Micro-Phyto Combined Remediation On Heavy Metal Polluted Channel Dredged Sediment

Charactering with abundant, high moisture content and complex compose, polluted dredged sediment being randomly dumped and stored not only affect the landscape, but also may produce secondary pollution, and further cause adverse effects to the environment and human health. However, the organic matter and rich balanced nutrition contained in dredged sediment is valuable biological resources. Therefore, as with to the dredged sediment with different pollution characteristics, putting forward various bioremediation methods and utilization way can effectively realize harmless and resource recovery of dredged sediment. Selecting Yangtze river basin dredged sediment as the research object, this study analyzed and evaluated its nutrient characteristics and heavy metal pollution, for assessing the practicable of its garden utilization, and setting the goal remediation heavy metal; screening of cadmium resistant microbes and suitable plants; reinforcement effect of cadmium resistant microbes on phytoremediation was researched to ultimately build plant-microbe combined remediation system suitable for the Yangtze river waterway dredging sediment. The results of the study are as follows:1. The pH, moisture content, organic matter and available P content of Yangtze river waterway dredging sediment are moderate, with the scopes of 7.28-7.74,3.75%-28.27%, 14.21～121.84 ppm,1.88%～5.29% and 16.96～65.38 ppm respectively. Available N (67.12～87.97 ppm) and available K (2.78-20.11 ppm) are low but can consider adding extra nitrogen and potassium source while recycling use it. The dredging sediments are suffering some level of Cu, Pb and Zn pollution, but the enrichment effects are all not significant. However, Cd pollution and enrichment is serious enough to cause long-term adverse effects to environment.2. Two strains of cadmium resistant microbes screened from Yangtze river waterway dredging sediment:Bc2 is Empedobacter Brevis, Bc4 is Delftia Tsuruhatensis. The two strains can tolerate 150 and 125 mg/kg of Cd pollution respectively, absorb about 80% of the Cd in liquid medium, and promote the Cd in soil convert from stable forms to unstable forms. In addition, the optimum growth temperature of Bc2 and Bc4 are 24℃ and 37℃ respectively, the optimum growth pH range are 6.8～6.8, and the optimum carbon source are small molecule alcohol and glucose;3. Accumulation coefficient of the 14 kinds of indigenous plants taken from Yangtze river basin are proofed to be too low to remediate Cd pollution; This study selecte two kinds of Cd hyperaccumulator:Brassica juncea and Solanum nigrum L., four kinds of gardening or floricultural plants:Lolium perenne L., Elymus dahuricus Turcz., Canna indica and Medicago sativa L.. The maximum enrichment of Cd content of the six plants are 318.77 mg/kg,182.58 mg/kg,148.22 mg/kg,225.47 mg/kg,42.32 mg/kg,137.32 mg/kg, corresponding to the Cd concentration in soil is 125 mg/kg,50 mg/kg and 80 mg/kg and 80 mg/kg,50 mg/kg and 80 mg/kg, respectively; above ground biomass and Cd content are firstly increase and then decrease with the increase of the concentration of Cd in soil. The maximum absorption from high to low was Brassica juncea, Lolium perenne L., Solanum nigrum L., Elymus dahuricus Turcz., Canna indica, Medicago sativa L.4. Results of pot experiments for 2 months showed that, Among all of the plant-microbe remediation systems, cadmium absorption of ground plants from high to low are respectively:Lolium perenne L.-mixed bacteria>Brassica juncea-mixed bacteria> Brassica juncea- Bc2> Brassica juncea - Bc4> Elymus dahuricus Turcz.- mixed bacteria> Lolium perenne L.-Bc4> Lolium perenne L.- Bc2> Elymus dahuricus Turcz.- Bc4> Elymus dahuricus Turcz.- Bc2> Solanum nigrum L.- mixed bacteria> Solanum nigrum L.-Bc4> Solanum nigrum L.- Bc2. besides, the two cadmium resistant microbes can promote the growth and Cd enrichment capacity of the repair plants. Promoting effect of mixed bacteria is most obvious. The single bacterium of Bc2 plays better promoting effect on Brassica juncea, and the single bacterium Bc4 plays better promoting effect on Solanum nigrum L., Lolium perenne L. and Elymus dahuricus Turcz.