Simulated Application Of Calcium Alginate Crosslinked Zeolite Microspheres For Removal Of Heavy Metals From Sludge

A large amount of sludge will be produced every day in the sewage treatment plant.The content of organic matter,nitrogen and phosphorus is far higher than the content of the corresponding components in the soil in the northwest,and it has an excellent prospect for the application of agricultural fertilizer.The biggest limiting factor is the problem of excessive heavy metals in the sludge.In this paper,a new type of heavy metal adsorption microsphere was prepared by adding sodium alginate and zeolite into calcium chloride solution to produce a new type of heavy metal adsorption microspheres.First,the adsorption characteristics of heavy metal ions represented by Pb²⁺and Cd²⁺in the solution were studied by the calcium alginate crosslinked zeolite microspheres;Five steps extraction method combined with atomic absorption spectrophotometer was used to measure the contents of Pb,Cu,Cd and Zn of four kinds of heavy metals in the dry sludge samples of three sewage treatment plants in Xi'an,The five forms were divided into unstable and stable states with the migration intensity and the harm to the environment?T1>T2>T3>T4>T5?,T1,T2,T3 and T4 belong to the unstable state,T5 belongs to the stable state,and the environmental risk assessment is carried out by the land accumulation index method;Finally,based on the characteristics of calcium alginate cross linked zeolite microspheres for adsorption of heavy metals,a laboratory simulation study was carried out,The results of the study are as follows:?1?The adsorption saturation of alginate crosslinked zeolite microspheres at Pb and Cd ions of 150mg/L is 21.6mg/g and 12.4mg/g respectively.The adsorption of heavy metal ions accords with the quasi two level kinetic model and chemical adsorption.Compared with the same conditions,the adsorption saturation of single zeolite 17.1mg/g and6.7mg/g increased by 26.3%and 85.1%respectively,especially for Cd adsorption saturation.?2?A large number of negative carboxylic acid root ions?COO-?can be combined with Pb²⁺and Cd²⁺in calcium alginate.The heavy metal salts of algic acid are deposited in the capsule and are independent of the active sites of zeolite.Weaken the mutual inhibition of lead and cadmium and increase the adsorption saturation capacity of alginate crosslinked zeolite microspheres when the two heavy metals coexist.It can adapt to the conditions of coexistence of heavy metal ions and is suitable for treating municipal sludge containing heavy metals.?3?The environmental risk assessment was carried out from the sludge utilization index method of three sewage treatment plants.Pb and Zn were moderate pollution,Cd and Cu were strong pollution levels.The entry into the ecological environment without treatment would cause serious harm,especially Cd and Pb have strong toxicity.?4?The sludge produced by the A²/O bioreactor of the Xi'an sewerage wastewater treatment plant was simulated and treated with calcium alginate crosslinked zeolite microspheres,the environmental risk assessment of heavy metals in the sludge was reduced to the level of Pb and Zn from moderate pollution to no pollution level.The strong pollution of Cd and Cu has been reduced to moderate pollution level,and the treated sludge is more suitable for compost.