Reuse And Treatment Of Heavy Metals-containing Wastewater

There exists a severe water resource crisis, especially shortage because of water quality contaminated by heavy metals in our country. The discharge of heavy metals containing wastewater not only causes waste of resources but also influences the safety of drinking water. The treatment of heavy metals containing wastewaters has always been an important project in the field of world environmental protection. At present, the accumulating effect of the discharges in the field of nonferrous-smelting industry has become the biggest potential danger in drinking water resources. It is of very importance to study on the novel technique for treatment and reuse of heavy metals containing wastewater, to resolve water resource crisis and to improve sustainable development of non-ferrous industry.The lime milk neutralization - complexing - circumfluence technique based on the characteristics and reuse of heavy metals containing wastewater from nonferrous industry was brought forward, combining with practical producing process. With this novel technique the technical problem that only under the condition of high pH value can the purified water treated by traditional lime milk neutralization technology satisfy the discharge standard has been solved. The objective that the nonferrous heavy metal containing wastewater has satisfied the discharge standard when the pH value was controlled to 8.5 has been achieved and the concentration of Ca²⁺ has declined to about 400 mg/L. The new style activated factor PMB with strong flocculent ability in the water treatment process was developed. The requirement for the quantity of the reflux residue during the water treatment process can be fully satisfied when the reflux ratio was controlled at 5%. The average moisture content of the residue after concentration was 77.29%, dropped 20.69% compared with that of the traditional lime milk neutralized residue (97.98%). The heavy metal content in the residue formed in the novel treatment technique has been increased to 31%-33% from 25%-27% of the old technique, contributing to the recycle of the heavy metals. The process of the new technique was stable and reliable and all the heavy metal (Zinc, Lead, Copper, Cadmium, Arsenic) ionsand the pH value of purified water has satisfied the Integrated Wastewater Discharge Standard(GB8978-1996) during 4 months industrial operation.Water quality stabilizing reagent with the performance of scale retardance and corrosion inhibition satisfying the excellent correlative standard was designed and developed according to the relationship between structure-activity and synergistic effect, scale retardance performance of the designed water quality stabilizing reagent was investigated by the experiments of static quick scale retardance and dynamic scale retardance. In order to discuss the mechanism of water quality stabilizing reagent inhibiting or delaying the formation of CaCO₃ and CaSO₄, some modem testing methods, such as SEM, XRD and so on, were adopted to analysis the phase and microstructure of the formed scale. Water quality stabilizing reagent adsorbed on the crystal surface and lattice point of CaCO₃, CaSO₄ hinders or distorts the growth of the crystals, and then scale formation process was destroyed, the aims of corrosion inhibition and scale retardance were realized. Industrial experimental research indicates that it is obvious in decreasing the trend of scale formation and corrosion of recycle water with addition, of YJ water quality stabilizing reagent into the treatment system. Dynamic fouling thermal resistance of recycle water is less than 1×10^-4m²Â·h·c/kcal, fouling adhesion velocity is less than 15mg/cm²Â·mon, all indexes of purified water could satisfy the requirement of recycle water.The effect of the purified water reuse on zinc electrolysis process was investigated by Linear Sweep Voltammetry, Tafel plot, AC Impedance, Chronoampermetry, and so on. It could be found that stabilizing reagents could increase cathode polarization of zinc electrolysis process through adsorption on the electrode/electrolyte interface, being helpful for grain refinement and zinc layer smoothing. Water quality stabilizing reagents inhibit hydrogen evolution reaction to some degree, contributing to the improvement of current efficiency of zinc electrolysis.For the deeply purification of the lime-purified water the bio-formulation B was designed, and the technique of "biological adsorption-decalcification" was put forward. Based on the properties of heavy metals in purified water, after characterization and adjustment using addition agent H, bio-formulation B is designed and developed with the main composition of the waste activated sludge from municipal sewage treatment plant, it contained a lot of functional bacteria with high efficiency. The technological conditions of treatment of heavy metal containing wastewater with lower concentration were optimized, the system of bio-formulation B and Na₂CO₃ used to deeply purification - decalcification controlled freely was combined. Biosorption behaviors of heavy metal ions, such as Cu²⁺, Cd²⁺ and Zn²⁺, were carried out using waste activated sludge as adsorption material, and effects of parameters, such as pH value, temperature, reaction time and sorption duration, were studied in details. The results indicate that the removal rates of Cu²⁺,Zn²⁺,Cd²⁺ with low concentration are 96.47%, 80%, 90% respectively adsorbed by waste activated sludge. The optimum conditions were obtained through experiment with the heavy metal removing and decalcification using bio-formulation B and Na₂CO₃ individually. Under the optimum conditions the continuous experiments were carried on, the concentration of Cu²⁺, Pb²⁺, Zn²⁺, Cd²⁺, and Ca²⁺ can satisfy tlie Water Quality Standard for Drinking Water Sources(CJ3020-93). The reusing-rate reached to 100%, or realized zero draining. The operating cost was 0.84yuan/m³ under the scale of 32m³/h, the operating cost only was 0.5271 yuan/m³ under the scale of 1000m³/h.The adsorption model of the heavy metal ions by bio-formulation was built. In single heavy metal ion system, the sorption process of Cu²⁺,Zn²⁺ and Cd²⁺ are in accordance with Freundlich model. According to the Zeta potential the PAM was helpful for the precipitation during the process of lime-purified effluent using bio-formulation B and K₂CO₃ waste liquid, while during the process of lime-purified effluent using bio-formulation B and Na₂CO₃ waste liquid, there was the same precipitation effect without PAM. The mechanism of treatment of heavy metals and decalcification by bio-formulation B were researched by the modem test and analytical method, such as XRD, IR and so on. The reaction product was mainly crystalline solid CaCO₃ both using two kinds of waste liquid. It has been identified that there exist a lot of functional groups and chemical bonds, such as -C=O, -NH₂, C=C or double bond in benzene ring, CH_3-, CH_2-, and -C-O- existing in the bio-formulation B. Because of the adsorption of heavy metal and the alkaline media of wastewater, their peaks intension and positions changed. During the treatment of lime-purified water, the heavy metals were deeply removal through the functions of adsorption, complexing, precipitaion, ion-exchange by the bio-formulation B and its metabolite. The Ca²⁺ was removed with addition of Na₂CO₃, and the concentration of Ca²⁺ could be controlled freely.