Co-pyrolysis with pine sawdust reduces the environmental risks of copper and zinc in dredged sediment and improves its adsorption capacity for cadmium

β-tricalcium phosphate enhanced biomineralization of Cd2+ and Pb2+ by Sporosarcina ureilytica HJ1 and Sporosarcina pasteurii HJ2

Microbiologically induced CaCO3 precipitation (MICP) has been proposed as a potential bioremediation method to immobilize contaminating metals. In this study, carbonate mineralizing bacteria HJ1 and HJ2, isolated from heavy metal contaminated soil, was employed for Cd2+ and Pb2+ immobilization with or without β-tricalcium phosphate addition. Compared with the only treatments amended with strains, the combined application of β-tricalcium phosphate and HJ1 improved the immobilization rates of Cd and Pb by 1.49 and 1.70 times at 24 h, and the combined application of β-tricalcium phosphate and HJ2 increased the immobilization rates of Cd and Pb by 1.25 and 1.79 times. The characterization of biomineralization products revealed that Cd2+ and Pb2+ primarily immobilized from the liquid phase as CdCO3 and PbCO3, and the addition of β-tricalcium phosphate facilitated the formation of Ca4.03Cd0.97(PO4)3(OH) and Pb3(PO4)2. Also, the calcium source was related to the speciation of carbonate precipitation and improved the Cd and Pb remediation efficiency. This research demonstrated the feasibility and effectiveness of MICP combined with β-tricalcium phosphate in immobilization of Cd and Pb, which will provide a fundamental basis for future applications of MICP to mitigate soil heavy metal pollutions.

Stabilization of heavy metals in solid waste and sludge pyrolysis by intercalation-exfoliation modified vermiculite

Increasing amounts of solid waste and sludge have created many environmental management problems. Pyrolysis can effectively reduce the volume of solid waste and sludge, but there is still the problem of heavy metal contamination, which limits the application of pyrolysis in environmental management. The intercalated-exfoliated modified vermiculite (IEMV) by intercalators of sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide were used to control the release of Cd, Cr, Cu, Zn and Pb during pyrolysis process of sludge or solid waste. The retention of heavy metals in sludge was generally better than that in solid waste. The IEMV by octadecyltrimethylammonium bromide as the intercalator calcined 800 °C (STAB-800) was the best additive for heavy metal retention, and the retention of Cr, Cu and Zn was significantly better than that of Pb and Cd. Cr, Cu, Zn and Pb were at low risk, while Cd had considerable risk under certain circumstances. New models were proposed to comprehensively evaluate the results of the risk and forms of heavy metals, and the increasing temperature was beneficial in reducing the hazards of heavy metals by the addition of STAB-800. The reaction mechanism of heavy metals with vermiculite was revealed by simulation of reaction sites, Fukui Function and Frontier Molecular Orbital. Thermal activation-intercalated-exfoliated modified vermiculite (T-IEMV) is more reactive and had more active sites for heavy metals. Mg atoms and outermost O atoms are the main atoms for T-IEMV to react with heavy metals. The Cr, Cu and Zn have better adsorption capacity by T-IEMV than Pb and Cd. This study provides a new insight into managing solid waste and sludge and controlling heavy metal environmental pollution.

New insights into the sustainable use of co-pyrolyzed dredged sediment for the in situ remediation of Cd polluted sediments in coastal rivers

The remediation of Cd-polluted sediment in coastal rivers is essential because of its potential hazards to river and marine ecosystems. Herein, a co-pyrolysis product of contaminated dredged sediment (S@BC) was innovatively applied to cap and immobilize Cd-contaminated sediment in coastal rivers in situ, and their remediation efficiencies, mechanisms, and microbial responses were explored based on a 360 d incubation experiment. The results showed that although S@BC immobilization and capping restrained sediment Cd release to the overlying water, S@BC capping presented a high inhibitory efficiency (66.0% vs. 95.3% at 360 d). Fraction analysis indicated that labile Cd was partially transformed to stable fraction after remediation, with decreases of 0.5%- 32.7% in the acid-soluble fraction and increases of 5.0%- 182.8% in the residual fraction. S@BC immobilization and capping had minor influences on the sediment bacterial community structure compared to the control. S@BC could directly adsorb sediment mobile Cd (precipitation and complexation) to inhibit Cd release and change sediment properties (e.g., pH and cation exchange capacity) to indirectly reduce Cd release. Particularly, S@BC capping also promoted Cd stabilization by enhancing the sediment sulfate reduction process. Comparatively, S@BC capping was a priority approach for Cd-polluted sediment remediation. This study provides new insights into the remediation of Cd-contaminated sediments in coastal rivers.

Efficient removal of Cd(II) and Pb(II) from aqueous solution using biochars derived from food waste

Massive amount of food waste has been generated annually, posing a threat to ecological sustainability and the social economy due to current disposal methods. Urgent action is needed worldwide to convert the traditional pathway for treating food waste into a sustainable bioeconomy, as this will significantly benefit food chain management. This study explores the use of pyrolysis to produce different types of food waste biochars and investigates their adsorption capabilities for removing Cd2+ and Pb2+ in aqueous solution. The results indicated that co-pyrolysis biochar from fresh food waste and rice husk (FWRB) exhibited superior adsorption performance for Cd2+ (61.84 mg·g-1) and Pb2+ (245.52 mg·g-1), respectively. Pseudo-second-order kinetics (0.74 ≤ R2 ≤ 0.98) and Langmuir isotherms (0.87 ≤ R2 ≤ 0.98) indicated that the immobilized Cd2+ and Pb2+ on biochars were mainly attributed to the chemisorption, including precipitation with minerals (e.g., carbonates, silicates, and phosphate), complexation with functional groups (-OH), cation exchange (-COO-), and coordination with π-electrons. Furthermore, FWRB demonstrated reduced EC and Na content in comparison to food waste digestate biochar (FWDB) and food waste digestate co-pyrolysis with sawdust biochar (FWSB), with levels of Cd and Pb falling below China's current guideline thresholds. These findings suggested that co-pyrolysis of fresh food waste with rice husk could be applicable to the recycling of food waste into biochar products for heavy metal stabilization in contaminated water and soils.

In-depth analysis of the effect of catalysts on plasma technologies for treatment of various wastes

Energy security and waste management are gaining global attention. The modern world is producing a large amount of liquid and solid waste as a result of the increasing population and industrialization. A circular economy encourages the conversion of waste to energy and other value-added products. Waste processing requires a sustainable route for a healthy society and clean environment. One of the emerging solutions for waste treatment is plasma technology. It converts waste into syngas, oil, and char/slag depending on the thermal/non-thermal processes. Most of all the types of carbonaceous wastes can be treated by plasma processes. The addition of a catalyst to the plasma process is a developing field as plasma processes are energy intensive. This paper covers the detailed concept of plasma and catalysis. It comprises various types of plasma (non-thermal and thermal) and catalysts (zeolites, oxides, and salts) which have been used for waste treatment. Catalyst addition improves gas yield and hydrogen selectivity at moderate temperatures. Depending on the properties of the catalyst and type of plasma, comprehensive points are listed for the selection of the right catalyst for a plasma process. This review offers an in-depth analysis of the research in the field of waste-to-energy using plasma-catalytic processes.