Influent Dissolved Oxygen Concentration Research Articles

Denitrification performance of sulfur-based autotrophic denitrification and biomass‑sulfur-based mixotrophic denitrification in solid-phase denitrifying reactors using novel composite filters

Both the elemental sulfur-based autotrophic denitrification (ESAD) and the biomass‑sulfur-based mixotrophic (simultaneous autotrophic and heterotrophic) denitrification processes (BSMD) are efficient methods for removing nitrate from wastewater. However, a comparative analysis of the denitrification capacity of the BSMD and ESAD in the packed bed reactors is still lacking. In this paper, corncob powder was selected as the biomass source to prepare biomass‑sulfur-based composite filter (BSCF) for the BSMD process. The denitrification performances of the three identical lab-scale bioreactors packed with varying elemental sulfur-based composite filters (ESCFs) were compared under varying loading conditions, and the optimal ESCF of the ESAD system was 2:1 by weight ratio of sulfur powder to shell powder. In pilot-scale experiments, the results showed that BSCF could decrease the sulfate productivity and gave better denitrification performance than the ESCF with the optimal nitrate removal rate (NRR) of 504 ± 12.3 mg NO3−-N·L−1·d−1. In addition, the two-stage flushing strategy (for the removal of aged sludge) can effectively improve the denitrification capacity, while the denitrification will be inhibited when the influent dissolved oxygen concentration was higher than 4.5 mg L−1. Moreover, the heterotrophs and autotrophs were abundant in the reactors. Over time, the abundance of autotrophs increased while that of heterotrophs decreased. Overall, BSCF could be a promising and economic technology to improve the effluent quality.

Effects of dissolved oxygen on the start-up of manganese oxides filter for catalytic oxidative removal of manganese from groundwater

The structure and reactivity of manganese oxides (MnOx) are sensitive to the solution environment. To explore the effects of dissolved oxygen (DO) on the formation of MnOx in manganese removal filters, two identical filters were initialized by dosing potassium permanganate and manganese chloride with different influent DO concentrations. During the start-up process, the structural characteristics of the MnOx filter media in two filters were probed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer-Emmett-Teller (BET) specific surface area, and X-ray photoelectron spectroscopy (XPS). Results of XRD analyses revealed that DO had great influence on the crystal structure of the samples. The crystallization of the MnOx samples in filter D1 (DO = 6.5 ± 0.5 mg/L) gradually increased with running time, while the MnOx samples in filter D2 (DO = 1.5 ± 0.5 mg/L) remained the same. The morphologies of the MnOx changed from aggregated particles to a wrinkled shape in both filters. Results of compositional analyses showed that the high DO condition was beneficial for the insertion of Ca, as well as the ion exchange of Ca and K, in the interlayer region of the MnOx. The MnOx that formed at high DO conditions possessed greater manganese removal activity than that formed at low DO conditions; this was related with the abundant lattice oxygen. Vacancy defects played an important role in the removal of manganese at low DO conditions. Through this study it is suggested that aqueous DO is a critical environmental factor controlling MnOx structure and reactivity in the environment. This study provides significant insights into future applications of the manganese removal techniques.

Heterotrophic denitrification of aquaculture effluent using fluidized sand biofilters

The ability to consistently and cost-effectively reduce nitrate-nitrogen loads in effluent from recirculating aquaculture systems would enhance the industry's environmental stewardship and allow improved facility proximity to large markets in sensitive watersheds. Heterotrophic denitrification technologies specifically employing organic carbon found in aquaculture system waste offer a unique synergy for treatment of land-based, closed-containment production outflows. For space-efficient fluidized sand biofilters to be used as such denitrification reactors, system parameters (e.g., influent dissolved oxygen and carbon to nitrogen ratios, C:N) must be evaluated to most effectively use an endogenous carbon source. The objectives of this work were to quantify nitrate removal under a range of C:Ns and to explore the biofilter bacterial community using three replicated fluidized sand biofilters (height 3.9m, diameter 0.31m; fluidized sand volume plus biofilm volume of 0.206m3) operated at a hydraulic retention time of 15min and a hydraulic loading rate of 188L/minm2 at The Conservation Fund Freshwater Institute in Shepherdstown, West Virginia, USA. Nitrate reduction was consistently observed during the biofilter study period (26.9±0.9% removal efficiency; 402±14g NO3-N/(m3biofilterd)) although nitrite-N and total ammonium nitrogen concentrations slightly increased (11 and 13% increases, respectively). Nitrate removal efficiency was correlated with carbonaceous oxygen demand to nitrate ratios (R2>0.70). Nitrate removal rates during the study period were moderately negatively correlated with influent dissolved oxygen concentration indicating it may be possible the biofilter hydraulic retention time was too short to provide optimized nitrate removal. It is reasonable to assume that the efficiency of nitrate removal across the fluidized sand biofilters could be substantially increased, as long as organic carbon was not limiting, by increasing biofilter bed depths (to 6–10m), and thus hydraulic retention time. These findings provide a low-cost yet effective technology to remove nitrate-nitrogen from effluent waters of land-based closed-containment aquaculture systems.

High-rate nitrogen removal and microbial community of an up-flow anammox reactor with ceramics as biomass carrier

Nitrogen removal performance and responsible microbial community of anammox process at low temperatures, and long term effect of dissolved oxygen (DO) on the performance of anammox process were investigated in a biofilm reactor, which was operated at 33±1°C (159d) and 20±2°C (162d) with an influent DO concentration of 0.7–1.5mgL−1. Nitrogen removal recovered to 70% after 2wk with the temperature drastically decreasing from 33±1°C to 20±2°C. At 20±2°C, the average effluent (NH4+–N+NO2−–N) concentration was 0.08±0.08mgL−1 at a hydraulic retention time of 1.5h. A total nitrogen removal efficiency of the reactor of 1.0gNL−1d−1 was obtained for up to one month while the nitrogen loading rate was 1.16gNL−1d−1. Results of T-RFLP and 16S rRNA phylogenic analysis revealed that Candidatus Jettenia asiatica, as confirmed to adapt to low temperature, was considered to be responsible for the stable and high nitrogen removal performance.

Nano-FeS Inhibits UO2 Reoxidation under Varied Oxic Conditions

Bioreductive in situ treatment of U-contaminated groundwater can convert soluble U(VI) species to immobile reduced U(IV) solid phases such as UO2(s) to contain U movement. Once active bioremediation is halted, UO2 may be subsequently reoxidized if oxidants such as oxygen enter the reducing zone. However, iron sulfide minerals that form during bioreduction may serve as electron sources or oxygen scavengers and inhibit UO2 reoxidation upon oxygen intrusion. In this study, flow-through reactor experiments examined the abiotic kinetics of UO2 oxidative dissolution in the presence of oxygen and nanoparticulate FeS as a function of pH, dissolved oxygen (DO) concentration, and FeS content. The UO2 dissolution rates in the presence of FeS were over 1 order of magnitude lower than those in the absence of FeS under otherwise comparable oxic conditions. FeS effectively scavenged DO and preferentially reacted with oxygen, contributing to a largely unreacted UO2 solid phase during an "inhibition period" as determined by X-ray absorption spectroscopy (XAS). The removal of DO by FeS was significant but incomplete during the inhibition period, resulting in surface-oxidation-limited dissolution and greater UO2 dissolution rate with increasing influent DO concentration and decreasing FeS content. Although the rate was independent of solution pH in the range of 6.1-8.1, the length of the inhibition period was shortened by substantial FeS dissolution at slightly acidic pH. The reducing capacity of FeS was greatest at basic pH where surface-mediated FeS oxidation dominated.

Tolerance Level of Dissolved Oxygen to Feed into Anaerobic Ammonium Oxidation (anammox) Reactor

In order to assess the stability of nitrogen removal systems utilizing anaerobic ammonium oxidation (anammox), it is necessary to study effects of influent dissolved oxygen (DO) on anammox activity since effluent from nitritation process feed to anammox process. In this study, the effects of influent DO on anammox bacteria entrapped in gel carriers were investigated using continuous feeding tests. The tests were performed in duplicate to confirm the reproducibility and anammox activities were evaluated under different DO concentration of 0 from 5 mg/L in influent. These results suggested that the DO concentration in influent to anammox reactor must be less than 2.5 mg/L. In addition, it was shown that the effect of influent DO on the anammox reaction is reversible because fallen anammox activity by influent DO of 5 mg/L recovered when the influent DO concentration was decreased to less than 1 mg/L.

Stable Partial Nitrification in an Up-Flow Fixed-Bed Bioreactor Under an Oxygen-Limiting Environment

Abstract Stable partial nitrification followed by a denitrification or anammox process is a cost-effective alternative to conventional biological nitrogen removal processes, especially for wastewaters having a low carbon-to nitrogen (C/N) ratio. This article addresses partial nitrification in an up-flow fixed-film bioreactor operated for more than 265 days using low C/N synthetic wastewater. The study was carried out in the absence of external aeration, for further cutting down the cost of treatment. By controlling influent dissolved oxygen (DO) at 1 mg/L, stable partial nitrification with more than 85% efficiency was achieved (influent NH3N: 102.6 ± 4.6 mg N/L). Maximum ammonium removal rate of 210.5 ± 6.7 mg N/L/day was obtained at a hydraulic retention time (HRT) of 18 h. Oxygen uptake at influent DO concentration of 1 mg/L was practically negligible compared to the amount of ammonia oxidized to nitrite. Partial nitrification was taking place devoid of oxygen consumption. A possible mechanism of partia...

Chemisorption of oxygen onto activated carbon can enhance the stability of biological perchlorate reduction in fixed bed biofilm reactors

Fixed bed biofilm reactors with granular activated carbon (GAC) or glass beads as support media were used to evaluate the influence of short-term (12 h) and long-term (23 days) increases of influent dissolved oxygen (DO) concentrations on biological perchlorate removal. The goal was to evaluate the extent by which chemisorption of oxygen to GAC can enhance the stability of biological perchlorate reduction. Baseline influent concentrations were 50 μg/L of perchlorate, 2 mg/L of acetate as C, and 1 mg/L of DO. Perchlorate removal in the glass bead reactor seized immediately after increasing influent DO concentrations from 1 to 4 mg/L since glass beads have no sorptive capacity. In the biologically active carbon (BAC) reactor, chemisorption of oxygen to GAC removed a substantial fraction of the influent DO, and perchlorate removal was maintained during short-term increases of influent DO levels up to 8 mg/L. During long-term exposure to influent DO concentrations of 8.5 mg/L, effluent perchlorate and DO concentrations increased slowly. Subsequent exposure of the BAC reactor bed to low DO concentrations partially regenerated the capacity for oxygen chemisorption. Microbial analyses indicated similar microbial communities in both reactors, which confirmed that the differences in reactor performance during dynamic loading conditions could be attributed to the sorptive properties of GAC. Using a sorptive biofilm support medium can enhance biological perchlorate removal under dynamic loading conditions.

Effect of backwashing on perchlorate removal in fixed bed biofilm reactors

The influence of backwashing on biological perchlorate reduction was evaluated in two laboratory scale fixed bed biofilm reactors using 1- or 3-mm glass beads as support media. Influent perchlorate concentrations were 50 μg/L and acetate was added as the electron donor at a concentration of 2 mg C/L. Perchlorate removal was evaluated at various influent dissolved oxygen (DO) concentrations. Complete perchlorate removal was achieved with an influent DO concentration of 1 mg/L resulting in bulk phase DO concentrations below the detection limit of 0.01 mg/L. The influence of increasing influent DO concentrations for 12 h periods was evaluated before and after individual backwash events. Partial perchlorate removal was achieved with an influent DO concentration of 3.5 mg/L before a strong backwash (bulk phase DO concentrations of approximately 0.2 mg/L), while no perchlorate removal was observed after the strong backwash at the same influent DO level (bulk phase DO concentrations of approximately 0.8 mg/L). The immediate effect of backwashing depended on influent DO concentrations. With influent DO concentrations of 1 mg/L, strong backwashing resulted in a brief (<12 h) increase of effluent perchlorate concentrations up to 20 μg/L; more pronounced effects were observed with influent DO concentrations of 3 mg/L. Daily weak backwashing had a small and, over time, decreasing negative influence on perchlorate reduction, while daily strong backwashing ultimately resulted in the breakdown of perchlorate removal with influent DO concentrations of 3 mg/L.

Monitoring the impact of dissolved oxygen and nitrite on anoxic biofilm in continuous denitrification process.

An anoxic biofilm involved in continuous denitrification process was monitored to investigate the effect of different concentrations of influent dissolved oxygen (DO) or nitrite on the biofilm. Microelectrode measurements evidenced nitrate removal activity of biofilm. When different concentrations of DO were applied to the reactor, generally decreased concentrations of DO were observed as bed depth increased from the bottom of the reactor. Greatest decrease of the DO was observed in the lower 20% of the bed depth. Nitrate removal efficiency was inversely proportional to influent DO concentrations (8.3-11.9 DO mg L(-1)) or nitrite loading rates (0-5.5 N-NO2- kg m(-3) day(-1)) employed in this study. Nitrite loading rates to achieve more than 90% of nitrate removal efficiency were 1.46 N-NO2- kg m(-3) day(-1) or less at pH 7.5 and 0.34 N-NO2- kg m(-3) day(-1) or less at pH 6.8. Nitrate removal efficiency was 63% or more within the lower 20% of the bed depth at the nitrite loading rates that allowed more than 90% of nitrate removal efficiency of the reactor. The results of this study provide first quantitative data that nitrate removal performance of an anoxic biofilm is inhibited by DO or nitrite, reported to be a limiting factor in the suspended biological denitrification process.

The sensitivity of fixed-bed biological perchlorate removal to changes in operating conditions and water quality characteristics

Flow rate, electron donor addition, and biomass control were evaluated in order to optimize perchlorate (ClO 4 −) removal from drinking water using biologically active carbon (BAC) filtration. Influent dissolved oxygen (DO) was lowered from ambient conditions to approximately 2.5 mg/L for all experiments using a nitrogen sparge. When influent nitrate concentration was 0–2.0 mg/L, 1.6–2.8 mg/L as carbon of acetate or ethanol was required to achieve and sustain the complete removal of 50 μg/L perchlorate in a BAC filter. Most or all of the exogenous acetate and ethanol was removed during biofiltration. When a 72-h electron donor feed failure was simulated, a maximum perchlorate breakthrough of 18 μg/L was observed and, once electron donor was reapplied, 9 days were required to reestablish complete perchlorate removal. During a 24-h electron donor feed failure simulation, the maximum effluent perchlorate concentration detected was 6.7 μg/L. Within 24 h of reactivating the electron donor, the filter regained its capacity to consistently remove 50 μg/L perchlorate to below detection. Although biomass growth diminished the filter's ability to consistently remove perchlorate, a cleaning procedure immediately restored stable, complete perchlorate removal. This cleaning procedure was required approximately every 50 days (4800 bed volumes) when influent DO concentration was 2.5 mg/L. Empty-bed contact time (EBCT) experiments showed that 80% perchlorate removal was achieved using a 5-min EBCT, and complete perchlorate removal was observed for an EBCT of 9 min. It was also demonstrated that BAC filtration consistently removed perchlorate to below detection for influent perchlorate concentrations ranging from 10 to 300 μg/L, influent sulfate concentrations between 0 and 220 mg/L, influent pH values of 6.5–9.0, and operating temperatures of 5–22°C.

Reduction of bromate in a BAC filter

Water treatment plants already using ozone and GAC filters can readily implement this method of removing bromate.Bromate removal was observed during biologically active carbon (BAC) filtration. Microorganisms in the BAC reduced bromate to bromide, although the formation of other intermediate species is possible. The effects of dissolved oxygen (DO) concentration, nitrate concentration, and empty bed contact time (EBCT) on microbial bromate reduction were examined. Oxygen and nitrate, common microbial electron acceptors, hindered bromate reduction. For example, at an influent DO concentration of 2 mg/L in a BAC filter with a 25‐min EBCT, bromate was reduced by 86 percent at an influent nitrate concentration of 0.2 mg/L, whereas it was reduced by 76 percent at an influent nitrate concentration of 5.1 mg/L. In general, lengthening the EBCT increased bromate removal. Biological bromate removal in a conventional ozone–granular activated carbon plant was deemed possible if the DO concentration in the BAC filter is controlled.