Study On The Technology Of In-Situ Remediation By Carbon Adsorbent Of Contaminated Sediment

In the water treatment project, sediment remediation is necessary and can not be replaced.Sediment is the main reservoirs of water pollutants (heavy metals, nutrients, POPs),it is the internal source of secondary pollution.The technology which uses carbonaceous repair agent as in situ capping technology of covering materials is being developed and gradually applied in the field of sediment restoration, it relies on the strong adsorption capacity of carbonaceous adsorbent, to adsorb and fix the pollutants in sediments, thus reducing the bioavailability of pollutants. This paper takes the sediment contaminated by POPs as the research object, using six kinds of adsorbents as sediment remediation agent, with polyethylene (PE) passive sampling membrane to evaluate the effects. In laboratory, in situ remediation of polluted sediment static simulation experiment was perfomed, repairing kinds of pollutants of polycyclic aromatic hydrocarbons (PAHs), benzene series and phthalic acid esters (PAEs).Repairing effects and mechanism are studied. Meanwhile at a tributary of the Po River in Shenyang, in-situ coverage repairing experiment was conducted and the treatment effects were studied. The research conclusions are as follows:Analysis of adsorbent physicochemical properties and surface characterization results show that:compared with the power plant ash (Liaocheng power plant ash:2.90m2/g, Donghai power plant ash 7.96m2/g) and ash (13.05m2/g) repair agent, activated carbon adsorptions have bigger surface area (coconut shell granular activated carbon:309.25m2/g, shell granular activated carbon:190.95m2/g, powdered coconut shell activated carbon:1522.95m2/g), micropores and mesopores accounted for the main contribution(micropores all take more than 90%).The results of infrared spectroscopy show that biomass power plant ash and plant ash carries with polar groups (halogen groups, etc.), and characteristic absorption of saturated alkanes, aromatic and aliphatic ether appeared on activated carbons, it can be assumed that biomass power plant ash and plant ash may have strong adsorption and fixation ability for more polar pullutants, while the activated carbons may have strong adsorption and fixation ability for less polar pullutants.Laboratory static simulation experiment result indicates that the six kinds of repairing agent show very good effect of adsorbing and fixing for PAHs.At the time when added repair agents for 2-4 months, PAHs pore water concentrations decreased the fastest, and at 4 months pore water concentrations decreased more than 65%,10 months they came up to more than 90%, treatment effectiveness ranking:coconut shell granule activated carbon> shell granule activated carbon>powdered coconut shell activated carbon>plant ash>Donghai power plant ash> Liaocheng power plant ash.The governance effect of PAEs showed that:activated carbon restoration agents governance effect are better than that of power plant ash and plant ash, because the activated carbon have larger surface area, and their surface carries fewer polar functional groups; power plant ash and plant ash gradually slowed down in 2 months in absorbing PAEs. After 10 months, coconut shell activated carbon particles has the best effect for absorbing PAEs,its pore water concentrations decreased 96.11 percent. Teatment effectiveness ranking:coconut shell granular activated carbon>shell granular activated carbon> powdered coconut shell activated carbon> plant ash> Liaocheng Power Plant Ash> Donghai power plant ash.The governance effect of benzene series showed that:after 2 months of treatment, power plant ash has a huge advantage to absorb benzene, the concentration dropped sharply, the pore water concentrations of benzene reduction rates were 71.70% and 69.84%, far higher than the activated carbon repair agent; but 4 months later, the adsorption speed dropped sharply, while activated carbon repair agent maintained fixation and adsorption of benzene; 10 months later, the fixation efficiency of Liaocheng and the Dong hai power plant ash on the benzene were 85.31% and 87.44%, lower than that of granular activated carbon (99.95%) powdered coconut shell activated carbon(97.33%) and coconut shell activated carbon particles (93.21%).Second order kinetic equation can well fit the PAEs in different adsorption agent on the adsorption process, the R2> 0.95, the R2 of Elovich kinetic equations are between 70.59%-95.10%. The test results show that the adsorption behavior of PAEs in the adsorbent, there is obviously a two reaction processes, four months before, adsorbent absorbed adsorption very fast, and after 4 months, it decreased gradually, and begin to reach adsorption equilibrium state.The Elovich equation fitting results show that plant ash and power plant ash required a short time to reach balanced condition while activated carbon adsorbents required longer time.In field experiment, the difference of repairing effect of coconut shell activated carbon and activated carbon shell between each sampling point is large, appearing the phenomenon of pollutant concentrations at a certain point of the sudden high or sudden low. The reason is that the activated carbon density is small, difficult to stabilize covering on the surface of the sediment, though it has been taken certain measures, difficult to stop rivers within the physical impact. The repair effect of coal based activated carbon is the best,it has the highest removal rate of all kinds of pollutants, which of phthalic acid esters (PAEs) removal rate reached 99.09%. The reason is coal based activated carbon has relatively more developed gap structure, strong adsorption capacity, at the same time, it has high density and high chemical stability, so it can be covered on the surface of the river sediment continuously steadily, and it’s more suitable for on-site repair engineering.