| The silicon dioxide、aluminum oxide and ferric oxide were extracted from fly ash in thispaper. Then the sludge conditioner was prepared using the above substances and was used inthe sludge dewatering conditioning. And the self-made conditioner was contrasted with polyaluminum chloride (PAC) and cationic polyacrylamide(CPAM) to assess the conditioningeffect of the flocculants. To take full advantages of the fly ash, the fly ash remaining after theextraction was also used in the sludge conditioning in this paper. In order to fully utilize thesludge and o solve the problem of weight increment of the filter cake caused by inorganicconditioner and fly ash, the preparation of fly ash-sludge unburned filter using filter cake afterthe dewatering was studied. The main contents are as follows.The extraction conditions of silicon dioxide were optimized by single factor test andorthogonal test. And the preferred extraction conditions were as follows: the temperature was80℃, the time was20h and the alkali concentration was3mol/L. The concentration of thesilicon dioxide in the filtrate was0.485mol/L and the extraction rate was27.4%in thiscondition. Then the alkali leaching residue was washed to nearly neutral and the acid leachingorthogonal test was studied. The better extraction conditions were as follows: the temperaturewas70℃, the time was2h, the liquid to solid ratio was7.5:1and the hydrochloric acidconcentration was15%. And the extraction rate of aluminum oxide was31.6%, the ferricoxide was53.54%in this condition.The sludge conditioner was synthetized using silicon in alkaline leaching solution andaluminum ion、 iron ion in acid leaching solution. The effect of nSi: n(Al+Fe), the pH of thereaction solution and the reaction temperature on the performance of the conditioner wasstudied by orthogonal test. The optimal combination was determined using the specificresistance of sludge as the evaluation index: nSi:n(Al+Fe)=1:2, the pH of reaction solutionwas3.5and the reaction temperature was50°C. The measurement of the properties and thecharacterization of the synthetic conditioner were studied. The XRD and IR spectra show thatthe conditioner was an amorphous polymeric substance composed of elements such asaluminium、iron and silicon. The observation of SEM shows that the conditioner has annetwork structure and can connect and netting the sludge flocs and so improve the sludge dewatering performance.The self-made sludge conditioner was used in the sludge conditioning and compared withPAC. The conditioning properties of CPAM as well as fly ash, alkali leaching fly ash and acidleaching fly ash were also investigated in this paper. The tests of vacuum filtration, sludgesettling, centrifugal dewatering and conditioning agents used in combination were mainlystudied.The effects of self made conditioner, PAC, CPAM as well as three types of fly ashes onthe sludge specific resistance, cake moisture content and filtrate water quality were studied inthe vacuum filtration tests. The results indicated that the effect of self-made conditioner wassuperior to PAC on the sludge specific resistance. The sludge specific resistance were0.2210~9s~2/g and0.4310~9s~2/g respectively after the conditioning of self-made conditionerand PAC under the same dosage of3.610-3mol/L. The sludge specific resistance was0.1410~9s~2/g after the conditioning of CPAM under the optimum dosage of50mg/L, and wasbetter than self-made conditioner and PAC. The sludge specific resistance was also decreasedafter the conditioning of three types of fly ashes and the effect of acid leaching fly ash was thebest. The self-made conditioner, PAC and CPAM had little contribution to the decline of cakemoisture content. And the cake moisture content after the conditioning of self-madeconditioner was slightly lower than PAC and CPAM. The cake moisture content decreased a lotafter the conditioning of three types of fly ashes. In the aspect of filtrate water quality, theCPAM had a higher removal rate of turbidity and CODcr, and the TP removal rate of self-madeconditioner and PAC was better than CPAM. All of the three flocculation conditioners hadlower ammonia nitrogen removal rate. The improvement effect of self-made conditioner onfiltrate water quality was better than the PAC overall.All the three types of flocculation conditioners had promoting effect on sludge settlingproperties, and CPAM was better than self-made conditioner and PAC. The three types of flyashes can also improve the sludge settling properties, and the alkaline leaching fly ash had thebest effect.The results of centrifugal dewatering tests showed that the direct centrifugal efficiency ofraw sludge was poor. The effect was best when the dosage of CPAM was50mg/L, and thecake moisture content was91.12%after5min of centrifugation. It was better at the dosage of 3.6×10-3mol/L when using self-made conditioner, and the cake moisture content was90.82%after5min of centrifugation. The cake moisture content was91.14%after5min ofcentrifugation when the dosage of PAC was7.2×10-3mol/L, but still not as good as CPAM andself-made conditioner.The joint conditioning of the self-made conditioner, acid leaching fly ash and CPAM wasstudied on the basis of the above tests. The specific resistance was the minimum0.1910~9s~2/gwhen the dosage of self-made conditioner was1.8×10-3mol/L and the dosage of CPAM wasfixed at30mg/L in the joint conditioning test. However, the specific resistance was0.2010~9s~2/g after the conditioning of CPAM alone at the dosage of50mg/L. It can be seenthat the same effect can be achieved in the case of reducing the dosage of CPAM when the jointconditioning was used. The specific resistance was0.1410~9s~2/g when the dosage of acidleaching fly ash was15g/L and the dosage of CPAM was fixed at30mg/L in the jointconditioning test and was less than that after the conditioning of CPAM at the dosage of50mg/L. In addition, the specific resistance can fall below0.2010~9s~2/g only when the dosageof acid leaching fly ash was more than25g/L. It can be seen that the joint use can reduce thedosage of the CPAM and the acid leaching fly ash. The effect of joint use between self-madeconditioner and acid leaching fly ash was evident when the dosage of acid leaching fly ashwas less than20g/L and the dosage of self-made conditioner was fixed at1.8×10-3mol/L overthis. More than20g/L after joint conditioning The effect of joint use was not obvious when thedosage of acid leaching fly ash was more than20g/L. The specific resistance was0.710~9s~2/gafter the conditioning of acid leaching fly ash alone when the dosage was10g/L, but thesludge specific resistance can be reduced to0.3110~9s~2/g and become easily dehydrated whenthe joint conditioning was used.The other factors affecting the sludge conditioning effects as well as the conditioningmechanism were analyzed meanwhile in the paper. And the disposal means of dewateringsludge were discussed at the same time.The preparation of fly ash-sludge non-fired filter material using acid leaching fly ash andsludge was investigated. The better conditions obtained through the orthogonal tests were asfollows: the ratio of the addition of the acid leaching fly ash and cement was8:2, the additionof the sludge was10%, the addition of lime and gypsum was10%and the pore-forming agent was5%. The filter material was prepared under these conditions and was used for theperformance tests and the research of morphology and structure. The results showed that theperformance of the prepared filter material meets the standards of the fly ash filter material.And the surface of the filter material was rough, the specific surface area was large. So it wasconducive to the hanging film of the microbe and can be used as a water treatment filtermaterial. |
PDF Full Text Request