Ferric Coagulation Research Articles

Ferric sulfate coagulation and powdered activated carbon adsorption as simultaneous treatment to reuse the medium in Arthrospira platensis cultivation

AbstractBACKGROUNDCyanobacteriae and microalgae industries require large amounts of water for their cultivation. Reusing the Arthrospira platensis culture medium is scarcely evaluated in the literature. This work evaluates coagulation and adsorption as a simultaneous process to treat A. platensis spent medium by applying different concentrations of powdered activated carbon (PAC) and ferric sulfate (S) and by using different contact times (T) to remove organic matter and pigments.RESULTSThe process efficiency was measured by removal of both organic matter and pigments by absorbance at 254 and 440 nm, respectively. The highest maximum cell concentration (4863 ± 64 mg L−1) and protein content values (60.0 ± 0.6%) were observed in a medium treated with optimal conditions using PAC = 40.0 mg L−1, S = 32.8 mg L−1 and T = 36.1 min. Under such conditions, chlorophyll‐a biomass content of 24.5 ± 0.6 mg g dry cell−1 and chlorophyll‐a productivity of 16.8 ± 0.1 mg L−1 d−1 were obtained.CONCLUSIONSCoagulation and adsorption as a simultaneus treatment allowing reuse of the spent medium of A. platensis cultivation can diminish not only its production costs but also environmental pollution. The biomass produced in the treated medium contains more protein and chlorophyll than that produced in the standard medium. © 2015 Society of Chemical Industry

Pilot-scale study of vertical flow constructed wetland combined with trickling filter and ferric chloride coagulation: influence of irregular operational conditions.

The aim of this study was to characterize the efficiency of an intensified process of vertical flow constructed wetland having the following particularities: (i) biological pretreatment by trickling filter, (ii) FeCl3 injection for dissolved phosphorus removal and (iii) succession of different levels of redox conditions along the process line. A pilot-scale set-up designed to simulate a real-scale plant was constructed and operated using real wastewater. The influences of FeCl3 injection and water saturation level within the vertical flow constructed wetland stage on treatment performances were studied. Three different water saturation levels were compared by monitoring: suspended solids (SS), total phosphorus (TP), dissolved chemical oxygen demand (COD), ammonium, nitrate, phosphate, iron, and manganese. The results confirmed the good overall efficiency of the process and the contribution of the trickling filter pretreatment to COD removal and nitrification. The effects of water saturation level and FeCl3 injection on phosphorus removal were evaluated by analysis of the correlations between the variables. Under unsaturated conditions, good nitrification and no denitrification were observed. Under partly saturated conditions, both nitrification and denitrification were obtained, along with a good retention of SSs. Finally, under saturated conditions, the performance was decreased for almost all parameters.

Applying chemical sedimentation process in drinking water treatment plant to address the emergent arsenic spills in water sources

Arsenic (As) spills occurred more frequently and sometimes polluted water sources in recent years in China. It is as urgent need to develop emergency treatment technologies to address the arsenic threat for large-scale water treatment plants. In response, we developed a chemical sedimentation technology to remove arsenic contaminants for water treatment plants. Bench-scale experiments were conducted to investigate the efficiency of arsenic removal and the influencing factors of the chemical sedimentation treatment process. The influencing factors included the choice and dosage of coagulants, the valence of arsenic and pH value of solution. The As(V) contaminants can be almost completely removed by ferric or alum coagulants. The As(III) contaminants are more recalcitrant to chemical sedimentation, 75% for ferric coagulant and 40% for alum coagulant. The quantitative results of arsenic removal load by different ferric or alum coagulants were presented to help determine the para- meters for arsenic treatment technology. The dominant mechanism for arsenic removal is static combination, or adsorption of negative arsenic species onto positive ferric hydroxide or alum hydroxide flocs. The efficiency of this treatment technology has also been demonstrated by a real production test in one water treatment plant with arsenic- rich source water and one emergency response. This technology was verified to be quick to set-up, easy to operate and highly efficient even for high concentration of arsenic.

Concentration of Cryptosporidium oocysts from river water by coagulation and foam separation combined with acid dissolution of ferric flocs

Cryptosporidium is an extremely virulent microorganism; contamination of water works systems by Cryptosporidium oocysts is a serious issue in public health. However, a great deal of effort is required to detect oocysts in source water for drinking, because the oocysts have to be concentrated from a large volume of water before detection. In this study, the concentration of oocysts in oocyst-polluted artificial river water was examined by coagulation and foam separation. The oocysts concentrated in the foam water were purified using immunomagnetic separation and assessed using epifluorescence microscopy. When ferric coagulation was performed prior to foam separation, oocysts were effectively removed from the river water and concentrated in the foam within 10 min. The removal efficiency was greater than 96% at the optimum iron and casein concentrations of 5 mg-Fe L−1 and 20 mg L−1, respectively. Furthermore, the number of recovered oocysts in the solution obtained by the dissolution of the collected ferric flocs from foam water was the same as that obtained using the Japanese standard procedure for detection of Cryptosporidium in water using membrane filtration. This is a novel method of concentrating Cryptosporidium oocysts for detection in river water using a coagulation and foam separation combined with acid dissolution of ferric flocs; the method is easy to use, rapid, and efficient.

철염 응집과 펜톤 산화를 이용한 인의 존재형태별 처리

Effects of <TEX>$H_2O_2$</TEX> addition for fenton oxidation on iron coagulation for treatment of phosphorus species, such as orthophosphate, metaphosphate, pyrophosphate, organic phosphate, were investigated. The effects of coagulant dosage, hydrogen peroxide dosage and the combined sequence ferric coagulation and <TEX>$H_2O_2$</TEX> addition for fenton oxidation and coagulation were studied. The characteristics of floc growth rate were monitored using the PDA. The removal efficiencies of phosphorus species by iron coagulation were increased as Fe/P molar ratio increased. However, the removal efficiencies of metaphosphate, pyrophosphate, organic phosphate by a ferric coagulation were not increased as Fe/P molar ratio increased. The removal efficiency of metaphosphate, pyrophosphate, organic phosphate was increased by using iron coagulation and <TEX>$H_2O_2$</TEX> addition for fenton oxidation. The result indicated that non-reactive phosphorus after iron coagulation was changed to reactive phosphorus by <TEX>$H_2O_2$</TEX> addition for fenton oxidation and the oxidized iron enhanced the coagulation efficiencies.

Comparison of reverse osmosis membrane fouling characteristics in full-scale leachate treatment systems with chemical coagulation and microfiltration pre-treatments.

Fouling characteristics of reverse osmosis (RO) membrane with chemical coagulation and microfiltration (MF) pre-treatment were investigated at full-scale leachate treatment systems. In chemical coagulation pre-treatment, solid separation from stabilized leachate was performed by ferric chloride coagulation followed by sand filtration. Meanwhile, MF pre-treatment and the RO system utilized direct filtration using a 0.03 µm membrane without chemical addition. MF pre-treatment yielded better pollutant removals in terms of organics and nitrogen. The study on effect of pre-treatment on RO membrane fouling revealed that accumulated foulant on the RO membrane in MF pre-treatment was significantly lower than that of chemical coagulation. Nevertheless, NaOH cleaning of the fouled RO membrane after chemical coagulation pre-treatment could better recover its permeate flux, thus suggesting that the formation of a loose-structure cake layer by chemical coagulation pre-treatment could allow effective penetration of chemical cleaning and detachment of foulant layer from the membrane surface.

The fate of Microcystis aeruginosa cells during the ferric chloride coagulation and flocs storage processes

Microcystis blooms could cause severe problems for drinking water supplies with their associated microcystins (MCs). As the majority of MCs are retained inside the cells, the effective removal of the intact Microcystis cells to avoid the release of additional MCs plays an important role in drinking water treatment. This study evaluated the effect of ferric chloride (FeCl3) coagulation and the flocs storage process on the integrity of Microcystis aeruginosa cells and the intracellular MCs release (and possible degradation) in both processes. Multiple analysis techniques including scanning electron microscopy and chlorophyll fluorescence were used to assess the integrity of M. aeruginosa. In the coagulation process, the coagulant dosage and mechanical actions caused no cell damage, and all the cells remained intact. Furthermore, 100 mg/L FeCl3 was effective in removing the extracellular MCs. In the flocs storage process, a number of intracellular MCs were released into the supernatant, but the cells remained viable up to 10 d.

Removal of As(III) and As(V) by ferric salts coagulation – Implications of particle size and zeta potential of precipitates

This study investigates the removal of As(III) and As(V) by ferric salts coagulation under solution chemistry influences with particular emphasis on the role of zeta potential and size of the precipitates. The results indicate that As(III) removal efficiency increased with increase of solution pH, but there was almost no correlation with zeta potential of the precipitates. In contrast, the highest As(V) removal occurred in the pH range of positive zeta potentials and the removal efficiencies declined significantly as the precipitates became more negatively charged at high pH values. The relative importance of the two coagulation removal mechanisms, co-precipitation and adsorption, was found to be dependent on the solution pH. The sizes of the early-formed precipitates were in the colloidal range, with the largest size being at the isoelectric point (IEP). Precipitate sizes affected the residual Fe level at certain pH values after microfiltration and sand filtration, but showed much less effect on the arsenic removal. Electrolyte concentrations showed a noticeable effect on the precipitate size, but only a small effect on the arsenic removal. Humic acid exhibited profound influences both on zeta potential, size of the precipitates and arsenic removal.

How the novel integration of electrolysis in tidal flow constructed wetlands intensifies nutrient removal and odor control

Intensified nutrient removal and odor control in a novel electrolysis-integrated tidal flow constructed wetland were evaluated. The average removal efficiencies of COD and NH4+-N were above 85% and 80% in the two experimental wetlands at influent COD concentration of 300mg/L and ammonium nitrogen concentration of 60mg/L regardless of electrolysis integration. Effluent nitrate concentration decreased from 2.5mg/L to 0.5mg/L with the reduction in current intensity from 1.5mA/cm2 to 0.57mA/cm2. This result reveals the important role of current intensity in nitrogen transformation. Owing to the ferrous and ferric iron coagulant formed through the electro-dissolution of the iron anode, electrolysis integration not only exerted a positive effect on phosphorus removal but also effectively inhibited sulfide accumulation for odor control. Although electrolysis operation enhanced nutrient removal and promoted the emission of CH4, no significant difference was observed in the microbial communities and abundance of the two experimental wetlands.

Reuse of ferric sludge as an iron source for the Fenton-based process in wastewater treatment

Abstract A mature municipal landfill leachate (S1), a wood soaking basin effluent from a plywood manufacturing plant (S2), and a leachate collected from a semicoke landfill area of an oil-shale thermal treatment plant (S3) were subjected to the Fenton/Fenton-based treatment (H 2 O 2 /Fe 2+ , H 2 O 2 /Fe 3+ and H 2 O 2 /sludge systems). The results of ferric coagulation trials indicated a high efficacy in S2; thus, only pre-coagulated samples (cS2) were further treated by the H 2 O 2 /iron systems. Irrespective of reaction duration, S1 was more recalcitrant to oxidation than cS2 and S3. The optimal COD/H 2 O 2 weight ratio for cS2 and S3 was 1:1 with respective 21(35) and 36(45)% residual COD(DOC). In the case of S1, the COD/H 2 O 2 w/w of 1:3.45 proved the most efficient with 30 and 35% residual COD and DOC, respectively. The results also indicated an increase in BOD 7 /COD ratio and a reduction in the acute toxicity to Daphnia magna of the studied wastewater samples after the Fenton/Fenton-based treatment. The application of the Fenton-based process catalysed with iron-containing sludge exhibited efficacies similar to classical Fenton treatment over four reuse cycles. The reuse of ferric sludge without any regeneration as an iron source in the Fenton-based process was displayed as a feasible solution to minimise the production of hazardous ferric waste and reduce the overall cost of the treatment process.

Removal of antimony (III) from polluted surface water using a hybrid coagulation–flocculation–ultrafiltration (CF–UF) process

Abstract Antimony is a pollutant that is classified as high priority by the United States Environmental Protection Agency (USEPA) and the European Union (EU). In this work, a hybrid coagulation–flocculation–ultrafiltration (CF–UF) process was developed to remove antimony (III) from polluted surface water, and the process parameters, including the ferric coagulant (FC) dose, pH and initial contaminant loading, were systematically optimized. The results indicated that the optimum FC dose and solution pH range were 0.4 mM and 7.1–9.0, respectively. Under these conditions, the antimony (III) concentrations in the CF–UF effluent were as low as 1.0–2.0 μg L−1, which is significantly lower than drinking water standards (USEPA,

Examination of the physical properties of Microcystis aeruginosa flocs produced on coagulation with metal salts

Coagulation–flocculation (C–F) is a key barrier to cyanobacterial and algal cell infiltration in water treatment plants during seasonal blooms. However, the resultant cell floc properties, in terms of size, strength and density, which dominate under different coagulation conditions and govern cell removal, are not well understood. This paper investigated the floc properties produced during C–F of the cyanobacterium, Microcystis aeruginosa, under low and high doses of aluminium sulphate and ferric chloride coagulants and at different pH values, so as to promote charge neutralisation (CN) and sweep flocculation (SF) dominant conditions (or a combination of these). It was demonstrated that application of ferric chloride produced larger flocs that resulted in higher cell removal during jar testing. These flocs were also larger than those observed for natural organic matter (NOM) and kaolin, suggesting a role of algogenic organic matter (AOM) as an inherent bioflocculant. Under SF conditions, stronger flocs were produced; however, these had lower capacity for size recovery after exposure to high shear. Analysis of particle size distribution demonstrated that large scale fragmentation followed by erosion dominated for CN while erosion dominated under SF conditions. Overall, marked differences were observed dependent on the coagulation regime imposed that have implications for improving robustness of cell removal by downstream separation processes. While the cyanobacterium, M. aeruginosa, appeared to share general floc characteristics commonly observed for NOM and kaolin flocs, there were distinct differences in terms of size and strength, which may be attributed to AOM.

Reuse of recovered coagulants in water treatment: An investigation on the effect coagulant purity has on treatment performance

Coagulant recovery offers many potential benefits to water treatment, by reducing chemical demand and waste production. The key obstacle to successful implementation is achieving the same levels of treatment quality and process economics as commercial coagulants.This study has evaluated the selectivity of pressure-filtration in the role of a low-cost coagulant recovery technology from waterworks sludge. The treatment performance of the purified recovered coagulant was directly compared to fresh and raw recovered coagulants. DOC and turbidity removal by recovered coagulants was close to that of commercial coagulants, indicating that coagulant can be successfully recovered and regenerated by acidifying waterworks sludge. However, performance was less consistent, with a much narrower optimum charge neutralisation window and 10–30% worse removal performance under optimum conditions. This inferior performance was particularly evident for recovered ferric coagulants. The impact of this was confirmed by measuring THM formation potential and residual metals concentrations, showing 30–300% higher THMFPs when recovered coagulants were used.This study confirms that pressure-filtration can be operated on an economically viable basis, in terms of mass flux and fouling. However, the selectivity currently falls short of the purity required for potable treatment, due to incomplete rejection of sludge contaminants.

Intensified nitrogen and phosphorus removal in a novel electrolysis-integrated tidal flow constructed wetland system

A novel electrolysis-integrated tidal flow constructed wetland (CW) system was developed in this study. The dynamics of intensified nitrogen and phosphorus removal and that of hydrogen sulphide control were evaluated. Ammonium removal of up to 80% was achieved with an inflow concentration of 60 mg/L in wetland systems with and without electrolysis integration. Effluent nitrate concentration decreased from 2 mg/L to less than 0.5 mg/L with the decrease in current intensity from 1.5 mA/cm2 to 0.57 mA/cm2 in the electrolysis-integrated wetland system, thus indicating that the current intensity of electrolysis plays an important role in nitrogen transformations. Phosphorus removal was significantly enhanced, exceeding 95% in the electrolysis-integrated CW system because of the in-situ formation of a ferric iron coagulant through the electro-dissolution of a sacrificial iron anode. Moreover, the electrolyzed wetland system effectively inhibits sulphide accumulation as a result of a sulphide precipitation coupled with ferrous-iron electro-dissolution and/or an inhibition of bacterial sulphate reduction under increased aerobic conditions.

Implementing Treatment Sequences to Promote Reduction of DBPs in Small Drinking Water Systems

The performance of three drinking water treatment sequences found in small community systems in reducing disinfection by-product precursor concentrations and the corresponding disinfection by-product formation potential was evaluated. Raw water quality and its potential for effective removal were characterized by the specific ultraviolet absorbance (SUVA) components of absorbance of ultraviolet light at 254 nm wavelength (UV254) and dissolved organic carbon (DOC). The results demonstrate that, for the source water qualities tested (hydrophobic SUVA with moderate DOC content, 2.0 to 4.8 L/(mg.m) and 4.1 to 6.3 mg DOC/L), there was a tendency to produce a higher percentage of total trihalomethane (TTHM) over the five regulated species of haloacetic acid (HAA5). The treatment sequence and chemical selection play a critical role in the ability of a small community system operator to achieve compliance with the concentration of regulated disinfection by-products. For the waters tested ferric chloride coagulants perform better at reducing the higher molecular weight, hydrophobic organic precursors. Powdered activated carbon does not perform as well with these source waters unless its application is followed by a clarification process that effectively forms a sludge blanket. This research provides additional criteria for linking source water quality with treatment sequence for sustainable management of disinfection by-product (DBP) compliance.

Rethinking the role of in-line coagulation in tertiary membrane filtration of municipal effluents

In-line coagulation with aluminum or iron salts and ultrafiltration (UF) or microfiltration (MF) membranes is a valuable treatment option. The efficiency of the treatment is often evaluated by the achieved separation degree. That separation-oriented approach implies the coagulation with doses that are prohibitively high for many operations including the tertiary effluent treatment. The main purpose of the advanced wastewater treatment however is the retention of microorganisms and suspended solids, and that goal can be achieved even without coagulants. Thus the in-line coagulation can pursue the prevention or minimization of the irreversible fouling as an ultimate goal not related to the maximal separation of organic and inorganic impurities.Pilot experiments at conventional activated sludge (CAS) municipal wastewater treatment plant confirmed that the addition of 1mg/L Fe3+ prevents the irreversible fouling as efficiently as the addition of 5 and 10mg/L Fe3+. The economic impact of the suggested alteration is significant. Estimated operational expenses (OPEX) of a filtration at 60 LMH with 45min cycles and 1 chemical – enhanced backwash per day is around 2cents (€)/m3, almost a half of an OPEX of the separation-oriented treatment.Intermittent in-line coagulation down to first 2.5min of 30 and 45min filtration cycles is another cost-effective method to successfully depress the fouling. The success is explained by two-stage kinetics of a cake formation. At ripening stage, a layer of flocks restricted by a membrane gradually covers its surface and forms an initial dynamic cake. At operable stage, the cake entraps fresh solutes and prevents their contact with a membrane surface even without a coagulant. A superposition of two approaches reduces the consumption of ferric chloride coagulant by 94%.

Effect of ferric chloride coagulation, lime precipitation, electrocoagulation and the Fenton's reagent on the particle size distribution of olive mill wastewater

Size fractionation of olive mill wastewater (COD:155000 mg/L; TOC:40000 mg/L; BOD5:37700 mg/L; total phenols:4100 mg/L; absorbance at 395 nm:145 cm-1) before and after FeCl3 coagulation, Ca(OH)2 precipitation, electrocoagulation and the Fenton process was investigated. Particulate organic compounds were the major components of COD (54%), TOC (43%), BOD5 (43%), absorbance (57%), followed by an appreciable soluble size fraction. For the total phenols parameter, a dominant fraction (54%) appeared in the colloidal (5–8 nm) size range besides significant particulate (22%) and soluble (24%) size fractions. FeCl3coagulation and Ca(OH)2 precipitation appeared to be most efficient in organic matter removal, whereas electrocoagulation was superior in phenolics removal. No shift in the size distribution pattern was observed after chemical treatment since phase-transfer was the dominant removal mechanism of the selected processes. The highest inhibition of the Vibrio fischeri photobacteria was observed in the particulate size range and decreased in the solube size range due to the elimination of the phenolic content.

Treatment of poly- and perfluoroalkyl substances in U.S. full-scale water treatment systems

The near ubiquitous presence of poly- and perfluoroalkyl substances (PFASs) in humans has raised concerns about potential human health effects from these chemicals, some of which are both extremely persistent and bioaccumulative. Because some of these chemicals are highly water soluble, one major pathway for human exposure is the consumption of contaminated drinking water. This study measured concentrations of PFASs in 18 raw drinking water sources and 2 treated wastewater effluents and evaluated 15 full-scale treatment systems for the attenuation of PFASs in water treatment utilities throughout the U.S. A liquid-chromatography tandem mass-spectrometry method was used to enable measurement of a suite of 23 PFASs, including perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs). Despite the differences in reporting levels, the PFASs that were detected in >70% of the source water samples (n = 39) included PFSAs, perfluorobutane sulfonic acid (74%), perfluorohexane sulfonic acid (79%), and perfluorooctane sulfonic acid (84%), and PFCAs, perfluoropentanoic acid (74%), perfluorohexanoic acid (79%), perfluoroheptanoic acid (74%), and perfluorooctanoic acid (74%). More importantly, water treatment techniques such as ferric or alum coagulation, granular/micro-/ultra- filtration, aeration, oxidation (i.e., permanganate, ultraviolet/hydrogen peroxide), and disinfection (i.e., ozonation, chlorine dioxide, chlorination, and chloramination) were mostly ineffective in removing PFASs. However, anion exchange and granular activated carbon treatment preferably removed longer-chain PFASs and the PFSAs compared to the PFCAs, and reverse osmosis demonstrated significant removal for all the PFASs, including the smallest PFAS, perfluorobutanoic acid.

Biological nutrient removal by internal circulation upflow sludge blanket reactor after landfill leachate pretreatment

The removal of biological nutrient from mature landfill leachate with a high nitrogen load by an internal circulation upflow sludge blanket (ICUSB) reactor was studied. The reactor is a set of anaerobic-anoxic-aerobic (A2/O) bioreactors, developed on the basis of an expended granular sludge blanket (EGSB), granular sequencing batch reactor (GSBR) and intermittent cycle extended aeration system (ICEAS). Leachate was subjected to stripping by agitation process and poly ferric sulfate coagulation as a pretreatment process, in order to reduce both ammonia toxicity to microorganisms and the organic contents. The reactor was operated under three different operating systems, consisting of recycling sludge with air (A2/O), recycling sludge without air (low oxygen) and a combination of both (A2/O and low oxygen). The lowest effluent nutrient levels were realised by the combined system of A2/O and low oxygen, which resulted in effluent of chemical oxygen demand (COD), NH3-N and biological oxygen demand (BOD5) concentrations of 98.20, 13.50 and 22.50 mg/L. The optimal operating conditions for the efficient removal of biological nutrient using the ICUSB reactor were examined to evaluate the influence of the parameters on its performance. The results showed that average removal efficiencies of COD and NH3-N of 96.49% and 99.39%, respectively were achieved under the condition of a hydraulic retention time of 12 hr, including 4 hr of pumping air into the reactor, with dissolved oxygen at an rate of 4 mg/L and an upflow velocity 2 m/hr. These combined processes were successfully employed and effectively decreased pollutant loading.

Development of a new poly silicate ferric coagulant and its application to coagulation-membrane filtration hybrid system in wastewater treatment

Coagulation is one of the effective pretreatment stages in membrane filtration of wastewaters to produce clean water. Using a suitable coagulant, one can mitigate membrane fouling. Membrane fouling is a process where particles deposit onto a membrane surface or into membrane pores in a way that degrades the membrane’s performance. Research in this area is currently being focused on development of improved coagulation reagents such as poly silicate ferric (PSiFe), which has a high molecular weight and large number of positive surface charges with high efficiency at low doses. In this paper, PSiFe was prepared by following two approaches: (a) acidification of water glass solution using HCl followed by FeCl3 addition (old-PSiFe); (b) acidification of water glass solution by passing it through an acidic ion exchange resin followed by fresh FeCl3 addition under different Fe/Si molar ratios (new-PSiFe). These coagulants were characterised by X-ray diffraction and scanning electron microscopy. According to coagulation jar test results when Fe/Si = 1, the best performance was achieved in terms of turbidity, total organic carbon (TOC) and UV254 removals. Another aspect is the comparison of the old-PSiFe, FeCl3 and new-PSiFe which showed that in a membrane filtration system, using the new-PSiFe not only reduces the required transmembrane pressure (TMP) due to lower fouling, but also improves the TOC removal efficiency.