The Research On Biological Risk And Control Measures For Biological Activated Carbon Process

In this paper，after investigating and researching the biological risk of thebiological activated carbon process, we research how to control in a long term thebiological safety of the water out from biological activated carbon process, and suggestvalid measures to achieve the biological safety for the out-water of biological activatedcarbon process.In biological activated carbon process, microbial biomass increase with depthdeclining. When water temperature is between25-30℃, the total bacterial count ofout-water of biological activated carbon process is in104order of magnitude, and themaximum value is6.13×104CFU/ml. In biological activated carbon process, it isexisting that invertebrates such as rotifers, cyclops and nauplius break out. In theprocess of investigation, there are two peaks of rotifers in out-water and the maximumvalue is602ind/m³; there are three peaks of cyclops in out-water and the maximumvalue is370ind/m³; and there are three peaks of nauplius in out-water and themaximum value is139ind/m³. The abundance of rotifers and cyclops in the carbonlayer will influence the one in out-water.The microbial biomass on carbon and the total bacterial count in water willincrease with filter speed increasing, and this leads to increased risk of water microbes.When the filter speed increases from8m/h up to10m/h, the microbial biomass oncarbon changes most significantly and increased3.0×10⁶CFU/g. The risk ofoutbreaks and reveal of microorganisms and invertebrates will be reduced significantly,when the filter speed is8m/h.In biological activated carbon process, it will lead to turbidity of out-water frombiological activated carbon process slightly increasing that improve the backwashingstrength. At the end of a filter cycle, the microbial biomass of out-water frombiological activated carbon process with different backwashing strength have nodifference. When the reverse washing intensity is6.6L/m²Â·s, the peak of rotifers in theout-water is610ind/m³ï¼Œyet When the backwashing intensity is16.0L/m²Â·s, the peakof rotifers in the out-water is130ind/m³ï¼Œand this indicates improving the reverse washintensity can reduce the density of invertebrates such as rotifers, cyclops and naupliusin the out-water. Besides, increasing the backwashing strength can greatly reduce thecyclops abundance in the activated carbon filter layer. In addition, the rotifers abundance in the carbon layer will irregularly appears peak, and the peak of rotiferswill increase with the back washing being increasing.For biological activated carbon process, extending filter cycle can reduce themicrobial biomass in out-water. For six days filter cycle, there is the lowest averagemicrobial biomass in out-water-25000CFU/mL. Shorting filter cycle can significantlyreduce the invertebrate abundance in the activated carbon layer and out-water. Whenfilter cycle is1d, the peak of invertebrate can be effectively avoided.Adjusting the operation parameters barely influences the pH in out-water ofbiological activated carbon process. Lowering filter speed will lead to DOconsumption increases, and when the filter speed reduces to6m/h from8m/h, the DOconsumption reduces1.0mg/L. Reducing filter speed, backwashing strength andextending filter cycle will achieve that biological activated carbon process can increasethe removal rate of COD_Mnand UV₂₅₄.