Research On Enhanced Separation Of Organic/Inorganic Components From Sewer Sludge And Preparation Of Modified Cement

Sewer sludge is the main cause of overflow pollution during the rainy season,which can cause irreversible damage to the surrounding ecological environment.The traditional treatment and disposal methods of sewer sludge are unscientific and untimely,posing a significant threat to the environment and having a low value of recycling.There is an urgent need to update and upgrade the current sewer sludge treatment methods,adapt to the national ecological environment protection strategy.This research proposes to strengthen the treatment of sewer sludge to improve the quality of the treated product.Firstly,chemical treatment is used to strengthen the separation of organic/inorganic components from sewer sludge to improve the relative content of inorganic components.Subsequently,through the combination of PAC and Ca O,the sewer sludge separated from organic components is subjected to enhanced coagulation and dehydration,reducing the moisture content of the sludge,further improving the proportion of inorganic components,and enhancing the value of building materials reuse.Finally,the comprehensively treated dewatered sewer sludge was mixed with cement to prepare modified cement,and the acid corrosion resistance of the modified cement was investigated.The main experimental conclusions are as follows:（1）All six treatments selected for this study enhanced the solubilisation of organic matter fractions from the sewer sludge.The enhanced solubilisation of COD reached 7.4,3.3,24.7,7.3,5.7 and 4.8 times that of the blank control after 12 hours of treatment with Na OH,Ca（OH）₂,alkali-heat,resin,plant ash and sodium chloride respectively.The highest rate of VSS reduction（50.6%）was achieved in the sewer sludge after alkali-heat treatment,followed by Na OH（41.0%）,resin（36.7%）,plant ash（30.0%）,Ca（OH）₂（13.2%）and sodium chloride（13.0%）.The VSS reduction pattern was consistent with the COD leaching pattern,indicating that the source of supernatant COD was mainly the leaching and release of organic matter from the solid phase of the sewer sludge.The results of 3D-EEM showed that the alkali-heat treatment significantly promoted the release of humic acid-like substances,and Na OH,resin and plant ash treatments significantly leached tryptophan-like proteins and soluble microbial by-products.The fluorescence peaks after Ca（OH）₂ and Na Cl treatment were relatively weak and the release of fluorescent substances was limited during the treatment period.By cracking and separating the endogenous organic matter of the sewer sludge,the stabilisation of the sewer sludge is achieved and the relative proportion of inorganic components is increased,providing favourable conditions for subsequent resourceful disposal.（2）The combined conditioning of PAC and Ca O can effectively improve the dewatering performance of sewer sludge.For the sludge after alkali-heat treatment,the optimal dosage of PAC is 0.0212 g Al/g SS,and the water content,CST,and SRF of the sludge decreased by 9.8%,96.6%,and 98.0%compared to the blank control group,respectively.For the sludge treated with resin,the optimal dosage of PAC is 0.0059 g Al/g SS,and the water content,CST,and SRF decrease by 8.6%,93.3%,and 99.2%,respectively.For the sludge treated with plant ash,the optimal dosage of PAC is 0.0159g Al/g SS,and the water content,CST,and SRF decrease by 12.6%,39.5%,and 76.9%,respectively.The optimal Ca O conditioning concentration of sludge treated with alkali-heat,resin,and plant ash is 8 g/L.During the PAC conditioning process,the changes in sludge EPS organic components（proteins,polysaccharides,and humic acids）are consistent with the dehydration performance.The mechanism analysis shows that PAC improves the sludge dewatering performance through adsorption,neutralization,and compression of double electric layers,promoting the discharge of internal bound water.Ca O mainly serves as a skeleton support between sludge particles,maintaining the pore structure of the sludge cake during high-pressure dehydration,and allowing the internal water to be smoothly discharged along the pores.Zeta potential and correlation analysis also prove that PAC mainly improves sludge dewatering performance through adsorption,neutralization,and compression of double electric layers.Through intensive coagulation and dewatering treatment,the water content and organic fraction of the sewer sludge is significantly reduced and the relative content of the inorganic fraction is increased,reducing the likelihood of leakage during transport and increasing the value of the treatment product for resourceful reuse.（3）The modified cement with dewatered sewer sludge particles exhibits excellent acid corrosion resistance.The results of infrared spectroscopy,thermogravimetry,and XRD analysis showed that the hydration process of the cement blocks with various admixtures was similar,and the sludge particles did not have a negative impact on the hydration process.After 90 days of corrosion,the modified cement is weakly eroded,with less dissolution of internal substances.Sludge particles improve the acid resistance of the modified cement.The verification results of the acid corrosion resistance performance of modified cement show that after 90 days of corrosion,the mass loss rates of cement test blocks with four admixtures of 10%,20%,30%,and 40%respectively reach 13.5%,13.4%,10.5%,7.4%,and 6.7%,and the acid corrosion resistance effect increases by0.92%,21.8%,45.2%,and 50.1%,respectively.The larger the sludge particle ratio,the smaller the increase in environmental p H during corrosion,indicating that the modified cement exhibits chemical inertness during the corrosion process.Through comprehensive analysis,the addition of PAC in the enhanced coagulation dehydration experiment helps to transform the aluminum phase products（such as calcium aluminate and aluminum oxide gel）in the hydration products,and inhibits the increase of Ca（OH）₂ content.The transformation of chemical properties makes the modified cement show relative chemical inertia in the acidic environment,so the acid resistance of the modified cement is improved.The results show that the sludge product after comprehensive treatment have strong recycling value for building materials.After comprehensive treatment,the sludge product has a strong potential for reuse as building materials,providing proof of feasibility for new resource disposal and helping to realise a new model of"closed-loop management"of sewer sludge.