Oxidation-reduction Potential Control Research Articles

ORP-regulated natural accumulation of pyruvate in Actinobacillus succinogenes 130Z

Pyruvate, a pivotal metabolite in the glycolytic pathway, typically confronts substantial barriers to its natural accumulation within microbial cells. This study successfully facilitated the natural accumulation of pyruvate in Actinobacillus succinogenes 130Z by fine-tuning the oxidation-reduction potential (ORP) in the fermentation milieu. A mechanistic exploration revealed that the accumulation of pyruvate was optimized when ORP conditions favorably modulated pyruvate kinase activity and concurrently suppressed succinate dehydrogenase activity. By integrating the influence of metal ions on enzymatic functions with an innovative aluminum ion-mediated ORP control strategy, we achieved a pyruvate yield of 27.54 g/L over 20 hours, which constitutes an 89.54 % increase compared to the baseline. Additionally, the production rate of pyruvate reached 1.38 g/L·h. This investigation not only elucidates the metabolic underpinnings that facilitate the natural enrichment of glycolytic intermediates in Actinobacillus succinogenes 130Z but also lays a robust theoretical foundation for the industrial-scale fermentation of pyruvate. Moreover, the capability to efficiently and rapidly concentrate essential platform metabolites within the glycolytic pathway is of paramount significance, potentially propelling forward the research and synthesis of various downstream metabolic products.

Potential of single and designed mixed cultures to enhance the bioleaching of chalcopyrite by oxidation-reduction potential control

Biomining is the extraction of target metals from ores or wastes such as the dissolution of chalcopyrite for copper recovery. A key outstanding topic of study is to improve the rate and total copper released from chalcopyrite that can become ‘passivated’ by surface layers, which hinders oxidative attack on the metal sulfide bond. One strategy to increase chalcopyrite bioleaching is to control of the oxidation-reduction potential in the desired range by using ‘weak’ iron oxidizers. In this study, 15 acidophilic species were evaluated for their ability to catalyze chalcopyrite dissolution that resulted in the addition of Acidithiobacillus ferrianus, Sulfobacillus thermotolerans, and Metallosphaera sedula to the known ‘weak’ iron oxidizing species. Based upon these data, four microbial consortia were designed including mesophiles (25° and 37 °C), moderate thermophiles (49 °C), and thermophiles (70 °C) that increased copper recoveries by up to 32% compared to abiotic controls. The best performing consortium was the moderate thermophiles Sulfobacillus thermotolerans, Sulfobacillus acidophilus, and Ferroplasma acidiphilum that maintained the oxidation-reduction potential in the desired range. However, the consortia also showed evidence of synergistic interactions between ‘weak’ iron oxidizers that increased the efficiency of ferrous iron oxidation that resulted in oxidation-reduction potentials above the desired range and lower copper release. Therefore, while designing microbial consortia is a promising strategy to improve the performance of chalcopyrite bioleaching, care must be taken to ensure synergistic effects do not result in high oxidation-reduction potentials.

Nitrous oxide emissions from two full-scale membrane-aerated biofilm reactors

The upcoming change of legislation in some European countries where wastewater treatment facilities will start to be taxed based on direct greenhouse gas (GHG) emissions will force water utilities to take a closer look at nitrous oxide (N2O) production. In this study, we report for the first time N2O emissions from two full-scale size membrane aerated biofilm reactors (MABR) (R1, R2) from two different manufacturers treating municipal wastewater. N2O was monitored continuously for 12 months in both the MABR exhaust gas and liquid phase. Multivariate analysis was used to assess process performance. Results show that emission factors (EFN2O) for both R1 and R2 (0.88 ± 1.28 and 0.82 ± 0.86 %) were very similar to each other and below the standard value from the Intergovernmental Panel on Climate Change (IPCC) 2019 (1.6 %). More specifically, N2O was predominantly emitted in the MABR exhaust gas (NTRexh) and was strongly correlated to the ammonia/um load (NHx,load). Nevertheless, the implemented Oxidation Reduction Potential (ORP) control strategy increased the bulk contribution (NTRbulk), impacting the overall EFN2O. A thorough analysis of dynamic data reveals that the changes in the external aeration (EA)/loading rate patterns suggested by ORP control substantially impacted N2O mass transfer and biological production processes. It also suggests that NTRexh is mainly caused by ammonia-oxidizing organisms (AOO) activity, while ordinary heterotrophic organisms (OHO) are responsible for NTRbulk. Different methods for calculating EFN2O were compared, and results showed EFN2O would range from 0.6 to 5.5 depending on the assumptions made. Based on existing literature, a strong correlation between EFN2O and nitrogen loading rate (R2 = 0.73) was found for different technologies. Overall, an average EFN2O of 0.86 % N2O-N per N load was found with a nitrogen loading rate >200 g N m−3 d−1, which supports the hypothesis that MABR technology can achieve intensified biological nutrient removal without increasing N2O emissions.

Control of redox potential in a novel continuous bioelectrochemical system led to remarkable metabolic and energetic responses of Clostridium pasteurianum grown on glycerol

BackgroundElectro-fermentation (EF) is an emerging tool for bioprocess intensification. Benefits are especially expected for bioprocesses in which the cells are enabled to exchange electrons with electrode surfaces directly. It has also been demonstrated that the use of electrical energy in BES can increase bioprocess performance by indirect secondary effects. In this case, the electricity is used to alter process parameters and indirectly activate desired pathways. In many bioprocesses, oxidation-reduction potential (ORP) is a crucial process parameter. While C. pasteurianum fermentation of glycerol has been shown to be significantly influenced electrochemically, the underlying mechanisms are not clear. To this end, we developed a system for the electrochemical control of ORP in continuous culture to quantitatively study the effects of ORP alteration on C. pasteurianum by metabolic flux analysis (MFA), targeted metabolomics, sensitivity and regulation analysis.ResultsIn the ORP range of −462 mV to −250 mV, the developed algorithm enabled a stable anodic electrochemical control of ORP at desired set-points and a fixed dilution rate of 0.1 h−1. An overall increase of 57% in the molar yield for 1,3-propanediol was observed by an ORP increase from −462 to −250 mV. MFA suggests that C. pasteurianum possesses and uses cellular energy generation mechanisms in addition to substrate-level phosphorylation. The sensitivity analysis showed that ORP exerted its strongest impact on the reaction of pyruvate-ferredoxin-oxidoreductase. The regulation analysis revealed that this influence is mainly of a direct nature. Hence, the observed metabolic shifts are primarily caused by direct inhibition of the enzyme upon electrochemical production of oxygen. A similar effect was observed for the enzyme pyruvate-formate-lyase at elevated ORP levels.ConclusionsThe results show that electrochemical ORP alteration is a suitable tool to steer the metabolism of C. pasteurianum and increase product yield for 1,3-propanediol in continuous culture. The approach might also be useful for application with further anaerobic or anoxic bioprocesses. However, to maximize the technique's efficiency, it is essential to understand the chemistry behind the ORP change and how the microbial system responds to it by transmitted or direct effects.

Enhancement of butanol production in Clostridium acetobutylicum SE25 through oxidation-reduction potential regulation and analysis of its metabolic mechanisms

In this study, an exogenous regulatory strategy named as oxidation-reduction potential (ORP) regulation was performed in the butanol biosynthesis process by Clostridium acetobutylicum SE25 to accelerate the carbon metabolism flow to butanol and enhance butanol production. The findings show that the dithiothreitol and potassium ferricyanide were the optimal redox agents for regulating the ORP of the fermentation system. Specifically, when the ORP value of fermentation broth was controlled at −400 mV, the highest production of butanol (14.30 ± 0.65 g/L) was obtained, which was 10.80 % higher than that of the control group. And the yield and productivity of butanol were 0.24 g/g and 0.24 g/L/h, respectively. Furthermore, the physiological mechanisms of the effects of different ORP levels on butanol synthesis was investigated, and the results demonstrate that ORP could both regulate the level and ratio of energy charge and NADH/NAD+, and redistribute metabolic flux. Thus, the ORP control strategy, according to the results in this study, is an effective and attainable approach to obtain the high production of butanol.

Controlled oxidation-reduction potential on dark fermentative hydrogen production from glycerol: Impacts on metabolic pathways and microbial diversity of an acidogenic sludge

The oxidation-reduction potential (ORP) is an important factor in H2 production via dark fermentation however its effect over microbial diversity in an acidogenic sludge has not, been well studied. This work studies the effect of ORP controlled by hydrogen peroxide and potassium ferricyanide on continuous hydrogen production and microbial diversity in an acidogenic sludge fed (HRT 12 h and pH 5.5) with glycerol. Results show that the more oxidizing ORP control environment (−540 mV) improves H2 yield by 50–70% (0.31–0.51 molH2/mol glycerol) over non-ORP control conditions. Oxidizing ORP values were shown to enrich microorganisms of the genus Clostridium, which have been linked to high H2 yields. Therefore, controlling ORP in an acidogenic sludge was shown to directly modify microbial diversity at the genus level, and could likely to indirectly regulate metabolic function. Additionally, metabolic pathways were regulated by the kind of agent used.

Optimization of Energy Consumption in the Biological Reactor of a Wastewater Treatment Plant by Means of Oxy Fuzzy and ORP Control

Aeration of the biological reactor in wastewater treatment plants (WWTPs) represents one of the major cost items, which may account for more than 50% of the total energy consumption. Therefore, airflow rate must be supplied based on the real needs of the biological reactions and the goals to be achieved in terms of removal efficiency and effluent quality. Among the different strategies available to optimize energy consumption of air supply, the Oxy Fuzzy logic and oxidation reduction potential (ORP)-based control systems have proven to be efficient and reliable. The present study compares the effects of these two control systems in terms of energy consumption and efficiency of COD and ammonia oxidation in the activated sludge reactors of two WWTPs for domestic sewage. Both systems allowed to largely comply with the limits set on the effluent for COD and ammonia in spite of the dynamic pattern of the influent load. The Oxy Fuzzy system led to reducing energy consumption by 13% while the ORP control system only by 2%, as average per year. The Oxy Fuzzy system showed higher flexibility, being more capable of adapting the set-points in relation to the influent load. The ORP system seemed to be more suitable for plants where the influent load does not change significantly: the set-points are fixed and the input load can be properly managed only for limited variations.

Nutrient Removal and Nitrous Oxide Emission by a Two-Step Fed SBR in Treating Dairy Manure Wastewater

Abstract. In this study, a two-step fed sequencing batch reactor (SBR) was employed to treat dairy manure wastewater to remove nutrients, including nitrogen, phosphorus, 5-day biochemical oxygen demand (BOD5), and chemical oxygen demand (COD), and to examine the associated nitrous oxide (N2O) emission by the SBR treatment. The SBR was operated on an 8 h cycle with preset time periods for different phases, including anoxic/anaerobic/aerobic phases. The results showed that the SBR system could effectively reduce the nutrients in the wastewater, with removal efficiencies reaching 86.6%, 95.6%, 98.8%, 100%, 97.9%, 95.6%, and 99.8%, respectively, for volatile solids (VS), volatile suspended solids (VSS), total Kjeldahl nitrogen (TKN), ammonium nitrogen (NH4+-N), total phosphorus (TP), COD, and BOD5. However, the SBR could not complete denitrification at the end of the cycle, with 12 mg L-1 nitrate left in the effluent, possibly due to suppression of denitrifiers by the anoxic/aeration phase that was placed almost at the end of cycle and overprovided oxygen to the liquid. Denitrification was found to be a major process for N2O generation, so reducing denitrification time in the cycle is recommended, given that the overall performance of the SBR system in removing nutrients was not compromised. Using oxidation-reduction potential (ORP) alone to automate the SBR control was not sufficient to avoid failure of the system. Keywords: Dairy manure wastewater, Nitrous oxide emission, Nutrient removal, ORP control, Sequencing batch reactor, Two-step fed strategy.

Effects of oxidation–reduction potential control and sequential use of biological treatment on the electrochemical Fenton-type process

This paper reports on the effects of an oxidation–reduction potential (ORP) control on the electrochemical Fenton-type process (EFT process) and the efficacy of a combined approach, namely, the EFT process with an ORP control together with an activated sludge process, on the treatment of wastewater contaminated with 1,4-dioxane. The EFT process with an ORP control was able to improve the current efficiency from 16.9% to 73.6–81.9%. A superior performance for both the current efficiency and the treated water quality was recorded by the EFT process with an ORP control of 1000mV. This superior result was ascribed to the approach preventing an excessive accumulation of hypochlorous acid. Two combined processes, namely, an activated sludge process followed by the EFT process with an ORP control (AS-EFT process) and the EFT process with an ORP control followed by an activated sludge process (EFT-AS process), were examined by using 1,4-dioxane contaminated municipal wastewater. As a result, the AS-EFT process was superior to the EFT-AS process in respects of both energy consumption and the performance of chemical oxygen demand (COD) removal, as well as the removal of 1,4-dioxane, due to the smaller COD loading onto the EFT reactor in the AS-EFT process.

Control of oxidation-reduction potential during Cheddar cheese ripening and its effect on the production of volatile flavour compounds.

In cheese, a negative oxidation-reduction (redox) potential is required for the stability of aroma, especially that associated with volatile sulphur compounds. To control the redox potential during ripening, redox agents were added to the salted curd of Cheddar cheese before pressing. The control cheese contained only salt, while different oxidising or reducing agents were added with the NaCl to the experimental cheeses. KIO3 (at 0·05, 0·1 and 1%, w/w) was used as the oxidising agent while cysteine (at 2%, w/w) and Na2S2O4 (at 0·05 and 0·1%, w/w) were used as reducing agents. During ripening the redox potential of the cheeses made with the reducing agents did not differ significantly from the control cheese (E h ≈ -120 mV) while the cheeses made with 0·1 and 0·05% KIO3 had a significantly higher and positive redox potential in the first month of ripening. Cheese made with 1% KIO3 had positive values of redox potential throughout ripening but no starter lactic acid bacteria survived in this cheese; however, numbers of starter organisms in all other cheeses were similar. Principal component analysis (PCA) of the volatile compounds clearly separated the cheeses made with the reducing agents from cheeses made with the oxidising agents at 2 month of ripening. Cheeses with reducing agents were characterized by the presence of sulphur compounds whereas cheeses made with KIO3 were characterized mainly by aldehydes. At 6 month of ripening, separation by PCA was less evident. These findings support the hypothesis that redox potential could be controlled during ripening and that this parameter has an influence on the development of cheese flavour.

Phosphorus release from coastal sediments: Impacts of the oxidation-reduction potential and sulfide

The release of phosphorus (P) from benthic sediments can affect the P content, nutrient status and quality of overlying waters in coastal ecosystem. This study was carried out to investigate the influence of oxidation-reduction potential (ORP) and sulfide on P release from sediments in the coastal estuary of the Yuniao River, China. The results showed that ferric iron-bound P was the main P burial phase in the sediments. The P concentration in overlying water increased with ORP decrease and sulfide increase, displaying a significant linear correlation with the ORP and sulfide concentration. The results indicate that decreased ORP may elevate the zero equilibrium phosphorus concentration, enhancing the capability of P release. And increased sulfide may react or capture reactive iron in sediments, reducing the P adsorption capacity and accelerating P release. Therefore, the control of ORP and sulfide production is important in the sink/source conversion of P in coastal sediments.

Primary Copper Ore Leaching by Leaching Solution Adjusted Oxidation-Reduction Potential in Column

Copper ore is classified into three groups; primary copper sulfide, copper oxide and secondary copper sulfide. Leaching copper from primary copper sulfide, such as chalcopyrite, with sulfuric acid takes longer time than from copper oxide and secondary copper sulfide. As such, an oxidant is required to extract copper from chalcopyrite. In this study, column leaching tests were carried out using primary copper sulfide ores produced in an iron oxide copper gold (IOCG) deposit and rich in iron in coparison to porphyry copper ores. The columns of 10 cm diameter and 100 cm long had a double tube structure so that the column temperature can be kept at desired temperature by circulating warm water in the outer tube. The oxidation-reduction potential (ORP) of the leaching solutions were adjustedto 400, 450 and 500 mV vs Ag/AgCl. The column leaching test using just pH 2.0 sulfuric acid without adjustment of ORP at 45 °C got a copper recovery rate of 37 % in 400 days. On the other hand, with ORP adjusted leaching solutions of pH 2.0 sulfuric acid containing 500 mg/L Fe, the copper recovery rate reached up to 87 % in 400 days.In addition, it was necessary to keep the temperature above 45 oC to enhance copper leaching by ORP adjusted leaching solution. The result of the column leaching test at room temperature (around 30 °C) using ORP adjusted leaching solution shows that the recovery rate of copper is lower than the result at 45 °C. The ORP adjustment of leaching solution is effective for leaching copper from primary copper sulfide ore, however, the leaching temperature needs to be kept above 45 °C. As a result, it makes clear that copper leaching is enhanced by utilization of ORP adjusted leaching solutions and suggests that the solution ORP control is important to the application of bioleaching.

A modified oxic-settling-anaerobic activated sludge process using gravity thickening for excess sludge reduction.

Oxic-settling-anaerobic process (OSA) was known as a cost-effective way to reduce the excess sludge production with simple upgrade of conventional activated sludge process (CAS). A low oxidation-reduction potential (ORP) level was the key factor to sludge decay and lysis in the sludge holding tank of the OSA process. However, the ORP control with nitrogen purge or chemical dosing in the OSA process would induce extra expense and complicate the operation. Hence, in this study, a sludge holding tank using gravity thickening was applied to OSA process to reduce the excess sludge production without any ORP control. Results showed that the modified OSA process not only reduced the excess sludge production effectively but also improved the sludge settleability without affected the treatment capacity. The reduction of the excess sludge production in the modified OSA process resulted from interactions among lots of factors. The key element of the process was the gravity thickening sludge holding tank.

Microbial community analysis of anaerobic bio-corrosion in different ORP profiles

The effect of ORP (oxidation–reduction potential) on the bacterial community and corrosion rate was investigated in this study. A continuous sulfate-reducing bacteria (SRB)-enriched reactor equipped with an ORP controller was operated from anaerobic to anoxic condition in this bio-corrosion experiment for over 200 days. Testing mild steel coupons were placed into the reactor for immersion test which was used to compare with the result of electrochemical corrosion current density. The results showed that as the ORP increased, the sulfide, corrosion current density and the proportion of SRB in microbial community would decrease. This study employed oxygen to change the microbial communities, which successfully enabled heterotrophs to inhibit SRB even under excessive TOC and sulfate inflow conditions. However, from the results of corrosion weight loss it could be discovered that the fact of higher control of ORP leading to better corrosion inhibition was not certain. Once the ORP was controlled to −250 mV, the same result could be achieved as well as the ORP being controlled to −180 mV. In addition to the advantage of energy-saving, controlling ORP at −250 mV can also prevent more corrosion reactions from possibly being caused by other microorganisms in the continuous rising of ORP.

Effect of controlled extracellular oxidation–reduction potential on microbial metabolism and proteolysis in buckwheat sourdough

The aim of this study was to keep constant the extracellular oxidation–reduction potential (ORP) and to observe the microbial activity changes in gluten-free (GF) sourdough fermentations with lactic acid bacteria (Weissella cibaria, Pediococcus pentosaceus and coculture of both microorganisms). ORP (Eh7) was held constant at ca. +350 and −300 mV by gas sparging with air and N2/H2, respectively, to achieve oxidizing or reducing conditions during buckwheat sourdough fermentations. Microbial metabolism, free thiols, proteolysis and volatile compounds were monitored. Oxidizing conditions increased the acidification rate of W. cibaria and mixed culture (mix), which contains P. pentosaceus and W. cibaria. Reducing conditions exhibited a slow acidification rate and low microbial cell density upon fermentation. Oxidizing conditions changed lactic to acetic acid ratio of W. cibaria and mix culture from 7.9 ± 1.3 and 16.0 ± 0.6 (control conditions) to 0.5 ± 0.1 and 1.2 ± 0.2 (oxidizing conditions). A release of glucose and fructose was observed by W. cibaria and P. pentosaceus under oxidizing conditions. Free thiols content was increased by reducing conditions in fermentations with P. pentosaceus. Free amino nitrogen and free amino acid content were highly increased by reducing conditions in fermentations with W. cibaria. Free amino acid release was mainly influenced by low ORP and low pH values. Extracellular redox potential changes exhibited profile modifications of volatile compounds. Oxidizing conditions promoted a higher variety in volatile compounds as compared to the profile obtained under reducing conditions. It has been demonstrated that the extracellular ORP control has an influence on the microbial activity in buckwheat sourdoughs. Oxidizing and reducing conditions can influence the microbial activity differently and thus the final quality of GF sourdough. This is a new alternative approach for GF sourdough production and it could provide an improvement of raw materials, which can be used for GF bread production.

A technique to determine nitrogen removal rates in systems performing simultaneous nitrification and denitrification

This paper reports on a possible technique to determine specific nitrification and denitrification rates (SNR and SDNR) in an oxidation-reduction potential (ORP) controlled, intermittent aeration (IA) tank, in which simultaneous nitrification and denitrification (SND) occurred. In addition, SNRs in a three-stage Bardenpho aerobic zone and SDNRs in its anoxic zone were determined. This research was done at bench scale. The technique involves a steady-state run and two additional transient-state tests (created by either ammonia or nitrate shock loading). The rates obtained, using this technique, are the maximum rates possible in a continuous process under certain, improvised conditions. The technique is extremely flexible and generates data relating the rate to substrate concentration in one steady-state run. Data analysis was performed using the integral method; an excellent agreement between predicted and experimental data was found. Zero-order kinetics could describe nitrification in an ammonia concentration range of 1–30 mg/L and denitrification in a nitrate concentration range of 10–30 mg/L. The SNRs in the intermittently aerated, complete-mix (IACM) tank (0.39–1.69 mg g–1 h–1) were considerably lower than those in the 3-stage Bardenpho aerobic zone (3.4–3.81 mg g–1 h–1) due mainly to imposed dissolved oxygen limitations. The SDNRs in the IACM tank were in a range of 0.16–1.26 mg g–1 h–1, which were also considerably lower than that in the 3-stage Bardenpho anoxic zone (2.0–2.5 mg g–1 h–1). Key words: acetate, denitrification, intermittent aeration, kinetics, methanol, nitrification, ORP control, simultaneous nitrification and denitrification.

Determination of chlorine demand in water and wastewater chlorination by oxidation-reduction potential

Chlorination is the most practical way for the destruction of pathogenic and other harmful organisms in water and wastewater treatment plants. However, highly erratic concentrations of ammonia is contained in most water and wastewater treatment plants, which will react to chlorine and seriously alter the required chlorine dosages in the control of chlorination. The conventional control of chlorine dosage is widely practical throughout the batch breakpoint chlorination test in the laboratory, which is not feasible for the requirement of real-time regulation of the chlorine demands. In this study, a simple automatic oxidation-reduction potential (ORP) titration system was developed for on-line determination of the chlorine demand. The experimental results showed that different decrease tendencies on ORP slope profiles were found to correlate to the ammonia concentrations in samples. In addition, the required chlorine demands were found to correlate to ammonia concentrations with a linear relationship. The ORP control strategy was, therefore, developed for on-line determination of the chlorine demands. Applying this ORP control strategy, the required chlorine demands were precisely predicted, and good disinfection efficiency was obtained in the wastewater chlorination experiments.

Fermentation of a low VFA wastewater in an activated primary tank

A low volatile fatty acid wastewater from a Barcelona residential area was prefermented in a laboratory-scale primary clarifier operated as a prefermenter -an activated primary tank. Total suspended solids (TSS), oxidation-reduction potential (ORP) and temperature were measured in the prefermenter. Influent and effluent were characterised through chemical oxygen demand (COD), soluble COD, volatile fatty acids (VFA), VFA potential, soluble PO4-P, NH4-N, pH and alkalinity. Solids retention times (SRT) of 5 d and 10 d were tested. Best results were obtained for the 5 d SRT with the prefermenter covered for better temperature and ORP control. For these conditions, COD solubilisation was measured as 22 mg COD/l, 66 mg COD/g influent particulate COD, or 91 mg COD/g influent VSS. VFA-formation was measured as 34 mg VFA-COD/l, 142 mg VFA-COD/g influent VSS, or 77 mg VFA-COD/g influent COD. These values indicate remarkable solubilisation and fermentation in the prefermenter. The VFA/PO4-P ratio was improved from 0.9 to 5.5 mg VFA-COD/mg PO4-P, but did not approach the recommended value for biological P removal (20 mg/mg). VFA production could not reach the influent VFA-potential either (110 mg VFA-COD/l) and VFA-potential was lower in effluent than in influent. With a 5 d SRT and the prefermenter uncovered, a small VFA formation and no solubilisation were observed. This was interpreted as the VFA being formed from the influent soluble COD. With a 10 d SRT, a very low ORP was measured. Neither solubilisation nor VFA production were detected in the prefermenter. Concurrent acidogenic fermentation and methanogenesis are compatible with these results. P and N solubilisation was low or moderate in the prefermenter over all periods, and increased with increasing SRT and TSS, and decreasing ORP, and pH and alkalinity were quite stable, due to the high influent alkalinity and the moderate VFA formation and N solubilisation. WaterSA Vol.28(1) 2002: 89-98

EVALUATION OF ENHANCED MIXING AND ORP CONTROL FOR WASTEWATER DISINFECTION

EVALUATION OF ENHANCED MIXING AND ORP CONTROL FOR WASTEWATER DISINFECTIONA wastewater disinfection system utilizing oxidation-reduction potential (ORP) control and enhanced mixing sodium hypochlorite chemical feed was evaluated. The principal objective of the testing was to reduce effluent total residual chlorine (TRC) concentrations while not compromising compliance with effluent fecal coliform concentrations. The system was evaluated by comparison of effluent fecal...Author(s)Timothy J. GroningerGuy A. ApicellaEric DelvaLuis CarrioSourceProceedings of the Water Environment FederationSubjectSession 38 - Disinfection/Innovative Technology Forum: Hot Topics in DisinfectionDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2002ISSN1938-6478SICI1938-6478(20020101)2002:14L.595;1-DOI10.2175/193864702784248133Volume / Issue2002 / 14Content sourceWEFTECFirst / last page(s)595 - 627Copyright2002Word count156

PH and Oxidation–Reduction Potential Control Strategy for Optimization of Nitrogen Removal in an Alternating Aerobic–Anoxic System

An alternating aerobic and anoxic (AAA) system is a continuous-flow, activated-sludge process in which the environmental conditions necessary to meet the specific requirements for aerobic nitrification and anoxic denitrification are created. Because of stricter regulations on wastewater effluent and concerns on energy consumption, the process control of the system is now becoming more important. A bench-scale AAA system with different fixed aeration ratios was operated for more than 8 months to evaluate effects of the total cycle time and aeration ratio on the system performance and to develop a feasible control scheme. With supplemental organic addition, the system shows removal efficiencies of 85 to 90% and 78 to 82% for chemical oxygen demand and total nitrogen, respectively. The oxidation-reduction potential (ORP) and pH profiles indicate that the aerobic cycle can be controlled by a control point (ammonia valley) on the pH profile indicating the end of nitrification and the anoxic cycle controlled by another point (nitrate knee) on the ORP profile signifying the end of denitrification. Thus, a dual control strategy with the pH and ORP control points was used for terminating aerobic-anoxic and initiating anoxic-aerobic cycles in an AAA system. The performance of the online control system is excellent, with a significant energy saving (average aeration ratio, fa = 0.23) as compared to the fixed time systems (fa = 0.33 to approximately 0.5).