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The Anaerobic-Anoxic/Nitrification (A2N) system is a continuous-flow, two-sludge process in which Poly-p bacteria are capable of taking up phosphate under anoxic conditions using nitrate as an electron acceptor. The process is very efficient because it maximizes the utilization of organic substrate for phosphorus and nitrogen removal. Further, the process solves the competition for organic substrate among Poly-p organisms and denitrifies as well as the problem of overgrowing of slow nitrifiers by fast organotrophs. An experimental lab-scale A2N system fed with domestic sewage was tested over a period of 260 days. The purpose of the experiment was to examine phosphorus removal capacity of a modified A2N two-sludge system. Factors affecting phosphorus and nitrogen removal by the A2N system were investigated. These factors were the influent COD/TN ratio, Sludge Retention Time (SRT), Bypass Sludgy Flow rate (BSF), and Return Sludge Flow rate (RSF). Results indicated that optimum conditions for phosphorus and nitrogen removal were the influent COD/TN ratio around 6.49, the SRT of 14 days, and the BSF and RSF were fixed about 26%–33% of influent flow rate. [ABSTRACT FROM AUTHOR]

A new low cost technology for simultaneous carbon–nitrogen removal from soybean wastewater has been developed in this study. The technology is performed through shortcut nitrification–denitrification. The process operated under real-time control of aeration and mixing time. The shortcut nitrification–denitrification in sequencing batch reactor (SBR) was achieved efficiently and steadily by controlling temperature (28 ± 0.5°C) and using real-time control strategies. This enabled the prevention of nitrite oxidation, leading to lower operational costs. The feasibility of oxidation–reduction potential (ORP) and pH value as control parameter for shortcut nitrification–denitrification process was also investigated. Results showed that the average removal efficiency of ammonium was more than 95%, and nitrosation rate () was reached to 96%. At the same time, the variation of oxidation–reduction potential (ORP) and pH value was well related to organic matter degradation and ammonium oxidation in SBR. So that judgment on the ending of nitrification and denitrification can be based on the inflection point on the varied curve of ORP and pH throughout each SBR processing cycle, and thus reducing aeration and mixing time for saving energy source. The method saves organic energy up to 40% of chemical oxygen demand (COD) in denitrification process, which should reduce the need for an extra external source of organic carbon. Shorter hydraulic retention time should allow the volume of the reactors to diminish, and thus diminish investment costs. Lower oxygen demand of about 25% gives lower exploitation costs. [ABSTRACT FROM AUTHOR]

Quantitative Structure-Activity Relationship (QSAR) between the bio-toxicity of seventy-eight kinds of substituted benzene chemicals to yeast Saccharomyces cerevisiae (lg(1/C[SUBmiz])) and the components of vertex degree autocorrelation vectors (values of A, B, C and D) was studied by using the software of Artificial Neural (Network (ANN). The key factors of the autocorrelation descriptors for the lg (1/C[SUBmiz]) value of yeast Saccharomyces cerevisiae, A [0], A [1], C [3], C [5] and D [3] were selected from twenty-four descriptors, and were explained theoretically in this paper. The QSAR-ANN model has been used to predict the bio-toxicity of twenty-three substituted benzene chemicals. The correlation between C[SUBmiz] and LC[SUB50] was also discussed, and the liner correlation equation between them was established. [ABSTRACT FROM AUTHOR]

In order to study the nitrogen removal via nitrite at normal temperature in anoxic/oxic (A/O) process for treating domestic wastewater, the influence of pH, free ammonia (FA), dissolved oxygen (DO), and hydraulic retention time (HRT) were studied. Results indicated that it was possible to remove nitrogen via nitrite in A/O process, if the temperature was between 18 and 25°C and pH was below 7.5. Even if FA was as low as 0.06 mg NH[SUB3]-N/L, it would inhibit the nitrobacteria. However, FA could not be the sole factor. Whether denitrification went thoroughly or not could affect the nitrification pathway. If denitrification went well, nitrite accumulation could recover in a short while. Nitritification lagged nitratification, so that short HRT would help nitrite accumulation. On the other hand, extended aeration would reduce nitrite accumulation. [ABSTRACT FROM AUTHOR]

Based on the analysis of information flow through the Artificial Neural Network (ANN), a new screening rule of the molecular structure parameter in Quantitative Structure-Activity Relationship (QSAR) was presented by comparing of the values of connection weights and biases of the ANN model. The result showed that model quality and prediction ability of QSAR model, which was constructed by screening structural parameter with ANN, were better than by the method with MLR. The method established the foundation for further study in the mechanism research of the bio-toxicity of organic chemicals. [ABSTRACT FROM AUTHOR]