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Sungai Siak merupakan sungai yang menjadi sumber air bagi masyarakat bahkan hewan dan tumbuhan untuk memenuhi kebutuhan sebagai kelangsungan hidup, sehingga kualtias air sungai ini perlu dijaga dan dipelihara. Analisa kapasitas muatan sumber polusi pada air sungai merupakan proses yang rumit sehingga dapat direpresentasikan dengan pendekatan model Qual2Kw. Model ini dapat mendeskripsikan hasil parameter kualitas air yang mendekati angka aktual setelah melakukan kalibrasi. Parameter DO pada skenario 1 dimana tidak menginput debit limbah atau sumber pencemaran maka segmen Tandun merupakan nilai parameter terendah yaitu 4,49 mg/l dan tidak memenuhi standar kualitas air baku mutu kelas I, sedangkan untuk ammonia (NH4) tertinggi berada pada segmen Teluk Ketari yaitu 0,43 mg/l dan nilai ini masih memenuhi standar kualitias air baku mutu kelas I. Skenario 2 dengan menginput debit limbah maka parameter DO hanya pada segmen Petapahan yang memenuhi buku mutu dengan nilai 6,20 mg/l sedangkan untuk NH4 nilai tertinggi berada pada segmen Pantai Cermin dengan nilai 0,04 mg/l dimana angka ini masih memenuhi baku mutu.

Cr (VI) is hazardous to humans and our environment. Leersia hexandra Swartz (L. hexandra) is the first wet chromium hyperaccumulator found in China. This study constructed the L. hexandra constructed wetland-microbial fuel cell (CW-MFC) system to treat Cr (VI) wastewater. It also determined the effects of different dissolved oxygen (DO) concentrations on power generation, pollutant removal, and Cr (VI) reduction. Cathode aeration promoted the voltage output and pollutant removal of the L. hexandra CW-MFC when the DO concentration was 4.5 mg·L−1: the highest voltage was 520 mV, the chemical oxygen demand (COD) removal rate was 93.73%, and the Cr (VI) removal rate was 97.77%. Moreover, the increase in the DO concentration improved the absorption of heavy metal Cr by the substrate and L. hexandra, and promoted the transformation from Cr (VI) to Cr (III). Chromium mostly exists as a residue with low toxicity and low mobility in L. hexandra and the substrate. This proves that the increased DO concentration promotes the redox reaction in the system and plants, reducing Cr (VI) to Cr (III). At the same time, the key micro-organism Geobacter that enhances the performance of the system and Cr (VI) reduction was found. The research results can provide a reference for the subsequent CW-MFC treatment of actual Cr-containing wastewater.

Resumen Contexto: La transferencia del oxígeno disuelto (OD) es un tema de importancia para la calidad del agua. Diversos dispositivos se han diseñado para suministrar el OD requerido en algunos cuerpos de agua durante su tratamiento y restauración; sin embargo, estos conllevan un alto consumo de energía, requiriendo optimizar los parámetros de uso. Método: Este trabajo estudió el efecto de la potencia y número de aspas utilizadas en un aireador de eje horizontal. Las mediciones se realizaron en muestras de agua anóxica, utilizando tres dispositivos aireadores conformados por 6, 12 y 24 aspas, variando la velocidad de rotación a partir del voltaje suministrado. Resultados: Los mayores valores obtenidos del coeficiente de transferencia K L a se presentan en dispositivos con mayor cantidad de aspas. Sin embargo, la eficiencia estándar de aireación (SAE) y la eficiencia de transferencia de oxígeno estándar (SOTR) revelaron que el dispositivo con 6 aspas presenta una mayor eficiencia energética. Conclusiones: Se demostró que la transferencia de OD no depende únicamente de los impactos asociados al número de aspas, y que la máxima eficiencia en la transferencia se obtiene con un menor número de aspas. Estos resultados pueden contribuir en mejorar el entendimiento del funcionamiento de estos sistemas mecánicos en términos de transferencia de OD. Abstract Context: Dissolved oxygen (DO) transfer is an important matter for water quality. Several devices have been designed to supply the required DO in some bodies of water during their treatment and restoration. However, these entail a high energy consumption, thus requiring the optimization of use parameters. Method: This work studies the effect of the power and number of paddles used in a horizontal axis aerator. Measurements were made on anoxic water samples using three mechanical aerating devices made up of 6, 12, and 24 paddles while varying the rotation speed from the supplied voltage. Results: The highest values obtained for the transfer coefficient K L a are reported by devices with a greater number of blades. Nevertheless, the Standard Aeration Efficiency (SAE) and the Standard Oxygen Transfer Rate (SOTR) efficiency reveal that the 6-paddle wheels are more energy-efficient. Conclusions: It is shown that DO transfer does not depend solely on the impacts associated with the number of paddles, and that the maximum transfer efficiency is obtained with a lower number of paddles. These results contribute to improving the understanding of the operation of these mechanical systems in terms of DO transfer.

The River Ganga (2,525 km long) is the largest River basin in India, covering 26.2 percent of India's total geographical area and recently granted living entity status by the court. It is the holiest River and also among the dirtiest in the world. That’s why it is mandatory to maintain its water quality (WQ). Though, monitoring and assessment of WQ of a River is a very challenging task. In this research work, Soft Computing (SC) based popular and commononly used Artificial Neural Network (ANN) technique has been used for modelling the WQ of the Ganga River by developing a prediction model based on six different training functions. Five sampling stations along this River stretch were selected from DEVPRAYAG to ROORKEE in the Uttarakhand state of India. The monthly data sets of five water quality parameters temperature, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD) and total coliform (TC) for the time period from 2001 to 2015 have been taken. The feed forward error back propagation neural network method has been used to develop the WQ-prediction model by conducting various experiments following a neural network structure of 5-10-1, 0.1 as a training goal and various training functions. Using the Mean square error (MSE) statistical method the prediction performance of the developed model was evaluated. The model developed with traincgp (Conjugate Gradient with Polak-Ribiere Restarts) comes out to be the worst one (MSE=0.786) while the other model with trainlm (Levenberg-Marquardt backpropagation) rule proved to be the best one (MSE=0.163) among others. Consequently, it is found that ANNs are capable of predicting WQ of the River Ganga with acceptable results.

To evaluate the hypothesis that plant-mediated oxygen supplies decrease methane (CH4) production and total global warming potential (GWP) in a tropical peatland, the authors compared the fluxes and dissolved concentrations of greenhouse gases [GHGs; CH4, carbon dioxide (CO2) and nitrous oxide (N2O)] and dissolved oxygen (DO) at multiple peatland ecosystems in Central Kalimantan, Indonesia. Study ecosystems included tropical peat swamp forest and degraded peatland areas that were burned and/or drained during the rainy season. CH4 fluxes were significantly influenced by land use and drainage, which were highest in the flooded burnt sites (5.75 +/- 6.66 mg C m(-2) h(-1)) followed by the flooded forest sites (1.37 +/- 2.03 mg C m(-2) h(-1)), the drained burnt site (0.220 +/- 0.143 mg C m(-2) h(-1)), and the drained forest site (0.0084 +/- 0.0321 mg C m(-2) h(-1)). Dissolved CH4 concentrations were also significantly affected by land use and drainage, which were highest in the flooded burnt sites (124 +/- 84 mu mol L-1) followed by the drained burnt site (45.2 +/- 29.8 mu mol L-1), the flooded forest sites (1.15 +/- 1.38 mu mol L-1) and the drained forest site (0.860 +/- 0.819 mu mol L-1). DO concentrations were influenced by land use only, which were significantly higher in the forest sites (6.9 +/- 5.6 mu mol L-1) compared to the burnt sites (4.0 +/- 2.9 mu mol L-1). These results suggest that CH4 produced in the peat might be oxidized by plant-mediated oxygen supply in the forest sites. CO2 fluxes were significantly higher in the drained forest site (340 +/- 250 mg C m(-2) h(-1) with a water table level of -20 to -60 cm) than in the drained burnt site (108 +/- 115 mg C m(-2) h(-1) with a water table level of -15 to +10 cm). Dissolved CO2 concentrations were 0.6-3.5 mmol L-1, also highest in the drained forest site. These results suggested enhanced CO2 emission by aerobic peat decomposition and plant respiration in the drained forest site. N2O fluxes ranged from -2.4 to -8.7 mu g N m(-2) h(-1) in the flooded sites and from 3.4 to 8.1 mu g N m(-2) h(-1) in the drained sites. The negative N2O fluxes might be caused by N2O consumption by denitrification under flooded conditions. Dissolved N2O concentrations were 0.005-0.22 mu mol L-1 but occurred at < 0.01 mu mol L-1 in most cases. GWP was mainly determined by CO2 flux, with the highest levels in the drained forest site. Despite having almost the same CO2 flux, GWP in the flooded burnt sites was 20% higher than that in the flooded forest sites due to the large CH4 emission (not significant). N2O fluxes made little contribution to GWP.

Micro-nano bubbles (MNBs) are tiny bubbles with diameters on the order of micrometers and nanometers, showing great potential in environmental remediation. However, the application is only in the beginning stages and remains to be intensively studied. In order to explore the possible use of MNBs in groundwater contaminant removal, this study focuses on the transport of MNBs in porous media and dissolution processes. The bubble diameter distribution was obtained under different conditions by a laser particle analyzer. The permeability of MNB water through sand was compared with that of air-free water. Moreover, the mass transfer features of dissolved oxygen in water with MNBs were studied. The results show that the bubble diameter distribution is influenced by the surfactant concentration in the water. The existence of MNBs in pore water has no impact on the hydraulic conductivity of sand. Furthermore, the dissolved oxygen (DO) in water is greatly increased by the MNBs, which will predictably improve the aerobic bioremediation of groundwater. The results are meaningful and instructive in the further study of MNB research and applications in groundwater bioremediation.

In situ observations of physical, chemical, and biological parameters of the Qatari water column were conducted to understand the temporal (seasonal) and spatial (regional) variability in the vertical and horizontal distribution of oceanographic properties within the exclusive economic zone (EEZ) of Qatar. Samples were collected from 5 different offshore shallow and deep stations covering the northern and eastern marine regions of the Qatar EEZ during two seasons: late summer (September 2014) and winter (January 2015). Eighteen (18) water samples were analyzed for temperature, salinity, density, dissolved oxygen concentration, dissolved oxygen saturation (DO%), and chlorophyll-a concentration (Chl-a). These data reveal several interesting and unique features that are related to surface warming that give rise to a large excess of evaporation over precipitation, resulting in the formation of several high salinity water masses. The deep offshore EEZ of Qatar was characterized by stratification (seasonal thermocline and pycnocline) during summer when deep water temperature was about 23.5°C (colder than the surface 32.6°C) where reduced stratification appeared to dominate in winter. Well-oxygenated water exists within the surface layer (0-23 m) during both summer and winter. Oxygen saturation layer (concentration 4.53 ml/l; saturation 94.49%) in the deep water extends to bottom (63 m) in winter however oxygen level falls below the summer thermocline (1.35 ml/l corresponding to 28.95% saturation) at Station 5 (63 m depth). Chl-a concentration was high in summer due to high primary productivity but remained sustained at moderate levels in winter. The procedures and methods were carefully applied to ensure the accuracy of the study results. In-situ measurements have high reliability in detecting hydrographic properties; however, it is costly, time consuming, requires ship time and as well as large number of scientific personnel and resources.

The design and development of the neural network (NN)-based controller performance for the activated sludge process in sequencing batch reactor (SBR) is presented in this paper. Here we give a comparative study of various neural network (NN)-based controllers such as the direct inverse control, internal model control (IMC) and hybrid NN control strategies to maintain the dissolved oxygen (DO) level of an activated sludge system by manipulating the air flow rate. The NN inverse model-based controller with the model-based scheme represents the controller, which relies solely upon the simple NN inverse model. In the IMC, both the forward and inverse models are used directly as elements within the feedback loop. The hybrid NN control consists of a basic NN controller in parallel with a proportional integral (PI) controller. Various simulation tests involving multiple set-point changes, disturbances rejection and noise effects were performed to review the performances of these various controllers. From the results it can be seen that hybrid controller gives the best results in tracking set-point changes under disturbances and noise effects. � Springer-Verlag 2005.

The effects of oxygenation and aeration on water quality, rainbow trout (Oncorhynchus mykiss) production, and economics were compared at the Wytheville State Fish Hatchery (WSFH) for 270 days. Mean dissolved oxygen (DO) concentrations and delta DO were significantly higher (P < 0.001) in the oxygenated raceways (9.5 and 2.75 mg/L, respectively) compared to aerated raceways (7.4 and 0.57 mg/L). Total settleable solids loads were significantly greater (P < 0.001) in aerated raceways (10.3 g/L/day) than in oxygenated raceways (8.8 g/L/day). Dissolved nitrogen (%), total gas pressure, and other water quality parameters (CO2, nitrite nitrogen, alkalinity, pH, and TAN) did not differ significantly between the treatments (P > 0.05). Raceway trout production (kg/day), trout growth rates (grams), feed conversion rate (FCR), and fish survival were not significantly different between treatments (P > 0.05). Blood hematocrit (Hct) and percent visceral mass were significantly elevated (P < 0.001) in oxygenated raceways compared to aerated raceways at 46 and 14.4% and 44 and 13%, respectively. Carrying capacity estimates derived from fish loading trials were significantly different (P < 0.001) at 3,355 and 2,217 kg/raceway in oxygenated and aerated raceways, respectively. Estimates of carrying capacity calculated using a fish loading (Ld) equation were also significantly different (P < 0.001) at 1,530 and 990 kg for oxygenated and aerated raceways, respectively. Oxygen injection increased the cost of production by $0.20/kg, however, net present value analysis (NPV) of oxygenated and aerated raceways over 5 years at a 10% discount rate yielded estimates of $50,666.51 and $32,742.15, respectively. Oxygen injection is an effective means of increasing DO concentrations, reducing effluent solids loading, and increasing raceway carrying capacity. Master of Science

Bio-based and biodegradable polymers are regarded as potential replacements of traditional fossil based plastics. Polyhydroxyalkanoates (PHAs) are widely studied biopolymers due to their broad range of thermal and mechanical properties. The impacts of operational conditions, such as pH, temperature, organic loading rate and sludge retention time, in PHA production process by mixed microbial cultures (MMCs) have been evaluated by previous studies, but the influence of dissolved oxygen (DO), which is directly related to process energetic demand, was rarely discussed. This thesis is focused on the effects of DO on the microbial culture selection and PHA accumulation stages, as well as the impact of DO on a combined PHA production and nutrient removal process for wastewater treatment. Efficient Plasticicumulans dominating microbial cultures were enriched under both high DO (3.47 ± 1.12 mg/L) and low DO (0.86 ± 0.50 mg/L) conditions in the feast phase containing mostly the same populations but with different relative abundance. Butyrate and valerate were found to be the preferred substrates as compared to acetate and propionate regardless of DO concentrations. Compared to acetate and propionate, the butyrate and valerate uptakes were not significantly impacted by low DO levels in the PHA accumulation stage. A metabolic model was developed for the first time to describe the substrate preference among multiple volatile fatty acids (VFAs), providing a successful approach for PHA composition prediction and process efficiency optimization when four competing VFAs are supplied. Further, DO level control through both the feast and famine phases of culture selection was applied, at 3.79±0.65 mg/L and 0.48±0.29 mg/L respectively. The low DO level in both the feast and famine phases proved to be insufficient for successful MMC enrichment. By characterizing the microbial evolution under the unlimited DO conditions, it was found that Paracoccus was the dominating population (>50%) in the selected cultures, and substrate competition was correlated with the abundance of Plasticicumulans during culture selection. In order to optimize the integrated PHA production and nutrient removal process fed with ammonia-rich feedstocks in full scale implementation, the impact of DO on both processes was investigated. Much higher DO affinity for VFA consumption was observed as compared to nitrification. A DO control strategy was proposed based on the observation that the PHA production was not influenced while nitrogen was removed by simultaneous nitrification and denitrification processes when controlling DO at low levels (e.g. 0.4-0.8 mg/L).