Effects Of Pomelo Peel Biochars On The Adsorption Of PCP And Phosphorus In Wetland Soils

Biochars are carbon-enriched and porous materials, which are produced by thepyrolysis of biomass in anaerobic or limited oxygen condition. Biochars can improvesoil textures, contribute positively to plant biomass and reduce environmental risk oforganic pollutants and heavy metals. Biochars often have the high specific surfacearea and micro-porosity, which act as efficient sorbents for a range of organiccontaminants and heavy metals. Thus, it is expected that biochar has significanteffects on the mitigation, transformation and bioavailability of these pollutants in theenvironment.In the study, biochars (BC300and BC600) derived from pomelo peel by theoxygen-limited pyrolysis temperatures of300°C and600°C, and the characteristics ofpomelo peel biochars were evaluated using elemental, specific surface area, electronmicroscopy scanning and Fourier Transform Infrared Spectroscopy (FTIR). Thesorption of pentachlorphenol (PCP) and phosphorus using pomelo peel biochars fromwetland soils in Liaohe Estuary and Jiaozhou Bay were studied, and the pyrolysistemperature，the amount of biochars，reaction temperature and pH were discussed.The preliminary sorption mechanism of PCP and phosphorus in soils amended withBC600was studiedbased on the adsorption kinetics and thermodynamics. Theapplication effects of BC600input on soils and environmental effects on remediationof contaminated soils would be confirmed. The research results have theoreticalsignificance and application prospects for protecting the soil environment andimproving soil quality. The main results are presented as follows:(1) Two types of pomelo peel biochars (BC300and BC600) have high C content anda large number of organic functional groups. Compared with BC300, the yield ofBC600decreased, and BC600possessed larger pore volume and higher specificsurface area. With the increase of the pyrolytic temperature，the aromaticity increasedwhereas the polarity decreased.(2) Compared with soils without biochar amendment, the application of BC300andBC600in soils could enhance the sorption of the PCP, and the adsorption capacity ofPCP was enhanced with the increase of the adding amount of BC300and BC600. The adsorption of PCP in soil amended with BC600greater than the soil amended withBC300. However, the phosphorus adsorption capacity of the soil amended withBC300and BC600was inhibited, and sorption capacity of phosphorus decreased withthe increase of the adding amount of BC300and BC600. The adsorption ofphosphorus in soil amended with BC600greater than the soil amended with BC300.(3) The thermodynamic parameters were calculated by Gibbs equation. It wasindicated that the adsorption of PCP in soil amended with BC600was spontaneousand exothermic reaction, and the adsorption of phosphorus in soil with BC600amendment was spontaneous and endothermic reaction. The sorption capacity of PCPin soil amended with BC600decreased with the solution pH increasing. Sorption ofphosphorus first increased rapidly, then leveled off and finally increased quickly withthe increase of the solution pH.(4) The phosphorus adsorption of soil with BC600amendment was affected by theinitial phosphorus concentration (Co). The zero equilibrium phosphorus concentration(EPCo) in wetland soils from Liaohe Estuary and Jiaozhou Bay which amended withBC600were0.155mg/L and0.229mg/L, respectively. When Co<EPCo, the soilsdesorbed phosphorus, or else the soils adsorbed phosphorus. The sorption ofphosphorus in soils with BC600amendment was enhanced with the increase of theinitial phosphorus concentration (Co).(5) The time-resolved curves of pentachlorophenol and phosphorus adsorption onBC600-amended soil followed the pseudo-second-order kinetic model. Theintra-particle diffusion is not the only rate limiting step, but also other kinetic modelsmay control the rate of adsorption. The adsorption behavior fitted well with the Linearand Freundlich sorption isotherm equation, respectively. The adsorption process ofpentachlorophenol and phosphorus by pomelo peel biochar-amended soil may involvenot only physical but also chemical sorption processes.