Biological Nitrogen Removal System Research Articles

Full-Scale Operating Experience with a Biological Nitrogen Removal System

Full-Scale Operating Experience with a Biological Nitrogen Removal System

Full-Scale Operating Experience with a Biological Phosphorus and Nitrogen Removal System Treating High-Strength Potato Processing Wastewater

Full-Scale Operating Experience with a Biological Phosphorus and Nitrogen Removal System Treating High-Strength Potato Processing Wastewater

Biological nitrogen removal from coke plant wastewater with external carbon addition

Coke plant wastewater containing high concentrations of ammonia and toxic compounds such as phenol and cyanide was treated using a biological nitrogen removal (BNR) system comprising carbon removal, nitrification, and dentrification stages. The objective of this study was to investigate the feasibility of complete ammonia removal from the coke plant wastewater using a sequential BNR process with external carbon addition. Sodium acetate was introduced as an external carbon source to the denitrification stage after oxidation of phenol and other carbonaceous compounds in the carbon‐removal stage. The efficiency of denitrification was strongly affected by the loading rate of the external carbon source, and its optimal rate was determined based on the ratio of chemical oxygen demand to nitrate‐ and nitrite‐nitrogen (COD:NOx‐N) of the denitrification stage. The overall removal efficiency of major soluble pollutants in the wastewater was greater than 95% in the BNR system. When a step input of phenol was introduced to check the stability of the overall system, the nitrification was markedly inhibited because of the incomplete degradation of phenol in the carbon‐removal stage. However, after this brief inhibition, the nitrification stage recovered to its normal efficiency within 18 days.

Eliminating Backflow in Retrofit BNR Systems

The retrofit of an existing activated sludge system with a biological nitrogen removal system requires the installation of a baffle wall to separate the biological nitrogen removal anoxic and oxic zones. The baffle wall consists of a weir and a submerged orifice. An experimental investigation of the hydraulics of the anoxic/oxic baffle wall is presented. It is shown that backflow from the oxic zone to the anoxic zone can occur if the baffle wall is not designed properly. This backflow will reduce the efficiency of the biological nitrogen removal process. Based on the experimental data, a design procedure that eliminates backflow over the anoxic/oxic baffle wall is developed. The design procedure introduces a backflow parameter that is a dimensionless number dependent on the total discharge, orifice area, tank depth, and oxic zone air concentration. The resulting design offers an economical alternative to designs implementing a valve option.

On-line estimations of settling capacity in secondary clarifier

In a biological nitrogen removal system, efficient performance of the secondary clarifier is essential since the system depends on a high concentration of active biological solids being available in the biological reactor. Estimations of the current capacity of the clarifier can be made from observing maximum feasible solids flux to the clarifier which does not cause escape of sludge. The aim of this work is to demonstrate a method to establish maximum feasible solids flux, the limiting solids flux, from on-line operational data. In this method the solids flux into the clarifier is calculated from on-line measurements of effluent flow and of suspended solids in the biological reactor, and a known value of return sludge flow. From relations between solids flux and sludge blanket height, the value of limiting flux is estimated. This method is based on the assumption that the movement of sludge blanket height is directly related to changes in the solids flux. When the limiting solids flux is estimated from on-line measurements a measurement of the capacity of the clarifier is retrieved. The suggested method also gives an early warning to prevent sludge escape from the clarifier.

On-line estimations of settling capacity in secondary clarifier

In a biological nitrogen removal system, efficient performance of the secondary clarifier is essential since the system depends on a high concentration of active biological solids being available in the biological reactor. Estimations of the current capacity of the clarifier can be made from observing maximum feasible solids flux to the clarifier which does not cause escape of sludge. The aim of this work is to demonstrate a method to establish maximum feasible solids flux, the limiting solids flux, from on-line operational data. In this method the solids flux into the clarifier is calculated from on-line measurements of effluent flow and of suspended solids in the biological reactor, and a known value of return sludge flow. From relations between solids flux and sludge blanket height, the value of limiting flux is estimated. This method is based on the assumption that the movement of sludge blanket height is directly related to changes in the solids flux. When the limiting solids flux is estimated from on-line measurements a measurement of the capacity of the clarifier is retrieved. The suggested method also gives an early warning to prevent sludge escape from the clarifier.

Nitrification Treatability of Whole Microorganisms Immobilized by the PVA-Freezing Method

We used whole microorganisms immobilized by the PVA-freezing method (in order to prevent microorganism wash-out) to investigate the efficiency of nitrification. In general, denitrified or oxidized effluents are recycled to the nitrification tank to provide alkalinity control in biological nitrogen removal systems. We found that allowable volumetric loading during nitrification was different for the recycling and once-through operations, using a biofilm nitrogen removal system in a fixed bed. Then, the nitrification efficiency of a recycling operation in a biological nitrogen removal system was compared with that of a once-through operation, using immobilized microorganisms. The results showed that the ratio of allowable volumetric loading in the recycling operation was 60% of that in the once-through operation.

A Study of Nitrification Utilizing Whole Microorganisms Immobilized by the PVA-Freezing Method

The particular characteristics of nitrifying bacteria are that they have a reduced tendency to flocculate, a lower specific growth rate and a higher specific nitrification rate. Accordingly, we used whole microorganisms immobilized by the PVA-freezing method (in order to prevent microorganism wash-out) to investigate the characteristics and efficiency of their nitrification. The following results were obtained.By comparsion with suspended microorganisms, the nitrification rate of immobilized microorganisms was not as affected by temperature and their storage stability was better.The nitrification efficiency of a recycling operation in a biological nitrogen removal system was compared with that of a once-through operation, using immobilized microorganisms. The results showed that the ratio of allowable volumetric loading in the recycling operation was 60% of that in the once-through operation.