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Phytoextraction using hyperaccumulating plants is generally time-consuming and requires the cessation of agriculture. We coupled chelators and a co-cropping system to enhance phytoextraction rates, while allowing for agricultural production. An experiment on I m3 lysimeter beds was conducted with a co-cropping system consisting of the hyperaccumulator Sedum alfredii and low-accumulating corn (Zea Mays, cv. Huidan-4), with addition ofa mixture of chelators (MC), to assess the efficiency of chelator enhanced co-crop phytoextraction and the leaching risk caused by the chelator. The results showed that the addition of MC promoted the growth of S. alfredii in the first crop (spring-summer season) and significantly increased the metal phytoextraction. The DTPA-extractable and total metal concentrations in the topsoil were also reduced more significantly with the addition of MC compared with the control treatments. However, mono-cropped S. alfredii without MC was more suitable for maximizing S. alfredii growth and therefore phytoextraction of Zn and Cd during the autumn-winter seasons. No adverse impact to groundwater due to MC application was observed during the experiments with three crops and three MC applications. But elevated total Cd and Pb concentrations among subsoils compared to the initial subsoil concentrations were found for the co-crop + MC treatment after the third crop.

S. occidentalis can be used in pharmacology and vegetation restoration. A pot experiment was conducted to study the effects of biochar and mycorrhizal fungus inoculation on plant growth and heavy metal accumulation. The mycorrhizal infection rate was increased by apple branch biochar but decreased by coconut husk iron-modified biochar. Conversely, soil pH was not affected by mycorrhizal inoculation but was increased by biochar. Compared to the uninoculated control, the combination of apple branch biochar and mycorrhizal inoculation significantly increased the growth of stems, leaves and roots by 226.46%, 163.15% and 86.00%, respectively. The application of apple branch biochar increased the root Pb content, while root Cd, Cr, Cu and Fe were decreased by 36.30%, 13.63%, 3.09% and 7.66%, respectively. Furthermore, the content of all elements in the stems and leaves also decreased. The application of iron-modified biochar alone increased the content of all the elements in the roots by 4.23-109.33%. But their contents in stems and leaves were decreased by iron-modified biochar and mycorrhizal inoculation alone. The combination of biochar and mycorrhizal inoculation most effectively promoted plant growth, enhanced heavy metal uptake by the roots and produced a barrier effect that reduced the transfer of heavy metals from the roots to the shoots. This might constitute a feasible means of promoting the safe utilization of S. occidentalis in phytoremediation.

High concentrations of heavy metals and organic pollutants in municipal sewage sludge are key factors limiting its use in agriculture. The objectives of this study were to decrease the heavy metal and polycyclic aromatic hydrocarbon concentrations in sewage sludge by phytotreatment and to determine, in a field experiment, whether co-planting is more effective than using a mono-crop of Sedum alfredii. Four treatments were used in the plot experiment: no sludge, no plants, S. alfredii and co-planting S. alfredii and Alocasia marorrhiza. The results showed that co-planting produced tubers and shoots of A. marorrhiza that were suitable as a safe animal feed and good organic K fertilizer, respectively. Co-planting was more effective than mono-planting at reducing concentrations of total Zn and diethylenetriaminepentaacetic acid (DTPA)-extractable Zn, Cd, and Cu in the sludge. Co-planting decreased the concentrations of DTPA-extractable heavy metals and benzo[a]pyrene (B[a]P) in the sludge significantly compared with the unplanted sludge. Decreases of 87, 75, 85, 31, and 64% were obtained for B[a]P and DTPA-extractable Zn, Cd, Cu, and Pb, respectively, compared with the fresh sludge. These results indicate that co-planting can reduce significantly the environmental risks associated with heavy metals and B[a]P in sewage sludge for further disposal.

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