Dissolved Organic Carbon Adsorption Research Articles

Long-Term Fertilization Contributes to Carbon Saturation in Neutral-To-Alkaline Soils but not in Acidic Soils

ABSTRACT The study investigated the adsorption of dissolved organic carbon (DOC) on Chinese soils from four long-term experiments involving five treatments: (1) no fertilization (control), (2–4) inorganic nitrogen (N), phosphorus (P), and potassium (K) fertilization (N, NP, and NPK), (5) NPK plus manure (NPKM). The results showed that DOC adsorption followed a modified Langmuir isotherm model effectively (R2 = 0.912 ~ 0.991). The maximum adsorption capacity (Q max ) (i.e. saturation deficits) generally increased with increasing soil organic carbon (SOC) due to fertilization in Luvic Phaeozem, Haplic Gypsisols, and Eutric Cambisols. However, it decreased significantly in acidic soils (Haplic Acrisols) from 15.59 g/kg for control, to 13.96, 13.03, 9.30 and 8.02 g/kg for N, NP, NPK and NPKM, respectively. Moreover, long-term fertilization, particularly with organic fertilization (e.g. NPKM), resulted in an increase of carbon (C) saturation by 1.42 g/kg (5.52%) in Luvic Phaeozem, 9.27 g/kg (44.29%) in Haplic Gypsisols, and 3.75 g/kg (27.66%) in Eutric Cambisols; however, there was a slight decrease by 1.70 g/kg (−7.49%) in Haplic Acrisols. Canonical correlation analysis (CCA) revealed that clay content and soil available iron (AFe) might be the crucial factors controlling C deficits, and subsequently, C saturation, along with current SOC. In conclusion, long-term fertilization contributed to C saturation in neutral-to-alkaline soils, but not in acidic soils. Thus, further attention should be paid to the long-term effects of fertilization on C saturation.

Insight into the interaction of tetrabromobisphenol A with sediment-derived dissolved organic carbon in a multiphase system by direct immersion solid phase microextraction

Tetrabromobisphenol A (TBBPA), a ubiquitously used commercial brominated flame retardant (BFR), has been widely detected in aquatic environments, and has aroused much attention due to its potential adverse effects on aquatic organisms. However, current research on the environmental fate and transport of TBBPA in the sediment–dissolved organic carbon (DOC)–water polyphase system is lacking. In this study, the sorption behavior of TBBPA in a water–DOC–sediment system was investigated using the direct-immersion solid-phase microextraction (DI-SPME) method, and the free dissolved concentration (Cw-SPME) and DOC adsorption concentration (CDOC) of TBBPA in water were measured by applying this DI-SPME approach. In addition, the effects of pH, ionic strength, and soluble organic concentration on the adsorption of TBBPA in the multiphase system were evaluated. The adsorption kinetics experimental results show that the adsorption behavior of TBBPA on sediments conforms to a linear model, suggesting that it could be mainly absorbed by sediments. The solid–water partition coefficient (Kd) of TBBPA was artificially reduced 1.54 times using the traditional liquid–liquid extraction method because the sorption behavior of the DOC was ignored, which could be accurately corrected using the DI-SPME method. The logKd and logKOC of TBBPA in the multiphase system were 4.12 ± 0.25 and 6.48 ± 0.25, respectively. Finally, the interference experiment revealed that the sorption behavior of TBBPA was affected by the pH, ionic strength (calcium ion), and humic acid concentration, apart from the lead ion concentration itself.

Estimation and potential ecological risk assessment of multiphase PAEs in mangrove wetlands in Dongzhai Harbor, Hainan

With the application of plastic products, phthalates now widely occur in various environmental media. A large number of ecological risk assessment experiments have only been carried out on a single medium such as water or sediment. There are few reports of ecological risk assessments based on the phase states of phthalic acid esters (PAEs) such as the free dissolved state and the dissolved organic carbon (DOC) adsorption state. In this study, the concentrations of the free dissolved state, the DOC adsorption state, and the easily released PAEs in the sediments, as well as the dissolved organic carbon release potential and their influencing factors were calculated in the Dongzhaigang water body. The potential ecological risks posed by state-of-the-art PAEs were investigated. The average concentration of six freely dissolved PAEs in water was 0.542 (0.226–1.115) μg/L, accounting for 76.3 % of the total PAEs. The PAEs with the highest concentrations in the free dissolved state were di-n-butyl phthalate (DBP, 0.383 μg/L), followed by Di(2-ethylhexyl) phthalate (DEHP, 0.094 μg/L). The average concentration of all six PAEs (∑6PAEs) adsorbed by the DOC in the water was 0.172 μg/L, accounting for 23.74 % of all of the PAEs. The DOC-adsorbed DEHP (0.148 μg/L) accounted for about 86 % of the six adsorbed PAEs. Sediment organic carbon may affect the release potential of the DOC through changing the soluble organic carbon concentration. Most types of PAEs in water posed low risk to organisms. However, DBP posed low and medium risk to algae and crustaceans, and medium risk to fish. Medium or high risk of DEHP to algae, crustaceans and fish was observed. The high ecological risk of PAEs related to sediments were only found at S13 and S14. Generally, the potential ecological risk of PAEs in sediment was more stable than that in water bodies.

Effects of Biostimulants and Fertilization on Nutrient Uptake by Grass and Composition of Soil Pore Water Versus 0.01 M CaCl2 Soil Extracts

ABSTRACT Humic substances are increasingly used as biostimulants in agriculture because of their supposed effects on nutrient uptake and crop yield. The objective of this study was to assess the effect of fulvic acid (FA) and humic acid (HA) addition with and without fertilization (N, P, K, S, and Ca) on (i) grass yield (Poa trivialis) and nutrient uptake and (ii) composition of soil porewater and 0.01 M CaCl2 soil extracts. Therefore, a pot experiment was performed using a loamy soil and a non-calcareous sandy soil. Fertilization increased N and P uptake and grass yield but there was no effect of FA or HA application (200 mg C kg−1 soil) regardless of whether N or P was the growth limiting nutrient. Nutrient availability was assessed in soil pore water samples extracted by centrifugating moist soil and by 0.01 M CaCl2 extracts of oven-dried soil. HA and FA had no effect on the availability of NO3 or ortho-P, neither in soil porewater nor in 0.01 M CaCl2 soil extracts. Fertilization led to an increase in 0.01 M CaCl2-extractable ortho-P but, remarkably, to a decrease in ortho-P and Dissolved Organic Carbon (DOC) concentrations in soil pore water samples. This discrepancy was explained by the higher ionic strength of pore water in the fertilized soils, which caused the pH to drop by 0.2 to 0.4 units and thereby stimulated adsorption of ortho-P and DOC to reactive soil minerals. Such salt-induced effects do not occur in 0.01 M CaCl2 soil extracts where the ionic strength is nearly constant.

Coupled influence of pH and dissolved organic carbon on the immobilization of phosphorus by lanthanum-modified zeolite

Wind-driven waves and currents in shallow lakes frequently trigger the resuspension of sediments in the photic layer, which is characterized with a high pH and high dissolved organic carbon (DOC) concentration. The mechanism of phosphorus-inactivating agents (PIAs) immobilizing phosphorus under the coupled influence of pH and DOC is not clarified, and the applicability of PIAs in eutrophic shallow lakes is thus still doubtful. We found that, under the coupled influence of pH and DOC, the uptake of phosphate by LMZ was affected mainly by pH at low DOC concentrations and by DOC at high DOC concentrations. A high pH (9.3) and high DOC concentration (24.7 mg/L) greatly increased the release of phosphorus from sediment to water. However, the addition of LMZ substantially reduced the P concentrations in water, mainly via capture of dissolved inorganic phosphorus. The results of the reversibility of the adsorption of phosphates and DOC showed that phosphate had much higher affinity than DOC towards LMZ. The phosphate once adsorbed on LMZ was resistant to release when exposed to conditions of either a high pH (9.5), high DOC concentration (250 mg/L) or both; i.e., only <5% of the adsorbed phosphate is releasable. Therefore, we proposed that, to avoid the coupled influence of pH and DOC in the photic layer of eutrophic shallow lakes, LMZ could be applied in multiple low doses in the season when the growth of algae is minimal (a low pH and low DOC concentration).

Poorly crystalline iron and aluminium oxides contribute to the carbon saturation and sorption of dissolved organic carbon in the soil

AbstractSoil carbon (C) saturation implies an upper limit to a soil's capacity to store C depending on the contents of silt + clay and poorly crystalline Fe and Al oxides. We hypothesized that the poorly crystalline Fe and Al oxides in silt + clay fraction increased the C saturation and thus reduced the capacity of the soil to sorb additional C input. To test the hypothesis, we studied the sorption of dissolved organic carbon (DOC) on silt + clay fractions (&lt;53 µm) of highly weathered oxic soils, collected from three different land uses (i.e., improved pasture, cropping and forest). Soils with high carbon saturation desorbed 38% more C than soils with low C saturation upon addition of DOC, whereas adsorption of DOC was only observed at higher concentration (&gt;15 g kg−1). While high Al oxide concentration significantly increased both the saturation and desorption of DOC, the high Fe oxide concentration significantly increased the desorption of DOC, supporting the proposition that both oxides have influence on the DOC sorption in soil. Our findings provide a new insight into the chemical control of stabilization and destabilization of DOC in soil.

Competitive adsorption of phosphate and dissolved organic carbon on lanthanum modified zeolite

Lanthanum (hydr)oxide-based materials are attractive as highly efficient adsorbents for phosphate removal from both sewage and lake environment. However, dissolved organic carbon (DOC) coexists in the waters and exact information is still lacking on how DOC influence the phosphate adsorption process. In this study, competitive adsorption of phosphate and DOC on lanthanum modified zeolite (LMZ) was investigated using humic acid as the representative. In LMZ, lanthanum hydroxide was shown to be the active ingredient accounting for >98% of the binding sites of both phosphate and DOC. Without competition, the maximum adsorption capacity of phosphate and DOC estimated from the Langmuir isotherm model was 52.25 and 41.32 mg/g, respectively. When coexisted, DOC did not affect the adsorption of phosphate while phosphate reduced the adsorption of DOC by ~40%. In addition, preloading LMZ with DOC had little effect on phosphate adsorption while coating with phosphate substantially lowered DOC adsorption. Furthermore, phosphate can release most of the adsorbed DOC (>60%), while DOC can not replace adsorbed phosphate (<2%). The adsorption kinetics of both phosphate and DOC was best described by the psudo-second-order model (r2 > 0.999). The adsorption of both phosphate and DOC increased with decreasing pH or increasing ionic strength. We proposed that phosphate was competitive than DOC for the ligand exchange sites of singly-coordinated hydroxyls, but DOC can be solely adsorbed onto the uncharged hydroxyls via hydrogen bonding.

Clay Minerals as the Key to the Sequestration of Carbon in Soils

AbstractResults from earlier laboratory and field experiments were interrogated for the possibilities of sequestration, or long-term accumulation, of carbon from excess greenhouse gases in the atmosphere. In the laboratory study, samples of three (top) soils dominated by kaolinite and illite (together), smectite, and allophane were examined for the adsorption and desorption of dissolved organic carbon (DOC). Adsorption and desorption of DOC were carried out on clay fractions extracted physically and after first native organic matter and then iron oxides were removed chemically. Labeled organic material was added to the soils to assess the priming effect of organic carbon (OC). In the field, changes in OC were measured in sandy soils that had been amended by additions of clay for between 3 and 17 years, both through incorporation of exogenous clay and delving of in situ clay. The laboratory experiments demonstrated that a portion of DOC was held strongly in all soils. The amount of DOC adsorbed depended on clay mineral types, including Fe oxides. Much adsorbed DOC was lost by desorption in water and a substantial amount of native OC was lost on priming with new OC. Addition of clay to soils led to increased OC. Therefore, addition of clay to soil may enhance net sequestration of C. Organic carbon close to mineral surfaces or within microaggregates is held most strongly. Carbon sequestration may occur in subsoils with unsaturated mineral surfaces. However, incorporation of carbon into macroaggregates from enhanced plant growth might be most effective in removing excess carbon from the atmosphere, albeit over the short-term.

Effect of nano-scale, reduced graphene oxide on the degradation of bisphenol A in real tertiary treated wastewater with the persulfate/UV-C process

In this study, the effect of home-made, reduced graphene oxide (rGO) nanoparticles on persulfate (PS)/UV-C oxidation of bisphenol A (BPA; 8.8 μM), an endocrine disruptor and model micropollutant, in real tertiary treated urban wastewater (TWW) was examined. Experimental results revealed that the presence of rGO induced a significant improvement in the degradation of BPA by the PS/UV-C treatment system. Fast and complete BPA removal accompanied with 44% dissolved organic carbon (DOC) abatement was achieved within 30 min at reaction conditions of 0.01 g/L rGO, 0.125 mM PS, at the natural pH of the TWW (pH = 7.5). This high performance on BPA degradation at the natural pH TWW could be attributable to the synergistic effect between the rGO nanoparticles and the PS/UV-C photochemical oxidation causing additional activation of PS and adsorption of BPA, DOC and degradation products onto the rGO surface. Radical quenching studies revealed that sulfate radicals prevailed over hydroxyl radicals. The Vibrio fischeri bioluminescence inhibition assay indicated that no toxic degradation products were formed during rGO/PS/UV-C treatment. By liquid chromatography time of flight mass spectrometry (LC-TOF-MS) analysis the formation of thirteen degradation products during PS/UV-C and rGO/PS/UV-C treatment of BPA was confirmed. This study underlined that the combined rGO/PS/UV-C treatment process could offer a sustainable, ecotoxicologically safe and kinetically attractive solution for the effective elimination of micropollutants from waters and wastewaters.

Potential of Biofilters for Treatment of De-Icing Chemicals

Organic de-icing chemicals, such as propylene glycol and potassium formate, cause environmental degradation in receiving water if left untreated, due to the high organic load resulting in oxygen depletion. Biofilters are commonly used for the treatment of biodegradable organic carbon in water treatment. This study investigated the potential for using biofilters for treating organic de-icing compounds. Lab-scale adsorption tests using filter media made of crushed clay (Filtralite) and granular activated carbon were conducted. Further, a column filtration experiment testing two different crushed clay size ranges was carried out investigating the effect of filter media depth, nutrient addition, and filtration rate. The surrogate parameter used to monitor the removal of de-icing chemicals was dissolved organic carbon (DOC). The adsorption test showed no significant adsorption of DOC was observed. The column test showed that the most active separation occurred in the first ~20 cm of the filter depth. This was confirmed by results from (1) water quality analysis (i.e., DOC removal and adenosine tri-phosphate (ATP) measurement); and (2) calculations based on a filtration performance analysis (Iwasaki model) and filter hydraulic evaluation (Lindquist diagram). The results showed that, for the highest C:N:P ratio tested (molar ratio of 24:7:1), 50–60% DOC removal was achieved. The addition of nutrients was found to be important for determining the biofilter performance.

The adsorption of dissolved organic carbon onto glass fiber filters and its effect on the measurement of particulate organic carbon: A laboratory and modeling exercise.

Particulate organic carbon (POC) represents a small portion of total carbon in the ocean. However, it plays a large role in the turnover of organic matter through the biological pump and other processes. Early on since the development of the POC measurement technique in the 1960s, it was known that dissolved organic carbon (DOC) adsorbs and is retained both on and in the filter. That retained DOC is measured as if it was part of the particulate fraction, an artifact that can cause significant overestimates of POC concentration. We set out to address the long-standing question of whether the magnitude of the DOC adsorption is affected by the quantity and quality of the dissolved organic matter in the sample. However, our results precluded an unequivocal answer to that question; nevertheless, the experimental data generated did allow us to develop and test predictive models that relate the mass of carbon adsorbed to the volume of sample filtered. The results indicate that the uptake of DOC can be predicted using an exponential model and that a saturation point is approached when approximately a half-liter of water is filtered. This model can be a valuable tool for correcting existing POC data sets that did not account for DOC adsorption. Nonetheless, this approach should not be regarded as a substitute for collecting in situ filter blanks in parallel with POC samples to prop-erly correct for this artifact.

ORCHIDEE-SOM: modeling soil organic carbon (SOC) and dissolved organic carbon (DOC) dynamics along vertical soil profiles in Europe

Abstract. Current land surface models (LSMs) typically represent soils in a very simplistic way, assuming soil organic carbon (SOC) as a bulk, and thus impeding a correct representation of deep soil carbon dynamics. Moreover, LSMs generally neglect the production and export of dissolved organic carbon (DOC) from soils to rivers, leading to overestimations of the potential carbon sequestration on land. This common oversimplified processing of SOC in LSMs is partly responsible for the large uncertainty in the predictions of the soil carbon response to climate change. In this study, we present a new soil carbon module called ORCHIDEE-SOM, embedded within the land surface model ORCHIDEE, which is able to reproduce the DOC and SOC dynamics in a vertically discretized soil to 2 m. The model includes processes of biological production and consumption of SOC and DOC, DOC adsorption on and desorption from soil minerals, diffusion of SOC and DOC, and DOC transport with water through and out of the soils to rivers. We evaluated ORCHIDEE-SOM against observations of DOC concentrations and SOC stocks from four European sites with different vegetation covers: a coniferous forest, a deciduous forest, a grassland, and a cropland. The model was able to reproduce the SOC stocks along their vertical profiles at the four sites and the DOC concentrations within the range of measurements, with the exception of the DOC concentrations in the upper soil horizon at the coniferous forest. However, the model was not able to fully capture the temporal dynamics of DOC concentrations. Further model improvements should focus on a plant- and depth-dependent parameterization of the new input model parameters, such as the turnover times of DOC and the microbial carbon use efficiency. We suggest that this new soil module, when parameterized for global simulations, will improve the representation of the global carbon cycle in LSMs, thus helping to constrain the predictions of the future SOC response to global warming.

Removal of organic matter from reservoir water: mechanisms underpinning surface chemistry of natural adsorbents

One of the key challenges in water treatment industry is the removal of organic compounds by cost-effective methods. This study evaluated the adsorptive removal of dissolved organic carbon (DOC) from reservoir water using fuller’s earth (FE) in comparison with natural (SQ) and modified quartz (MSQ) sands. The removal capacities of FE at different contact times, pH levels, adsorbent dosages and initial DOC concentrations were compared with both the quartz sands. The optimum DOC removals by FE and SQs were achieved at contact time of 60 and 30 min, pH level of 6 and 4, and at adsorbent dose of 1.5 g/150 mL and 10 g/100 mL, respectively. The adsorption capacity of FE (1.05 mg/g) was much higher compared to the MSQ (0.04 mg/g) and SQ (0.01 mg/g). Adsorption equilibrium data better fitted to the Freundlich model than to the Langmuir model, suggesting that adsorption occurred primarily through multilayer formation onto the surfaces of FE and SQ. The pseudo-second-order model described the uptake kinetics more effectively than the pseudo-first-order and intra-particle diffusion models, indicating that the mechanism was primarily governed by chemisorption. These observations were well supported by the physiochemical characteristics and charge behaviour of the adsorbents. In mass-transfer study, the results of liquid film diffusion model showed that the adsorption of DOC on FE was not controlled by film diffusion, but other mechanisms also played an essential role. This study demonstrates that FE is an effective adsorbent for the removal of DOC in surface water treatment.

Influence of physico-chemical properties of soil clay fractions on the retention of dissolved organic carbon.

This study investigated the effects of surface functional groups, cation exchange capacity (CEC), surface charge, sesquioxides and specific surface area (SSA) of three soil clay fractions (SCFs) (kaolinite-illite, smectite and allophane) on the retention of dissolved organic carbon (DOC) in soils. Physico-chemical properties of the SCFs before and after removing native carbon and/or sesquioxides were characterised, and the DOC adsorption-desorption tests were conducted by a batch method. Native organic carbon (OC)/sesquioxide removal treatments led to a small change in the CEC values of kaolinite-illite, but significant changes in those of smectite and allophane. The net negative surface charge increased in all samples with an increase in pH indicating their variable charge characteristics. The removal of native OC resulted in a slight increase in the net positive charge on soil clay surfaces, while sesquioxide removal increased the negative charge. Changes in the functional groups on the SCF surfaces contributed to the changes in CEC and zeta potential values. There was a strong relationship (R 2=0.93, p<0.05) between the Langmuir maximum DOC adsorption capacity (Q max) and SSA. The Q max value also showed a moderately strong relationship (R 2=0.55, p<0.05) with zeta potential (at pH 7). Q max was only poorly correlated with CEC and native OC content. Therefore, along with SSA, the surface charge and functional groups of SCFs played the key role in determining the adsorption affinity and hence retention of DOC in soils.

Ozone regeneration of granular activated carbon for trihalomethane control

Spatial and temporal variations of trihalomethanes (THMs) in distribution systems have challenged water treatment facilities to comply with disinfection byproduct rules. In this study, granular activated carbon (GAC) and modified GAC (i.e., Ag-GAC and TiO2-GAC) were used to treat chlorinated tap water containing CHCl3 (15–21μg/L), CHBrCl2 (13–16μg/L), CHBr2Cl (13–14μg/L), and CHBr3 (3μg/L). Following breakthrough of dissolved organic carbon (DOC), GAC were regenerated using conventional and novel methods. GAC regeneration efficiency was assessed by measuring adsorptive (DOC, UV absorbance at 254nm, and THMs) and physical (surface area and pore volume) properties. Thermal regeneration resulted in a brief period of additional DOC adsorption (bed volume, BV, ∼6000), while ozone regeneration was ineffective regardless of the GAC type. THM adsorption was restored by either method (e.g., BV for ≥80% breakthrough, CHBr3 ∼44,000>CHBr2Cl ∼35,000>CHBrCl2 ∼31,000>CHCl3 ∼7000). Cellular and attached adenosine triphosphate measurements illustrated the antimicrobial effects of Ag-GAC, which may have allowed for the extended THM adsorption compared to the other GAC types. The results illustrate that ozone regeneration may be a viable in-situ alternative for the adsorption of THMs during localized treatment in drinking water distribution systems.

Adsorption-desorption behavior of dissolved organic carbon by soil clay fractions of varying mineralogy

Soil clay minerals significantly influence the accumulation and stabilization of organic carbon (OC). However, the effect of interactions among phyllosilicate clay minerals, native OC and sesquioxides (Fe/Al oxides) on the adsorption-desorption of dissolved organic carbon (DOC) under different background electrolyte types and concentration is poorly understood. A set of batch adsorption-desorption experiments were conducted using pedogenic clays extracted from soils dominated by kaolinite-illite (Kaol-Ill), smectite (Smec) and allophane (Allo). The clay samples were sequentially treated to remove native OC and sesquioxides, and tested for adsorption-desorption of DOC under various solution conditions. All the experiments were conducted at pH7 using water extractable fraction of OC from wheat residues. DOC adsorption increased with increasing background electrolyte concentration, and the presence of Ca2+ significantly enhanced the uptake in comparison to Na+ due to a possible cationic bridging effect. Under all electrolyte conditions, the maximum DOC adsorption capacity (Qmax) (mgg−1) of the soil clay fractions (SCF) maintained the order: Allo>Smec>Kaol-Ill. A similar order was also observed when the adsorption capacities were normalized to the specific surface area (SSA) of the SCFs (mgm−2). DOC adsorption showed a positive relationship with SSA, and sesquioxides and allophanic minerals provided the largest contributions to the SSA in the SCF. Removal of sesquioxides from the SCF resulted in a decrease in SSA and thus DOC adsorption, whereas removal of native OC increased the SSA and subsequent DOC adsorption. Because this study used pedogenic SCFs which represented soils formed in different environments instead of processed clays from geological deposits, it provided realistic information about the interaction of DOC with SCF in relation to their native OC and sesquioxide contents. It also revealed the importance of Ca2+ in enhancing the carbon adsorption capacities of these SCFs.

Activated carbon selection for the adsorption of marine DOC and analysis of DOC fractionation

Adsorption on granular activated carbon (GAC) and fractionation of marine dissolved organic carbon (DOC) was investigated with the objective of mitigating RO membrane biofouling in the context of a reverse osmosis process for seawater pretreated by ultrafiltration. The behaviours of six commercial GAC compounds were compared. Batch kinetics experiments showed that 80% of DOC in seawater was adsorbed within four hours. Adsorption kinetics fitted the Ho and McKay model well, and isotherms followed the Freundlich model. GAC A and GAC F had the best adsorption capacities. For GAC A, the adsorption mechanism was mainly related to high occupation of the porous volume, whereas for GAC F, the adsorption was mainly related to electrostatic interactions. GAC A was selected for a fixed bed column experiment continuously fed with seawater as GAC F released acidic groups into the feed water. This filtration set-up enabled more than 70% of DOC to be removed from seawater. Moreover, LC-OCD analysis showed that GAC A filtration drastically reduced DOC fractions, including colloidal transparent exopolymer particles (cTEP) by 92% and neutral low molecular weight molecules by 80%, thus reducing the potential for biofouling of the RO membranes.

Attapulgite as Potential Adsorbent for Dissolved Organic Carbon From Oily Water

The adsorption capacity of attapulgite, a natural clay, for the removal of dissolved organic carbon (DOC) from oily water was investigated in a batch system. The aim of this study was to understand the mechanism associated with the removal of DOC by attapulgite. The effectiveness of attapulgite to adsorb DOC was investigated as a function of equilibrium time, initial DOC concentration, solution pH, temperature, and attapulgite concentration. Two particle sizes of attapulgite were used, granular (1 mm) and powder (0.25 mm). In most cases, the equilibrium data fit best with the Langmuir isotherm. The maximum monolayer coverage was found to be 31 mg/g for granular and 65 mg/g for powder attapulgite. The separation factor, RL, from the Langmuir isotherm and, n, the constant from the Freundlich isotherm indicated favorable adsorption. Changes in the pH of the oily water had no significant influence on the adsorption capacity. The adsorption follows the pseudo‐second order model. The governing transport mechanisms in the sorption process appear to be both external mass transfer and intra‐particle diffusion. The adsorption process was found exothermic in nature. The Langmuir isotherm model equation was adopted to design a single‐stage batch absorber for DOC adsorption onto attapulgite. The study demonstrated that attapulgite can be utilized as a potential alternative low‐cost adsorbent for the removal of DOC from oily water.

Removal of Dissolved Organic Carbon from Oily Produced Water by Adsorption onto Date Seeds: Equilibrium, Kinetic, and Thermodynamic Studies

The feasibility of date seeds as a new low-cost natural adsorbent for the removal of dissolved organic carbon (DOC) from oily produced water was investigated. The aim of this study was to elucidate the mechanism associated with the removal of DOC and to find the best equilibrium isotherms and kinetic models for DOC removal in batch adsorption experiments. The effect of various physicochemical parameters such as initial DOC concentration (18.5–93.5 mg/L), solution pH (4–9), temperature (25–45 °C), and date seeds dosages (0.5–2.0 g) was evaluated. The equilibrium stage was attained after a contact time of 120 min. The maximum DOC removal was 82 % for 93.5 mg/L of DOC concentration. The equilibrium data were well represented by the Langmuir isotherm. The maximum monolayer adsorption capacity of date seeds was found to be 74.62 mg/g. The separation factor, R L, from the Langmuir equation and the Freundlich constant, n, indicated a favorable adsorption. The kinetic studies indicated that the adsorption process follows the pseudo-second-order kinetics. The adsorption of DOC is governed by both surface and pore diffusion. The results revealed that the DOC uptake decreases when temperature and pH increases. The adsorption process has been found exothermic in nature, and the thermodynamic parameters were determined. The Langmuir isotherm model equation was adopted to design a single-stage batch absorber for DOC adsorption onto date seeds. The study demonstrated that date seeds can be considered as a promising low-cost adsorbent for the removal of DOC from oily produced water.

Dissolved organic matter release and retention in ultisols in relation to land use patterns

The application of organic fertilizer to maintain soil fertility and crop yield has been practiced for thousands of years in China. This practice improves soil carbon sequestration, due to the high level of dissolved organic matter (DOM) in organic manure. In this study, batch equilibrium studies were conducted to examine the capacity of three ultisols from areas under different land use patterns to retain dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) extracted from rape cake and chicken manure. The results showed that the amount of DOM removed or released in solution by the soil was a linear function of the initial amount added to the soil–water system; therefore, analysis of sorption isotherms was best conducted using the initial mass isotherm IM method. The ultisol retained, on average, 19.9% of the total DOC and 41.7% of the total DON in solution, suggesting that ultisol has a relatively low DOC adsorption capacity. The ultisol from a bamboo forest was found to have a higher capacity than that from a pear orchard to retain DOC and DON. The adsorption affinities of DOM according to soil type were in the following order: bamboo forest (BF)>tea garden (TG)>pear orchard (PO). These results suggested that the continuous application of high doses of organic manure, particularly rape cake, may saturate the DOC adsorptive sites, thereby permitting increased leaching of DOC and the possibility of ground water contamination. Furthermore, we note that amorphous Fe and Al oxides play an important role in the adsorption capacity of both DOC and DON in ultisols.