Impact Of Dissolved Oxygen Concentration Research Articles

Sequential bio-treatment of ammonia-rich wastewater from Chinese medicine residue utilization: Regulation of dissolved oxygen

To effectively treat actual ammonia-rich CMR from resource utilization wastewater, we optimized an anaerobic-microaerobic two-stage expanded granular sludge bed (EGSB) and moving bed sequencing batch reactor (MBSBR) combined system. By controlling dissolved oxygen (DO) levels, impressive removal efficiencies were achieved. Microaeration, contrasting with anaerobic conditions, bolstered dehydrogenase activity and electron transfer, thereby augmenting the functional microorganism community. The heightened relative abundance of Synergistetes and Proteobacteria facilitated hydrolytic acidification, fostering nitrogen and phosphorus removal. Furthermore, we examined the impact of DO concentration in MBSBR on pollutant removal and microbial metabolic activity, pinpointing 2.5 mg/L as the optimal DO concentration for superior removal performance and energy conservation.

Organic electrochemical transistors for monitoring dissolved oxygen in aqueous electrolytes of zinc ion batteries

Dissolved oxygen (DO) in the electrolyte of aqueous zinc ion batteries (AZIBs) can cause irreversible side reactions in zinc metal anode. Therefore, the accurate detection of the DO concentration in the aqueous electrolyte is crucial for the performance promotion and mechanistic studies of AZIBs. Herein, organic electrochemical transistor (OECT) based DO sensors are developed by utilizing a carbon fiber (CF) derived CF/platinum/Nafion/polydimethylsiloxane composite as the gate electrode and amine-doped poly(3,4-ethylenedioxythiophene): polystyrene sulfonate as the channel semiconductor. Operating at a gate-source voltage of −0.1 V and a drain-source voltage of −0.025 V, the OECT-DO sensor demonstrates a high sensitivity (141 mV decade−1), a low detection limit (0.0011 mg L−1), a wide linear range (0.027–8.7 mg L−1), and good stability, which are attributed to the transconductance capability of OECT. The exceptional performance of the OECT-DO sensor enables the accurate monitoring of DO content in aqueous zinc sulfate electrolyte, which provides an opportunity to gain an insight of the impact of DO concentration on the zinc metal electrode. This study not only provides a cost-effective and efficient solution for detecting DO concentration in aqueous electrolytes, but also explores the potential applications of OECT sensors in the energy storage devices.

Dissolved oxygen benefits N-decanoyl-homoserine lactone regulated biological nitrogen removal system to resist acute ZnO nanoparticle exposure

The beneficial effects of N-decanoyl-homoserine lactone (C10-HSL), one of the typical N-acyl-homoserine lactones on biological nitrogen removal (BNR) system to resist the acute exposure of zinc oxide nanoparticles (ZnO NPs) has attracted extensive attentions. Nevertheless, the potential impact of dissolved oxygen (DO) concentration on the regulatory capacity of C10-HSL in the BNR system has yet to be investigated. This study conducted a systematic investigation of the impact of DO concentration on the C10-HSL-regulated BNR system against short-term ZnO NP exposure. Based on the findings, sufficient DO played a crucial role to improve the BNR system's resistance capacity to ZnO NPs. Under the micro-aerobic condition (0.5 mg/L DO), the BNR system was more sensitive to ZnO NPs. The ZnO NPs induced increased intracellular reactive oxygen species (ROS) accumulation, reduced antioxidant enzyme activities, and decreased specific ammonia oxidation rates in the BNR system. Furthermore, the exogenous C10-HSL had a positive effect on the BNR system's resistance to ZnO NP-induced stress, primarily by decreasing ZnO NPs-induced ROS generation and improving ammonia monooxygenase activities, especially under low DO concentrations. The findings contributed to the theoretical foundation for regulation strategy development of wastewater treatment plants under NP shock threat.

Improvement of Final Settling Tanks Performance by Using Chemical Additions

Biological treatment in wastewater treatment plants WWTPs consists of two main tanks, aeration tank and final settling tank. Aeration process using in return activated sludge system is very costly and it is required to operate WWTPs with low dissolved oxygen (DO) concentration in aeration process without risking poor effluent quality. To apply this study, a plant model for the addition of chemicals must be made with the necessary calibration of this model. Laboratory experiments were started between November 2017 and June 2018. This paper will discuss the impact of DO concentration on sludge properties by using a pilot plant model WWTP and find the optimum doses of Hydrogen peroxide H2O2 concentration with using low DO concentration to achieve good sedimentation. In this study the DO set-point was changed every 3 weeks between 0.5 mg/l and 4.5 mg/l for a few months. Experiments were carried out to The optimal ratio and dosage of H2O2 /Fe+2 was 5 as 30/6 mg/l. BOD, COD, TSS and VSS removal efficiency by using H2O2 /Fe+2 were 91%, 89% 90% & 89%, respectively with DO = 1.5 mg/l at an increased rates were 21.3%, 25.4%, 20% & 12.7%, respectively. Results of paper proves that the addition of optimum H2O2 will save 2 mg/l of DO concentration and providing a high cost of using electricity and mechanical equipment compared to the non-use of H2O2.

Oxygen Half-Saturation Constants for Pharmaceuticals in Activated Sludge and Microbial Community Activity under Varied Oxygen Levels

Aeration accounts for the largest energy demand in conventional activated sludge wastewater treatment. Emerging aeration control strategies for energy conservation have significantly reduced operational bulk liquid dissolved oxygen (DO) from above 2 mg/L to at or below 0.5 mg/L. As we move toward low DO treatment processes, there is a need to understand how low DO impacts the kinetics of micropollutant biotransformation. The objective of this study was to characterize the impact of DO concentration on pharmaceutical biotransformation rates via two approaches: (1) Determine oxygen half saturation constants that describe the community-wide impact of DO on biotransformation rates. (2) Evaluate shifts in the microbial community 16S rRNA pool due to DO concentration. Batch experiments were performed at several DO concentrations using biomass from a full-scale wastewater treatment plant. Results reveal that substantial reductions in bulk liquid DO concentrations to 0.5 mg-O2/L are possible without compromising pharmaceutical biotransformation rates. Sequencing of cDNA generated from community rRNA revealed that diverse, low abundance community members may play important roles in pharmaceutical transformation. The results of this work advance our ability to predict and model the impact of DO on pharmaceutical biotransformations during wastewater treatment and identify taxonomic groups associated with those biotransformations.

The link of feast-phase dissolved oxygen (DO) with substrate competition and microbial selection in PHA production

Polyhydroxyalkanoates (PHAs) are biobased and biodegradable polyesters with the potential to replace conventional plastics. Aeration requires large amounts of energy in PHA production by mixed microbial cultures (MMCs), particularly during the feast phase due to substrate uptake. The objective of this study was to investigate the impact of DO concentrations on microbial selection, substrate competition and PHA production performance by MMCs. This represents the first study investigating DO impact on PHA production while feeding the multiple volatile fatty acids (VFAs) typically encountered in real fermented feedstocks, as well as the substrate preferences at different DO levels. Efficient microbial cultures were enriched under both high (3.47 ± 1.12 mg/L) and low (0.86 ± 0.50 mg/L) DO conditions in the feast phase containing mostly the same populations but with different relative abundance. The most abundant microorganisms in the two MMCs were Plasticicumulans, Zoogloea, Paracoccus, and Flavobacterium. Butyrate and valerate were found to be the preferred substrates as compared to acetate and propionate regardless of DO concentrations. In the accumulation step, the PHA storage capacity and yield were less affected by the change of DO levels when applying the culture selected under low DO in the feast phase (PHA storage capacity >60% and yield > 0.9 Cmol PHA/Cmol VFA). A high DO level is required for maximal PHA accumulation rates with the four VFAs (acetate, propionate, butyrate and valerate) present, due to the lower specific uptake rates of acetate and propionate under low DO conditions. However, butyrate and valerate specific uptake rates were less impacted by DO levels and hence low DO for PHA accumulation may be effective when feed is composed of these substrates only.

Formation of nitrous oxide in a gradient of oxygenation and nitrogen loading rate during denitrification of nitrite and nitrate

Nitrous oxide (N2O) emission has been observed during denitrification of nitrate via nitrite as intermediate. With a laboratory-scale reactor (2.4L), the N2O emission was characterized under a gradient of DO concentration from 0 to 0.7mg/L, different ratio of nitrite versus nitrate and different nitrite feed mode. The N2O emission was influenced by the level of dissolved oxygen (DO) and nitrite accumulation. The higher DO level and the higher ratio of nitrite versus nitrate resulted in the higher N2O emission. Using nitrite as sole electron acceptor at the same loading rate, the sequence of N2O emission with three different feed modes was: pulse>step-wise>continuous feed. The N2O emitted in pulse feed reactors was 3.1–4.2 and 8.2–11.7 folds of that in the step-wise feed and continuous feed reactors, respectively. With continuous feed mode, the impact of DO concentration on the mass of N2O emitted was limited while the higher N2O emission occurred at the higher nitrite loading rate.

Evaluation of deammonification process performance at different aeration strategies

In a deammonification process applied in the moving bed biofilm reactor (MBBR) oxygen is a crucial parameter for the process performance and efficiency. The objective of this study was to investigate different aeration strategies, characterised by the ratio between non-aerated and aerated phase times (R) and dissolved oxygen concentrations (DO). The series of batch tests were conducted with variable DO concentrations (2, 3, 4 mg L(-1)) and R values (0-continuous aeration; 1/3, 1, 3-intermittent aeration) but with the same initial ammonium concentration, volume of the moving bed and temperature. It was found that the impact of DO on deammonification was dependent on the R value. At R=0 and R=1/3, an increase of DO caused a significant increase in nitrogen removal rate, whereas for R=1 and R=3 similar rates of the process were observed irrespectively of the DO. The highest nitrogen removal rate of 3.33 g N m(-2) d(-1) (efficiency equal to 69.5%) was obtained at R=1/3 and DO=4 mg L(-1). Significantly lower nitrogen removal rates (1.17-1.58 g N m(-2) d(-1)) were observed at R=1 and R=3 for each examined DO. It was a consequence reduced aerated phase duration times and lesser amounts of residual nitrite in non-aerated phases as compared to R=1/3.