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This study was conducted to evaluate the phosphate sorption properties of eggshell (ES) and calcined ESs (C-ESs) in a high-concentration phosphate solution. The C-ESs yield decreased rapidly at 900 °C, indicating that the CaCO3 constituting the ES was converted to CaO by the high calcination temperature. The optimum calcination temperature for phosphate removal using C-ES was 900 °C. The actual sorption amount of phosphate by ES and C-ES900 was in agreement with the Langmuir isothermal sorption equation, and the maximum sorption capacities derived from this equation were 178.6 and 270.3 mg/g, respectively. The sorption rate of phosphate by ES and C-ES900 was divided into two stages: an initial fast sorption stage, followed by a slow sorption stage. The sorption of phosphate by ES was dominantly influenced by the initial pH and salt concentration, whereas C-ES900 exhibited a constant sorption capacity regardless of environmental changes. The SEM–EDS and XRD results demonstrated that phosphate was successfully adsorbed on the ES and C-SE900 surfaces. In this study, it was found that the sorption of phosphate by ES occurred via ion exchange and precipitation reactions and that the sorption of phosphate by C-ES900 was dominantly affected by precipitation. Above all, C-ES can be applied as an effective adsorbent for removing high concentrations of phosphate under a wide range of environmental conditions.

This study aimed to characterize the bacterial community of commercial potting soils with or without Listeria monocytogenes inoculation at 5–35 °C using 16S metagenomic sequencing and evaluate the effect of natural amendments on the reduction L. monocytogenes in non-sterile potting soils. An increase in the expected operational taxonomic units of each sample with or without L. monocytogenes was proportional to the increasing storage temperatures after 5 days. Biodiversity was distinct among all potting soils for Shannon and inverse Simpson indices, with the highest diversity being observed in a soil sample stored at 35 °C for 5 days with L. monocytogenes. An increase in richness and diversity of soil bacterial community structure positively correlated with less survival of the invading L. monocytogenes. Particularly, garlic extract was demonstrated as a promising soil-amendment substrate, reducing L. monocytogenes by ≥ 4.50 log CFU/g in potting soils stored at 35 °C.

This study was undertaken to investigate crop productivity, nitrogen use efficiency (AE_N, agronomic efficiency of N; ARF_N, apparent recovery fraction of N), and nitrous oxide (N2O) emission after...

Fe-impregnated biochar (Fe-BC) as high-efficiency heterogeneous Fenton catalyst was synthesized and evaluated in detail for its catalytic activity, stability and reusability under various conditions. The optimal conditions for the Fenton oxidation of methylene blue (MB) as model dye were determined as 0.075 g/L H2O2, 0.5 g/L Fe-BC for 0.1 g/L MB, which resulted in optimum Dye:Fecat:H2O2 ratio of 1:5:0.75 (on g/L basis) or [Dye]:[Fetotal]:[H2O2] molar ratio of 1:6.2:7.0 respectively. The effective degradation of MB was identified over a wider pH range, and even after four consecutive runs Fe-BC maintained above 95% MB removal rate within 3 min of treatment with low Fe release, indicating strong stability and reusability. Under the optimum Dye:Fecat:H2O2 (g/L) condition at initial pH 4, the Fe-BC achieved 99.9% removal efficiency of MB within 3 min in heterogeneous Fenton reaction (HEFR) with much less H2O2 concentration and low catalyst dosage, demonstrating its efficiency and cost-effectiveness compared to other Fenton reaction catalysts. The removal velocity of MB showed two rate steps: a fast first stage followed by a slow stage with the rate in the order of H2O2/Fe-BC ⋙ H2O2/biochar > biochar > H2O2. Overall, the developed Fe-BC is more economical with strong stability and recyclability for use in HEFR for treating recalcitrant pollutants.

Real time estimation of actual and imminent wave fields in the vicinity of ships and floating structures are important for safe and efficient operations. According to the relevant literature, three different approaches have been used practically: the use of wave buoys, ship radars (e.g. X-band and K-band radars) / satellite and ship motions. The present study employs artificial neural networks and machine learning type modelling to extend the previous research on neighboring wave field estimation to consider the relative heading between the ship and the waves. For the different cases evaluated, the proposed machine learning model showed very good prediction for relative heading. Some of the results from this study are presented in this paper., OCEANS 2021, September 20–23, 2021, San Diego, CA, USA

To improve the agricultural environment, utilization of biochar and organic materials from paddy fields gaining importance. This is because the long-term use of inorganic fertilizers aggravates the soil environment, and also because rice paddy is a major source of CH4 and N2O emissions during rice cultivation which involves continuous flooding. Recently, the application of organic materials and biochar to the soil has received increasing attention due to their potential benefits related to soil quality, crop growth, and greenhouse gas emission. This study examines the influence of biochar and straw treatments on rice growth, soil physicochemical properties, and global warming potential in the paddy field. Five treatments were applied for the study: control (Cn), inorganic fertilizer (IF), barley straw biochar (BC), barley straw (BS), and BC + BS. Soil quality after rice harvesting improved in the BC treated group. The yield components of rice were also improved in the BC + BS, compared to other treatments. These effects resulted in increased rice yield and uptake of nutrient contents in the BC + BS treatment. Total fluxes of CH4 and N2O relative to global warming significantly decreased by 37.3% and 65.2% in the BC + BS group than in the IF treatment, respectively. Consequentially, a cropping system with BC and BS is an effective strategy to improve rice productivity and soil quality and also reduce GHG emissions from paddy fields, thereby alleviating global warming.

The purpose of this study was to determine the properties of biochar prepared at higher than normal biochar production temperature and to evaluate adsorption/desorption characteristics for three commonly used dyes of different charge and molecular nature: Methylene Blue (MB), Orange G (OG) and Congo Red (CR). The switchgrass-biochar was prepared at common pyrolysis temperature of 600 °C (SB600) and higher than normal temperature of 900 °C (SB900). The results showed that the carbon content of the two biochars was similar, but most carbon in SB900 was graphitized based on FTIR and XRD observation. Dye adsorption isotherms by SB600 and SB900 was well described Langmuir model with maximum adsorption capacity of MB, OG and CR being 37.6, 8.2 and 8.0 mg/g for SB600 and 196.1, 38.2 and 22.6 mg/g for SB900, respectively. The adsorption kinetics of dyes by both biochars were well described by pseudo-second order model. In addition, intraparticle diffusion model showed that MB adsorption was predominantly by inner pore diffusion rather than by outer boundary, while OG and CR were more adsorbed by the outer boundary. These results indicated that the strong dye adsorption by SB900 compared to SB600 was due to the significantly enhanced surface area at the high pyrolysis temperature. Additionally, the greater adsorption of cationic MB by SBs than that of anionic OG and CR was attributable to the small molecular weight, favorable electrostatic property, and strong π-π interaction of the former with biochar surface as opposed to the latter. Overall, the SB900 maintained > 85% adsorption of maximum capacity even after four adsorption-desorption consecutive cycles and could be used as an effective adsorbent for cationic dye removal from wastewater.

Alkaline hydrolysis was used to develop a liquid fertilizer which was then applied to hot pepper plants in field in order to assess its potential to be used as a fertilizer. The treatments were control (Cn), developed liquid fertilizer (DLF), inorganic fertilizer (NPK), and DLF + NPK treatments. The chemical properties of the final DLF product were a pH of 10.2, TN of 2.26%, and K of 6.12%, respectively. The length and weight of the plant in hot pepper cultivation were higher in the order of DLF + NPK > NPK > DLF > Cn treatment. The fresh weight of hot pepper under DLF + NPK treatment increased by 312% compared to control. Although the DLF showed a significant increase in fruit length and fruit fresh weight in the hot pepper cultivation compared to the control, the effect of DLF treatment on plant growth was limited due to the unbalanced N-to-P ratios in the DLF. In the potting experiment, the DLF could potentially be used as a supplement to inorganic fertilizer, demonstrating that alkaline hydrolysis is a promising technique for recycling bio-hazardous materials such as infected animal carcasses into value-added liquid fertilizer.

Arctic shipping activities have been steadily increased due to global warming and economic benefit. As a result, there are more demands to estimate the ship performance in various ice conditions at the early design stage. In this paper, a CFD-DEM coupled approach was applied to estimate the ice resistance and broken ice behavior around the hull including hydrodynamic interactions. For the simulation, the moving ship in the stationary ice field was implemented using the overset grid technique. The estimated ice resistance as well as ice behaviors around the hull from the simulations were compared with model test results and underwater videos of the same vessel in a similar ice condition. The results demonstrated good agreement with model test measurements and further improvement for actual application was discussed in the paper, ASME 2021 40th International Conference on Ocean, Offshore and Arctic Engineering, OMAE2021, June 21-30, 2021, Virtual, Online

The applications of a Smoothed Particle Hydrodynamics (SPH)-based, a Finite Volume Method (FVM)-based and a Boundary Element Method (BEM)-based tools to investigate the nonlinear interactions between large waves and a submerged horizontal circular structure and to some extent a rectangular cylinder at various submergence depths in deep water conditions are presented. The main aim is to validate the Lagrangian technique based SPH tool to predict the wave-structure interaction forces under large waves. The features of typical force curves in a wave cycle, the magnitude of wave forces, and the influence of relative axis depth of the structure in deep water conditions are investigated, primarily using an open-sourced SPH tool. Simulations were carried out in 2D with one deepwater wave at multiple submergence depths. The water surface elevations are predicted at different near- and far-field locations. The time-averaged mean and the average amplitude of the horizontal and vertical forces acting on the cylindrical model at various submergence depths are plotted and then physically interpreted. The wave forces and surface elevations are compared with the available published experimental studies and CFD (both FVM and BEM) predictions. Good agreement between the SPH predictions and the measurements was obtained for the submerged body’s surface elevation and hydrodynamic forces at all submergence depths. The FVM tends to overestimate the wave forces compared to the SPH predictions and the measurements, particularly for the shallowly submerged structure when extreme wave breaking occurs. The BEM predictions are reasonable for the non-wave breaking cases., 40th International Conference on Ocean, Offshore & Arctic Engineering, OMAE 2021, June 21-30, 2021, Virtual Conference, Online

This study evaluated the characteristics and mechanism of phosphate adsorption by fly ash discharged from a biomass thermal power plant (BTP-FA) under various environmental conditions in order to increase the recyclability of BTP-FA. The phosphate adsorption properties of BTP-FA and fly ash derived from coal thermal power plant (CTP-FA) were better matched by those predicted by the Langmuir isothermal model and the pseudo-second-order model, and their maximum adsorption capacities were 62.1 and 4.1 mg/g, respectively. It was found that the adsorption of phosphate by BTP-FA was predominantly influenced by the outer boundary layer rather than the inner diffusion in the pores. The phosphate adsorption process by BTP-FA was greatly influenced by the initial pH and the BTP-FA dose. Therefore, to effectively treat phosphate using BTP-FA, the concentration and flow rate of phosphate in the incoming wastewater must be considered. The concentration of dissolved calcium from BTP-FA decreased sharply during the phosphate adsorption process compared to that in the phosphate-free solution. This was thought to be due to surface adsorption/reaction between calcium and phosphate. The SEM–EDS and FTIR results also supported the surface adsorption/precipitation reaction of Ca-P. Recycling fly ash discharged from biomass power plants as phosphate adsorbents is expected to contribute not only to waste reduction, but also to wastewater purification.

An amendment to this paper has been published and can be accessed via the original article.

Real time estimation of actual and imminent wave fields in the vicinity of ships and floating structures are important for safe and efficient operations. Historically, three main approaches have been cited in the open literatures with varying degrees of accuracies: the use of wave buoys, ship radars (e.g. X-band and K-band radars) / satellite and ship motions. This paper presents two methods to predict approaching waves using ship motions by employing artificial neural networks and machine learning. Another method based on Short Time Fourier Transform (STFT) of the ship motion data was also used for cross comparison. Both methods were tested in head sea condition only with different ship speeds and sea states. The method based on machine learning estimates the wave elevations as time series, whereas STFT gives its estimates as spectrum. Both methods gave very good results.

The objective of this study was to determine methane yields (MY) of organic wastes in biogasification facilities according to the mixing ratio of food waste/food waste leachate and sewage sludge. One biogasification facility that treated sewage sludge only was compared with three biogasification facilities treating sewage sludge and food waste. The theoretical MY was derived based on analyses of carbohydrate, fat, and protein to examine the efficiency of the biogasification facility. The average actual MY was 0.424 Sm3CH4/kg volatile solids, which corresponded to 83.7% of theoretical MY. In the case of combined anaerobic digestion (CD) mixing with food waste/food waste leachate, inhibitory factors (volatile fatty acids [VFAs], total nitrogen [TN], and organic matter contents) showed the tendency to have relatively higher values in CD facilities than in the biogasification facility treating sewage sludge only. Mean concentrations of VFAs and TN in the anaerobic digester effluent, and the organic loading rate were 406 mg/L, 3,721 mg/L, and 1.62 kg volatile solids/m3 day, respectively. The influence of anaerobic digester effluent was in charge of 10% within the influent environmental loading rate from the sewage treatment plants associated with the biogasification facilities. Analyses of the microbial community showed that a remarkable change in the structure of methanogens was directly related to different MY in each plant. In particular, Methanoculleus and Methanosaeta increased with an increasing ratio of food waste/food waste leachate to sludge, while Methanococcus and Methanosarcina decreased. In conclusion, CD showed steady operational conditions and high efficiency of MY by injecting food waste/food waste leachate into the anaerobic digester. It met the current criteria for integrated treatment of organic waste in biogasification facilities in South Korea.

This study was conducted to evaluate the effect of sequential presoaking and chlorine dioxide (ClO2) on the reduction of pathogenic Escherichia coli and Salmonella spp. in alfalfa. When unsoaked and presoaked alfalfa were exposed to 200 ppm ClO2 for 15 min, the population of E. coli and Salmonella spp. on presoaked seeds reduced more than those on unsoaked seeds by 2.07 and 1.43 log CFU g−1 (p E. coli and Salmonella spp. in alfalfa seeds immersed in water for 5 h, presoaked seeds were exposed to four different concentrations of ClO2 (50, 100, 150, and 200 ppm) for 15, 30, 45, and 60 min. The most effective condition to eliminate E. coli and Salmonella spp. from alfalfa seeds was sequential immersion in water for 5 h and 200 ppm ClO2 treatment for 1 h. After the optimal condition was applied to eight kinds of sprout seeds, the pathogens were completely inactivated in all seeds, except radish seeds. Growth of pathogenic E. coli and Salmonella spp. during sprouting after ClO2 treatment of alfalfa seeds was also completely inactivated. However, the germination rate of seeds did not significantly decrease after ClO2 treatment. In addition, ClO2 residues were not present in any sprout during 3 days of cultivation. These results demonstrated that sequential presoaking and 200 ppm ClO2 treatment is the optimal seed disinfection treatment to prevent foodborne diseases associated with sprout consumption.

The presence of perfluorooctanoic acid (PFOA) and perfluorooctanesulphonic acid (PFOS) in crops is an important consideration for food safety. The soil organic matter (SOM) content may affect the adsorption potential of PFOA and PFOS in water and soil and their subsequent uptake in crops. To better understand these dynamics, the adsorption and uptake of PFOA and PFOS in lettuce were investigated using granular activated carbon (GAC)-treated soils with varying SOM content. The adsorption potential of GAC was investigated, with maximum adsorption capacities for PFOA and PFOS calculated to be 9.091 mg g−1 and 27.778 mg g−1, respectively. These values decreased to 5.208 mg g−1 and 17.241 mg g−1, respectively, after the addition of 0.04 wt% humic acid. The average plant uptake factor (PUF) in low and high perfluoroalkyl and polyfluoroalkyl acid (PFAA)-contaminated soils with 4.0 wt% SOM was restricted to 0.353 for PFOA and 0.108 for PFOS. The PUFs were approximately two times lower than those for soil with 2.6 wt% SOM. Addition of 1 wt% GAC to the soil successfully reduced the PUF by up to 99.4%, with values of 0.006 (PFOA) and 0.005 (PFOS) in 2.6 wt% SOM-treated soil and 0.079 (PFOA) and 0.023 (PFOS) in 4.0 wt% SOM-treated soil. Although the PUF in the GAC-treated soil was drastically decreased, the PUF of the soil with 4.0 wt% SOM was at least four times higher than that with 2.6 wt% SOM. Therefore, SOM content is an important consideration in the remediation of PFOA- and PFOS-contaminated farmland soil using carbonaceous adsorbent.

This study was conducted to explore the potential capacity for the removal of heavy metals from the fly ash (FA) and bottom ash (BA) emitted by wood pellet thermal power plants. Fly ash consists of inorganic compounds such as CaSiO3, P2O5, and K2O, whereas BA shows properties very similar to the biochar derived from organic biomass. The adsorption properties of both FA and BA for Cd were described well by the Langmuir and pseudo-second-order models, and the maximum adsorption capacity of FA for Cd was 4.2 times higher than that of BA. The results indicate that FA can be applied to the treatment of wastewater that contains heavy metals over pH range from 2–6; however, BA is considered to be most effective for application with wastewater that contains heavy metals at a pH of 5–6. Study of the mechanism concluded that the adsorption of Cd by FA is dominated by the formation of Cd2SiO4 complexes by chemical reactions between CaSiO3 and Cd ions as well as via the precipitation of Cd(OH)2 in the neutral and alkaline solutions that is caused by the dissolution of K. It was found that the adsorption of Cd by BA was influenced by the binding of functional groups (C C and C OH), coupled CaCO3 dissolution-CdCO3 precipitation reaction and ion exchange between some minerals with Si and Cd ions in weakly acidic conditions. Results indicate that the FA and BA emitted from wood pellet thermal power plants have high potential for heavy metal removal, and their practical use in the purification and restoration of heavy metals could be an effective way to reduce the waste produced by power plants and clean the environment.

This study was conducted to evaluate (i) the characteristics of ammonia gas emissions from soybean cultivation soils amended with varying levels of urea and soil water, and (ii) the rate of reduction in ammonia emissions that could be obtained by applying mixed microorganisms (MM) to the urea-treated soils. The ammonia gas emissions from all treatments except the control were highest on day 2 of a laboratory-scale experiment and decreased gradually thereafter. The ammonia gas emissions from the soils increased with increasing urea and soil water contents. However, there were less emissions from soils treated with MM than those from the urea only treatment, and emissions also decreased significantly as the concentration of MM increased. In a field-scale experiment, the total cumulative emissions of ammonia from soil treated with a combination of chemical fertilizers and MM was reduced to 85.8% of that from the soil treated with chemical fertilizers only. Although we infer that MM can be used as an agent to reduce ammonia gas emissions from actual soils used for soybean cultivation, our knowledge of the processes involved in reducing ammonia emissions using microbial treatment is still limited. Consequently, further studies are required to investigate the efficient control of ammonia gas emissions from agricultural soils through the application of microorganisms.

This study is to compare biogas potentials with the theoretical methane yields of swine manure from livestock farm (LF) and in situ biogasification facilities treating swine manure. In the case of LF, theoretical methane yield based on VS and CODcr by element analysis was 0.39 Sm3CH4/kg and 30.96 Sm3CH4/ton, respectively. For the in situ biogasification facilities, theoretical methane yield based on VS and CODcr by element analysis was 0.30 Sm3CH4/kg and 8.28 Sm3CH4/ton, respectively. Theoretical methane yields based on the weight of swine manure from LF were about three times higher than those from in situ facilities (ISF). As a result, when swine manure has reached the ISF, the decrement of about 24.5–73.3% in the methane yield could be seen due to the 3–6-month stationing of swine manure in the storage tank of LF. In order to improve the biogasification efficiency of swine manure, it is important to maintain high concentration of swine manure during the collection process from LF.

This study was conducted to investigate soil quality, Chinese cabbage growth, and N2O emission after biochar application in an upland field in South Korea. Each of the barley straw biochar (BC, applied at 10 ton ha-1), inorganic fertilizer (IF, applied at N-P-K = 320-78-198 kg ha-1), and BC + IF treatment areas were separated by a control (Cn) treatment area. Soils treated with BC and BC + IF treatments had lower bulk density and higher porosity than those in the Cn treatment areas. Soil chemical properties (pH, TN, Avail. P2O5, and CEC) after biochar addition were improved. In particular, soil pH and CEC related to crop nutrient availability were significantly increased in BC areas compared to those in Cn and IF areas. Fresh weights of Chinese cabbage grown under BC, IF, and BC + IF treatment conditions increased by 64.9, 78.4, and 112.0%, respectively, over that in the Cn treatment area. Total nutrient (TN, TP, and K) uptakes among the treatment areas were, in declining order, BC + IF (14.51 g plant-1) > IF > BC > Cn. More interestingly, the BC application had a positive effect on growth of Chinese cabbage under IF application conditions, and there was a tight relationship between the effect of BC application on Chinese cabbage growth and that of agronomic IF application efficiency. Compared to the IF results, total N2O flux was lower with BC (flux decreased by 60.6%) or BC + IF (flux decreased by 22.3%) treatments. These results indicate that Chinese cabbage yield, when cultivated in soil conditions such as those in an upland field in South Korea, can be increased by application of BC or a combination of BC and IF.

Mercury adsorption characteristics of Mississippi River deltaic plain (MRDP) freshwater marsh soil in the Louisiana Gulf coast were evaluated under various conditions. Mercury adsorption was well described by pseudo-second order and Langmuir isotherm models with maximum adsorption capacity of 39.8 mg g−1. Additional fitting of intraparticle model showed that mercury in the MRDP freshwater marsh soil was controlled by both external surface adsorption and intraparticle diffusion. The partition of adsorbed mercury (mg g−1) revealed that mercury was primarily adsorbed into organic-bond fraction (12.09) and soluble/exchangeable fraction (10.85), which accounted for 63.5% of the total adsorption, followed by manganese oxide-bound (7.50), easily mobilizable carbonate-bound (4.53), amorphous iron oxide-bound (0.55), crystalline Fe oxide-bound (0.41), and residual fraction (0.16). Mercury adsorption capacity was generally elevated along with increasing solution pH even though dominant species of mercury were non-ionic HgCl2, HgClOH and Hg(OH)2 at between pH 3 and 9. In addition, increasing background NaCl concentration and the presence of humic acid decreased mercury adsorption, whereas the presence of phosphate, sulfate and nitrate enhanced mercury adsorption. Mercury adsorption in the MRDP freshwater marsh soil was reduced by the presence of Pb, Cu, Cd and Zn with Pb showing the greatest competitive adsorption. Overall the adsorption capacity of mercury in the MRDP freshwater marsh soil was found to be significantly influenced by potential environmental changes, and such factors should be considered in order to manage the risks associated with mercury in this MRDP wetland for responding to future climate change scenarios.

This study evaluated the adsorption properties of arsenic (As) by lignin biochar (LBC) decorated with Zn (Z-LBC) derived from the impregnation reaction of ZnCl2 colloid and the pyrolysis process. The carbon contents of LBC and Z-LBC were 92.8% and 80.2%, respectively. The carbon content in Z-LBC was lower than that of LBC, demonstrating that Zn was clearly deposited in Z-LBC. The surface area of Z-LBC (255 m2/g) was higher than that of LBC (244 m2/g) and showed a more well-developed pore structure. The adsorption amounts of As by pure lignin, LBC, and Z-LBC were 0.44, 1.50, and 18.3 mg/g, respectively, and Z-LBC showed a strong affinity for As. The optimal isotherm and kinetic models for predicting the adsorption of As by Z-LBC were the Langmuir isotherm and pseudo-second order kinetic model, respectively, and the maximum adsorption capacity derived from the Langmuir isotherm was 20.2 mg/g. The adsorption properties of As by Z-LBC were dominantly influenced by the initial pH and Z-LBC dose. In addition, FTIR analysis clearly showed a difference in the functional group of Z-LBC before and after As adsorption, which proved that As was adsorbed on the surface of Z-LBC. Overall, Z-LBC is derived from the impregnation reaction of the ZnCl2 colloid, and the pyrolysis process is adequately utilized as an adsorbent for As removal. However, since the amount of As adsorbed by Z-LBC is greatly affected by the initial pH and Z-LBC dose, a management plan will be necessary.

Iron-impregnated biochar (Fe-BC) was developed through one-step pyrolysis, characterized, and directly compared with Fe-impregnated activated carbon (Fe-AC) for the removal of methylene blue (MB) in a heterogeneous Fenton reaction (HFR). Fe-BC exhibited significantly higher Fe impregnation efficiency than Fe-AC at the same pyrolysis temperature of 600 °C. Analyses via X-ray absorption near-edge spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy revealed that both Fe-BC and Fe-AC contained Fe species such as Fe3O4, FeOOH, and Fe2O3, with Fe-BC having significantly more reduced Fe(II) than Fe-AC. This result is clear evidence that Fe-BC had better catalytic activity for MB than Fe-AC. The removal efficiencies of MB and total organic carbon by Fe-BC and Fe-AC prepared with optimum Fe impregnation concentration (0.25 M Fe) were 98.3 % and 46.3 %, respectively. In particular, Fe-BC removal of MB was predominantly by degradation due to the HFR, while adsorption was dominant in the case of Fe-AC. In particular, Fe-BC (0.25 M Fe impregnation) showed higher MB treatment efficiency (≥ 65.7 %) and stable release of Fe ions (

Biochar has been suggested as new adsorbent for removing heavy metals from aqueous solutions. However, adsorption nature of biochar is influenced by feedstock-specific properties. In this study, experiments were performed to characterize the effect of cation exchange on adsorption behavior of Cu and Zn in single- and binary-metal systems by rice straw biochar (RSB) made by pyrolysis at 600 °C. Result of kinetic experiment showed that the Cu and Zn in aqueous solution were rapidly adsorbed from the RSB in the first 2 h and then reached the equilibrium after 4 h. The fitting of intraparticale diffusion model showed fast Cu diffusion into boundary layer and pores of biochar than Zn. In parallel with 2.65 meq L−1 Cu and 1.79 meq L−1 Zn being adsorbed by RSB, up to 1.65 and 0.76 meq L−1 exchangeable cations were released into the solution, indicating that cation exchange could contribute 62.3 and 42.5% to Cu and Zn sorption by RSB. Langmuir maximum adsorption capacities (a) of RSB for Cu and Zn were 56.5 and 38.6 mg g−1 in single-metal system and 40.2 and 7.9 mg g−1 in binary-metal system, respectively. Overall, the results demonstrate that the Cu and Zn adsorption by RSB was closely related to the exchangeable cation. The application of RSB could be especially attractive when considering biochar with high cation exchange capacities.

The objective of this study was to evaluate adsorption characteristics of phosphate by rapid cooled basic oxygen furnace slag (RC-BOFS) through various conditions and removal rate of phosphate in small-scale constructed wetland with RC-BOFS as filter material. The phosphate adsorption by RC-BOFS was rapid in the first 0.5 h and the pseudo-second-order kinetic model fit the data better than the pseudo-first-order kinetic model. The maximum phosphate adsorption capacities of RC-BOFS under different pH were in the following order: 3.57 mg P g−1 (pH 5) > 2.47 mg P g−1 (pH 7) > 1.46 mg P g−1 (pH 9). Small-size RC-BOFS (0.8–2.3 mm) was more efficient with 23% higher phosphate adsorption than big-size RC-BOFS (2.3–4.6 mm). Characterization of RC-BOFS before and after phosphate adsorption by XRD, FTIR and SEM-EDS indicated that phosphate adsorption by RC-BOFS was dominated by metal oxide and precipitation by calcium and was closely related to the slag chemical properties. The phosphate saturation time in constructed wetland with coarse sand was predicted about 292 days, whereas the longevity of constructed wetland with adding about 25% RC-BOFS to the coarse sand can significantly increase up to 1349 days. It was concluded that the horizontal flow constructed wetland with sand 75%:RC-BOFS 25% ratio could achieve high phosphate removal rate and near-neutral pH for meeting the acceptable water quality discharge standard from water treatment plant.