Studies On Zero Liquid Discharge(ZLD) Technology Of Wet Flue Gas Desulfurization Wastewater From Coal-fired Power Plants

There are many kinds of pollutants in desulfurization wastewater from Coal-fired Power Plants, such as suspended solids, salinity, heavy metal ions(cadmium, mercury, lead, nickel, etc.), fluoride, sulfide, COD and other indicators, the contents of which were more than the national discharge standard and can lead to heavey environment pollutions. If the wastewater was discharged directly, the environments would be polluted seriously, and human health would be endanged further. Therefore, it was imperative to study the comprehensive utilization technology of desulfurization wastewater, via the Zero Liquid Discharge(ZLD) technology of desulfurization wastewater, significant environmental benefits, economic benefits and social benefit would be achieved.The physicochemical method and adsorption were used to pretreat the desulfurization wastewater from a Coal-fired Power Plant in Jiangsu, and the optimal operating parameters were achieved via orthogonal tests, and then the Evaporation crystallization was used to further dispose the pretreated wastewater so that the recycling water and salts from the wastewater can be obtained, which resulted in the achievements of the Zero Liquld Discharge(ZLD) technology of desulfurization wastewater.The main conclusions were as follows:The physicochemical method was mainly composed of neutralization precipitation, sulfide precipitation and coagulation. the optimal operating parameters of the physicochemical method were achieved via orthogonal tests. When the neutralization precipitation was controlled at p H= 9, stirring speed 200 r/min, stirring time 20 min, the removal rate of the lead, cadmium and nickel ions were 97.14%、69.13%, 79.81% respectively. When the addition of Na2 S was 21mg/L, stirring speed 200 r/min, stirring time 40 min, the removal rate of the lead ions was 80.94% during the sulfide precipitation. When the addition of coagulant PAFS and PAM were 2.5 m L/L and 2.0 m L/L respectively, the turbidity of the treated wastewater was decreased 91.3%.The KOH activated, magnetic-loaded and sulfur-loaded biomass activated carbon were prepared by biochar. The pore structure parameters of modified activated carbons were greater than that of the raw charcoal. The KOH activated carbon contained more acid carboxyl groups and less lactone groups. The magnetic-loaded biomass activated carbon contained more carboxyl and carbonyl groups, and less lactone groups and phenol hydroxyl. The sulfur-loaded biomass activated carbon contained more carboxyl, and less lactone and carbonyl groups.Experiments of the adsorption effect of p H, temperature and operating time on Pb(II)、Cd(II)、Ni(II) were carried out, and the results showed that the optimal operating p H value was 6. There was competitive adsorption during various heavy metal ions in mixture system, and the removal sequence was Cd(II) > Ni(II) > Pb(II), lead and nickel was inhibited by cadmium. Comprehensively, the removal efficiency of the magnetic-loaded biomass activated carbon was better than the other twos.During the further treatments of wastewater by evaporation crystallization, the industrial salt, with uniform size distribution and the average crystal size of 414 μm was obtained at the evaporation rate of 50 m L/h and seeds-loaded 2%. The quality of industrial salt met the national refined industrial salt secondary standard(GB/T 5462-2003), and condensate water reached the standard of industrial boiler water(GB/1576-2008).