Residual Turbidity Research Articles

Simultaneous presence of poly titanium chloride and Fe2O3-Mn2O3 nanocomposite in the enhanced coagulation for high rate As(V) removal from contaminated water

High rate Arsenic (As (V)) removal from contaminated water resources was investigated by simultaneous presence of poly titanium chloride (PTC) and Fe2O3-Mn2O3 nanocomposite in the enhanced coagulation process along with precipitated flocs recirculation. In this study, the synthesis of Fe2O3-Mn2O3 and PTC and their characteristics, the effective parameters in the enhanced coagulation process, including pH, coagulants dosage, initial concentrations of As (V), nanocomposite dosage, as well as the rate of precipitated floc recirculation were tested. According to the FTIR analysis, the prepared PTC coagulant contained −OH, Ti−OH, and TiO bonds, confirming coagulant polymerization. The highest As (V) removal efficiency (99.96 %) by PTC + Fe2O3-Mn2O3 occurred at pH 7, coagulant dose of 20 mg/L, and up to 300 μg/LAs (V) initial concentration. Moreover, the residual turbidity was 4NTU and the residual As (V) was less than 0.1 μg/L. However, in absence of nanocomposite, the residual As (V) was 17.1 μg/L in optimal conditions. The FESEM-EDX analysis confirmed coagulant-nanocomposites combined flocs formation and the presence of Fe, Mn and As elements in flocs. The precipitated flocs recirculation had also a significant effect on reducing the coagulant dosage; moreover, with a 10 % combined flocs recirculation, the consumption of PTC coagulant dosage decreased by 25 %. Therefore, the enhanced coagulation process in the presence of Fe2O3-Mn2O3 nanocomposite along with the precipitated flocs recirculation could be introduced as an effective and efficient process in Arsenic removal from contaminated water.

The role of ballast specific gravity and velocity gradient in ballasted flocculation

This study investigated the concealed interaction between applied velocity gradient (G value) and ballast specific gravity (SG) in ballasted flocculation (BF). The objective was to unravel the participation of applied surface concentration (SC: 0.005 m2L−1–0.02 m2L−1) of high specific gravity ballasts (SG: 2.9–5.57) in BF aggregation phenomenon at varied velocity gradients (G value: 750s−1–1250s−1). Static mixer was used to perform the BF experiments, and aggregated flocs were characterized using charge coupled device (CCD) camera. The results revealed that conventionally adopted velocity gradient (G value: 150s-1 - 300s-1) in BF studies was insufficient for efficient floc development due to inadequate suspension of denser ballasts during mixing. This resulted in poor turbidity removal (< 40 %) and immature slow settling flocs (< 25 mh−1) despite higher ballast consumption. However, appropriate optimization of G value (1250s−1) corresponding to high specific gravity ballast (SG: 5.57) resulted in 99.5 % turbidity removal (residual turbidity: 1NTU) achieved in a shorter settling interval of 30 s consuming significantly less ballast concentration. This expeditious settling phenomenon was also evident in CCD camera observations of the ballasted flocs achieving superficial settling velocity (105mh-1). Therefore, it was concluded that appropriate optimization of the G value corresponding to the pertinent concentration of denser ballasts can exhibit rapid elimination of micropollutants, and superficial sedimentation with efficient material and energy use. This can lead to efficient BF design with a short HRT, compact footprint, and ability to handle highly turbid influent.

The removal of turbid materials from AMD using bentonite clay, Fe or Al salt, MgCO3 and flocculent with varying agitations

Abstract A series of experiments was conducted using 200 mL of acid mine drainage (AMD) collected from Krugersdorp, South Africa, to determine turbid materials removal efficiency of a combination of bentonite clay, Fe or Al salt and MgCO3. The sample was poured into five 500 mL glass beakers using bentonite clay, FeCl3, AlCl3 and MgCO3 dosage respectively. The samples were treated in jar test at rapid and slow mixing, allowed to settle for 1 hour, then the pH, conductivity, total suspended solids (TSS), dissolved oxygen (DO) and oxidation reduction potential (ORP) were measured (exp A). A second and third similar sets of experiments were conducted with a combination of bentonite clay and MgCO3 (flocculent) dosage (exp B), and FeCl3 with slow mixing only (exp C). Experimental results revealed that the pH of treated effluent with bentonite clay does not exhibit significant increasing trend because of insignificant hydrolysis, whereas the pH of samples with FeCl3, AlCl3 and MgCO3 exhibit a slight decreasing trend, showing a low rate of hydrolysis. The DO and ORP of treated effluent does not show a significant changing trend compared to the untreated AMD sample. Residual TSS of the AMD samples treated with a flocculent is lower than the samples treated with bentonite clay, FeCl, AlCl3 and MgCO3. Residual turbidity of the samples with rapid mixing is identical to that of the corresponding samples with slow mixing. TSS removal efficiency of a flocculent is higher compared to other reagents. The results show that synthetic flocculent is an ideal replacement for inorganic coagulants. The scanning electron microscopy (SEM) micrographs exhibit slides with dense-sponge like flocs showing high adsorption capacity.

An Experimental Study on Treatment of Wastewater Utilizing Moringa Oleifera and Vigna Unguiculata Seeds: A Sustainable Approach

Wastewater treatment requires coagulants in a sedimentation-filtration stage for which effective coagulants were needed. Moringa oleifera and Vigna unguiculata shows adequate water-soluble proteins that show active coagulant properties. Jar test analysis shows that chemical coagulant Alum gives optimum dosage at 2ml volumetric dosage while in comparison to that, M. oleifera gives optimum dosage at 4ml volumetric dosage and Vigna unguiculata at 5ml volumetric dosage for collected wastewater. A comparative study shows that both Natural coagulants show active turbidity removing efficiency at a little higher volumetric dosage. For various concentrations from 2%, 4%, and 6%, both natural coagulants have the most soluble required solution effect at 2% concentration, which helps in effective removal of residual turbidity. Preparation of natural coagulants solution is effortless and have fewer environment impacts than chemical coagulant, the usefulness of this natural coagulant will be helpful to meet with eco-friendly treatment and a better sustainable approach.

Enhancement of flocculation and dewaterability of a highly stable activated sludge using a hybrid system of organic coagulants and polyelectrolytes

This study investigates the influence of hybrid coagulation-flocculation system on the flocculation and dewaterability efficiency of a real highly stable activated sludge obtained from the membrane bioreactor tank of a petroleum industry. Two organic coagulants, polyDADMAC (FL 4440) and polyamine (FL 2949), coupled with differently structured polyacrylamides (PAMs) are used. Residual turbidity, Zeta potential (ζ), flocs size, and capillary suction time (CST) are used to assess the impact of the hybrid system on the degree of flocculation and dewaterability of MBR sludge. The study reveals that electrical double layer compression, which lowers the electrostatic repulsion between the particles, contributes to the improvement in flocculation behavior. Addition of FL 4440 and FL 2949 prior to PAM has greatly reduced the turbidity and ζ of the sludge suspension by decreasing the required doses of PAMs from 67 % to 80 % depending on the type of the PAMs used. Addition of FL 2949 and FL 4440 has strong influence on the linear structured PAMs with 71 and 80 % reduction in the required PAM’s dose for the 40 % Charge density (CD) (FO 4490 SSH) and 60 % CD (FO 4690 SSH), respectively followed by slightly and highly branched structured PAMs. Similar observations have been noted for flocs size and dewaterability (CST) measurements of the flocculated MBR sludge. Overall, this study has successfully determined the effect of hybrid coagulation-flocculation on the flocculation performance of MBR sludge.

Removal of titanium dioxide nanoparticles from wastewater using traditional chemical coagulants and chitosan

AbstractAlum and ferric chloride were used individually as coagulants to remove P25 TiO2 nanoparticles (NPs) from a simulated wastewater. Previous studies have addressed the use of alum, polyaluminum chloride, chitosan, and polyaluminum chloride with chitosan for coagulation of NPs. A goal of this study was to reduce chemical usage associated with wastewater treatment by examining the coagulation effectiveness of chitosan in conjunction with alum. To further reduce chemical consumption during coagulation, the initial solution pH was limited to 6 or 8. A range of alum doses removed NPs from pH 8 wastewater to achieve residual turbidity &lt;1 NTU. NP removal from pH 6 solutions produced water with residual turbidity &lt;2 NTU only at lower initial NP concentrations. For pH 8 solutions, ferric chloride produced treated water with residual turbidity &lt;1 NTU but at higher doses than required for alum. While chitosan alone did not significantly reduce turbidity, the use of alum and chitosan together reduced the optimal alum dose by 10% and also reduced alum treatment acidification. Therefore, the use of chitosan in coagulation can potentially reduce chemical usage during water treatment and the energy and water consumption associated with chemical production. Use of alum with low chitosan concentrations produces faster settling floc, which can potentially reduce settling tank volume and produce an effluent containing lower aluminum concentrations.

Effect of rapid-mixing conditions on the evolution of micro-flocs to final aggregates during two-stage alum addition

ABSTRACT In a coagulation-flocculation process, optimal separation of the resultant aggregates plays a decisive role on coagulation performance and provides a lower burden for subsequent treatment units. This separation highly depends on the stability of the micro-flocs formed during the initial, rapid stage of coagulation. In this work, a two-stage addition of aluminium sulphate (alum, Al2(SO4)3) was employed by adding 0.04 and 0.08 mM Al2(SO4)3 at the beginning and the end of rapid mixing, respectively. The coagulation performance and floc characteristics were compared to conventional single addition with the same total coagulant dosage, and the effects of variable rapid-mixing speeds (160–850 rpm) and duration time (10–120 s) were investigated. The results showed that the residual turbidity of two-stage coagulant addition was 85.1% lower than single addition when applied at a mixing speed of 580 rpm and a duration time of 120 s. The underlying coagulation mechanism revealed that the two-step addition more effectively neutralized colloids and formed larger aggregates that settled better and could more easily be removed. Moreover, the aggregates were less firm, which was attributed to different interactions among the micro-flocs, the second addition of Al2(SO4)3 and destabilized colloids. The present work provides data to broaden the window of rapid-mixing environments for more effective coagulation.

Characterization and application of poly-ferric-titanium-silicate-sulfate in disperse and reactive dye wastewaters treatment

A novel coagulant poly-ferric-titanium-silicate-sulfate (PFTS) was synthesized and employed to treat two typical kinds of dye wastewaters—disperse blue and reactive yellow. The results indicated that PFTS with a Si/Fe molar ratio of 0.02 exhibited superior coagulation performance, especially under alkaline condition. The residual turbidity after coagulation by PFTS was only half of that after coagulation by poly-ferric-titanium sulfate (T-PSF). The sludge volume index was also reduced by PFTS compared to T-PSF in reactive dye treatment. Through the structure and morphology investigation of PFTS, it was found that new bonds of Si–O–Fe, Si–O–Ti and Fe–OH (Si–OH) were formed, and multi-branched structures and expanded surface area were generated. Additionally, compared with T-PSF, the floc strength and the floc size were also enhanced by PFTS, which was attributed to the polymerization between polysilicic acid and Fe/Ti which formed multi-branched structures, and finally adsorption and bridging ability of the coagulant was improved. Furthermore, the floc formed in reactive yellow wastewater treatment was larger and looser than that formed in disperse blue wastewater, with poorer strength and recovery ability, which can also interpret the better coagulation efficiency in disperse dye water treatment. From the results of coagulant characterization, zeta potential and flocs properties, it can be inferred that charge neutralization by the positive charged hydrolysate of coagulant was identified as the critical effect in disperse dyes removal, while the sweep and adsorption of metal hydroxyl compound formed during the hydrolysis of coagulants were considered to play a key role in reactive dye removal.

Parametric and kinetic investigations on segregated and mixed textile effluent streams using Moringa oleifera seed powders of different sizes

This study aimed at evaluating the Moringa oleifera (M. oleifera) seed powder for treatment of segregated (dye rich, DR; and starch rich, SR) and mixed wastewater (AM) streams of a textile industry. Two different sizes (<600 μm and <300 μm) of seed powders (coarse powder, CP; fine powder, FP) were prepared and characterized in terms of point of zero charge, swelling ratio, Fourier Transform Infrared Spectroscopy, X-ray diffraction analysis, and zeta potential measurements. The swelling ratio for CP and FP were observed as 38 and 42.6%, respectively. The pHzpc values were found to be varying between 5.5–6 for both powders. The effect of different operational parameters such as dose of coagulant, 1–8 g/L; sedimentation time, 30–360 min; coagulation-flocculation pH, 6–9 was investigated in this study, with respect to turbidity as performance indicator. The chemical oxygen demand (COD) and color measurements were done after the optimization of operational parameters. At optimized pH (DR, 6.5; SR, 7.5; AM, 8.0), the optimum dose of CP and FP were determined as 3, 3, 2 and 3, 2, 1 mg/L for DR, SR, and AM wastewater samples, respectively. With respect to residual turbidity, optimum sedimentation time was observed as 300, 240, 60, 60, 120, and 120 min for DR_CP, DR_FP, SR_CP, SR_FP, AM_CP, AM_FP, respectively. The sedimentation kinetic investigations revealed that turbidity removal follows second-order kinetics for both the studied coagulants. Statistical analysis revealed that CP has the potential of better color and COD removal, as compared to FP.

Comparative Evaluation of Glycine max L. and Alum for Turbid Water Treatment

Disadvantages associated with chemical coagulants and goal of sustainable development have shifted the focus to natural plant-based coagulants. Raw and defatted soybean (Glycine max L.) seed powder, as innovative and eco-friendly coagulant, was appraised in detail for turbid water treatment and compared with alum in this study. Design of experiments was conducted by employing response surface method which lacks in past studies pertaining to plant-based coagulants. Experiments were conducted with lab prepared turbid water with initial turbidity of 200 NTU and wide range of pH (2–10) and dose (20–100 mg/L). Results revealed that raw and defatted soybean gave residual turbidities of 4 and 3 NTU at optimum conditions which were comparable to alum. Analysis of variance (ANOVA) identified that pH was more significant parameter as compared with dose for soybean and alum, while interaction of pH and dose was most significant in case of defatted soybean. Characterization of the coagulants and flocs, by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM), revealed that postulated mechanism of coagulation for plant-based coagulants is adsorption and charge neutralization. Cost of treating 1000 m3 of water by raw and defatted soybean is lower (US$12 and US$3.9 respectively) compared with alum (US$31.2).

Aluminum sludge thickening: Novel helical pipes for aggregation by dual flocculation and thickening by filtration applied to water treatment plants

There are significant challenges associated with sludge treatment in water treatment plants (WTP). Treatment aims to remove water that makes up the sludge, and consists of three consecutive steps: suspension flocculation, thickening and drying. In this study, the flocculation of the sludge was the main objective, and it was evaluated through a novel Helical Tubular Flocculator (HTF) followed by a static thickener. The study explored the mechanisms involved with the flocculation process, by tracing the sludge characteristics, from the study of hydraulic and hydrodynamic parameters performed in HTF units. The sludge used in this study was sampled in settling basins of a conventional WTP with a total solid concentration (TS) of 5 g L−1, due to the dilution with tap water. Regarding the conditioning with flocculant polymers, two mechanisms were evaluated. First, cationic polymer conditioning in a dosage of 15 mg in (gTS)−1. Second, dual flocculation, with the implementation of cationic and anionic polymers at a dosage of 4 mg in (gTS)−1 each one. The studies involving dimensional parameters of the tested HTFs demonstrated that the best configuration of the unit presented 12 m of flexible tubing with an inner diameter of 1.25 cm wrapped in a 10 cm PVC pipe, operating at a flow rate of 3 L min−1. Under these optimal conditions, the dual flocculation mechanism had advantages over single polymer flocculation. As a result, it was possible to reduce, approximately, 50% of the total volume of polymers prepared from the same concentration, maintaining the flocs formation. The application of polymers and the use of this helical hydraulic mixing enabled a compact thickening unit that has had great potential for industrial application. Results showed that the helical flocculator presented residual turbidity in the clarified water, after sedimentation, up to ten times lower (8.5 UNT) than that registered by the mechanical mixing, maintaining similar hydraulic and hydrodynamic patterns. The sludge thickening was evaluated by filtration, after flocculation, through a static thickener constructed. Results showed a high concentration of solids, and it was possible to record concentrations higher than 18%, from the sludge at the initial concentration of 0.5%. The data showed the high performance of the helical flocculator in the treatment of WTP wastes by aggregation with high solids content, as well as the thickening by filtration in the static thickener, and it validated a compact treatment process applicable to sludge.

Using recycled chemical sludge as a coagulant aid in chemical wastewater treatment in Mobarakeh Steel Complex

Coagulation–flocculation is a process commonly applied to treat many types of industrial wastewater. However, chemicals used in a wastewater treatment plant, including coagulants/flocculants, are costly. This study evaluated the feasibility of recycling the chemical sludge of the Mobarakeh Steel Complex (MSC), and using it as a coagulant aid in the process of wastewater treatment. The experiments were conducted in a jar test apparatus in consecutive cycles by adding a fraction of the settled sludge to samples. The response surface methodology (RSM) was employed to design the experiments and optimize the process. The response in the RSM model was residual turbidity, and the factors affecting the response included the sludge recycle ratio and return sludge cycle number. The sludge volume index (SVI) of the chemical sludge was also examined in each cycle of the tests to assess the sludge quality. The results revealed that recycling the sludge reduced the use of chemicals up to 60%. Finally, it was concluded that flocculation sludge could be considered as an alternative to chemicals, without adversely affecting the removal efficiency. Furthermore, SVI results showed that an increase in the number of cycles led to a decrease in SVI in each cycle, resulting in sludge volume reduction, better dewatering, and decreased sludge treatment costs.

Optimization of an electrocoagulation-flotation system for domestic wastewater treatment and reuse

ABSTRACT The risks inherent to the inadequate domestic wastewater disposal, allied to the water growing demand, scarcity, and pollution problems, have highlighted the importance of adopting treatment techniques that not only target the sewage discharge, but also its reuse. For this reason, the objective of this study was to evaluate the best conditions of an electrocoagulation-flotation system for domestic wastewater treatment and urban reuse. To achieve this, an effects study followed by two rotatable central composite experimental designs 2² was performed, considering: agitation, electrical current, electrolysis time, inter-electrodes distance, and initial pH. The electrocoagulation-flotation system was composed of a cylindrical acrylic reactor with a working volume of 1 L, with two aluminium electrodes connected to a direct-current power supply. Results showed that electrical current and electrolysis time were the most influent operational parameters on domestic wastewater treatment in the electrocoagulation-flotation system. The initial pH adjustment was also important due the pH increase tendency observed in the results. The best conditions of agitation, inter-electrodes distance, electrolysis time, electrical current, and initial pH for domestic wastewater treatment and urban reuse were 262.5 rpm, 1 cm, 25 min, 1.65 A, and 6, respectively. Under these conditions, turbidity and colour removals higher than 98% and 92% were reached respectively, as well as residual turbidity lower than 6 NTU and final pH of 8 were achieved, following the Brazilian standards and guidelines for urban reuse. Thus, the electrocoagulation-flotation system studied was effective for domestic wastewater treatment and reuse for urban supply purposes.

The Situation Of Water Treatment Plant In Mosul City

The present paper dealt with the evalution of quantiy and qualtiy of water treatmetn plants WTPs withen Mosul city. According to the total productivity of WTPs the per capita share of water was 785 L/d, and after subtracting the losses and violation upon the water supply network that reaches upto 50% the per capita portion of water becomes 392 L/d. For the quality of water; the study revealed that there are a segnificant effect of the WTPs processes upon the water quality parameters of the product water comparing with the raw water, and the quality of product water is withen the Iraqi dirnking water spicifications regarding to the parameters taken into account withen the study. This study concentric to the turbidity removal by WTPs because these plants are designed to reduce the turbidity of water to acceptable levels withen the Iraqi specification. turbidity of water is out of the specification in 13% of the samplise with different portions through the WTPs, but the highst was at aldanadan and alsaheroon plants. Duncn test revealed that there are a significant different betweent the average of the residual turbidity and between the average of percentage removal of turbidity between WTPs and the worest plant from the residual turbidity are alsaheroon, alghzlani and aldanadan. And the woreste plant from the percent turbidity removal are alaiser aljadeed and alaiser altawsie.

Flocculation Behavior of Borax Clayey Tailings in Mono- and Dual- Flocculant Systems: Effect of Tailings Slurry Characteristics and polyDADMAC Type

The effect of tailings slurry characteristics such as solid ratio and solid particle size both, in mono- and dualflocculant systems, were studied as well as the effect of POLYDADMAC type in dual-flocculant system. Oppositely charged flocculants, a polyacrylamide (PAM)-typed anionic and two poly diallyl-dimethyl-ammonium chloride(polyDADMAC)-typed cationic polymers, were employed for the flocculation. Tailings slurry samples were taken on different dates from the discharge point of Kırka Borax Concentrator. Flocculation performance was characterized by the initial settling rate as well as the residual turbidity of supernatant and the extent of sediment compaction. All tests were performed at the natural pH of the tailings slurry (~pH 9.4) at which borax buffered the suspension. The results showed that an increase in solid load of the tailings slurry results in a dramatic decrease in settling rate of flocculated tailings regardless of flocculant system employed. This can be attributed to the possible change in rheological property of the slurry due to the increasing clay content of the slurry with solid ratio. While the solid ratio has an influence on the settling rate of the flocculated tailings, the amount of slimes determines the optimum dosage of cationic flocculant to obtain clear supernatant in dual-flocculant system. When anionic and cationic flocculants were used in combination, the best synergy was achieved with low weight cationic flocculant. Increasing molecular weight of the cationic flocculant from low to medium resulted in two-fold increase in the required dosage to obtain the same flocculation performance. In dualflocculant system, optimum results were obtained by anionic and cationic flocculant combination at around 0.4 kg/ton and 0.8 kg/ton solid dosages, respectively, indicating 11.7 cm/min of settling rate and 85.7% of transmittance value.

Modeling and optimization of the flocculation process of polydisperse travertine suspension employing an eco-friendly hybrid flocculant

One of the major problems in the stone processing industry is the creation of wastewater with a high degree of residual turbidity and the use of high water volume. Therefore, the treatment of waste water and its reuse is very important in terms of economic and environmental considerations. In the present study, the flocculation performance of hybrid flocculant naturally derived from chitosan and plant was statistically investigated for the clarification of travertine processing wastewater, in terms of the residual turbidity/turbidity removal efficiency and settled sludge volume, containing micron and sub-micron particles with median particle sizes of 9.32 μm and negative surface charges dominating at all pHs that produced a high degree of stability. TOPSIS (technique for order preference by similarity to ideal solution) method by using the Taguchi factorial design is used to optimize the operating variables such as hybrid flocculant dosage, suspension pH, and mixing time to find out the optimum operating conditions optimizing selected quality criteria such as turbidity removal and settled sludge volume. The flocculant dosage affected significant residual turbidity of the suspension as well as the turbidity removal efficiency and the settleable solid volume. A total of 87.90% in the residual turbidity value and 1.67% in the turbidity removal efficiency improvement rate was obtained with the use of TOPSIS-based Taguchi optimization methodology. Another important factor was determined as the suspension pH. The amount of settleable solid increased with the increasing of suspension pH. The residual turbidity value indicated a tendency to increase at first and then decrease with the increasing of suspension pH. A total of 8.15% improvement rate in the residual turbidity value was achieved compared with the values in the literature using hybrid flocculant and multi-response optimization techniques.

Removal of natural organic matter and ammonia from dam water by enhanced coagulation combined with adsorption on powdered composite nano-adsorbent

Abstract Enhanced coagulation and adsorption were investigated in separate and combined processes to alleviate problems created by high levels of NOM (15 mg L−1) and ammonia (2.5 mg L−1 NH4-N) in dam water. Raw water acidification to pH 6.2 with optimised enhanced coagulation in jar tests achieved effective (68%) DOC reduction and satisfactory residual turbidity, aluminium, and colour, however removed only 5% ammonia. Adsorption on the nano-adsorbent (termed ACZ) led to 45% DOC reduction and excellent 58% ammonia removal in 30 min. Concurrent enhanced coagulation and complementary adsorption using only 80 mg L−1 alum and 150 mg L−1 ACZ doses showed high performance with 76% ammonia, 90% DOC, and 95% trihalomethanes formation potential (THMFP) reduction in 20 min time. Concurrent treatment can be simply implemented utilising readily available rapid mixers and flocculators, and operated on demand. Pre-adsorption and consecutive enhanced coagulation using the same alum and ACZ doses resulted in slightly better DOC but reduced (61%) ammonia removal. The results showed that concurrent treatment could safely resolve a challenging operational problem. ACZ combines the distinct advantages of zeolite and activated carbon in a single product, and may find additional uses in removing taste and odour, heavy metals, and synthetic organic matter from ground and surface waters.

Analysis of Suspended Sediment Variability in a Large Highly Turbid Estuary Using a 5‐Year‐Long Remotely Sensed Data Archive at High Resolution

AbstractSpatial variability of surface suspended particulate matter (SPM) concentration in the Gironde estuary and their relationships with environmental forcing are investigated through high spatial resolution multispectral data collected from July 2013 to August 2018 by the Operational Land Imager (Landsat‐8/OLI) and MultiSpectral Instrument (Sentinel‐2/MSI). A principal component analysis using the T‐mode orientation is applied to the discontinuous multiannual time series composed of 41 remotely sensed images. The three first principal components (PC1, PC2, and PC3) explain 65.7% of the total variance. The SPM distribution associated with PC1 and PC2 exhibits a privileged along‐estuary direction of the oscillation modes, while the spatial patterns of PC3 are clearly dominated by lateral oscillations opposing channels and shoals. The main environmental factors affecting the SPM distribution are identified by the analysis of their temporal patterns. The tidal range and the daily river discharge control the spatial patterns of PC1 and PC2, while the tidal cycles and the wind speed are significantly correlated with PC3. Furthermore, the analysis in the along‐estuary and lateral directions shows marked longitudinal and transverse SPM gradients and a strong control of bathymetry on the SPM spatial distribution. For the first time, we highlight that the maxima of surface residual turbidity are located on the shoals regardless of the environmental (tidal and hydrological) conditions. Compared to previous studies, usually based on single‐point in‐water column measurements, these results provide a novel and complementary description of the spatial variability of SPM. They are useful to validate sediment transport numerical models, but also may improve our understanding of suspended sediment dynamics in estuarine systems governed by an estuarine turbidity maximum.

Fabricating a hydrophobic modified flocculant through UVC irradiation initiation for metalworking wastewater treatment

In this work, a hydrophobically modified cationic polyacrylamide (CPAC) flocculant was polymerized by short-wave ultraviolet (UVC) initiation with acrylamide, acryloyloxyethyl trimethylammonium chloride, and coconut diethanolamide (CDEA) as monomers to enhance the destabilization and separation efficiency of emulsified oil and particles/colloids from metalworking fluids wastewater (MWFs). The parameters for flocculant polymerization were optimized, and the features of UVC-initiated polymerization were studied. Moreover, the structural and morphological characteristics of the polymers were explored, and the flocculation performance of CPAC in MWFs treatment was evaluated. The characterization results suggested that flocculants with a multilayer, loose-sheet morphology and intrinsic viscosity of 11.32dLg−1 could be successfully polymerized by UVC-initiated polymerization. Compared with traditional UV, UVC irradiation initiation promoted the copolymerization of flocculants with a high monomer conversion rate and intrinsic viscosity. We observed the low dosage requirement and acid resistance of the flocculant synthesized by UVC-initiated polymerization, which produced the lowest residual turbidity, highest chemical oxygen demand, and most efficient oil removal during MWFs treatment among the samples studied. Besides charge neutralization and bridging effects, the adsorption effect between hydrophobic CDEA blocks and nonpolar oil/colloids facilitated the formation of microflocs and improved the flocculation efficiency of the flocculant.

Prediction of Optimal Coagulant Injection Dosages and pH in Wastewater Using Visual MINTEQ Model

The secondary wastewater treatment effluents without further advanced sewage treatment were used as raw water, and the changes in pH, electric conductivity (EC), total dissolved solids (TDS), and turbidity according to dosages of coagulant injection were investigated through both Jar-test and Visual MINTEQ model. Then, the changes in water quality between Jar-test measurement and Visual MINTEQ prediction were evaluated. From the measurement results from Jar-test, the residual turbidity decreased, and reached lower values around 1.63 NTU with the increase in the coagulant dosages. Regardless of the type of coagulant, the pH decreased as the dosage of coagulant injection increased. From the prediction results of Visual MINTEQ model, the optimal dosages of coagulant injection for both Al2(SO4)3 and FeCl3 were estimated to be less than 0.1 mM. The optimal dosages of coagulant injection displayed slight differences between measured values through Jar-test and predicted value through Visual MINTEQ modeling, and this difference is mainly due to the complex functions of solubility differences between Al2(SO4)3 and FeCl3 at pH 6~7 and the ignorance of reactions of organic matters and other ions with Al2(SO4)3 and FeCl3 in the Visual MINTEQ model. Measured pH values gradually decreased with the increase in the dosage of coagulant injection whereas predicted pH values sharply decreased with the increase in the dosage of coagulant injection. From the results, Visual MINTEQ model can predict the similar values of composition and concentration in ions and pH in treated water up to some critical dosage of coagulant injection (i.e., 0.7 mM). However, Visual MINTEQ model can not predict the detail water chemistry in effluents with various compounds at trace levels and with high dosages of coagulation injection.