Transformation mechanism of nutrient elements in the process of biochar preparation for returning biochar to soil

Returning biochar to soil is a heavily researched topic because biochar functions well for soil improvement. There is a significant loss of nutrients, which occurs during biochar preparation before biochar is returned to soil,thereby seriously undermining biochar＇s efficacy. Therefore, the transformation mechanisms of biochar p H,mass, nutrients and metals during pyrolysis under different atmospheres and temperatures were studied such that the best method for biochar preparation could be developed. Several conclusions can be reached：（1） a CO2 atmosphere is better than a N2 atmosphere for biochar preparation, although preparation in a CO2 atmosphere is not a common practice for biochar producers;（2） 350 ℃is the best temperature for biochar preparation because the amount of nutrient loss is notably low based on the premise of straw transferred into biochar; and（3） transforming mechanisms of pH, N, P and K are also involved in the biochar preparation process.

Preparation of high water-retaining biochar and its mechanism of alleviating drought stress in the soil and plant system

To explore the effect of biochar on alleviating plant drought stress after being applied to soil,we prepared biochar using rice straw as raw material according to different pyrolysis temperatures(400,600 and 800°C)and reaction atmosphere(CO_(2)and N_(2)).The effect of different pyrolysis conditions on the water retention performance of biochar was studied.The early high water-retaining biochar materials were selected and wheat seeds were selected for the verification experiment of returning to the field in pots.Biochar with high porosity(specific surface area and total pore volume)and more surface hydrophilic functional groups(mainly-OH and-COOH)can indeed improve soil water retention performance.It is mainly reflected in the increase in the dry weight and fresh weight of wheat and the soil moisture content in the treatment group with the addition of biochar water retention agent.Among them,the growth rates of fresh weight and dry weight of wheat in the C800 treatment group were 11.51%and 10.64%,and the soil moisture content increased by 1.89%.It is worth noting that the application of biochar cannot completely alleviate the impact of drought stress on plants,but it can reduce the amount of water irrigation to a certain extent.Considering the quality of biochar,the biochar material(C800)prepared under the pyrolysis temperature of 800°C and the reaction atmosphere of CO_(2)has high water retention performance.

Study on principles and mechanisms of new biochar passivation of cadmium in soil

At present,many researchers have studied the modification of biochar and explored the adsorption of cadmium by modified biochar.The adsorption capacity of cadmium for general modified biochar is about 30-150 mg/g.The new biochar(BM)we studied greatly improves the adsorption effect of cadmium in water,and the maximum adsorption capacity of cadmium can reach 400 mg/g,so we tried to apply it to the passivated cadmium in polluted farmland soil.This paper discusses the mechanism of BM passivation of heavy metal cadmium in soil and its protective effect on crop growth.The study found that:(1)the content of cadmium in wheat was 3.98 mg/kg in the soil with BM800.The addition of BM800 reduced the cadmium content of wheat by 75.43%compared with the blank control group;(2)BM contains special iron-containing functional group(-Fe-OOC-,-Fe-R-COOH,-Fe-R-OH,etc.)and aromatic structure C=Cπ,and these structures can react with cadmium to form stable complexes(C=Cπ-Cd,(FeO)2Cd,(Fe-RO)2Cd,etc.);(3)there are special mineral crystal structures XiFeYjOk in BM.XiFeYjOk can react with cadmium to form Cd-XiFejOk.Cd-XiFejOk can stably exist in biochar,and can provide more adsorption sites,which strengthens the adsorption and passivation of cadmium in soil by BM.

Effect and mechanism of changes in physical structure and chemical composition of new biochar on Cu(Ⅱ)adsorption in an aqueous solution

To improve the adsorption effect of biochar on heavy metal Cu(II),we prepared new biochar and explored its modification process influence on original biochar’s physical structure and chemical composition as well as its adsorption mechanism for Cu(II)in an aqueous solution.Through research work,we have reached some significant conclusions:(1)The modified biochar(M2-800)can adsorb Cu(II)at the rate of 98.039 mg g–1,38.8 times higher than that of the original biochar C800(2.525 mg g–1);(2)The biochar modification process boosts its etching and pore expansion,helping Cu(II)enter the inner surface of the adsorbent,but chemical adsorption is still the most essential fixation method for Cu(II);(3)The alkaline modification process promotes the formation of oxygen-containing functional groups,in which–OH/–COOH and iron ions would form C-O-Fe structures such as hydroxyl bridges(Fe-O–)and carboxy bridges(Fe-OOC–);(4)Carboxyl is the primary site of Cu(II)fixation in M2-800,and M2-800 has higher electronegativity(–47.8 mV)and larger pH(11.61),so that Cu(II)can be removed by electrostatic attraction and precipitation.

A steam dried municipal solid waste gasification and melting process

Considering high-moisture municipal solid waste(MSW)of China,a steam dried MSW gasification and melting process was proposed,the feasibility was tested,and the mass and energy balance was analyzed.Preliminary experiments were conducted using a fixed-bed drying apparatus,a 200 kg per day fluidized-bed gasifier,and a swirl melting furnace.Moisture percentage was reduced from 50%to 20%roughly when MSW was dried by slightly superheated steam of 150℃-350℃ within 40 min.When the temperature was less than 250℃,no incondensable gas was produced during the drying process.The gasifier ran at 550℃-700℃with an air equivalence ratio(ER)of 0.2-0.4.The temperature of the swirl melting furnace reached about 1240℃ when the gasification ER was 0.3 and the total ER was 1.1.At these conditions,the fly ash concentration in the flue gas was 1.7 g·(Nm^(3))^(-1),which meant over 95%fly ash was trapped in the furnace and discharged as slag.85%of Ni and Cr were bound in the slag,as well as 60%of Cu.The mass and energy balance analysis indicates that the boiler heat efficiency of an industrial MSW incineration plant reaches 86.97%when MSWis dried by steam of 200℃.The boiler heat efficiency is sensitive to three important parameters,including the temperature of preheated MSW,the moisture percentage of dried MSWand the fly ash percentage in the total ash.