Supernatant Turbidity Research Articles

Thickening and dewatering of waste activated sludge from WWTP with semi-coke powder

ABSTRACT Semi-coke powder was selected as the conditioner to improve waste-activated sludge (WAS) dewaterability. The specific resistance to filtration (SRF) of the conditioned WAS with 250% semi-coke powder declined significantly from 1.47 × 1013 m/kg to 1.82 × 1011m/kg, the moisture content (MC) of filter cake also obviously decreased from 87.8% to 61.3%, and the turbidity of supernatant was lowered to 1.5–3 NTU. The low calorific value of filter cake was enhanced to 22.47 MJ/kg.

Thermoresponsive Starch for the Flocculation of Oil Sands Mature Fine Tailings.

The reclamation of land and recovery of water from tailing ponds created during bitumen extraction from oil sands is a major technical and environmental challenge. In the current study, thermoresponsive hydroxybutylated (HB) corn starch (HB-CS) and potato starch (HB-PS), with lower critical solution temperatures (LCSTs) ranging from 36 to 45 °C, were examined as flocculants for oil sands mature fine tailings (MFT). The ability of different doses of the HB-CS and HB-PS to flocculate 2 and 10 wt % MFT, prepared by diluting 35 wt % MFT in tap water, in terms of the initial settling rate (ISR), supernatant turbidity (ST), sediment solids content (SSC), and water recovery (WR), was examined at temperatures below and above their LCSTs. The thermoresponsive HB-CS and HB-PS were good flocculants of MFT, and their thermoresponsive behavior was essential for optimal results in that they were considerably more effective in several aspects at temperatures above their LCSTs than below. In terms of ISRs, the HB-PS was a considerably better flocculant than the HB-CS, and this was especially so with the 10 wt % MFT. With the HB-PS, the ISR was lower when using diluted MFT prepared with tap water as opposed to simulated oil sands process water.

Flocculating and dewatering of kaolin suspensions with different forms of poly(acrylamide‐co‐diallyl dimethylammonium chloride)

AbstractRecently, polymeric nanofibres have been considered for the rapid flocculation and dewatering of oil sands tailings. Apparently due to their fast initial interaction with the suspended fine particles, polymer nanofibres performed better than their parent water‐soluble polymer solutions. To further understand this mechanism, a model study was conducted using kaolin suspensions and poly(acrylamide‐co‐diallyl dimethylammonium chloride) nanofibres and powders. The initial settling rate, supernatant turbidity, water recovery, capillary suction time, and solids content were measured to determine the effect of using nanofibres on solid‐liquid separation. Nanofibres performed similarly to, or better than, equivalent polymer solutions in terms of initial settling rate and supernatant clarity at higher dosages and kaolin loadings. The kaolin studies showed that polymer nanofibres could absorb onto clay particles faster, and produce bigger flocs more rapidly, supposedly due to their high surface area to volume ratio. Our results indicate that polymer nanofibres, as well as polymer powders, may be successfully used to treat mature fine tailings produced from oil sands.

Application of Polyaluminum Chloride-Polyacrylamide as New Water Treatment Material for the Removal of Natural Organic Matter

Natural organic matter (NOM) is easily soluble in surface water and difficult to be removed thoroughly. In this paper, polyaluminum chloride-polyacrylamide (PAC-PAM), as a new water treatment material, was proposed to solve this problem by coagulation treatment. The performance, mechanism and kinetic process of NOM removal were investigated systematically. Results showed that the optimum dosage of PAC and PAM was 10 mg/L and 0.5 mg/L for NOM removal of Yellow River water. In this condition, NOM could be removed effectively due to positively charged PAM addition. The size, growth rate and recovery factor of flocs generated by PAC-PAM reached 419 μm, 34.9 μm/min and 0.48, respectively, while only 355 μm, 27.9 μm/min and 0.31 were obtained by PAC. Moreover, the adsorption and bridging effect of PAM assisted the formation of multi-branched flocs, which brought fast settle velocity and low turbidity of supernatant after coagulation.

Comparison of ultra-flocculation reactors applied to fine quartz slurries

Ultraflocculation can be defined as: flocculation performed in a highly non-uniform hydrodynamic field (ε>1 [J/kg·s], G > 103 [s-1]) in a short period of time (t<10 [s]), which is used mainly to aggregate fine particles in dispersed, and diluted systems.In this study, four hydraulic ultra-flocculation reactors were tested, UF1, UF2, UF3 and UF4 with tangential inlets/outlets and a cylindrical body, the inside of which varies by reactor. Model flocculated fine quartz slurries were employed as material. Based on a comparison of the three flocculation process indicators – initial settling velocity, supernatant turbidity, and sludge volume – in general the reactors present better performance than that in the base case. There was an average improvement in settling velocity of 300[%], turbidity remains below 100 [NTU], and sludge volume values indicated a higher possibility of water recirculation. Additionally, it was observed that the ultra-flocculation process could be used in relatively concentrated suspensions (φ>10-2) with treatment times below to 5 [s].

Amylopectin-graft-polyacrylamide for the flocculation and dewatering of oil sands tailings

A series of amylopectin-graft-polyacrylamides with varying molecular structures were synthesized and used to flocculate and dewater oil sands tailings. Amylopectin-graft-polyacrylamides made with different grafting frequencies and lengths were compared with commercial polyacrylamide flocculants according to supernatant turbidity, sediment solids content, and capillary suction time. Thanks to their hydrophobic core, amylopectin-graft-polyacrylamides formed sediments with higher solids content than the commercial polyacrylamides used in our experiments, suggesting that they are an attractive alternative to treat oil sands tailings.

Flocculation Behavior of Borax Clayey Tailings in Mono- and Dual- Flocculant Systems: Effect of Tailings Slurry Characteristics and polyDADMAC Type

The effect of tailings slurry characteristics such as solid ratio and solid particle size both, in mono- and dualflocculant systems, were studied as well as the effect of POLYDADMAC type in dual-flocculant system. Oppositely charged flocculants, a polyacrylamide (PAM)-typed anionic and two poly diallyl-dimethyl-ammonium chloride(polyDADMAC)-typed cationic polymers, were employed for the flocculation. Tailings slurry samples were taken on different dates from the discharge point of Kırka Borax Concentrator. Flocculation performance was characterized by the initial settling rate as well as the residual turbidity of supernatant and the extent of sediment compaction. All tests were performed at the natural pH of the tailings slurry (~pH 9.4) at which borax buffered the suspension. The results showed that an increase in solid load of the tailings slurry results in a dramatic decrease in settling rate of flocculated tailings regardless of flocculant system employed. This can be attributed to the possible change in rheological property of the slurry due to the increasing clay content of the slurry with solid ratio. While the solid ratio has an influence on the settling rate of the flocculated tailings, the amount of slimes determines the optimum dosage of cationic flocculant to obtain clear supernatant in dual-flocculant system. When anionic and cationic flocculants were used in combination, the best synergy was achieved with low weight cationic flocculant. Increasing molecular weight of the cationic flocculant from low to medium resulted in two-fold increase in the required dosage to obtain the same flocculation performance. In dualflocculant system, optimum results were obtained by anionic and cationic flocculant combination at around 0.4 kg/ton and 0.8 kg/ton solid dosages, respectively, indicating 11.7 cm/min of settling rate and 85.7% of transmittance value.

Characterization and sludge dewaterability evaluation of a chitosan‐based flocculant CMCTS‐g‐CPAM

AbstractIn this work, a new cationic flocculant, CMCTS‐g‐CPAM was synthesized by acrylamide (AM), methacryloyloxyethyltrimethylammonium chloride (DMC) and carboxymethyl chitosan (CMCTS) through UV initiated graft polymerization techniques. The structure of CMCTS‐g‐CPAM was analysed by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (1H NMR) and X‐ray diffraction (XRD) techniques which indicates that AM and DMC are grafted successfully onto CMCTS to obtain CMCTS‐g‐CPAM. The potential of CMCTS‐g‐CPAM for the sludge dewatering was investigated. The effects of cationic degree, intrinsic viscosity, dosage and pH on the sludge dewatering performance were studied. The results indicate that the optimal dewatering performance with minimum supernatant turbidity of 5.40 NTU, the moisture content of the filter cake of 79.28% and the specific resistance of the sludge of 1.96 × 1013 m/kg was obtained at 30 mg/L CMCTS‐g‐CPAM at pH 9–10. Finally, from the microscopic and electron micrographs investigation, it was confirmed that the particle size of the CMCTS‐g‐CPAM treated sludge was significantly large to enhance hydrophobicity and improve dewatering performance.

Preparation of acrylamide and carboxymethyl cellulose graft copolymers and the effect of molecular weight on the flocculation properties in simulated dyeing wastewater under different pH conditions

In this study, graft copolymers with different graft ratios (GRs) and molecular weights (MWs) were prepared by water bath polymerization using acrylamide (AM) and carboxymethyl cellulose (CMC) as substrates; additionally, the best preparation parameters were provided. The MW of the copolymer was inversely correlated with the GR (R = −0.82). The obtained graft copolymer was characterized by FTIR, 1H NMR, XPS and DSC. The results showed that CMC and AM were successfully copolymerized and the thermal stability of the product is improved. The graft copolymers with different MWs were used to flocculate a simulated dyeing wastewater at pH values of 3, 5, 7, 9 and 11. The results showed that as the molecular weight of the graft copolymers increased, the average flocculation settling ratio decreased drastically from 61.2% to 19.4% at pH 3, and the higher the MW, the better the flocculation settling performance. But the average settling ratio increased sharply at pH 11, and the increase grew from 21.0% to 50.3%. The larger the MW, the more obvious the decrease in flocculation sedimentation performance. The supernatant turbidity was reduced from 13324 NTU to less than 150 NTU, and the turbidity removal ratio exceeded 99%. The flocculation mechanism was discussed.

Coagulation/flocculation process for marble processing plant effluent: Modelling and optimization through response surface methodology

AbstractIn this study, the coagulation‐flocculation of a wastewater discharged from a marble processing plant was statistically analyzed and optimized. To make a systematic investigation on the coagulation‐flocculation of the highly turbid wastewater (&gt;1000 NTU), the response surface methodology was used to estimate a capable quadratic model with R‐squared value of 98.84%. According to this model, the most critical parameter was the suspension pH with a p‐value &lt; 0.0001. Furthermore, the PEO‐flocculant was proven as a substantial agglomerating reagent specifically at pH 12. On the other hand, no significant turbidity removal was observed upon the addition of the Fe‐coagulant. When the experimental parameters of the coagulation‐flocculation were optimized, it was found out that the minimum supernatant turbidity value of 3.81 NTU can be achieved by using the minimum amount of the Fe‐coagulant:50 mg/l, and the maximum amount of the PEO‐flocculant of 1.5 ppm at pH 11.5‐12.0. In conclusion, it was proved that the significance of the calcium dissolved from the marble particles was greater than the Fe‐coagulant in this process. The hydrolyzed calcium (CaOH+) species established a chemical bridge between the particle and the polymer and, as a result, enhanced the performance of the flocculation at the alkaline pH values.

Evaluation of the effect of hydraulic shear intensity on coal-slime water flocculation in a gradient fluidized bed

Fluid shear plays a paramount role in flocculation. In present work, a fluidized bed flocculator with a decreasing fluid shear intensity in steps, called gradient fluidized bed (GFB) flocculator, was developed according to the self-preserving nature of floc size distribution and the flocculation kinetics. Then flocculation experiments were conducted to evaluate the performance of the GFB flocculator on flocculating coal-slime water in different flow rates. Results show that the flocculation of the GFB flocculator reducing the supernatant turbidity by 32% when compared with a pipe one, exhibiting obvious advantages. When the superficial velocity was 0.44m/s, the velocity gradient along the height of the GFB decreased from 240 to 145s−1, contributing the best result that the flocs size up to 1mm and the turbidity of the supernatant lower to 17 NTU. It can be concluded that GFB should be an efficient flocculator for flocculating coal-slime water when a reasonable apparent velocity is well conducted.

Water soluble polymeric nanofibres for rapid flocculation and enhanced dewatering of mature fine tailings

AbstractWater‐soluble polymer flocculants have been used to efficiently release entrapped water in oil sands tailings by bridging fine particles to create large heavier flocs which can then settle faster and release water more efficiently. Due to their initial interaction with the fine particles suspended in tailings, polymer nanofibres may perform better than their parent polymers because of the entire surface of the nanofibres being fully accessible to the fine particles. In this work, commercially available poly(acrylamide‐co‐diallyl dimethylammonium chloride) was chosen as a basis for this study. Initial settling rate, supernatant turbidity, water recovery, capillary suction time, and solids content were measured to determine the effect of polymer nanofibres on solid‐liquid separation. The solid forms of the polymer (either as nanofibre or powder) perform better than the polymer solution in each test, with optimum dosages of 5 wt% mature fine tailings (MFT) loading. Nanofibres could achieve settling rates of 60 m/h, while the other forms were only able to achieve 42 m/h. Additionally, the turbidity of the supernatant obtained after flocculation with nanofibres was 15 nephelometric turbidity units (NTU), while the polymer solution and powder produced turbidites of 162 NTU and 70 NTU, respectively. In addition, polymer nanofibres and powders generated larger flocs compared to the polymer solution, which produced small, homogenized flocs.

Improving flocculation and dewatering performance of iron tailings thickeners

Most of the mineral processing and hydrometallurgical plants consume large volumes of water. A portion of this water is recycled to the process while the remainder is lost. This necessitates optimization of dewatering systems particularly in arid and semi-arid mining regions. In this paper the bench and full-scale flocculation behavior of iron ore tailings is investigated in order to improve the dewatering performance of tailings thickeners of an iron beneficiation plant. In the batch settling tests, the effect of flocculant dosage (5–20 g/t solid), slurry solids concentration (3–12 %), pH (4–12), and flocculant dilution (0.05–1 %) on the flocculation performance (settling rate, supernatant turbidity, and sediment volume) was studied. The results reveal that the flocculation performance improves at higher slurry pH and flocculate dosage as well as lower slurry solids content. In the plant-site experiments, the influence of increasing the slurry pH (from 8.1–11.2) and dosage of flocculant (from 8 to 13 g/t solid) together with flocculant injection strategy on the thickening performance was examined. The thickeners underflow density and overflow clarity increased with raising the slurry pH and flocculant dosage as well as distributing the flocculant solution at different locations along the feed stream. The proposed modifications were accompanied by a reduction of 23% in the total water consumption corresponding to an annual savings of $576,000.

Flocculation behaviour of bentonite clay-water systems

ABSTRACTThe effect of polyacrylamide (PAM) as flocculant, NaCl electrolyte concentration and pH on the degree of flocculation of bentonite suspension has been investigated. It has been observed that the increase in PAM dosage reduces the residual turbidity and improves the settling rate of the bentonite particles. At higher pH conditions bentonite dispersions are highly flocculated having high settling rates and low supernatant turbidity. The combined effect of salt concentration and PAM dosage improved the overall flocculation efficiency of the system.

Hairy cationic nanocrystalline cellulose as a novel flocculant of clay

HypothesisThe present paper investigates, for the first time, the potential of cationic hairy cellulose nanocrystals (CNCC) to induce the flocculation of a model suspension of kaolinite. CNCC belong to a brand new family of nanocelluloses characterized for presenting a crystalline rod-like body and functionalized amorphous chains at both ends. Given that these chains can be easily tuned, these nanocelluloses present a high potential as fit-to-purpose flocculants. ExperimentsCNCC were produced through periodate oxidation, cationization and thermal treatment of cellulose. Flocculation was monitored by both photometric dispersion analysis and laser reflectance. Flocs were characterized by the determination of zeta potential, supernatant turbidity removal and optical microscopy. A recently developed machine learning random forest regression model was used to estimate fractal dimension (Df) from chord length distribution data. FindingsAlthough a high efficiency was achieved for CNCC dosages between 7.5 and 75 mg/g, the maximum floc size and the fastest flocculation were found near the isoelectric point (10–30 mg/g). Thus, CNCC acted through charge neutralization mechanism. The model used to estimate flocs Df was found very successful to describe the flocculation process. The clay/CNCC flocs Df values suggest a relation between floc conformation and CNCC dosage, presenting an opener structure when closer to the isoelectric point.

Effects of ballasting particles on settling rate of iron ore tailings

The high density or large size grains are proposed to be added as ballasting particles to achieve a high settling rate and low supernatant turbidity for fine particle flocs during the settlement of ore tailings. Settling tests on iron ore tailings were carried out to evaluate the effects of size, density, and dosage of ballasting particles on initial settling rate and turbidity. The results showed that low density (2.65 g/cm3) particles and medium density (4.67 g/cm3) particles contributed to the increase in settling rate of the tailing slurry at all size fractions from 0.074 to 0.5 mm, with the peak performance obtained between 0.125–0.2 mm, whereas high density (6.14 g/cm3) particles only accelerated the process with the particle size not larger than 0.2 mm. It is supposed that there is a close relationship between ballasting particle properties and floc strength. The acceleration effect dominates when flocs are strong enough to bear the ballasting particles; deceleration occurs when ballasting particles are oversize, over-density, or overdosed, causing the breakage of flocs.

Synthesis, Characterization, and Sludge Dewaterability Evaluation of the Chitosan-Based Flocculant CCPAD.

Carboxymethyl chitosan (CMCS), acrylamide, and methacryloxyethyltrimethyl ammonium chloride were used as co-monomers to produce a sludge dewatering agent carboxymethyl chitosan-graft-poly(acrylamide-methacryloxyethyltrimethyl ammonium chloride) (CCPAD) by UV-induced graft polymerization. Single-factor experiments and response surface methodology were employed to investigate and optimize the grafting rate, grafting efficiency, and intrinsic viscosity influenced by the total monomer concentration, CMCS concentration, cationic degree, pH value, and illumination time. The structure, surface morphology, and thermal stability of CCPAD were characterized by infrared spectroscopy, hydrogen nuclear magnetic resonance, X-ray diffraction, scanning electron microscopy, and differential thermal-thermogravimetry. The raw sludge with 97.9% water content was sourced from the concentrated tank of a sewage treatment plant and used in the sludge condition experiments. In addition, CCPAD was applied as the sludge conditioner to investigate the effects of cationic degree, intrinsic viscosity, and pH on the supernatant turbidity, moisture content, specific resistance to filtration, and sludge settling ratio. Moreover, the mechanism of sludge conditioning by CCPAD was discussed by examining the zeta potential and extracellular polymeric substance (EPS) content of the supernatant. The sludge dewatering results confirmed that CCPAD had excellent performance for improving sludge dewaterability.

Effect on composition and quantity of extracellular polymeric substances in an innovative hybrid membrane bioreactor under different sludge retention times

ABSTRACTThis study investigated the influence of sludge retention time (SRT) in three hybrid membrane bioreactors to treat domestic wastewater at different SRTs (10, 20, and 40 d) simultaneously, based on extracellular polymeric substances (EPS) analysis. The results showed that significant positive correlation existed between SRT and humic acids quantity in TB-EPS, humic acids quantity in S-EPS, DNA quantity in S-EPS, and total quantity in TB-EPS, with the correlation coefficient 0.9992, 0.9980, 0.9973, 0.9821, respectively. Significant negative correlation existed in SRT and proteins in TB-EPS, proteins quantity in S-EPS, and polysaccharose in S-EPS, with the correlation coefficient 0.9993, 0.9107, 0.8552, respectively. A high logarithmic relationship existed between supernatant turbidity and SVI. The optimal SRT was 20 d and the corresponding operational cycle of the membrane module was 109 d.

Drilling fluid waste treatment using polysaccharide-grafted copolymers

A large amount of drilling fluid waste is produced as effluents during exploration and production of oil and gas. Such effluents need to be treated before their final disposal. Efficient coagulation/flocculation can reduce the total amount of disposed effluent, and both coagulation by inorganic salts and flocculation by synthetic flocculants are found to be very effective. The graft-copolymers-based flocculants were prepared using a potassium persulfate initiator solution made by grafting copolymerisation of polyacrylamide onto polysaccharide backbones (starch, guar gum and amylose) in our laboratory. The synthesised graft copolymers have been characterised using various instrumental methods of analysis. The effects of various synthetic flocculants and their concentrations have been studied in combination with the coagulants on coagulation/flocculation of bentonite-based drilling fluid waste have been studied. The effects of coagulant/flocculant dosage, electrolyte concentration and pH on the degree of flocculation of bentonite-based drilling fluid waste was investigated. It was observed that the increase in coagulant/flocculant dosage reduces the residual turbidity and improves the settling rate of the drilling fluid waste. At higher pH conditions, drilling fluid waste dispersions are highly flocculated and have high settling rates and low supernatant turbidity. The combined effect of salt concentration and coagulant/flocculant dosage improves the overall flocculation efficiency of the system.

Influence of polyelectrolyte architecture on the electrokinetics and dewaterability of industrial membrane bioreactor activated sludge

Improvement of sludge dewaterability is greatly hindered by the presence of large amounts of interstitial water molecules trapped in the sludge as a result of strong hydrophilic characteristics. This study has investigated the influence of six different polyacrylamide (PAM) flocculants with different molecular architecture (linear, slightly and highly branched), charge density (CD) and molecular weight (MW) on the electro-kinetics and dewatering of highly stable industrial membrane bioreactor (MBR) sludge. The impact of PAM on flocculation is manifested in the supernatant turbidity, particle zeta potential, sludge capillary suction time (CST), floc size and settleability. Turbidity removal and reduction in zeta potential are used to identify the optimum polymer dose. An optimum dose of 70 mg.L−1 has been determined for linear PAM of 40% CD. However, a highly-branched PAM, with the same CD, has shown an optimum value of 30 mg.L−1. In all cases, a turbidity removal of more than 99% and CST reduction of 51–64% is attained; the linear PAMs have resulted in the highest CST reduction. Higher PAM doses have resulted in larger flocs and the maximum particle size is observed at the saturation point. The reduction in sludge volume relates with the floc size and PAM dose. For sludge conditioning and dewaterability, highly branched PAM with low MW has shown superior performance over linear high MW PAM. Enhancement of flocculation and dewatering is correlated with the surface charge neutralization and bridging mechanisms.