The Preparation Of Sewage Sludge Based Biochar And Its Application In Adsorption Of Nitrogen And Phosphorus

This study investigated the physical and chemical properties as well as the adsorption capacity of ammonia nitrogen(NH4+-N) and total phosphorus(TP) of the sludge based biochar(SBC). Firstly, the optimum pyrolysis conditions of sludge were found through the single factor test. Secondly, the physical properties and capacity of NH4+-N, TP adsorption by unfermented sludge based biochar(SBC) and fermented sludge based biochar(FSBC) were investigated. In order to improve the properties and adsorption capacity of SBC, different proportion of fly ash or corn straw were added into the sludge, respectively, to analysis the impact of inorganic and organic material on biochar by mixed with sludge and to make sure the optimum mixing proportion. In addition, in order to study which components facilitated the adsorption capacity of biochar, Si O2, Fe2O3, Al2O3, Ca O, Mg O were doped with sludge, respectively. Finally, three kinds of modification methods were adopted to enhance the recovery rate of SBC. The research contents were as follows:(1) The results found out the best pyrolysis condition, which were heating 700 ℃ for 120 min. On this condition, SBC has the highest values of SBET and pore volume, which reached to 75.04 m2/g and 0.12 cm3/g, respectively. The iodine and methylene blue adsorption value of SBC were 540.51 mg/g, 10.47 mg/g, respectively.(2) It was found that the specific surface area of FSBC was higher than that of SBC, indicating fermentation was conducive to the development of pore structure. The results of NH4+-N, TP adsorption indicated that the adsorption was accorded with Langmuir isotherms and the kinetic equations belonged to pseudo-second-order kinetics. The adsorption capacity of NH4+-N among three carbon materials was CAC >FSBC >SBC. For TP, the result was FSBC >SBC >CAC. The adsorption capacity of NH4+-N, TP by FSBC was better compared with SBC. The maximum adsorption capacity of NH4+-N by FSBC can reach 8.62 mg/g, and the TP could reach 5.10 mg/g. When applied for the authentic wastewater, the removal ability of NH4+-N, TP were CAC >FSBC >SBC. The TP removal efficiency by CAC and FSBC was 31 % and 27 %, respectively. And the NH4+-N removal efficiency by CAC and FSBC was 7 % and 4 %, respectively. The NH4+-N, TP adsorption capacity by FSBC was closed to the CAC, indicating that FSBC was a promising low cost materials for NH4+ and TP adsorption in future.(3) When the mass ratio of sludge and fly ash was 1:1, NH4+-N adsorption capacity can reach to 28.20 mg/g, and the TP adsorption capacity was of 26 mg/g, which was far higher than that of SBC. Adding fly ash could improve the NH4+-N and TP adsorption capacity of biochar, but the SBET and methylene blue adsorption value of the SFBC were decreased. The addition of fly ash decreased the content of organic in sludge, thus going against the pore development of the SBC. By adding of the main components of fly ash, we found that Fe2O3, Al2O3, Ca O inhibited the sludge pyrolysis. The results showed that the addition of ferric oxide, calcium oxide could greatly promote the cation exchange capacity as well as NH4+-N, TP adsorption capacity of SBC.(4) when the sludge:straw(dry mass) = 2:1, the physical properties of SBC was the best compared to other groups, of which the SBET, pore volume and the methylene blue adsorption value were 157.52 m2 / g, 0.1800 cm3/g, and 14.80 mg/g, respectively. Corn straw improved the content of organic matter in sludge, and had a synergistic effect in the process of pyrolysis, thus promoting the porosity of SBC. In simulated wastewater, the TP adsorption capacity of SSBC-5 was the highest, and reached to 10.76 mg/g. The NH4+-N adsorption capacity of SSBC-2 was up to 12.2895 mg/g in both simulated and authentic wastewater. For authentic wastewater, SSBC-2 had the highest removal rate of NH4+-N and TP. Especially, the NH4+-N removal rate could reach 65.37 %.(5) The SBET and pore volume of SBC were modified by the third magnetization method, which increased by 100.68 m2/g, 0.2030 cm3/g, respectively. The saturation magnetic intensity was up to 24.26 emu/g. In simulated wastewater, the trend of NH4+-N was MBC-3 >MBC-2 >MBC-1 > SBC; the trend of TP adsorption ability was MBC-1 >MBC-2 > MBC-3 >SBC. In authentic wastewater, the result of NH4+-N, TP removal rate was MBC-3 >MBC-2 >MBC-1 >SBC. The maximum NH4+-N and TP removal rate of MBC-3 was 68.70 %, 17.74 %, respectively. With a magnet collecting the MBC after adsorption, recovery rate could reach to more than 70 %, the recovery rate of MBC-3 was the highest, which could reach to 86.5 %.