Additional Coagulant Research Articles

Water recovery and treatment of spent filter backwash from drinking water using chemical reactor-ultrafiltration process

During routine operations of water treatment plant (WTP), production of spent filter backwash water (SFBW) is inevitable that imposes high operation and maintenance costs. The study investigates treatment and water recovery from SFBW from WTP via combined chemical reactor-ultrafiltration (CR-UF) process. The daily generated SFBW from full-scale treatment plants were treated by the pilot pant of CR-UF process, which is comprised of a primary sedimentation basin, coagulation and flocculation tank immersed UF membrane module. The optimum conditions for CR process were pH 7.5 and FeCl3 dose 20 mg/L, which led to significant removal of turbidity, color, and UV254 that are equal to 97.11 ± 0.10 %, 63.31 ± 1.98 %, and 30.74 ± 0.72 %, respectively. The CR-UF produced permeate with very low turbidity (0.3 ± 0.01 NTU and 93.0 ± 1.1 % removal) has met the water standard of 5 NTU. During the continuous operation of CR-UF process and after three consecutive cycles of UF backwashing, initial flux slightly declined from 8.57 L/m2.h in the 1st cycle to 8.20 L/m2.h in the 3rd cycle, demonstrating the irreversible fouling due to nanoparticle blocking. In four proposed blending of SFBW, the amount of UV254 and TOC did not change significantly (<1 % increase), and additional coagulant was not needed. The hazard index (HI) values for all the population groups were <1, suggesting a minimal adverse health risk regarding the consumption of treated SFBW by the CR-UF process. Overall, the permeate stream of CR-UF process can be reused as a source of raw water for drinking water treatment plant.

Ultrafiltration with in-line coagulation (FeCl3) to enhance arsenic removal and improve drinking water quality: From bench to pilot-scale

There is a growing interest in advanced technologies to guarantee drinking water safety in scenarios of increasingly polluted water sources. Based on that, this paper discusses the use of ultrafiltration membranes aided by in-line coagulation with FeCl3 (0.086 – 0.172 mg/L) to improve the resilience of drinking water treatment plants. The process was considered after the settling units and was first studied on a bench scale, later validated in a pilot plant that operated continuously for approximately 31 days. In experiments without an in-line dose of FeCl3, the average flux values corresponded to 189.9 ± 11.8 L/m2h, compared with 193.4 ± 5.3 L/m2h for experiments when the coagulant was considered. The flux decay was lower in experiments with an in-line dose of FeCl3 (J/J0 > 0.95) and analysis of particle sizes revealed that the average diameter increased from 24.1 to 29.2 µm after the coagulant was added. Consequences related to a greater particle size were a fouling layer more porous permeable, and with a lower hydraulic resistance. The additional coagulant dosage also acts on the residual natural organic matter, monitored by excitation-emission matrices. Furthermore, the results show that the concentrate recirculation to the beginning of the water treatment plant did not affect its overall performance. In fact, concentrate recycling would increase the recovery rate of ultrafiltration membranes and reduce losses during water treatment. Similar observations were obtained in pilot-scale operations, that validated the in-line dose on a more representative system that is closer to the full-scale treatment process.

Understanding and mitigating effects of brine discharge to wastewater on primary sedimentation

AbstractAs the implementation of full advanced treatment with reverse osmosis (RO) grows in response to water scarcity, the effects of RO brine disposal to sewersheds on wastewater treatment will become an increasingly important consideration. Unfortunately, there is little existing literature on the actual effects of brine augmentation on wastewater flocculation and settling. In this study, RO brine from a wastewater reuse system was blended into raw wastewater. Jar tests of chemically enhanced primary treatment (CEPT) were conducted with varying brine blends and ferric chloride coagulant doses. Brine augmentation, at volumetric fractions ranging from 2.7% to 54% of the primary influent, was observed to affect CEPT performance, as removal of turbidity and total suspended solids (TSS) decreased in response to increasing brine share. Control jars with 0% brine generally had greater than 80%–90% TSS removal at the baseline coagulant dose of 12.5 mg/L, and this decreased to around 70% at 27% brine and less than 70% at 54% brine. This effect was observed to be roughly proportional to the level of brine addition, and it appears to be driven by changes to the properties of the fluid and primary particles as a result of brine addition. Adding brine both increases the density and viscosity of the fluid through higher total dissolved solids and decreases the density of the primary particles that make up the floc by contributing dissolved organics rejected by RO. CEPT performance was restored to its current baseline of around 80%–90% removal of TSS and turbidity by increasing ferric chloride dose (and thus floc density), with 17 mg/L required at 2.5% brine share and 30 mg/L required at 15% brine share. Overall, there was a roughly linear relationship between influent brine proportion and additional coagulant required to bring CEPT performance back up to brine‐free levels. The impact observed in this study suggests a topic for future research with other sources of brine and other coagulants.Article Impact StatementBy investigating primary settling affected by RO brine, this work addresses a topic of current interest that has not been widely studied.

Prothrombin Complex Concentrates: Potentially Thrombogenic Materials and Clues to the Mechanism of Thrombosis In Vivo

Factors affecting the coagulant activity of two different prothrombin complex concentrates have been investigated using a sensitive in vitro assay developed in this laboratory. One concentrate contained substantial amounts of potentially thrombogenic material, while the other, which was deliberately fortified with antithrombin III and heparin during production, was judged to be relatively nonthrombogenic. The coagulant activity of the thrombogenic concentrate has been partially identified and was due largely to the presence of coagulation factos IXa and Xa. Neither concentrate contained detectable thrombin. However, after incubation with calcium or various polyamines, large amounts of additional coagulant material, including thrombin, appeared. Heparin and antithrombin III not only neutralized the thrombogenic materials present in the thrombogenic concentrate, but also inhibited the de novo generation of coagulant enzymes during incubation with calcium. The implication of these studies on the preparation of prothrombin complex concentrates and on host susceptibility to thrombosis during the clinical use of these concentrates is discussed.

Surface water treatment benefits from the presence of algae: Influence of algae on the coagulation behavior of polytitanium chloride

Titanium-based coagulation has proved to be effective for algae-laden micro-polluted water purification processes. However, the influence of algae inclusion in surface water treatment by titanium coagulation is barely reported. This study reports the influence of both Microcystis aeruginosa and Microcystis wesenbergii in surface water during polytitanium coagulation. Jar tests were performed to evaluate coagulation performance using both algae-free (controlled) and algae-laden water samples, and floc properties were studied using a laser diffraction particle size analyzer for online monitoring. Results show that polytitanium coagulation can be highly effective in algae separation, removing up to 98% from surface water. Additionally, the presence of algae enhanced organic matter removal by up to 30% compared to controlled water containing only organic matter. Polytitanium coagulation achieved significant removal of fluorescent organic materials and organic matter with a wide range of molecular weight distribution (693–4945 Da) even in the presence of algae species in surface water. The presence of algae cells and/or algal organic matter is likely to function as an additional coagulant or flocculation aid, assisting polytitanium coagulation through adsorption and bridging effects. Although the dominant coagulation mechanisms with polytitanium coagulant were influenced by the coagulant dosage and initial solution pH, algae species in surface water could enhance the charge neutralization capability of the polytitanium coagulant. Algae-rich flocs were also more prone to breakage with strength factors approximately 10% lower than those of algae-free flocs. Loose structure of the flocs will require careful handling of the flocs during coagulation-sedimentation-filtration processes.

Effect of additional polyaluminum chloride and polyacrylamide on the evolution of floc characteristics during floc breakage and re-growth process

Abstract Effect of additional coagulant on floc breakage and re-growth process was investigated regarding coagulation performance and floc properties. Polyaluminum chloride (PACl) and cationic polyacrylamide (PAM) were used as additional coagulants and dosed at half way of the first breakage stage. The results indicated that additional coagulant was conductive to floc re-growth after first breakage regardless of coagulant type. Moreover, additional PACl still facilitated floc re-growth after second breakage. Compared to PACl, additional PAM couldn’t enhance floc re-growth after second breakage. Results of different additional dosages showed that floc recoverability after first breakage was elevated with increasing additional PACl dosage, but presented initially increasing and then decreasing trend when higher PAM dosage was added. In addition, floc recoverability after second breakage was elevated at higher dosages of additional PACl, whereas floc recoverability after second breakage with additional PAM was nearly same as that without additional PAM. It seems likely that the inactive surface points and coverage extent of broken flocs were dominant parameters for PACl addition and PAM addition, respectively.

Breakage and regrowth of flocs formed by sweep coagulation using additional coagulant of poly aluminium chloride and non-ionic polyacrylamide.

The breakage and regrowth of flocs formed by sweep flocculation were investigated on different flocculation mechanisms using additional dosage coagulant of poly aluminium chloride (PACl) and non-ionic polyacrylamide (PAM) to explore the reversibility after floc breakage. The optimal dosage of PACl was 0.15mM (as alum), and zeta potential exceeding 1mV meant that sweep flocculation was dominant in the pre-flocculated process. Re-coagulation efficiency increased with additional coagulants dosing, and sedimentation rates of flocs re-formed by small additional dosage of non-ionic PAM are faster than that of flocs re-formed by additional PACl. For additional inorganic coagulant (PACl) during regrowth processes, few negatively charged particles that existed in water sample restricted the effect of charge neutralization. An amorphous aluminum hydroxide precipitation could re-activate the weaker points on the broken floc surface, but regrown flocs have loose structure indicating worse settleability. For additional non-ionic PAM dosing, lower dosage showed large values of fractal dimension and average size, probably due to that unfolded curly molecular chain and exposed amide groups of non-ionic PAM which provide superb conditions for amide group interacting with particles. The use of non-ionic PAM in flocculation has advantage of being more effective than the cationic PACl, probably because it may avoid the re-stabilization of broken flocs by polymer adsorption driven by electrostatic attraction. Hence, appropriate dosing of PAM after breakage could improve the flocs characteristics with large size and compact structure.

Influence of flocs breakage process on membrane fouling in coagulation/ultrafiltration process—Effect of additional coagulant of poly-aluminum chloride and polyacrylamide

The additional coagulant dosing strategy was applied in a coagulation–ultrafiltration (UF) process for treatment of drinking water. When poly-aluminum chloride (PACl) dose was set as the optimal coagulant dosage (alum 0.15mM), the additional PACl and polyacrylamide (PAM) were added after breakage to further examine their benefits and impact on membrane fouling. The average size of flocs re-formed with additional non-ionic PAM was larger than that of additional PACl. The fractal dimension of flocs (dpf) was proved to play an important role on membrane fouling. Broken flocs re-formed with additional non-ionic PAM has more convoluted boundaries and lower effective density than the one with additional PACl, which is available to form loose and porosity cake layer on surface of membrane. Microscopic observations of membrane surface demonstrated that there was obvious correlation between the structure of cake layer and the fractal dimension of flocs. Besides, reversible fouling (RF) and irreversible fouling (IF) were also investigated in our study. The additional PACl dosing could lower membrane fouling, but irreversible fouling did not reduce because much more positive charged of flocs may adsorb on the surface of membrane under electrostatic attraction. As for non-ionic PAM, both of RF and IF were simultaneously decreased. As a result, the structural characteristics and surface electrical of flocs are two main mechanisms caused irreversible fouling.

The effect of re-aggregated floc by additional coagulant on membrane

The removal of turbidity, organic and inorganic contaminants in drinking water treatment plants is well established by using the hybrid membrane system combined with conventional coagulation and filtration techniques. It is well known that the aggregation of fine particles and colloids into larger particles can improve membrane filtration performance. However, flocs are easily broken by many factors such as when the pump has an impeller. Alternatively, in this study, the additional coagulant dose was applied for effective regrowth of the floc. The flocs formed by poly aluminum chloride (PACl) are artificially broken down by increasing the paddle speed such as the impeller of a feed pump and the effects of re-aggregation are compared both with additional coagulant and without it. The re-growth flocculation size index (FI) with additional coagulant and without it was 0.20 and 0.15, respectively, when the total coagulant dosage was 20mg/L. The flux decline rates according to additional coagulant dosage also differed. The flux decline rate of the flocs without additional dosage was 7.5 times larger than that of the flocs with additional dosage. Namely, the additional dosage process was more effective than the conventional process when the total amount of coagulant was the same.

Effect of dosage strategy on Al-humic flocs growth and re-growth

The ability of flocs growth has a significant effect on the efficiency of solid/liquid separation during coagulation process. The growth and re-growth of flocs by one time or continuous dosage were explored at neutral pH, including one time and continuous additional dosage strategy after flocs breakage. The size of flocs formed by continuous dosage before breakage was much larger than the one formed by one time dosage. There was significant irreversibility of floc breakage when no additional coagulant was added. For the one with one time initial dosage strategy, the size of re-grown flocs by one time additional dosage was nearly the same as that before breakage. The re-grown flocs formed by continuous additional dosage were a little smaller than that formed by one time additional dosage. It definitely showed that the growth or connection of flocs was probably not determined by the flocs size distribution and fractal dimension, but by the surface activity of flocs. Additional dosage could improve flocs re-grown ability because the surface activity of broken flocs was repaired by adding new alum.

Effect of second coagulant addition on coagulation efficiency, floc properties and residual Al for humic acid treatment by Al13 polymer and polyaluminum chloride (PACl)

Influence of second dose on coagulation efficiency, floc re-growth, fractal structure and residual Al of the effluent in humic acid (HA) coagulation with Al13 polymer ([Al13O4(OH)24(H2O)12]7+) and PACl were comparatively investigated in this study. Effects of breakage shear on the floc properties generated in the coagulation with and without additional dose were also investigated. The results indicated that additional dose during breakage could essentially improve the HA removal efficiency and floc re-growth in both Al13 and PACl coagulations. Second doses of Al13 at 0.5 and 1.0mg/L resulted in better turbidity and UV254 removal as well as floc re-growth rather than higher additional dose of 1.5 and 2.0mg/L; while in PACl coagulation, more efficient HA removal and better floc re-growth were obtained at higher additional doses (1.0, 1.5 and 2.0mg/L). Small additional Al13 could apparently increase the Df of re-formed flocs while the additional PACl displayed inconspicuous effect on floc Df. The additional coagulant dose could alleviate the further decrease of re-grown floc size with increased breakage shear for both coagulants. The residual Al analysis implied that two-stage addition contributed to lower residual Al in effluent than one-time addition mode with the same total coagulant concentration.

Breakage and re-growth of flocs: Effect of additional doses of coagulant species

Several polyaluminum chloride (PACl) coagulants were prepared, with different OH/Al ratios (B values), and characterized by Ferron assay. These were used in studies of floc formation, breakage and re-growth with kaolin suspensions under controlled shear conditions, using a continuous optical monitoring method. Particular attention was paid to the effect of small additional coagulant dosages, added during the floc breakage period, on the re-growth of broken flocs. The results showed that the re-growth ability was greatly dependent on the nature of the PACl species added as second coagulant. The re-growth ability of broken flocs was greatest when the second coagulant was PACl 0 (i.e. AlCl 3, with B = 0) and least with PACl 25 ( B = 2.5). In the latter case there was no effect on floc re-growth, irrespective of the initial coagulant used. PACls with intermediate B values gave some improvement in floc re-growth, but less than that with PACl 0. Additional dosage of PACl 0 gave re-grown flocs about the same size or even larger than those before breakage. The re-growth of broken flocs is significantly correlated with the species Al a (monomeric) and Al b (polymeric), as determined by Ferron assay. The amorphous hydroxide precipitate formed from PACl 0, (mainly Al a) can greatly improve the adhesion between broken flocs and give complete re-growth. However, for PACl 25, mostly composed of Al b, the nature of the precipitate is different and there is no effect on floc re-growth.

Breakage and Regrowth of Al-Humic Flocs - Effect of Additional Coagulant Dosage

The growth, breakage and regrowth of flocs formed by aluminum sulfate (alum) with humic acid (HA) in water at neutral pH was investigated by jar testing with continuous optical monitoring. Various initial dosages of alum and different breakage shears were investigated to compare the floc strengths and to explore the growth of flocs and regrowth of broken flocs. In all cases there was significant irreversibility of floc breakage when no additional coagulant was added. On the other hand, when a small additional dosage of alum was added to the suspension during floc breakage, the size of regrown flocs was higher than that before breakage. The result did not change with the variation of the initial dosage of alum, and the intensity and duration of floc breakage, provided that the additional coagulant was added shortly before the end of the breakage process. It seems that aluminum hydroxide is better able to form flocs, when newly precipitated, rather than after an extended period of high shear.

The effect of additional coagulant on the re-growth of alum–kaolin flocs

The process of floc formation, breakage and re-growth by aluminum sulfate (alum) with kaolin suspension was investigated by continuous optical monitoring. This paper focuses on the re-growth ability of broken flocs after an additional low dosage of alum, added during floc breakage. When coagulated by charge neutralization at pH 5, the broken flocs could re-grow almost fully without additional coagulant dosage. In this case an additional low dosage of alum during floc breakage lowered re-growth ability of broken flocs, because of charge reversal and restabilization of the clay particles. However, without additional coagulant dosage, broken flocs showed incomplete re-growth ability at pH 7, where an amorphous hydroxide precipitate was formed. In this case, additional dosage of coagulant led to re-grown flocs that were larger than those before breakage. It is likely that, under these conditions, new precipitate coats the surface of the broken flocs so that stronger bonds are formed between floc fragments. It seems that surface characteristics of flocs and not just their zeta potential are important in influencing the re-growth of flocs.

Covalently Bound Organic Silicate Aluminum Hybrid Coagulants: Preparation, Characterization, and Coagulation Behavior

Covalently bound organic silicate aluminum hybrid coagulants were synthesized by employing two silane coupling agents [diethoxydimethylsilane (DEDMS), gamma-aminopropylmethyldiethoxysilane (APDES)] as silicon sources. An additional coagulant was synthesized using anothersilane-tetraethylorthosilicate (TEOS) for comparison. Both the coagulant with DEDMS and that with APDES as the silicon source were shown to be covalently bound by infrared (IR) analysis. All three hybrid coagulants were characterized by pH, zeta potential, Al species distribution, and transmission electron microscopy (TEM) analysis. The results indicated that the silicon source played a significant role in aspects of the chemical and physical structure, Al species distribution, and electrochemistry characteristics. Specifically, the coagulant with APDES as the silicon source featured the highest zeta potential value, the highest content of Al13, and reticulated aggregate. The coagulation behaviors of the three hybrid coagulants were also investigated by treating synthetic water containing humic acid (HA). The hybrid coagulant with APDES as the silicon source exhibited the best coagulation behavior in terms of HA removal and turbidity removal, due to the combination of the zeta potential, Al species distribution, and organic functional groups.

STUDIES ON THE EFFICACY OF BRIDELIA FERRUGINEA BENTH BARK EXTRACT FOR DOMESTIC WASTEWATER TREATMENT

The efficacy of Bridelia ferruginea Benth bark extract in wastewater treatment was investigated. Chemical analysis found the bark to contain potassium, sodium, calcium, magnesium, zinc, manganese, iron and copper. Phytochemical tests revealed the bark to contain tannins, phlobatannins, saponins, alkaloids, and steroids. Comparative studies using varying concentrations (0.5, 1.0, 2.5 and 5.0 % w/v) with alum and ferric chloride showed that the bark extract was effective in the clarification and sedimentation of total solids in the waste water sample. The optimum dose achieved was 2.5 % w/v with a minimum of 24 hours contact time. The total bacteria counts were reduced by 46 % after 24 hours when the extract was used whereas ferric chloride achieved 50 % reduction and alum achieved 55 % reduction under similar conditions. The feasibility of using the bark extract as an additional coagulant is therefore discussed. KEYWORDS: Bridelia ferruginea, Sedimentation, Total bacteria count, Wastewater treatment Bull. Chem. Soc. Ethiop. 2007, 21(2), 205-211.

Use of ferrate pre-oxidation in enhancing the treatment of NOM-rich lake waters

Natural organic materials (NOMs) have a very strong influence on the stability of inorganic particles through interactions (e.g. adsorption, coating, and so on), and thus make the surface water with high NOM content difficult to be coagulated. In this study, standard jar tests and a pilot study were conducted to evaluate the effectiveness of ferrate pre-oxidation in enhancing the coagulation of NOM-rich lake water. A substantial reduction of residual turbidity after sedimentation and filtration was obtained by ferrate pre-oxidation at low dosage (1–5 mg L‒1 as K2FeO4). It was suggested that in order to maintain an acceptable residual turbidity, ferrate pre-oxidation can substantially reduce the dosage of coagulant. The improvement of water quality, as indicated by the reduction of color, DOC, iron, manganese, total bacteria, was observed to be similar in nature to the enhancement of residual turbidity. Formation of additional coagulant (Fe (III)) after decomposition was believed to be an important role of ferrate in enhancing coagulation. Ferrate could be employed in drinking water treatment by simple addition of ferrate solution just before coagulation.

Influence of Dissolved Organic Matter on Coagulation/Flocculation of Wastewater by Alum

The influence of different humic substances and linear alkylbenzene sulfonate on chemical treatment of a synthetic wastewater was investigated at pH=6-6.5. In soft water, humus significantly inhibited particle destabilization. The additional coagulant dosages needed for efficient coagulation corresponded to the dosages required for humus removal from pure solutions. Adsorption of humus onto precipitated hydroxide was regarded as being the major mechanism of interaction here. In hard water, high concentrations of humus seemed to impair aggregation of microflocs. This was attributed to the formation of soluble calcium humate complexes in raw water that may adsorb more slowly on precipitated hydroxide than dissolved humus. Precipitation of phosphate was not affected by humus in a definite way. A clear influence of LAS on coagulation was not found.