Study Of Hydroxyl Aluminum Enhances Sludge Dewatering Efficiency And Chloride Ion Migration

Excess sludge is the main by-product of sewage biochemical treatment.With the substantial increase of sewage treatment capacity,the yield of excess sludge is also increasing day by day,and the water content of sludge is generally greater than 95%.For further disposal of sludge,sludge dewatering is particularly important.The commonly used pretreatment method of sludge deep dewatering in China is chemical conditioning.Considering sludge reduction treatment and subsequent resource disposal has become a hot issue in sludge treatment and disposal.In this paper,three kinds of aluminum salt flocculants were used to conduct chemical conditioning of residual sludge to study the improvement effect of different forms of hydroxyl aluminum on sludge dewatering,and to analyze the change characteristics of different components of sludge extracellular polymer（EPS）,and to explore the influence of EPS on the flocculation behavior of different forms of hydroxyl aluminum.Then the typical flocculant polyaluminium chloride（PAC）in the process of regulating the migration behavior of chloride ions,comparing with the conventional chemical conditioners ferric chloride（Fe Cl₃）and cationic polyacrylamide（PAM）and lime（Ca O）to regulate the sludge chloride ion migration patterns,provide a reference for subsequent free-pollution disposal sludge.The main contents and results of the study are as follows:（1）When three kinds of aluminum salt flocculants were selected for sludge conditioning,it was found that the medium-poly aluminum（Al_b）had the best sludge dewatering effect due to its high molecular weight and high charge density,which formed electric neutralization with negatively charged particles in the sludge.During sludge conditioning,hydrolysis adsorption and precipitation mainly occurred in the low-poly aluminum（Al_a）.The main action modes of high polyaluminum（Al_c）in sludge are net trapping and scavenging and adsorption bridging.When the dosage of the three aluminum salt flocculants increased from 0 g Al/gTSS to 0.06 g Al/gTSS,the contents of SEPS and LB-EPS in the sludge decreased,and the sludge dewatering effect became better.TB-EPS was transformed into SEPS and LB-EPS by increasing the dosage.The content of SEPS and LB-EPS increased,and the dehydration performance became worse.When the sludge was treated with 0.08 g Al/gTSS,the protein content in SEPS and TB-EPS decreased.The contents of humic acid and polysaccharide in TB-EPS decreased,while those in S-EPS increased.The results indicated that the decrease of protein content in S-EPS could improve the dewatering performance of sludge.（2）After adding PAC for conditioning,the chloride content in the sludge system increased by 4 times compared with that in the original sludge.The addition of PAC was the main reason for the increase in the chloride content in the sludge system.After conditioning,the sludge is filtered and dehydrated.The filtered and dehydrated sludge can effectively reduce the content of chloride ion in the sludge cake,which is conducive to the subsequent harmless disposal of sludge.The content of chloride ion measured by acid dissolution method for sludge cake treatment is higher than that by water dissolution method,because part of chlorine element in sludge exists in the crystal lattice,which is difficult to be removed by pressure filtration dehydration process.PAC combined with PAM can effectively improve the sludge dewatering performance.With the increase of PAM dosage,the content of chloride ions in the filtrate decreases,and chloride ions mostly exist in the mud cake,which is not conducive to the subsequent disposal of sludge.PAC is combined with lime to adjust the sludge,and the addition of lime will increase the p H of the sludge system,which is not conducive to sludge dehydration.The addition of lime increases the chloride ion in the filtrate.According to the law of mass conservation,the addition of lime can reduce the content of chloride ion in the sludge cake.