Heavy metal pollution in soil–crop systems has attracted great attention globally, caused by rapid urbanization and intensive industrialization. The research aims to investigate the environmental quality of the agricultural production area in Taizhou City, a typical economic region that is along the Yangtze River in the Southeast of China. A total of 370 sampling sites were chosen, with 370 soil, rice (Oryza sativa L.) and wheat (Triticum aestivum L.) samples collected, respectively, for measuring and analyzing the status, spatial distribution and pollution level of different heavy metals. The mean values of soil Cr, Pb, Cd, As and Hg were 66.78, 32.88, 0.23, 8.16 and 0.16 mg/kg, which were lower than the risk control standard values (RCV). However, the mean values of Pb, Cd and Hg were 1.25-, 1.77- and 2-fold larger than their soil background values (SBV) due to the intensive anthropogenic activities. The average content of Cd in rice exceeded its food safety limiting values (FCV) by 0.05 mg/kg, and the average contents of Pb in rice and wheat both exceeded the relevant FSV by 0.42 and 0.186 mg/kg, respectively. In addition, the maximum As and Cr contents in rice and wheat could be 0.13, 0.46 mg/kg and 0.63, 3.5 mg/kg larger than the relative FCVs in certain areas. Most of the high-value areas of soil and crop heavy metals were mainly located in Xinghua City, Taixing City and Jiangyan District, which had a similar distribution pattern with local industries or anthropogenic activities. The heavy metal pollution in soils and crops was found to be inconsistent, as 8.94% of the arable land possessed lightly metal pollution, while 3.18% of the area of rice and 4.0% of the area of wheat suffered severe pollution, with excessive accumulation of Cr, Pb and Cd. Based on the heavy metal pollution assessment of soil–crop systems, approximately 83% of the study area possessed medium or higher environmental quality, which was preferable for agricultural production. Our results implied that the spatial distribution and pollution level of the heavy metals in soil–crop systems were significantly influenced by industrial activities, followed by agricultural sources, transportation emissions and so on. Therefore, continuous monitoring and source control of heavy metals, especially for Cr, Pb and Cd, should be conducted to ensure the regional environmental quality and food security.

The accumulation of lead (Pb) in sediments from anthropogenic activities possesses serious threats to ecosystem and human health. Recycling of sediments for agricultural plantation is politically encouraged while their applications are still limited due to the high cost and poor environmental compatibility of existing remediation techniques. Electro-kinetic remediation (EKR) enhanced with electrode polarity inversion (EPI) strategy was an effective technique for Pb decontamination from low permeable matrix. However, lacking full understanding of the interactions between Pb and sediment constituents restricts the wide application of this technology. In this study, an innovative approach based on model simulation and feasibility analysis was proposed for guiding the pilot-scale remediation and recycling of Pb-polluted sediments. Initially, a specific two-dimensional (2D) model that consisted of transport-reactive modules was designed, with assumptions of operating parameters and reaction equations. A three-step sequential non-iterative split-operator computation scheme was implemented to simulate the electrochemical variables of EKR. The predicted results indicated that the electrode reversal should be conducted around 48 h to avoid pH polarization and Pb precipitation. In addition, 12 h was suggested to be the preferable EPI duration as the shortest time required (226 h) to remove the target level of sediment Pb. Afterwards, a comparative study was performed between the experimental and simulated data to validate the model accuracy. Good agreements were achieved in spite of minor discrepancies which suggested the designed model could approximately predict the performance of EPI-enhanced EKR. Finally, the feasibility analysis was conducted based on a parametric study. In consideration of energy utilization efficiency, concentration of 220 mg/kg was determined as the lower limit of safety threshold for Pb removal. In this level, the maximum energy consumption (EC), materials, electrolyte post-treatment, and labor expenditure for sediments remediation were 110 $/m3, 450 $/remediation unit, 2 $/L, and 300 $/remediation unit, respectively, and the agricultural eco-environment was safe during the recycling process. We believed that the methodology and results in this study could be employed as an useful tool to support the designation of full-scale EKR and the reutilization of contaminated sediments.

For aquaculture wastewater with low ammonium nitrogen concentration, combining the carrier adsorption and biological nitrogen removal processes can maximize their respective advantages. Functional ceramsite that has excellent ammonium nitrogen adsorption performance and excellent biocompatibility was the key to the moving bed biofilm reactor (MBBR) adsorption—shortcut simultaneous nitrification and denitrification (shortcut SND) process. Our group prepared a high-strength lightweight ceramsite that met those requirements. In this study, we applied functional ceramsite in MBBR to cope with low-concentration ammonium aquaculture wastewater. The findings show that utilizing functional ceramsite as a filler was conducive to the adhesion of microorganisms. The biofilm has a minimal effect on the adsorption capacity of ceramsite due to the existence of pores on its surface. Our study further examined the ${\mathrm{NH}}_4^{+}$-N adsorption mechanism of bio-ceramsite. The Freundlich adsorption isotherm model and the quasi-second-order kinetic model had better fitting effects on the ${\mathrm{NH}}_4^{+}$-N adsorption process. The adsorption of bio-ceramsite to ${\mathrm{NH}}_4^{+}$-N was an endothermic process that included physical and chemical adsorption. Furthermore, the results of adsorption thermodynamics suggested that bio-ceramsite has an affinity for the adsorption of ${\mathrm{NH}}_4^{+}$-N. Consequently, this functional ceramsite can be a promising option for MBBR to improve nitrogen removal from aquaculture wastewater.