Process evaluation of an alternating aerobic-anoxic process applied in a sequencing batch reactor for nitrogen removal

In order to improve the nitrogen removal efficiency and save operational cost,the feasibility of the alternating aerobic-anoxic process(AAA process)applied in a sequencing batch reactor(SBR)system for nitrogen removal was investigated.Under sufficient influent alkalinity,the AAA process did not have an advantage over one aerobic-anoxic(OAA)cycle on treatment efficiency because microorganisms had an adaptive stage at the alternating aerobic-anoxic transition,which would prolong the total cycling time.On the contrary,the AAA process made the system control more complicated.Under deficient influent alkalinity,when compared to OAA,the AAA process improved treatment efficiency and effluent quality with NH4+-N in the effluent below the detection limit.In the nitrification,the average stoichiometric ratio between alka-linity consumption and ammonia oxidation is calculated to be 7.07 mg CaCO_(3)/mg NH4+-N.In the denitrification,the aver-age stoichiometric ratio between alkalinity production and N_(3)^(−)-N reduction is about 3.57 mg CaCO(3)/mg NO_(3)^(−)-N.As a result,half of the alkalinity previously consumed during the aerobic nitrification was recovered during the subsequent anoxic denitrification period.That was why the higher treat-ment efficiency in the AAA process was achieved without the supplement of bicarbonate alkalinity.If the lack of alkalinity in the influent was less than 1/3 of that needed,there is no need for external alkalinity addition and treatment efficiency was the same as that under sufficient influent alkalinity.Even if the lack of alkalinity in the influent was more than 1/3 of that needed,the AAA process was an optimal strategy because it reduced the external alkalinity addition and saved on operational cost.

Cascaded Simultaneous Nitrification and Denitrification Process for Nitrogen and Phosphorus Reduction from RO Reject Wastewater： A Bench-Scale Study

The use of the reverse osmosis （RO） process, for refining secondary or tertiary effluent from plants treating domestic wastewater, is rapidly increasing. However, the disposal of the RO reject water poses a problem due to the presence of very high concentrations of salts, metals, and nutrients in it. This paper contains results of a bench-scale study aimed at reducing nutrients from RO-discarded streams utilizing a sequential bioreactors system, under partial aerobic and anoxic conditions. The tests were performed on synthetic wastewater resembling RO-reject water of an operating treatment plant, with glucose, methanol or acetate added to the water as sources of carbon. Study results indicate that the RO process removed about 50-60% of the total nitrogen and 50% of the phosphate; it reduced chemical oxygen demand （COD） by 79 to 82%, and affected no change in the metal concentrations. A clear cut removal preference for any one of the external carbon sources was not observed, although a slight advantage of glucose and methanol was recorded. The process maintained about 20% of the rector volume in the anoxic environment.

Effects of Aerobic and Anoxic Conditions on the Corrosion Behavior of NiCu Low Alloy Steel in the Simulated Groundwater Solutions

The present work focused on investigating the corrosion behavior of NiCu low alloy steel in 0.05 M NaHCO_(3) solutions with different Cl−concentrations under the aerobic–anoxic condition.The results showed that NiCu steel tended to be pseudo-passivated in the solutions of 0.05 M NaHCO_(3) and 0.05 M NaHCO_(3)+0.01 M NaCl exposed to air.The cathodic process transformed from oxygen reduction to the common reduction of oxygen andα-FeOOH,while the anodic process was the iron dissolution.As Cl^(−)increased to 0.1 M,the steel tended to be activity dissolution.Due to the blocking effect of rust layer on the oxygen,the cathodic process transformed to the reduction ofα-FeOOH.After the solutions were deoxidized,the cathodic process was controlled by only rust reduction.Meanwhile,both the cathodic process and anodic process of NiCu steel corrosion were significantly inhibited.During the whole aerobic–anoxic immersion,the corrosion rate of NiCu steel increased with Cl^(−)concentration.It was not only related to the promotion of Cl^(−)on the anodic dissolution of steel,but also related to the cathodic reduction of moreα-FeOOH generated,which could accelerate the cathodic process.