The Pollution Characteristics And Environment Risk Of Heavy Metals In Swine Manure Hydrochar

The scale of livestock and poultry raising in our country is growing,particularly,the scale of the pig industry has achieved tremendous development.While meeting the needs of the people,the pollution caused by the pig farms to the ecological environment,especially the fecal and urine pollution,has become serious increasingly and has become an important factor affecting the sustainable development of the pig industry.In recent years,hydrothermal carbonization technology has been widely used in the process of biomass raw materials,and hydrothermal carbonization technology can reduce the risk of heavy metals in biomass raw materials to a certain extent.This topic uses pig poos as raw material,and adopts different carbonization temperature,carbonization time,the amount of sulfuric acid added and the amount of potassium hydroxide added to carry out rapid treatment of hydrothermal carbonization,to study hydrochars'yield,physicochemical properties,main nutrients,drying characteristics,total amount of heavy metals,forms of heavy metal and environmental risk assessment of heavy metals in pig manure under different conditions.The yield of hydrochars produced by hydrothermal carbonization of swine manure was between49.79%and 88.68%,and the highest yield was at 6.9 g/100 g obtained by adding potassium hydroxide.The pH value is between 5.5 and 6.2,so swine manure hydrochars show weak acidity.The total nutrient content of pig manure hydrochar meets the NY525-2012 standard of organic fertilizer.It is more favorable for the increase of total nitrogen,total phosphorus and organic carbon under alkaline conditions.In general,hydrothermal carbonization reduces the mineral content in pig manure.The drying characteristics of hydrochar can be improved by increasing the carbonation temperature and time and adding the amount of sulfuric acid.The drying characteristics of alkaline hydrochar are similar to that of raw materials.The contents of Cu,Zn and Mn in swine manure and hydrochar were higher than the contents of other four?As,Pb,Cd and Cr?.With the increase of carbonation temperature and time,the heavy metals in hydrochar have obvious enrichment.Both acidic and alkaline conditions can reduce the total amount of heavy metals in hydrochar.Cu and Zn in swine manure were mainly interchangeable and reducible,respectively,indicating higher biological availability of heavy metals in swine manure.hydrocharization can effectively reduce the bioavailability of heavy metals in swine manure,the most influential is the carbonization temperature.With the increase of temperature,time and potassium hydroxide content,the content of heavy metals in hydrochar increases and the passivation effect is obvious.Under the condition of acidic hydrocharization,the oxidizable state in hydrochar is transformed to the exchangeable state and reducible state.With the increase of additive amount,the bioavailable state content of heavy metals in hydrochar increases.Comprehensively comparing the values of I_geo,Er,RI and RAC in hydrochar and their pollution levels under different carbonization conditions,we can conclude that:The main risk of heavy metals in pig poos are Cu and Zn.Higher carbonization temperature and longer carbonization time contribute to lower the risk of heavy metal pollution.When the carbonization time is 1h,220°C is the minimum carbonization temperature of heavy metal pollution of hydrochar;when the carbonization temperature is160°C,5h is the most suitable carbonization time for reducing heavy metal pollution in hydrochar.Through risk assessment,it is unfavorable to reduce the risk of heavy metal pollution under acidic conditions,and it is beneficial to reduce the risk of heavy metal pollution under alkaline conditions.