With the extensive application of graphene oxide (GO), it is noticeable that part of GO is directly/indirectly released into the environment and widespread research indicated that it had adverse influences on human health and ecological balance. In this work, a novel nanobelt-like Ca/Al layered double hydroxides (CA-LDH) was synthesized and applied as efficient coagulant for the removal of GO from aqueous solutions. The results indicated that neutral pH, co-existing cations and higher temperature were beneficial to the coagulation of GO. The sequence of cation effect for promoting of GO coagulation was Ca2+ > Mg2+ > K+ > Na+, whereas the effect of anions on GO coagulation was PO43− > CO32− > SO42− > Cl−. Comparing with anions, the cations showed more dominate effect for GO coagulation than anions. Hydrogen bonds and electrostatic interaction were the main coagulation mechanisms for GO coagulation, which were evidenced by FT-IR and XPS analysis. Specifically, for the first time, the reclaimed product of CA-LDH after GO coagulation (CA-LDH + GO) was applied as adsorbents for the secondary application in the removal of heavy metal ions from aqueous solutions. Interestingly, the CA-LDH + GO still had high adsorption capacities, i.e., the maximum adsorption capacities (qmax) for Cu(II), Pb(II), and Cr(VI) were 122.7 mg/g, 221.2 mg/g and 64.4 mg/g, respectively, higher than other similar materials. This paper highlighted the LDH-based nanomaterials are promising materials for the elimination of environmental pollutants and the migration and transformation of carbon nanomaterials in the natural environment.

In this study, cassava starch wastewater was subjected to coagulation/flocculation (C/F) combined with microfiltration (MF) to improve the final quality of treated water. In the C/F tests of the effluent, the best concentration of the natural coagulant (Tanfloc POP) was determined from a statistical analysis of color removal and turbidity data. The supernatant produced in the C/F step was subjected to MF while varying the transmembrane pressure to evaluate the permeate fluxes, fouling mechanism, and permeate quality. The mathematical model that best represented the filtration process was the fouling mechanism of partial membrane pore blockage. The best experimental conditions for coagulant dosage, settling time, and MF pressure in the combined C/F-MF process were 320 mg L⁻¹, 15 min, and 1.4 bar, respectively. The highest overall removal efficiency rates achieved were 99% color, 91% cyanide, 75% total organic carbon, and 100% turbidity, demonstrating the promising potential of the combined C/F-MF process in the treatment of cassava starch wastewater.

Present study investigates the coagulation ability of Plantago ovata (P. ovata) seed extracts for turbidity removal. The active coagulant agents were successfully extracted from P. ovata seeds using different solvents such as distilled water (PO-DW), tap water (PO-TW), NaCl (PO-NaCl), and ammonium acetate (PO-AA). Experiments were conducted in batch mode for initial turbidity such as 500 NTU (high), 150 NTU (medium), and 50 NTU (low). Results demonstrated that P. ovata extracts are less efficient in low turbidities, while PO-NaCl was found to provide high coagulation activity in all initial turbidity concentrations compared to other extracts. PO-NaCl was able to remove 98.2, 94.9, and 80.2% of turbidity from water having in initial turbidities of 500, 150, and 50 NTU, respectively. Coagulation activity of the extract was the best when the extraction was performed for 50 min at room temperature. Jar test procedure with the coagulation time of 1 min and flocculation time of 30 min was optimized, irrespective of the initial turbidity. The optimum settling time for 500, 150, and 50 NTU water samples were 20, 30, and 90 min, respectively. PO-NaCl was used in different pH turbid solutions and it was found to be working very efficiently in alkaline conditions. The coagulation efficiency of the coagulant stored in refrigerator was higher than that stored at room temperature. Thus, the natural coagulants extracted from P. ovata seeds revealed to be effective for turbidity removal.

The main objective of the present paper is to evaluate the use of Moringa oleifera (MO) as a natural coagulant in coagulation/flocculation/sedimentation (CFS) followed by the microfiltration (MF) or nanofiltration (NF) process in dairy wastewater treatment, focusing on determining the best association of treatments that can generate wastewater for reuse purposes. The association of CFS-MF-NF treatments showed a high removal efficiency for chemical oxygen demand (COD) (mean of 96%), turbidity, and color (mean of 99%) meeting water reuse standards, allowing the reutilization of the wastewater, in relation to the analyzed parameters. The results indicate a lower membrane fouling rate (63%), an increase in permeate flow, and better quality of the permeate, proving that the CFS-MF-NF treatment is the most suitable among all the tested treatments. Finally, the treated wastewater obtained with this process presents better quality than the wastewater obtained with the conventional treatments.

In the present study, the ability of Hibiscus rosa-sinensis leaf extract (HLE) to act as a natural coagulant for the water treatment was tested. Synthetic turbid solutions were prepared using kaolinite, and the efficiency of HLE was examined for low and high turbid solutions. HLE was very effective in high turbid solutions than in low turbid water and follows enmeshment mechanism of destabilization. An insignificant effect of alkalinity on the performance of HLE was observed. The addition of NaCl increased the dissolution of coagulation active species and enhanced the efficiency of HLE, significantly. Hydroxyl and carboxyl groups present in HLE were the major functional groups responsible for the bonding between coagulant and kaolinite. The efficiency of alum was very high compared to that of HLE in both turbid solutions. But the optimal dosages of HLE were lesser than that of alum. Thus, HLE can be used as a coagulant aid for the effective treatment of water.

Natural polymeric flocculant shows effectiveness in wastewater treatment without increasing the environmental burden. The extracellular substance produced by Paenibacillus mucilaginosus WL412 was identified as an anionic polysaccharide composed of five types of monosaccharides, namely, D-mannose, D-glucuronic acid, D-glucose, D-galactose, and L-fucose with the molar ratio of 2.8:1.2:2.0:1.8:0.8. The purified polysaccharide, POS412, presented high efficiency in flocculating coal washing wastewater and kaolin suspension without the assistance of inorganic coagulants. Addition of POS412 resulted in the polymer bridging phenomenon in suspensions, which was observed by means of scanning electron microscopic imaging, size grading, and ζ-potential analyses. More importantly, POS412 exhibited satisfactory stability after storage in various conditions. The flocculation rate was more than 91% for coal washing wastewater when POS412 was stored for 264 h in the wide range of pH (3–11) and temperature (20–50 °C) before use. Results indicate that POS412 is a competent bioflocculant for wastewater treatment.

It is confirmed that nano-ZnO (nZnO) has impact on environment and is considered as heavy metal pollutants. It is a new technology that applies coagulation process to simultaneous removal of the nanoparticles and heavy metals. Environmental chemical behavior of ZnO in water, such as the dispersion, aggregation, sedimentation, and dissolution of releasing metal ions, has been systematically studied in this paper. The result shows that three kinds of nZnO state such as compacted sediment, suspended, and released is separately 36.54 %, 40.61 %, and 22.86 %. Enteromorpha polysaccharide (Ep) was used together with polyaluminum chloride (PAC) in surface water purification. In order to study the mechanism of simultaneous removal of residual nZnO particles and Zn²⁺, coagulation process was further applied in this study. The evolution of flocs size, strength, and recovery ability and fractal structure due to Ep addition was systematically studied in this paper. Results indicated that PAC-Ep was efficient in removing nZnO and Zn²⁺, which leads to more than 95 % particles, 50–60 % natural organic matter (NOM) removed, and 35 % of resolved heavy metal ion adsorbing-chelation. Ep was an efficient coagulant aid in enhancing performance of coagulation and generating flocs with bigger sizes, faster growth rates, and higher recovery abilities. Additionally, the flocs formed by PAC-Ep presented a much looser structure than flocs formed only by PAC. Graphical abstract ᅟ

A new commercial cationic polyelectrolyte chitosan (CM), obtained from the waste of mushroom production, was examined using models of water and wastewater namely kaolin and palm oil mill effluent (pome). As it is biocompatible, widely available, and economically feasible, chitosan mushroom has high potential to be a suitable replacement for alum. Also, it can be a promising alternative to chitosan obtained traditionally from Crustaceans due to its higher zeta potential and homogeneity based on the raw material required for its production. A wide range of coagulant dose (5–60 mg l⁻¹) and wastewater pH (2–12) were taken into account to find the optimal conditions of coagulation. The optimal doses are 10 and 20 mg l⁻¹ at best pH (11 and 3) when treated with kaolin and palm oil mill effluent, respectively, while 1200 mg l⁻¹ of alum was not enough to reach the efficiency of chitosan mushroom. On the other hand, the optimum dose of chitosan mushroom (20 mg l⁻¹) at pH 3 of pome produced (75, 73, and 98%) removal of chemical oxygen demand (COD), biological oxygen demand (BOD), and total suspended solids (TSS), respectively. The significant potential of chitosan mushroom was proved by zeta potential measurement. Indeed, it possesses the highest zeta potential (+70 mV) as compared to the traditional chitosan produced from crustaceans. In short, chitosan mushroom as a biocoagulant is eco-friendly and it enhances water quality that meets the requirements of environmental conservatives.

Without treatment, waterworks sludge is ineffective as an adsorbent. In this study, raw waterworks sludge was used as the raw material to prepare modified sludge particles through high-temperature calcination and alkali modification. The feasibility of using a combination of modified particles and polyaluminum chloride (PAC) as a coagulant for treatment of slightly polluted source water was also investigated. The composition, structure, and surface properties of the modified particles were characterized, and their capabilities for removing ammonia nitrogen and turbidity were determined. The results indicate that the optimal preparation conditions for the modified sludge particles were achieved by preparing the particles with a roasting temperature of 483.12 °C, a roasting time of 3.32 h, and a lye concentration of 3.75%. Furthermore, enhanced coagulation is strengthened with the addition of modified sludge particles, which is reflected by reduction of the required PAC dose and enhancement of the removal efficiency of ammonia nitrogen and turbidity by over 80 and 93%, respectively. Additional factors such as pH, temperature, dose, and dosing sequence were also evaluated. The optimum doses of modified particles and PAC were 40 and 15 mg/L, respectively, and adding modified particles at the same time as or prior to adding PAC improves removal efficiency.

Titanium-based coagulation is expected to achieve both efficient water purification and sludge recycling. This study is the first attempt to use titanium tetrachloride (TiCl₄) for silver nanoparticle (AgNP)-humic acid composite contaminant removal in a coagulation-ultrafiltration (C-UF) process, where characterization of flocs and membrane fouling under varied coagulant dose, initial solution pH, and AgNP concentration conditions are the main contents. Results suggested that the TiCl₄ achieved high AgNP removal in the form of silver nanoparticle through adsorption and sweep flocculation and simultaneously exerted additional 68.2 % higher dissolved organic carbon removal than Al₂(SO₄)₃. The TiCl₄ produced larger and stronger flocs but with weaker recoverability and less compact degree than did Al₂(SO₄)₃. Floc properties were independent of AgNP concentration except floc fractal dimension, which was negatively correlated with AgNP concentration. The TiCl₄ precoagulation caused less membrane fouling within wider pH range than Al₂(SO₄)₃ did in the C-UF process. Incorporation of AgNPs during the TiCl₄ pretreatment process facilitated the mitigation of membrane fouling, which was, however, negligibly influenced by AgNP concentration in the case of Al₂(SO₄)₃.