Increase In Dissolved Oxygen Concentration Research Articles

Effects of multi-plant harvesting on nitrogen removal and recovery in constructed wetlands

The harvesting of plants is considered an effective method for nutrient recovery in constructed wetlands (CWs). However, excessive plant harvesting can lead to a decrease in plant biomass. It remains unclear what harvesting frequency can optimize plant nutrient uptake and pollutant removal. In this study, CWs planted with Myriophyllum aquaticum were constructed, and three different frequencies of plant harvesting (high: 45 days/time; low: 90 days/time; none: CK) were set to investigate nitrogen removal and its influencing mechanism, as well as the capacity for plant nutrient recovery. The results showed that the average removal efficiencies of ammonia nitrogen (NH4+-N) at 45 days/time, 90 days/time, and CK were 90.3%, 90.8%, and 88.3% respectively, while the corresponding total nitrogen (TN) were 61.2%, 67.4%, and 67.4%. Dissolved oxygen (DO) concentration and water temperature were identified as the main environmental factors affecting nitrogen removal efficiency. Low harvest frequency (90 days/time) increased DO concentration and NH4+-N removal efficiency without impacting TN removal. Additionally, TN recovery from plants under high and low harvest was found to be approximately 9.21–9.32 times higher than that from no harvest conditions. The above studies indicated that a harvest frequency of every 90 days was one appropriate option for M. aquaticum, which not only increased NH4+-N removal efficiencies but also facilitated more efficient nitrogen recovery from the wetland system.

Mechanism of Iris sibirica and aeration combination on promoting the water purification performance of constructed wetland under low temperature.

Temperature is an important factor affecting the water purification performance of constructed wetland (CW). In the previous study, the combined measures of Iris sibirica and aeration at the bottom of the first quarter filtration chamber could improve the pollutant removal capacity of CW at low temperature. However, the mechanism between the combined measures of Iris sibirica and aeration on enhancing the performance of domestic sewage treatment is unclear. Our study aims to provide scientific validation for the combined measure through monitoring the concentrations of dissolved oxygen (DO), chemical oxygen demand (CODCr), ammonia nitrogen (NH4+-N), and total nitrogen (TN) along the water flow pathway of the CW and measuring the superoxide dismutase (SOD) activities of the plants and the abundance of nitrogen cycle-related microbial functional genes in the substrates of CW to explore the mechanism of combined measures promoting the removal efficiency of the CW under low-temperature stress. Results showed that aerating at the bottom of the first quarter filtration chamber increased DO concentration in the front part of the CW, which benefited the aerobic removal of pollutants and the activities of microorganisms, and the removal CODCr and NH4+-N occurred mainly in the front part of the CW. SOD activities showed that I. sibirica had better resistance to low temperature than Canna indica did. The combined measures of I. sibirica and aeration activated the activities of microorganisms, increased the abundance of the denitrification process genes along the water flow pathway and formed a clear nitrification-denitrification zone in the CW, thus promoted the nitrogen removal efficiency at low temperature. Therefore, this study confirmed the feasibility of the combined measures from a mechanistic perspective.

Hypolimnetic aeration optimization based on reservoir thermal stratification simulation

Hypolimnetic aeration is an effective management strategy for mitigating oxygen deficiency in dam reservoirs caused by thermal stratification (ThS). However, designing an optimal hypolimnetic aeration system based on dissolved oxygen (DO) concentration evaluation has yet to be considered in the literature. This study proposed an innovative optimization model utilizing the non-dominated sorting genetic algorithm-II (NSGA-II) for up to 4 aerators, considering two main objectives: (i) minimizing DO concentration deviation from the standard limit and (ii) minimizing aerator(s) operation energy. This optimization model was developed based on five primary decision variables: the location of the aerator(s) (length and depth), the aeration rate, and the operating time (start and end date). The NSGA-II optimization approach was coupled with the CE-QUAL-W2 simulation model for each identified period of ThS to simulate DO concentrations. To satisfy the conflicting objectives of the primary beneficiaries involving the Ministry of Energy and the Regional Water Organization, a two-step decision-making framework was introduced, utilizing the Nash bargaining (NB) and weighting method (WM) techniques. In order to show the practicality and effectiveness of the suggested framework in enhancing the DO concentration within a dam reservoir, the novel simulation optimization framework was implemented in a real-world case study of the Karkheh dam reservoir (KDR) in Iran. The findings revealed that applying an optimal hypolimnetic aeration system significantly improved the DO concentration, reaching at least twice the level without an aerator. However, the influence of aerators was not long-lasting, gradually diminishing when their operations ceased. Considering the importance of increasing DO concentration to mitigate the adverse effects of ThS, the four-aerators system was chosen as the optimal compromise design for the KDR.

Effect of regulating dissolved oxygen concentration in pulp with aerated gas on pyrite flotation

Moderate oxidation is beneficial to the flotation of sulfide ores, but the exact dissolved oxygen (DO) concentration suitable for flotation is still unclear. In this work, a self–made vacuum aeration flotation equipment was designed and assembled to accurately control the DO concentration in pulp by adjusting the relative proportion of O2/N2 during aeration, and the effect of DO concentration on the floatability and surface properties of pyrite as well as the interaction between pyrite and xanthate was studied. Microflotation experiments, contact angle, time–of–flight secondary ion mass spectrometry, X–ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, electrochemical and localized electrochemical impedance spectroscopy measurements were conducted in this investigation. The results showed that the flotation recovery of pyrite could be remarkably affected by DO concentration in pulp; it increased first and then decreased with the increase of DO concentration; an optimal DO concentration (DO = 3.3 mg/L) was helpful for pyrite flotation recovery; both the formation of dixanthogen and the avoidance of excessive iron oxide/hydroxide formed on pyrite surface were the key to improve the pyrite recovery. This research is expected to be applied in optimizing the flotation separation by DO-pH combined detection and regulation, strengthening the green flotation of sulfide ore with low collectors, and the design and manufacture of new closed and efficient sulfide ore flotation equipment.

Hump and mass-transfer characteristics of dissolved oxygen induced by gaseous cavitation in a space micropump

Fuel transportation in on-orbit refueling and circulation systems used in space involves dynamic transitions in the gas–liquid behaviors. Based on our verified innovative computational model of dynamic dissolution and evolution, the interesting “hump characteristics” of the dissolved oxygen concentration (DOC) were discussed, and the space-spatial evolution of gas–liquid mass transfer were compared. The hump phenomenon is related to the evolution of gas in the suction chamber. The processes undergone by the released gas, including the local evolution, evolution expansion, and global evolution, which were observed for the first time in rotating machinery owing to the pressure fluctuations caused by the impeller. Limited by the mass-transfer rate, the pressure increase in the impeller was significantly greater than the increase in the DOC, and thus there was no gas evolution inside the impeller. With an increase in the initial DOC, the near-zero mass-transfer rate band split into two and moved downstream of the blade, indicating a dynamic balance between the dissolution and evolution. Moreover, the flow separation and vortices near the clearance widened the band and decreased the dissolution rate. The current research provides an in-depth understanding of the dynamic changes in the gas–liquid behavior of on-orbit refueling systems.

New insights into arsenate removal during siderite oxidation by dissolved oxygen

Nowadays, arsenic (As) pollution in aquatic environments severely threatens the health of human beings. Although it has been known that siderite is capable of As adsorption and dissolved oxygen (DO) enhances the adsorption, effects of DO concentrations on As(V) adsorption onto siderite remain elusive. In this study, As(V) removal was investigated by synthesized siderite from aqueous solutions with different DO concentrations. Arsenic(V) adsorption kinetics were conformed to the pseudo-second-order model. As(V) adsorption onto siderite was enhanced in the presence of dissolved oxygen, but the excess DO concentration did not increase As(V) adsorption since Fe(III) oxides were coated onto the pristine siderite surface, preventing the mineral from further oxidation. With the increase in DO concentration, the rate of Fe(II) oxidation decreased, which was the kinetic-limited step during As(V) removal by siderite with the presence of DO. The theoretically generated Fe(III) was stoichiometrically proportional to the consumed oxygen. Microscopic characteristics by means of XRD, SEM, TEM, FTIR and XPS indicated that the adsorption was dominated by the chemical process via the As(V) complexation with siderite and co-precipitation with produced Fe(III) oxides. This study reveals the mechanisms of As(V) adsorption during siderite oxidation under different DO concentrations and emphasizes the importance of siderite oxidation in As(V) fate in aqueous systems.

Spatio-temporal dynamics of dissolved oxygen and its influencing factors in Lake Xiannv Jiangxi, China

为探究深水湖库溶解氧的时空分布规律及其主控因素，本文以南方亚热带大型深水湖库——江西省仙女湖为研究对象，基于2008—2021年仙女湖4个国控站点溶解氧的历史数据分析其年际变化的规律及原因；另于2016年水污染事件发生前（2014年5月-2015年4月）及水污染事件结束后（2018年1月-2018年12月）对仙女湖进行加密逐月监测，采用结构方程模型（SEM）分析仙女湖溶解氧的主要驱动因素。研究结果表明，2008—2021年仙女湖水体溶解氧浓度先下降后上升，变化范围为5.1~18.7 mg/L，季节均值为春季>冬季>秋季>夏季。水污染事件发生前高溶解氧区域多出现在舞龙湖湖心区及湖出口位置，水温、叶绿素a浓度和浊度是溶解氧浓度变化的主要驱动因素；水污染事件结束后高溶解氧区域多出现在钤阳湖及舞龙湖枝杈状湖湾位置，叶绿素a浓度及营养盐浓度成为溶解氧浓度变化的主要驱动因素；而pH与溶解氧主要是协同变化的关系。根据对仙女湖最深点（江口）的垂向监测结果，溶解氧的垂向差异为夏季>秋季>春季>冬季，夏、秋季在5 m以下出现低溶解氧（DO<5 mg/L）区域，且夏季观察到明显的温跃层及温跃层内溶解氧的极小值现象。总体来说，水污染事件使得仙女湖水体营养平衡被打破，营养盐浓度大幅上升导致的浮游植物数量增多是仙女湖水体表层溶解氧浓度升高的主要原因，而深水溶解氧浓度变化则与水温、水深密切相关。;To systematically explore the spatial-temporal distribution and main controlling factors of dissolved oxygen (DO) in deep lakes, we take Lake Xiannv, a large subtropical reservoir in south China, as the research object. By collecting the historical data of DO at four state-controlled points in Lake Xiannv from 2008 to 2021 to analyze its interannual changes. We also conducted intensive monthly monitoring of Lake Xiannv from May 2014 to April 2015 and from January 2018 to December 2018, which were before and after the water pollution accident in 2016. The factors influencing DO in Lake Xiannv were quantitatively analyzed by the structural equation model (SEM). Results showed that from 2008 to 2021, the DO concentration of Lake Xiannv first decreased and then increased, with a range of 5.1-18.7 mg/L, and the seasonal means were spring>winter>autumn>summer. Before the water pollution accident, the DO concentration in the central area and the outlet of Lake Wulong was higher and water temperature, chlorophyll-a and turbidity were the main driving factors for the change of DO. After the accident, the DO concentration in Lake Qianyang and the bays of Lake Wulong was higher and chlorophyll-a and water nutrition were the main driving factors for the change of DO. There are common changes between pH and DO. The vertical monitoring results of the deepest point (Jiangkou) showed that the vertical changes of water temperature and DO in Lake Xiannv were summer>autumn>spring>winter. We found that there were low DO (DO<5 mg/L) zones below 5 m of the lake in summer and autumn, thermocline and metalimnetic oxygen minimum (MOM) were observed in summer. In general, the water pollution accident broke the nutrient balance of Lake Xiannv, and the large increase in nutrient concentration led to an increase of phytoplankton, which was the main reason for the increase in DO concentration on the surface of Lake Xiannv, and the changing of deep-water DO concentration is closely related to water temperature and water depth.

Response of antibiotic resistance genes and microbial niches to dissolved oxygen in an oxygen-based membrane biofilm reactor during greywater treatment

Linear alkylbenzene sulfonates (LAS) in greywater (GW) will simulate antibiotic resistance genes (ARGs) production in the biofilm-based system. Our study emphasizes the dissolved oxygen (DO)-dependent ARGs accumulation and microbial niches succession in an oxygen-based membrane biofilm reactor (O2-MBfR) treating GW, as well as revealing the key roles of EPS. Changing DO concentrations led to significant differences in ARGs production, EPS secretion and microbial communities, as well as the organics and nitrogen removal efficiency. Increasing DO concentration from 0.2 to 0.4 mg/L led to improved organics (> 90%) and nitrogen removal, as well as less EPS (especially for proteins and carbohydrates) and ARGs accumulation (e.g., intI-1, korB and sul-2) in the biofilm; the high-DO-concentration accumulated microbial niches, including Flavobacteriaceae and Cyanobacteria that revealed by LEfSe analysis, contributed to both nitrogen reduction and organics biodegradation. While, the inefficient electron acceptor at low DO conditions (0.2 mg/L) reduced the organics and nitrogen removal efficiency, as well as the improved accumulation of EPS in biofilm; high EPS enabled the capture of residual LAS from the liquid phase, which stimulated the production of ARGs by the distinct microbial community compositions. These findings suggested the DO-based ARGs reduction regulation strategy in the O2-MBfR treating GW.

Study on aeration performance of different types of piano key weir

Abstract Aeration is the process of increasing the dissolved oxygen (DO) content of water, which is an important water quality parameter for the survival of aquatic life. In this process, large amounts of air bubbles develop; as a result, contact surface area increases, and hence the water-air-mass transfer accelerates. There are numerous methods for increasing DO concentration in water, including self-aeration, mechanical aeration, chemical aeration, and hydraulic structures. The hydraulic structures are an economical and efficient way of enhancing stream/river water aeration. Even though the water only comes into contact with the structure for a short while, it increases the amount of DO in a river system. In this study, an experimental investigation has been carried out to determine the aeration performance of different types of piano key weir (PKW). To this end, three different types (type-A, type-B, and type-C) of PKW laboratory-scaled models were tested. The results demonstrated that the type-A PKW created maximum oxygen transfer efficiency of the three PKW types. In addition, the results show that the aeration efficiency of all PKW models increases with drop height but decreases with increasing discharge over the weirs.

포기조에서 산기관의 설치위치가 용존산소에 미치는 영향 연구

Currently, countries worldwide are trying to reduce greenhouse gases, and Korea also attempts to decrease industrial greenhouse gas emissions. Aeration is the most energy-demanding process in a sewage treatment facility. Improvements in the aeration process''s efficiency will significantly contribute to national goals and climate change response. We conduct the aeration performance test to derive the optimum conditions for the diffuser arrangement and its installation depth in the aeration tank. The ball-type diffusers are installed at about 1/3 level (900 mm below the water surface) and 2/3 level (1,800 mm below the water level) of the water tank. We observed the change in aeration tank dissolved oxygen (DO) concentration with the blown air volume and time. The average increase in DO concentration ranged from 1.13 mg/L to 1.73 mg/L when aeration was conducted at the middle of the aeration tank. In contrast, the average increase in DO concentration ranged from 0.52 mg/L to 1.04 mg/L when aeration devices were installed at the bottom of the aeration tank. These results indicated that installing diffusers in the middle depth of the aeration tank was more effective for oxygen delivery and power requirement. The average air power required to drive the DO between 0.5 mg/L and 3.0 mg/L for an hour is found as 0.42 kWh and 0.38 kWh for the bottom and middle part of the tank, respectively. The results show 9.5% energy saving for aeration in the middle. The results reveal that the lower the depth of the aeration diffuser installation, the better the oxygen delivery. Therefore, it will be possible to construct an aeration system with better energy efficiency when aeration diffusers are installed at low-water-depths.

Effects of dissolved oxygen on the sludge dewaterability and extracellular polymeric substances distribution by bioleaching

Bioleaching is a biological conditioning technology for sludge, which not only improves sludge dewatering performance but also removes heavy metals from sludge. As the bioleaching process is a comprehensive biological and chemical process, it is necessary to explore the effects of dissolved oxygen (DO) concentrations on bioleaching efficiency. Three bioleaching experiments with different DO concentrations (T1: 0.8–3.1 mg/L, T2: 3.1–5.5 mg/L, T3: 5.5–7.5 mg/L) were conducted for five days. The sludge dewatering efficiency was evaluated using capillary suction time (CST) and specific resistance to filtration (SRF). The relationship between sludge dewaterability and extracellular polymeric substance (EPS) fraction distribution was investigated. In the treatment with the highest DO concentration, the minimum values of SRF and CST were 4.31 × 1011 m/kg and 13.5 s, which occurred earlier than the treatment with the lower DO concentrations by approximately 24–48 h. A significant decrease (83.4–93.2%) in tightly bound EPS (TB-EPS) protein (PN) was observed in all treatments, while a positive correlation (r = 0.924, P < 0.01) was observed between SRF and PN content in TB-EPS. A relatively higher abundance of Acidithiobacillus was found with the increase in DO concentration. Additionally, other genera including Metallibacterium, Alicyclobacillus, Acidibacter, Acidocella, and Luteococcus also played important roles in EPS biodegradation. These results revealed that increasing the DO concentration could improve sludge dewatering performance and heavy metal removal by enhancing bioleaching microbial activity, the degradation of PN in TB-EPS, and sludge floc fragmentation, but only if sufficient energy sources were provided.

Enhanced nitrogen removal from high-strength ammonium wastewater by improving heterotrophic nitrification-aerobic denitrification process: Insight into the influence of dissolved oxygen in the outer layer of the biofilm

This work aims to optimize the process of heterotrophic nitrification-aerobic denitrification (HN-AD) in the membrane-aerated biofilm reactor (MABR) by way of increasing the dissolved oxygen (DO) concentration in the outer layer biofilm to treat high-strength ammonium-nitrogen (NH4+-N) wastewater. The results show that the removal efficiencies of NH4+-N, total nitrogen (TN) and chemical oxygen demand (COD) increased by 42.4%, 65.7%, and 15.2%, respectively, in MABR-1 with high-DO concentrations than in MABR-2 with low-DO concentrations in the outer layer biofilm. High-DO concentrations in the outer layer biofilm increased the thickness of the aerobic layer to encourage HN-AD bacteria enrichment, which paved the way for nitrogen removal enhancement in MABR-1. Moreover, based on the analysis of functional gene expressions predicted by PICRUSt2, the relative abundances of seven key genes (hao, nirK, napA, napB, norB, norC and nosZ) relating to HN-AD bacteria in the MABR-1 significantly increased, indicating that DO increasing in the outer layer biofilm remarkably promoted the occurrence of HN-AD process. From the viewpoint of economic efficiency, the advantage of the novel strategy of increasing DO concentrations in the outer layer biofilm is that this optimized alternative for the MABR provides a superior nitrogen removal process in the high-strength NH4+-N wastewater treatment.

Biological Reduction of Organic Matter in Buji River Sediment (Shenzhen, China) with Artificial Oxygenation

In this work, artificial oxygenation treatment (pure oxygen aeration or oxygen enriched water injection) combined with the introduction of exogenous microorganisms was employed to purify urban river sediment for the first time. Results showed that the developed in situ remediation strategy could increase the dissolved oxygen (DO) concentration and oxidation-reduction potential (ORP) value of the sediments. Benefiting from the increase of DO concentration, the bacterial diversity was enhanced. The highest removal efficiencies of organic matter were 18.4% and 22.3% through pure oxygen aeration and oxygen enriched water injection, respectively. More importantly, overlying water quality was not affected. By comparison, oxygen enriched water injection treatment could achieve better performance on sediment purification. Introducing exogenous microorganisms further reduced the organic matter content of the sediment. In short, the current work not only proposed a promising strategy for controlling urban river sediment pollution, but also provided novel insight for the understanding of river sediment containing highly concentrated organic matter.

Mutual Interaction between Temperature and DO Set Point on AOB and NOB Activity during Shortcut Nitrification in a Sequencing Batch Reactor in Terms of Energy Consumption Optimization

Recently, many wastewater treatment plants (WWTPs) have had to deal with serious problems related to the restrictive requirements regarding the effluent quality, as well as significant energy consumption associated with it. In this situation, mainstream deammonification and/or shortened nitrification-denitrification via nitrite (so-called “nitrite shunt”) is a new promising strategy. This study shows the mechanisms and operating conditions (e.g., dissolved oxygen (DO) concentration, temp.), leading to the complete domination of ammonium oxidizing bacteria (AOB) over nitrite oxidizing bacteria (NOB) under aerobic conditions. Its successful application as shortcut nitrification in the sequencing batch reactor (SBR) technology will represent a paradigm shift for the wastewater industry, offering the opportunity for efficient wastewater treatment, energy-neutral or even energy-positive facilities, and substantial reductions in treatment costs. In this study, under low and moderate temperatures (10–16 °C), averaged DO concentrations (0.7 mg O2/L) were preferable to ensure beneficial AOB activity over NOB, by maintaining reasonable energy consumption. Elevated temperatures (~30 °C), as well as increased DO concentration, were recognized as beneficial for the NOB activity stimulation, thus under such conditions, the DO limitation seems to be a more prospective approach.

A synergistic effect of dissolved oxygen, $$HCO_3^-$$, and Cl− on the electrochemical corrosion behavior of X70 pipeline steel in the oilfield soil environment

The pipeline corrosion phenomenon in the Liaohe oilfield has become severe in recent years, and X70 steel has been extensively employed as a high-strength pipeline material in this oilfield. Therefore, in this study, the electrochemical corrosion of X70 steel in the simulated Liaohe oilfield soil solution was investigated under the combined action of dissolved oxygen (DO), $$HCO_3^-$$ , and Cl−. The corrosion behavior of X70 steel was examined by both the orthogonal test and the fitting analysis. It was found that DO, $$HCO_3^-$$ , and Cl− had profound influences on the corrosion behavior of X70 steel. When concentrations of $$HCO_3^-$$ , and Cl− were stable in the solution, both current corrosion density and corrosion rate gradually increased with the increasing DO concentration. When concentrations of DO and Cl− were constant, the current corrosion density also increased with the increasing $$HCO_3^-$$ concentration. When concentrations of DO and $$HCO_3^-$$ were constant, the current corrosion density decreased significantly with the decreasing Cl− concentration. In the soil solution, the corrosive effect of Cl− ions were found to be the least among all three factors, whereas $$HCO_3^-$$ ions had the greatest influence on the corrosion behavior of X70 steel.

Effects of dissolved oxygen on partial slip fretting corrosion of Alloy 690TT in high temperature pure water

Partial slip fretting corrosion of Alloy 690TT comes up in the steam generator of a nuclear power plant, in which the damage mechanisms are transformed as dissolved oxygen (DO) varies. In this work, the coupling between the action of oxide particles sticking into the surface and the electrochemical corrosion caused severe pitting-like damage, which was enhanced by an increase in DO concentration increasing the wear volume. The initiation of fatigue cracking was controlled by the slip dissolution along with the competition between the film rupture rate and the repassivation rate as DO changes.

Effect of Dissolved Oxygen Concentration on the Microbiologically Influenced Corrosion of Q235 Carbon Steel by Halophilic Archaeon Natronorubrum tibetense.

The influence of dissolved oxygen concentration (DOC) on the microbiologically influenced corrosion (MIC) of Q235 carbon steel in the culture medium of halophilic archaeon Natronorubrum tibetense was investigated. The increase of DOC from 0.0 to 3.0 ppm was found to strengthen the oxygen concentration cell by promoting cathodic reaction. Meanwhile, the increased DOC also promoted archaeal cell growth, which could consume more metallic iron as energy source and aggravated the localized corrosion. When the DOC further increased to 5.0 ppm, the uniform corrosion was dominant as the biofilms became uniformly presented on the steel surface. Combined with the stronger inhibition effect of oxygen diffusion by the increased biofilm coverage, the MIC of carbon steel in the 5.0 ppm medium was weaker than that in the 3.0 ppm medium. From weight loss and electrochemical tests, the results all demonstrated that the carbon steel in the 3.0 ppm medium had the largest corrosion rate.

Effect of dissolved oxygen on efficiency of TOC reduction by UV at 185 nm in an ultrapure water production system

The effect of dissolved oxygen (DO) on the degradation of methanol by ultraviolet (UV) light at 185 nm (UV-185) was examined in this study. The experiments were conducted using a bench-scale experimental apparatus that was operated under continuous conditions. In the control tests with various DO conditions, it was confirmed that UV irradiation of water without methanol produced approximately 54 μg/L of H2O2 and removed 15%–90% of the DO. The production of H2O2 was affected by the mixing conditions within the UV reactor and the dose of UV. The degradation efficiency of methanol by UV-185 irradiation improved linearly with increasing DO concentration, with more than 90% DO consumption. The maximum total organic carbon (TOC) removal rate was observed at 100 μg/L DO and 433 mW·sec/cm2, the highest DO and dosage conditions in this study. The production of H2O2 was also affected by DO concentration in the feed water, especially at the high UV dosage, in which lower H2O2 production was observed at higher DO.

Potential of using nonwoven polyester fabric (NWPF) as a packing media in multistage passively aerated biological filter for municipal wastewater treatment

AbstractThe performance of a multistage passively aerated biological filter (PABF) packed with Nonwoven polyester fabric (NWPF) for municipal wastewater treatment was investigated under different operating conditions. The system was operated at different hydraulic retention times (HRTs) of 2.3, 1.72 and 1.38 h and corresponding to organic loading rates (OLRs) of 1.77, 2.15 and 2.9 kg BOD/m3. d. Increasing HRT and decreasing OLR, increased dissolved oxygen (DO) and consequently increased the removal rate of organic matters (87%), suspended solids (95.8%) and ammonia (88%). Profile results from different compartments showed that the major part of organic and suspended matters was removed in the upper layers of the system, whereas most of the suspended solids were trapped, while the nitrification process took place in the lower part of the PABF system because of the increase in DO concentrations. The results proved the advantage of using NWPF. It has pleated and rough surface which retain more biomass compared with plain surface. Excess biomass produced from PABF was negligible compared to conventional treatment systems.

Enhanced production of novel halostable recombinant endoglucanase derived from the metagenomic library using fed-batch fermentation

Abstract A novel halostable endoglucanase Cel5R obtained from soil metagenomic library was cloned and expressed in Escherichia coli BL21 (DE3). In this study, we investigated the effect of dissolved oxygen concentration (DOC) on plasmid stability and effect of complex nitrogen source on the production of protein. With the increase in DOC from 30% to 50%, the production of protein also increased from 500 mg/l to 3 g/l. Besides, the addition of yeast extract and tryptone increased the production of endoglucanase up to 5 g/l. Overall, the production of endoglucanase showed an increase of 40-folds from shake flask to fed-batch fermentation. Biochemical characterization of the purified enzyme revealed that the enzyme retained its 100% catalytic activity after incubation with different concentrations of salts (NaCl, KCl, and LiCl) for 30 days, confirming it to be a halostable enzyme. It is the highest reported production of a recombinant endoglucanase, further increasing its potential for industrial applications.