Coagulation behavior of polyaluminum chloride: Effects of pH and coagulant dosage

Optimization use of watermelon rind in the coagulation-flocculation process by Box Behnken design for copper, zinc, and turbidity removal

Watermelon rinds were investigated as a bio-coagulant for treating water contaminated by metals and turbidity, owing to their biodegradability and greater environmental friendliness compared to chemical coagulants. Fourier transform infrared spectroscopy, scanning electron microscopy paired with energy dispersive X-ray analysis and X-ray diffraction characterized the watermelon rinds before and after use. A Box-Behnken experimental design optimized the most influential parameters of initial pH, coagulant dose, and particle size based on response surface methodology. This analysis revealed the experimental data fit quadratic polynomial models, achieving maximum removal efficiencies of 97.51 % for zinc, 99.88 % for copper, and 99.21 % for turbidity under optimal conditions. Statistical analysis confirmed the models effectively captured the experimental data. Analysis of variance denoted the high significance of the quadratic effects of dose and pH. Removal of metal ions Zn2+ and Cu2+ was significantly impacted by these factors. The watermelon rind powder retained its coagulation efficiency after five cycles of reuse, with removal rates of 80.04 % for Zn, 88.33 % for Cu and 86.24 % for turbidity. These results demonstrate the potential of watermelon rind as an alternative coagulant for wastewater treatment. Further testing on real industrial effluents at larger scales would help assess their feasibility for real-world applications.

Premise setting for sustainable developing adsorption in environmental remediation using graphitic carbon nitride@agar-derived porous carbon composite

In the adsorption process for wastewater treatment, the adsorbent plays an important role. A composite adsorptive material composed of graphitic carbon nitride and agar-derived porous carbon (CNPC) was fabricated from simple precursors (melamine, thiourea, and agar) and through a facile procedure with different melamine and thiourea ratios. Characterization of CNPC proved a successful formation of a porous structure consisting of mesopores and macropores, wherein CNPC holds distinctive electrochemical (lowered resistance and higher specific capacity) and photochemical properties (lowered bandgap to 2.33 eV) thanks to the combination of graphitic carbon nitride (CN) and agar-derived porous carbon (PC). Inheriting the immanent nature, CNPC was subjected to the adsorption of methylene blue (MB) dye in an aqueous solution. The highest adsorption capacity was 133 mg/g for CNPC-4 which was prepared using a melamine to thiourea ratio of 4:4 - equivalent to the removal rate of 53.2 % and following the pseudo-I-order reaction rate. The effect of pH points out that pH 7 and 9 were susceptible to maximum removal and pretreatment is not required while the optimal ratio of 7.5 mg of MB and 30 mg of material was also determined to yield the highest performance. Furthermore, the reusability of the material for three consecutive cycles was evaluated based on two methods pyrolysis at 200 °C and photocatalytic degradation by irradiation under visible light. In general, the photocatalytic regeneration pathway is more ample and efficient than pyrolysis in terms of energy efficiency (saving energy over 10 times) and adsorption capacity stability. As a whole, the construction of accessible regenerative and stable adsorbent could be a venturing step into the sustainable development spearhead for industries.

Dewatering and strength characteristics of dredged slurry under curing-flocculation-vacuum filtration

Addressing the substantial yearly production of waste dredged slurry with high water content, it is imperative to adopt effective technical treatments for sustainable development. This paper establishes that the curing-flocculation-vacuum filtration (C-F-VF) method efficiently converts high-water content dredged slurry into back-fill soil, achieving rapid dewatering. The study delves into the mechanism facilitating swift dewatering and the heightened mechanical properties of the dewatered soil. The synergy of curing, flocculation, and vacuum filtration expedites the dewatering process. The pre-addition of a curing agent reduces the zeta potential of the slurry, enhancing its efficiency in subsequent flocculation and vacuum filtration. Although the curing agent experiences some loss during vacuum filtration, over 91.22% remains in the dewatered soil, fortifying its strength. Soil strength correlates with the water content post-vacuum filtration and the amount of cement added pre-filtration, with a proposed relevant strength prediction formula.

Effectiveness of Opuntia ficus indica (cactus) fruit juice for sludge conditioning

The possibility of using Opuntia ficus indica fruit juice (OFIFJ) as a bioflocculant for conditioning the synthetic kaolin sludge and sewage sludge (region Oran, Algeria, and Pau, France) was studied. Turbidity of the supernatant, dryness of the sludge cake, and total time of filtration (TTF) were examined parameters. Using vacuum filtration, lime was also tested as a chemical conditioner and gives good results on Lescar (France) sewage sludge in terms of cake's dryness, filtrate quality, turbidity (13.54%), and total time of filtration (TTF = 85.29%), comparing to the industrial polymer (Sedifloc 408C; turbidity; 8.33% and TTF: 2.94%). For the sewage sludge of Oran (Algeria), the results obtained with OFIFJ were compared to those obtained with the cladodes juice of the same plant OFIC, and also with a cationic polymer (Superfloc 8396). For an optimum dosage, it showed that OFIFJ has a flocculation activity as same as the cladodes juice OFIC for sludge conditioning and gives better results in terms of turbidity (dosage of 22.4 g/kg DM: 3.7 NTU for OFIC, dosage of 8.36: 3.63 NTU for OFIFJ. Dryness was enhanced from 14.91 to 22.93% (OFIC 16 g/kg DM) and to 24.48% (OFIF 20.9 g/kg DM) but for TTF, we found the opposite. In fact, this plant showed to be an available, biodegradable, and non-toxic flocculant. For kaolin synthetic sludge (30%), the optimum dosages of those conditioners were found to be 0.066 g kg-1 for OFIC, comparing between vacuum filtration and filtration compression; turbidity was enhanced for both techniques, contrary to dryness. Concerning the Oran city sewage sludge, both turbidity and dryness were optimized. Same thing for the France sewage sludge, all the studied parameters were enhanced with the two studied bioflocculants.

Response surface optimization of chemical coagulation for solid-liquid separation of dairy manure slurry through Box-Behnken design with desirability function

Discharging livestock manure slurry without proper treatment causes various environmental and sociological problems. Chemical coagulation is a widely used and easily applicable method for treating such wastewater. However, the technique requires optimization to enhance coagulation efficiency while minimizing chemical usage. In this study, we propose an efficient, low-cost, and environmentally safe chemical coagulation method for solid-liquid separation of dairy manure slurry. Experiments were conducted in laboratory jar tests using dairy manure slurry to investigate the impact of coagulants, specifically polyaluminum chloride (PAC) and cationic polyacrylamide (CPAM), as well as pH, on the process of solid-liquid separation. Preliminary ranges of PAC, CPAM, and pH were estimated through single-factor experiments. Coagulation optimization and modeling were performed using the response surface methodology (RSM) with the Box-Behnken design (BBD), wherein the desired goal of each parameter was set to maximize solid-liquid separation efficiency while reducing chemical dosage to maintain residual aluminum (Al) concentrations below water quality standards. Numerical optimization predicted that the optimal dosages were 75 mg/L of PAC and 35 mg/L of CPAM at pH 7. Under these conditions, removal efficiencies of 99% for turbidity and 97% for chemical oxygen demand (COD) were achieved, with a minimal residual Al concentration of 0.045 mg/L. Positive zeta potential values in the treated water confirmed complete separation of negatively charged solids in the dairy manure slurry. The response values predicted by BBD aligned with the experimental results, and the analysis of variance (ANOVA) demonstrated the predictability and accuracy of the response models. Consequently, this study highlights the practical application of RSM with BBD in optimizing chemical coagulation using PAC and CPAM to achieve efficient solid-liquid separation in livestock wastewater while maintaining low residual Al concentrations.

Improved 31P NMR analysis of phosphorus in highly mineralized lake water using a modified pretreatment procedure with H resin

³¹P Nuclear Magnetic Resonance (³¹P NMR) is an important analytical tool for identifying and quantifying phosphorus-based compounds in aquatic environments. However, the precipitation method typically used for analyzing phosphorus species via ³¹P NMR has limited application. To expand the scope of the method and apply it to highly mineralized rivers and lakes worldwide, we present an optimization technique that employs H resin to assist phosphorus (P) enrichment in highly mineralized lake water. To explore how to reduce analysis interference from salt in highly mineralized water and improve the accuracy of P analysis using ³¹P NMR, we conducted case studies on Lake Hulun and Qing River. This study aimed to increase the efficiency of phosphorus extraction in highly mineralized water samples by using H resin and optimizing key parameters. The optimization procedure included determining the enriched water volume, H resin treatment time, AlCl₃ addition amount, and precipitation time. The final recommended optimization enrichment procedure involves treating 10 L of filtered water sample with 150 g of Milli-Q water-washed H resin for 30 s, adjusting the pH of the treated sample to 6-7, adding 1.6 g of AlCl₃, stirring the mixture, and allowing the solution to settle for 9 h to collect the flocculated precipitate. The precipitate was then extracted with 30 mL of 1 M NaOH +0.05 M DETA extraction solution at 25 °C for 16 h, and the supernatant was separated and lyophilized. The lyophilized sample was redissolved in 1 mL of 1 M NaOH +0.05 M EDTA. This optimized analytical method using ³¹P NMR effectively identified phosphorus species in highly mineralized natural waters and can be applied to other highly mineralized lake waters globally.

Study on the operation performance and floc adhesion mechanism of dissolved air flotation equipment

As a critical air dissolving system, the performance of air flotation equipment directly determines the adhesion efficiency and pollutant removal efficiency of air flotation processes. The factors affecting the performance of air flotation equipment and the relationships between equipment performance and pollution removal efficiency were studied. The results show that when the dissolved gas pressure was 0.4 MPa and the air intake rate was 24 mL/min, the dissolved gas efficiency of the equipment reached its highest value of 55%, the average particle size of bubbles was maintained at 24 µm, and the dissolved oxygen (DO) content significantly increased. When the dissolved gas pressure was 0.4 MPa, the air intake rate was 24 mL/min, and the coagulant dose was 6 mg/L; the removal rates for turbidity, chlorophyll-a, total organic carbon (TOC), and UV absorbance at 254 nm (UV₂₅₄) reached 95.76%, 96.41%, 34.21%, and 65.96%, respectively. The degree of pollutant removal was positively correlated with changes to the equipment performance parameters. Microbubbles (MBs) showed good removal of high-molecular weight, strongly hydrophobic organic matter and showed some removal of the trihalomethane formation potential (THMFP) of the water. The removal mechanism mainly depended on the hydrophobic interactions of the MBs with algae and organic matter. The flocs and MBs collided and adhered to form air-entrained flocs. The separation of air-entrained flocs depended on the relationship between the surface load and the rising velocity. The surface load has to be lower than the rising velocity of the minimum air-entrained flocs to ensure good effluent outcomes.

Automated Monitoring of a High-Speed Flocculation Flat-Bottomed Sludge Blanket Clarifier Pond during Drought and Flood Conditions

The occasional rains that occur during dry seasons often stir up the bottom sediment of reservoirs, which leads to high turbidity and electrical conductivity in raw waters received by water utility companies. A newly developed real-time precision multi-layer sensor (RPMS) system was used to monitor a high-speed flocculation flat-bottomed sludge blanket clarifier (HFSBC) pond in real time to solve the water quality problems caused by drought and flood conditions. The RPMS is capable of monitoring the thickness of a sludge blanket; if the coagulation and sedimentation processes of the HFSBC are not working well, the sludge blanket will be thin and have a low sludge concentration. Conversely, if the HFSBC is working properly, the sludge blanket will have a thick and highly concentrated layer of sludge. Any heavy metals that are not removed by water treatment processes will enter the water supply network, which will result in poor water quality for end users. Against the backdrop of intensifying climate change, the enhancement of automated monitoring systems and adaptation processes will be an important part of efforts to minimize and resolve acute changes in water quality.

Applicability of the linearized Poisson-Boltzmann theory to contact angle problems and application to the carbon dioxide-brine-solid systems

In colloidal science and bioelectrostatics, the linear Poisson Boltzmann equation (LPBE) has been used extensively for the calculation of potential and surface charge density. Its fundamental assumption rests on the premises of low surface potential. In the geological sequestration of carbon dioxide in saline aquifers, very low pH conditions coupled with adsorption induced reduction of surface charge density result in low pH conditions that fit into the LPB theory. In this work, the Gouy–Chapman model of the electrical double layer has been employed in addition to the LPBE theory to develop a contact angle model that is a second-degree polynomial in pH. Our model contains the point of zero charge pH of solid surface. To render the model applicable to heterogeneous surfaces, we have further developed a model for the effective value of the point of zero charge pH. The point of zero charge pH model when integrated into our model enabled us to determine the point of zero charge pH of sandstone, quartz and mica using literature based experimental data. In this regard, a literature based thermodynamic model was used to calculate carbon dioxide solubility and pH of aqueous solution. Values of point of zero charge pH determined in this paper agree with reported ones. The novelty of our work stems from the fact that we have used the LPB theory in the context of interfacial science completely different from the classical approach, where the focus is on interparticle electrostatics involving colloidal stabilization.

'Floc and Sink' Technique Removes Cyanobacteria and Microcystins from Tropical Reservoir Water

Combining coagulants with ballast (natural soil or modified clay) to remove cyanobacteria from the water column is a promising tool to mitigate nuisance blooms. Nevertheless, the possible effects of this technique on different toxin-producing cyanobacteria species have not been thoroughly investigated. This laboratory study evaluated the potential effects of the "Floc and Sink" technique on releasing microcystins (MC) from the precipitated biomass. A combined treatment of polyaluminium chloride (PAC) with lanthanum modified bentonite (LMB) and/or local red soil (LRS) was applied to the bloom material (mainly Dolichospermum circinalis and Microcystis aeruginosa) of a tropical reservoir. Intra and extracellular MC and biomass removal were evaluated. PAC alone was not efficient to remove the biomass, while PAC + LMB + LRS was the most efficient and removed 4.3-7.5 times more biomass than other treatments. Intracellular MC concentrations ranged between 12 and 2.180 µg L^-1 independent from the biomass. PAC treatment increased extracellular MC concentrations from 3.5 to 6 times. However, when combined with ballast, extracellular MC was up to 4.2 times lower in the top of the test tubes. Nevertheless, PAC + LRS and PAC + LMB + LRS treatments showed extracellular MC concentration eight times higher than controls in the bottom. Our results showed that Floc and Sink appears to be more promising in removing cyanobacteria and extracellular MC from the water column than a sole coagulant (PAC).

Aloe vera as Promising Material for Water Treatment: A Review

Aloe vera plant offers a sustainable solution for the removal of various pollutants from water. Due to its chemical composition, Aloe vera has been explored as coagulant/flocculant and biosorbent for water treatment. Most of the used materials displayed significant pollutants removals depending on the used preparation methods. AV-based materials have been investigated and successfully used as coagulant/flocculant for water treatment at laboratory scale. Selected AV-based materials could reduce the solids (total suspended solids (TSS), suspended solids (SS), total dissolved solids (TDS), and dissolved solids (DS)), turbidity, chemical oxygen demand (COD), biochemical oxygen demand (BOD), heavy metals, and color, with removal percentages varied depending on the coagulant/flocculant materials and on the wastewater characteristics. In the same context, AV materials can be used as biological flocculant for wastewater sludge treatment, allowing good solid–liquid separation and promoting sludge settling. Moreover, using different methods, AV material-based biosorbents were prepared and successfully used for pollutants (heavy metal dyes and phenol) elimination from water. Related results showed significant pollutant removal efficiency associated with an interesting adsorption capacity comparable to other biosorbents derived from natural products. Interestingly, the enzymatic system of Aloe vera (carboxypeptidase, glutathione peroxidase, and superoxide dismutase) has been exploited to degrade textile dyes. The obtained results showed high promise for removal efficiencies of various kinds of pollutants. However, results varied depending on the methodology used to prepare the Aloe vera based materials. Because of its valuable properties (composition, abundance, ecofriendly and biodegradable), Aloe vera may be useful for water treatment.

Influences of coagulation pretreatment on the characteristics of crude oil electric desalting wastewaters

Highly polluted crude oil electric desalting wastewaters (EDWs) severely affect the efficiency of refinery wastewater treatment plants (WWTPs). Coagulation is an efficient pretreatment to reduce the impacts of EDWs. In the present study, the influences of coagulation pretreatment on the characteristics of EDWs of three typical Chinese crude oils, Liaohe heavy oil (LHO), Karamay heavy oil (KHO) and Daqing light oil (DLO), were investigated. The stability of three raw EDWs was broken and the contents of organic pollutants were significantly reduced by aluminum sulfate coagulation. More soluble COD and polar oils were removed from LHO-EDW (1241 and 98 mg L^-1) and KHO-EDW (779 and 57 mg L^-1) compared to DLO-EDW (417 and 11 mg L^-1). Coagulation significantly changed the compositions of the organic pollutants of two heavy oil EDWs; however, slightly influenced DLO-EDW, particularly the polar organic pollutants. Most types of aromatic compounds, aliphatic acids and O_x polar compounds were removed from two heavy oil EDWs, but mainly alkanes were removed from DLO-EDW. As such, the differences in the types of dominant polar compounds became insignificant among treated heavy oil and light oil EDWs. Coagulation notably decreased the acute biotoxicity and improved the biodegradability of all treated EDWs. The residual organic nitrogen compounds in treated KHO-EDW contributed to a higher residual biotoxicity compared to treated LHO-EDW. The results demonstrate that coagulation can effectively improve the qualities of heavy oil EDWs by lowering the contents of organic pollutants and removing recalcitrant compounds, thus guaranteeing the efficiency of refinery WWTPs.

Polysulfone-Polyvinyl Pyrrolidone Blend Polymer Composite Membranes for Batik Industrial Wastewater Treatment

Batik wastewater, in general, is colored and has high concentrations of BOD (biological oxygen demand), COD (chemical oxygen demand), and dissolved and suspended solids. Polysulfone (PSf)-based membranes with the addition of polyvinyl pyrrolidone (PVP) were prepared to treat batik industrial wastewater. PSf/PVP membranes were prepared using the phase inversion method with N-methyl-2 pyrrolidone (NMP) as the solvent. Based on the membrane characterization through FESEM, water contact angle, porosity, and mechanical tests showed a phenomenon where the addition of PVP provided thermodynamic and kinetic effects on membrane formation, thereby affecting porosity, thickness, and hydrophilicity of the membranes. The study aims to observe the effect of adding PVP on polysulfone membrane permeability and antifouling performance on a laboratory scale through the ultrafiltration (UF) process. With the addition of PVP, the operational pressure of the polysulfone membrane was reduced compared to that without PVP. Based on the membrane filtration results, the highest removal efficiencies of COD, TDS (total dissolved solid), and conductivity achieved in the study were 80.4, 84.6, and 83.6%, respectively, on the PSf/PVP 0.35 membrane operated at 4 bar. Moreover, the highest color removal efficiency was 85.73% on the PSf/PVP 0.25 operated at 5 bar. The antifouling performance was identified by calculating the value of total, reversible, and irreversible membrane fouling, wherein in this study, the membrane with the best antifouling performance was PSf/PVP 0.25.

Solids management in freshwater-recirculating aquaculture systems: Effectivity of inorganic and organic coagulants and the impact of operating parameters

Coagulants are widely used for solids (uneaten food, faeces, etc.) management in recirculating aquaculture systems (RAS), but no recent research has been performed on the effectiveness of different coagulants in treatment of aquaculture sludge. This study examined the effectivity of selected inorganic (polyaluminium chloride, PAC) and organic products (polyamine- and starch-based) as coagulant agents for solids management in RAS. Reductions in residual concentrations of total phosphorus (tot-P), phosphate‑phosphorus (PO₄-P), suspended solids (SS) total nitrogen (tot-N), nitrate‑nitrogen (NO₃-N), ammonium‑nitrogen (NH₄-N), aluminium (Al) and chemical oxygen demand (COD) in reject water were determined. The effect of process parameters (coagulant type, dose, mixing and sedimentation time) on sludge treatment was also evaluated. The PAC products tested were most effective at concentrating pollutants (Tot-P, PO₄-P, SS, COD) in RAS sludge into the solid phase. The organic products tested, especially a high-molecular-weight polyamine product (pAmine1), achieved good performance and can be considered a valid alternative to inorganic salts. At optimum dose, PAC (dose 32 mg/L) and pAmine1 (dose 15 mg/L) removed, respectively, 99.4% and 82.8% of turbidity, 98.2% and 65.4% of PO₄-P and 97.7% and 73.6% of SS. The mixing time applied in flocculation and the time allowed for sedimentation had significant effects on coagulant performance, with the organic coagulants being most affected. Flocculation times of 5-15 min and sedimentation times of 15-60 min showed good results and can be used as a starting point in process optimisation with both inorganic and organic coagulants. The use of coagulants for treatment of RAS sludge enhances flock formation and improves particle settling characteristics, substantially decreasing nutrient, organics and solids concentration in reject water.

Decentralised, small-scale coagulation-membrane treatment of wastewater from metal recycling villages - a case study from Vietnam

Effective treatment of wastewaters laden with heavy metals is critical to the sustainable social and economic growth of metal recycling villages in Vietnam. Currently, most wastewaters from metal recycling villages in Vietnam are directly discharged, posing great threats to the environment and human health. In this study, a small-scale combined coagulation-membrane filtration treatment of wastewater collected from a metal recycling village in Vietnam was experimentally investigated. The experimental results manifested the technical viability of the combined coagulation-membrane filtration process for the treatment of the heavily polluted metal recycling wastewater for beneficial reuse. In this combined treatment process, coagulation using ferric chloride (FeCl₂) served as a pre-treatment prior to the microfiltration (MF)/reverse osmosis (RO) process. Under the optimised conditions, coagulation at the dosage of 0.2 g FeCl₂ per 1,000 ml wastewater removed more than 90% of heavy metals (i.e. most notably including aluminium and chromium) from the wastewater, reducing the aluminium and chromium concentrations in the wastewater from 548.0 to 52.3 mg/L to 32.6 and 1.7 mg/L, respectively. The MF treatment of the wastewater following the coagulation further removed suspended solids and organic matters, rendering the wastewater safe for the subsequent RO filtration with respect to membrane fouling. Given the efficient pre-treatment of coagulation and MF, the RO process at the controlled water recovery of 50% was able to effectively treat the wastewater to potable water.

Organic polyelectrolytes as the sole precipitation agent in municipal wastewater treatment

In municipal wastewater treatment, inorganic coagulants (IC), e.g. polyaluminium chloride (PAC), are normally used to remove pollutants such as dissolved and particulate nutrients, in a process called coagulation/flocculation. However, IC use has been linked to issues e.g. in effluent water post-treatment, sludge management and disposal (IC increase sludge volume and metal concentrations in sludge), etc., raising uncertainties about their overall cost-efficiency and environmental benefits. In this study, the suitability of organic coagulants (OC) as sole precipitation agents to replace IC (PAC) was investigated. A total of 10 synthetic (i.e. polyDADMACs and polyamines) and semi-natural (chitosan, starch, and tannin-based) OC products were tested in treatment of samples from primary sedimentation and secondary sedimentation stages of municipal wastewater treatment, and their performance was compared with that of PAC. The study was conducted using the jar test methodology. The coagulants were tested for their ability to remove target pollutants (e.g. BOD₇, COD, SS, tot-P, PO₄-P, tot-N) and form rapidly settling flocs. In general, higher (up to 60%) coagulant doses were needed in treatment of secondary wastewater samples than primary samples. In comparison with the OC doses required for effective treatment, the PAC doses were higher (up to 80%). In treatment of secondary wastewater samples, OC with high molecular weight (MW) and high charge density (CD) (e.g. pAmine1) achieved best removal of target pollutants (e.g. 72% SS, 87% PO₄-P, 88% BOD₇), followed by PAC. In treatment of primary wastewater, PAC performed best (removing e.g. 96% SS, 96% PO₄-P), closely followed by chitosan and polyamine products. Based on these results, polyamine products with high MW and (very) high CDs have the potential to act as the sole precipitation agent in both primary and secondary stages of municipal wastewater treatment. Further research is needed to determine the effect of residual coagulant on downstream water and sludge treatment processes (e.g. activated sludge process, sludge dewatering, etc.).

Mucilage Extracted from Dragon Fruit Peel (Hylocereus undatus) as Flocculant for Treatment of Dye Wastewater by Coagulation and Flocculation Process

Dye wastewater from textile industries shows very low biodegradability due to high molecular weight and complex structures of dyes. So far, the most simple method for treatment of this type of wastewater has been coagulation and flocculation. This study determined the removal of turbidity and other pollutants from dye wastewater by mucilage extracted from the peel of dragon fruit (Hylocereus undatus) and its effect in reducing synthetic chemical polyaluminum chloride (PACl) used in coagulation and flocculation (CF) process. The removal of turbidity in a sequent CF process using PACl and dragon fruit mucilage was investigated based on Jar tests. Maximum coagulation efficiencies of PACl were typically observed at pH 4.0-6.0 and PACl concentrations of about 100-150 mg/L depending on types of wastewater, whereas optimal settling times were 30-60 minutes, respectively. The addition of dragon fruit mucilage (0.5-50 mg/L) after PACl (75-245 mg/L) resulted in turbidity removal efficiencies up to 95%. The addition of mucilage extracted from dragon fruit peels was proven to increase turbidity removal efficiency and decrease PACl use. The increase of turbidity removal was often estimated at 10-32%, whereas PACl used was about 3-10% less compared to total PACl needed for obtaining comparable efficiency when used alone. The flocculation activity of mucilage was also compared to polyacrylamide (PAM)—a synthetically organic flocculant. Since the peel of a dragon fruit is an abundant agriculture waste in Vietnam, using its extracted mucilage as a flocculant is an environmentally friendly method.

Response surface methodology applied to tropical freshwater treatment

This paper presents the profits and disadvantages of the chemometrics approach instead of the one-factor-at-a-time (OFAT) coagulation diagram approach for tropical water physicochemical treatment. Central composite design associate to response surface methodology (CCD-RSM) is used to find the real best conditions for coagulant dosage and pH aiming at high-turbidity removal. The number of experiments needed to chemometrics model construction (12) is comparatively smaller than that used in the coagulation diagram (84), saving financial and environmental resources. Arguments for Water Treatment Plants (WTP) considering the replacement of coagulation diagram approach by the CCD-RSM approach in drinking water treatment are presented. Chemometrics models are all constructed on a free software platform, providing the best pH within the range 7.7-8.1, and the best coagulant dosage (polyaluminium chloride, PAC) between 2.0 and 3.1 mg Al₂O₃ L^-1 (equivalent in mass). CCD-RSM provides a faster, lower-cost and more reliable alternative tool for WTP decision-making instead of the OFAT model, mainly for waters more affected by seasonal effects as can be seen in tropical and subtropical countries.

Charge Neutralization Mechanism Efficiency in Water with High Color Turbidity Ratio Using Aluminium Sulfate and Flocculation Index

Most of the water supplied in Brazil comes from water streams that may have higher values for apparent color than turbidity. Treatability trials were performed for color and turbidity removal to evaluate the advantages of coagulation during the charge neutralization mechanism when compared to sweep flocculation for water with those characteristics. There were three types of trials: conventional Jar Test with raw water, with and without filtration, and in a pilot Water Treatment Plant, direct downward filtration, with synthetic water. Auxiliary equipment such as Continuous Flocculation Monitoring Equipment (CFME) and image analysis were used to evaluate the growth of flocs. In the Jar Tests experiments, similar levels of color (61.49%) and turbidity (61.30%) removal were observed, with a lower dosage of coagulant (46 mg/L) in the charge neutralization mechanism compared to the ones with sweep flocculation (58.22% for color and 54.73% for turbidity removal with 52 mg/L of aluminium sulfate). Similar results were found on pilot plant. At filtration rates of 180 and 300 m3 m−2 day−1, sweep flocculation mechanism had shorter filtration cycle (<5 m3) compared to other mechanisms. Therefore, a change in the operation of Water Treatment plants that use a coagulant dosage associated with sweep flocculation can bring advantages such as the reduction of coagulant consumption and sludge productions, as well as the increase of chlorine disinfection and filtration cycles.

Investigating the Effects of Polyaluminum Chloride on the Properties of Ordinary Portland Cement

This study investigates the mechanical and microstructural properties of paste comprising ordinary Portland cement (OPC) added with polyaluminum chloride (PACl). The properties of the resulting mixture are analyzed using compressive strength, X-ray diffraction, scanning electron microscopy (SEM), mercury intrusion porosimetry, and thermogravimetric analysis. The results show that the addition of PACl improves the mechanical properties of OPC paste, that calcium-(aluminum)-silicate-hydrate (C-(A)-S-H) gel and Friedel’s salt are the major products forming from the reaction with the aluminum and chloride ions in PACl, and that the portlandite content decreases. Moreover, the size and number of micropores decrease, and compressive strength increases. All these phenomena are amplified by increasing PACl content. SEM images confirm these findings by revealing Friedel’s salt in the micropores. Thus, this work confirms that adding PACl to OPC results in a mixture with superior mechanical and microstructural properties.

Evaluating the influence of pH adjustment on chemical purification efficiency and the suitability of industrial by-products as alkaline agents

Metal salts of iron are currently used in several treatment facilities purifying peat extraction runoff water. Although chemical purification is considered best available technology for the treatment of this natural humic water, fluctuations in purification efficiency occur with low pH (3-4) and high metal concentration found in treated waters. The need for pH neutralisation increases the costs and overall environmental impacts related to chemical purification. The use of industrial by-products can decrease costs while supporting the sustainable use of natural resources and the principle of a circular economy. This study investigated the suitability of a range of calcium-based alkaline products (including by-products of the paper, cement and mineral industries) for neutralisation of chemically treated runoff water. The influence of the time of pH adjustment relative to time of coagulant addition (before coagulant, after but within coagulation, during flocculation and after sedimentation) on purification efficiency was evaluated. The hypotheses that the physical form of the coagulant was a relevant factor affecting purification was also assessed. The best performing pH-adjusting products were cement kiln dust (CaO and SiO₂) and Mahtikalkki (Ca(OH)₂, CaCO₃ and CaO), by-products of the cement and paper industry, respectively. Time of pH adjustment in relation to time of coagulation addition had a significant influence on purification efficiency, especially when solid coagulant was used. Adjustment of pH at 30 s before coagulant dosing resulted in a negative effect on treatment results. Based on results obtained, suitable points of pH adjustment are during the flocculation stage or at the outlet of sedimentation, particularly if solid coagulants are used.

Drinking water treatment using a submerged internal-circulation membrane coagulation reactor coupled with permanganate oxidation

A submerged internal circulating membrane coagulation reactor (MCR) was used to treat surface water to produce drinking water. Polyaluminum chloride (PACl) was used as coagulant, and a hydrophilic polyvinylidene fluoride (PVDF) submerged hollow fiber microfiltration membrane was employed. The influences of trans-membrane pressure (TMP), zeta potential (ZP) of the suspended particles in raw water, and KMnO₄ dosing on water flux and the removal of turbidity and organic matter were systematically investigated. Continuous bench-scale experiments showed that the permeate quality of the MCR satisfied the requirement for a centralized water supply, according to the Standards for Drinking Water Quality of China (GB 5749-2006), as evaluated by turbidity (<1 NTU) and total organic carbon (TOC) (<5mg/L) measurements. Besides water flux, the removal of turbidity, TOC and dissolved organic carbon (DOC) in the raw water also increased with increasing TMP in the range of 0.01-0.05MPa. High ZP induced by PACl, such as 5-9mV, led to an increase in the number of fine and total particles in the MCR, and consequently caused serious membrane fouling and high permeate turbidity. However, the removal of TOC and DOC increased with increasing ZP. A slightly positive ZP, such as 1-2mV, corresponding to charge neutralization coagulation, was favorable for membrane fouling control. Moreover, dosing with KMnO₄ could further improve the removal of turbidity and DOC, thereby mitigating membrane fouling. The results are helpful for the application of the MCR in producing drinking water and also beneficial to the research and application of other coagulation and membrane separation hybrid processes.

Characterization of Flocs and Floc Size Distributions Using Image Analysis

A nonintrusive digital imaging process was developed to study particle size distributions created through flocculation and sedimentation. Quantification of particle size distributions under different operating conditions can be of use in the understanding of aggregation mechanisms. This process was calibrated by measuring standardized polystyrene particles of known size and was utilized to count and measure individual kaolin clay particles as well as aggregates formed by coagulation with polyaluminum chloride and flocculation. Identification of out-of-focus flocs was automated with LabVIEW and used to remove them from the database that was analyzed. The particle diameter of the test suspension of kaolinite clay was measured to be 7.7 ± 3.8 μm and a linear relationship was obtained between turbidity and the concentration of clay particles determined by imaging. The analysis technique was applied to characterize flocs and floc particle size distribution as a function of coagulant dose. Removal of flocs by sedimentation was characterized by imaging, and the negative logarithm of the fraction of turbidity remaining after settling had a linear relationship with the logarithm of aluminum dose. The maximum floc size observed in the settled water was less than 120 μm, which was in accordance with the value predicted by a model for the capture velocity of the experimental tube settler of 0.21 mm/s.

Nanofiltration based water reclamation from tannery effluent following coagulation pretreatment

Coagulation-nanofiltration based integrated treatment scheme was employed in the present study to maximize the removal of toxic Cr(VI) species from tannery effluents. The coagulation pretreatment step using aluminium sulphate hexadecahydrate (alum) was optimized by response surface methodology (RSM). A nanofiltration unit was integrated with this coagulation pre-treatment unit and the resulting flux decline and permeate quality were investigated. Herein, the coagulation was conducted under response surface-optimized operating conditions. The hybrid process demonstrated high chromium(VI) removal efficiency over 98%. Besides, fouling of two of the tested nanofiltration membranes (NF1 and NF3) was relatively mitigated after feed pretreatment. Nanofiltration permeation fluxes as high as 80-100L/m(2)h were thereby obtained. The resulting permeate stream quality post nanofiltration (NF3) was found to be suitable for effective reuse in tanneries, keeping the Cr(VI) concentration (0.13mg/L), Biochemical Oxygen Demand (BOD) (65mg/L), Chemical Oxygen Demand (COD) (142mg/L), Total Dissolved Solids (TDS) (108mg/L), Total Solids (TS) (86mg/L) and conductivity levels (14mho/cm) in perspective. The process water reclaiming ability of nanofiltration was thereby substantiated and the effectiveness of the proposed hybrid system was thus affirmed.