Construction Of Nitrogen Containing Model Compound Of Sewage Sludge And Study On The Transformation Pathway Of Nitrogen During Microwave Pyrolysis

The microwave pyrolysis of sludge has become a hot technology of reduction, recycling and stabilization for its advantages such as quick heating rate, thorough disposal and high energy recovery. But the high nitrogen content of 3.3⁷.7wt% was still one of the factors that restrict the spread of pyrolysis because 30⁸0% of the nitrogen will convert into NOx precursors as hazardous by-products.Taken the sewage sludge as the study object, this article used XPS to detect the nitrogen containing functional groups of sludge; then determined the consistent of amino acids in sludge protein, according to which the nitrogen containing model compound was constructed; and the feasibility of nitrogen containing model compound was verified by the comparison of NH₃ and HCN yield between sludge and itself, along with the selection of factors that affected the pyrolysis characteristic of sludge. At last, the transformation ways of nitrogen in the pyrolysis process was inferred by the intermediates detected by GC-MS.The results shows that the nitrogen are exist in the forms of ammonium salt, nitrate or nitrite, protein, pyridine and pyrrole, which account to 10% of total nitrogen, and other 90% are in the protein. The analysis of amino composition in the protein shows that threonine, proline, glycine, glutamic acid, leucine, arginine and alanine are the main amino acids in the sludge, which account to 82% of all. Yet the methionine and histidine are the least ones less than 1%. From the comparison with MBR and SBR sludge, it can be found that different wastewater source and different process has little influence on the composition of amino acids. The model compound was consisted of eight richful amino acids. The mass ratio of the eight main amino acids which formed the nitrogen containing model compound are 15:6:6:16:21:6:21:9.In the study of factors that affected the yield of NH₃ and HCN from the pyrolysis of sludge, it can be concluded that final pyrolysis temperature and the moisture content played the decisive role; both were increasing along with the raise of final temperature. The NH₃ yield of wet sludge raised from 16.76% to 30.29% as the temperature raised from 300℃to 1000℃. And the NH₃ yield of dried sludge and wet ones at 800℃are 8.82% and 19.4% respectively. The deashing of sludge can also increase the yield of NH₃ and HCN. Compared the NH₃ and HCN yield of two nitrogen containing model compounds with deashing sludge, it can be found that the soy protein was more similar to the deashing sludge in the gas yield laws, so it is more suitable for the nitrogen containing model compound. Then taken the compounents of gaseous pyrolysate that detected by GC/MS as intermediates, it can be inferred that the cleavage of peptide bonds to form amines, imines and nitriles is the first step in the pyrolysis processing of soy protein. Then the HCN was produced by the futher cracking of nitriles. The formation of NH₃ needs H radicals to hydrogenate the amino group or imino group, even the cyanogen group.The research above revealed the conversion means of nitrogen during the pyrolysis of protein and sludge, and provide the theoretical basis for the controlling of generation of nitrogen containing gaseous pollutants.