Chemical Oxygen Demand Fractions Research Articles

Application of environmentally friendly technologies for the management of nanofiltration concentrate from landfill leachate

In this study, the treatability of leachate nanofiltration (NF) concentrate using the modified Fenton process was investigated. The modified Fenton process employs an environmentally friendly oxidant (sodium percarbonate, SPC), an environmentally friendly catalyst (Fe2+), and environmentally friendly activators (electrooxidation-ultraviolet, EO-UV). The study aimed at enhancing the biological degradability of leachate NF concentrate and was conducted in two stages. In the first stage, the process variables of the SPC/Fe2+ process were optimized. In the second stage, combined processes were applied under optimum conditions. With the SPC/Fe2+ process under optimum conditions (pH: 5, SPC dose: 10 mM, Fe2+ concentration: 50 mM, reaction time: 60 min, pre-catalyst dosing), removal efficiencies of 53.5%, 47.1%, and 61.6% were obtained for chemical oxygen demand (COD), UV254, and color, respectively. After optimizing the operational parameters of the SPC/Fe2+ process, combined processes of EO/SPC/Fe2+ and UV/SPC/Fe2+ were applied, and higher pollutant removal efficiencies were achieved with the EO/SPC/Fe2+ process. Under optimum conditions, removal efficiencies of 75.3%, 80.5%, and 85.6% were achieved for COD, UV254, and color, respectively. The first-order reaction rate constant was 0.022 1/min for the EO/SPC/Fe2+ process. The biochemical oxygen demand (BOD)/COD, which increased from 0.040 to 0.080 with the SPC/Fe2+ process, reached 0.455 with the EO/SPC/Fe2+ process. Additionally, with the EO/SPC/Fe2+ process, the biologically degradable COD ratio of leachate NF concentrate increased from 16.7% to 83.5%, and the soluble COD fraction increased from 72.7% to 89.5%.

Enhancing anaerobic digestion of dewatered sewage sludge through thermal hydrolysis pretreatment: Performance evaluation and microbial community analysis

This study explored the effectiveness of thermal hydrolysis (TH) in conditioning dewatered sewage sludge (DSS) for enhanced anaerobic digestion (AD). The TH pretreatment employed in this study (30 min at 170°C and 6 bar) significantly improved the bioavailability of DSS. The degree of solubilization varied with the physicochemical characteristics of DSS collected over three seasons: 16.8–24.8% on a volatile solids (VS) basis and 9.4–33.7% on a chemical oxygen demand (COD) basis. Correspondingly, the dissolved fraction of VS in DSS increased by 2.1–3.4-fold, and the soluble fraction of COD rose by 1.4–2.9-fold. The duplicate anaerobic reactors treating the TH-pretreated DSS did not achieve steady-state operation at the intended design organic loading rate (OLR) of 3.8 g VS/L·d, but showed stable performance at an OLR of 3.4 g VS/L·d with significantly higher methane yield (0.26–0.29 L/g VS fed) and VS removal (35–38%) than those reported for untreated DSS and comparable to TH-pretreated DSS. The reactors' microbial community structures changed dynamically as the OLR varied, with shifts in dominance between acetoclastic and hydrogenotrophic methanogens. The results highlight the promising potential of TH-AD process for efficiently treating DSS while emphasizing the importance of optimizing OLR for stable operation.

Nutrients removal by high-rate activated sludge and its effects on the mainstream wastewater treatment

Conventional wastewater treatment technologies often involve energy-intensive processes, creating a need for more sustainable and efficient solutions. The high-rate activated sludge (HRAS) process, characterized by short sludge and hydraulic retention times, demonstrates proficient chemical oxygen demand (COD) removal with minimal oxidation and energy expenditure, positioning it as a promising approach for achieving energy-efficient wastewater treatment.This study addresses the nutrient removal efficiency of a demonstration-scale pilot plant (35 m3·d-1) operating for 497 days. It investigates the correlation between nutrient removal efficiencies, COD fractions, and suspended solids removal in real wastewater, without primary clarification.The process consistently achieves average removal efficiencies: 23% for total Kjeldahl Nitrogen (TKN), 7.3% for N-NH4+, 56% for total phosphorus (TP), and 11% for P-PO43-. The superior TP removal is attributed to the high particulate influent fractions (81%), underscoring the pivotal role of settling efficiency. The HRAS process effectively controls TP peak values, although its influence on TKN peaks is somewhat limited. This underscores HRAS's proficiency in mitigating phosphorus spikes in influent wastewater. In contrast, the lower TKN removal is associated with diminished particulate inlet fractions (46%).Nutrient removal mechanisms in HRAS mirror those of COD, primarily revolving around adsorption and entrapment processes, as opposed to conventional biological pathways. It also highlights the independence of oxidized COD, nitrogen, and phosphorus removal. Furthermore, a comprehensive analysis of the COD/TKN within HRAS effluent unveils the presence of a short-cut nitrification/denitrification process, supplemented by Anammox in the sidestream, as the most suitable pathway for downstream nitrogen removal. This revelation signifies a substantial advancement and positions HRAS as a potential initial stage of a partial nitritation/Anammox (PN/A) process within mainstream wastewater treatment.

Insight into the effect of particulate organic matter on sludge granulation at the low organic load: Sludge characteristics, extracellular polymeric substances and microbial communities response

This paper investigated the effect of particulate organic matter (POM) on sludge granulation under low organic load. The results showed that POM promoted the formation of aerobic granular sludge (AGS) with a chemical oxygen demand (COD) fraction of 25%, and POM also enhanced the sludge settleability and biomass retention. However, when the COD fraction of POM increased to 50% and 75%, the AGS performance deteriorated. The analysis of extracellular polymeric substances revealed that the POM (accounted for ≤ 50% of COD in the influent) suppressed the secretion of extracellular protein. Analysis of the microbial community showed that species diversity was lower in the POM-fed system, with Rhodocyclaceae being the predominant bacteria responsible for carbon source degradation. Additionally, molecular ecological network analysis demonstrated that when the COD fraction of the POM exceeded 50%, the connectivity and modularity between microbial species decreased, which may explain the sludge performance deterioration.

Analysis of particle size distribution of organic carbon for landfill leachate—implications for sustainable treatment

AbstractBACKGROUNDLandfill leachate has a complex composition requiring experimental support to formulate a sustainable treatment strategy. This study utilized the particle size distribution (PSD) of the chemical oxygen demand (COD) content to assess the profile of biodegradable and inert COD fractions; it also emphasized the functions and benefits of ultrafiltration and nanofiltration modules coupled to an activated sludge process. The evaluation profited from the field data of a landfill site in Istanbul, where the leachate was actually treated in a membrane bioreactor (MBR) plant.RESULTSCOD and total nitrogen levels fluctuated between 10 100–31 200 mg L−1 and 1150–2800 mg L−1, respectively. PSD analysis for COD, conducted at two extremes, displayed similar results, where the majority of the COD was observed to accumulate at the low extremity of the particle size, 70–72% below 2 nm. Therefore, direct membrane filtration of leachate yielded low COD removals that were limited to 9% with ultrafiltration and to 31–35% with nanofiltration. COD fractionation indicated a ratio of 5% for the inert COD in leachate. The permeate COD of ultrafiltration in the existing plant was 2000 mg L−1, much higher than the inert fraction ratio, which was further reduced to 266 mg L−1 by nanofiltration.CONCLUSIONPSD analysis was an integral complement of respirometry for establishing the size‐biodegradation relationships of different COD fractions. It located the majority of soluble COD fractions below 0.55 nm, thus implying the necessity of a biological process. PSD also identified the generation of soluble residual metabolic products, indicating that residual COD escaping treatment would be equally significant to the removal potential of the biodegradable substrate. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Simulating the impact of ozonation on biodegradation characteristics of industrial wastewater concentrated with membrane filtration

The biodegradation of raw wastewater for an organized industrial zone has been studied by means of dedicated respirometric and analytical experiments. The experimental results indicated that the investigated industrial wastewater contains mainly the soluble (slowly) hydrolysable fraction of chemical oxygen demand (COD) (58 %) while readily biodegradable and soluble inert fractions were in the order of 19 % and 3 %, respectively. Full-scale dynamic modeling results successfully confirmed the validity of estimated COD fraction and biodegradation kinetics. End of pipe wastewater reuse potential studied with a pilot plant revealed that almost 100 % soluble inert organics could be concentrated in reverse osmosis (RO) reject. Expectedly, the concentration was far above the COD discharge limit of 200 mg/L. Subsequently, the application of specific ozone dose around 7 kg O3/(kg COD·hour) on RO concentrates was not sufficient to secure the discharge limit by itself. However, the ozone oxidation converted 85 % of inert COD into the (soluble) slowly biodegradable organic matter. The modeling studies also showed that biodegradable organic matter generated by ozonation has much lower degradation kinetics compared to mainstream sequencing batch reactor system.

Predictive modeling to determine oxygen and ozone doses applicable to in situ remediation of polluted water bodies

This work shows the results for the first time of calibrating and validating a mathematical model, capable of predicting the amounts of O3 and O2 necessary to reduce pollution levels in a lake based on the chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total nitrogen (TN), total phosphorus (TP) and fecal coliforms (FC) concentrations. The model was designed to treat a natural or artificial lake as though it were an aerated lagoon operating as an idealized continuous flow complete-mix reactor. The O3 yield constant for eliminating the non-biodegradable fraction of COD and for deactivating fecal coliforms were laboratory derived and calibrated with field values. Based on the field parameters, the model accurately predicted a reduction in BOD5, COD, TN, TP and FC of 53%, 51%, 39%, 42% and 98%, respectively. The model proved to be effective in predicting O2 and O3 demand and time of recovery of a polluted water body.

Advanced treatment of dye manufacturing wastewater by electrocoagulation and electro-Fenton processes: Effect on COD fractions, energy consumption, and sludge analysis

This study investigated chemical oxygen demand (COD), color number (CN), and UV254 removal from dye manufacturing wastewater via electrocoagulation (EC) and electro-Fenton (EF) processes. The effects of current density, initial pH, reaction time, and H2O2/COD ratio on the EC and EF processes were evaluated and optimum operating conditions were determined. The effects of EC and EF processes on COD fractions and the specific energy consumption of both processes were evaluated. Sludge analyses were conducted by organic removal to sludge ratio (ORSR) and Fourier Transform Infrared Spectroscopy spectra were assessed for characterization of generated sludge. Optimum operation conditions for the EC process were 21 mA/cm2 current density, 7.3 initial pH, and 25 min reaction time while they were 21 mA/cm2 current density, 3.5 initial pH, 1.25 H2O2/COD ratio, and 35 min reaction time for EF process. Under optimum conditions COD, CN, and UV254 removal efficiencies were 38.5%, 90.1%, and 52.5%, respectively in EC process and 54.8%, 94.2%, and 88.1%, respectively in EF process. Both processes have a positive effect on the increase of biodegradable and soluble COD fractions. Higher ORSR and lower specific energy consumption were provided by the EF process under optimum conditions. The EF process is more effective when pollutant removal efficiencies, ORSR, and specific energy consumption are considered.

COD fractionation and solubility assessment of sonicated waste‐activated sludge

AbstractUltrasonic treatment is adopted as one of the important strategies to accelerate the hydrolysis of waste‐activated sludge (WAS). This study intends to optimize amplitude and time for ultrasonic treatment of WAS using statistically designed experiments that would render a better degree of disintegration, measured in terms of chemical oxygen demand (COD) solubilization. The main and interaction effects of nonlinear regression analysis revealed a significant interaction between amplitude and time over the degree of sludge disintegration. The ultrasonic density of 0.45 W/mL for 30 min favored a 153.84% increase in COD solubilization with a 27.65% degree of sludge disintegration. This condition also favored the minimum specific energy input of 801.58 kJ/g total suspended solids compared to other sonication conditions. Besides, the sludge volume index was reduced by 45% and 26% at the ultrasonic density of 0.45 W/mL for 60 and 30 min, respectively. Microscopic examination of WAS revealed disintegration of bacterial flocs during the ultrasonication process releasing filamentous bacteria with smaller floc sizes. The results from this study indicate that higher ultrasonic density for short time could improve the sludge disintegration with minimum specific energy input.

A New Activated Sludge Model with Membrane Separation-Implications for Sewage and Textile Effluent.

A new model for the activated sludge process with membrane separation is presented, based on the effective filtration size. A new size threshold is imposed by the membrane module. The model structure requires a modified fractionation of the chemical oxygen demand and includes chemical oxygen demand fractions entrapped in the reactor or in the flocs as model components. This way, it offers an accurate mechanistic interpretation of microbial mechanisms taking place in membrane activated sludge systems. Denim processing wastewater was selected for model implementation, which emphasized the significance of entrapped fractions of soluble hydrolysable and soluble inert chemical oxygen demand responsible for better effluent quality, while underlining the shortcomings of existing activated sludge models prescribed for systems with conventional gravity settling. The model also introduced particle size distribution analysis as a new experimental instrument complementing respirometric assessments, for an accurate description of chemical oxygen demand fractions with different biodegradation characteristics in related model evaluations.

Anaerobic hydrolysis of complex substrates in full-scale aerobic granular sludge: enzymatic activity determined in different sludge fractions

Complex substrates, like proteins, carbohydrates, and lipids, are major components of domestic wastewater, and yet their degradation in biofilm-based wastewater treatment technologies, such as aerobic granular sludge (AGS), is not well understood. Hydrolysis is considered the rate-limiting step in the bioconversion of complex substrates, and as such, it will impact the utilization of a large wastewater COD (chemical oxygen demand) fraction by the biofilms or granules. To study the hydrolysis of complex substrates within these types of biomass, this paper investigates the anaerobic activity of major hydrolytic enzymes in the different sludge fractions of a full-scale AGS reactor. Chromogenic substrates were used under fully mixed anaerobic conditions to determine lipase, protease, α-glucosidase, and β-glucosidase activities in large granules (>1 mm in diameter), small granules (0.2–1 mm), flocculent sludge (0.045–0.2 mm), and bulk liquid. Furthermore, composition and hydrolytic activity of influent wastewater samples were determined. Our results showed an overcapacity of the sludge to hydrolyze wastewater soluble and colloidal polymeric substrates. The highest specific hydrolytic activity was associated with the flocculent sludge fraction (1.5–7.5 times that of large and smaller granules), in agreement with its large available surface area. However, the biomass in the full-scale reactor consisted of 84% large granules, making the large granules account for 55–68% of the total hydrolytic activity potential in the reactor. These observations shine a new light on the contribution of large granules to the conversion of polymeric COD and suggest that large granules can hydrolyze a significant amount of this influent fraction. The anaerobic removal of polymeric soluble and colloidal substrates could clarify the stable granule formation that is observed in full-scale installations, even when those are fed with complex wastewaters.Key points• Large and small granules contain >70% of the hydrolysis potential in an AGS reactor.• Flocculent sludge has high hydrolytic activity but constitutes <10% VS in AGS.• AGS has an overcapacity to hydrolyze complex substrates in domestic wastewater.Graphical abstract

Particle size distribution of chemical oxygen demand in industrial effluents: impact on effective filtration size and modelling of membrane bioreactors

AbstractThis study reviews particle size distribution (PSD) analysis for industrial effluents. Evaluation of available experimental data indicated that the approach started with arbitrary selection of size distribution. Following a pioneering study on pulp and paper effluent, sequential filtration and ultrafiltration has established itself as a prescribed methodology complementing respirometric assessment of chemical oxygen demand (COD) fractionation based on biodegradation characteristics. Results indicated that most industrial effluents exhibited a COD distribution where soluble fractions accounted for the majority of the total COD, with significant implications for the understanding of membrane bioreactor (MBR) systems. Observations on the accumulation of soluble COD in the reactor to levels much higher than the permeate COD paved the way to define an experimental PSD methodology for assessing the effective filtration size for the membrane module. This novel parameter considered in the light of reported PSD analyses showed that a portion of what was conventionally considered soluble COD would be retained by the size barrier of the membrane and recycled back to the reactor. Thus, MBR systems require a new mathematical model structure that would include a modified COD fractionation, account for the retained COD fractions as additional model components and utilize related mass balance relationships in order to yield an accurate mechanistic description of microbial reactions taking place in the system. © 2021 Society of Chemical Industry (SCI).

Critical evaluation of respirometric and physicochemical methods for characterization of municipal wastewater during wet-weather events

Having a reliable influent wastewater characterization is a key factor for designing effective emergency response plans to mitigate the impact of wet-weather events on wastewater treatment plants (WWTPs). This study aims to critically evaluate the application of wastewater characterization methods for fractionating organic matter in influent municipal wastewater during wet-weather events. To this end, sampling campaigns were set up during various wet-weather events at the largest Italian WWTP. The samples were analyzed by physicochemical and respirometric techniques to assess the chemical oxygen demand (COD) fractions. The role of filter pore size and sample pre-treatment in estimating the soluble COD fractions was assessed. Several long-term BOD experiments were performed to measure biodegradable COD fractions, and the reproducibility of the results is demonstrated. Single and multiple-OUR bioassays were conducted to estimate the readily (Ss) and the slowly (Xs) biodegradable fractions. The heterotrophic yield coefficient (YH) was found to be highly influenced by the history of the biomass and the type of substrate consumed, limiting the application of the respirometry tests during wet-weather events. Dilute wastewater confronted the respirometry assays with some practical complications due to inadequate equipment sensitivity and unprecedented oxygen inputs. A comparative analysis of COD fractions showed that a marked divergence might exist between the two fractionation methods during wet-weather events. Finally, an integrated approach is proposed for more reliable wastewater characterization during wet-weather events.

Performance of dynamic anaerobic membrane bioreactor (DAnMBR) with phase separation in treating high strength food processing wastewater

Food processing wastewater (FPW) contains high levels of oil and grease (O&G), especially from factories that produce fast food such as nuggets, sausages, and burger patties from beef, poultry, and fish. Therefore, the feasibility of replacing conventional membranes for the treatment of FPW with low-cost dynamic membranes (DM) as an alternative was investigated in this study. An anaerobic DM bioreactor (DAnMBR) was operated for 90 days to evaluate the treatment performance using real FPW under different organic loading rates (OLR) of 3.5, 5.0, 6.5, and 7.0 g COD (chemical oxygen demand)/Lday. Once the reactor had reached a steady-state of 90% COD removal, the feed to the reactor was supplemented incrementally with FPW from 10% to 90% as COD to allow the methanogenic bacteria to acclimate any potential inhibitory effects from its recalcitrant content. The bioreactor presented a stable performance at OLR 5.0 g COD/Lday with 97.5% removal of COD and reached 20 mg/L total suspended solids (TSS) discharge. A significant correlation between COD fractions removed via acidogenesis and methanogenesis with different OLR was found, indicating that the increase in treatment performance is beneficial to the methanogenic archaea activity. The methane gas production yield achieved a maximum of 0.40 L methane/g CODadded at OLR 3.5 and 5.0 g COD/Lday. The average permeate flux in these studies is around 60 L/m2h. The DM fouled after 57 days (at flux 27.16 L/m2h immediate drop to 2.16 L/m2h) when operated at 3.5 g COD/Lday. After it fouled, the membrane underwent physical cleaning, backwashed in-situ for 5 min, and reused again without any chemical cleaning. The improved filtration resistance is contributed by the occurrence of DM fouling induced by the soluble microbial products (SMP) and extracellular polymeric substances (EPS) release as well as the increased protein/carbohydrate (P/C) ratio in the mixed liquor.

Particle size distribution as a major characteristic of domestic wastewater: implications for the modeling and design of membrane bioreactors

AbstractThis study reviews the evolution of the concept and the methodology of particle size distribution (PSD) analysis for sewage. Evaluation of experimental data indicated that the analytical approach started with an empirical identification of soluble, colloidal and supra‐colloidal organic matter. Then, it evolved into a sequential filtration and ultrafiltration methodology, yielding results useful enough to be an integral complement of respirometric chemical oxygen demand (COD) fractionation based on biodegradation characteristics. Default values could be defined for the distribution of COD fractions in terms of both size and biodegradation characteristics, which practically showed similar profiles, suggesting that PSD of COD could be directly used for model evaluation and design of activated sludge configurations. Size distribution of COD in sewage should be regarded as a prerequisite for activated sludge systems with a membrane module, mainly to assess the fate of COD fractions that would be entrapped and recycled back to the reactor by membrane filtration. © 2020 Society of Chemical Industry

SMP Production in an Anaerobic Submerged Membrane Bioreactor (AnMBR) at Different Organic Loading Rates.

Anaerobic membrane bioreactors (AnMBRs) have demonstrated an excellent capability to treat domestic wastewater. However, biofouling reduces membrane permeability, increasing operational costs and overall energy demand. Soluble microbial products (SMPs) that build up on the membrane surface play a significant role in the biofouling. In this study, the production of SMPs in a 32 L submerged AnMBR operated at three different organic loads (3.0, 4.1 and 1.2 kg chemical oxygen demand (COD)/m3d for phases 1, 2 and 3, respectively) during long-term operation of the reactor (144, 83 and 94 days) were evaluated. The samples were taken from both the permeate and the sludge at three different heights (0.14, 0.44 and 0.75 m). Higher production of SMPs was obtained in phase 2, which was proportional to the membrane fouling. There were no statistically significant differences (p > 0.05) in the SMPs extracted from sludge at different heights among the three phases. In the permeate of phases 1, 2 and 3, the membrane allowed the removal of 56%, 70% and 64% of the SMP concentration in the sludge. SMPs were characterized by molecular weight (MW). A bimodal behavior was obtained, where fractions prevailed with an MW < 1 kDa, associated with SMPs as utilization-associated products (UAPs) caused fouling by the pore-blocking mechanism. The chemical analysis found that, in the SMPs, the unknown COD predominated over the known COD, such as carbohydrates and proteins. These results suggest that further studies in SMP characterization should focus on the unknown COD fraction to understand the membrane fouling in AnMBR systems better.

Anatomy of the organic carbon in an industrial wastewater: Implications of particle size distribution, respirometry and process modelling

This study evaluated the fate of chemical oxygen demand (COD) fractions of an organized industrial district effluent treated with pilot membrane bioreactor (MBR) system. A series of respirometric analyses were performed on raw wastewater together with 450 nm, 100 kDa and 1 kDa filtered samples obtained from particle size distribution (PSD) experiments. The PSD analysis revealed that more than 300 mg/L of the influent COD accumulated in the lowest size range (<2 nm), accounting for 49–52 % of the total COD. The bulk (64 %) of the influent COD consisted of soluble hydrolysable COD (SH1). The hydrolysis rates for SH1 (0.80–1.28 1/day) were slightly below the levels suggested for domestic wastewaters, indicating the presence of inhibitory compounds in industrial wastewaters. The COD removal efficiency of MBR pilot was found as 85 %; however, 43 % of effluent COD (106 mg/L) still included rapidly hydrolysable organics in the size bracket of 5–30 nm. In this respect, the COD fractions for activated sludge process models used for MBR applications require a new-insight to correctly reflect organic matter balances in the treatment system.

Impact of differences in speciation of organic compounds in wastewater from large WWTPs on technological parameters, economic efficiency and modelling of chemically assisted primary sedimentation process

The aim of the study was to supplement the information missing in the literature on the influence of organic compounds speciation (percentage of chemical oxygen demand (COD) fractions, readily biodegradable and non–biodegradable dissolved organic matter; slowly biodegradable and non‒biodegradable insoluble organic matter) in wastewater on chemically assisted primary sedimentation process and its potential impact on the energy and economic balance of the plant. The statistical modelling of the chemically assisted primary sedimentation process using artificial neural networks (ANN) was a novelty. It was also important to check the differences resulting from the use of coagulants, polyelectolites and their doses. For both large wastewater treatment plants (>500,000 people equivalent) located in the various regions of the country in Central Europe only ferric chloride had a positive balance. The addition of polyelectrolyte in the Wroclaw wastewater did not affect the chemically assisted primary sedimentation process but in the Bialystok wastewater it strengthened the process effect. In both plants only doses from 10 to 40 mgFe/dm3 are cost-effective. The results indicate that the addition of polyelectrolyte should be taken into account in this application and was correlated with the amount of colloidal COD fractions in wastewater. The developed ANN models reflected well the effectiveness of COD removal in both large WWTP while the sensitivity analysis of individual ANN models showed differences in the variables affecting the calculation process of both models, despite similar values of parameters characterizing wastewater in both wastewater treatment plants.

Uncertainty and sensitivity analysis for reducing greenhouse gas emissions from wastewater treatment plants.

This paper presents the sensitivity and uncertainty analysis of a plant-wide mathematical model for wastewater treatment plants (WWTPs). The mathematical model assesses direct and indirect (due to the energy consumption) greenhouse gases (GHG) emissions from a WWTP employing a whole-plant approach. The model includes: (i) the kinetic/mass-balance based model regarding nitrogen; (ii) two-step nitrification process; (iii) N2O formation both during nitrification and denitrification (as dissolved and off-gas concentration). Important model factors have been selected by using the Extended-Fourier Amplitude Sensitivity Testing (FAST) global sensitivity analysis method. A scenario analysis has been performed in order to evaluate the uncertainty related to all selected important model factors (scenario 1), important model factors related to the influent features (scenario 2) and important model factors related to the operational conditions (scenario 3). The main objective of this paper was to analyse the key factors and sources of uncertainty at a plant-wide scale influencing the most relevant model outputs: direct and indirect (DIR,CO2eq and IND,CO2eq, respectively), effluent quality index (EQI), chemical oxygen demand (COD) and total nitrogen (TN) effluent concentration (CODOUT and TNOUT, respectively). Sensitivity analysis shows that model factors related to the influent wastewater and primary effluent COD fractionation exhibit a significant impact on direct, indirect and EQI model factors. Uncertainty analysis reveals that outflow TNOUT has the highest uncertainty in terms of relative uncertainty band for scenario 1 and scenario 2. Therefore, uncertainty of influential model factors and influent fractionation factors has a relevant role on total nitrogen prediction. Results of the uncertainty analysis show that the uncertainty of model prediction decreases after fixing stoichiometric/kinetic model factors.

Influence of Operating Parameters on the Fraction of Oil Oxidized During Electrocoagulation of Produced Water

Even though electrocoagulation (EC) is a waste treatment process which separates the pollutants from the bulk to a solid phase, it is often reported that a part of the waste is getting mineralized during EC. The present study aims at finding the best combination of operating parameters which can maximize the part of organic matter removed by an oxidative mechanism during the EC treatment of produced water. It is found that current density and salt concentration strongly influenced the fraction of chemical oxygen demand (COD) oxidized. At optimum operating conditions (current density, 0.75 A/dm2; time, 30 min; initial pH, 9; and salt concentration, 3 g/L), a maximum of about 77% COD was found oxidized from a stable oil-in-water emulsion of concentration 1280 mg/L. The corresponding total COD removal by EC was observed to be 82%. The proposed methodology is very much appropriate in terms of lower footprint for produced water treatment, especially in offshore basins, due to three reasons such as fast operation, lower sludge production, and the supporting electrolyte available in situ. Furthermore, based on the results obtained, a second-order regression model was proposed to predict the responses, viz. COD removal and fraction of COD oxidized. Analysis of variance (ANOVA) studies showed that the model is valid and equipped to predict the responses well, evident from the high R2 value of the model.