Research Study On The Effect Of Using Walnut Shell As Skeleton Builder On Properties Of The Sludge Dewatering

The moisture content of sludge is high and difficult to dehydrate, if themoisture in sludge can be efficiently removed, so the sludge volume can bereduced greatly, the end cost of transportation and sludge disposal can bereduced. Before dealing with sewage sludge, we usually use mechanicaldehydration to increase solid content of sludge. However, the speed of sludgefiltration is slow, mechanical dewatering cost is very high. The difficulty ofsludge dewatering is associated with the high content of organic matter andcolloid in sludge solids. Chemical flocculation conditioning reduces the filtrationresistance and helps to improve sludge filtering performance, but in themechanical dewatering stage, due to the high compression, flocculation sludgecake was difficult to achieve a higher solid content, and cake particles wereeasily deformed due to the closure of cake pore followed by the filtration of thesludge was reduced. Agricultural wastes walnut shell as skeleton builder canincrease its structural characteristics and compaction of sludge incompressible,supply water path, thereby improved the sludge dewatering performance and thecake performance. In this study, by measuring before and after adding walnutshells and polyacrylamide (PAM) flocculated sludge before and after addingwalnut shells mixed sludge cake moisture content filter specific resistance (SRF),capillary suction time (CST) and other parameters measuring the performanceimprovement of walnut shell on sludge dewatering, the experiments are asfollows:(1)Testing the basic properties of walnut shell and test the basiccharacteristics of the sludgeThe walnut shell true density was similar to the density of water, so it waseasy to be floated. The walnut shell had a low ash content, when the particle size was <0.25mm, the maximum ash content was2.62%. Three types of raw sludgewere greater than1.0×1013m/kg, so they were difficult to mechanicaldehydration.(2)The influence of dehydration methods for sludge dewatering effectVacuum filtration sludge dewatering significantly was better than centrifuge.However, due to the centrifugal sludge conditioning walnut shell, walnut shellfloating on the surface or at the bottom of the mud layer deposition affected itsuniform distribution in the mud layer. Therefore, after the walnut shellconditioned sludge should adopt vacuum filtration to study.(3)Effect of PAM on sludge conditioningSludge PAM conditioning effects proved electric neutralization effect andadsorption bridging-traditional flocculation mechanism, the results showed thatwithin a certain range, after conditioning with anionic polyacrylamide (APAM)and cationic polyacrylamide (CPAM),the dewatering performance of the sludgehad been effectively improved and CPAM had a stronger sludge flocculationthan APAM.(4)Walnut shell on sludge conditioningAdding walnut shell to the sludge, the results showed regardless of thewalnut shell size, with the increasing amount of walnut shell, the cake moisturecontent decreased gradually. When the amount of the walnut shells remainedunchanged, the smaller walnut shells particle size, the lower the moisture contentof cake. Optimal addition of walnut shells and sludge dry weight ratio was4:6,the optimum particle size was <0.25mm. The actual size of the operation wasdetermined in accordance with the further addition and disposal requirements.(5)Walnut shell and PAM conditioning effect on sludge dewateringperformanceCompared with other conditioning methods, the mixed sludge moisturecontent combined with walnut shells and CPAM conditioning cake wasminimum. After15min vacuum filtration, the sludge mixed cake moisturecontent was68.99%, which was conditioned with CPAM and walnut shell, thewalnut shell conditioning was68.99%, the CPAM conditioning was68.27%theAPAM conditioning was73.40%, while the original sludge was73.79%.Increase CPAM dose could not significantly improve sludge dewatering rate, walnut shell as the only conditioners need high dose, improvement of sludgedehydration were limited. If use a combination of these, they will interact withsludge solid, formed a uniform permeability structure, improved the dehydrationeffect greatly.