Modification Of Pyrolytic Biochar And Toxicity Evaluation

Pyrolytic biochar, a novel environmental material, though its removal of organic pollution and altering soil property have been massively reported previously, the adsorption mechanism of antibiotics and toxicity assessment have not been thoroughly investigated. In this work, the ubiquitous rice husk biochar was modified by methanol to enhance tetracycline (TC) adsorption capacities, and the adsorption mechanism for TC antibiotics was systematically investigated. Furthermore, the effect of environment conditions and underlying adsorption mechanism between modified biochar and TCs were also elucidated. In addition, the toxic mechanism of water extractions were investigated in view of chemical composition of biochars produced under different pyrolysis conditions. This research would provide the important information for the practical utilization and massive production of biochar in soil remediation and TC contaminated aquatic environment. The main contents and conclusions of this research are as follows:1. Experiment results demonstrated that the adsorption affinity of biochar changes with TC structure. The different substituent group in sorbate can change ionic forms involved in adsorption process under various pH value. Compared with tetracycline and chlorotetracycline, oxytetracycline exhibits stronger adsorption on the biochar, which is ascribed to OH groups of oxytetracycline, indicating H-bonding between functional groups of the TCs and the carbon-based material play an important role.2. The modified biochar exhibited an enhancement of adsorption capacity compared with Ori-char. X-ray photoelectron spectroscopy (XPS) suggested the main factor responsible for the improvement of TC adsorption is the change in O-containing groups after modification, which can form stronger H-bonding and n-π EDA interactions with TCs. Furthermore, the continuously operated fixed bed experiment suggested that the modified biochar has a great potential application not only in industrial wastewater but also in surface water containing low concentrations of TC.3. The adsorption behavior of TC on biochar is influenced by environmental factors, and acidic condition is more favorable for the adsorption process. In addition, low concentration (1.0mg/L) of humic acid and divalent cations (Mg2+and Ca2+) can cause inhibitory effects on biochar adsorption.4. The Typha angustifolia-derived (TA-derived) biochar exhibited toxicity to soil microorganism whereas rice husk and sawdust have no effect on microbial growth. The toxicity increased with production temperature during slow pyrolysis. Thus rice husk-derived and sawdust-derived biochars can be directly utilized in soil remediation.5. In comparison with gel permeation chromatography (GPC) and XPS results, it can be inferred that toxic nature of TA-derived biochar water extracts toward microbes may be attributed to some low molecule weight substances with carboxyl and hydroxyl homologous series.6. Biochars prepared in low temperature can release more organic carbon、 nitrogen and phosphorus source, which effectively boosts soil fertility and improve crop productivity. In contrast, biochar produced in high pyrolysis temperature can release more alkali metal and increase soil pH to reform acid soil.