On Oxidation-reduction Potential Research Articles

Sequential removal of selenate, nitrate and sulfate and recovery of elemental selenium in a multi-stage bioreactor process with redox potential feedback control

Bioreduction can facilitate oxyanions removal from wastewater. However, simultaneously removing selenate, nitrate and sulfate and recovering high-purity elemental selenium (Se0) from wastewater by a single system is difficult and may lead to carcinogenic selenium monosulfide (SeS) formation. To solve this issue, a two-stage biological fluidized bed (FBR) process with ethanol dosing based on oxidation-reduction potential (ORP) feedback control was developed in this study. FBR1 performance was first evaluated at various ORP setpoints (between −520 and −360 mV vs. Ag/AgCl) and elevated sulfate concentration. Subsequently, ethanol-fed FBR2 was used to reduce sulfate from FBR1 effluent, followed by an aerated sulfide oxidation reactor (SOR). At − 520 mV≤ ORPs≤ −480 mV, FBR1 removed 100 ± 0.1% nitrate and 99.7 ± 0.3% selenate without sulfate reduction. At ORPs ≥ −440 mV, selenate reduction was incomplete, whereas nitrate removal remained stable. Se0 recovery efficiency from FBR1 effluent was 37.5% with 71% Se purity. FBR2 converted 86% of the remaining sulfate in FBR1 effluent to hydrogen sulfide, but the over-oxidation of dissolved sulfide in SOR decreased the overall sulfate removal efficiency to ~46.3%. Overall, the two-stage FBR process with ORP feedback dosing of ethanol was effective for sequentially removing selenate, nitrate and sulfate and recovering Se0 from wastewater.

Unravelling the enhancement of biohydrogen production via adding magnetite nanoparticles and applying electrical energy input

Magnetite nanoparticles (MNP)-caused enhancements for H2 yield (HY) are usually justified based on oxidation-reduction potential (ORP), iron ions (Fe+2/+3) concentration, and enzymatic activity, that is pH-dependent. However, the questions “If pH, ORP, and Fe+2/+3 impacts are excluded, will MNP-caused HY enhancement be still present? and how electrical energy input (EEI) affects HY?” are still unanswered. Herein, control, MNP-supplemented, EEI-applied, FeCl3-, and Na2S-supplemented batches, referred as G1, G2, G3, G5, and G6, respectively were conducted, under fixed pH (6.0 ± 0.1). G5 and G6 targeted quantifying sole impact of Fe+2/+3, and ORP, respectively on HY. G1, G2, G3, G5, and G6 achieved HY values of 1.10 ± 0.05, 1.66 ± 0.07, 1.38 ± 0.06, 1.18 ± 0.04, and 1.16 ± 0.05 mol H2/molhexose, respectively. Neither Fe+2/+3 release nor ORP reduction significantly affected HY. Further, Clostridium amylolyticum dominance was almost similar among G2, and G3. Metabolites flux analysis and functional genes’ prediction highlighted that G2 achieved highest hydrogenase expression and lowest homoacetogenic H2 consumption.

Redox potential as a key parameter for monitoring and optimization of xylose fermentation with yeast Spathaspora passalidarum under limited-oxygen conditions.

The determination of optimum values of volumetric oxygen transfer coefficient (kLa) for Spathaspora passalidarum is an important aspect for the optimization of ethanol production from pentoses since oxygen plays a key role on yeast metabolism. By studying the fermentation of a xylose and glucose mixture, the highest ethanol volumetric productivity was achieved at a kLa of 45h-1 (1.12gethanol L-1h-1), reducing the fermentation time to half when compared to other oxygen-limiting conditions that were considered optimum for other native strains, besides increasing xylose consumption rates. The high cell density fermentation showed to be a good strategy to be applied in industrial processes with S. passalidarum, enabling the complete exhaustion of a high initial substrate concentration (90gL-1) in less than 24h, with a final ethanol titer of 28.61 (± 0.42) gL-1. By performing a detailed investigation on oxidation-reduction potential (ORP), it was possible to conclude that the highest ethanol formation rates were registered at oxireduction potential values around - 100mV, becoming an important parameter to be controlled when oxygen-limiting conditions are applied in industrial fermentations. The oxygen availability also affected the activity of enzyme XR and its preference for NADH or NADPH, directly affecting the activity of enzyme XDH and the redox imbalance on the xylose pathway. In addition, respirometric parameters were determined for the yeast S. passalidarum under an aerobic growth condition.

Mechanisms of enhanced bio-H2 production in Ethanoligenens harbinense by l-cysteine supplementation: Analyses at growth and gene transcription levels

Bio-H2, produced from lignocellulosic biomass or organic wastewater, is an ideal future energy candidate due to its feature of renewability and sustainability. In order to uncover the mechanisms of the reducing agent of l-cysteine in bio-H2 production process, effects of l-cysteine on oxidation–reduction potential (ORP), cell growth, H2 yield by Ethanoligenens harbinense were investigated. Meanwhile, effects of l-cysteine on the expression of genes such as [FeFe]-hydrogenase (hydA), acetate kinase (AK), alcohol dehydrogenase (ADH), and lactate dehydrogenase (LDH) were analysed by quantitative reverse transcription PCR (qRT-PCR). The maximum H2 yield of 1.88 mol-H2/mol-glucose and dry cell weight of 0.92 g/L, which were about 1.57 and 1.51 folds of that of negative control, were obtained with supplementation of 800 mg/L l-cysteine. The experimental results indicated that the supplementation of l-cysteine at a suitable dosage (<800 mg/L) can enhances the H2 production by E. harbinense. The underlying mechanisms include decreasing ORP, promoting cell growth, and stimulating expression of key functional genes (hydA, AK, and ADH) involved in H2 production, together promoted the H2 release and enhanced the H2 production rate.

Evaluation strategy for the control of the copper removal process based on oxidation–reduction potential

The copper removal process purifies copper from leaching solutions with zinc powder in reactors. Due to the complex reaction mechanism and unavailability of online measurements, zinc powder is usually added inexactly, which easily leads to unstable production. This paper proposes an online evaluation method based on oxidation–reduction potential (ORP) for the control of the copper removal process. A kinetic model is designed to translate the production requirements to evaluation indexes of ORP, and the process is then graded by evaluating the fuzzified ORP and its trends according to these indexes. By analyzing these evaluation grades, the process condition is divided into several classes, and each condition class corresponds to a control method set. The industrial experiments show that the copper removal performance is improved by using the proposed evaluation and control strategy.

Influence of lactic acid bacteria on the oxidation–reduction potential of buckwheat (Fagopyrum esculentum Moench) sourdoughs

The influence of lactic acid bacteria (LAB) growth on oxidation–reduction potential (ORP) of buckwheat sourdoughs was investigated. Sourdough fermentations are widely used for the production of bread and other bakery products. Until now the pH value is the most used control parameter taken into account during sourdough technology and no information is available about the influence of sourdough microbiota on the ORP or the use of redox potential (Eh7) measurements as a fermentation control parameter. The influence of growth and metabolism of lactobacilli on the oxidation–reduction potential of buckwheat (Fagopyrum esculentum Moench) sourdoughs was investigated. Upon inoculation with LAB, ORP changes were observed. Each strain exhibits a different ORP time course curve. The Eh7 after 8 h using Lactobacillus plantarum, Lactobacillus sakei, Weissella cibaria and Pediococcus pentosaceus reached 89.2 ± 4, 104.5 ± 15.3, 30.2 ± 4 and 181.5 ± 2.6 mV, respectively. W. cibaria showed the highest reducing activity and P. pentosaceus the lowest one. The maximal reduction rate was neither correlated with the highest acidification rate nor with the maximal growth rate. Nevertheless, the reduction rate shows a similar trend like the acidification rate during the time course of fermentation. The ORP changes occurred concomitantly with the acidification, and the acid production decreased after 2 h from the reducing step. These results showed the possibility to carry out ORP measurements in dough system. As strains exhibit very characteristic ORP curves, this parameter can be used as real-time control tool to monitor the time course of fermentation and metabolic activity. This enables an evidence-based determination of fermentation end and/or (intermediate) harvesting point, which is especially helpful in the development of new cereal fermentation types as in gluten-free sourdoughs.

Influence of flooding and metal immobilising soil amendments on availability of metals for willows and earthworms in calcareous dredged sediment-derived soils

Soil amendments previously shown to be effective in reducing metal bioavailability and/or mobility in calcareous metal-polluted soils were tested on a calcareous dredged sediment-derived soil with 26 mg Cd/kg dry soil, 2200 mg Cr/kg dry soil, 220 mg Pb/kg dry soil, and 3000 mg Zn/kg dry soil. The amendments were 5% modified aluminosilicate (AS), 10% w/w lignin, 1% w/w diammonium phosphate (DAP, (NH 4) 2HPO 4), 1% w/w MnO, and 5% w/w CaSO 4. In an additional treatment, the contaminated soil was submerged. Endpoints were metal uptake in Salix cinerea and Lumbricus terrestris, and effect on oxidation–reduction potential (ORP) in submerged soils. Results illustrated that the selected soil amendments were not effective in reducing ecological risk to vegetation or soil inhabiting invertebrates, as metal uptake in willows and earthworms did not significantly decrease following their application. Flooding the polluted soil resulted in metal uptake in S. cinerea comparable with concentrations for an uncontaminated soil.

Determination of chemical oxygen demand (COD) using ultrasound digestion and oxidation-reduction potential-based titration

A new method for determining wastewater chemical oxygen demand (COD) using ultrasonic digestion and titration based on oxidation reduction potential (ORP) was developed. COD values of potassium hydrogen phthalate solution obtained by ultrasonic digestion were well matched with those obtained using Standard Methods. When applied to determine COD of real wastewater collected from a local treatment plant, results from the new method were within 80% to 90% of those obtained using Standard Methods. Nonetheless, the proposed strategy has the potential to be implemented into an online COD analyzing system.

Stabilisation of dairy wastewater using limited-aeration treatments in batch reactors

This research was conducted to study the treatment of dairy wastewater using limited-aeration treatments. The following process parameters were examined during the treatment process: (1) oxidation–reduction status; (2) organic matter degradation; (3) kinetics of bio-stabilisation; and (4) loss of ammonia. Results showed that during the first 3–4 days of limited-aeration treatments at 0.034 and 0.067 l [air] l −1 [manure] min −1 , dissolved oxygen (DO) remained close to the detection limit but, based on oxidation–reduction potential (ORP) levels (−30 to 100 mV), the wastewater oxidation–reduction status remained anoxic; the environment remained aerobic after this phase. The 70% maximum removal of both chemical oxygen demand (COD) and total volatile solids (TVS) observed by day 8 of treatment at either aeration rate indicated that the two-fold decrease in the aeration rate did not alter the ultimate reduction of the organic strength. Linear regressions performed on the COD against the TVS data obtained during this treatment indicate excellent linear relationships between the two parameters manifested in significantly high correlation coefficients ranging between 0.96 and 0.97. Either of the two parameters can thus be used to monitor the stabilisation of the wastewater and to determine the kinetics of bio-stabilisation. The kinetic studies established bio-stabilisation constants of 0.168 and 0.144 day −1 at the aeration rates of 0.067 and 0.034 l [air] l −1 [manure] min −1 , respectively. Accordingly, 50% bio-stabilisation (also referred to as half-life decay period) was achieved in approximately 4 and 5 days of treatment, respectively; meaning that reducing the aeration rate by 50% increased the half-life decay period by 25%, while reducing the decay rate by only approximately 14%. Effectively therefore, it is more economically prudent to aerate at the lower than at the higher airflow rate. In addition, a significantly higher ammonia loss was unaccounted for at the higher aeration rate (34% net loss) than at the lower aeration rate (23% net loss).

Combined cupric- and cuprous-binding peptides are effective in preventing IL-8 release from endothelial cells and redox reactions

Copper mobilization and subsequent redox reactions have been implicated in the pathogenesis of numerous inflammation-based diseases. Reduction of the cupric ion (Cu 2+) to the cuprous ion (Cu +) is necessary for the production of copper-induced reactive oxygen species (ROS). Peptides, designed to bind both Cu 2+ and Cu + and have the ability to prevent copper redox reactions, were studied. The peptides DAHGMTCA NC and DAHKGMTCA NC were effective at preventing the formation of thiobarbituric acid-reactive species (TBARS) in a copper/ascorbate solution at a 1:1 peptide/Cu ratio. This was observed in the reducing potential of the copper/ascorbate solutions containing these peptides at a 1:1 ratio based on oxidation–reduction potential (ORP) measurements. The peptide DAHGMTCA RC was effective at a 2:1 ratio, but not at a 1:1 ratio in which an increase in the oxidation potential was observed. This suggests that a positively charged amino acid such as arginine (R) in the Cu +-binding motif interferes with metal chelation. All peptides tested were effective at preventing IL-8 release from phorbol 12-myristate 13-acetate (PMA)/copper-stimulated human umbilical vein endothelial cells (HUVEC). The use of Cu +/Cu 2+-binding peptides might be beneficial in the treatment of ROS-related diseases associated with copper.

Control and nitrogen load estimation of aerobic stage in full-scale sequencing batch reactor to treat strong nitrogen swine wastewater

Three different control methods based on oxidation reduction potential (ORP) and dissolved oxygen (DO) for determining aeration time were evaluated for swine wastewater treatment at full-scale SBR. For determining theEnding Point of Ammonia Oxidation (EPAO), the plateau in ORP profile, the derivative of DO, and absolute DO were tested. Below 0.5 kg NH4+-N/m3·day of influent loading rate, three control methods produced good results; however, above this loading rate, only absolute DO method was feasible. The volumetric ammonia nitrogen load at the sub-cycle (Kg NH4+-N/m3/sub-cycle) had an effect on the period of aeration. To put it more concretely, the higher loading rate required a longer ammonia nitrogen oxidation period. To estimate nitrogen load, the length of low DO period, which was defined as the required time to reach 3 mg DO/l from the start of aeration, was the most proper parameter.

Automatic control of external carbon source addition for nitrogen removal in sewage with low C/N ratios

For cost-effective nitrogen removal from sewage with low C/N ratios, an automatic control system for the addition of external carbon based on oxidation-reduction potential (ORP) data in an anoxic reactor has been developed. In this study, it was carried out with a pilot-scale modified Bardenpho process. This consisted of anoxic1, aerobic1, anoxic2 and aerobic2 stages with an external recycle ratio of 150% (Q/Qinf), and a media packing ratio of 2.4%-2.9% (v/v) in the aerobic reactor. As a result of applying the automatic control system for the minimization of the external carbon source dosage, the dosage was decreased by about 20%. This estimate was based on ORP compared with a stable dosage of 75 mg/L based on the C/NOx-N ratio of the anoxic influent. It was necessary that the ORP set-value be regulated from -120 mV to -80 mV because influent NH4+-N concentration varied from 12 to 15 mg/L due to rainfall. Correspondingly, the demanded dosages were decreased. Drift of the the real-time value in control system was more stable after changing the ORP set-value from -120 mV to -80 mV.

Online estimation of wastewater nitrifiable nitrogen, nitrification and denitrification rates, using ORP and DO dynamics

Biological nitrogen removal is susceptible to disturbances in activated sludge processes. Significant improvement of performances are obtained by controlling the process taking into account wastewater modifications and sludge activity. In this work a specific sensor is developed, based on oxidation-reduction potential (ORP) and dissolved oxygen (DO) measurements performed in a completely mixed reactor which can be the activated sludge basin itself. This reactor is continuously fed by wastewater and sludge issued from the recirculation stream of the process, and submitted to alternating aeration. DO profiles and ORP bending point are linked to nitrification and denitrification in the sensor. Signal dynamics are treated with a physical model for simultaneously estimating nitrifiable nitrogen concentration in wastewater, nitrification rate, and denitrification rate. Results show very good prediction of experimental oxygen profiles and the software sensor allows us to recalculate nitrate and ammonia profiles in the reactor with a good accuracy. The estimation of nitrifiable nitrogen and removal rates has been validated experimentally. The system allows us to follow highly variable influent nitrogen concentration, toxic events, and changes in the COD concentration or quality in wastewater.

Relationship between release of nitric oxide and CO 2 and their dependence on oxidation reduction potential in wastewater treatment

Nitric oxide (NO) is an intermediate of denitrification process and can be produced by denitrifiers, nitrifiers and other bacteria. In our experiments we measured the dynamic flow of NO depending on oxidation reduction potential (ORP). Different ORP-ranges were related to various carbon loading stages in the wastewater treatment pilot plant. Nitrification and denitrification were achieved by a sequence of aeration and non-aeration periods. Our measurements show that different carbon loading conditions (low feed, balanced and overloaded conditions) did not change the range of the mixing ratio of NO emissions when the aeration conditions like air-flow and temperature were kept constant. Minimum and maximum NO mixing ratios were 34.7 and 91.8 ppbv; 52.3 and 91.3 ppbv; 57.6 and 109 ppbv for low feed, balanced and overloaded conditions, respectively. The curve of the NO graph relied on nitrification/denitrification dynamics. The dependence of NO release on different ORP and CO 2-release during the various conditions are shown. Longer aeration times resulted in an increased release of gaseous NO. The net-release of NO g −1 nitrogen removed was between 0.014% and 0.028%. The NO fluxes to the air were observed between 8.3 and 14.9 mg m −2d −1NO. The major release occurred during high aeration periods whereas the concentration of dissolved [NO aq] in the wastewater was less than 0.05% of the gaseous release due to very low solubility of the NO.