Comparative study of two biological nitrogen removal processes:A/O process and step-feeding process

Two biological nitrogen removal processes are compared in the aspect of nitrogen removal, process operation and energy saving. Results show that when the returned sludge ratio is 50% of the inflow rate, the step-feeding process achieves over 80% total nitrogen （TN） removal efficiency, but the TN removal efficiency of the A/O process is only 40%. Moreover, filamentous sludge bulking can be well restrained in the step-feeding process. Given the conditions of a returned sludge ratio of 100% and a nitrifying liquor recycle ratio of 200%, the TN removal efficiency is 78.32% in the A/O process, but the sludge volume index （SVI） value increases to 143 mL/g. In the step-feeding process, the SVI is only 94.4 mL/g when the TN removal efficiency reaches 81. 1%. The step-feeding process has distinct advantages over the A/O process in the aspects of practicability, nitrogen removal and operating stability.

A novel integrated step-feed biofilm process for the treatment of decentralized domestic wastewater in rural areas of China

For wastewater treatment in rural areas, a novel three-stage step-feed wastewater treatment system, combined with a drop-aeration biofilm process, was tested in the laboratory to investigate its performance in removing suspended solids （SS）, chemical oxygen demand （COD）, NH4＋-N, total nitrogen （TN）, and total phosphorus （TP）. The removal rates of SS, COD and NH4＋-N were 90%, 80%, and 90% in efluent concentrations less than 10 mg/L, 50 mg/L and 8 mg/L, respectively. The TP removal rate was less satisfactory. The C/N ratio in the raw wastewater was often less than 3.5, and the removal efficiency of TN was therefore limited. A carbon-release batch experiment was carried out to measure the feasibility of enhancing denitrification at low influent C/N ratios. The result showed that the C/N could be over 9.0 in the supernatant. Polymerase chain reaction denaturing gradient gel electrophoresis technology was used to reveal the changes in the bacterial community during different stages of the integrated step-feed biofilm process. The results showed that banding patterns and the distribution of dominant bands for the same experimental period in different aerobic zones were similar. Phylogenetic analysis indicated that lanes 10, 11 and 12, which presented three aerobic zones at the same operation period, had the closest phylogenetic relationship among the lanes.

Enhanced Biological Nutrients Removal in Modified Step-feed Anaerobic/Anoxic/Oxic Process

In order to enhance phosphorus removal in traditional step-feed anoxic/oxic nitrogen removal process,a modified pilot-scale step-feed anaerobic/anoxic/oxic(SFA 2/O) system was developed,which combined a reactor similar to UCT-type configuration and two-stage anoxic/oxic process.The simultaneous nitrogen and phosphorus removal capacities and the potential of denitrifying phosphorus removal,in particular,were investigated with four different feeding patterns using real municipal wastewater.The results showed that the feeding ratios(Q1)in the first stage determined the nutrient removal performance in the SFA 2/O system.The average phosphorus removal efficiency increased from 19.17% to 96.25% as Q1 was gradually increased from run 1 to run 4,but the nitrogen removal efficiency exhibited a different tendency,which attained a maximum 73.61%in run 3 and then decreased to 59.62%in run 4.As a compromise between nitrogen and phosphorus removal,run 3 (Q1=0.45Qtotal) was identified as the optimal and stable case with the maximum anoxic phosphorus uptake rate of 1.58 mg·(g MLSS)-1 ·h-1.The results of batch tests showed that ratio of the anoxic phosphate uptake capacity to the aerobic phosphate uptake capacity increased from 11.96% to 36.85% with the optimal influent feeding ratio to the system in run 3,which demonstrated that the denitrifying polyP accumulating organisms could be accumulated and contributed more to the total phosphorus removal by optimizing the inflow ratio distribution.However,the nitrate recirculation to anoxic zone and influent feeding ratios should be carefully controlled for carbon source saving.

Performance evaluation of a modified step-feed anaerobic/anoxic/oxic process for organic and nutrient removal

A pilot scale modified step-feed process was lmproved to increase nutrient/N ano P） ano organic removal operations from municipal wastewater. It combined the step-feed process and a method named ＂University of Cape Town （UCT）＂. The effect of nutrient ratios and inflow distribution ratios were studied. The highest uptake efficiency of 95% for chemical oxygen demand （COD） has been achieved at the inflow distribution ratio of 40/35/25. However, maximum removal efficiency obtained for total nitrogen （TN） and phosphorus at 93% and 78%, respectively. The average mixed liquor suspended solids （MLSS） was 5500 mg·L- 1. In addition, convenient values for dissolved oxygen （DO） concentration, and pH were obtained throughout different stages. The proposed system was identified to be an appropriate enhanced biological nutrient removal process for wastewater treatment plants owing to relatively high nutrient removal, sturdy sludge settle ability and COD removal.

Automatic control strategy for step feed anoxic/aerobic biological nitrogen removal process

Control of sludge age and mixed liquid suspended solids concentration in the activated sludge process is critical for ensuring effective wastewater treatment. A nonlinear dynamic model for a step-feed activated sludge process was developed in this study. The system is based on the control of the sludge age and mixed liquor suspended solids in the aerator of last stage by adjusting the sludge recycle and wastage flow rates respectively. The simulation results showed that the sludge age remained nearly constant at a value of 16 d in the variation of the influent characteristics. The mixed liquor suspended solids in the aerator of last stage were also maintained to a desired value of 2500 g/m3 by adjusting wastage flow rates.

Nitrogen removal and simultaneous nitrification and denitrification in a fluidized bed step-feed process

For urban wastewater treatment,we conducted a novel four-stage step-feed wastewater treatment system combined with a fluidized bed laboratory experiment to investigate chemical oxygen demand（COD）,NH4＋-N,and total nitrogen（TN） removal performance.The removal rates of COD,NH4＋-N and TN were 88.2%,95.7%,and 86.4% with e？uent concentrations of COD,NH4＋-N and TN less than 50,8,and 10 mg/L,respectively.Biomass and bacterial activities were also measured,with results showing more nitrobacteria in the activated sludge than in the biofilm;however,bacterial activity of the biofilm biomass and the activated sludge were similar.Nitrogen concentrations during the process were also detected,with simultaneous nitrification and denitrification found to be obvious.

Denitrification and phosphorus uptake by DPAOs using nitrite as an electron acceptor by step-feed strategies

Denitrifying phosphorus accumulating organ- isms （DPAOs） using nitrite as an electron acceptor can reduce more energy. However, nitrite has been reported to have an inhibition on denitrifying phosphorus removal. In this study, the step-feed strategy was proposed to achieve low nitrite concentration, which can avoid or relieve nitrite inhibition. The results showed that denitrification rate, phosphorus uptake rate and the ratio of the phosphorus uptaken to nitrite denitrified （anoxic P/N ratio） increased when the nitrite concentration was 15 rag. L-1 after step- feeding nitrite. The maximum denitrification rate and phosphorus uptake rate was 12.73 mg NO2-N.g MLSS- 1· h- 1 and 18.75 mg PO34--P- g MLSS- 1. h- 1, respec- tively. These rates were higher than that using nitrate （15 mg. L-l） as an electron acceptor. The maximum anoxic P/N ratio was 1.55 mg PO43- -Pmg NO2-N-1. When the nitrite concentration increased from 15 to 20 mg NO2 -N ~ L-I after addition of nitrite, the anoxic phosphorus uptake was inhibited by 64.85%, and the denitrification by DPAOs was inhibited by 61.25%. Denitrification rate by DPAOs decreased gradually when nitrite （about 20 mg · L-1） was added in the step-feed SBR. These results indicated that the step-feed strategy can be used to achieve denitrifying phosphorus removal using nitrite as an electron acceptor, and nitrite concentration should be maintained at low level （ 〈 15 mg. L-1 in this study）.

Field experiment on biological contact oxidation process to treat polluted river water in the Dianchi Lake watershed

In this study two types of biological contact oxidation processes(BCOP),a step-feed(SBCOP)unit and an inter-recycle(IBCOP)unit,were designed to investigate the treatment of heavily polluted river water.The Daqing River,which is the largest pollutant contributor to the Dianchi Lake,one of the most eutrophic freshwater lakes in China,was taken for the case study.It was found that the SBCOP had higher adaptability and better performance in the reduction of COD,TN,and TP,which made it applicable for the treatment of polluted river water entering the Dianchi Lake.Nitrification rate was observed to be greatly affected by the influent temperature.During each season,the nitrification in the SBCOP was higher than that in the IBCOP.TN removal efficiency in the SBCOP was higher than that in the IBCOP during the winter and spring but poorer during the summer,possibly due to the inhibition of denitrification by higher dissolved oxygen level in the summer.Moreover,symbiotic algaebacteria growth may be conducive to the removal of pollutants.