Coagulation-flocculation Treatment Research Articles

Electrochemical coagulation of treated wastewaters for reuse

In this work, the disinfection capability of electrocoagulation with iron and aluminium electrodes is studied. To do this, two different effluents of conventional municipal wastewater treatment plants (WWTP) are treated. Results show that electrocoagulation is able to reduce satisfactorily chemical oxygen demand, turbidity and nutrients and it allows increasing significantly the water quality. Likewise, it does not affect conductivity (just the contrary conventional coagulation–flocculation treatment) and helps to buffer pH in a value around 8. Precipitation, floc enmeshment and adsorption seem to be the primary mechanisms in this process. Regarding the variation of faecal coliforms, this technique behaves as a disinfection technology and allows increasing the efficiencies of WWTP processes in a very cheaper way. Energy consumption lower than 0.2 kWh m-3 is required to attain standard disinfection levels.

Coliforms and Helminth Eggs Removals by Coagulation-Flocculation Treatment Based on Natural Polymers

Wastewater from a municipal wastewater treatment plant (Mexico) was treated by a coagulation-flocculation using natural gums. The residual water was characterized in terms of organic load, and biological contaminants, i.e. total Coliforms (TC), fecal Coliforms (FC) and helminth eggs (HE). The sample has values of 2.8 × 107 MPN/100 ml, 8.48 × 106 MPN/100 ml and 470 HE/L is regarded to TC, FC and HH, respectively. The HE identified in the wastewaters were Diphyllobothrium latum, Ascaris lumbricoides, Hymenolepis nana and Toxocara canis. From several gums, Hydroxypropyl triammonium chloride guar gum (HPTAC-guar) was selected as the most adequate coagulant-flocculant for the class of municipal wastewater (MWW). A diminution of 82% for TC, 94% for FC and 99% for HE was obtained. Besides, the reduction of chemical oxygen demand (COD) and turbidity removals were 46% and 39% respectively. The natural gum mixed with Ca(OH)2, obtained removals of 52% for TC, 100% for HE, 47% for COD and 30% for turbidity.

Alteration of in vitro and acute in vivo toxicity of textile dyeing wastewater after chemical and biological remediation

Textile industry is one of the most common and essential sectors in Tunisia. However, the treatment of textile effluents becomes a university because of their toxic impacts on waters, soils, flora, and fauna. The aim of this work was to evaluate the ability of Pseudomonas putida mt-2 to decolorize a textile wastewater and to compare the biologic decolorization process to the chemical one currently used by the textile industry. P. putida exhibited a high decolorizing capacity of the studied effluent, compared to the coagulation-flocculation method with decolorization percentage of 86% and 34.5%, respectively. Genotoxicity of the studied effluent, before and after decolorization by P. putida mt-2, was evaluated in vitro, using the SOS chromotest, and in vivo, in mouse bone marrow, by assessing the percentage of cells bearing different chromosome aberrations compared to not treated mice. In addition, textile effluent statistically significant influenced acetylcholinesterase and butyrylcholinesterase activities and lipid peroxidation (p < 0.01) when compared to not-treated mice. Coagulation-flocculation treatment process used by industry was revealed to be ineffective. Indeed toxicities persisted after treatment and the effluent did not show any statistically significant decrease in toxicities compared to non-treated effluent. Our results indicate that P. putida is a promising and improved alternative to treating industrial scale effluent compared to current chemical decolorization procedures used by the Tunisian textile industry.

Use of nanoparticular and soluble anionic celluloses in coagulation-flocculation treatment of kaolin suspension

In this work, the effectiveness of a novel, combined coagulation-flocculation treatment based on alum and soluble or nanoparticular anionic derivatives of dialdehyde cellulose, ADAC, was evaluated by studying the removal of colloidal material in a model suspension containing kaolin. Four different ADACs with varying degrees of substitution, size and water solubility were synthesized by periodate oxidation and sulfonation of cellulose. The effects of ADAC dosage, solution pH and temperature on flocculation were studied by measuring residual turbidity of the settled suspension. Moreover, the charge densities, sizes, ζ-potentials and stability of the ADACs in aqueous solutions were studied. The combined treatment was effective in the removal of colloidal particles, as demonstrated by reduced residual turbidity with remarkably lower total chemical consumption compared with coagulation with alum alone. Of the ADACs, samples with lower solubility that contained cellulose nanoparticles performed better than the fully water-soluble sample. Due to the restricted pH tolerance of alum, the combined treatment was effective only at acidic conditions (pH < 5), although the ADACs were found to be stable in a much broader pH range (pH of 3 to about 9). ADACs also retained strong activity at higher temperatures (30–60 °C) and after several days of storage in aqueous solution.

Management of wastewater from the vegetable dehydration industry in Egypt – a case study

Management of wastewater from the vegetable dehydration industry was the subject of this study. A continuous monitoring programme for wastewater was carried out for almost four months. The characterization of the wastewater indicated that the vegetable dehydration wastewater contains moderate concentrations of organics, solids and nutrients. The wastewater was subjected to three different treatment processes, namely aerobic treatment, anaerobic treatment and chemical coagulation–flocculation treatment. For aerobic treatment, the removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD5) and total suspended solids (TSS) was accomplished within 5 h, and no further reduction was observed after that, with the steady state COD and BOD5 removal efficiencies being 95%±10% and 97%±8%, respectively. For anaerobic treatment, the removal efficiencies for COD, BOD5 and TSS were 67–81%, 70–86% and 56–69%, respectively at hydraulic retention times (HRTs) of 5, 6 and 8 h. Chemical coagulation–flocculation treatment also achieved good results. The COD removal efficiency was 72%, 51% and 75% for ferric chloride (56 g/m3 of wastewater), lime (140 g/m3 of wastewater) and ferric chloride aided with lime (100 g/m3 for ferric chloride and 200 g/m3 for lime), respectively. The corresponding TSS removal values were 92%±17%, 20%±7% and 93%±9%. Based on the available results and the seasonally operated mode of this industry in Egypt, the chemical coagulation–flocculation process is therefore considered to be moste applicable from a technical point of view and for the simplicity of operation and maintenance.

OPTIMIZATION OF COAGULATION-FLOCCULATION AND OZONATION PROCESSES FOR THE TREATMENT OF KRAFT PULP MILL EFFLUENT

A study on the effect of ozonation and coagulation- flocculation processes on kraft pulp mill effluents has been carried out. The objectives were to determine (1)best chemical combination for coagulation-flocculation, (2)optimum pH for ozonation and to evaluate (3)suitability of ozonation as pre and post treatment of coagulation-flocculation. Removal efficiencies of color, turbidity and phenolic compounds were investigated under different conditions. Results indicated that initial acidic pH in the effluent is more favorable for ozonation at the experimented O3 flow rate. Use of 0.1g/L AlCl3.2H2O with 0.05g/L polyacrylamide gives the maximum reductions of color, turbidity and phenolic compounds in the effluent. Coagulation-flocculation followed by ozonation is a better system for the treatment of kraft pulp mill effluent. This system can reduce all the three parameters by about 90%.

Characterisation of medical-waste sterilisation-plant wastewater and a preliminary study of coagulation–flocculation treatment options

Wastewater from a medical-waste sterilisation plant (MWSP) contains unique pollutants and requires on-site treatment to prevent contamination of the municipal sewage system and receiving water bodies. Therefore, to meet the prescribed discharge standards and comply with the legal regulations, pre-treatment must be applied to MWSP wastewater. In this study, the capabilities of coagulation-flocculation processes were investigated for MWSP wastewater treatment. Processes using ferric chloride, ferrous sulfate and aluminium sulfate as coagulants were characterised. During the coagulation experiments, seven different coagulant dosages and four different pH values were evaluated to determine the optimum coagulant dosage and pH value. The highest removal efficiency of chemical oxygen demand (COD) was obtained using 300 mg/L of ferric chloride at pH 10. A COD removal of about 60% as well as considerable reductions in the amounts of suspended solids, nitrogen and phosphorus were realised.

Colour, turbidity and COD removal from old landfill leachate by coagulation-flocculation treatment

The application of different coagulants and flocculants to leachate from an old landfill to determine the optimum conditions for removal of organic matter, colour and turbidity is studied. Ferric chloride, aluminium sulphate, aluminium polychloride (PAX) and polyacrylamide polyelectrolytes were tested. Higher pollutant removals (73% COD, 98% colour and 100% turbidity) were obtained using ferric chloride at pH 5.0-5.5 and for a dosage of 0.6 g Fe l(- 1). The volume of sludge generated after centrifugation represents about 4.0-4.6% when ferric chloride or aluminium sulphate is used, and 10% when employing aluminium polychloride. When flocculants were also added, the results obtained were similar to those found when adding only coagulants, although a considerable increase in the settling rate was obtained.

Application of response surface methodology (RSM) to optimize coagulation–flocculation treatment of leachate using poly-aluminum chloride (PAC) and alum

Coagulation–flocculation is a relatively simple physical–chemical technique in treatment of old and stabilized leachate which has been practiced using a variety of conventional coagulants. Polymeric forms of metal coagulants which are increasingly applied in water treatment are not well documented in leachate treatment. In this research, capability of poly-aluminum chloride (PAC) in the treatment of stabilized leachate from Pulau Burung Landfill Site (PBLS), Penang, Malaysia was studied. The removal efficiencies for chemical oxygen demand (COD), turbidity, color and total suspended solid (TSS) obtained using PAC were compared with those obtained using alum as a conventional coagulant. Central composite design (CCD) and response surface method (RSM) were applied to optimize the operating variables viz. coagulant dosage and pH. Quadratic models developed for the four responses (COD, turbidity, color and TSS) studied indicated the optimum conditions to be PAC dosage of 2 g/L at pH 7.5 and alum dosage of 9.5 g/L at pH 7. The experimental data and model predictions agreed well. COD, turbidity, color and TSS removal efficiencies of 43.1, 94.0, 90.7, and 92.2% for PAC, and 62.8, 88.4, 86.4, and 90.1% for alum were demonstrated.

Treatment of paper pulp and paper mill wastewater by coagulation–flocculation followed by heterogeneous photocatalysis

In this work is investigated the combined treatment of post-bleaching effluent from a cellulose and paper industry. The biodegradability index determined by the biochemical oxygen demand (BOD)/chemical oxygen demand (COD) ratio of in natura sample was 0.11, which implies little biodegradability and that it may not be discharged to the environment without previous treatment. First, the effluent was submitted to the coagulation–flocculation treatment applying FeCl 3 as the coagulating agent and chitosan as an auxiliary. In sequence, the aqueous soluble phase obtained from the first treatment was submitted to a UV/TiO 2/H 2O 2 system using mercury lamps. The optimized coagulation experimental conditions were chosen: pH 6.0, 80 mg L −1 of FeCl 3·6H 2O, and 50 mg L −1 of chitosan. The optimized photocatalysis conditions were: pH 3.0 in 0.50 g L −1 of TiO 2 and 10 mmol L −1 of H 2O 2. COD values for the in natura sample was 1303 mg L −1 and after the optimized conditions of coagulation without chitosan and in chitosan presence were 545 and 516 mg L −1, respectively. Effluent turbidity decreased sharply after coagulations (from 10 FTU of in natura samples to 2.5 FTU without chitosan and 1.1 FTU with chitosan). Similarly, a decrease was observed for concentrations of N-ammoniac, N-organic, nitrate, nitrite, phosphate, and sulfate ions after coagulation. Additionally, it was observed an absorbance reduction of 90% at the wavelength of 500 nm and of 70–80% in regions corresponding to aliphatic and aromatic groups (254, 280, and 310 nm). The use of chitosan for quantitative purposes was not so efficient; however, it improves sedimentation and compaction. COD results of photolyzed samples by UV/H 2O 2 were 344 mg L −1, UV/TiO 2 326 mg L −1, and UV/TiO 2/H 2O 2 246 mg L −1. The reduction in absorbance intensity was approximately 98% for aliphatic and aromatic chromophores, and 100% for chromophores absorbing at 500 nm with color disappearance. During photodegradation, SO 4 2− was formed (∼340 mg L −1 for the coagulated sample to ∼525 mg L −1) suggesting again the mineralization of the pollutant. The combined method (coagulation followed by photocatalysis) resulted in a biodegradability index of 0.71, transparency, and absence of color and odor in the treated water, suggesting again good water quality. This result is reinforced by the toxicity studies employing Artemia salina bioassay, which showed that an expressive decrease in toxic pollutants in effluents after treatment, mainly by combined processes. The wastewater treatment carried out in association at optimized experimental conditions provided good results.

Applicability of coagulation/flocculation and electrochemical processes to the purification of biologically treated vinasse effluent

We investigated the use of coagulation/flocculation (CF) and electrochemical oxidation (EO) processes to purify vinasse that had already been biologically treated (vinasse BT). The CF process was analyzed as a function of the concentration of the coagulant (FeCl 3) and the pH of the vinasse BT. After the CF process, EO was performed by potentiostatic electrolysis with a Ti/RuPb(40%)O x anode and Ti/PtPd(10%)O x cathode. The EO process was analyzed as a function of pH of vinasse CF treated and electrolysis time. The efficiencies of the CF and OE treatments on the vinasse BT were quantified in terms of the removal of chemical oxygen demand (COD), color and turbidity. The experimental results showed that the CF process with a coagulant concentration of 20 g/L and a pH of 8.4 removes a significant amount of COD (84%), color and turbidity (∼99%). The subsequent EO step satisfactorily complemented the purification of vinasse BT by CF, yielding removal efficiencies of more than 95% for COD and on the order of 100% for color and turbidity. We suggest that the mineralization via electrochemistry took place by indirect oxidation, mediated by active chlorine derived from FeCl 3 added during the CF treatment step.

Preliminary evaluation of the electrochemical and chemical coagulation processes in the post-treatment of effluent from an upflow anaerobic sludge blanket (UASB) reactor

The main objective of this paper was to perform a preliminary comparative study between chemical and electrochemical coagulation processes, both followed by flocculation and sedimentation of an effluent from an upflow anaerobic sludge blanket (UASB) reactor treating simulated wastewater from an unbleached Kraft pulp mill. The electrochemical treatment removed up to 67% (with aluminum electrodes) and 82% (with stainless-steel electrodes) of the remaining chemical oxygen demand (COD) and 84% (stainless steel) and 98% (aluminum) of the color in the wastewater. These efficiencies were achieved with an energy consumption ranging from 14 to 20 Wh l −1. The coagulation–flocculation treatment with ferric chloride and aluminum sulfate removed up to 87% and 90% of COD and 94% and 98% of color, respectively. The addition of a high molecular weight cationic polymer enhanced both COD and color removal efficiencies. The two post-treatment processes proved to be technically feasible; however the economical feasibility could not be assessed since the experiments were performed with small reactors that could distort scale factors.

Two-Factor Design For Coagulant/Flocculant Doses Effect for Solid-Liquid Separation of Dairy Manure

Screened dairy manure, with a total solids content equal to 34.7 g TS l−1, was subjected to a coagulation-flocculation treatment using FeCl3 as coagulant and a medium cationic polyacrylamide (MCP1). The effect of changing doses of the additives (FeCl3 and MCP1) on the properties of supernatant fractions was studied by means of design of response surface using "Statgraphics Plus 3.0" program. The results showed that the values of concentrations found in supernatants obtained after settling of the flocs for two of the dependent variables studied, filtrate chemical oxygen demand (CODf) and total organic carbon (TOC), were significantly influenced by both the FeCl3 and MCP1 doses at an error lower than 5%. The values of concentrations of the remaining variables studied (TS, VS, CODt, CODvfa) were significantly influenced only by the MCP1 dose at an error lower than 5%. The predictive model obtained the best satisfactory parameters for TOC supernatant's concentration (R2=0.980, F-ratio=438.89 (p-value<0.05)) and the worse for VS (R2=0.783, F-ratio=33.43 (p-value<0.05)).

Assessment of electrochemical and chemical coagulation as post-treatment for the effluents of a UASB reactor treating cellulose pulp mill wastewater

This paper presents results from exploratory experiments to test the technical feasibility of electrolytic treatment and coagulation followed by flocculation and sedimentation as post-treatment for the effluent of an UASB reactor treating simulated wastewater from an unbleached Kraft pulp mill. The electrolytic treatment provided up to 67% removal of the remaining COD and 98% of color removal. To achieve these efficiencies the energy consumption ranged from 14 Wh x l(-1) to 20 Wh x l(-1). The coagulation-flocculation treatment followed by settling required 350-400 mg x l(-1) of aluminium sulfate. The addition of a high molecular weight cationic polymer enhanced both COD and color removal. Both post-treatment processes are technically feasible.

Estimating the Removal of Anthropogenic Organic Chemicals from Raw Drinking Water by Coagulation Flocculation

A mathematical model was developed to estimate the efficacy of coagulation–flocculation treatment for removing neutral hydrophobic organic chemicals from raw drinking water. The model assumed that the only significant removal mechanism was the destabilization and settling of organic matter containing sorbed anthropogenic organic compounds. The model was validated with standard jar tests using compounds with a range of hydrophobicities (logKow=1.89to5.48), including contaminant candidate list chemicals, pesticides, pharmaceuticals, and endocrine disrupting chemicals. Final concentrations of test compounds after coagulation and flocculation were in good agreement with model estimations for synthetic waters composed of Aldrich (Milwaukee, WI) humic acid solutions. The final compound concentrations in coagulated natural waters from two drinking water reservoirs were about 80% lower than those estimated with the model. Overestimations of treated water concentrations by the model were attributed to an increase in sorption by natural organic matter when coiled in aluminum hydroxide flocs, compared to sorption to dispersed natural organic matter in untreated water.

Membrane bio-reactor for advanced textile wastewater treatment and reuse

Textile wastewater contains slowly- or non-biodegradable organic substances whose removal or transformation calls for advanced tertiary treatments downstream Activated Sludge Treatment Plants (ASTP). This work is focused on the treatment of textile industry wastewater using Membrane Bio-reactor (MBR) technology. An experimental activity was carried out at the Baciacavallo Wastewater Treatment Plant (WWTP) (Prato, Italy) to verify the efficiency of a pilot-scale MBR for the treatment of municipal wastewater, in which textile industry wastewater predominates. In the Baciacavallo WWTP the biological section is followed by a coagulation-flocculation treatment and ozonation. During the 5 months experimental period, the pilot-scale MBR proved to be very effective for wastewater reclamation. On average, removal efficiency of the pilot plant (93% for COD, 96% for ammonium and 99% for total suspended solids) was higher than the WWTP ones. Color was removed as in the WWTP. Anionic surf actants removal of pilot plant and WWTP were very similar (92.5 and 93.3% respectively), while the non-ionic surfactants removal was higher in the pilot plant (99.2 vs. 97.1). In conclusion the MBR technology demonstrated to be effective for textile wastewater reclamation, leading both to an improvement of pollutants removal and to a draw-plate simplification.

Microscopic observation of particle reduction in slaughterhouse wastewater by coagulation–flocculation using ferric sulphate as coagulant and different coagulant aids

A coagulation–flocculation treatment has been applied to a slaughterhouse liquid effluent, using ferric sulphate as coagulant and activated silica, powdered activated carbon, cationic polyacrylamide, polyvinyl alcohol, polyacrylic acid and anionic polyacrylamide as coagulant aids in order to improve the settling time. Once the optimal conditions had been established (speed and time of stirring during flocculation step, pH, coagulant and coagulant aid doses), the efficiency of the coagulation–flocculation process was studied by comparing the particle size distribution before and after the addition of the coagulant. When ferric sulphate was used without the coagulant aids, particle removal efficiency varied with size, although overall efficiency was quite substantial (87%). The use of coagulant aids improved the removal efficiency, except in the case of activated silica, when it fell to 78%. In all other cases removal efficiency values between 93% (for polyvinyl alcohol) and 99% (for anionic polyacrylamide) were reached.

Optimization of the coagulation–flocculation treatment: influence of rapid mix parameters

Turbid waters, containing suspended and colloidal particles, are normally treated by coagulation–flocculation followed by clarification; the process usually consists of the rapid dispersal of a coagulant into the raw water followed by an intense agitation commonly defined as rapid mixing. Rapid mixing is influenced by chemical and physical parameters and the final result of the whole treatment depends on this step. The study focused on the most important parameters of rapid mix design: velocity gradient and rapid mix time. Wastewaters from a tannery processing stored ovine hides were treated with aluminium(III) or iron(III) salts. Experimental results indicate that rapid mix time has a strong influence on final results; an optimal combination of rapid mix parameters was determined. The same approach was applied to highly turbid synthetic water, obtained through dissolving kaolin in distilled water and the results compared with those obtained for the tannery wastewater. It was confirmed that high turbidity removal can be achieved both with a short mixing time (about 10 s) and a long mixing time (60–90 s).