Effect Of Alkaline Conditions On The Disintegration Of Gelatinous Structure And Adhesion Resistance Promotion Of Sewer Pipeline Sediments

The sewer system is one of the essential infrastructures in urban engineering,which plays an important role in collecting and conveying domestic sewage/industrial wastewater.At the same time,it also shoulders the important responsibilities of water environment pollution prevention and control,water resources protection and so on in the city.Particulate matters are susceptible to settling and siltation in sewer pipes at low flow rates and during long periods of conveyance,which brings numerous hazardous risks,such as sewer blockage,sewer corrosion,sediment overflow pollution,etc.The gelatinous and glutinous structure induced strong hydraulic erosion resistance and bottom siltation of sediments in sewer systems.In this paper,from the principle of adhesion action and key factors of sewage pipe sediment,we propose to use sodium hydroxide,alkaline plant ash,sodium pyrophosphate and coupling treatment to break the gelatinous structure of sediment and enhance its adhesion resistance,and then further explore sediment management from the perspective of sediment anti-scouring mechanism.The sediment was cultivated by using a laboratory-scale fully mixed reactor with an electronic constant velocity stirrer to simulate a gravity flow sewage pipeline.The effects on sediment adhesion properties and erosion resistance were investigated in terms of sediment particle initiation and average adhesion changes.The disintegration efficiency of gelatinous structure was assessed in terms of sediment biopolymer release,extracellular polymer molecular deconstruction and outward migration,microbial cell lysis,as well as changes in surface electronegativity.Correlation analysis was used to identify the response factors for sediment erosion promotion.Research indicated:（1）The alkaline hydrolysis could impair gelatinous adhesion and erosion resistance of sewer sediments.The rising p H continuously contributed to reducing sediment adhesion and promoting hydraulic floating.Alkaline hydrolysis resulted in the sparing of EPS protein structure and functional group changes,i.e.,the shift of the molecular structure of tyrosine and tryptophan-like proteins fromα-helix toβ-turn.Subsequent internal disruption of the sediment triggers out-migration and dissolution of the gelatinous biopolymers（proteins,humic acids and polysaccharides）.EPS matrix electronegativity increases and the ability of adhesion aggregation in the deposit is eliminated.The economic benefits of alkaline hydrolysis are significant,with the price per meter of pipe sediment cleaned being 29.51-55.02%of that of high-pressure water jet flushing and perforated pipe flushing,an economically sustainable strategy that will improve the ability of drainage pipes to self-clean under gravity effluent shear stress.（2）Under the application of plant ash,the sensitivity of sewer pipeline sediment to sewage flow is enhanced,which effectively weakens the erosion resistance of sediment to hydraulic shear stress in the sewer system.After 0.10g Plant ash/g TS treatment for7h,the average adhesion force was sufficient to reduce by 91.14%,the shear stress value at zero shear rate was reduced by 76%,and the sediment particles initiation was increased by 10.98 times.Dense cracks and pores on the surface of the sediment were confirmed by scanning electron microscopy and specific surface area analyzer,and the gelatinous structure was significantly disintegrated.The economic and environmental benefits of alkaline plant ash as a solid waste,at almost no cost and even better than sodium hydroxide,for sediment flushing management would be incalculable.In the strong attack of grass ash on sediments,tyrosine-like proteins,tryptophan-like proteins,soluble microbial by-products and proteinα-helix structure showed significant positive correlations with adhesion,positive correlation means that matter is more easily deconstructed and transferred to the outer layers;humic acid-like substances,fulvic acid-like substances and proteinβ-turn structures showed negative correlations with adhesion,The negative correlation is attributed to the outward migration of material in response to oxaliplatin,a structurally stable substance that may have a greater effect on adhesion.O-P-O,C=C,C=O,N-H,C-N,C-O-C,C-OH and other functional groups are closely related to adhesion.（3）Sodium pyrophosphate coupled alkaline hydrolysis induces disintegration of the sediment EPS matrix and deterioration of the gelatinous adhesion function.At an optimal dose of 0.25 g Na₄P₂O₇/g TS,sodium pyrophosphate had a slight weakening effect on the adhesion properties of the deposits,with the average adhesion force reduced from 4.52n N to 2.37 n N.However,under 0.25g Na₄P₂O₇/g TS coupled with alkaline hydrolysis,the sediment adhesion performance was severely reduced,and the average adhesion force decreased from 4.52n N to 0.98n N.During treatment,EPS migrates and transforms according to the process of non-extractable EPS→TB-EPS→LB-EPS→S-EPS,in which a large amount of humic acid migrates and dissolves,followed by proteins,thus triggering changes in sediment gel biopolymer functional groups as well as enhanced surface electronegativity,which accelerates the sediment adhesion resistance.