Preparation Of Coating Materials For Sewage Pipes And Its Experimental Research On Anti-microbial Corrosion

As a conscience project for the healthy life of residents,municipal sewage pipe network plays an important role in urban sewage treatment system.During the daily operation and maintenance of sewage pipe network,there are many problems,among which the problem of pipe corrosion caused by acid production by microorganisms is particularly serious.At present,sewage pipe anti-corrosion measures are divided into three main categories:optimization of pipeline design,control of sulfide in the pipeline,and improving the performance of materials.Among them,the control method of improving material performance has received wide attention because it does not require operation and management,and the advantages of adding chemicals.Among many materials,aluminate cement and aluminous geopolymer have become a hot spot for research because of their excellent anti-corrosion properties such as high acid neutralization ability,hydrated aluminous gel protective layer,inhibition of acid-producing bacteria activity and high wear resistance.In this study,drinking water treatment sludge（DWTS）was used as a supplementary cementitious material to be compounded with ordinary silicate cement to increase the aluminum content of the cementitious system to improve the corrosion resistance of the cementitious material and to realize the solid waste resource utilization of the feedwater sludge.However,the optimal pretreatment temperature of DWTS and the corrosion resistance of DWTS modified materials in the corrosive environment of sewage microorganisms and the potential anti-corrosion mechanism are not clear.In this paper,the corrosion characteristics of DWTS modified silicate coating materials in the corrosive environment of sewage microorganisms are investigated and the corrosion resistance mechanism is speculated with the ultimate purpose of slowing down the corrosion of sewage pipes with DWTS modified silicate coating materials as the anticorrosion method.The study concluded as follows.（1）The contents of SiO₂and Al₂O₃ in DWTS are 35.58%and 32.26%,respectively,which meet the requirement of pozzolanic activity.The suitable heat treatment range of DWTS is from 400°C to 1000°C,and DWTS calcined at 800°C has the highest reactivity due to the presence of a large amount ofγ-Al₂O₃(Al^IV)and amorphous SiO₂（Q⁴）,and the hydration is C-A-S-H.The mineral structure of DWTS changes during calcination similarly to the transition from kaolinite to metakaolinite and eventually to mullite.The content of TOC in sludge is an important index that restricts whether it can be used as a supplementary cementitious material.The TOC in the original sludge is 5.78%,and when the treatment temperature is higher than 400°C,the TOC content can be controlled to less than 0.5%.（2）The doping amount of DWTS will affect the mechanical properties,setting time,hydration characteristics and corrosion resistance of the system to different degrees.For the mechanical properties,when the dosing is lower than 15%,the flexural and compressive properties of the cementitious system are improved,but when the dosing is higher than 25%,DWTS will have a negative impact on the system;for the setting time,DWTS causes the aluminum content in the system to rise,showing the phenomenon of rapid setting and early strength development,and the relatively high specific surface area of sludge will cause the standard consistency of water demand to rise;for the hydration characteristics,DWTS affects the hydration process of the system through filling,dilution and pozzolanic activity at the same time,promoting the generation of hydration products such as C-A-S-H and C-A-H,but the incorporation of a large amount of sludge will cause stronger carbonization phenomenon;for corrosion resistance characteristics,due to the presence of more hydration products containing aluminum in the system and the dilution effect reduces the generation of corrosion products such as gypsum,the incorporation of DWTS after the system has certain anti-corrosion properties,but the higher dosing will cause the system porosity rise,its anti-corrosion performance is poor.Comprehensive evaluation,DWTS modified cement-based coating materials of the better doping amount of 15%.（3）The admixture of DWTS will cause the concentration of Al³⁺in the biofilm of the coating surface to increase from 1.64 mg/L to 6.83 mg/L to 9.65 mg/L,and mainly enriched in TB-EPS.As the Al³⁺precipitation will have a toxic inhibition effect on the biofilm,reducing the amount of biofilm on the surface of the coating and causing the microorganisms to release more proteins and polysaccharides into the extracellular polymer for protection.However,the biofilm in the stabilization phase adapts to the toxic inhibition of Al³⁺and causes the whole biofilm to be more dense due to the bridging effect of Al³⁺in each carbon and oxygen-containing group of TB-EPS.The optimum pretreatment temperature of DWTS is 800°C and the optimum sludge substitution ratio in the cementitious system is 15%,and the anti-corrosion mechanism of the coating material is mainly due to the higher denseness of the cementitious system at the better material ratio,the higher C-A-S-H and C-A-H hydration products showed anti-corrosion properties,rather than the poor microbial activity in the biofilm due to Al³⁺precipitation caused by DWTS,i.e.,the weak inhibition of aluminum ions.