[Effect of co-planting of Sedum alfredii and Zea mays on Zn-contaminated sewage sludge].

The sewage sludge produced in Guangzhou and other cities contains heavy metals such as Zn which exceeds the national standard for agricultural use and should be taken into consideration. A phyto-treatment system consisted of metal hyperaccumulator Sedum afredii Hance and low-accumulating corn was exploited to phytoextract metals from sludge, in order to reduce heavy metals in sludge and meanwhile to stabilize the sludge and gain innocuous agricultural products. The two plants were co-cropped directly on the sludge plots, the plant biomass and metal uptake were determined as well as the changes of the treated sludge. A pot experiment was conducted to study the interaction mechanisms between the two plant roots. The results of the experiment in plots showed that the efficiency of the phyto-extraction of Zn/Cd by S. alfredii was significantly improved by co-planting and Zn content in S. alfredii reached 9 910 mgx kg(-1), 1.5 folds of that in the mono-crop. Meanwhile the produced corn grain was conformed to the national standards for foods or feeds concerning heavy metals and the treated sludge was biologically stabilized. The results from the pot experiment studying the interaction mechanisms showed that corn roots, separated from S. alfredii with a mesh barrier, decreased pH in the sludge solution, increased DOC and resulted in higher Zn/Cd concentration than that of S. alfredii mono-crop, which caused more Zn/Cd transported to the S. alfredii side and then enhanced the uptake of the heavy metals by the hyperaccumulator.