesia. This study aimed to investigate the efficiency of a conventional drinking water treatment plant (WTP) in removing DOM and chloroform forming potential (CHCl3FP), and evaluate surrogate parameters for CHCl3FP. Samples were taken during the rainy season and the dry season from raw water, after secondary treatment and after the rapid sand filter. DOM was characterized based on the A254, A355, SUVA, dissolved organic carbon (DOC), and fluorescence DOM (FDOM) parameters. The composition of the DOM was identified using the peak picking method. Overall, from raw to finished water, the WTP performed better in the rainy season with 55.96% reduction of DOC and 63.45% reduction of A355 as compared to the dry season with 53.27% reduction of DOC and 24.18% reduction of A355.The overall removal of humic and tryptophan compounds during the rainy season was 33.33% and 37.50%, respectively. In the dry season, humic compounds were reduced by 18.80%, while tryptophan increased threefold. A355 can serve as a surrogate parameter for CHCl3FP in raw water and water after secondary treatment, containing more humic-like compounds than tryptophan-like compounds.

Linking transformations of organic carbon to post-treatment performance in a biological water recycling system

Ozone, electrolysis and granular activated carbon (GAC) were examined as potential post-treatments to follow a household-scale biologically activated membrane bioreactor (BAMBi), treating a wash water containing trace urine and feces contamination. Each post-treatment was evaluated for abilities and reaction preferences to remove or transform dissolved organic carbon (DOC), chemical structures that contribute color, and assimilable organic carbon (AOC), which can support bacterial regrowth. Batch treatment with each technology demonstrated an ability to remove ≥95% DOC. Ozone demonstrated a reaction selectivity through increased reaction rates with larger compounds and color-contributing compounds. Electrolysis and GAC demonstrated generally less-selective reactivity. Adding post-treatments to full-scale systems reduced DOC (55–91%), AOC (34–62%), and color (75–98%), without significant reaction selectivity. These reductions in DOC and AOC were not linked to reduction of bacterial concentrations in treated water. Reductions in bacterial concentrations were observed with ozone and electrolysis, but this is credited to oxidation chemicals produced in these systems and not the removal or transformations of organic materials.

Factors impacting electrocoagulation treatment of hydraulic fracturing fluids and removal of common fluid additives and scaling ions

This research presents 56 experiments on hydraulic fracturing flowback and produced waters to evaluate common factors affecting electrocoagulation (EC) removal of turbidity, chemical oxygen demand (COD), dissolved organic carbon (DOC) and final pH. Additionally, qualitative reductions in the common fluid additives polyethylene glycols (PEGs) and polypropylene glycols (PPGs), which can interfere with reuse in hydraulic fracturing, were evaluated by mass spectrometry for the first time. Design of experiments tested five EC process control factors: electrode material, current, initial pH, treatment time, and number of electrodes. Turbidity reductions were high (>90 %), and a maximum of 37.4 % of COD and 54.0 % of DOC was removed. Due to low variability, no factors were significant for turbidity reduction, while current, treatment time, and numbers of electrodes were significant factors for COD and DOC reduction. pH increased with iron electrodes and was neutralized with aluminum electrodes. Both PEGs and PPGs were removed, and PPGs were removed to a greater extent. Removal of these compounds increased as they became more hydrophobic as suggested by their logKow values. Some analysis was done on removal of common scaling ions (Ba, Ca, Mg, Sr) with removal possibly related to the pH of the water.

Filter Media-Packed Bed Reactor Fortification with Biochar to Enhance Wastewater Quality

Contamination of water sources by inappropriately disposed poorly treated wastewater from countryside establishments is a worldwide challenge. This study tested the effectiveness of retrofitting sand (Sa)- and gas–concrete (GC)-packed reactors with biochar (C) in removing turbidity, dissolved organic carbon (DOC), phosphate (PO43−), and total phosphorus (Ptot) from wastewater. The down-flow reactors were each intermittently loaded with 0.063 L/d for 399 days. In general, all reactors achieved &lt;3 NTU (Nephelometric Turbidity Units) effluent turbidity (99% efficiency). GC reactors dominated in inlet PO43− (6.1 mg/L) and DOC (25.3 mg/L) reduction, trapping &gt;95% and &gt;60%, respectively. Compared to Sa (PO43−: 35%, DOC: 52%), the fortified sand (SaC) filter attenuated more PO43− (&gt;42%) and DOC (&gt;58%). Student t-tests revealed that C significantly improved the Sa PO43− (p = 0.022) and DOC (p = 0.034) removal efficacy. From regression analysis, 53%, 81%, and 85% PO43− sorption variation in Sa, C, and SaC, respectively, were explained by variation in their effluent pH measures. Similarly, a strong linear correlation occurred between PO43− sorption efficiency and pH of fortified (r &gt; 0.7) and reference (r = 0.6) GC filters thus suggesting chemisorption mechanisms. Therefore, whereby only sand may be available for treating septic tank effluents, fortifying it with biochar may be a possible measure to improve its efficacy.

Applicability of advanced oxidation processes in removing anthropogenically influenced chlorination disinfection byproduct precursors in a developing country

The studies on occurrence of contaminants of emerging concern in drinking water treatment plants or even wastewater treatment plants in developing country like India, are very limited. Trihalomethanes (THMs) is one such contaminant of concern in drinking water treatment sector. THMs are the major disinfection byproducts (DBPs) formed during the widely used chlorination process. Their identification and removal is of utmost importance in developed as well as developing nations. This study is first of its kind to assess the removal of mixture of urban run-off driven organic matter, agricultural run-off driven organic matter, untreated sewage effluent driven organic matter and little natural organic matter (NOM) (altogether NefOM) (major DBP precursors) using advanced oxidation processes (AOPs) in the Indian region. Since, NOM vary geographically, this study will add up to applicability of generally utilized AOPs for removal of site explicit (Indian) NefOM. Trihalomethanes at a conventional water treatment plant at Mathura and a moving bed biofilm based non-conventional water treatment plant at Agra were monitored over a year, demonstrating the inability of the water treatment plants to limit formation of DBPs from Yamuna inlet water at any time of the year. Various AOPs (UV–H2O2, O3–H2O2, O3) and UV (ultraviolet) photolysis were assessed for their ability to decrease the trihalomethane forming potential (THMFP) by degrading the contaminants in the waters of Yamuna. Kinetic studies were conducted to evaluate the selected AOPs based on their ability to mineralize dissolved organic carbon (DOC), and decrease UV254 at various pH, UV intensities, and ozone and hydrogen peroxide concentrations. UV-L/H2O2 at an intensity of 47 mJ/cm2/min, pH = 7, and at hydrogen peroxide concentration of 0.5 mM provided an optimum reduction of DOC (64%) and UV254 (87%). Fractionation studies indicated that treatment by UV-L/H2O2 leads to the most significant decrease in the hydrophobic fraction of the water, while further study indicated that UV-L/H2O2 also showed maximum attenuation of THMFP.

Effects of rainfall reduction on the quantity and spectroscopic characteristics of soil dissolved organic matter in a subtropical natural Castanopsis carlesii forest.

The alteration of rainfall pattern under the background of global climate change may affect the quantity and quality of soil dissolved organic matter (DOM). To better understand the responses of soil DOM to rainfall reduction in subtropical forests, we conducted a 6-year rainfall reduction experiment. There were three treatments: control (CK), 30% rainfall reduction (-30%), and 60% rainfall reduction (-60%). With ultraviolet-visible, infrared and three-dimensional fluorescence spectroscopy, we investigated the effects of rainfall reduction on the quantity and structure of DOM from different soil layers of a natural Castanopsis carlesii forest in subtropical China. Rainfall significantly reduced the content of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in the 0-10 cm soil layer. Specifically, less decreases of DOC than DON were found under the -30% treatment, while more reduction of DOC than DON for the -60% treatment. Under each treatment, the contents of DOC and DON were significantly higher in the 0-10 cm soil layer than that in the 10-20 cm soil layer. Relatively more microbial metabolite with complex structures, such as aromatic humus and alkanes, contributed to soil DOM from the -30% treatment than that from the -60% treatment. Beyond water availability, microbial activity was a key factor regulating the quantity and structure of soil DOM in response to rainfall reduction.

High temperature-produced biochar can be efficient in nitrate loss prevention and carbon sequestration

The effects of biochar on soil properties including nutrients have been reported in previous studies, but few studies targeted on soil nitrogen. Moreover, there remains a lack of studies considering the liberation of ammonia during the ammonium (N-NH4+) adsorption process. Our study aimed to fill this research gap. A pot incubation experiment was conducted for 84 days, with ten different soils and four rates of wood chip-based biochar (0.5, 2, 4, and 8%). Biochar's effect on soil ammonium was inconsistent and insignificant in most of the incubated soils at all biochar rates. This finding contradicted our Langmuir model, which estimated maximum ammonium adsorption capacity of biochar as 6.66 mg of N-NH4+ per g of biochar. Soil response in nitrate (N-NO3−) and dissolved organic carbon (DOC) followed a similar declining trend in all soils in both incubation periods, with the effect boosted according to the biochar application rate. The Langmuir isotherm estimated the maximum N-NO3− adsorption capacity of our biochar as 11.3 mg g−1. Soil original properties determined amount of nitrate and DOC reduction after biochar addition. Our result also indicated poor estimation of ammonium adsorption by biochar due to the liberation of ammonia. As a result, we strongly recommend that ammonia liberation should be considered during adsorption experiments and more studies in this field.