The effects of various copper (Cu) concentrations on the antioxidative system in the roots of Medicago sativa were explored. The results indicated that the Cu content of the roots reached a value of 854 μg g−1 DW at 10 μm Cu and a value of 4415 μg g−1 DW at 100 μm Cu, suggesting that M. sativa has better ability to tolerate and accumulate Cu than other Cu‐bioaccumulators, and is a potential plant for phytoremediation. Treatment with Cu resulted in a significant increment in the levels of H2O2, O2˙− and OH˙. The reduced form of ascorbate and glutathione reached a peak at 30 μm Cu, and was followed by a sharp depletion to a lower level than that of the control. In contrast, the levels of the oxidised forms of ascorbate and glutathione showed a progressive increment with increasing Cu concentrations, suggesting that the antioxidant system was unable to cope with Cu stress at higher Cu levels. Under the Cu concentrations tested, the activity of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) increased at lower Cu concentrations, and then decreased, reaching a maximum at 30 μm of Cu for APX and GR, at 10 μm for CAT, whereas the activities of guaiacol peroxidase (POD, EC 1.11.1.7) were gradually increased with increasing Cu concentrations. PAGE analysis of superoxide dismutase (SOD, EC 1.1.5.1.1) revealed that one band is a Mn‐SOD and five bands are identified as Cu, Zn‐SOD, whereas Fe‐SOD isoforms were not found in the roots of alfalfa. Cu at 10–100 μm increased the intensity of constitutive isozymes of CAT, APX and POD, whereas it decreased the intensity of isozymes of glucose‐6‐phosphate dehydrogenase (G6PDH, EC 1.1.1.49) significantly. The activities of lipoxygenases (LOX, EC 1.13.11.12) were gradually augmented with increasing Cu concentrations, demonstrating that LOXs are probably involved in production of lipid hydroperoxides and superoxide anion. There was a continuous and pronounced enhancement in the activity of esterase (EST, EC 3.1.1.1) in roots treated with 10–30 Cu μm, whereas EST activity in roots exposed to above 30 μm Cu declined, suggesting that EST plays a protective role under lower Cu concentrations stress.

In order to study the reducing and reusing of petrochemical residual sludge and solve the technical problem of traditional anaerobic digestion, the contrast research was carried out between the mesophilic (30 ı C) and thermophilic (60 ı C) anaerobic digestion. The result showed that the efficiency of thermophilic digestion was twice as big as that of mesophilic digestion. When sludge dosage increased, the concentration of volatile fatty acid rose sharply and pH value decreased correspondingly. When the reaction became stable, the concentration of volatile fatty acid began to drop and the corresponding pH value began to rise gradually. At each sludge dosage, alkalinity dropped first and then increased with the reaction carried on. In a different sludge dosage, the fluctuation of pH, volatile fatty acid, and alkalinity under the thermophilic condition was less than that under the mesophilic condition by a different sludge dosage. Through the experiment of sludge digestions, the optimizing technical conditions are as follows: biochemical reaction of residual sludge input rate: 10%; retention time: 10 days at a high temperature of 60 ı C by full agitation.