Robust Regulation of Alkalinity in Highly Uncertain Continuous Anaerobic Digestion Processes

In this paper, a multiple‐input multiple‐output (MIMO) model‐based robust control scheme is proposed for the indirect control of both total alkalinity and the ratio (intermediate alkalinity)/(total alkalinity) by regulating volatile fatty acid concentrations and strong ions concentration, while guaranteeing the so‐called operational stability in anaerobic digestion (AD) processes. The proposed MIMO regulator is an adaptive controller derived from an AD model which incorporates the physicochemical equilibrium of the system as well as the use of a robust interval observer to estimate key process bounds that are used in the computation of the control efforts. Numerical simulations were carried out for a number of operating conditions under the most uncertain scenarios. Results showed that the proposed multivariable control law is able to recover the system stability around a pre‐determined set point in the face of parameter uncertainty and load disturbances.     

Amelioration of Carbon Removal Prediction for an Activated Sludge Process using an Artificial Neural Network (ANN)

A dynamic simulation model of the Ankara central wastewater treatment plant (ACWTP) was evaluated for the prediction of effluent COD concentrations. Firstly, a mechanistic model of the municipal wastewater treatment process was developed based on Activated Sludge Model No. 1 (ASM1) by using a GPS‐X computer program. Then, the mechanistic model was combined with a feed‐forward back‐propagation neural network in parallel configuration. The appropriate architecture of the neural network models was determined through several iterative steps of training and testing of the models. Both models were run with the data obtained from the plant operation and laboratory analysis to predict the dynamic behavior of the process. Using these two models, effluent COD concentrations were predicted and the results were compared for the purpose of evaluation of treatment performance. It was observed that the ASM1 ANN model approach gave better results and better described the operational conditions of the plant than ASM1.     

Prediction of Chemical Oxygen Demand (COD) Based on Wavelet Decomposition and Neural Networks

The chemical oxygen demand (COD) parameter of a wastewater treatment plant is predicted based on wavelet decomposition, entropy, and neural networks (NN) for rapid COD analysis. This paper also describes the usage of wavelet and NNs for parameter prediction. Data from a wastewater treatment plant in Malatya, Turkey, were used. This dataset consists of daily values of influents and effluents for a year. To reduce the dimension of input parameters and to decrease the NN training time, wavelet decomposition and entropy were used. Test results were presented graphically. The test results of the trained model were found to be closer to the measured COD values.     

SGBR Performance on the Basis of Color and COD Removal from Textile Wastewater

This study focused on removal of color and chemical oxygen demand (COD) parameter from textile effluents using a static granular bed reactor (SGBR), which has never been used to treat textile effluents previously. With an organic loading rate (OLR) of 1 kg/m³ day and a hydraulic retention time (HRT) of 48 h, COD and color removal efficiencies were 74 and 61%, respectively, while the removal efficiencies were 72 and 57%, respectively, with OLR of 1.7 kg/(m³ day) and HRT of 24 h. It was concluded that the SGBR could be used as an alternative method to treat and decolorize textile effluents. First order and modified Stover–Kincannon models were used to develop a kinetic model using the experimental data with correlation coefficients (R²) of 0.39 and 0.94, respectively. In regard with the calculated correlation coefficients, modified Stover–Kincannon model, which was used to model anerobic biofilters in previous studies, fitted best with the experimental data and it was stated that SGBR worked as an anerobic biofilter.     

Effect of Different Leachate/Acetate Ratios in a Submerged Anaerobic Membrane Bioreactor (SAnMBR)

Leachate treatment using a membrane bioreactor is an effective method. This study presents a configuration including an anaerobic bioreactor and a membrane module, called submerged anaerobic membrane bioreactor (SAnMBR), for treating influent with leachate/acetate rations (L/A), that were kept to be 10, 25, 50, 75, and 100% at a constant SRT (100 days). COD removal decreased from 85 to 75% when the L/A ratio increased from 10 to 100. To prevent membrane fouling, a SAnMBR was operated in the case of circulation of mixed liquor under continuous and intermittent suction. The average fluxes were 2.60 and 0.40 L/m² h at the periods of intermittent and continuous suction, respectively. The methane production varied between 0.25 and 0.32 L CH₄/g COD_removed.     

Degradation of Acid Pharmaceuticals in the UV/H2O2 Process: Effects of Humic Acid and Inorganic Salts

The presence of acid pharmaceuticals in water environments poses a potential threat to ecosystems and human health. Recent research has shown that photo oxidation processes are much more effective for removing these pharmaceuticals. However, the existence of humic acid (HA) could inhibit the clearance efficiency of this process. In this study, we investigated the photochemical degradation of six selected acid pharmaceuticals in surface water and effluent from wastewater treatment plants using the UV/H₂O₂ process. The results showed that HA can act as a photo sensitizer or a ^. OH sink, and its concentration had a significant inhibitory effect on the degradation of acid pharmaceuticals. Most of these pharmaceuticals were inhibited during this process when HA was added to deionized water solutions. In addition, the effects of chloride, bicarbonate, and nitrate on the degradation of these pharmaceuticals were different. The removal efficiency of these acid pharmaceuticals is lower in natural samples than in deionized samples because of the complex constituents in the latter.     

Photocatalytic Degradation of Dye C.I. Direct Blue 78 Using TiO2 Nanoparticles Immobilized on Recycled Wool‐Based Nonwoven Material

This paper discusses the possibility of immobilization of TiO₂ nanoparticles onto recycled wool‐based nonwoven material, which can be utilized for removal of dyes from wastewater. The photocatalytic activity of TiO₂ nanoparticles deposited on the nonwoven material was evaluated in the aqueous solution of direct dye C.I. Direct Blue 78 under the UV illumination. Nonwoven material modified with TiO₂ nanoparticles provides complete removal of dye from the solution already after 4–6 h of UV illumination. However, photodegradation of the dye adsorbed on the nonwoven material was obtained within 24 h of UV illumination. The rate of dye adsorption and photodegradation depends on the amount of deposited TiO₂ nanoparticles. The increase of initial dye concentration induced decrease in photocatalytic efficiency of immobilized TiO₂ nanoparticles. The highest photodegradation rate was achieved in acidic conditions. Elevated temperatures positively affected the removal of dye from solution. Photocatalytic activity of TiO₂ nanoparticles deposited on nonwoven material was preserved after three photodegradation cycles.     

无机阴离子及溶解性有机质对程海化学需氧量测定值的影响

自2005年以来,程海水体的化学需氧量(COD)持续升高,而生化需氧量(BOD)却维持不变,高锰酸盐指数(COD_(Mn))升高也较缓慢.为研究程海COD持续升高的原因,选取程海水体中具有代表性的无机阴离子(Cl~-、F~-、S~(2-)、HCO_3~-)和溶解性有机质(DOM)中不同浓度的胡敏酸(HA)、富里酸(FA)和商品化腐殖酸(SHA),研究其对COD和COD_(Mn)测定的影响,探讨Cl~-和DOM共同存在下对COD测定的影响.结果表明:程海水体中Cl~-浓度对COD存在显著影响,产生的COD值为5.42 mg/L,S~(2-)、F~-和HCO_3~-对COD影响较小;各离子对COD_(Mn)的影响很小;不同浓度梯度的HA、FA和SHA与COD测定结果呈显著线性相关,氧化1 mg C HA、FA和SHA所产生的COD值分别为2.164、1.964和2.362 mg;氧化1 mg C HA和FA所产生的COD_(Mn)值分别为0.646和0.344 mg;DOM对COD测定值的影响显著大于对COD_(Mn)测定值的影响;且一定浓度Cl~-的存在增强了FA与HA对COD测定的影响.该研究为进一步阐明程海COD逐步升高,COD_(Mn)值缓慢升高的内在原因奠定了基础.     

Enhancing the Sustainability of Household Fe0/Sand Filters by Using Bimetallics and MnO2

Filtration systems containing metallic iron as reactive medium (Fe⁰ beds) have been intensively used for water treatment during the last two decades. The sustainability of Fe⁰ beds is severely confined by two major factors: (i) reactivity loss as result of the formation of an oxide scale on Fe⁰ and (ii) permeability loss due to pore filling by generated iron corrosion products. Both factors are inherent to iron corrosion at pH > 4.5 and are common during the lifespan of a Fe⁰ bed. It is of great practical significance to improve the performance of Fe⁰ beds by properly addressing these key factors. Recent studies have shown that both reactivity loss and permeability loss could be addressed by mixing Fe⁰ and inert materials. For a non‐porous additive like quartz, the threshold value for the Fe⁰ volumetric proportion is 51%. Using the Fe⁰/quartz system as reference, this study theoretically discusses the possibility of (i) replacing Fe⁰ by bimetallic systems (e.g., Fe⁰/Cu⁰), or (ii) partially replacing quartz by a reactive metal oxide (MnO₂ or TiO₂) to improve the efficiency of Fe⁰ beds. Results confirmed the suitability of both tools for sustaining Fe⁰ bed performance. It is shown that using a Fe⁰:MnO₂ system with the volumetric proportion 51:49 will yield a filter with 40% residual porosity at Fe⁰ depletion (MnO₂ porosity 62%). This study improves Fe⁰ bed design and can be considered as a basis for further refinement and detailed research for efficient Fe⁰ filters.     

Treatment of Refractory Organics Contained in Actual Agro‐Industrial Wastewaters by UV/H2O2

In this work, the treatment of actual agro‐industrial wastewaters (IWW) by a UV/H₂O₂ process has been investigated. The aqueous wastes were received from industrial olive oil mills and then treated by laboratory scale physicochemical methods, i. e., coagulation using ferrous and aluminum sulfate, decantation, filtration and adsorption on activated carbon. These wastes are brown colored effluents and have a residual chemical oxygen demand (COD) in the range of 1800 to 3500 mgO₂ L^–1, which cannot be further eliminated with physicochemical processes. The UV/H₂O₂ treatments were carried out under monochromatic irradiation at 254 nm using a thermostated reactor equipped with a mercury vapor lamp located in an axial position. The effects of initial H₂O₂ concentration, initial COD, pH and temperature have been studied in order to determine the optimum conditions for maximum color and COD removals. The experimental results reveal the suitability of the UV/H₂O₂ process for both removal of high levels of COD and effectively decolorizing the solution. In particular, 95% of color removal and 90% of COD removal were obtained under conditions of pH = 5 and 32°C using 2.75 g H₂O₂ g^–1 COD L^–1 during 6 h of UV‐irradiation. The treatment is unaffected by pH over the range 2 to 9. In addition, the COD removal is improved by increasing the temperature, whereas the color removal has not been affected by this parameter. The results show that the hydroxyl radicals generated from the catalytic decomposition of H₂O₂ by UV‐irradiation of the solution could be successfully used to mineralize the organics contained in IWW. The mineralization of the organics seems to occur in three main sequential steps: the first is the rapid decomposition of tannins leading to aromatic compounds, which are confirmed by the decolorization of the IWW; the second step corresponds to the oxidation of aromatics leading to aliphatic intermediates, which occurs by the cleavage of an aromatic ring, and is established by the removal of aromatics, and the final step is the slow oxidation of the aliphatic intermediates, which is measured by the COD removal.     

The structure and sharpness of (Mg,Fe)2SiO4 phase transformations in the transition zone

To calculate accurately the pressure interval and mineral proportions (i.e. yields) across the olivine to wadsleyite and wadsleyite to ringwoodite transformations requires a detailed knowledge of the non-ideality of Fe-Mg mixing in these (Mg,Fe)₂SiO₄ solid solutions. In order to constrain the activity-composition relations that describe non-ideal mixing, Fe-Mg partitioning experiments have been conducted between magnesiowüstite and (Mg,Fe)₂SiO₄ olivine, wadsleyite and ringwoodite as a function of pressure at 1400°C. Using known activity-composition relations for magnesiowüstite the corresponding relations for the three polymorphs were determined from the partitioning data. In all experiments the presence of metallic iron ensured redox conditions compatible with the Earth’s transition zone. The non-ideality of the (Mg,Fe)₂SiO₄ solid solutions was found to decrease in the order W^wadsleyite_FeMg>W^ringwoodite_FeMg>W^olivine_FeMg. These partitioning data were used, along with published phase equilibria measurements for the Mg₂SiO₄ and Fe₂SiO₄ end-member transformations, to produce an internally consistent thermodynamic model for the Mg₂SiO₄-Fe₂SiO₄ system at 1400°C. Using this model the pressure interval of the olivine to wadsleyite transformation is calculated to be significantly smaller than previous determinations. By combining these results with Fe-Mg partitioning data for garnet, the widths of transition zone phase transformations in a peridotite composition were calculated. The olivine to wadsleyite transformation at 1400°C in dry peridotite was found to occur over a pressure interval equivalent to approximately 6 km depth and the mineral yields were found to vary almost linearly with depth across the transformation. This transformation is likely to be even sharper at higher temperatures or could be significantly broader in wet mantle or in regions with a significant vertical component of mantle flow. The entire range of estimated widths for the 410 km discontinuity (4-35 km) could, therefore, be explained by the olivine to wadsleyite transformation in a peridotite composition over a range of quite plausible mantle temperatures and H₂O contents. The wadsleyite to ringwoodite transformation in peridotite mantle was calculated to take place over an interval of 20 km at 1400°C. This transformation yield was also found to be near linear.