The Production Of Sewage Sludge-biochar Through Microwave Pyrolysis

Sewage sludge is one of the most important technologies in sewage sludge treatment and disposal and the production of sewage sludge-biochar is an effective way to realize the reduction and recycling of the sludge.The addition of chemical activation agent is conductive to accelerate the dehydration and to produce more porous structure during the pyrolysis process,If the chemical activation agent(zinc chloride)is also beneficial to the sewage sludge dewatering,the zinc chloride can be added during the dewatering process which is before the pyrolysis process.In that way,the zinc chloride will play an important role on both dewatering process and pyrolysis process and also reduce the energy consumption of the whole process.Based on that hypothesis,the effect of the zinc chloride of different concentration was analyzed in this experiment.The result indicated that the addition of zinc chloride can effectively reduce the water content of the sludge and reduce the capillary time.In other words,the addition of the zinc chloride can effectively improve the sludge dewatering performance.The influence of the different concentration of zinc chloride on the soluble polysaccharide,soluble protein,zeta potential and particle size distribution was analyzed in this experiment,some conclusions can be draw that the addition of zinc chloride can reduce the soluble protein content、improve the soluble polysaccharide content,the zinc chloride is also conductive to change the surface electrical behavior of the sewage sludge,reduce the surface negative charge and therefore reduce the repulsion force between the sludge floc and make the sludge reunite more easily.The result of the particle size distribution indicated that the zinc chloride can improve the particle size of the sewage sludge.In conclusion,the addition of the zinc chloride can effectively improve the sludge dewatering performance.During the pyrolysis process,the pyrolysis temperature and chemical activation agent will affect the physicochemical property and surface characteristics of the biochar.The increasing temperature can reduce the yield of the biochar,but the changes of the content of the zinc chloride have no significant influence on the characteristics of the biochar.The increasing temperature and increasing addition of zinc chloride content are conductive to increase the ash content,duing to fact that the decomposition of the alkali metal oxide,and the zinc chloride content also has no significant influence on the pH of biochar.Both the increasing temperature and increasing addition of the zinc chloride has effectively reduce the surface negative charge of the biochar,also promote the aromatization of the organic matter.At the same time,Increasing temperature and increasing zinc chloride content are both beneficial to produce more porous structure,but too high temperature will reduce the surface area of the biochar,because it will result collapse of the some micropore.The increasing zinc chloride content can significantly increase the surface area.The retention time will influence the forms of the heavy metals in biochar,during the pyrolysis process,the form of heavy metal As were changed from F1,F2,F3 to F4,that is the pyrolysis process has positive influence on As stabilization.With the increasing of the pyrolysis temperature,the forms of Cd was changed from F3 into F1,F4;Cr was changed from F2 forms into F1 and F4 forms;For heavy metal Cu,The increasing temperature was conductive to improve the forms of F1,F2,F3 and reduce the F4 form;During the pyrolysis process,the form of Pb was changed from F4 into F1 and F2;the forms of Ni were changed from F1,F2 into F3 and the forms of Zn was changed from F1 into F2,F3 and F4 forms.The computed result of RAC model indicated that: in certain interval,the increasing retention time was conductive to reduce the risk of the heavy metal,but too long retention time also improve the heavy metal risk.The calculated result of the Igeo showed that the increasing retention time can result in the enrichment of the heavy metals,also result in the increase of the risk.The result of the Er meant that increasing retention time increase the risk of Ni、Pb、Zn and Cd.In conclusion,pyrolysis process don’t promote the stability of the all the heavy metals.Much more attention still should be paid on the heavy metals during the application of the biochar.During the future study,the stabilization of the heavy metals in biochar is the most important problems should be solvedThe addition of calcium salt had some influence on the forms of inorganic phosphate,reduce the leaching concentration of the phosphate and improve the phosphorus adsorption capacity;What’s more,the pH and the initial concentration of the phosphate also have some influence on the adsorption capacity.The mechanism of the phosphate adsorption included: physical adsorption 、 anion exchange and precipitation.