Reduction Potential Measurements Research Articles

Infiltration of secondary treated wastewater into an oxic aquifer: Hydrochemical insights from a large-scale sand tank experiment

To mitigate groundwater level decline, managed aquifer recharge (MAR) with secondary treated wastewater (STWW) is increasingly considered and implemented. However, the effectiveness and potential risks of such systems need evaluation prior to implementation. In this study, we present a large-scale sand tank experiment to analyse processes related to the infiltration of real STWW through the vadose zone and subsequent mixing with oxic native groundwater. The varying composition of STWW from 15 infiltration cycles over six months of operation and the retention times were the main drivers of the observed processes, which were characterized by a wide range of analytical techniques such as in situ high-resolution oxidation–reduction potential (ORP) measurements, closed mass balances of solutes, characterization of dissolved organic carbon (DOC), stable nitrate isotopes analysis, as well as numerical flow and transport modelling. Depending on the composition and infiltration rates of the STWW, both nitrification and denitrification could be observed, even simultaneously at different locations in the tank. Furthermore, due to the variability of the real STWW we observed enhanced arsenic mobilisation during times of elevated phosphate concentrations of the infiltrating STWW. Additionally, uranium was mobilised in our experimental system via carbonate mineral dissolution caused by the infiltrating STWW which was undersaturated of calcite for all infiltration cycles. Overall, our results showed the importance of conducting studies with waters of complex matrix, such as real STWW, and considering mixing with groundwater to assess the full range of possible processes encountered at MAR field sites.

Predicting leachate impact on groundwater using electrical conductivity and oxidation–reduction potential measurements: An empirical and theoretical approach

This study developed innovative predictive models of groundwater pollution using in situ electrical conductivity (EC) and oxidation–reduction potential (ORP) measurements at livestock carcass burial sites. Combined electrode analysis (EC and ORP) and machine learning techniques efficiently and accurately distinguished between leachate and background groundwater. Two models—empirical and theoretical—were constructed based on a supervised classification framework. The empirical model constructs a classifier with high accuracy, sensitivity, and specificity, utilizing the comprehensive in situ EC and ORP measurements. The theoretical model with only two end members achieves comparable performance by simulating the leachate–groundwater interactions using a geochemical mixing model. Besides enhancing the early detection capabilities, our approach considerably reduces the reliance on extensive hydrochemical analyses, thus streamlining the monitoring process. Moreover, the use of field parameters was found to proactively identify potential pollution incidents, enhancing the efficiency of groundwater monitoring strategies. Our approach is applicable to various waste disposal sites, indicating its extensive potential for environmental monitoring and management.

Analysis of the electron transfer pathway in small laccase by EPR and UV–vis spectroscopy coupled with redox titration

Bacterial small laccases (SLAC) are promising industrial biocatalysts due to their ability to oxidize a broad range of substrates with exceptional thermostability and tolerance for alkaline pH. Electron transfer between substrate, copper centers, and O2 is one of the key steps in the catalytic turnover of SLAC. However, limited research has been conducted on the electron transfer pathway of SLAC and SLAC-catalyzed reactions, hindering further engineering of SLAC to produce tunable biocatalysts for novel applications. Herein, the combinational use of electron paramagnetic resonance (EPR) and ultraviolet–visible (UV–vis) spectroscopic methods coupled with redox titration were employed to monitor the electron transfer processes and obtain further insights into the electron transfer pathway in SLAC. The reduction potentials for type 1 copper (T1Cu), type 2 copper (T2Cu) and type 3 copper (T3Cu) were determined to be 367 ± 2 mV, 378 ± 5 mV and 403 ± 2 mV, respectively. Moreover, the reduction potential of a selected substrate of SLAC, hydroquinone (HQ), was determined to be 288 mV using cyclic voltammetry (CV). In this way, an electron transfer pathway was identified based on the reduction potentials. Specifically, electrons are transferred from HQ to T1Cu, then to T2Cu and T3Cu, and finally to O2. Furthermore, superhyperfine splitting observed via EPR during redox titration indicated a modification in the covalency of T2Cu upon electron uptake, suggesting a conformational alteration in the protein environment surrounding the copper sites, which could potentially influence the reduction potential of the copper sites during catalytic processes. The results presented here not only provide a comprehensive method for analyzing the electron transfer pathway in metalloenzymes through reduction potential measurements, but also offer valuable insights for further engineering and directed evolution studies of SLAC in the aim for biotechnological and industrial applications.

Abiotic dechlorination in the presence of ferrous minerals

Laboratory batch experiments were performed to assess the reduction of trichloroethene (TCE) and oxygen via natural ferrous minerals. TCE reduction under anoxic conditions was measured via the generation of reduced gases, while oxygen reduction via the generation of hydroxyl radicals was measured as a surrogate for potential TCE oxidation. Results showed that TCE reduction under anoxic conditions was observed for ankerite, siderite, and illite, but not for biotite; acetylene was the primary identified dechlorination product. With the exception of biotite, first-order dechlorination rate constants increased with increasing ferrous content of the mineral, with rate constants ranging from 3.1 × 10−8 to 4.8 10−7 L g−1 d−1. Measured reduction potentials (mV vs SHE) ranged from −104 for illite to +84 for biotite. When normalizing measured first-order dechlorination rate constants to the estimated ferrous iron mineral specific surface area (where surface area was based on nitrogen adsorption analysis of the minerals), TCE dechlorination rate constants increased with increasing reduction potentials. Under oxic conditions, hydroxyl radicals were generated with each of the four minerals. However, mineral activity showed no readily apparent correlation to ferrous content or mineral surface area. In terms of TCE and oxygen reduced per mole of ferrous iron initially present in each mineral, illite was the most reactive of the four minerals. Together, these results suggest that several ferrous minerals may contribute to abiotic dechlorination in the natural environment, and (at least for TCE reduction under anoxic conditions) measurement of ferrous mineral content and reduction potential may serve as useful tools for estimating TCE first-order abiotic dechlorination rate constants.

Mononuclear and Dinuclear Copper Complexes of Tridentate Redox-active Ligands with Tunable H-bonding Donors: Structure, Spectroscopy and H+ /e- Reactivity.

In this research article, we describe the synthesis and characterization of mononuclear and dinuclear Cu complexes bound by a family of tridentate redox-active ligands with tunable H-bonding donors. The mononuclear Cu-anion complexes were oxidized to the corresponding "high-valent" intermediates by oxidation of the redox-active ligand. These species were capable of oxidizing phenols with weak O-H bonds via H-atom abstraction. Thermodynamic analysis of the H-atom abstractions, which included reduction potential measurements, pKa determination and kinetic studies, revealed that modification of the anion coordinated to the Cu and changes in the H-bonding donor did not lead to major differences in the reactivity of the "high-valent" CuY complexes (Y: hydroxide, phenolate and acetate), which indicated that the tridentate ligand scaffold acts as the H+ and e- acceptor.

In-situ biochemical process monitoring and spatial variation of micro-environmental condition in constructed wetland

The purpose of research was to study spatial micro-environmental condition variation in rhizosphere of uniform size root zone media of horizontal flow constructed wetland for pH, temperature, dissolved oxygen and oxidation reduction potential using in situ electrode based measurement system and evaluate oxidation reduction potential for process monitoring and design application. Micro-environmental conditions and their interactions within the microcosm planted with Vetiveria zizanioides was studied using design of experiment methodology. Spatial variation of oxidation reduction potential was found to be in range of −72 mV to −172 mV, pH in range of 7.0 to 7.8 and temperature variation from 25.6°C to 31.8°C within the microcosm. Statistical validation using general linear model indicates only organic loading is the significant factor contributing for variation of all micro-environmental parameters. The results highlight in situ measurement of Oxidation reduction potential can be used as a single representative parameter for monitoring and determine performance of constructed wetland.

Predicting Abiotic Reduction Rates Using Cryogenically Collected Soil Cores and Mediated Reduction Potential Measurements

Abiotic reduction of contaminants in iron-based laboratory model systems has been studied extensively, but the resulting understanding is not sufficient to allow prediction of reaction rates under ...

Prototyping kinase inhibitor-cytotoxin anticancer mutual prodrugs activated by tumour hypoxia: A chemical proof of concept study

Amide- and ester-linked kinase inhibitor-cytotoxin conjugates were rationally designed and synthesised as prototype hypoxia-activated anticancer mutual prodrugs. Chemical reduction of an aryl nitro trigger moiety was shown to initiate a spontaneous cyclisation/fragmentation reaction that simultaneously released the kinase inhibitor semaxanib (SU5416) and the amine- or alcohol-linked cytotoxin from the prodrugs. Preliminary cell testing and reduction potential measurements support optimisation of the compounds towards tumour-selective mutual prodrugs.

Monitoring the Enzymatic Oxidation of Xenobiotics by Hydrogen Peroxide through Oxidation–Reduction Potential Measurements

In this work, three xenobiotics (orange II, phenol, and bisphenol A) were oxidized by hydrogen peroxide in the presence of a horseradish peroxidase (HRP) using a fed-batch system. During the experiments, the oxidation–reduction potential (ORP) of the reaction mixture was measured continuously. Results demonstrate that ORP values only increased when both substrates of the enzyme (hydrogen peroxide and the target compound) were present in the reaction mixture. For all of the tested pollutants, the continuous addition of hydrogen peroxide caused an increase in ORP values. When the reducing substrate was depleted, the addition of an excess of hydrogen peroxide caused a decrease of ORP values. The time at which ORP reached a maximum represented the end of the oxidation process. This maximum could be easily detected by means of the derivative of ORP as a function of time. To extend the application of the developed technique, the enzymatic oxidation of a binary mixture of BPA and OII was also followed using ORP measurements. Results were similar to those observed with only one reducing substrate. This work demonstrates that ORP measurements can be useful to maximize hydrogen peroxide efficiency through the controlled addition of the oxidant during the oxidation of OII, phenol, and BPA catalyzed by HRP. This approach allows a minimization of time and process costs since the reaction end-point can be easily detected on a real-time basis.

Detection of drinking water contamination event with Mahalanobis distance method, using on-line monitoring sensors and manual measurement data

Abstract Concerns about drinking water (DW) quality contamination during water distribution raise a need for real-time monitoring and rapid contamination detection. Early warning systems (EWS) are a potential solution. The EWS consist of multiple conventional sensors that provide the real-time measurements and algorithms that allow the recognizing of contamination events from normal operating conditions. In most cases, these algorithms have been established with artificial data, while data from real and biological contamination events are limited. The goal of the study was the event detection performance of the Mahalanobis distance method in combination with on-line DW quality monitoring sensors and manual measurements of grab samples for potential DW biological contamination scenarios. In this study three contamination scenarios were simulated in a pilot-scale DW distribution system: untreated river water, groundwater and wastewater intrusion, which represent realistic contamination scenarios and imply biological contamination. Temperature, electrical conductivity (EC), total organic carbon (TOC), chlorine ion (Cl-), oxidation–reduction potential (ORP), pH sensors and turbidity measurements were used as on-line sensors and for manual measurements. Novel adenosine-triphosphate and flow cytometric measurements were used for biological water quality evaluation. The results showed contamination detection probability from 56% to 89%, where the best performance was obtained with manual measurements. The probability of false alarm was 5–6% both for on-line and manual measurements. The Mahalanobis distance method with DW quality sensors has a good potential to be applied in EWS. However, the sustainability of the on-line measurement system and/or the detection algorithm should be improved.

Using aerated gravel-packed contact bed and constructed wetland system for polluted river water purification: A case study in Taiwan

Summary The Ju-Liao Stream is one of the most contaminated streams in Kaohsiung City, Taiwan. A constructed wetland (CW) system was built in 2010 for polluted stream water purification and ecosystem improvement. An aerated gravel-packed contact bed (CB) system was built in 2011 and part of the stream water was treated by the CB before discharging to the CW. The influent rates of the CW and CB were approximately 5570 and 900 m3/d, respectively. The CW contained one free-water surface basin planted with emergent wetland plants, followed by the plug-flow channel-shaped free-water surface basin planted with emergent and floating wetland plants. The mean measured hydraulic loading rate (HLR), hydraulic retention time (HRT), water depth, and total volume of wetland system were 1.7 m/d, 0.68 d, 0.7 m, and 4400 m3, respectively. The aeration zone of the CB system had a dimension of 24 m (L) × 8 m (W) × 3 m (H), which was filled with gravels (average diameter = 5 cm) with a porosity of 0.4, and the aeration rate was 7.8 m3/min. Results show that the CB system was able to remove 69% of suspended solid (SS), 86% of biochemical oxygen demand (BOD), and 58% of total nitrogen (TN). Up to 82% of BOD and 27% of TN could be removed in the CW system. Removal efficiency of SS was affected by the growth of chlorophyll a in the CW system due to the growth of algae. The observed first-order decay rates (k) for BOD and TN in CB were 9.3 and 4.2 1/d, and the k values for BOD and TN removal in CW were 2.5 and 0.45 1/d. The high pollutant removal efficiencies in the CB system indicate that the system could enhance the organic and nutrient removal through the biological processes effectively. Sediments contained high total organic matter (1.9–4.5%), sediment total nitrogen (6.4–10.1 g/kg), sediment total phosphorus (0.59–0.94 g/kg), and sediment oxygen demand (0.9–4.1 g O2/m2 d). The organic and nutrient-abundant sediments resulted in reduced conditions (oxidation–reduction potential measurements

Aqueous Phase Synthesis of CuIn Alloy Nanoparticles and Its Application for CIGS Solar Cell

Among various low cost solar cells with high efficiency, CIGS (Cu(In,Ga)Se2) type solar cell shows attractive performances. These CIGS type solar cell is synthesized by gas phase method or liquid phase reduction method in organic solvents. However, in the case of former, productivity is relatively low, since vaporizing temperature of three or more elements is extremely different, which read the large amount of waste of resources. On the other hand, in the case of later, synthesis costs become increase because of the use of organic solvents. Thus, to decreasing the cost of CIGS type solar cell, synthesis method with high recovery rate and without the using of organic solvents is required.Until now, we reported that the synthesis of uniform and well crystallized alloy nanoparticles, such as Pd20Te7 and Bi2Te3 by restrict controlling the homogenization of metallic complexes in the aqueous solution under room temperature [1]. In this method, reduction rate of the metal species can be controlled under the room temperature, nevertheless ternary, or more, alloy nano materials with uniform and well crystallized structure was not synthesized until now.Therefore, in this study, CI nanoparticles were synthesized by obeying the calculation results and reduction potential measurements. CIS semiconductor was tried to synthesize through selenided reaction of CI nanoparticles synthesized. Solar cell ability was also investigated.Metallic complexes in the aqueous solution was restricted to homogenized species by utilizing the theoretical calculation method using the critical stability constants. Detailed calculation procedure was summarized in Ref. 1. Amine-based and/or carboxyl-based complexing reagent, were used for the complex reagents. Reduction potential of Cu (and/or In) complexes was measured, and synthesized materials were analyzed by XRD.Calculation was performed for various system, such as the Cu-NO3-OH-glycine system (dissolution of Cu(NO3)2 and glycine). By obeying the calculation results and also electrochemical potential measurement, various copper complexes was successfully restricted to single species, such as [(Cu2+)(Gly)2], at the pH range over 10, and relationship between stability constants of complex reagents and reduction potential were summarized. As a results, CuIn nanoparticles can be successfully synthesized.CuInSe semiconductor materials were also synthesized by gas phase selenided reaction of the CuIn thin film on the substrate. XRD mesurments shows that synthesized materials were single phase of CuInSe alloy. Synthesized CuInSe thin film on the substrate shows the voltage under the irradiation of light. Thus, by using this easy methods, solar cell can be constructed.This work was supported by the Grant-in-Aid for Challenging Exploratory Research (No. 25550085).

Experimental and theoretical spectroscopic and electronic properties enriched with NBO analysis for 1-methyl-3-nitropyrazole and 1-methyl-5-nitropyrazole

Both experimental and calculated spectral and electronic properties of two isomers 1-methyl-3-nitropyrazole and 1-methyl-5-nitropyrazole have been demonstrated and discussed in details based on normal mode analysis. The fully anharmonic infrared spectra with calculated anharmonic intensities for fundamental bands, overtones and combination bands were also reported. The stability of title molecules arising from hyper conjugative interaction have been demonstrated using natural bond orbital (NBO) analysis. Electron affinities clearly point that 1-methyl-5-nitropyrazole should be much more susceptible to reduction process than 1-methyl-3-nitropyrazole what has been experimentally confirmed by measurement of reduction potential. For 1-methyl-5-nitropyrazole, unambiguous assignment of values of proton and carbon chemical shifts to appropriate protons and carbons has been made thanks to full analysis of 1H and 13C NMR spectra and two dimensional (2D) 1H1H and 1H13C NMR COSY spectroscopy.

Utilization of fruit by-products for organic reducing agent in indigo dyeing

This study aimed to investigate the efficacy of banana peel extract as a possible substitute for the environmentally unfavorable sodium dithionite in cellulosic fiber dyeing with indigo. Antioxidant activity and total sugar content of the banana peel extract were measured. Composition of the extract was investigated by GC/MS analysis. Its reducing power for synthetic indigo was evaluated by reduction potential measurements and dyeing tests. It was shown that the studied extract could be applied successfully in the reduction of indigo in spite of their lower reducing power when compared with that of sodium dithionite. In dyeing study, sodium dithionite showed its superiority in term of reducing power over the studied extract but the studied extract was superior stability of reduction to sodium dithionite. So, it can be concluded that banana peel extract could be a biodegradable and sustainable alternative to sodium dithionite as a reducing agent in indigo dyeing processes.

Electron Transfer between Iron Minerals and Quinones: Estimating the Reduction Potential of the Fe(II)-Goethite Surface from AQDS Speciation

Redox reactions at iron mineral surfaces play an important role in controlling biogeochemical processes of natural porous media such as sediments, soils and aquifers, especially in the presence of recurrent variations in redox conditions. Ferrous iron associated with iron mineral phases forms highly reactive species and is regarded as a key factor in determining pathways, rates, and extent of chemically and microbially driven electron transfer processes across the iron mineral-water interface. Due to their transient nature and heterogeneity a detailed characterization of such surface bound Fe(II) species in terms of redox potential is still missing. To this end, we used the nonsorbing anthraquinone-2,6-disulfonate (AQDS) as a redox probe and studied the thermodynamics of its redox reactions in heterogeneous iron systems, namely goethite-Fe(II). Our results provide a thermodynamic basis for and are consistent with earlier observations on the ability of AQDS to "shuttle" electrons between microbes and iron oxide minerals. On the basis of equilibrium AQDS speciation we reported for the first time robust reduction potential measurements of reactive iron species present at goethite in aqueous systems (EH,Fe-GT ≈ -170 mV). Due to the high redox buffer intensity of heterogeneous mixed valent iron systems, this value might be characteristic for many iron-reducing environments in the subsurface at circumneutral pH. Our results corroborate the picture of a dynamic remodelling of Fe(II)/Fe(III) surface sites at goethite in response to oxidation/reduction events. As quinones play an essential role in the electron transport systems of microbes, the proposed method can be considered as a biomimetic approach to determine "effective" biogeochemical reduction potentials in heterogeneous iron systems.

The mechanism of substrate inhibition in human indoleamine 2,3-dioxygenase.

Indoleamine 2,3-dioxygenase catalyzes the O2-dependent oxidation of l-tryptophan (l-Trp) to N-formylkynurenine (NFK) as part of the kynurenine pathway. Inhibition of enzyme activity at high l-Trp concentrations was first noted more than 30 years ago, but the mechanism of inhibition has not been established. Using a combination of kinetic and reduction potential measurements, we present evidence showing that inhibition of enzyme activity in human indoleamine 2,3-dioxygenase (hIDO) and a number of site-directed variants during turnover with l-tryptophan (l-Trp) can be accounted for by the sequential, ordered binding of O2 and l-Trp. Analysis of the data shows that at low concentrations of l-Trp, O2 binds first followed by the binding of l-Trp; at higher concentrations of l-Trp, the order of binding is reversed. In addition, we show that the heme reduction potential (Em0) has a regulatory role in controlling the overall rate of catalysis (and hence the extent of inhibition) because there is a quantifiable correlation between Em0 (that increases in the presence of l-Trp) and the rate constant for O2 binding. This means that the initial formation of ferric superoxide (Fe3+–O2•–) from Fe2+-O2 becomes thermodynamically less favorable as substrate binds, and we propose that it is the slowing down of this oxidation step at higher concentrations of substrate that is the origin of the inhibition. In contrast, we show that regeneration of the ferrous enzyme (and formation of NFK) in the final step of the mechanism, which formally requires reduction of the heme, is facilitated by the higher reduction potential in the substrate-bound enzyme and the two constants (kcat and Em0) are shown also to be correlated. Thus, the overall catalytic activity is balanced between the equal and opposite dependencies of the initial and final steps of the mechanism on the heme reduction potential. This tuning of the reduction potential provides a simple mechanism for regulation of the reactivity, which may be used more widely across this family of enzymes.

Evidence for the Active Species Involved in the Photodegradation Process of Methyl Orange on TiO2

Active species such as holes, electrons, hydroxyl radicals (•OH), and superoxide radicals (O2•–) involved in the photodegradation process of methyl orange (MO) over TiO2 photocatalyst were detected by several techniques. Using different types of active species scavengers, the results showed that the MO oxidation was driven mainly by the participation of O2•–, holes and •OH radicals. Characterized by the liquid chromatography/mass spectrometry, the transversion of the degradation products with the light irradiation time was first analyzed. Combined with the measurement of oxidation reduction potential, dissolved oxygen, conductivity, and pH values, the degradation process of MO on TiO2 under the effect of the active species was revealed. This was the first time that electrodes were introduced to track the degradation process in situ, and these parameters would be helpful to explain the degradation processes of other organic pollutants.

Genus-specific and phase-dependent effects of nitrate on a sulfate-reducing bacterial community as revealed by dsrB-based DGGE analyses of wastewater reactors

The biogenic production of hydrogen sulfide is a serious problem associated with wastewater treatment. The aim of this study was to investigate the inhibitory effect of nitrate on the dynamics of sulfate-reducing bacteria (SRB) community in a laboratory-scale wastewater reactor, originating from a denitrifying plant using activated sludge. For this purpose, denaturing gradient gel electrophoresis (DGGE) analysis targeting the dsrB (dissimilatory sulfite reductase) gene was used in combination with chemical analyses and measurement of oxidation and reduction potential (ORP). The reactors were initially dosed with 1.0 and 4.0g/L potassium nitrate and anaerobically incubated for 490h. Addition of 4.0g/L nitrate to the reactor was associated with a prolonged inhibition (over 300h, i.e., 12.5days) of sulfate reduction and this was consistent with a rapid decrease in ORP associated with nitrate depletion. The DGGE analysis revealed that nitrate addition remarkably attenuated a distinct group of dsrB related to Desulfovibrio, whereas other dsrB groups were not influenced. Furthermore, another sulfate reduction by Syntrophobacter in the later stages of the incubation period occurred in both reactors (regardless of the nitrate concentration), suggesting that different SRB groups are associated with sulfate reduction at different stages of the wastewater treatment process.

Effects of Nano Zero-Valent Iron on Oxidation−Reduction Potential

Oxidation-reduction potential (ORP) measurements have been widely used to assess the results of injection of nano zerovalent iron (nZVI) for groundwater remediation, but the significance of these measurements has never been established. Using rotating disk electrodes (RDE) in suspensions of nZVI, we found the electrode response to be highly complex but also a very sensitive probe for a range of fundamentally significant processes. The time dependence of the electrode response reflects both a primary effect (attachment of nZVI onto the electrode surface) and several secondary effects (esp., oxidation of iron and variations in dissolved H2 concentration). At nZVI concentrations above ∼200 mg/L, attachment of nZVI to the electrode is sufficient to give it the electrochemical characteristics of an Fe(0) electrode, making the electrode relatively insensitive to changes in solution chemistry. Lower nZVI concentrations give a proportional response in ORP, but much of this effect is mediated by the secondary effects noted above. Coating the nZVI with natural organic matter (NOM), or the organic polymers used to make stabile suspensions of nZVI, moderates its effect on ORP measurments. Our results provide the basis for interpretating ORP measurements used to characterize the results of injecting nZVI into groundwater.

Treatment of pulp and paper mill wastewater with various molecular weight of polyDADMAC induced flocculation

The flocculation performances of different molecular weight of polydiallyldimethylammonium chloride (polyDADMAC) in the treatment of pulp and paper mill wastewater were studied. The molecular weights used were 8.5×104, 8.8×104, 10.5×104 and 15.7×104g/mol. The flocculation performance test was carried out in jar tests with polyDADMAC dosages ranging from 0.4 to 2.0mgL−1. The test was conducted with rapid mixing at 200rpm for 2min, followed by slow mixing at 40rpm for 10min and a settling time of 5min. The effectiveness of the flocculation was measured based on the reduction of the turbidity, the total suspended solids (TSSs), chemical on demand (COD) reduction and zeta potential measurements. It was found that the flocculation performance of higher molecular weight samples was more efficient compared with that of lower molecular weights. This might be due to the bridging mechanism, which occurred concurrently with the charge neutralization effect during flocculation.