Optimisation of the coagulation-flocculation process of raw water by optimal design method

Combined Application of Coagulation/Flocculation/Sedimentation and Membrane Separation for the Treatment of Laundry Wastewater

The wastewater from industrial laundries has a high quantity of contaminants from the washing process, as well as chemical additives. Aiming at the treatment of this type of wastewater, the present study evaluated the performance of a combined coagulation/flocculation/sedimentation process (C/F/S) and membrane separation to treat laundry wastewater in relation to physicochemical parameters of water quality. For this purpose, a Doehlert experimental design was applied to the C/F/S step using the natural coagulant Tanfloc POP® with maximum color and turbidity removal efficiency obtained of 80.27% and 86.50%, respectively, under conditions of pH of 6.4 and a coagulant concentration of 110 mg·L−1. The supernatant from the C/F/S step was used in the sequential microfiltration (MF) and ultrafiltration (UF) experiments. The maximum values of color, total nitrogen, dissolved solids, and turbidity removal were similar to MF and UF membranes at transmembrane pressure of 1.4 bar, with the greatest flow of permeates (92.2 L·h−1·m−2) presented by the MF membrane at 1.4 bar. The total efficiency of the combined C/F/S-MF process indicated the quality of the treated wastewater since it reduced 98.4% of the color, 99.1% of turbidity, 71.7% of the surfactants, and more than 55% of the total dissolved solids (TDS), chemical oxygen demand (COD), and total organic carbon (TOC) from the industrial laundry wastewater. This study showed that the C/F/S-MF combined process could be an efficient treatment of laundry wastewater.

Chemical treatment response to variations in non-point pollution water quality: results of a factorial design experiment

Chemical treatment of non-point derived pollution often suffers from undesirable oscillations in purification efficiency due to variations in runoff water quality. This study examined the response of the chemical purification process to variations in water quality using a 2(k) factorial design for runoff water rich in humic substances. The four k factors evaluated and the levels applied were: organic matter as dissolved organic carbon (DOC) (20-70 mg/L), suspended solids (SS) (10-60 mg/L), initial water pH (4.5-7), and applied coagulant dosage (ferric sulphate) (35-100 mg/L). Indicators of purification efficiency were residual concentration of DOC, SS and total phosphorus (tot-P). Analysis of variance and factor effect calculations showed that the initial DOC concentration in raw water samples and its interactions with the coagulant dosage applied exerted the most significant influence on the chemical purification process, substantially affecting the residual concentration of DOC, SS and tot-P. The variations applied to the factors SS and pH only slightly affected purification efficiency. The results can be used in the design of purification systems with high organic matter load variation, e.g. peat extraction runoff.

Flocculation characteristics of polyacrylamide grafted cellulose from Phyllostachys heterocycla: An efficient and eco-friendly flocculant

This work presents a synthesis process and flocculation characteristics of an eco-friendly flocculant based on bamboo pulp cellulose (BPC) from Phyllostachys heterocycla. Ployacrylamide (PAM) was grafted onto the BPC by free-radical graft copolymerization in homogeneous aqueous solution. The optimal synthesis conditions of the bamboo pulp cellulose-graft-ployacrylamide flocculant (BPC-g-PAM) and its performance on wastewater treatments were investigated. A UV-based method was used to rapidly determine the degree of substitution (DS) of BPC. The results showed that, under the optimal synthesis conditions, the obtained BPC-g-PAM held a grafting ratio of 43.8% and DS of 1.31. Turbidity removal of the product reached 98.0% accompanying with the significant flocculation and sedimentation in target suspensions. The flocculation mechanism was explored by means of zeta potential method. For negatively charged contaminants, like kaolin clay particles, the BPC-g-PAM could remove the contaminants efficiently via bridging and charge neutralization in acidic or neutral environment.

Optimisation of chemical purification conditions for direct application of solid metal salt coagulants: treatment of peatland-derived diffuse runoff

The drainage of peatland areas for peat extraction, agriculture or bioenergy requires affordable, simple and reliable treatment methods that can purify waters rich in particulates and dissolved organic carbon. This work focused on the optimisation of chemical purification process for the direct dosage of solid metal salt coagulants. It investigated process requirements of solid coagulants and the influence of water quality, temperature and process parameters on their performance. This is the first attempt to provide information on specific process requirements of solid coagulants. Three solid inorganic coagulants were evaluated: aluminium sulphate, ferric sulphate and ferric aluminium sulphate. Pre-dissolved aluminium and ferric sulphate were also tested with the objective of identifying the effects of in-line coagulant dissolution on purification performance. It was determined that the pre-dissolution of the coagulants had a significant effect on coagulant performance and process requirements. Highest purification levels achieved by solid coagulants, even at 30% higher dosages, were generally lower (5%-30%) than those achieved by pre-dissolved coagulants. Furthermore, the mixing requirements of coagulants pre-dissolved prior to addition differed substantially from those of solid coagulants. The pH of the water samples being purified had a major influence on coagulant dosage and purification efficiency. Ferric sulphate (70 mg/L) was found to be the best performing solid coagulant achieving the following load removals: suspended solids (59%-88%), total organic carbon (56%-62%), total phosphorus (87%-90%), phosphate phosphorus (85%-92%) and total nitrogen (33%-44%). The results show that the use of solid coagulants is a viable option for the treatment of peatland-derived runoff water if solid coagulant-specific process requirements, such as mixing and settling time, are considered.

The use of chitosan as a coagulant in the pre-treatment of turbid sea water

One of the problems that encounters desalination industry is the fouling that takes place due to the poor quality of the sea water received, especially when it rains. In such a situation, the sea water reaches the desalination plant having high turbidity. Chitosan was tested as a coagulant in the removal of the turbidity of sea water to replace inorganic coagulants having hazardous effects. Jar test was performed to test some factors that may affect the coagulation process. The factors tested were dose of coagulant (0-370 mg/L), initial pH (2-11), type of coagulant (chitosan versus metal coagulants), and the chitosan solvent. Chitosan's turbidity removal efficiency was found to be greater than ferrous sulfate and comparable to that of alum. While most researches emphasize the use of chitosan in acidic or neutral media, it worked well in the alkaline pH. The highest turbidity removal efficiency of 97.5% was obtained at initial pH of 8.1. The optimum dose was found to be 18 mg/L. Chitosan dissolved in HCl was found to perform better than that dissolved in acetic acid. Comparable turbidity removal efficiencies were obtained using alum and chitosan. However, much higher doses were used when using alum which implies higher cost and increase of residual aluminum concentration in treated water.

Harvesting Nannochloris oculata by inorganic electrolyte flocculation: effect of initial cell density, ionic strength, coagulant dosage, and media pH

Process variables affecting harvesting efficiency of Nannochloris oculata by AlCl(3) flocculation such as, cell density, ionic strength, coagulant dosage, media pH, and cell surface charge were investigated. Initial cell density and coagulant dosage had a significant effect on the removal efficiency; however, levels of ionic strength tested were not significant. Best flocculation conditions of investigated variables were: 0.0016 ng of AlCl(3)/cell, 3.0×10(7) cell/mL, and pH 5.3. Removal efficiency at optimum conditions and salt concentrations of: 0, 15, and 30 g/L NaCl was 96, 98, and 97 %, respectively. Low cell density cultures ∼10(6) cell/mL, required five times greater AlCl(3) dosage to achieve the same removal efficiency. Destabilization of algal cultures using 0.0032 ng of AlCl(3)/cell was observed by reducing the zeta potential to -22 mV. Acidification with HCl for conducting flocculation at pH 5.3 could be a significant cost burden unless is mitigated by selecting a low-buffering-capacity media.

Pretreatment of wastewater: optimal coagulant selection using Partial Order Scaling Analysis (POSA)

Jar-test is a well-known tool for chemical selection for physical-chemical wastewater treatment. Jar test results show the treatment efficiency in terms of suspended matter and organic matter removal. However, in spite of having all these results, coagulant selection is not an easy task because one coagulant can remove efficiently the suspended solids but at the same time increase the conductivity. This makes the final selection of coagulants very dependent on the relative importance assigned to each measured parameter. In this paper, the use of Partial Order Scaling Analysis (POSA) and multi-criteria decision analysis is proposed to help the selection of the coagulant and its concentration in a sequencing batch reactor (SBR). Therefore, starting from the parameters fixed by the jar-test results, these techniques will allow to weight these parameters, according to the judgments of wastewater experts, and to establish priorities among coagulants. An evaluation of two commonly used coagulation/flocculation aids (Alum and Ferric Chloride) was conducted and based on jar tests and POSA model, Ferric Chloride (100 ppm) was the best choice. The results obtained show that POSA and multi-criteria techniques are useful tools to select the optimal chemicals for the physical-technical treatment.

Integrated optimization of a waste water treatment plant using statistical analysis

In this research, a waste water treatment plant is systematically optimized. The waste water treatment plant is used to remove aluminium from waste water using precipitation, flocculation and flotation. In total 40 variables influence the combined unit. After systematic selection, the number of variables was reduced to six: the waste water flow, pH, agitation velocity, amount of poly-electrolyte, amount of dissolved air and aluminium concentration. For these variables an experimental design was set up and executed and the results were analyzed by means of ANOVA. With the results of the ANOVA, an empirical model was constructed. The model was used for maximization of the aluminium removal. Subsequently, validation experiments were performed to confirm the findings. The study showed that the amount of poly-electrolyte is a key factor for combined unit operation.

The pH as a key parameter in the choice between coagulation and electrocoagulation for the treatment of wastewaters

In this work, it is studied the influence of the pH of the waste in the coagulation with aluminum by conventional and electrochemical dosing. To do that, the speciation of aluminum as a function of the pH has been characterized, and this information has been used to interpret the results obtained in the treatments (by both coagulation methods) of a synthetic oil-in-water emulsion and an actual effluent of a door-manufacturing factory. Results show that a simple change in the pH of the wastes can result in a significant change in the efficiency of the coagulation process, and that if the same pH conditions are found at the end of the treatment, the efficiencies of the solution-dosing and of the electrochemical dosing technologies are very similar.

Removal of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans by three coagulants in simulated coagulation processes for drinking water treatment

Surface water from Guangzhou to which standard polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were added was treated by coagulation with ferric chloride (FC), polyaluminium chloride (PAC), and aluminium sulfate (AS) at optimum removal dosages for nature organic matter (NOM) to assess the polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) removal efficiencies. PCDD/Fs in suspended particulate matter (SPM) and treated water (TW) after coagulation were analysed. Low residual levels of PCDD/Fs were found in treated water after coagulation: 0.8% for FC, 0.9% for PAC, and 3.1% for AS. The removal efficiency calculated using these results was >99% for FC and PAC and 97-98% for AS. Most PCDD/Fs congeners could be removed by the three coagulation processes; the removal efficiency of FC and PAC was similar, and slightly higher than that of AS. The results also demonstrate that coagulation with FC preferentially removed tetra- and penta-substituted PCDD/Fs from raw water.

Performance optimization of coagulation/flocculation in the treatment of wastewater from a polyvinyl chloride plant

This paper presents results of an experimental study of coagulation/flocculation process of wastewater generated from a polyvinyl chloride (PVC) plant. The wastewater contains fine chlorine-based solid materials (i.e. latex). Experiments were carried out using a model wastewater which is chemically identical to the actual plant but is more consistent. Inorganic ions (Al2(SO4)3, FeCl3 and CaCl2) and a water soluble commercial polyelectrolyte (PE) were added to the wastewater sample. Coagulation efficiency was determined by measuring both the turbidity of the supernatants and the relative settlement of the flocs in the jar test. It was found that aluminum and ferric ions were more efficient than calcium ions as coagulants. The addition of polyelectrolyte was found to improve substantially the coagulation/flocculation process. It was found that the (Al2(SO4)3) combined with the polyelectrolyte at certain pH and agitation speed gave the best results compared to calcium chloride or ferric chloride when combined with the same concentration of polyelectrolyte. Only 0.0375g of a solution of (0.5% Al2(SO4)3) was required to coagulate the model wastewater. Ferric chloride (2.5% FeCl3) combined with the polyelectrolyte, on the other hand, required 0.1g while the optimum turbidity is almost the same. As for calcium chloride (2.5% CaCl2) it was found to be the least effective. The coagulation/flocculation process was found to be dependent on both pH and the agitation speed.

A novel method for on-line evaluation of floc size in coagulation process

Chemical coagulation is a simple and widely used water treatment process. A jar test based on the residual turbidity in the treated water was used to evaluate the optimal conditions for floc formation. However, the final residual turbidity does not show up variation of turbidity and floc formation during the flocculation process. Hence, a nephelometric turbidimeter method based on on-line monitoring was devised to determine the floc size variance during flocculation. A nephelometric turbidimeter coupled with a data acquisition unit was used to measure turbidity every second at 3 cm below the water surface during the coagulation process. Laboratory results indicated that this new instrument was capable of recording floc agglomeration during slow mixing very accurately. The standard deviation (SD) of the measured turbidity was proportional to the square root of the floc size; a greater SD indicated larger floc sizes. Hence, in addition to monitoring turbidity, the nephelometric turbidity meter is also a valuable tool to study the floc agglomeration process and variations in the resulting floc size. This method is simple and effective; it contributes significantly to the selection of coagulant and optimal flocculation conditions to improve water treatment.