| Based on the current problem of inadequate carbon sources in urban sewage treatment plants in China,some scholars have proposed the concept of carbonization of excess sludge.This is a good measure of resource reuse compared to the landfill disposal of excess sludge.At present,in the process of carbonization of excess sludge,physical or physicochemical methods are mostly used to destroy the cell wall and realize the release of organic matter in the excess sludge cells.Existing research shows that there is few lowmolecular-weight organic matter or VFA in the sludge after cell wall-breaking treatment,and hydrolyzing and acidifying treatment can help increase the VFA content.However,the broken sludge usually costs a long time to ferment and has a low VFA-conversion rate,which restricts the carbonization and utilization of the remaining sludge.In urban sewage plants,the proportion of inorganic substance in the excess sludge is getting higher.However,within the scope of reference data,it is found that there are few documents related to the carbonization of low organic excess sludge.In view of the above problems,based on the results of the group’s previous research "Microwave Treatment of Excess Sludge and Alkali-Soluble Elutriation Technology",this paper systematically studies the microwave pretreatment using comparative experimental methods with low-organic excess sludge.The characteristics of VFA conversion during the fermentation process of sludge mixture,sludge centrifugal supernatant,and sludge static mixed-upper-layersolution were studied after microwave heat treatment.On the basis of "microwave treatment and alkali-soluble elutriation",a technology of sludge static mixed-upper-layersolution fermentation that can remove the high inorganic influence in the native sludge is formed,assisting zero-valent iron acidification fermentation,and achieving the efficient conversion of low organic matter VFA carbon source.The primary results of research are as follows:(1)Use microwave treatment of alkali-soluble elutriation to process low organic excess sludge(VSS/SS = 0.34),and the pretreated sludge mixture was subjected to hydrolysis and fermentation experiments.The effects of hydrolysis acidification fermentation temperature,p H value and zero-valent iron on carbonization of excess sludge were studied.The study found that: as the temperature of traditional mixed-liquid fermentation increased,the result of excess sludge carbonization was improved;the effects of multiple temperatures on the carbonization effect of the sludge were compared,and it was concluded that 30℃ was the most suitable for anaerobic fermentation temperature.On this basis,the effect of initial p H on fermentation effect of excess sludge was investigated.The study found that it takes 8 days to obtain the maximum SCOD concentration and VFA output of traditional mixed-liquid fermentation.The comparison found that the maximum growth rate of SCOD was at p H=10.0,the VFA output was about1718 mg/L,accounting for 32.48% of SCOD.The proportion of acetic acid and propionic acid in VFA was low.In addition,by adding 3g/L of zero-valent iron to the system,the analysis found that the carbonization effect of the remaining sludge was enhanced,which not only increased the SCOD concentration and VFA production,but also shortened the fermentation time.Under each p H condition,when p H = 10.0,the maximum SCOD concentration was 5160mg/L,and after 6 days of fermentation time,the VFA concentration basically reached the maximum value of 3239mg/L.(2)The pretreated sludge was centrifuged,and the supernatant of the sludge was subjected to hydrolysis and fermentation experiments.The effect of p H on VFA was mainly studied.The analysis found that the time required for sludge acidification production to reach maximum concentration was shortened by using centrifugal supernatant to ferment,which took average of 3 days,and the VFA yield was greatly improved.After comprehensive consideration,it is concluded that p H = 5.0 as the sludge carbonization fermentation sludge centrifugal supernatant has better fermentation results,which can greatly increase the VFA yield(about 2679.31 mg/L),and improve the proportion of low-molecular organic acids such as acetic acid and propionic acid,which is conducive to reuse of excess sludge.(3)The pretreated sludge is allowed to stand still for 30 minutes,and separate.Obtain mixed-upper-layer-solution with the method of decantation,and then subjected to a hydrolytic acidification experiment.Studies have shown that the VSS / SS of the mixed supernatant is 0.51,which is a significant increase compared to 0.34 of the original sludge,which helps reduce the impact of inorganic matter on the sludge reuse process.The effect of p H on the efficiency of VFA conversion in anaerobic fermentation was further studied.The results show that when the organic matter ratio of the remaining sludge is increased,the SCOD release effect of the sludge can be enhanced,which is beneficial to the carbonization process of excess sludge.The growth rate of SCOD in the environment of p H10.0 reached 44.39%,and the maximum concentration of VFA was 3603 mg / L,accounting for 62.23% of SCOD.Based on this test,zero-valent iron was introduced to enhance anaerobic fermentation.The test showed that the concentration of SCOD was further increased.At p H 10.0,the maximum SCOD concentration exceeded 6300 mg / L,the VFA concentration reached 4982 mg / L and VFA / SCOD was about 80%,which was2.7 times the carbonization of the traditional mixed liquid,and fermentation time is shortened.In addition,when the p H on equal conditions,different fermentation methods have little effect on the C/N and C/P.Moreover,when p H = 10.0 it is basically greater than 18 and 61,which has a better carbon source result.It was concluded that by removing a large amount of inorganic matter in the excess sludge and adding zero-valent iron,the yield of low-molecular carbon sources during the anaerobic fermentation of the excess sludge was successfully enhanced. |
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