Thermochemical Liquefaction Of Sewage Sludge,Upgrading Of Its Derivative Bio-oil By Microemulsification And Application Of Char Residue As Adsorbent For Dye Wastewater Treatment

Safe and cost-effective disposal and reuse of sewage sludge(SS)from wastewater treatment plants is faced up with quite a challenge worldwide.The common procedure in the sludge treatment is to reduce toxicity,decrease volume,and convert sludge into useful resources.SS usually contains organic compounds and can be converted into biomass fuels.Sludge-to-energy technology such as thermochemical liquefaction is gaining increasing attention on the resource utilization of SS with the advantages of SS disposal and at the same time,energy recovery.However,the liquefaction bio-oil has the disadvantages of high viscosity,high contents of heavy metals,etc.Thus,it needs to be upgraded before usage.In the present research,liquid extraction was implemented to pretreat the sewage sludge before liquefaction in order to produce bio-oil and bio-char with low heavy metals risks to the environment.Liquefaction bio-oil was upgraded by microemulsification and microemulsion with preferable fuel properties was formed.Finally,the byproduct from liquefaction,biochar was used as a kind of adsorbent to treat dye polluted wastewater and received good results.On the whole,this research provided a feasible method to utilize sewage sludge.To be specific,this thesis focused on the following researches:Liquefaction of sewage sludge under different temperature(ranging from 280 to 360 ?)with liquefaction solvent acetone or ethanol was conducted.The results suggest that these liquefaction parameters effected on the yields of bio-oil and bio-char.Higher temperature resulted in higher bio-oil yield but lower bio-char yield.Liquefaction with acetone as the solvents led to higher bio-oil yield than ethanol one.When liquefaction of sewages sludge was implemented at 360 ? with acetone as the solvent,the bio-oil yield reached 44.12%.Additionally,liquefaction parameters also impacted on metal distribution between bio-oil and bio-char.Liquefaction promoted the increasing concentrations of metals in solid bio-char product,but increasing temperature led to more metals distribution in bio-oil especially metals like Cu,Cr,Hg,Cd,V,Co,and Sn.Although with higher total concentrations in bio-char,the F1 and F2 fraction of metals,which are the fractions with high mobility,reduced considerably compared with raw sewage sludge.However,the mobile FI fractions of heavy metals in bio-oil increased considerably,with bio-oil from liquefaction with ethanol at 260 ? had as high as 60.5%of the F1 fraction of Zn,meaning its high environmental risk.In addition,the environmental risk of bio-oil and bio-char from liquefaction with ethanol as the solvent was higher than that of acetone one,respectively.Sequential liquid extraction can be a feasible way to extract heavy metals before liquefaction in order to obtain bio-oil and bio-char with lower heavy metals and lower environmental risk.The results show that the organic matter loss of SS was not obvious and the relative bio-oil yield calculated based on raw SS only reduced a little.But the F1 fraction of heavy metals or the direct environmental risk of the bio-oil and bio-char reduced to a large extent.Considering the solvent consumption and energy input,extracting F1 and F2 of heavy metals in sewage sludge can be a favorable method to produce bio-oil with low environmental risk and at same time with high yield.Microemulsion,compared with emulsion,has the merits of better storage stability,thermal stability,and lower activation energy(better ignition performance)with less risk of phase separation.It can be treated as a promising bio-oil upgrading technology.By microemulsifying bio-oil into Span 80 based diesel microemulsion can make the most of the bio-oil to produce bio-oil/diesel microemulsion for engine use.Among the different bio-oil produced with varied liquefaction parameters,bio-oil from liquefaction with methanol as solvent performed better in terms of consumption of surfactant.The microemulsification of bio-oil in diesel and stability mechanism of the microemulsion system can be well described by combing“like dissolves like"and the spherical shell mechanism.As long as the byproduct bio-char from liquefaction of sewages sludge is concerned,it had small surface area and volume,but it had abundant surface oxygen-containing functional groups such as carboxyl groups,lactonic groups phenolic groups,and carbonylic groups.This enables bio-char to effectively remove cationic dyes such as Methylene blue and Malachite green from water.The adsorption capacities of these dyes reached as high as 40 mg/g and 45 mg/g,respectively.These bio-chars can be developed to be cationic pollutants oriented adsorbents.The adsorption mechanisms of Malachite green on bio-char can probably be explained by ion exchange and the effect of functional groups.In consideration of bio-char yield and adsorption effectiveness,liquefaction of sewage sludge with acetone at low temperature could contribute to effective adsorbent production.This study conducted research on liquefaction of sewage sludge for bio-oil production,bio-oil upgrading,and bio-char for adsorption application.This is a systematic study about disposal and make use of sewage sludge which could be practically useful.More investigation should be carried out for producing bio-oil and bio-char with good properties and optimize the microemulsification process,and further promoting the development of such a technology system.