Preparation Of Nano-metal Assisted Chars Derived From Solid Digestate For Degradation Of Aqueous Organic Pollutants

Solid digestate(SD),produced from the explosive growth of biogas projects which are established to sustain positive growth throughout China,is normally used as a fertilizer for crops without any further processing.Such an inappropriate application has led to a serious threat to the soil matrix and crop qualities and indirectly to human beings.In recent years,from the development and application of SD derived chars,it can be seen that a new value-added strategy of SD is gradually taking shape.This strategy can achieve the transfer of organic pollutants between phases in the adsorption,but the mineralization of the pollutants is rarely involved.In addition,there are still some drawbacks such as low removal efficiency of toxic metals,so it is far from meeting the needs of SD monetization.In this thesis,SD derived nano-metal assisted chars nanocomposites coupled with H2O2 systems were synthesized by combining"char technology","nano-technology" and "advanced oxidation technology" for efficient removal of emerging organic pollutants from wastewater,so as to upgrade the efficiency of SD monetization.The main conclusions are presented as below.1.Under experimental conditions with an initial TC concentration of 200 mg/L,20 mmol/L H2O2,0.5 g/L nanocomposite dosage,and 6 h of reaction time,SD derived nano-copper assisted biochar(Cu NPs@BC)could achieve 97.8%tetracycline(TC)oxidative degradation efficiency,which was much better than BC(31.2%)and Cu NPs(48.3%)did.It meant that the nanocomposite could achieve "1+1>2" aggregation potential effect,indicating that Cu NPs@BC could be used an effective "catalys" for H2O2 decomposition to degrade TC from wastewater.The enhancement effect was confirmed to be related to the synergistic effect between BC and Cu NPs due to the latter not only played an important role in activating H2O2 to produce·OH for TC degradation,but also released Cu(?)which strengthened the adsorption of TC.The possible degradation pathway and mechanism of TC in the Cu NPs@BC-H2O2 system were proposed by the determination of by-and end-products of TC.2.Findings showed that increase of pyrolysis temperature during BC and HDPC production led to the decrease of production rate and increased of its carbon content.HDPC produced from hydrothermal carbonization and pyrolysis had a higher surface area and pore volume than that from only pyrolysis.SD char precursors not only have differed affinity of TC,but also regulated the morphology and dispersion of the loaded Cu NPs,which affected the activation performance of the corresponding nanocomposites for H2O2.All the Cu NPs@BCs samples showed no statistically significant effect on TC adsorption,while Cu NPs@HDPC synthesized with high pyrolysis temperature enhanced the adsorption of TC.In the presence of H2O2,the Cu NPs@HDPC prepared at 700? had stronger activation ability of H2O2 and oxidative degradation rate of TC,which was reflected in the activity of well-dispersed Cu NPs.In addition,compared with granular activated carbon(GAC)with larger specific surface area and pore volume,the synthesized SD char-based nanocomposites had stronger TC affinity.Although the GAC-based nano-copper nanocomposite(Cu NPs@GAC)had well-dispersion of Cu NPs,the weak affinity led to low removal performance of TC.3.A series of Fe NPs@chars(Fe NPs@BC,Fe NPs@HC and Fe NPs@HDPC)were synthesized by an in-situ reduction method for obtaining efficient nanocomposites used in removal of TC from wastewater under As(?)co-existing condition.The results showed that Fe NPs successfully loaded on BC matrix were Fe3O4 and Fe0 by characterized with field emission scanning electron microscopy(FESEM),high resolution projection electron microscopy(HRTEM)and X-ray diffraction(XRD).Compared with the latter two nanocomposites,BC and Fe NPs,the Fe NPs@BC exhibited the best removal efficiencies of TC(100%)in the presence of As(?)(50?mol/L)under an optimum conditions of Fe NPs@BC(1.0 g/L),H2O2(10 mmol/L),and solution pH without no further adjustion.High level of As(?)inhibited the TC degradation by the Fe NPs@BC-H2O2 system due to the competitive effect of OH for As(?)oxidation and TC degradation.The above results showed that the strategy of loading Fe NPs on BC matrix maximized the value-added benefits of SD and achieved efficient removal of typical organic pollutants in binary systems4.The feasibility and applicability of hydrochar derived pyrolysis char-supported Cu NPs composite(Cu NPs@HDPC),synthesized from SD,for H2O2-led octocryclene(OC)degradation in aqueous solutions was investigated.The relatively large surface area and pore volume of the HDPC(191.4 m2/g and 0.11 cm3/g)led to a well-dispersed Cu NPs loading on its surface.The degradation efficiency of OC(50?mol/L)was 97.0%in the presence of Cu NPs@HDPC composite(0.5 g/L)and H2O2(20 mmol/L)at pH 5.6 within 4 h.This value was significantly higher than those in Cu NPs@BC(62.4%)and the integrated HDPC-Cu NPs(79.7%)under the same conditions.The·OH resulting from the redox reaction between the Cu species and the H2O2 on the HDPC surface,is the predominant factor responsible for the OC degradation in the solution.The·OH formation was also facilitated by a single-electron transfer from the HDPC surface,where the Cu NPs@HDPC composite with its C-OH functional group promoted the decomposition of H2O2.Seven oxidation by-products of the OC were included.These findings contribute to the development of another approach for cost-effective wastewater treatment by adding value to SD.In short,the above researches expand the scope of utilization of SD.The char-based nano-metal nanocomposites synthesized in this thesis could not only enhance the adsorption of multiple pollutants,but also play a vital role in reduction of the targets through advanced oxidation technology.This thesis provides a theoretical foundation for clarifying the function of SD-chars by studying the interaction between SD derived chars and nano-metals.