Biochar applied to soil under wastewater irrigation remained environmentally viable for the second season of potato cultivation

Migration and availability of Ni and Cd in industrial soils under different leaching conditions: Insights from DGT and DIFS models

Rainfall runoff can mobilize heavy metals in industrial soils, posing environmental risks. The mobility and distribution of heavy metals in different industrial soil layers are often overlooked. This study employed dynamic leaching experiments in layered soil columns with DGT (the diffusive gradients in thin films) measurements and DIFS (DGT-induced fluxes in soils and sediments) model to describe the migration, availability, and resupply ability of metals at different depths in surface and deep soil columns of industrial soils. Results showed significantly higher available concentrations (CDGT and CSoln) of Ni and Cd in surface soils compared to deep soils, likely due to the differences in soil physiochemical properties (contamination, pH, and soil texture). Continuous leaching promoted the migration of available Ni and Cd in surface soils. Maximum values of RNi (0.79-0.91) and RCd (0.75-0.80) were observed in the top layer (0-4 cm) of the surface soil, consistent with the trends of RFe. Combined DGT and DIFS model analysis implied higher potential availability and resupply of Ni and Cd in surface soil columns. These findings highlight the importance of considering dynamic leaching effects on heavy metal transport, availability, and release in industrial soils.

Engineered biochars for simultaneous immobilization of as and Cd in soil: Field evidence

Agricultural soil contamination by potentially toxic elements (PTEs) such as arsenic (As) and cadmium (Cd) poses a serious threat to food security. Immobilization serves as a widely used approach for the remediation of PTEs contaminated soils, nevertheless, the long-term effectiveness for the simultaneous immobilization of both cations and oxyanions remains a challenge. In order to effectively enhance the synergistic immobilization effect of soil As and Cd contaminated by multiple elements and improve the ecological environment of farmland. In this study, a typical polluted tailings area farmland was selected for situ immobilization experiments, and biochar was prepared from cow manure (CMB), rice straw (RSB), and pine wood (PWB) as raw materials. On this basis, the pristine biochar was modified with ferric chloride (F), potassium permanganate (K), magnesium chloride (M), and aluminum chloride (A), respectively. Furthermore, the immobilization effect of modified biochar on As-Cd and the stress effect on soil respiration were investigated. The results showed that CMB and RSB reduced the bioavailability of heavy metals, potassium permanganate has strong oxidizing properties, and the strong oxidability of potassium permanganate stimulated the generation of more oxygen-containing functional groups on the surface of biochar, thereby enhancing the adsorption and complexation effect of modified materials on As and Cd. Among them, the extracted Cd concentration of Diethylenetriamine pentaacetic acid (DTPA) in KCMB and KRSB in 2020 decreased by 8.23-43.12% and 9.67-35.29% compared to other treatments, respectively. Meanwhile, the KCMB and KRSB treatments also reduced the enrichment of As and Cd in plant tissues. In addition, the dissolved organic carbon (DOC) content in KCMB treatment was relatively high, and the carbon stability of the material was weakened. Simultaneously, the soil respiration emission of KCMB treatment was increased by 5.63% and 11.93% compared to KRSB and KPWB treatments, respectively. In addition, the structural equation also shows that DOC has a large positive effect on soil respiration. In summary, the KRSB treatment effectively achieve synergistic immobilization of As-Cd and provide important guiding significance for green and low-carbon remediation of polluted farmland.

Barley Straw Biochar and Compost Affect Heavy Metal Transport in Soil and Uptake by Potatoes Grown under Wastewater Irrigation

Wastewater can supplement freshwater in agriculture; however, it contains toxic heavy metals such as cadmium, chromium, and lead that are hazardous to humans and the environment. We investigated the effects of barley straw biochar, green and table waste compost, and their mix on heavy metal transport in soil and uptake by potatoes (Solanum tuberosum L.) irrigated with synthetic wastewater for two years. In both years, amending soil with compost significantly reduced (p ≤ 0.05) cadmium uptake in potato flesh, skin, roots, and stems; zinc uptake in potato skin and roots; and copper uptake in potato flesh due to increased soil cation-exchange capacity, dissolved organic carbon, and soil pH. Co-amending the soil with compost and 3% biochar significantly reduced (p ≤ 0.05) the bioavailability of cadmium, copper, and zinc in the contaminated soil. Relative to the non-amended soils, soil amendment with biochar, compost, and their mix affected neither the transport of chromium, iron, and lead in the soils nor their uptake by potatoes. It was concluded that amending soil with barley straw biochar and/or compost produced from city green table waste could be used to improve the safety of wastewater irrigated potatoes, depending on the biochar application rate and heavy metal type.

Feedstock type drives surface property, demineralization and element leaching of nitric acid-activated biochars more than pyrolysis temperature

Nitric acid activation (NA-A) effects on the surface properties, mineral phases and element compositions of biochars produced from four feedstocks at three temperatures were evaluated. NA-A increased biochar thermal stability, but its effect on ash content and surface area was feedstock-dependent, with ash content in manure pellet biochars less affected due to a high quartz content. Apart from the manure pellet biochars and the sawdust biochar produced at 400 °C, NA-A decreased the surface area of biochars by up to 100% due to reduced pore volume. Nitric acid significantly leached elements such as potassium from biochars due to protonation and their reactions with several mineral phases, such as sylvite, on the biochars (p < 0.05). This study shows that mineral phases and element compositions of nitric acid-activated biochars were driven more by the feedstock type than the pyrolysis temperature and the derived biochars would be poor adsorbents.

Effect of site hydrological conditions and soil aggregate sizes on the stabilization of heavy metals (Cu, Ni, Pb, Zn) by biochar

Biochar is a popular material that would effectively immobilize heavy metals in soil, which can greatly decrease the health risk of heavy metals. Although many previous studies have studied the immobilization of heavy metals by biochar, the influence of hydrological conditions on the immobilization effect is still not clear. This paper carried out column experiments to study the effect of fluctuating groundwater table on Cu, Ni, Pb, Zn distribution and speciation with the addition of biochar from pyrolysis of swine manure. Experimental results showed that biochar could significantly decrease the leaching toxicity of Cu and Ni by 24.4% and 44.7% respectively, while the immobilization effect of Pb and Zn was relatively insignificant. The average reduction percentage of bioavailable Cu was 14.5%, 39.5% and 33.3% in the unsaturated zone, fluctuating zone and saturated zone respectively, showing the better immobilization effect in the fluctuating zone and saturated zone. The residual fraction of heavy metals increased significantly after the addition of biochar, and the increase of residual fraction was larger in small soil aggregates. This study helped illustrate the influence of hydrological conditions and soil aggregate sizes on the stabilization effect of heavy metals by biochar, which could be used to guide the remediation process of sites contaminated by heavy metals.

Fuel, thermal and surface properties of microwave-pyrolyzed biochars depend on feedstock type and pyrolysis temperature

We evaluated the fuel, thermal and surface properties of twelve biochars produced from three lignocellulosic (canola straw, sawdust, wheat straw) and one non-lignocellulosic feedstock (manure pellet) pyrolyzed at three temperatures using a microwave. Regardless of feedstock type, increasing pyrolysis temperature progressively reduced the abundance of -OH functional group and yield, but increased pH and thermal stability of biochar. Gross calorific values (GCV), carbon stability, and degree of aromaticity of biochars derived from lignocellulosic feedstocks increased with increasing temperature due to decreased elemental oxygen content. However, high ash content in the non-lignocellulosic feedstock retarded its thermal degradation, producing biochars with low GCV. The specific surface area of biochars was low, with the highest value of 43 m² g^-1 achieved for sawdust biochar produced at 500 °C. We conclude that the fuel, thermal, and surface properties of the biochars were dependent on the feedstock type and pyrolysis temperature.