The Effects Of White-Rot Fungi On Lignin Biodegradation And Heavy Metals Inactivation In Sewage Composting

In this study, compost experiments were conducted with sewage sludge and rice straw as the main raw material, and four kinds of disposal methods were designed: compost without white-rot fungi and adding 1%, 2%, 5% white-rot fungi to the compost. The purposes of this study were mainly focused on the change of physical, chemical indicators, the form of heavy metals in the compost and the degradation rate of hemicelluloses, celluloses, lignin, through which in order to answer: l)whether the white-rot fungi could reduce the days when the compost were maturated and improve the efficiency composting; 2)whether the white-rot fungi could improve the degradation rate of the lignocellulose; 3)whether the white-rot fungi could do help for the stabilization of heavy metalsThe first part reported the temperature, pH, organic matter, seed germination rate and humus as the main technological indicators, and the quality and efficiency of composting with the white-rot fungi were discussed. The second part showed the results of the content of hemicelluloses, celluloses, lignin before and after composting in order to find out whether the white-rot fungi is able to improve the degradation rate of the lignocellulose. The third part measured the change of the forms of heavy metals during the composting, in order to judge whether the white-rot fungi could contribute to the stabilization of heavy metals.The main research results are as follows:(1) The high-temperature period was lengthened by 1 -2 days when inoculated with white-rot fungi, and thus the maturation period was successfully shortened. Treatments of adding 2% white-rot fungi and 5% white-rot fungi went into stable period earlier than others by 4-8 days.(2) The seed germination indicator was rising during the composting, and the seed germination indicator of the adding white-rot fungi treatments were higher than that of without white-rot fungi. The time required for 50% seed germination indicator were 36, 32, 28, and 28 days for without white-rot fungi and adding 1%, 2%, 5% white-rot fungi treatment, respectively.(3) The inoculation of white-rot fungi speeded up the degradation of organic matter at high temperature phase, and reduced the time of maturity. The contents of (HA+FA) and HA of the treatments with white-rot fungi increased sharply because of adding the white-rot fungi at 8-12th day of composting. The HA content of 2%,5% white-rot fungi declined sharply from 24th day of composting, showing that the compost quality became worse.(4) White-rot fungi contributed little to the degradation of hemicelluloses, celluloses, on the contrary, the degradation rate of hemicelluloses, celluloses in treatments without white-rot fungi was even higher than that of adding white-rot treatments. White-rot fungi improved the degradation of lignin, especially in adding 5% white-rot fungi treatment.(5) White-rot fungi helped reduce the percentage of acid exchange fractions, reducible ( Fe/Mn oxide ) fractions of heavy metals and enhance the percentage of the oxidation (organic/sulphide) fractions, residual fractions of heavy metals. Cu, Pb, Pb, Zn were better stabilized by adding white-rot fungi in compost. The effects of adding white-rot fungi were different on stabilization of the metals. The rate of acid exchange fractions and reducible ( Fe/Mn oxide ) fractions of the metals declined during the composting, which suggests that the inactivation of lead was best, and the rates were 34.8%,52.0%,61.3%,56.7% in compost without white-rot fungi and adding 1%, 2%, 5% white-rot fungi to the compost, respectively. The inactivation of zinc was the second, and then was cadmium, copper. The best inactivation of cadmium was disposaling of 5% white-rot fungi and its decline rate was 37.3%. The inactivation of copper had litter difference between disposal of with 1%, 2%, 5% white-rot fungi, and the decline rate of disposaling 2% white-rot fungi was largest, and its decline rate was 24.5%. The best inactivation of zinc was disposaling of with 5% white-rot fungi, and its decline rate was 35.9%.