Reaction And Product Formation Mechanism Of Dairy Manure Hydrothermal Treatment

Rapid development of the livestock and poultry industry promotes economic growth,but it also leads to increasingly serious environmental pollution.In addition to cellulose,hemicellulose,lignin,crude protein and crude fat,livestock manure contains many pathogenic bacteria,parasite ova and other microorganisms,which are harmful to human and livestock health.The harmless conversion and high-value utilization of livestock manure could be realized by the hydrothermal treatment.In this thesis,in order to explore the hydrothermal reaction mechanism and the effect of different reaction parameters on the characteristics of products,dairy manure were converted to hydrochar with high quality,bio-oil with various value-added components and aqueous phase products with rich inorganic nutrients.Moreover,the tentative exploration of hydrochar high-value utilization was investigated to provide some guidance for the resource and high-value utilization of livestock manure.The main results are as follows:?1?Firstly,the effect of reaction temperature,residence time and water-solid ratio on the yield of hydrochar from dairy manure hydrothermal treatment were studied.The results showed that the reaction temperature has a remarkable influence on the yield of hydrochar,and there was no interaction among these parameters.Then,the effect of reaction temperature on the characteristics of hydrochar and bio-oil were investigated.With the temperature increaing,the yield of hydrochar decrease from58.34 wt.%to 43.48 wt.%.Dehydration and decarboxylation reaction played a dominant role during the hydrothermal treatment process.Carbon microspheres could be observed on the surface of hydrochar obtained at 240?by SEM.The hydrchars of dairy manure had abundant functional groups by FTIR and XPS analysis.Py-GC/MS detected noticeable differences among the components of volatile products in hydrochar obtained at different temperatures.The identified chemical compounds were mainly aldehydes,ketones,esters,acids,furans,hydrocarbon,accharides,and phenols.In addition,the bio-oil was mainly composed of aldehydes,phenols,ketones,acids,and some small molecules and heterocyclic compounds.The bio-oil obtained at280?had the highest content of phenol compounds.?2?The influence of reaction temperature?150-270??,residence time?0.5-6 h?and water/manure ratio?200/25-200/5 mL/g?on the total nutrient content on the solid and liquid products were investigated using a 5-level,3-factor orthogonal test and principal components analysis.Reaction temperature had a noticeable effect on the total nutrient content of solid product.The maximum total nitrogen content of solid product was 22.92 mg/g,obtained at water/manure ratio of 200/20 g/mL and performed at 240?for 6 h.For obtaining the maximum total nitrogen content of liquid product,the most optimal conditions were 150?,1 h and 200/20 g/mL which produced TNC of 1619.55 mg/L.The proportion of ammonium?NH₄⁺-N?and orthophosphate(PO₄^3-)were also analyzed in the liquid product.The amount of NH₄⁺-N increased with reaction temperature increasing and water/manure ratio increasing,the main form of phosphorus?P?was PO₄^3-in the liquid product,and most of the potassium?K?were also dissolved in the liquid product.Most of Ca and Mg were transferred into solid products.?3?The effect of extraction solvents on the properties of hydrochar and bio-oil from hydrothermal treatment of dairy manure was investigated at 270?for 60 min.Five solvents were employed including three polar solvents?ethyl acetate,dichloromethane,diethyl ether?and two nonpolar solvents?n-hexane and petroleum ether?.The results showed that polar solvents tended to produce more reduction of hydrochar yields and higher yields of the bio-oils.The highest bio-oil yield of 27.19wt.%was obtained using dichloromethane.The polar solvents had a more positive effect than nonpolar solvents on the occurrence of disperse spherical microparticles and the augment of hydrochar specific surface area.The main compounds in the bio-oils from polar solvents mainly consisted of N-containing compounds,ketones,phenols and acids,while bio-oils from nonpolar solvents mainly consisted of esters,alkanes and aromatics.?4?The effect of two steps hydrothermal process on the properties of products from hydrothermal treatment of dairy manure were investigated.In the fisrt stage of hydrothermal carbonization?HTC?at low temperature,the reduction of total nitrogen was increased from 41.18%to 46.57%,indicating that the nitrogen in dairy manure was mainly transferred into bio-oil and aqueous phase product.In the second stage of hydrothermal treatment at high temperature,with the increase of temperature,decarboxylation,dehydration and demethylation reactions were the dominant pathway during the hydrothermal treatment of hydrochar obtained from the HTC at low temperature.With the extension of residence time,dehydration,demethylation and decarboxylation reactions played the leading role.SEM results showed that massive carbon microspheres still could be observed on the surface of hydrochar obtained by two steps hydrothermal treatment of dairy manure.And the bio-oil obtained from two steps treatment contained more acids,alcohols and aldehydes compounds.?5?A series of activated carbons?ACs?were obtained from dairy manure by hydrothermal carbonization pretreatment?at 270?for 1 h?and followed by chemical activation with KOH.The effects of parameters including activation temperature and hydrochar-KOH ratio on the surface structural properties and the electrochemical performance of ACs were investigated.With the activation temperature increasing,the micropore volume increased and the mesopore volume decreased,and the highest SSA of AC-700-1:1 sample was up to 166.00 m²/g.Porous lamellar structure were observed on the surface of ACs by SEM.The FTIR and XPS results showed the good oxygen functionalities and hydrophilia of ACs.XRD and Raman analysis revealed that existence of the structure of amorphous layers.The specific capacitance of AC-600-1:1 can reach 10.95 F/g at the current density of 1 A/g.The capacitance retention of AC-600-1:1 at 1 A/g after 5000 charge-discharge cycles reached 88.67%,indicating the good cycling stability.Overall,although the electrochemical performance of hydrochar-based activated carbons are not outstanding,it still shows a certain potential on the application of supercapacitor.