Effect Of Ash On Dewatering And Drying Performance Of Municipal Sludge

Guided by sludge recycling and based on existing sludge treatment and disposal equipment,in this paper,we proposed a new method of using ash residue as additive to improve sludge dewatering and drying properties,and selected Si O2,CaO,Fe2O3 and Al2O3as the additive.The synergistic effects of four metal oxides on sludge dewatering and drying performance were also discussed.Moreover,based on the cracking performance of sludge,the effects of adding ash residue on the chemical oxygen demand（COD）and extracellular polymer（EPS）of sludge were studied.The main research of this paper is as follows:（1）The effect of ash residue on sludge dehydration performance was studied by using SRF,SV30 and other index.It was found that when the amount of ash added was 20%（20%of the dry weight of sludge）,it had a promotion effect on sludge SV30,and the promotion effect was further enhanced with the increase of the addition amount.Through specific resistance experiment of the sludge,it was found that the addition of ash can promote the dehydration performance of the sludge.When the amount of ash added was 80%（80%of the dry weight of the sludge）,the SRF value of the sludge tended to be stable,and compared with the original sludge specific resistance（SRF）value,it was reduced by 63.66%.Four kinds of metal oxides were used as additives,the difference between SiO₂and sludge ash SRF minimum value was only 0.3×10¹²m/kg,CaO、Al₂O₃had stronger dehydration performance,compared with ash residue SRF respectively reduced by 0.83×10¹²m/kg and 1.44×10¹²m/kg;the SRF value of Fe₂O₃was smaller than that of ash residue.（2）When making raw mud into a mud cake with a thickness of 4-8 mm and placing at a constant temperature condition of 80-120℃,it was found that under the same mud cake thickness condition,the drying time decreased with the increase of the drying temperature;and the maximum drying rate showed a linear relationship with the drying temperature;under the same temperature conditions,the mud cake thickness had a linear relationship with the drying time,and the maximum drying rate decreased with the increase of the mud cake thickness,and the critical temperature was 100℃.Therefore,the thickness of the mud cake was set as 4 mm and the drying temperature was set as 100℃in subsequent experiments.（3）After examining the drying performance of the sludge with ash addition amounts of0%（SS）,20%（SS-20）,40%（SS-40）,60%（SS-60）,80%（SS-80）,and 100%（SS-100）,it was found that the ash addition amount was inversely proportional to the drying time,that was,the larger the ash addition amount,the shorter the drying time.SS-80 could achieve the maximum difference in a shorter time and shorten the drying time by 20 minutes compared to SS-20.The maximum drying rate of the mud cake reaches its maximum at SS-40,and the maximum drying rate was maintained at SS-60 and SS-80.When the mud cake maintains the same moisture content,the drying time of the mud cake decreased with the increase of the amount of ash added,and the decreasing trend was linearly correlated.Among them,the drying time of SS-80 was 120 min,which was 20%shorter than that of SS-150 min.The maximum drying rate curve of the mud cake showed a trend of first increasing and then decreasing,and reached the maximum at SS-80.The maximum drying rate was 1.09 g/（gH₂O·min）,which was 1.15times the maximum drying rate of SS.The effect of SiO₂on the drying performance of mud cake was similar to that of ash.The difference in drying rate between CaO and ash reaches the maximum when the addition amount was 80%,and the maximum difference was 0.08 g/（gH₂O·min）.The influence of Fe₂O₃and Al₂O₃on the drying performance of mud cake was similar,and both had little influence on the drying performance of mud cakes.（4）Soluble metal oxides in ash slag could act on LB-EPS（loosely bound）and TB-EPS（tightly bound）to oxidize and decompose them into S-EPS（dissolved）,and the maximum drying rate of mud cake was inversely related to TB-EPS,i.e.the smaller the TB-EPS,the greater the maximum drying rate of mud cake.（5）The contents of heavy metals and their compounded in the ash and raw mud all meeted the requirements of the mud quality（GB/T 23485-2009）for mixed landfill of sludge disposal in urban sewage treatment plants.According to the curve changes of heavy metals and their compounds in the mud cake with different ash addition amounts,it was determined that the optimal amount of ash added is 80%（80%of the dry basis weight of the sludge）.This ash addition amount could ensure both the degree of sludge cracking and the safety performance of the sludge.