Oxidation-reduction Potential Monitoring Research Articles

Desorption of Cadmium from Cocoa Waste Using Organic Acids

This study evaluated the desorption of cadmium (Cd) from cocoa waste-derived flour using organic acids. Cocoa pods were collected from Antioquia and Casanare, Colombia, to analyze the geographical Cd content and its distribution within the pod tissues. Acid selection was performed using a multi-criteria decision-making (MCDM) matrix, and Cd desorption was assessed through a full factorial 23 experimental design, considering acid concentration, pulp density, and agitation speed. Additionally, the oxidation–reduction potential (ORP) was monitored as an indicator of the electrochemical dynamics of the process. The results indicated that pods from Casanare exhibited higher Cd concentrations (1.63 ± 0.20 ppm) compared with those from Antioquia (0.87 ± 0.22 ppm), with 49.31% of the metal being accumulated in the pod. Parameters of citric acid at 0.5 M, 5 g/L pulp density, and 120 rpm were found to be optimal for the Cd desorption process, achieving over 95% efficiency. Based on ORP monitoring, a heuristic was proposed to determine the contact time during leaching. This work outlines a scalable process for Cd desorption, adding value to cocoa industry waste for potential applications.

Efficient butanol production from sweet sorghum stem juice by a co-culture system at an optimum temperature: Insights from oxidation-reduction potential monitoring and pilot scale validation

A two-stage co-culture approach was employed in an acetone-butanol-ethanol (ABE) fermentation. An obligate aerobic bacterium, Arthrobacter sp., was first grown for 6 h at 30 °C to create anaerobic conditions. Subsequently, Clostridium beijerinckii TISTR 1461 was inoculated and a fermentation was performed at 37 °C. To identify an intermediate temperature suitable for both microorganisms, their growth was examined at 30, 34, and 37 °C. C.beijerinckii exhibited the highest specific growth rate at 37 °C, while Arthrobacter sp. displayed similar growth rates at all tested temperatures. Butanol production from a synthetic medium (P2 medium) by C. beijerinckii at different temperatures using oxygen-free nitrogen (OFN) gas flushing as a control treatment revealed that fermentation at 37 °C gave the highest butanol concentration (PB, 9.98 g/L). Consequently, 37 °C was chosen for butanol production from sweet sorghum stem juice (SSJ) by co-culture of these two microorganisms in 1-L screw–capped bottles. Compared to the control treatment, higher PB (11.38 g/L), yield (YB/S, 0.37 g/g) and productivity (QB, 0.24 g/L·h) were achieved using the co-culture system. These results were further confirmed by monitoring the oxidation–reduction potential (ORP) during ABE fermentation in a 2-L stirred-tank bioreactor (STR). Moreover, when the co-culture fermentation at 37 °C was scaled up in a 30-L STR, the PB, YB/S and QB values were comparable to those obtained in the 2-L STR. Therefore, co-culture fermentation of Arthrobacter sp. and C.beijerinckii TISTR 1461 at 37 °C represents a promising method for large-scale butanol production.

Smart Strategic Management for the Cold Plasma Process Using ORP Monitoring and Total Organic Carbon Correlation

Assessing oxidation–reduction potential (ORP) is of paramount importance in the efficient management of wastewater within both chemical and biological treatment processes. However, despite its critical role, insufficient information exists about how reactive chemical species generated by cold plasma (CP) in chemical treatment are associated with ORP and air flow rate. Therefore, we aim to identify the correlation between ORP and the removal of organic pollutants when using CP treatment. Additionally, we introduce a machine-learning-based operation to predict removal efficiency in the CP process. Results reveal a significant correlation of over 0.9 between real-time ORP and total organic carbon (TOC), which underscores the efficacy of ORP as a key parameter. This approach made it possible to control OH radical generation by regulating the air flow rate of the CP. This study posits that smart management facilitated by machine learning has the potential to enhance the economic viability of CP feasibility while maintaining overall treatment performance.

Screen-printed Electrodes with Stable Solid-state Reference Electrode for Oxidation-reduction Potential (ORP) Measurement Applications

ORP is defined as the electromotive force between a noble metal electrode and a reference electrode when immersed in solution [1]. The electrochemical setup typically involves a platinum wire as a working electrode (sometimes gold, rarely silver) and a well-controlled reference electrode. When these electrodes are immersed together into a solution, an electron migration is produced between the working electrode and the solution. Depending on the nature of the species diluted, the working electrode loses electrons if the media is an oxidant, so the potential measured becomes positive. If the media is reductive, the working electrode gains electrons, and the resulting potential will be negative. Voltage is measured between both electrodes (working and reference electrode), so the ORP value is usually given in millivolts.ORP provides valuable information because it is a measure of sanitizer activity and water quality, due to the changes in ORP being associated with the existence of contaminants or biological activity. ORP measurements are also useful in several major industrial applications where maintaining potential in a production stage under control is a critical parameter or when it is necessary to assure the quality of water. Examples include cyanide oxidation or chrome reduction in wastewater treatment of metal-plating industry residues, bleach production and bleaching of paper, biological growth control in cooling towers and water quality monitoring in swimming pools, hot tubs, spas, or aquafarming.Screen-printed electrodes (SPEs) offer several interesting advantages in industrial applications such as point-of-care testing, usability, and a wide range of possible customizable setups. However, most SPEs include a pseudo-reference electrode fabricated with silver or silver/silver chloride. Since the KCl electrolyte is absent, this pseudo-reference electrode is exposed to media implying that the reference electrode is not under control, especially in aggressive media. In this publication, an SPE with a platinum paste working electrode and a controlled solid-state reference electrode is presented. Several experiments are included to show that these platforms offer ORP monitoring in household, industrial or laboratory applications.

Dynamics of the nitrification and sulfide‐driven autotrophic denitrification processes in a single reactor using oxidation–reduction potential as an indicator of the process effectiveness

AbstractBACKGROUNDThis paper evaluates the nitrification and sulfide‐driven autotrophic denitrification processes in a structured‐bed reactor subjected to recirculation and intermittent aeration (SBRRIA) applied to the post‐treatment of an anaerobic effluent. The SBRRIA reactor was operated during 130 days in which influent sulfide concentrations varied between 220.1 and 231.0 mg TDS L−1 (TDS, total dissolved solids). Temporal tests were performed to elucidate the dynamics and sulfide impacts on combined processes.RESULTSSulfide partially inhibited the nitrifying activity, resulting in low NH4+‐N oxidation. This fact affected the overall nitrogen removal performance as total‐N removal efficiencies of 50 and 55% were attained in Conditions III and IV, respectively. On the one hand, under continuous aeration and in the absence of sulfide, the oxidation–reduction potential (ORP) reached 50 mV (versus Ag/AgCl) after 250 min of experiment. On the other, when sulfide was continuously provided in the feeding, the ORP was maintained lower than zero. Under anoxic conditions, the effective use of sulfide as an electron donor by autotrophic denitrification was verified by ORP monitoring. However, a concentration of 260 mg TDS L−1 associated with high pH proved inhibitory for NO3− reduction.CONCLUSIONSBased on the results obtained, new strategies of adding sulfide to the SBRRIA should be tested to minimize its inhibitory effect on nitrification and improve nitrogen removal in this unit. © 2018 Society of Chemical Industry

Treatment of reverse-osmosis concentrate of printing and dyeing wastewater by electro-oxidation process with controlled oxidation-reduction potential (ORP)

Reverse osmosis concentrate (ROC) of printing and dyeing wastewater remains as a daunting environmental issue, which is characterized by high salinity, chemical oxygen demand (COD), chroma and low biodegradability. In this study electro-oxidation process (PbO2/Ti electrode) coupled with oxidation-reduction potential (ORP) online monitor was applied to treat such a ROC effluent. The results show that with the increase of specific electrical charge (Qsp), the removal efficiencies of COD, TN and chroma increased significantly at the incipience and then reached a gentle stage; the optimal total current efficiency (12.04 kWh m−3) was obtained with the current density of 10 mA cm−2 (Qsp, 3.0 Ah L−1). Meanwhile, some inorganic ions can be simultaneously removed to varying degrees. FTIR analyses indicated that the macromolecular organics were decomposed into smaller molecules. A multi-parameter linear relationship between ORP and Qsp, COD and Cl− concentration was established, which can quantitatively reflect the effect of current density, chloride ion concentration, pollutants and reaction time on the performance of the electro-oxidation system. As compared to a traditional constant-current system, the constant-ORP system developed in this study (through the back-propagation neural network [BPN] model with ORP monitoring) approximately reduced the energy cost by 24–29%. The present work is expected to provide a potential alternative in optimizing the electro-oxidation process.

Novel coprecipitation–oxidation method for recovering iron from steel waste pickling liquor

Waste pickling liquors (WPLs) containing high concentrations of iron and acid are hazardous waste products from the steel pickling processes. A novel combined coprecipitation–oxidation method for iron recovery by Fe3O4 nanoparticle production from the WPLs was developed in this study. An oxidation–reduction potential monitoring method was developed for real-time control of the Fe2+/Fe3+ molar ratio. The key coprecipitation–oxidation parameters were determined using the orthogonal experimental design method. The use of promoters greatly improved the Fe3O4 nanoparticle crystallinity, size, magnetization, and dispersion. X-ray diffraction patterns showed that the produced Fe3O4 nanoparticles were single phase. The Fe3O4 nanoparticles were approximately spherical and slightly agglomerated. Vibrating sample magnetometry showed that the Fe3O4 nanoparticles produced from the WPLs had good magnetic properties, with a saturation magnetization of 80.206 emu·g–1 and a remanence of 10.500 emu·g–1. The results show that this novel coprecipitation–oxidation method has great potential for recycling iron in WPLs.

Investigation of enhanced Fenton process (EFP) in color and COD removal of wastewater containing Acid Red 18 by response surface methodology: evaluation of EFP as post treatment

The purpose of this study was to investigate the application of enhanced Fenton process (EFP) using zero-valent iron combined with ultrasonic irradiation for treatment of wastewater containing acid red 18 (AR18) by response surface methodology. According to the analysis of variance results, the model presents high R2-value of 98.2 and 98.3% for the COD and AR18 dye removal, respectively, indicating that the model was successful. In this paper, the results of the monitoring of oxidation reduction potential and dissolved oxygen were presented to obtain the reaction time. At the 60 min of contact time, AR18 dye and COD removal efficiency raised more than 30 and 5% with the increase in Fenton reagents, respectively. Effluent without the presence of phosphate indicated 40% increment of AR18 dye removal in comparison to the influent with the presence of phosphate. Considering the EFP as post treatment of a sequencing batch reactor, the combination system improved the efficiency of high azo dye AR18 concentration wastewater treatment.

Abstract T P219: A Novel Method for Measuring Oxidative Stress in Patients with Stroke Symptoms

Introduction: A novel device was developed to measure oxidation reduction potential (ORP), which is the balance of oxidants and reductants, providing a direct measure of oxidative stress. Our purpose was to measure ORP in patients admitted with stroke symptoms. Methods: This prospective observational study included patients admitted to our Primary Stroke Center from 1/2010-12/2012; children ≤18 and transfers were excluded. We examined ORP’s association with stroke type, demographics (age, gender, race), NIHSS, thrombolytic therapy, and outcomes (in-hospital mortality, mRS, LOS, readmission) using Pearson correlation, generalized linear models, chi-square and student’s t-tests. Blinded operators tested plasma samples in duplicate for static ORP (resting ORP, mV), where greater values indicate more oxidative stress, as well as Capacity (antioxidant reserve, uC). Capacity was inverse-transformed (icORP), where greater values indicate less reserves. Results: There were 101 patients including 52 ischemic strokes, 10 hemorrhagic strokes, 19 TIAs, and 20 mimics. Six patients died (6%); arrival ORP was significantly lower in patients who died than who survived (sORP: 137.2 vs 163.9, p = 0.004; icORP: 2.7 vs. 4.5, p = 0.02); the change in ORP between day 2 and arrival (ΔORP) was significantly greater in patients who died (sORP: 26.3 vs 5.4, p = 0.002; icORP: 1.5 vs. 0.0, p = 0.004). Arrival ORP was lowest in patients with severe stroke, while ΔORP was greatest in these patients (table 1), independent of thrombolytic therapy (interaction p =0.36). Arrival ORP was positively correlated with LOS (p = 0.003). Conclusions: These results demonstrate the ability of ORP to identify oxidative stress and amount of antioxidant reserves in a stroke population. We propose ORP monitoring as a potentially useful tool in evaluation of acute stroke patients.

Effects of nitrate on the treatment of lead contaminated groundwater by nanoscale zerovalent iron

Nanoscale zerovalent iron (nZVI) is efficient for removing Pb2+ and nitrate from water. However, the influence of nitrate, a common groundwater anion, on Pb2+ removal by nZVI is not well understood. In this study, we showed that under excess Fe0 conditions (molar ratio of Fe0/nitrate>4), Pb2+ ions were immobilized more quickly (<5min) than in nitrate-free systems (∼15min) due to increasing pH. With nitrate in excess (molar ratio of Fe0/nitrate<4), nitrate stimulated the formation of crystal PbxFe3−xO4 (ferrite), which provided additional Pb2+ removal. However, ∼7% of immobilized Pb2+ ions were released into aqueous phase within 2h due to ferrite deformation. Oxidation–reduction potential (ORP) values below −600mV correlated with excess Fe0 conditions (complete Pb2+ immobilization), while ORP values ≥−475mV characterized excess nitrate conditions (ferrite process and Pb2+ release occurrence). This study indicates that ORP monitoring is important for proper management of nZVI-based remediation in the subsurface to avoid lead remobilization in the presence of nitrate.

Monitoring of ORP, pH and DO in heterogeneous Fenton oxidation using nZVI as a catalyst for the treatment of azo-dye textile wastewater

The nanoscale zero valent iron-Fenton (nZVI-Fenton) process combines the advantages of nZVI reduction and Fenton oxidation, was regarded as a very effective process for the treatment of azo-dye/textile wastewater. In this paper, we present the results of the investigation of the on-line monitoring of oxidation–reduction potential (ORP), pH, and dissolved oxygen (DO) to evaluate the effectiveness of the nZVI-Fenton process for the removal of color and chemical oxygen demand (COD) from azo-dyes textile wastewater. The experimental results indicated that the optimal doses of nZVI and H2O2 for color removal were 60–80mg/L and 300–400mg/L, respectively. The nZVI reduction removed around 80–90% of the color; however, less than 15% of the COD was removed. To attain the desired removal of COD, much higher doses of nZVI and H2O2 were required, i.e., 200–225mg/L and 1000–1125mg/L, respectively. ORP, pH, and DO had direct and meaningful correlations with the removal efficiencies of both color and COD. Thus, regression models and artificial neural networks (ANN) models were used to predict the color and COD removal efficiencies using the monitoring data acquired for ORP, pH, and DO. The ANN model provided very precise prediction results with R2 values in the range of 0.96–0.99. The predictions provided by the regression model had R2 values in the range of 0.92–0.95. These results indicated that on-line ORP, DO, and pH monitoring data can be used as input to either model to obtain a reliable evaluation of the effectiveness of the nZVI-Fenton process for the removal of color and COD from azo-dyes textile wastewater.

Possible control approaches of the Electro-Fenton process for textile wastewater treatment using on-line monitoring of DO and ORP

The Electro-Fenton (E-Fenton) process combines the advantages of electrochemical and Fenton processes, which is an effective and popular advanced oxidation process (AOP) for treating textile wastewater. Dynamically regulating the E-Fenton process is still difficult; however, it is critical for reducing operation costs and enhancing process performance. This paper presents the potentials of on-line monitoring of Oxidation Reduction Potential (ORP) and Dissolved Oxygen (DO) as key parameters to control the E-Fenton process for textile wastewater treatment. Experimental results have shown that the monitored DO and ORP profiles have high correlations with the trends of H2O2, Fe+2 and Fe+3 variations, which can help to identify over-dosing of H2O2. Both the multiple regression and the Artificial Neural Network (ANN) models were applied to predict the required Fe+2 doses using the monitoring ORP, DO, and COD removal targets. Very precise prediction results with the correlation coefficients (R2) of 0.95–0.99 were performed by the multiple regression models and the ANN models, respectively. As a result, the monitoring of DO and ORP have high potentials to effectively control the E-Fenton and contribute to the benefit of chemical cost savings.

Nitrogen Removal from Three-stage Oxidation-reduction System by Simulation of the Riparian Environment

Riparian zones (RZ) is area in which sediments typically exhibit strong redox transitions and play a key role in river metabolism. A three-stage oxidation-reduction cores device which perfuse with heterogeneous sediment (gravel and sand) was used in the present study to analyze nitrogen removal in the multiple oxidation-reduction environment of river. The monitoring of oxidation-reduction potential (ORP) on the device confirmed that the system was successfully reproduced three-stage oxidation-reduction gradient environment in riparian zones. The results indicated that ammonia nitrogen, nitrate nitrogen, total nitrogen (TN) and chemical oxygen demand (COD) can be removed effectively, and the removal rates are 72.05%, 99.28%, 78.17% and 77.64% respectively. And optimum removal efficiency of nitrogen was founded in the first-stage downflow column. The ratio of C/N and ammonia nitrogen load of influent influence the nitrogen removal effect, and maximum removal rate of nitrogen was observed under the condition that C/N is 8 and ammonia nitrogen load is 2.63g d-1 m-3.

Dosage Control of the Fenton Process for Color Removal of Textile Wastewater Applying ORP Monitoring and Artificial Neural Networks

Textile wastewater containing a high level of color and refractory chemical oxidation demand (COD) is difficult to treat using traditional wastewater treatment processes. Typically, a chemical process was suggested as a pretreatment to remove color and increase biodegradability of refractory organic materials. A biological process was then used to remove organic materials and reduce chemical costs for textile wastewater treatment. Fenton oxidation is one of the most effective chemical processes for removing color and COD for textile wastewater. In Fenton processes, oxidations by generated hydroxyl radical are the key factor for color removal in textile wastewaters; thus, monitoring oxidation reduction potential (ORP) should have high potential in Fenton dosage control for color removal in textile wastewater treatment. The main object of this study is to build a Fenton dosage control strategy that uses ORP monitoring and artificial neural network (ANN) models for removing color from textile wastewaters. Two wastewaters, synthetic and real textile, were used in this study. Experimental results have shown that the ANN models precisely represent the correlation between monitoring ORP, Fenton doses, color removal efficiency, and effluent color value, and therefore can be used to control Fenton doses for removing color from textile wastewater. Finally, another series of Fenton dose-control experiments for different color removal control targets were conducted to evaluate this proposed Fenton dose control strategy. Experimental results indicate that the proposed control strategy precisely controls the required Fenton doses for different control targets for both synthetic and real textile wastewaters, and result in reduced chemical costs.

Applicability of Oxidation Reduction Potential Response on a Full-Scale Intermittently Aerated Suspended Culture System

On-line monitoring of oxidation reduction potential (ORP) was conducted at the full-scale aeration basin operated with intermittent aeration schedules and fed with the wastewater generated from fruit fly rearing facility owned by the California Department of Food and Agriculture, Waimanalo, Hawaii. The characteristics of the wastewater were fluctuated, severely. The 90 percentile level of total chemical oxygen demand, total Kjeldahl nitrogen, and total suspended solids for the wastewater are 5,200, 142, and 3,350 mg/L, respectively. Two aeration schedules of 4 h aeration/2 h nonaeration and 3 h aeration/3 h nonaeration were investigated in this study. Typical ORP curve with bending points of β (beginning of denitrification), χ (disappearance of nitrate), and plateau (dORP/dt=0) were observed for both aeration schedules. The α (end of nitrification) value couldn’t detect in the aeration schedule of 3 h aeration/3 h nonaeration because of the ORP fluctuation at the onset of aeration. However, the α value detected without any difficulty for the aeration schedule of 4 h aeration/2 h nonaeration. This is due to the relatively lower gradient of the reduced substance concentration between supernatant and settled sludge layers during the air-off period. Through the ORP monitoring of the full-scale aeration basin treating fruit fly rearing facility wastewater, the aeration time can be reduced from 4 h to 3 h without deterioration of organic and nitrogen removal efficiencies. By reducing the aeration time, 25% of energy cost for aeration can be saved. From the result of real time monitoring of ORP response and water quality analysis of nitrogen, the behaviors of nitrogen forms are closely related to the ORP response. Therefore, the ORP monitoring is a practical and easy tool for the evaluation of the degree of nitrification and denitrification condition in biological wastewater-treatment systems.

Pilot-scale operation of thermophilic aerobic digestion for volatile fatty acid production and distribution

Thermophilic aerobic sludge digestion is operated at elevated temperatures, to achieve sludge stabilization, volatile solids (VS) destruction, and pasteurization. The thermophilic aerobic digestion (TAD) of sludge, under a "microaerated" condition, whereby the system oxygen demand exceeds the supply, has been found to accumulate high concentrations of volatile fatty acids (VFAs), namely acetate and propionate. This VFA-rich TAD supernatant is a potential carbon alternative for phosphorus and nitrogen removal enhancement in biological nutrient removal (BNR) processes. This pilot-scale continuous TAD operation was designed to produce VFA-rich supernatant, without sacrificing sludge solids destruction efficiency. A molecular weight cut-off (MWCO) method was used to analyze the carbonaceous and nutrient distributions in the TAD supernatant. Results suggested that real-time aeration control is necessary to control the micro-aeration operation and optimize the VFA production. The oxidation-reduction potential (ORP) did not correlate well to the actual VFA concentration; however, the ORP monitoring did reflect the status of the micro-aeration condition and the existence of VFAs in the system. The average VFA concentration was found to be in proportion to the sludge concentration in the feed. Also, a certain portion of VFAs was found to associate with particulates and colloids in the TAD supernatant. Key words: digested sludge supernatant, molecular weight cut-off, microaerated, thermophilic aerobic digestion, volatile fatty acids, volatile solids destruction, ultrafiltration.

Oxidation-Reduction Potential as a Monitoring Tool in a Low Dissolved Oxygen Wastewater Treatment Process

Research was undertaken to investigate the relationship between two biochemical events and the oxidation-reduction potential (ORP) measurement in a low dissolved oxygen (D.O.) wastewater treatment process. The biological events considered were the depletion of organic waste and the depletion of ammonia nitrogen. Two lab-scale sequencing batch reactors fed with a synthetic waste were operated under controlled conditions using seed material from a local wastewater treatment plant. The on-line monitoring of ORP, D.O., and pH was complemented by intensive track studies in which physical measurements of biochemical parameters such as chemical oxygen demand and TN were taken. The results indicated that low D.O. processes (e.g., the simultaneous nitrification/denitrification process) may have their own distinctive on-line profiles, with certain biochemical events such as the depletion of organic carbon and the depletion of ammonia nitrogen being readily detectable on the ORP profile. The fact that these specific events are displayed on the on-line ORP profile means that the profile could possibly be used as a process control parameter.

Application of oxidation–reduction potential as a controlling parameter in waste activated sludge hydrolysis

In order to destroy the refractory structure of waste activated sludge (WAS) and increase its biodegradability, chemical pretreatment by adding NaOH was used in this study to enhance the hydrolysis of the WAS collected from the Taipei Min-Sheng Sewage Municipal Wastewater Treatment Plant located in northern Taiwan. Experiments were conducted with four total suspended solids (TSS) concentrations (0.5–2.0%) and four NaOH dosages (20–80 meq/l) at 25 °C. It was found that the optimal condition for WAS hydrolysis was TSS of 1% and NaOH dosage of 40 meq/l; 45% of soluble chemical oxygen demand (SCOD) was solubilized in the pretreatment time of 10 h. When the WAS was hydrolyzed by adding NaOH, profiles of oxidation–reduction potential (ORP) values were monitored on-line; also, a model covering the relationship between the change of ORP value and increase in SCOD was developed. This verified that the ORP monitoring technique is not only useful to investigate the solubilization rate but also suitable for the determination of optimal solubilization in WAS treatment. Considering the release of nitrogen by alkaline pretreatment, profiles of total Kjeldahl nitrogen, ammonia-nitrogen and amino acids were investigated.

Improvement of nitrogen-removal efficiency using immobilized microorganisms with oxidation-reduction potential monitoring

The use of an immobilized-cell reactor for simultaneous carbon–nitrogen removal in wastewater with the monitoring of oxidation–reduction potential (ORP) in an intermittent aeration (IA) process was investigated. Under alternating aerated and nonaerated conditions, the ORP-time profile showed distinctive turning points that directly correlated with changes in the system chemistry and biological activity. The aeration ratio, defined as aeration time/cycle time, was optimum at 50% for obtaining the maximum efficiency of denitrification accompanied by sufficient nitrification. High simultaneous carbon–nitrogen removal efficiency could be achieved using the immobilized-cell reactor by applying the IA process. More than 90% of COD-removal efficiency and over 80% of total-nitrogen-removal efficiency were obtained using three aerobic–anoxic cycles per day at an aeration ratio of 50% and with a hydraulic retention time of 10 h. Journal of Industrial Microbiology & Biotechnology (2000) 25, 229–234.

Nutrient Removal and ORP Monitoring in the Intermittent Aeration System with Continuous Inflow

Intermittent aeration system with continuous inflow (IASWCI) was fed with synthetic wastewater to clarify the possibility of simultaneous removal of nitrogen, phosphorus, and organic substances by modifying operational schedule. This system was composed of aerobic, anoxic, anaerobic, aerobic, settle and decant phases in a single tank. Synthetic wastewater was flown continuously into the pre-react zone. Anaerobic phase was provided for the phosphorus release without mixing and aerating. The laboratory scale system was operated for four months. Phosphorus release from the sludge was measured in the anaerobic condition after denitrification. The following luxury uptake of phosphorus was observed the second aerobic phase. During 4 months, chemical oxygen demand (COD) removal efficiencies were greater than 90%. The average COD effluent was approximately 17 mgl−1. The effluent had, average, during phosphorus concentration less than 0.5 mgl−1, and ammonia nitrogen concentration lower than 3 mgl−1. A correlation exists between oxidation-reduction potential (ORP) and observed P release in the anaerobic phase, and ORP and measured P uptake in the second aerobic phase. In this case, ORP appears to be related to measured P release and P uptake, as is indicated by the good fit of the linear regression equation. It can be used to good advantage at the operational level to give plant operators a real time indication of P release and uptake condition in this process.