Study On Enhanced Primary Treatment Process And Preparation Of Biochar From Excess Sludge

In the urban sewage treatment process,the traditional activated sludge process has the characteristics of delayed aeration,large consumption of carbon sources and high sludge output,leading to the inconsistencies of the general trend of energy saving and emission reduction of international water treatment.Therefore,in this study,a kind of urban sewage treatment process without additional carbon sources is adopted,that is,chemical biological enhanced primary treatment-partial nitrification/anammox process,to realize the removal of organic matter,nitrogen and phosphorus in urban sewage.Firstly,the effect of different concentrations of polyferric chloride on the treatment of municipal sewage was studied through small laboratory experiments,and the flocculant dosage was applied to the field pilot plant to explore the effect of polyferric chloride enhanced bioflocculation on the treatment of municipal sewage,as well as the effect of iron salts on the activated sludge system of the plant.At the same time,in order to achieve the reduction and recycling of the remaining sludge,the remaining sludge in the first stage of enhanced treatment was collected,and then prepared into biochar through high-temperature pyrolysis.The surface structure of the biochar was analyzed,and the adsorption effect of sludge-based biochar on heavy metals in solution was explored(taking Cd²⁺as an example).The research contents and conclusions are as follows:?1?In the laboratory pilot experiment,the turbidity,Zeta potential,TP,COD and other indicators of sewage before and after the treatment of adding flocculant were measured to investigate the treatment effect of different concentrations of polyferric chloride on urban sewage.The results showed that it worked best on urban sewage treatment when the dosage of polyferric chloride was 45 mg/L,reaching the highest removal rate of COD and TP,as well as the lowest value of turbidity.?2?Polyferric chloride was applied to the field pilot plant to determine TP,COD and ammonia nitrogen in sewage before and after the adding of flocculant,and to explore the optimal dosage of polyferric chloride in the process of chemical enhanced biological flocculation.The results showed that adding 30 mg/L biological flocculation polymer ferric chloride contrast made TP removal rate increased by 39%and COD removal rate increased by 27%,while ammonia nitrogen removal rate did not change.The effect of polymeric ferric chloride enhanced biological flocculation on the treatment of urban sewage was ideal,the quality of effluent water could meet the requirements of typical shortcut nitrification/anaerobic ammonia oxidation process,which provided water quality for the successful start-up in the next phase of the pilot plant.?3?The effect of adding polymeric ferric chloride on the activated sludge system was further investigated.Through the measurement of SCOD in the effluent before and after dosing,it was found that polymeric ferric chloride had no effect on the removal of SCOD,mainly on the removal of colloids and particles;through the measurement of extracellular polymers in sludge,it was found that 30 mg/L of polymeric ferric chloride could inhibit the secretion of protein,resulting in the reduction of flocculation capacity of sludge itself.Next,the three-dimensional fluorescence spectrum of the influent and effluent water was tested.It was found that the three-dimensional fluorescence spectrum of the bioflocculation stage was weakened due to the removal of dissolved organic compounds from the raw water by the activated sludge,while the three-dimensional fluorescence spectrum of the synergistic flocculation stage of polymeric ferric chloride was greatly weakened due to the fluorescence quenching phenomenon caused by the presence of Fe³⁺in the sample.?4?In the pilot plant,the excess sludge in the first stage was collected and pyrolyzed to biochar at different temperatures.The results of scanning electron microscopy?SEM?showed that the surface morphology of biochar became more and more disorderly with the increase of carbonization temperature;FTIR showed that a large number of functional groups disappeared in the biochar during the process of carbonization temperature rising;Raman spectrum showed that the increase of carbonization temperature led to the obvious increase of the defect degree of biochar.The results of adsorption experiments showed that the biochar prepared at 800°C had the best adsorption effect on Cd²⁺at pH=7,and its adsorption process was more in line with the quasi second-order kinetic equation.X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?tests were carried out on the biochar before and after the reaction.The results showed that there was no formation of precipitate in the adsorption process,indicating that the adsorption mechanism of biochar on Cd²⁺was the complexation of surface functional groups.The same adsorption mechanism was also confirmed in the analysis of X-ray photoelectron spectroscopy.Figure[23]table[4]reference[111]...