The Study Of Biogas Permentation Of Chemical Humic Acids

Considerable organic waste will inevitably be produced in agriculture and industries. These wastes will have detrimental effect on environment without proper discharge and effective disposal and then even cause disruption to human beings and society. Nowadays, it is a consensus that organic residues have been labelled as "energy carrier" rather than waste. If the energy contained in these wastes could be recovered effectively, not only the disposal problem will be solved but also the consumption of fossil fuels can be reduced and so can reduce the GHG emission. Therefore, present study proposed "chemical transformation of humic acid" process to turn organic waste to resource, energy.First, the possibility of "chemical transformation of humic acid" from straw and black liquor was investigated and then the biogas potential of humic acid was tested. In terms of straw as raw material, the straw was cut into small piece with about 2 cm lengths and then immersed in the mixture of MgSO4、MgCl2 and CaCl2 solution for 1 week, last cooked. With humic acid conversion and content as indicators, taking the soaking solution concentration, liquid-solid ratio and cooking temperature experimental as factors, a series of tests was designed in order to determine the most suitable parameters of soaking liquid concentration, the liquid/solid ratio, and cooking temperature. Considering the black liquor, under agiven process conditions, with CO2 as acidifiers, the sodium ions in Papermaking (straw) black liquor were transformed into sodium carbonate (sodium bicarbonate) while the organic matter was transformed into humic acid and then separated as precipitation. Then the biogas potential of humic compounds was tested under different conditions and then optimizes the fermentation conditions further. The main conclusions are as follows:1 It is of possibility that chemical humic acid can be produced from straw. In the single factor experiment, the optimum reaction conditions by using straw as raw materials for chemical humic formation are as follows:reaction temperature of 170～180℃, liquid to solid ratio of 3.5 to 3.75:1, the soaking liquid concentration of 350-450g/L, reaction time of 3-5 h.2 Chemical humic acid production from black liquor is also feasible. COD and Na+ concentrations in the black liquor were 319,594 mg/L and 122 g/L respectively with specificgravity of 1.33. Middle sludge treatment method is superior to black liquid coupling humic acid (HA) transformation method. The optimal reaction temperature, reaction time, CO2 requirement, liquid-solid ratio, applied sludge and straw powder ratio were 200℃,2.5～3.5 h,0.35～0.4 mol/L,2:1-2.5:1,8:1～10:1, respectively. Final COD concentration decreased to be less than 100,000 mg/L with precipitation efficiency of 70.3% and humic acid content of 10%～20%.3 The humic acid substances should be pre-treated before fermentation in order to meet the fermentation conditions. Under the reasonable control of the reactor fermentation conditions, the best fermentation temperature is 38℃. With adding molybdenum, zinc, manganese, cobalt, nickel, boron salt of 0.5 mg/L respectively and copper of 0.3 mg/L to the influent water, the activity of methanogens was significantly enhanced and also the yield of methane. The highest methane content of 70～75% in biogas was obtained with the influent pH of 7 to 7.5.