Study On The Experiment Of Pretreatment Of Excess Sludge By Ultrasonic And Alkali

The limited step of anaerobic sludge digestion is sludge hydrolysis.The structur-e of the sludge floc consists of extracellular polymeric substances,cell walls and othe-r materials,inhibiting organic matter dissolving out in the cell and limiting the proce-ss of anaerobic digestion.In order to speed up the process of anaerobic digestion,it i s necessary to pretreat sevage sludge before anaerobic digestion of sludge,breaking t-he extracellular polymer and cell wall,dissolving out the cell contents in the cell.Byt his,the hydrolysis process is accelerated,it also shorten the digestion time and decre-ase digester volume,improving methane production purposes.In this paper,we use ultr asonic and alkali to accelerate the anaerobic digestion,and also,it is to improve the slu dge dewatering performance byultrosonic and alkali at the same time.Firstly,the sludge is pretreated by ultrasonic only,by four acoustic density-0.19W/ml,0.4 W/ml,0.75 W/ml and 1.5 W/ml,getting the phenomenon of added SCO D value in sludge increases with the increase of the acoustic density,and the maximu m value is:4275mg/L;the maximum reduction rate of TSS and VSS were 58.2%an d 56.3%in sludge;although the pH value and ammonia value changes a little,but th e anaerobic digestion not is influenced badly,and ammonia still exists in the form of protein,also is utilized by microorganism mostly.It is found that it is helpful to imp-r ove the dissolution rate when the sludge concentration was small,but the content of SCOD not increasing under the same sound energy density,so It is suggested that t-he concentration of 1%is better than 0.5%solid sludge.Secondly,using NaOH alone to solute sewage sludge,the pH value was 8,9,10,11,12.Under this kind of condi-tion,SCOD value of sludge added increases with the increase of pH value,the maximum value is 4027mg/L,when the sludge pH value was 12,the sludge pH value is also high after the treatment of sludge,influencing Microbial activity;Under the cond-ition of 11 and 10,the pH value changes greatly,it is conducive to the buffer action of the subsequent anaerobic digestion.Through detec-tion,the ammonia nitrogen content in sludge is about 4/5 less than ammonia value o-f ultrasonic sludge,which is due to inhibition of ammonia alkali leaching,not influe ncing the anaerobic digestion.Thirdly,combined treatment to sewage sludge by ultrasonic and alkali,two kin ds of a-coustic density(0.19W/ml and 0.5W/ml)ultrasonic were combined respectively with two kinds of alkali(NaOH 和Ca(OH)2),this kind of treatment method was app lied to sawage sludge.It showed different results due to flocculation of Ca2+ in Ca(OH)2 sludge flocs.Combined with Low acoustic density(0.19W/ml),the maximum got of SCOD value added is 4871mg/L,by NaOH treating sewage sludge,and the maximum got of SCOD value added is 3018mg/L,by Ca(OH)2 treating sewage sludg e;Combined with high energy density(0.5W/ml),the maximum got of SCOD value added is 4972mg/L,by NaOH treating sewage sludge,and the maximum got of SCO D value added is 4568mg/L,byCa(OH)2 treating sewage sludge.It is concluded that flocculation of Ca2+ play the main role at the low acoustic density and the flocculati on of Ca2+ is broken when the acoustic density is large enough.At last,this article detects the dewatering performance of sludge through four kinds of treatment method—combined pretreatment—ultrasonic and Ca(OH)2、no pretre-atment、only Ca(OH)2 and only ultrasound.Results got as follows:the filtration time of the first two is:760s and 1340s,indicating that the specific resistance of sludge is small,but the filter cake moisture content rate were 84.93%,75.23%;the sludge par ticles change so small and block upfilter paper after ultrasonic disintegration,so both consider pumping time of latter two is:9230s and 8820s,indicating that the specific resistance of sludge is large,but the filter cake moisture content rate were 73.23%、70.57%.The cake moisture content as the index,we get the moisture content of filter c ake for a minimum of 70.57%.Although the consider pumping time is long,but we c an find a suitable method to dewater the sludge pretreated by combined method(ultra sonic with Ca(OH)2).