Experimental Study On Enhancing Biological Nutrient Removal With Carriers

The low influent carbon resource is disadvantageous to Biological Nutrient Removal（BNR）. In theory, the more biomass in systerm may increase the ability of Biological NutrientRemoval in low carbon. In the previous studies and applications, the bifilm carriers werefilled in the aeration tank to increase the biomass to enhance the biological nutrient removal.However, phosphorus accumulation organisms （PAOs） must grow in dynamic environment.If the biofilm carriers is just added to the aeration tank, they can not circulate in―anaerobicâ†'anoxicâ†'aerobic‖tanks, and the phosphorus accumulation organisms will bedifficult to grow in the carriers. The characteristic of the phosphorus accumulation organismsis totally different from ordinary heterotrophic organisms （OHO） and nitrifiers （AOB&NOB）.In this study, the biofilm carriers are added into a SBR-type experiment and proposed torealize recirculation of carriers between―anaerobicâ†'aerobicâ†'anoxic‖zones. There aretwo parallel SBR systems in the experiment with and without carriers to compare and testwheather they could enhance the biological nutrient removal or not.The test preliminarily have shown that the total biomass can indeed increase greatlybeacause of the fluidized biofilm carriers （the filling rate is25％） added into systerm, thetotal amount of biomass in SBR₁with carriers reach about2.9times as SBR₀without carriers.When the suspended biomass （activated sludge） in the two reactors have few difference,obviously, the increased biomass is mainly the attached biomass （biofilm） growing on thecarriers. After a long running, it show that the effective biomass being bioactive on carriers iswell below than total solids, inorganic substance accounts for2/3of total solids （phosphatemakes up70ï¼…of inorganic ash, measured as calcium phosphate）. organic ingredients onlyaccounts for1/3. The LIVE/DEAD analysis of biofilm on carriers demonstrated that theviable cells only account for82ï¼…of total cells, which is less than94ï¼…of the activatedsludge.The treatment function tests show that total biomass in SBR₁folds increase in case oflow-carbon resource, but the function of enhancing biological nutrient removal is not clearlyat all, and weakened somewhat. Even under high carbon resource condition, SBR₁systermstill do not show better treatment than SBR₀. Laboratory scale test show that the nitrificationand denitrification ability, oxygen uptake rate and phosphorus uptake/release rate of specificmount of the biofilm on carriers is far below the activated sludge, that makes big discounts offgreat biomass, that is a departure from the previous.The effective biofilm playing the role of biological nutrient removal on carriers is verylow, that is obviously the chief cause not to enhance biological nutrient removal. Besides, Thebig mass transfer resistance and slow product diffision may also induce the biofilm not playthe due role. Except the problem concerning biomass on carriers, the continuous physical turbulence between carriers and activated sludge flocs result in bio-flocs smaller,sedimentation performance of activated sludge in SBR₁became poor, SVI reach220mL/g（SVI in SBR₀is only50mL/g）. The activated sludge can not form flocs, the most of bacteriais exposed to an unstable dynamic environment in long term and lose normal metabolicenviroment. Accordingly, the suspended biomass in SBR₁and SBR₀is same, but the actualtreatment function is certainly different.