Formation of aerobic granular sludge was investigated using a laboratory-scale continuous-flow reactor. Although it is generally thought that aerobic granular sludge can be formed only when a sequencing batch reactor (SBR) is used, formation of aerobic granular sludge was observed using a continuous-flow reactor in this study. The formation was observed only when nitrification well occurred in the reactor, and any indication of the aerobic granulation was not observed in the presence of nitrification inhibitor. Therefore, it was considered that existence of nitrifying bacteria is responsible for formation of the granular sludge. It has been reported that existence of slow growing organisms like nitrifying bacteria induces formation of granular sludge when an SBR is used. Hence, it was considered that formation of aerobic granular sludge is possible in the presence of certain population of nitrifying bacteria even when a continuous-flow reactor is used. To our best knowledge, this is the first study that indicates the possibility of forming aerobic granular sludge in a continuous-flow reactor where organic wastewater is fed. These findings will contribute to dissemination of aerobic granular sludge technology because continuous-flow reactors are more widely used all over the world than SBRs.
This paper presents a new knowledge discovery assistance method to improve wastewater treatment plant (WWTP) operation based on multivariate statistical process control (MSPC). The proposed method combines with MSPC by principal component analysis (PCA-MSPC) and monitoring of a pre-defined performance index for efficient and stable plant operation. Fault detection and isolation (FDI) related to the performance index is selectively performed by monitoring the time series data of the performance index wherein the sample points violating the control limit of Q statistic or that of T2 statistic in PCA-MSPC are indicated. Hidden patterns of probable cause variables to deteriorate the performance index are discovered from the FDI by observing the time series data of the isolated variables. Applications of the proposed method to real WWTPs illustrate the effectiveness of the proposed method by showing possible improvement for energy-saving operation and stable plant operation.
As a part of its "Safe, Better Tasting Tap Water" project, Tokyo Waterworks is installing additional chlorine injection (rechlorination) equipment at the water supply stations in order to stabilize and reduce the residual chlorine concentration in the entire service area by lowering the amount of chlorine injected at the purification plants. To effectively install the rechlorination equipment, the residual chlorine concentration prediction formula has been applied with time, water temperature, organic substance concentration (TOC) as the independent variables. Following certain adjustments to the prediction formula to take into consideration the decomposition of chlorine in the water supply station service reservoirs and in the transmission and distribution pipelines, the factors that caused the calculated concentration of residual chlorine to be higher than the actual concentration are now accounted for in the adjusted formula and the calculated values and actual values are closely aligned. Through the adjusted formula, it was determined that twelve water supply stations in the 23-ward area and seven in Tama area require rechlorination facilities given the reduced residual chlorine concentration at the purification plant outlets. As a result of this research, all necessary procedures are taking place to install the required equipment.
This study tried to use a sono-Fenton process to degrade the ethylenediamine in wastewater for enhancing its biodegradability and investigated the effect of experimental parameters, such as H2O2 and Fe2+ concentration and reaction temperature, on the degradation of ethylenediamine. The reaction was initiated at ethylenediamine concentration of 50 mg/L and pH 3. Experimental results indicated that the degradation of ethylenediamine was insignificant with a sole ultrasound for 60 min reaction, where the biodegradability (BOD5/COD) was slightly increased from 0 to 0.2. More than 50% of ethylenediamine degradation coupled with 20% DOC (dissolved organic carbon) removal was found at 100 mg/L H2O2 and 40 mg/L Fe2+ in sono-Fenton process. Biodegradability of treated wastewater was also effectively increased to 0.7, which could be supposed as a biodegradable wastewater. Five reaction temperatures were carried out in this study, where the 25°C was more suitable than other reaction temperatures for the degradation of ethylenediamine in wastewater. Based on the results shown in this study, sono-Fenton process not only could degrade the ethylenediamine and render it biodegradable but it could also be suitable as a pre-treatment method for the degradation of refractory ethylenediamine in wastewater before entering the biological treatment units.
Perfluorinated compounds including perfluorooctanoic acid (PFOA), which have been detected globally in the environment and in wildlife, have recently received a great deal of attention as environmental contaminants because they are ubiquitous in the environment. In this study, the effect of pH and coexisting ions on the decomposition of PFOA was evaluated under a combined treatment of ferric ion and ultraviolet radiation. The defluorination ratio at pH 2.0 after 72 hr was 101% of the initial PFOA concentration (48 μM). The defluorination rate constant of PFOA during the initial 4 hr at pH 2.0 was 56 × 10-3 hr-1. Furthermore, SO42- ions might have interfered with the complexation of PFOA with Fe3+. Moreover, hydroxyl radical was detected in the sample solution of pH 2.0, 3.0, and 3.5 using electron spin resonance spectroscopy. The hydroxyl radical oxidized Fe2+ to Fe3+, which was reduced by the PFOA decomposition. The strongest absorbance at 250 nm was observed at the sample solution at pH 2.0. Consequently, the photochemical decomposition for PFOA was more efficient at pH 2.0 due to the strong UV absorbance and the influence of the hydroxyl radical.
Nitrogenous compounds are ubiquitous in drinking water sources and they increase the chlorine demand of water, shift the breaking point, and also cause strong odors. The present study was performed to investigate the chlorine demands of selected amino acids and amino sugars in water. The results indicated that the chlorine demands of the precursors were in the order: aromatic amino acids (except histidine) › S-amino acids › non-S-amino acids and amino sugars. Aromatic amino acids were expected to have the highest chlorine demand due to chlorine substitution in both the aliphatic and aromatic parts of these molecules. However, the chlorine demand of histidine was threefold lower than those reported previously, which may be attributed to the experimental conditions or shorter contact time used in this study. The chlorine demands of most compounds did not show marked differences at contact times of 15 - 96 h, although some of the nitrogenous organic compounds showed an increasing trend in chlorine demand with time when our 24 h study was compared with previous studies conducted at 72 and 96 h. Chlorine demand in 24 h showed a good correlation with predicted data. Kinetic studies are required to understand how fast the precursors can react with chlorine in typical water treatment contact times and chlorine doses. The information presented here will be useful in controlling disinfection byproducts.
Humic substances are known to have great impact on heavy metal mobility in aquatic environments. Therefore, the complexation of humic substances, which was generated in landfilled municipal solid waste incineration (MSWI) residues, with heavy metals were investigated to evaluate their impact on heavy metal mobility in a landfill body. This study focused on copper complexation with landfill humic substances. Humic substances were extracted from 13-year-old landfilled MSWI residues. They were used for copper complexation experiments with initial copper concentrations ranging from 1.0 × 10-8 mol-Cu/L to 1.0 × 10-6 mol-Cu/L; humic/fulvic acid concentration of 47.61 mg-C/L; pH range from 6 to 8; and 24-hour contact time. 59.5% to 99.9% of spiked copper was bounded with humic substances at pH 6 to 8. This series of experiments suggested significant impact of humic substance complex on copper mobility in a landfill body. Humic acid had several orders of magnitude larger complexation capacity for copper than that of fulvic acid. Although copper complexation capacities of landfill humic/fulvic acid were much lower than those of generic humic/fulvic acid, landfill fulvic acid had comparable capacity with incubated fulvic acid. This implies similar characteristics of fulvic acid generated in MSWI residues regardless of the humification environment.
We analyzed the monthly data of discharge, ammonium, total phosphorus, and potassium in the lower Mekong River to discuss the applicability of the rating curve function to estimate the nutrient concentration and to understand the inundation effects for nutrient expansion. The various sources of nutrient in the upstream directly affected the water quality in the downstream. Although the sedimentation amount depends on the discharge affecting deposition and erosion, ammonium and potassium directly reached the lower Mekong area because there was no correlation between discharge and these water quality parameters. Therefore, we cannot apply the rating curve function for nutrient water quality in the lower Mekong River.
In the present study, granular gibbsite with vinyl acetate (20%, G-GB20) was used for the removal of phosphate from artificial sewage. The amount of phosphate adsorbed was studied using batch techniques. The effect of different parameters, namely contact time, initial concentration, solution pH, and temperature were investigated. The adsorption kinetics data were best described by the pseudo-second-order rate equation and equilibrium was achieved after 12 h. The Langmuir and Freundlich equations for describing adsorption equilibrium were applied to the experimental data. The correlation coefficients of the Langmuir and Freundlich equations were 0.960 - 0.996 and 0.960 - 0.995, respectively. A number of thermodynamic parameters, namely free energy, enthalpy, and entropy change for the adsorption of phosphate were evaluated and it was found that the reaction was spontaneous and endothermic in nature. Adsorbent (G-GB20) was used for repeated adsorption and desorption of phosphate and a breakthrough curve was obtained. It was shown that G-GB20 could be used three times for repetitive adsorption and desorption of phosphate. Results suggest that the prepared G-GB20 has great potential in the remediation of water contaminated by phosphate.
Sponges, as moving bed biofilm carriers, have shown promising nitrification performance but there is limited information on the mathematical models. With the aim of calculating mass transfer and reaction within sponge carriers, pore diffusion and advection inside the sponges were modelled. Computational Fluid Dynamics (CFD) was used to model the hydrodynamics and was combined with Discrete Element Method (DEM) to model sponges and air bubbles as particles in a tank with three different configurations of aeration. The slip velocity of sponges was used as a model interface to link external hydrodynamics to sponges' internal velocity. The effect of pore convection resistance on biofilm reaction could be characterized with a single non-dimensional variable: Damköhler number, Da, as the ratio of reaction rate to the pore convection rate. For Da › 1, pore diffusion inhibited reaction and an empirical correlation of the reduction in the effectiveness factor could be obtained. Under normal operating conditions, sponge diameters and aeration intensity had significant impact on internal mass transfer. In the case of a fixed bulk oxygen concentration, there was no significant difference in the internal mass transfer for different aerator types.
Catalytic degradation of 1,4-dioxane in a synthetic wastewater by ozonation with several iron species was investigated. Iron species discussed were zero-valent iron (Fe), ferrous ion (Fe2+), ferric ion (Fe3+), hematite (α-Fe2O3) and magnetite (Fe3O4). The addition of Fe accelerated the degradation rate of 1,4-dioxane at pH ranging from 3 to 9. The addition of Fe2+ and Fe3+ also enhanced the 1,4-dioxane degradation at pH 3, but the enhancement effects disappeared at higher pH. Iron oxides (α-Fe2O3 and Fe3O4) did not affect the degradation rate of 1,4-dioxane. Hydroxyl radical (•OH) production via the reaction of ozone with Fe2+/Fe3+ was believed to be responsible for the enhancement effects of Fe, Fe2+ and Fe3+. The production of Fe2+ and ozonide ion (•O3-) was expected via Fe corrosion by ozone. Therefore, •OH generated via both Fe2+ oxidation by ozone and •O3-/water reaction was also believed to contribute to the 1,4-dioxane degradation in ozonation with Fe addition, especially at pH 5 or higher.
The research aimed to evaluate the ability of anammox process using polyester non-woven materials as biomass carrier (PNBC) for nitrogen removal in latex processing wastewater. The experiment was operated at nitrogen loading rates (NLR) of 0.5; 1.0 and 2.0 kgN/(m3•day). The average total nitrogen (TN) removal efficiencies were 70% - 78% at all NLRs. The effluent NH4-N concentration was lower than that of the Vietnamese effluent standard limit, level B of QCVN 01:2008/BTNMT (40 mgN/L), at the NLR of 0.5 and 1.0 kgN/(m3•day). The PNBCR was able to run at NLRs higher than 2.0 kgN/(m3•day) and the effluent TN and NH4-N may meet the standard limits if the operation of partial nitritation could achieve the NH4-N:NO2-N ratio of 1.0:1.32 and producing less nitrate. The annamox removal rates obtained at all NLRs tested were in the range of industrial N removal applications. These findings may lead to the development of the PNBCR for latex processing wastewater treatment.