C. F. Ouyang

Modelling the steady-state effluent characteristics of the TNCU process under different return mixed liquid

Abstract The Activated Sludge Model No. 2d (ASM2d) was employed and modified to predict the effluent qualities of the modified enhanced biological phosphate removal (EBPR) system – TNCU. The TNCU process was composed of anaerobic/anoxic/oxide (A2O) process and rotating biological contactors (RBC) in each reactor. There were three modifications for the model in this study: (1) the biosorption effect of the soluble COD, (2) the ammonification of the organic nitrogen in influent wastewater, and (3) the growth of the heterotrophic organisms in the anaerobic tank. The influent wastewater qualities were fixed, the ratios of return sludge and SRT were 0.5 and 11 days, and the model plant was operated at three different mixed liquid recycling ratios (MLRR, 0.5, 1.25, 2). When a steady state was reached, the comparisons between the measured values and the model predicted values in each test were made. It shows a good consistency between them. According to the consistent results, the biosorption effect of the soluble COD and the ammonification of the organic nitrogen in influent wastewater were the important effects in activated sludge system. Additionally, the heterotrophic organisms might grow in the anaerobic tank. The heterotrophic organisms, phosphorus accumulating organisms and autotrophic organisms would decrease in the anaerobic tanks because the lysis reactions were the major reactions in the anaerobic tanks. They would increase in the aerobic tanks. Furthermore, it was indirectly proved that the denitrifying PAOs existed in the EBPR system.

Effects of flow velocity and depth on the rates of reaeration and bod removal in a shallow open channel

Abstract This study developed an analytical solution of reaeration rate coefficient (K2) and modified the equation of BOD removal in a shallow artificial open channel. A series of well-controlled batch tests were carried out to measure the KZ and BOD removal rate in the channel at different flow conditions. The results of these tests indicated that measured KZ within the developing zone of the laminar boundary layer is better described by the analytical solution of this study than by the five semi-empirical formulae mentioned in this paper. On the other hand, a resuspension-sedimentation coefficient, Rs , was added to the BOD removal equation to describe the variation in BOD due to varied flow conditions. Based on the results of the experimental data the following conclusions in the BOD removal process were reached. It was found that a direct correlation exists between the flow velocity to depth ratio (U/h) and the deoxygenation rate coefficient (KI), but there is an inverse correlation between U/h and Rs as well. This modified BOD removal equation can predict DOD removal rate at different travel times or known downstream distances in an open channel under varied flow conditions. 0 1997 IAWQ. Published by Elsevier Science Ltd

Denitrifying Characteristics of the Multiple Stages Enhanced Biological Nutrient Removal Process with External Carbon Sources

Abstract This research investigated denitrifying activity of activated sludge with three external carbon sources (sodium acetate, methanol and glucose) via a series of batch experiments. Activated sludge used was cultivated in a multiple stages enhanced biological nutrient removal (EBNR) process that exhibited high removal efficiency of effective carbon, nitrogen, and phosphorus. Results showed type of external carbon source had a significant influence on specific nitrate utilization rate, nitrite accumulation, adaptive time of microorganisms, and nitrate removal efficiency. Sodium acetate addition resulted in high phosphate concentration in effluent; meanwhile methanol caused increasing turbidity and carbon breakthrough problem. When glucose was fed to be the external carbon source, accumulative nitrite concentration was higher than that with sodium acetate or methanol addition. When sodium acetate, methanol and glucose were used to be the electron donor, average dosages for nitrate elimination were 6.97, 5.85, and 5.65 mg-COD/mg-N, respectively. Because the final polyhydroxyalkanoates (PHAs) concentrations contained within the biomass were more than the original level and no phosphate re-release was observed, glycogen-accumulating organisms (GAOs) might exist in the multiple stages EBNR process and increased carbon dosage for further nitrate removal.

Identification of the microbial diversity of wastewater nutrient removal processes using molecular biotechnology

The microbial communities of three sludge samples were identified by using a combined cloning-Denaturing Gradient Gel Electrophoresis (DGGE) method. Two communities were taken from the aerobic and the rotating biological contactor (RBC) of a novel hybrid system, named TNCU-I, which is a combined activated sludge-RBC bioprocess. The other sample was taken from the aerobic tank of a typical anaerobic-anoxic-aerobic (A2O) process. Acidovorax defluvii, Hydrogenophaga palleronii and Streptococcus suis were the most predominant bacteria, respectively, in TNCU-I activated sludge, TNCU-I RBC biofilm and A2O activated sludge, with abundances of 13.2%, 18.7% and 16.5%. Other predominant bacteria and their characteristics in wastewater treatment process are also described.

MODELLING THE STABLE EFFLUENT QUALITIES OF THE A2O PROCESS WITH ACTIVATED SLUDGE MODEL 2d UNDER DIFFERENT RETURN SUPERNATANT

Abstract A modified mathematical model based on the Activated Sludge Model No. 2d (ASM2d) was established to describe the effluent qualities of the enhanced biological phosphate removal (EBPR) system ‐ A2O. There were three modifications to the model in this study: (1) the biosorption effect of the soluble COD, (2) the hydrolysis of the organic nitrogen in influent wastewater, and (3) the growth of heterotrophic organisms in the anaerobic tank. The A2O process is composed of an anaerobic/anoxic/oxide process which removes biological phosphorus with simultaneous nitrification‐denitrification. The influent wastewater quality and quantity were fixed, the ratios of return sludge and sludge retention time were 0.25 and 12 days, and the model plant was operated at three different mixed liquid recycling ratios (MLRR, 0.5, 1.25, 2). When a steady state was reached, comparisons between the measured values and predicted values were made for each test. A good consistency between the test values and simulation values was shown. According to our results, the biosorption effect of the soluble COD and the hydrolysis of the organic nitrogen in influent wastewater are the important qualities in activated sludge systems. Additionally, heterotrophic organisms might grow in the anaerobic tank. Furthermore, it was indirectly proved that the denitrifying PAOs existed in the EBPR system.

Nitrogen removal from activated sludge process (ASP) treated municipal wastewater by biofilm channeling

Abstract The pathways and kinetic behaviors of nitrogen compounds have been examined in biofilm channeling for the purification of wastewa‐ter treated by the activated sludge process (ASP) under laminar and turbulent flow conditions. The continuous water flow experiments show that the flow velocity will significantly influence the nitrification and denitrification conversion rates. The optimal total Kjeldahl nitrogen (TKN‐N) and total nitrogen (TN‐N) removal rates can be achieved during the initial turbulent flow condition. Concentrations of TKN‐N and TN‐N variations in the biofilm channel follow zero order kinetics. In our 54‐m biofilm channel, pathways of nitrogen compound conversions demonstrate that trapped suspended solids in the biofilm form an anoxic environment and are hydrolyzed to produce a carbon source, which may be the main reason for the occurrence of denitrification. The nitrification and denitrification processes occur simultaneously in the biofilm channel.

The kinetic behaviors of simultaneous phosphorus release and denitrification on sludge for BNR processes

Abstract In this study, we investigated the kinetic behaviors of phosphorus release and denitrification on sludge for two biological nutrient removal (BNR) processes, i.e., suspension growth process (A2O) and combined suspension‐biofilm growth process (TNCU) under anoxic condition. The readily biodegradable substrate and nitrate loadings, 20–180 mg HAc‐COD/g MLSS and 4–25 mg NO3‐N/g MLSS respectively, are controlled in a batch reactor for phosphorus release and denitrification of sludge taken from A2O and TNCU processes under various SRT (5, 10 and 15 days) operating conditions. Experimental results indicated that the occurrence of simultaneous phosphorus release and denitrification is a kinetic competition mode under anoxic condition in the presence of a readily biodegradable substrate. Moreover, the available substrate in bulk solution determined the kinetic behaviors of phosphorus release and denitrification. To prevent nitrate inhibition, the sludge is exposed to a C/N ratio higher than 6.1 for phosph...

Step feeding strategy for enhancing nitrogen and phosphorus removal in AOAO process.

This study describes a biological process containing anaerobic/oxide/anoxic/oxide (AOAO) stages, which incorporates a stepwise feeding strategy to enhance nitrogen and phosphorus removal efficiencies. In the experimental reactors, synthetic wastewater was fed into the anaerobic stage and anoxic stage separately, while the substrates and nutrients were successfully consumed without recycling either nitrified effluent or external carbon sources. Experimental results demonstrated that the anoxic stage was provided an intrinsic sufficient carbon source and caused NOx (NO2-N + NO3-N) concentration to reduce from 11.85 mg/l to 5.65 mg/l. The total Kjeldahl nitrogen (TKN) removal rate was between 81.81% and 93.96%, while the PO4-P removal ratio was between 93% and 100%. The substrate fed into the anaerobic at flow rate Q1 and into the anoxic at flow rate Q2. In addition, three different ratios were performed with Q1/Q2 varied from 7/3, 8/2 to 9/1. The AOAO process clearly saves nearly one-third of the energy compared to the typical Biological nutrient removal (BNR) system A2O process.

Predicting effluent suspended solids from a dynamic enhanced biological phosphorus removal system using a neurogenetic model

Abstract This study applies the neurogenetic model, i.e. a hybrid intelligent system combining genetic algorithm (GA) with artificial neural networks (ANN), to accurately predict effluent suspended solids concentrations from an enhanced biological phosphorus removal (EBPR) system under typical diurnal variation of municipal wastewater. Continuous‐flow pilot plant experiments with automatic monitoring and control facilities were performed to assess the models applicability. The effluent suspended solids concentrations from the experiments closely corresponded to those predicted by the neurogenetic model developed herein.

Identification the microbial diversity in a municipal wastewater treatment plant using non‐cultured based methods

Abstract In this study, the microbial diversity of activated sludge and RBC (rotating biological contactor) biofilm at Taipei Min‐Sheng Municipal Wastewater Treatment Plant was investigated by a combined cloning‐DGGE (denaturing gradient gel electrophoresis) method. The microbial diversity showed that Pseudomonas spinosa, Zoogloea ramigera and Streptococcus penumoniae were the most predominant types of bacteria in the activated sludge, and in the first and fourth stages of the rotational biological contactor biofilm, respectively. The phylogenetic tree revealed that all the microbial community of these three samples could be divided into three linkages. Among these three linkages, one contained the most clones from rotational biological contactor samples, while others contained the most activated sludge clones. A higher abundance of filamentous bacteria was identified in the fourth stage of the rotational biological contactor biofilm. Additionally, among the three samples, the nitrifying bacteria and nitrification phenomenon were only observed in the fourth stage of the rotational biological contactor biofilm.