With the fast development of industrialization and urbanization, large amounts of organic pollutants are released into the natural environment. The efficient elimination of organic pollutants is thereby crucial for environmental pollution treatment and human health. In the last decades, photocatalytic degradation of persistent organic pollutants has attracted multidisciplinary interest because of its simple operation on a large scale. However, the whole processes for the photocatalytic degradation of organic pollutants are still unclear. In this perspective, the contribution of reactive species, the contribution of photocatalysts, the analysis of intermediate products, the charge transfer and fast carrier recombination are discussed on biochar-based photocatalysts.
Biochar has been reported to mitigate short-term methane (CH4) emissions from paddy soil. Currently, CH4 mitigation by biochar has primarily focused on the abundance and variations of methanogens and methanotrophs, and changes in their activities during methane production and consumption. However, long-term effects of biochar on methane mitigation from paddy soil remain controversial. This review overviewed the existing mechanisms for CH4 mitigation as a result of biochar application. In addition, the two existing opinions on the long-term CH4 mitigation effect upon biochar application were highlighted. Combining the already explored mechanisms of fresh biochar on CH4 mitigation from paddy soil and a novel discovery, the potential mechanisms of biochar on long-term methane emission response were proposed. This review also revealed the uncertain responses of biochar on long-term CH4 mitigation. Therefore, to achieve carbon neutral goal, it is important to further explore the mechanisms of long-term CH4 mitigation under biochar application.
In view of the risks induced by the inhibitory effects of applying impracticably large amounts of sewage sludge biochar (SSB) to the alkaline soil, this field study investigated the influence of moderate biochar amendments (0, 1500, 4500, and 9000 kg/hm2) on corn growth, alkaline soil properties, and the uptake of potentially toxic elements (PTEs). The results showed that applying more SSB would decrease the ammonium nitrogen concentration and increase the available phosphorus and potassium concentrations, which inhibited corn plant growth because of high background nutrient levels of the alkaline soil. When the alkaline soil was amended with 1500 kg/hm2 SSB, the dry weight of 100 niblets increased from 32.11 g in the control to 35.07 g. There was no significant variation in the total concentration of PTEs in the soil. The concentrations of Mn, Ni, Cu, and Zn in niblets decreased from 5.54, 0.83, 2.26, and 27.15 mg/kg in the control to 4.47, 0.62, 1.30, and 23.45 mg/kg, respectively. Accordingly, the health risk from corn consumption was significantly reduced. Furthermore, the combination of SSB and fertilizer improved corn growth and reduced the risk of consumption of PTEs. Therefore, considering the increase in corn fruit yield and the decrease in consumption risk, applying 1500 kg/hm2 of biochar to alkaline soils is a realistically achievable rate, which can broaden the utilization of SSB for remediation of different types of soil.
Biochar has been proposed as a soil amendment to reclaim salt-affected soils. However, the evaluation of the different biochar types in these soils is essential due to the significant variation among biochar feedstocks. In this study, biochars from sugarcane bagasse (SB), orange bagasse (OB), and corncob (CB) were applied alone and in the presence of gypsum (G) to test their potential to remediate a highly degraded saline-sodic soil in Brazil´s Northeast region. For that, we conducted a laboratory column-leaching experiment and a greenhouse study. After the column-leaching test, we analyzed the sodium adsorption ratio (SAR), the electrical conductivity of the saturation extract (ECe), the concentrations of major ions, and the exchangeable sodium percentage (ESP). Maize plants were grown in the leached soil in a greenhouse. Sugarcane- and corncob-derived biochars were more efficient than gypsum in reducing the soil salinity, bringing the indicators below threshold values, and optimizing soil reclamation time. Soil ECe, SAR, and ESP were reduced to 3.42 dS m−1, 1.64 (mmolc dm−3)0.5 and 4.86%, respectively, in the SB treatment; and to 3.19 dS m−1, 0.88 (mmolc dm−3)0.5 and 2.53%, respectively, in the CB treatment. Orange bagasse biochar did not effectively reduce the salinity indicators. All biochar treatments improved seed germination and plant growth. The SB, CB, SBG, and CBG treatments increased plant height (478–558%), shoot mass (783–983%), and root mass (386–500%), respectively. Therefore, the application of SB and CB is an effective alternative to remediate saline-sodic soils and to reduce the impact of soil salinity in the environment.
At present, many researchers have studied the modification of biochar and explored the adsorption of cadmium by modified biochar. The adsorption capacity of cadmium for general modified biochar is about 30–150 mg/g. The new biochar (BM) we studied greatly improves the adsorption effect of cadmium in water, and the maximum adsorption capacity of cadmium can reach 400 mg/g, so we tried to apply it to the passivated cadmium in polluted farmland soil. This paper discusses the mechanism of BM passivation of heavy metal cadmium in soil and its protective effect on crop growth. The study found that: (1) the content of cadmium in wheat was 3.98 mg/kg in the soil with BM800. The addition of BM800 reduced the cadmium content of wheat by 75.43% compared with the blank control group; (2) BM contains special iron-containing functional group (–Fe–OOC–, –Fe–R–COOH, –Fe–R–OH, etc.) and aromatic structure C=Cπ, and these structures can react with cadmium to form stable complexes (C=Cπ–Cd, (FeO)2Cd, (Fe–RO)2Cd, etc.); (3) there are special mineral crystal structures XiFeYjOk in BM. XiFeYjOk can react with cadmium to form Cd–XiFejOk. Cd–XiFejOk can stably exist in biochar, and can provide more adsorption sites, which strengthens the adsorption and passivation of cadmium in soil by BM.
Great progress has been made in recent years to alleviate the heavy metal pollution, but the development of low-cost and eco-friendly adsorbents is still challenging. In this work, MgO-loaded biochar, as a potential adsorbent, was successfully synthesized via copyrolysis of corn straw and MgCl2∙6H2O at 600 ℃ and used for heavy metal immobilization in aqueous solution and contaminated soil. Nemerow pollution index and potential ecological risk index methods were also used to assess the potential ecological risk of the metals in soil after remediation. The results showed MgO-laden biochar exhibited a much higher Cd2+ adsorption capacity than the pristine biochar. Pseudo-second-order and Langmuir/Langmuir–Freundlich equations could describe the adsorption kinetics and isotherm of Cd2+ well. The maximum adsorption capacity of Cd2+ could reach to 1058.8 mg g−1 estimated by Langmuir–Freundlich equation. Cd2+ adsorption on MgO-laden biochar composite mainly involved the hydrolyzation of MgO, ionization of Mg(OH)2 and precipitation of Cd2+ and OH−. In addition, complexes with oxygen-containing groups and adsorption by Mg(OH)2 also enhanced Cd immobilization. The result of soil-leaching test showed that the concentrations of TCLP-leaching (Toxicity Characteristic Leaching Procedure) Cd and Pb reduced by 22.4% and 29.0%, respectively, after 4% of MgO-laden biochar amendment, and the integrated pollution index and potential ecological risk decreased by 28.9% and 28.5%, respectively. These results suggest that MgO-laden corn straw biochar may be promising for application as a low-cost adsorbent for wastewater treatment and soil remediation.
Diclofenac is an ecotoxic pharmaceutical compound affecting both aquatic and terrestrial ecosystems even at low concentrations. In this study, batch adsorption experiments were conducted to remove sodium diclofenac (SD) from aqueous solutions using rice hull biochar (RHB) adsorbents. Higher SD removals were obtained with increasing initial SD concentration, RHB dosage, contact time, and decreasing initial pH. Isotherm studies revealed that Langmuir isotherm best fitted the experimental data with the highest coefficient of determination for both pH 2 (R2 = 0.9827) and pH 7 (R2 = 0.9460). For kinetic studies, the pseudo second-order model gave R2 = 0.9999 for both pH 2 and pH 7. SD removals reached up to 97% at pH 2 and up to 80% at pH 7. Higher SD removals were achieved at solution pH lower than the adsorbent pHpzc since electrostatic repulsion was eliminated. Fourier-transform infrared analysis showed the major involvement of C=O in the adsorption process. This study demonstrated the potential of using agricultural residues such as rice hulls for the treatment of wastewater contaminated with pharmaceutical compounds.
Peat remains the primary constituent of horticultural growing media in professional use. However, use of peat in horticultural growing media results in greenhouse gas emissions and biodiversity loss due to excavation of natural peatlands. Biochar is gaining attention as a sustainable alternative to peat use in horticulture. This study examined the potential of biochar produced from a particular type of sawmill residue, as a partial replacement for peat in horticultural growing media. Five treatments including peat only, biochar only, biochar and peat in 1:1, 1:3, and 3:1 (V/V) ratios were assessed. The addition of biochar into growing media increased the pH and EC of the medium. However, physical properties (air-filled porosity and water holding capacity) were negatively affected with the increase in biochar content in the medium. According to the germination test results, biochar significantly improved germination and the shoot and root length of germinated seeds of cress, lettuce and tomato when compared to peat-only and biochar-only treatments. The inclusion of biochar in 25–50% volume ratio improved plant growth parameters compared to peat-only and biochar-only media. Results obtained from this study suggest that sawmill residue offers great potential as a feedstock for biochar production and inclusion of biochar has positive effects on seed germination and plant growth that might compete with modified peat.
Many Hawaiian agricultural soils are acidic with low-nutrient retention; therefore, organic soil amendments are often used to improve soil properties and increase yields. Amendments can be incorporated for annual crops, but perennial orchards need surface application to avoid damaging surface roots. Pot trials compared responses to incorporated (IBC) or surface-applied (SBC) combination of hardwood biochar and chicken manure compost (4% v/v of each amendment) added to an Andisol and Oxisol. Soil pH was increased by 0.4–1.1 units in IBC and by 0.2–0.5 for SBC in the 0–10 cm soil layer. Both SBC and IBC increased soil total N, extractable P, Ca and Mg in the 0–10 cm soil layer. Soil pH, total C and extractable Ca were also higher in the 10–20 cm soil layer for IBC soil, indicating movement and/or leaching of amendments. Chinese cabbage biomass was 18–70% higher in the IBC and 14–47% higher in the SBC than that in the unamended soil, while papaya biomass was 23% and 19% higher in SBC and IBC, respectively. There was a greater response in the more acidic Andisol soil, with larger improvements in soil pH, plant nutrient uptake and root biomass than the Oxisol. Surface application was as effective in increasing plant growth as the incorporated amendment, providing evidence for farm scale assessment. Biochar and compost are recommended for use in tropical soils, and surface application may be beneficial to annual and perennial crops.
Previous research showed that biochar addition facilitated composting and elevated nutrient retention. However, few of these studies explored bacterial structure and abundance in the compost mixture and biochar additive. Thus, this study aims to distinguish bacterial communities in both compost and bamboo biochar (BB) additive. Results indicated that the dynamics of nutrient contents in compost and BB samples were in a similar pattern, although there were lower levels of nutrients and metals (i.e., Cu and Zn) in BB additives. The total number of operational taxonomic units (OTUs) in both compost and BB additives peaked on day 7 and then gradually reduced during composting. There was more abundance of bacteria in compost, whereas the diversity of bacteria was more in BB additives. Furthermore, the dominant bacteria in compost and BB samples were distinct at the different stages of composting. The Firmicutes steadily decreased in compost samples (from 34.78% to 7.65%), while it was the dominant phylum in BB additives during the whole composting period. Furthermore, Ruminofilibacter, Pseudoxanthomonas, and Actinomadura were the most abundant genera in compost samples than Pseudoxanthomonas, Azoarcus, and Paenibacillus in BB additives at the final stage of composting. Results from this study could provide a theoretical reference for the sound performance of biochar-added composting.