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A phosphorus-bearing product S-PAL obtained from nutrient-rich wastewater was reused as ameliorant for Cu, Pb and Cd immobilization in contaminated soil with three different rates (1%, 5% and 10% w/w). The 0.01 mol/L CaCl2 -extractability of metals significantly reduced with increasing rate of PAL and S-PAL in the first 7-day immobilization and insignificantly changed after 14-day immobilization. Compared with PAL, the lower metal extractability was observed after S-PAL addition. The BCR sequential extraction results showed that both of amendments were beneficial to transform acid soluble fraction to residual fraction. The XRD patterns of soil samples after immobilization evidenced that the formation of metal-bearing phosphate precipitates and the combination between functional groups such as Si-OH and metals played a key role for metal immobilization by S-PAL and PAL. Dominant phyla across all samples were Fusobacteria, Proteobacteria and Actinobacteria, and the relative abundance of Fusobacteria decreased under S-PAL treatment. The pH-dependent leaching test indicated that the metal release at a defined pH was not affected by the presence of PAL. Compared with S-PAL, the metals amended by PAL in soil were easier to release at acidic pH since the combination between functional groups and metals instead the formation of new metal-bearing precipitate.

Zinc is known as an essential element of human life. However, excessive zinc discharge into water and soil causes water pollution, leading to serious health issues such as septicemia, meningitis and iron-deficiency anemia. Here, a novel material made of struvite-supported diatomite was obtained from eutrophic water treated by mesoporous MgO-modified diatomite. This material was applied for zinc remediation in aqueous solutions and contaminated soils to test the reuse of P-containing products. Struvite-supported diatomite was characterized by field emission scanning electron microscopy and X-ray diffraction. Results show that the maximum removal efficiency of Zn(II) from wastewater streams reached 90.54% at an initial pH of 5 and struvite-supported diatomite dosage of 0.3 g/L. Moreover, the X-ray diffraction patterns of precipitates after Zn(II) sorption show that the combination between zinc and the phosphate group played a key role for zinc removal in solution. For Zn-contaminated soils amended with 10% struvite-supported diatomite, available Zn decreased by 65.38% and acid soluble Zn decreased by 56.9% after 56 days.

A waste–struvite/diatomite compound (MAP@Dia) recovered from nutrient-rich wastewater treated by MgO-modified diatomite (MgO@Dia) was provided to immobilize lead in aqueous solution and contaminated soil. The mechanism and effectiveness of lead immobilization was investigated, and the pHstat leaching test and fixed-bed column experiments were carried out to assess the risk of MAP@Dia reuse for lead immobilization. The results showed that MAP@Dia were effective in immobilizing lead in aqueous solution with adsorption capacity of 832.47–946.50 mg/g. The main mechanism of Pb immobilization by MAP@Dia could be contributed by surface complexation and dissolution of struvite followed by precipitation of hydroxypyromorphite Pb10(PO4)6(OH)2. Lead(II) concentration reduced from 269.61 to 78.26 mg/kg, and residual lead(II) increased to 53.14% in contaminated soil when the MAP@Dia application rate was 5%. The increased neutralization capacity (ANC) and lower lead extraction yields in pHstat leaching test in amended soil suggested 5 times of buffering capacity against potential acidic stresses and delayed triggering of “chemical time bombs.” The results of column studies demonstrated that amendment with MAP@Dia could reduce the risk of lead and phosphorus (P) leaching. This study revealed that MAP@Dia could provide an effective solution for both P recycling and lead immobilization in contaminated soil.

In this study, struvite-humic acid loaded biochar/bentonite composite (HMCC), a recovery product of humic acid, nitrogen and phosphorus from biogas slurry, was prepared and used for simultaneous control of Zn(II) and antibiotic resistance genes (ARGs) pollution in manure-soil. The adsorption performance and mechanism of Zn(II) on HMCC were first studied in aqueous solution. The adsorption data fitted well to the Freundlich isotherm model, and the primary mechanisms of Zn(II) absorbed by HMCC involved the formation of Zn3(PO4)2·4H2O and humic acid-metal complex. The changes of Zn(II) content, antibiotic resistance genes (ARGs) and bacterial communities during the remediation of Zn(II) contaminated manure-soil were analyzed simultaneously. With HMCC amendment, the content of bio-available Zn(II) (bio-Zn) efficiently reduced from 847.4 mg/g to 739.2 mg/g and the total relative abundance of ARGs accordingly decreased by 37.18%. RDA analysis indicated that soil pH and bio-Zn were the main contributors to the fluctuations of soil ARGs. Spearman correlation analysis revealed that the potential hosts for ARGs mainly belonged to the phylum Actinobacteria. In addition, HMCC addition increased the diversity of bacterial community but significantly reduced the abundance of an antibiotic resistant bacteria-Actinobacteria. It is the first study to demonstrate the feasibility of HMCC as an environmentally friendly amendment to immobilize Zn(II) and mitigate the dissemination of ARGs in manure-soil.