Study On Phosphorus Speciation Of Fecal Sludge Hydrochar And Loss Of Phosphorus In Simulated Soil Column

Fecal sludge has high moisture content,rich in N,P,K and other nutrient elements,and low content of heavy metals,with high agricultural resources potential.Hydrothermal carbonation as one of the important ways to biomass harmless and resource-based treat,which was more suitable for high moisture content biomass treatment than pyrolysis and gasification.So far,the phosphorus forms and leaching potential of fecal sludge and hydrochar needed to be further explored.In this study,the effect of temperature ranged from 180 to 240? on the physic-chemical characters of hydrochar from the fecal sludge was studied.The phosphorus components of fecal sludge and hydrochar were analyzed by modified Hedley phosphorus grouping method.At the same time,in order to investigate the loss of phosphorus in fecal sludge and hydrochar,the leaching of fecal sludge and hydrochar in soil was studied by soil leaching experiment.The following results and conclusions were drawn from the experimental study:?1?With the increase of hydrothermal temperature,the yield of hydrochar decreased,the content of ash increased,pH value and the content of total phosphorus increased,the content of organic matter,cation exchange capacity and total nitrogen decreased.Except that,C content increased,N,H,O content decreased.O/C,H/C ratio decreased,the polarity decreased,the degree of aromatization increased.?2?The hydrochar contained a large amount of inorganic substances such as SiO₂ and CaCO3,and the pores were mainly mesoporous.The hydrothermal carbonation temperature exceeded 240?,which would destroy the internal pore mechanism of hydrochar and reduce its specific surface area,which was not conducive to the soil application of hydrochar.?3?The content of organic phosphorus in fecal sludge accounted for 11.73%.With the hydrothermal carbonization temperature increased,the content of organic phosphorus in hydrochar decreased,while the content of inorganic phosphorus increased.Hydrothermal carbonization was beneficial to mineralization of organic phosphorus.Simultaneously,inorganic phosphorus was the main component of phosphorus in hydrochar,accounted for 92.47%⁹9.54% of total phosphorus.The C/P ratio of fecal sludge was 21.47,and the C/P ratio of hydrochar decreased with the increase of temperature,from 14.46 at 180? to 10.79 at 240?.?4?The contents of water extracted phosphorus,bioavailable phosphorus and residual phosphorus in fecal sludge were decreased from 8.55% and 32.05% to 1.65%².78% and 0.07%⁴.48%,respectively.With the temperature rose from 180? to 240?,the content of Fe,Al-P decreased gradually from 20.53% to 0.17%.The content of Ca,Mg-P increased from 72.20% to 98.10%.Compared with fecal sludge,the ratio of Fe,Al-P in hydrochar decreased significantly,and the ratio of Ca,Mg-P increased obviously.The process of hydrothermal carbonization was conducive to unstable forms of phosphorus to stabilize the form of phosphorus conversion,reduced the loss of phosphorus and increased the availability of plants.?5?Under different treatment conditions,the proportion of organic phosphorus and inorganic phosphorus in soil leaching solution was 9.35%²7.97% and 72.03%⁹0.65%,and phosphorus leaching was dominated by inorganic phosphorus.The concentration of TP in the leaching solution increased first and then decreased with the leaching time.The addition of fecal sludge and hydrochar increased the concentration of TP in soil leaching solution.Compared with the control group,the addition of 2%,4% and 8% increased by 2.89⁵.11,3.72⁹.35,7.64¹1.32 times and 1.36².01,1.52².25,1.84².53 times.Compared with the direct application of fecal sludge,the addition of hydrochar to increase the concentration of TP was smaller.?6?The total leaching loss of total phosphorus,inorganic phosphorus and organic phosphorus in fecal sludge group was 3.59⁷.69,3.66⁶.44 and 3.17¹5.34 times of the control group.The addition of hydrochar was 1.42¹.99,1.50¹.78,0.93³.31 times of the control group.Compared with the addition of fecal sludge,the addition of hydrothermal soil column,the phosphorus was not easy to leaching.