Preparation, Properties, Application Of Sludge-straw Based Actived Carbon

Large amounts of sludge are produced annually during the wastewater treatmentprocess in recent years. The reutilization of the sludge has becoming a hot researching spotfor its environmental and economic aspect. This paper is using the dewatered sludge as rawmaterials form Shang Hai Industrial Zone, selecting potassium hydroxide, phosphoric acidand zinc chloride as chemical activator to produce sludge derived activated carbons. Thepreparation process conditions and mechanism related were investigated in detail.Furthermore, the effectiveness of reed straw on the carbon content in sludge basedactivated carbon was investigated due to the fact that straw is rich in its cellulose and lignin.The effect of calcination temperature, concentration of activator was also studied inrespect to carbon’s iodine adsorption value, nitrogen adsorption isotherm, BET surfacearea, microstructure and surface functional groups. The feasibility of the sludge basedactivated carbon was evaluated by the comparison with commercial AC.The preparation conditions were optimized using iodine adsorption value as indicatorand the results are as follows:（1） The optimal activator concentration was0.2moL/L,shaking rate was60rpm and calcination was400℃when H₃PO₄was taken as a chemicalactivator, the iodine value was646.4mg/g.（2） The optimal activator concentration was0.8moL/L, shaking rate was60rpm and calcination was800℃when KOH was taken as achemical activator, the iodine value was524.5mg/g.（3） The optimal activatorconcentration was0.5moL/L, shaking rate was60rpm and calcination was800℃whenZnCl₂was taken as a chemical activator, the iodine value was571.1mg/g.The BET points were optimized by setting up24+24method to achieve a morereasonable result, meanwhile the testing time is within12hours.The effect of sludge to straw ratios was investigated in depth to find out the optimaladsorption iodine value of sludge and straw complex based activated carbon. This was dueto the fact that traditional sludge derived activated carbon was low in its carbon contentand high in its ash content. The researching results indicated the optimal iodine adsorptionvalue was575.5mg/L when0.8moL/L KOH was selected as activator, calcinationtemperature was600℃for2h and sludge to straw ratio was4:1. The iodine value was585.5mg/g when only using straw as the precursor at the conditions described above. Theadsorption iodine decreased when sludge to straw ratios decreased.The properties of commercial AC, sludge based AC （0.8moL/L KOH activated,calcinated in600℃for2h after acid washing） and straw&sludge mix based AC （straw tosludge ratio:1:1,0.8moL/L KOH activated, calcinated in600℃for2h after acid washing） were compared in respect to their BET surface, pore size distribution and adsorptionisotherm. The results suggested that the commercial AC had the highest BET surface（715.5m²/g）, while the other has the BET surface of607.7and430.3m²/g. respectively.Micro-pores are predominant in commercial AC and it has the volume of0.238mL/g,whereas sludge or sludge and straw mix based AC are all the porous adsorption materials,their total pore volume are0.504mL/g and0.367mL/g, respectively. The micro-porevolume takes13.3%and27.5%of the total pore volume in sludge and mix based AC,respectively, indicating that the straw is beneficial for the micro-pore’s formation in sludgebased AC. The results also showed that the BET surface could significantly be increasedby acid washing.Further analysis of adsorption isothermal curves of1-diazo-2-naphtol-4-sulfonicacid （1,2,4-Acid） revealed that straw integrated sludge AC had a good potential for1,2,4-Acid adsorption and the maximum adsorption quantity （Qm） was56.4mg/g at25℃, whereas the sludge based AC only had aQmof20.4mg/g.The above results indicate that the sludge activated carbon would be promisingporous adsorption materials due to its effectiveness compared with commercial AC and itmay provide an effective solution to use the sludge in a better way.