Experimental Study On Biological Denitrification Of SBR Short-Range Nitrification System Enhanced By Biochar

Compared with the conventional biological denitrification technique,the shortcut nitrification technique is featured by advantages of lower energy consumption,short hydraulic retention time and so on.However,while inhibiting nitrite oxidizing bacteria（NOB）,the shortcut nitrification technique will also affect the oxidation of NH₄⁺-N in water by ammonia oxidizing bacteria（AOB）,and there are issues like difficulties in initiating and stringent operating conditions in the shortcut nitrification technique.In terms of the above-mentioned issues,this experiment adopted the sequencing batch reactor（SBR）to process the artificial simulated nitrogen ammonia wastewater.By taking the aeration time and initial pH of aeration stage as automatic conditions,it initiated the SBR shortcut nitrification and analyzed the kinetics of NH₄⁺-N oxidation,which confirmed the optimum operating conditions for the SBR shortcut nitrification system.It also focused on studying the effects of biochar on NH₄⁺-N removal capacity,NO₂^--N accumulation capacity and sludge settling performance of the SBR shortcut nitrification system and explored the biological nitrogen removal technique of biochar enhancing the SBR shortcut nitrification system.The main research results are as follows:（1）When the aeration rate was 1.5 L/min and the initial pH was 8 during the aeration stage,AOB basically completed the oxidation of NH₄⁺-N in 360 min at the beginning of aeration,and there was a point of inflection in the DO concentration and pH change curve in the reactor.By taking 360 min of aeration duration and the initial pH of 8 at the beginning of aeration as initiating conditions to initiate the SBR shortcut nitrification system,the NO₂^--N accumulation rate（NAR）and the NH₄⁺-N removal rate（ARR）of the reactor reached 71.37%and 96.01%respectively in 30 d,and the SBR shortcut nitrification system was initiated successfully.Through analyzing the kinetics of NH₄⁺-N oxidation process,it could be found that the NH₄⁺-N oxidation in SBR shortcut nitrification system can be divided into two stages,in the first 2 hours,the oxidation reaction of NH₄⁺-N conformed to the zero-order reaction kinetic equation;and it confirmed to the first-order reaction kinetic equation in 2 to6 h.（2）Within the range of 15～35°C,both the ARR and the NAR of the reactor were directly proportional to the temperature.When temperature was higher（at 30～35°C）,it was proved that the increase of temperature has limited effect on the improvement of the ARR and the NAR.Within the range of 0.6±0.1～1.6±0.1 mg/L,the ARR of the reactor was directly proportional to the concentration of DO,and the NAR of the reactor was inversely proportional to the concentration of DO because the low concentration of DO had a more obvious inhibitory effect on NOB.Within the range of 7.0±0.2～8.0±0.2,the ARR of the reactor was inversely proportional to pH,and the NAR was directly proportional to pH.When the pH was at 8.5±0.2,the activities of AOB and NOB were inhibited,both the ARR and the NAR decreased at the same time.When the SRT was between the minimum generation period of AOB and NOB（8～12 d）,the sludge discharging of the reactor could accumulate AOB while“elutriating”NOB.Therefore,the SRT was 10 d,the NAR of the reactor was improved while the ARR was basically not affected.It could be determined that the optimum operating conditions of the SBR shortcut nitrification system was DO concentration in 1.0±0.1 mg/L,temperature at 30℃,pH at 8.5±0.2 and the SRT of 10 d.（3）After the biochar entering the SBR shortcut nitrification system,it firstly adsorbed NH₄⁺-N to improve the ARR of the reactor.Then,with the“biofilm culturing”growth of microorganisms on the surface and inside the pores of biochar,the oxidation ability of AOB on the surface of biochar to NH₄⁺-N was enhanced,the ARR of the reactor was further improved;but the denitrifying bacteria growing in the pores of biochar denitrify NO₂^--N under anoxic environment,and the NAR of the reactor was reduced.In the settling stage,the activated sludge could be flocculated and settled by using biochar as the flocculation core,and the sludge settling performance could be improved.（4）Different types of biochars have different reinforcement effects on the SBR shortcut nitrification biological nitrogen removal.The richer the pore structure of biochar,the more obvious its reinforcement effects on biological nitrogen removal in the SBR shortcut nitrification system.For different kinds of biochars,when the dosage of biochar was between 0.5～1.0 g/L,the reinforcement effect of biochar on the SBR shortcut nitrification biological nitrogen removal was proportional to the dosage.However,when the dosage of biochar was between（1.5～2.0 g/L）,it would lead to the reduction of oxygen transfer efficiency in the reactor and the decrease of ARR.