Hydrodynamic and Biochemical Impacts on the Development of Hypoxia in the Louisiana–Texas Shelf Part I: Numerical Modeling and Hypoxia Mechanisms

A three-dimensional coupled hydrodynamic–biogeochemical model with N, P, Si cycles and multiple phytoplankton and zooplankton functional groups was developed and applied to the Gulf of Mexico to study bottom dissolved oxygen dynamics. A 15-year hindcast was achieved covering the period of 2006–2020. Extensive model validation against in situ data demonstrates that the model is capable of reproducing vertical distributions of dissolved oxygen (DO), frequency distributions of hypoxia thickness, spatial distributions of bottom DO concentration and interannual variations of hypoxic area. The impacts of river plume and along-shore currents on bottom DO dynamics were examined based on multiyear bottom DO climatology, the corresponding long-term trends, and interannual variability. Model results suggest that mechanisms of bottom hypoxia developments are different between the west and east Louisiana–Texas Shelf waters. The mid-Atchafalaya nearshore (10–20 m) region firstly suffers from hypoxia in May, followed by the west-Mississippi nearshore region in June. Hypoxic waters expand in the following months and eventually merge in August. Sediment oxygen consumption (SOC) and water stratification (measured by potential energy anomaly, PEA) are two main factors modulating the variability of bottom DO concentration. Generalized Boosted Regression Models provide analysis of the relative importance of PEA and SOC. The analysis indicates that SOC is the main regulator in nearshore regions, and water stratification outcompetes the sedimentary biochemical processes in the offshore (20–50 m) regions. A strong quadratic relationship was found between hypoxic volume and hypoxic area, which suggests that the volume mostly results from the low DO in bottom water and can be potentially estimated based on the hypoxic area.

Prediction of DO Concentration in Nakdong River Estuary through Case Study Based on Long Short Term Memory Model

In this study, we carried out case study to predict dissolved oxygen (DO) concentration of Nakdong river estuary with LSTM model. we aimed to figure out a optimal model condition and appropriate predictor for prediction in dissolved oxygen concentration with model parameter and predictor as cases. Model parameter case study results showed that Epoch = 300 and Sequence length = 1 showed higher accuracy than other conditions. In predictor case study, it was highest accuracy where DO and Temperature were used as a predictor, it was caused by high correlation between DO concentration and Temperature. From above results, we figured out an appropriate model condition and predictor for prediction in DO concentration of Nakdong river estuary.

Organic Removal Treatment Using Microbubble Generator (MBG) in Eutrophic Disorder Condition

The Techno Park basin, built as an extension of a small tributary of the Code River primarily acts as a retention basin for runoff during the rainy season. It improves the quality of water that has been degraded by domestic wastewater discharge from the surrounding community. Therefore, this study aims to assess the extent to which water quality of the basin can be improved with aeration technology. The aeration technology is a Microbubble Generator (MBG) built using a 100 Watts submersible pump with three horizontal nozzles at a depth of 40 cm from the water surface. Furthermore, the profiles of dissolved oxygen (DO) concentration were measured at the basin’s inlet and outlet, as well as the depths of 1 m below surface water and the bottom of the basin. Diurnal DO was measured to investigate the causes of supersaturation. The aeration performance was also determined from the COD parameters at the inlet and outlet. Discharge measurements were then conducted on the tributary/drainage channel to the inlet basin. The result showed that the DO supersaturation concentration has been attributed to the contribution of photosynthesis from phytoplankton such as algae. Furthermore, no change in DO concentration was observed in a range of 1 m depth from the surface of the water to the bottom (0.3 - 0.14 mg-DO/l). In this eutrophic state, DO increased exponentially during the daytime hours and then decreased during the night. The daily measurement showed an increase in the average DO of 2.31 mg/l (standard deviation of 1.56 mg/l), with average CODinlet fluctuations of 18.79 mg/l (standard deviation of 13.56 mg/l) and average CODoutlet of 14.38 mg/l (standard deviation 2.94 mg/l). Due to additional DO concentration coming from eutrophication during daylight, it was not possible to make a precise assessment of the effectiveness of the MBG aerator.

Integration of anammox into the MBR process for main stream sewage treatment

The integration of Anaerobic ammonia oxidation (anammox) into the membrane bioreactor (MBR) process (AX-MBR) is proposed in this study to reduce operating costs. The temperature was not controlled during the study. Anammox, denitrification, and nitrification were studied in the AX-MBR for 210 days. The reactor was fed with mainstream sewage from Guilin City, China. The results showed that AX-MBR could run with reduced dissolved oxygen (DO) concentration, and COD, NH4+-N, and total nitrogen removal were maintained or improved. The microbial analysis results demonstrated that the added anammox sludge could survive in the AX-MBR, but the sludge microbial diversity decreased. Nitrospira, Candidatus Kuenenia, and Nitrosomonas dominated the anammox sludge. In a word, the AX-MBR developed in this study could treat mainstream sewage with the appropriate management, and the operation costs are expected to reduce by decreasing the amount of aeration.

Dissolved oxygen stratification in a small lake depending on water temperature and density and wind impact

The dissolved oxygen (DO) is one of the most important parameters in lakes ecosystem. Variability of DO in lakes is associated with the absorption of oxygen due to the decomposition of organic matter and chemical reactions and the release of oxygen as a result of photosynthesis. The DO concentration also depends on seasonal changes in water temperature and mixing regime. The aim of this work is to assess the influence of seasonal thermal and density stratification on the DO stratification in a small mesotrophic lake and to develop a regression DO model, with water temperature and density and characteristics of wind regime as independent variables. Long-term measurements of water temperature and DO in small Karelian Lake Vendyurskoe in 2007-2020 were used. At the stage of spring-summer heating, three periods are considered when the water column was in the state of homothermy (May 15-June 15), weak stratification (July 15-August 15), and strong stratification (July 15-August 15). The wind load (number of days with wind speed more than 3 m/s for each period) was analysed based on the weather station Petrozavodsk data. As a result of multiple regression analysis, taking into account the wind load, dependences of DO stratification on water temperature stratification (R2 = 0.51) and water density stratification (R2 = 0.61) are found. Obtained regression DO models can be used for solving various environmental tasks.

Modeling Spatial Patterns of Dissolved Oxygen and the Impact Mechanisms in a Cascade River

Dissolved oxygen (DO) concentration is an essential indicator for assessment of river ecosystems. A hydrodynamic and water quality mathematical model coupling one-dimensional and two-dimensional models is developed in this study. The characteristics of study area, flow velocity, temperature, and organic contamination are taken as consideration in the scenario setting. The changing processes of DO concentration are simulated in different scenarios, and the effects on DO concentration are discussed. Results indicate that: 1) A negative relation was present between DO concentration in Yongjiang River and releasing discharge of the Laokou hydro-project, since reoxygenation is greater than oxygen consumption along the river, DO concentration increases from upstream to downstream. 2) DO concentration increases with the releasing of DO in the water, which also varies along with the releasing of biochemical oxygen demand (BOD) concentration. Laokou exhibits the greatest increase of BOD, which ranges from 0.1 mg/L to 0.75 mg/L 3) The increasing of water temperature results in increased reoxygenation and a decrease in oxygen consumption. Our study shows that the water temperature increased from 19°C to 29 °C, and correspondingly saturated DO decreased from 9.25 mg/L to 7.54 mg/L. The study provides scientific support for ecology operation in the cascade river, and is expected to improve the water environment by reservoir regulation.

Effect of Integrating LED Lighting With Fiber Membranes On The Restoration of Eutrophic Waterbody And Its Optimal Application

In this study, laboratory experiments were used to compare the effects of two LED light sources (blue and red) combined with fiber membranes on the increase of Dissolved Oxygen (DO) in eutrophic water bodies for improvement of water quality. The results showed that the application of these two LED light sources can increase the DO concentration and oxidation-reduction potential (ORP), and eliminate the NH4+-N in water bodies and the phosphorus release from the sediment, resulting in the improvement of sediment. Specifically, the blue LED light source is more benefitable to the increase of the DO concentration than the red LED light source. After 28 days, the DO concentration increases to 10 mg/L, and the redox potential is higher than 50 mV with the elimination of NH4+-N. This study illustrated that LED light sources can significantly increase the DO and effectively improve the water quality in eutrophic water bodies.

Evaluasi Efektivitas Metode dan Media Filtrasi pada Pengolahan Air Limbah Tahu

Peningkatan jumlah industri tahu di Indonesia diiringi dengan meningkatnya jumlah limbah industri tahu yang perlu mendapat perhatian khusus. Limbah tahu dengan kandungan bahan organik tinggi memberikan dampak negatif bagi sistem perairan jika dibuang tanpa adanya pengolahan. Penelitian ini dilakukan dengan tujuan untuk mempelajari metode yang efektif dalam mengolah limbah tahu dengan variasi media filtrasi. Penelitian ini dilakukan dengan menggunakan 2 metode yang diperlakukan pada 2 kolom filtrasi dengan media filtrasi yang berbeda. Susunan media utama pada kolom filtrasi 1 berupa bioball dan kolom filtrasi 2 berupa bioring. Metode batch dan kontinyu diperlakukan pada dua jenis kolom filtrasi tersebut. Ketinggian total media filtrasi untuk setiap kolom adalah 20 cm dengan volume air limbah 5 liter. Hasil penelitian menunjukkan adanya peningkatan kualitas air limbah tahu pada sampel hari ke 1 dengan terjadinya penurunan konsentrasi COD pada kolom 1 dengan perlakuan metode batch sebanyak 18,12%. Peningkatan konsentrasi DO paling optimal pada kolom 1 dengan perlakuan metode kontinyu sebanyak 18,03%. Selanjutnya konsentrasi pH terjadi peningkatan secara signifikan pada kolom 2 dengan perlakuan metode batch sebanyak 41,27%. Sedangkan penurunan konsentrasi kekeruhan diperoleh pada kolom 1 dengan perlakuan metode batch sebanyak 57,22%. Perlakuan limbah tahu dengan metode batch pada waktu tinggal 1 hari memberikan peningkatan kualitas air limbah tahu yang lebih baik meskipun pada waktu tinggal yang lebih lama terjadi penurunan kualitas akibat terjadinya proses dekomposisi yang tidak terkontrol. Lebih lanjut, perlu dilakukan penelitian dengan melibatkan mikroorganisme selektif pada penyaring lambat dengan metode batch agar dihasilkan penurunan konsentrasi COD yang lebih signifikan. ABSTRACTThe increase in the number of tofu industries in Indonesia is accompanied by an increase in the amount of tofu industrial waste that needs special attention. Tofu waste with high organic matter content has a negative impact on aquatic systems if it is disposed of without treatment. The aim of this research was to study the effective method of treating tofu waste with a variety of filtration media. This research was conducted using 2 methods which were treated on 2 filtration columns with different filtration media. The composition of the main media in first filtration column is bioball and second filtration column is bioring. Batch and continuous methods are applied to the two types of filtration columns. The total height of the filtration media for each column is 20 cm with a volume of 5 liters of wastewater. The results showed an increase in the quality of tofu wastewater on the first day of the sample with a decrease in COD concentration in first column with the batch method treatment of 18.12%. The most optimal increase in DO concentration in first column with continuous method treatment was 18.03%. Furthermore, the pH concentration increased significantly in second column with the batch method treatment as much as 41.27%. While the decrease in turbidity concentration was obtained in column 1 with batch method treatment as much as 57.22%. The treatment of tofu waste using the batch method at a residence time of 1 day provides a better-quality improvement of tofu wastewater although at a longer residence time there is a decrease in quality due to an uncontrolled decomposition process. Furthermore, it is necessary to conduct research involving selective microorganisms in a slow filter with a batch method in order to produce a more significant reduction in COD concentration.

Transferencia de oxígeno en agua anóxica utilizando un dispositivo de aireadores de rueda de paletas a bajas revoluciones

The reduction of dissolved oxygen (DO) in water is associated with the effect of climate change. The lack of oxygen in water bodies directly affects the biological species present in different shallow water bodies such as swamps and wetlands, as well as in aquaculture processes. An optimal value in the DO concentration favors the reproduction of these biological species present in both artificial and natural environments. For this, various equipment has been developed to favor the increase of DO in the water to acceptable values. However, some of these systems are expensive, energy inefficient, and noisy which generate adverse impacts in aquatic ecosystems due to perturbances in the water. This study measures the efficiency (KgO2·kWh-1) of introducing DO into the water using a paddle wheel aerator system at low RPMs destined for shallow bodies of water. Tests were performed on anoxic water samples using aerators with 6, 12, and 24 paddles at the laboratory level. By increasing the voltage (6, 9, and 12V), the RPMs applied to each device through a geared motor is also increased. The results show a higher DO transfer rate in the 1 and 5 mg of O2·L-1 range. The best configuration concerning energy consumption worked at low RPMs using the 6-paddle wheel aerator at 6V. This establishes that, in addition to the management of low revolutions, the use of a smaller number of wheels favors an increase in efficiency during the DO restoration process in shallow water bodies.

Response of simultaneous nitrification-denitrification to DO increments in continuously aerated biofilm reactors for aquaculture wastewater treatment

Intensive aquaculture usually produces large volumes of nutrient-rich wastewater, which is essential to treat to avoid eutrophication. This study aimed to evaluate the performance of five, continuously aerated, biofilm reactors treating simulated, high-strength, aquaculture wastewater under different dissolved oxygen (DO) levels, and the effects of DO increments on simultaneous nitrification-denitrification (SND). Continuous aeration was beneficial to complete nitrification. Total inorganic nitrogen (TIN), principally ammonium, was mainly removed by SND. The SND rate response to different DO levels was fitted well by the power function of y = 54.81 + 371.58/(1 − 0.16*x)^(−1/0.24) (R2 = 0.897, P = 0.000). When the TIN was removed completely, the optimal SND rate was defined and corresponded to a value of 121.8%. Accordingly, the optimal DO concentration was calculated as 2.10 mg/L, close to the actual level of 1.83 mg/L, at which the highest proportional removals of total nitrogen (58.0%) and TIN (57.3%) were obtained. Phosphorus was also removed by denitrifying polyphosphate-accumulating organisms.