Preparation Of Granular Sludge From Water Supply Plants And The Control Of Heavy Metals In Urban Surface Runoff

Heavy metals carried by urban surface runoff enterd the surface water bodies under the action of rainfall erosion and had a serious impact on urban water environment.How to remove the heavy metals of water body effectively is of great significance to the urban water environment.Dewatered sludge from water supply plants with the high surface area used to adsorb and remove heavy metals in surface runoff.However,alumium sludge from water supply plants was block-shaped and easy to be consolidated.When used as adsorbent filler in engineerin application,it would lead to the decline of infiltration rate of facilities and accelerate the clogging of facilities and reduce the service life of facilities.It’s difficult to realize the long-term removal of heavy metals from runoff and the resource utilization of alumium sludge.Therefore,the purpose of the study was to develop and prepare a kind of granular sludge from water supply plants to achive the stable granulation,to clarify its adsorption performance and mechanism of heavy metals and to investigate its removal effect on heavy metals in simulated runoff when it used as a filler.Aiming at the problem of the sludge from water supply plants in the practical application,a series of different mass ratio of granular sludge was synthesized with dewatered sludge from water supply plants and clay,and hydraulic scouring loss rate,aluminium dissolution amount,sintering temperature and the adsorption effect of heavy metals and other multiple factors were investigated.Utimately,the dewatered sludge from water supply plants and clay quality ratio of 1:2 was determined to be the ready granular sludge.The granular sludge was characterized by scanning electron microscopy（SEM）,infrared spectrum（FTIR）and X-ray diffraction（XRD）.The results showed that the granular sludge exhibited rough surface and porous structure,specific surface area was 24.5261m²/g and the aperture was 0.08cm³/g;The main element of granular sludge were O、Si、Al、Fe and abundant functional active groups on the surface.The adsorption-desorption behaviors of Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺on granular sludge were investigated according to the static experiments.Results showed that the removal rate of Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺by granular sludge increased with the increase of reaction time and initial concentration.The pseudo-second-order kinetics equation and Langmuir isothermal equation could better describe the adsorption process of granular sludge on Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺,indicating that the adsorption mechanism of four heavy metal ions by granular sludge was monomolecular chemical adsorption.The adsorption of Cu²⁺,Zn²⁺and Cd²⁺by granular sludge were endothermic reaction with an increase in entropy and the better spontaneous adsorption reaction with the higher temperature.The adsorption of Pb²⁺was exothermic reaction with an decrease in entropy and the better spontaneous adsorption reaction with the lower temperature.The The removal efficiency of four metal ions by granular sludge increased with the increase of pH value.When the pH value was 4-5,the removal efficiency of Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺by granular sludge were the best.When four heavy metal ions coexisting,the granular sludge preferentially adsorbed Cu²⁺and the adsorption order of four heavy metals was:Cu²⁺>Pb²⁺>Cd²⁺>Zn²⁺.The main adsorption mechanism were electrostatic attraction,hydroxyl substituents and surface complexation.The desorption rate of Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺by granular sludge increased with the increase of time and reached the maximum at 300min.The desorption rate of Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺by granular sludge decreased with the increase of solution pH value.At pH 2,the desorption efficiency of Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺by granular sludge were better.The removal efficiency of the four heavy metal ions by granular sludge were still above 75%after adsorption-desorption three cycles,indicating that the granular sludge had better cyclic adsorption performance.The removal effect of heavy metals from urban runoff by using granular sludge fillers was investigated.The results showed that the removal efficiency of Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺by devices decreased with the increase of recurrence period and rainfall interval,and increased with the increase of rainfall duration and packing depth.The removal efficiency of heavy metals by device filled with granular sludge of water supply plants was better than that in devices filled with traditional media.The accumulated Cu、Zn、Pb、Cd could be released from granular sludge.The released amounts incrased with the increase of temperature and recurrence period and rainfall duration.However,the released amounts of granular sludge from water supply plants were less than inert filler under the influence of various factors.