Study on the removal of acid dyes using chitosan as a natural coagulant/coagulant aid

Efficiency of chitosan nanoparticle with polyaluminum chloride in dye removal from aqueous solutions: Optimization through response surface methodology (RSM) and central composite design (CCD)

According to the widespread use of polyaluminum chloride (PAC) in wastewater treatment and residual aluminum left in treated water, there is an urgent need to use environmentally friendly natural coagulants with conventional chemical coagulants to reduce their consumption. In this investigation, chitosan (CS) nanoparticles prepared as natural coagulant by ion gelation were applied to remove anionic dyes from aqueous solutions. For the characterization of the synthesized CS nanoparticles, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and zeta analyzer were used. The effects of different parameters, including pH, initial concentration of dye in addition to CS nanoparticles, and PAC dosages on adsorption efficiency were studied via response surface methodology (RSM) to determine the optimum conditions for maximum color removal. Results of the tests indicate that the use of CS nanoparticles and PAC with an interval of 30 s effectively increases the efficiency of color removal. The usage of PAC (80 mg/L) and CS nanoparticles (150 mL/L) at pH = 6.6 reaches the maximum color removal efficiency of 92 %. Accordingly, the use of CS nanoparticles as coagulant aid reduced the amount of needed PAC and enhanced the color removal efficiency. Furthermore, the exclusive effect of CS nanoparticles in the adsorption of dye revealed that the adsorption followed the Langmuir type II model, with an adsorption capacity of 1100 mg/g. The resulting data from the kinetic study indicated that the pseudo-second-order type II model was the most suitable model to describe the adsorption process of dye on CS nanoparticles. Based on the results, the CS nanoparticles have adequate potential to reduce the amount of needed PAC dosage for the treatment of water contaminated with anionic dyes.

Influence of Particle Size and Zeta Potential in Treating Highly Coloured Old Landfill Leachate by Tin Tetrachloride and Rubber Seed

Old leachate normally has a low organic compound content, poor biodegradability and is hard to biologically treat. The efficacy of tetravalent metal salts as a coagulant and the application of a natural coagulant as a flocculant in landfill leachate treatment is still inconclusive. Hence, this study aimed to evaluate the potential application of tin tetrachloride (SnCl₄) as the main coagulant and the rubber seed (Hevea brasiliensis) (RS) as the natural coagulant aid as the sole treatment in eradicating highly coloured and turbid stabilised landfill leachate present at one of the old local landfills in Malaysia. The standard jar test conducted revealed that SnCl₄ was able to eliminate 99% and 97.3% of suspended solids (SS) and colour, respectively, at pH8, with 10,000 mg/L dosages, an average particle size of 2419 d·nm, and a zeta potential (ZP) of −0.4 mV. However, RS was found to be ineffective as the main coagulant and could only remove 46.7% of SS and 76.5% of colour at pH3 with 6000 mg/L dosages, and also exhibited smaller particles (933 d·nm) with ZP values of −6.3 mV. When used as a coagulant aid, the polymer bridging mechanism in RS helped in reducing the SnCl₄ concentration from 10,000 mg/L to 8000 mg/L by maintaining the same performances. The presence of 1000 mg/L RS as a coagulant aid was able to remove 100% of SS and 97.6% of colour. The study concluded that RS has the potential to be used together with SnCl₄ in treating concentrated leachate with SS and colour.

Characterization of Two Cactus Formulation-Based Flocculants and Investigation on Their Flocculating Ability for Cationic and Anionic Dyes Removal

Dye invasion in wastewaters is undeniably one of the crucial environmental concerns in addition to the supplement of toxic synthetic chemical flocculants used for color removal using the conventional coagulation-flocculation process. With the aim to improve the flocculation stage in terms of reagents safety and ensure dyes removal, the present study explores the flocculating effectiveness of two natural, stable, and eco-friendly cactus formulations, namely 60 °C oven-dried (DP) and lyophilized (LP) cladodes. Both formulations were assessed to treat cationic (Methylene blue; MB) and anionic (Methyl Orange; MO) dye solutions as a substitution attempt for the currently questioned employed synthetic chemical flocculants. Obtained results demonstrate that, in conjunction with alum as coagulant, the lyophilized powder (LP) bio-based flocculant appears to be the most efficient cactus formulation, showing a significant color (83%) and a turbidity (69%) abatement for the cationic dye (MB) and, respectively, 63% and 62% for the anionic one (MO). Additionally, the flocculation activity of the LP formula remained high over an eight-month period of storage. Moreover, based on the Fourier transform infrared (FTIR) spectroscopic analysis and the chemical characterization of cactus formulations, the occurring flocculation mechanisms of the dye removal are presumed to be based on both adsorption and bridging phenomena. Further, the significant color and turbidity decline achieved upon the addition of the lyophilized cactus cladodes powder (LP), enhancing thus the coagulation performance of the alum-based coagulant, proved the effectiveness of this bio-flocculant compared to the commonly used chemical flocculant (polyacrylamide). Hence, it was suggested that lyophilized cactus cladodes as a natural flocculant could be one of the effective surrogates to chemical flocculants conventionally used in wastewater treatment for the sake of a safer and sustainable environment.

Nutrient Reduction of Dairy Manure Through Solid-Liquid Separation with Flocculation and Subsequent Microalgal Treatment

High concentrations of dairy operations in Southern Idaho have brought up big challenges for proper manure management to alleviate the eutrophication stress. In order to explore more technologies confronting the high nutrient load in dairy manure, a sequential process combining enhanced solid-liquid separation through flocculation-centrifuge and the subsequent microalgal growth in the liquid part was studied in this study. Solid-liquid separation by flocculation-centrifuge process, using a natural flocculant chitosan and a flocculation aid kaolin, was optimized through response surface methodology (RSM) technique using central composite design (CCD) method. Under the optimal flocculation-centrifuge pretreatment, i.e., the maximal total suspended solid (turbidity) removal group, turbidity, COD, TKN, and TP have been removed by 92.7%, 72.6%, 58.7%, and 43.0%, respectively. Applying 2-fold dilution, the supernatant from this treatment was further used for microalgae Chlorella vulgaris cultivation. COD, TKN, and TP were further reduced by 82.2%, 90.1%, and 83.4%, respectively. Turbidity was largely removed from the original dairy manure, providing a relatively clear solution that became suitable for photo-mixotrophic culture of microalgae.

Application of response surface methodology in physicochemical removal of dyes from wastewater: A critical review

Response surface methodology (RSM) is a powerful tool in designing the experiments and optimizing different environmental processes. However, when it comes to wastewater treatment and specifically dye-containing wastewater, two questions arise; "Is RSM being used correctly?" and "Are all capabilities of RSM being exploited properly?". The current review paper aims to answer these questions by scrutinizing different physicochemical processes that utilized RSM in dye removal. The literature that applied RSM to adsorption, advanced oxidation processes, coagulation/flocculation and electrocoagulation processes were critically reviewed in this paper. The common errors in applying RSM to physicochemical removal of dyes are identified and some suggestions are made for future studies.

A review on chitosan-based flocculants and their applications in water treatment

In recent years, the use of chitosan and its derivatives as flocculants in water treatment has received considerable attention due to their many advantages, including their widespread availability, environmental friendliness, biodegradability, and prominent structural features. However, it is a significant strategy for selection and design of the high-performance materials on the basis of their structure-activity relationships. Here we describe several of the chemical modification methods commonly used to prepare chitosan-based flocculants. These methods allow convenient control and adjustment of the structures of the obtained materials to meet the different practical requirements. The influence of structural elements of the chitosan-based flocculants on their flocculation properties are emphasized in this review by examining different flocculation mechanisms and their applications in the treatment of various wastewaters containing different pollutants (insoluble suspended colloids but also dissolved matters). Above all, the chitosan-based flocculants with proper structures by precise structure control bear great application potentials in water treatment.

Post-treatment of sanitary landfill leachate by coagulation-flocculation using chitosan as primary coagulant

Chitosan was chosen as an alternative primary coagulant in a complementary coagulation-flocculation treatment of sanitary landfill leachate with the aim of removing recalcitrant organic matter. In order to optimize the process conditions, central composite design and response surface methodology were applied. To evaluate the performance of the process using chitosan, we also carried out tests with aluminium sulphate (Al(2) (SO(4))(3).14 H(2)O) as coagulant. In addition, acute toxicity tests were carried using the duckweed Lemna minor and the guppy fish Poecilia reticulata as test organisms. The analytic hierarchy process was employed for selecting the most appropriate coagulant. Mean values of true colour removal efficiency of 80% and turbidity removal efficiency of 91.4% were reached at chitosan dosages of 960 mg L(-1) at pH 8.5. The acute toxicity tests showed that organisms were sensitive to all samples, mainly after coagulation-flocculation using chitosan. CE(50) for L. minor was not determined because there was no inhibition of the average growth rate and biomass production; LC(50) for P. reticulata was 23% (v v(-1)). Multi-criteria analysis showed that alum was the most appropriate coagulant. Therefore, chitosan as primary coagulant was not considered to be a viable alternative in the post-treatment of landfill leachate.