Polyacrylamide Dosage Research Articles

Enhanced precipitation performance for treating high-phosphorus wastewater using novel magnetic seeds from coal fly ash

Magnetic coagulation is a promising approach for treating high phosphorous (high-P) wastewater by enhancing precipitation efficiency using magnetic particles. In this study, a cost-effective and environmentally friendly magnetic seed from coal fly ash (MS-CFA) was used as an alternative material for Fe3O4 magnetic seed (MS) coagulation. The potential effect of MS-CFA was explored to reduce the settling time and the dosage of coagulant aid of polyacrylamide (PAM) in treating high-phosphorous (high-P) simulated wastewater at 100 and 200 mg P/L. The physicochemical characteristics of MS-CFA were analysed through particle size distribution (20–100 μm), pore size distribution (14–30 nm), specific surface area (1.654 m2/g), X-ray diffraction (XRD), specific gravity (4.2), and magnetic induction intensity (49.8 emu/g). The characteristics met the requirements as magnetic coagulation material. MS-CFA was combined with polyaluminum chloride (PAC) and polyacrylamide (PAM) to improve phosphorous precipitation performance. The synergised magnetic coagulation effect using MS-CFA and PAM reduced the settling time of flocs to less than 1 min due to the high specific gravity. This represents a reduction of 90% of the settling time compared to the control using PAM alone (15 min) without MS-CFA. MS-CFA efficiently reduced PAM dosage by 83% and 87% for treating 100 and 200 mg P/L, respectively. The presence of PAM (1 mg/L for 100 mg P/L and 2 mg/L for 200 mg P/L) was imperative for binding the MS-CFA and flocs, hence increasing the particle size of the magnetic flocs. The characteristics of the magnetic flocs were analysed through microscopy, particle size distribution, zeta potential measurements, and magnetic induction intensity. The characteristics of the magnetic flocs confirmed that MS-CFA could be an alternative material for Fe3O4 as the magnetic seeds in the magnetic coagulation process for treating high-P wastewater.

The Role of Rheological Additives on Fresh and Hardened Properties of Cemented Paste Backfill.

Cemented paste backfill (CPB) has become a significant structural material in most mines across the world. In this study, the effects of chemical rheological additives including viscosity modifying agent (i.e., polyacrylamide) and polycarboxylate superplasticizer (PCE) on fresh and hardened properties of CPB with different water-to-solid (W/S) ratios and water-to-cement (W/C) ratios were investigated. The microstructure of CPB specimens was also characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and backscattered electron image (SEM-BSE). The obtained results indicate that PAM (polyacrylamide) dosage and W/S are the most significant parameters influencing the workability of fresh CPB mixtures. For the hardened CPB specimens, the decreasing W/S ratio leads to higher flexural and compressive strength values and lower dry shrinkage strains. The interfacial transition zone (ITZ) between the cement matrix and the tailings sand was also observed to be narrower, with fewer micro cracks and capillary pores. Meanwhile, the existence of PAM decreased the number of hydration products and retarded the hydration reaction. Overall, the CPBs with high W/C ratios (i.e., 1.0 and 1.2), low W/S ratios (i.e., 0.3), and moderate amounts of rheological additives (i.e., 0.05% PAM and 1.0% PCE) have excellent fresh and hardened properties. The findings of this study contribute to better optimization of CPB mixtures in backfill construction, bringing benefits of low costs and low environmental impacts.

Intermittent swelling and shrinkage of a highly expansive soil treated with polyacrylamide

This laboratory study examines the potential use of an anionic polyacrylamide (PAM)-based material as an environmentally sustainable additive for the stabilization of an expansive soil from South Australia. The experimental program consisted of consistency limits, sediment volume, compaction and oedometer cyclic swell–shrink tests, performed using distilled water and four different PAM-to-water solutions of P D = 0.1 g/L, 0.2 g/L, 0.4 g/L and 0.6 g/L as the mixing liquids. Overall, the relative swelling and shrinkage strains were found to decrease with increasing number of applied swell–shrink cycles, with an ‘elastic equilibrium’ condition achieved on the conclusion of four cycles. The propensity for swelling/shrinkage potential reduction (for any given cycle) was found to be in favor of increasing the PAM dosage up to P D = 0.2 g/L, beyond which the excess PAM molecules self-associate as aggregates, thereby functioning as a lubricant instead of a flocculant; this critical dosage was termed ‘maximum flocculation dosage’ (MFD). The MFD assertion was discussed and validated using the consistency limits and sediment volume properties, both exhibiting only marginal variations beyond the identified MFD of P D = 0.2 g/L. The accumulated axial strain progressively transitioned from ‘expansive’ for the unamended soil to an ideal ‘neutral’ state at the MFD, while higher dosages demonstrated undesirable ‘contractive’ states.

Coagulation-flocculation performance and floc properties for microplastics removal by magnesium hydroxide and PAM

Microplastics (MPs) have attracted much attention worldwide as one kind of emerging pollutant, with the social demand for plastic products surging and microplastic pollution increasingly serious. In this experiment, magnesium hydroxide formed under alkaline conditions was combined with anionic polyacrylamide (PAM) as a dual-coagulant to deal with the simulated natural water containing polyethylene (PE). And the whole process was monitored by intelligent Photometric Dispersion Analyzer (iPDA), the Flocculation Index (FI) value of flocs and MPs removal efficiency were used as indicators to evaluate coagulation-flocculation performance. The results suggested that the flocs formed were not sufficient to remove PE particles only in the case of dosing magnesium ion. When PAM was added after magnesium hydroxide formation, the maximum FI value reached up to 7.2 and the PE removal efficiency was greatly improved, reaching 84.9% ± 3%. Additionally, flocs settling rate with average size of 57.19 µm reached to 4.8 × 10−3 m/s. At the same time, the types, dosing time and dosage of anionic PAM also had a great influence on the removal of MPs. Based on investigations of zeta potential and floc properties, adsorption bridging and sweeping were the main coagulation mechanisms. The MPs removal behaviors exhibited during coagulation processes have potential application in water treatment.

Effect of magnetization pretreatment of coal slime water flocculating sedimentation

ABSTRACT Sedimentation of coal slime water (CSW) is an important process in coal processing plants. However, CSW is difficult to settle because of its high content of clay minerals and fine particles. In this paper, the effect of magnetization pretreatment on CSW flocculating sedimentation is investigated. The mechanisms of magnetization pretreatment were studied by measuring CSW’s viscosity and zeta potential and calculating particle’s hydration film thickness using Einstein’s viscosity equation. The results show that the CSW flocculating sedimentation is enhanced by magnetization pretreatment. The optimum dosage of polyacrylamide was 6.0 mg/L and the best magnetic field strength and magnetization time was 0.3 T and 3 min, respectively. As the settling velocity was increased, the turbidity of the supernatant was reduced by magnetization pretreatment. Moreover, after magnetization pretreatment, the absolute value of the zeta potential and the viscosity were reduced, and the hydrated film thickness of coal particles was decreased from 305 nm to 155 nm. Magnetization pretreatment decreased the settling resistance and reduced the electrostatic repulsion and hydration forces between coal particles, thus promoting CSW flocculating sedimentation. It is demonstrated that magnetization pretreatment introduces a new path improve CSW settlement.

Pilot test of simultaneous removal of silica, hardness, and turbidity from gray water using circulating pellet fluidized bed

A pilot test was performed by applying a circulating pellet fluidized bed (CPFB) system during the simultaneous removal of silica, hardness, and turbidity from gray water generated from the coal gasification of a coal-to-liquids company in Shanxi Province, China. The effects of a magnesium agent (MgO) and coagulant (Al2(SO4)3) in the CPFB system on the simultaneous treatment of silica, hardness, and turbidity in gray water were investigated, and the removal mechanism was explored. The test results demonstrated that when the MgO and Al2(SO4)3 dosages were 500 mg/L and 660 mg/L, NaOH and polyacrylamide dosages were 200 mg/L and 4 mg/L, respectively, and the removal efficiencies of silica and total hardness exceeded 80% and 55% in the effluent, respectively, with the effluent turbidity remaining below 5 nephelometric turbidity units. The comprehensive cost of dosage agents was approximately 0.22 USD/m3. Physical characterizations of the sludge using scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy revealed that silica was primarily removed through silicate precipitation and adsorption by compounds such as Mg(OH)2. The findings confirmed that the CPFB technology can reduce the silica, total hardness, and turbidity contents within the desired range, and thus, this study provides useful design parameters and an engineering basis for the development of subsequent gray water treatment processes.

Coal Fly Ash and Polyacrylamide Influence Transport and Redistribution of Soil Nitrogen in a Sandy Sloping Land

Sandy soils are prone to nutrient losses, and consequently do not have as much as agricultural productivity as other soils. In this study, coal fly ash (CFA) and anionic polyacrylamide (PAM) granules were used as a sandy soil amendment. The two additives were incorporated to the sandy soil layer (depth of 0.2 m, slope gradient of 10°) at three CFA dosages and two PAM dosages. Urea was applied uniformly onto the low-nitrogen (N) soil surface prior to the simulated rainfall experiment (rainfall intensity of 1.5 mm/min). The results showed that compared with no addition of CFA and PAM, the addition of CFA and/or PAM caused some increases in the cumulative NO3−-N and NH4+-N losses with surface runoff; when the rainfall event ended, 15% CFA alone treatment and 0.01–0.02% PAM alone treatment resulted in small but significant increases in the cumulative runoff-associated NO3−-N concentration (p < 0.05), meanwhile 10% CFA + 0.01% PAM treatment and 15% CFA alone treatment resulted in nonsignificant small increases in the cumulative runoff-associated NH4+-N concentration (p > 0.05). After the rainfall event, both CFA and PAM alone treatments increased the concentrations of NO3−-N and NH4+-N retained in the sandy soil layer compared with the unamended soil. As the CFA and PAM co-application rates increased, the additive effect of CFA and PAM on improving the nutrient retention of sandy soil increased.

Efficiency and Mechanism of Advanced Treatment for Phosphate Wastewater by High Efficiency and Low Consumption Coagulation and Phosphorus Removal System

Beaker coagulation experiments were carried out using polyaluminium chloride (PAC), polyferric sulfate (FPS), polyacrylamide (PAM), polyaluminum chloride (PAFC), polyaluminum sulfate (PAFS) and polyacrylamide (PAFC). The phosphorus removal effects of several flocculants were compared. The best combination coagulant PAM-PAC/PFS with high efficiency and economy was selected. The best ratio of PAC/PFS is 1:1, and the dosage of PAM is 1mg/L. The experiment determined the optimal hydraulic conditions: fast agitation and addition of PAC/PFS at a speed of 400 r/min for 1 min. PAM was added during slow agitation at a speed of 100 r/min for 6 min. The phosphorus removal system has a good effect on the removal of total phosphorus and other water quality indicators in the mine drainage of many phosphate mines, and all of them can meet the discharge standards.

A comprehensive analysis of an effective flocculation method for high quality microalgal biomass harvesting

Flocculation is a low-cost harvesting technique for microalgae biomass production, but flocculation efficiency is species dependent. In this study, we investigated the efficacy of two synthetic (polyacrylamide) and one natural (chitosan) flocculants against three algal species: the cyanobacterium Synechocystis sp., the freshwater Chlorella vulgaris, and the marine Phaeodactylum tricornutum at laboratory and pilot scales to evaluate harvesting efficiency, biomass integrity and media recycling. Growth phase affected the harvesting efficiency of the eukaryotic microalgae. The flocculation was optimal at stationary phase with high flocculation efficiency achieved using polyacrylamides at 24–36 mg/g dry weight. The effect of the flocculants on the harvested biomass was investigated. The flocculated Synechocystis sp. showed a higher proportion of compromised cells compared to C. vulgaris and P. tricornutum likely due to differences in cell walls composition. Compromised cells could lead to the release of valuable products into the surrounding growth media during flocculation. The residual culture media was recycled once with no impact on cell growth for all treatments and algal species. The flocculation technique was demonstrated at pilot-scale using 350 L microalgal suspension, showing an efficiency of 82–90% at a polyacrylamide dosage of 6.5–10 mg/L. This efficiency and the biomass quality are comparable to the laboratory-scale results. Overall, results indicate that polyacrylamide flocculants work on a wide range of species without the need for pre-treatment. The information generated in this study can contribute to making the microalgae industry more competitive.

Formation, breakage, and re-growth of quartz flocs generated by non-ionic high molecular weight polyacrylamide

Flotation of fine mineral particles is one of the major challenges faced by the minerals industries worldwide. Flocculation of these fine particles prior to flotation, to form separate hydrophobic and hydrophilic flocs, is one of the methods to tackle this challenge. In order to gain a better understanding of the properties of hydrophilic polymer flocs for the intended flocculation flotation, this paper reports testwork completed on the formation, breakage, and re-growth of quartz flocs when non-ionic high molecular weight polyacrylamide (PAM) was used as a flocculant under different test conditions in an alkaline environment. Focused beam reflectance measurement (FBRM) particle size analyses, coupled with sedimentation tests and optical microscope observations were performed to monitor the real-time evolution and change of quartz flocs. In addition, adsorption experiments and zeta potential measurements were carried out and used as parameters in the DLVO theory interaction energy estimation. The results of DLVO theory interaction energy estimation, settling experiments and optical microscope observations showed that the quartz particles dispersed well in slurry at pH 9. PAM had a strong flocculation ability to quartz particles, the peak values of floc size were affected by both the stirring rate and PAM concentration. In addition, the degree of floc breakage depended on the increased stirring rate and the shear time. Floc re-growth occurred to different extents according to the breakage durations and PAM dosages.

Degradation of Polyacrylamide (PAM) and methane production by mesophilic and thermophilic anaerobic digestion: Effect of temperature and concentration

Polyacrylamide (PAM) is generally employed in wastewater treatment processes such as sludge dewatering and therefore exists in the sludge. Furthermore, it degrades slowly and can deteriorate methane yield during anaerobic digestion (AD). The impact or fate of PAM in AD under thermophilic conditions is still unclear. This study mainly focuses on PAM degradation and enhanced methane production from PAM-added sludge during 15 days of thermophilic (55°C) AD compared to mesophilic (35°C) AD. Sludge and PAM dose from 10 to 50 g/kg TSS were used. The results showed that PAM degraded by 76% to 78% with acrylamide (AM) content of 0.2 to 3.3 mg/L in thermophilic AD. However, it degraded only 27% to 30% with AM content of 0.5 to 7.2 mg/L in mesophilic AD. The methane yield was almost 230 to 238.4 mL g VSS on the 8th day in thermophilic AD but was 115.2 to 128.6 mL/g VSS in mesophilic AD. Mechanism investigation revealed that thermophilic AD with continuous stirring not only enhanced PAM degradation but also boosted the organics release from the sludge with added PAM and gave higher methane yield than mesophilic AD.

Phosphorous removal improvements and cost reductions leveraging cationic polymers and anionic polyacrylamides in Chemically Enhanced Treatment Wetland (CETW) systems

Many wetland systems worldwide struggle with high nutrient influx from urban and agricultural inputs that often disturbs ecosystem balance. In the Florida Everglades, concentrations above 15 μg P L−1 have been shown to affect ecosystem balance and have long term effects on downstream periphyton, detritus, soil and macrophyte. Current Stormwater Treatment Areas (STAs) have been shown to effectively lower P levels on average to 41 μg P L−1 (SD of 31 μg P L−1). These levels, released into downstream Water Conservation Areas, exceed a long-term goal of 10 μg L−1 total P targeted for STA outflow concentrations. Here, we look at enhancing P removal through chemical addition to treatment wetland systems through a series of in-situ mesocosm studies informed through laboratory jar tests. In-situ mesocosm results showed Fe and Al metal-based coagulants lowered filtered total phosphorus (FTP) levels but they did not create settleable flocs, thus resulting in no change or even higher unfiltered total phosphorus (UTP) levels when compared to non-dosed control mesocosms. Proprietary cationic polymer blends and anionic polyacrylamide (PAM) added post coagulant dosing were tested to enhance P-removal performance. Cationic polymer addition significantly lowered FTP when combined with Al-based coagulants, suggesting enhanced charge neutralization, and improved UTP removal when combined with Fe-based coagulants, signifying improved bridging or electrostatic patch formation to create larger/denser floc. The addition of PAM after coagulant dosing generally did not improve FTP removal but did improve UTP removal when dosed at levels >0.5 mg L−1. For Fe-based systems, doubling PAM dosage (from 0.5 to 1.0 mg L−1) was slightly more beneficial for UTP removal than doubling coagulant blend dosage. For Al-based systems, doubling coagulant blend dosage was slightly more effective for UTP removal than doubling PAM dosage, but the difference was not significant. The chemical cost savings from utilizing PAMS were large: doubling coagulant blend dose increased chemical costs by $28,000–$100,000 per 1B L of water treated depending upon blend, while doubling PAM dose marginally increased chemical costs by $1700. Wetlands enhanced with chemical addition achieved levels as low as 20–25 μg L−1 UTP and <10 μg L−1 FTP under field conditions. These were lower than average achievable levels by non-dosed mesocosms (84 μg L−1 UTP and 43 μg L−1 FTP). While the goal of 10 μg L−1 total P was not met by these chemically enhanced treatment wetland (CETW) systems, strategic placement to treat water prior to entrance into STAs can potentially help STAs meet this criterion by extending the STAs' effectiveness and lifespan. More importantly, these systems can help mitigate downstream ecosystem imbalance and combat the formation and migration of a moving P front.

Colour removal from biologically treated landfill leachate with tannin-based coagulant

High humic substances remaining after biological treatment led to high colour values in landfill leachate which require treatment to make it dischargeable into the water stream. To date, limited studies were performed in using tannin-based coagulant as post-treatment for decolourisation of landfill leachate. In this work, the effectiveness of removing the colour from biologically treated landfill leachate (BTLL) via coagulation-flocculation process was studied. A tannin-based coagulant was used as coagulant with the aid of anionic and cationic polyacrylamide (PAM) as flocculant. Initially, jar test experiments were conducted with a varying dosage of coagulant and initial leachate pH. Next, tests were carried out with different values of PAM dosage, flocculation time as well as sedimentation time to find out the optimum condition for colour removal. The supernatant layer of treated leachate from each test was analysed for colour, zeta potential, pH and conductivity. At optimum leachate pH of 5, experiments with 3 min flocculation time and sedimentation time of 10 min resulted in the highest colour removal (81.8%) at coagulant dosage of 100 mg/L, with 1 mg/L anionic PAM (APAM) being added. Coagulation flocculation system of OF as tannin-based coagulant with APAM as flocculant showed the promising result in decolourisation of BTLL.

Enhanced treatment of flush-dairy manure in anaerobic sequencing batch reactors using a cationic polymer

Anaerobic sequencing batch reactors (ASBR) are preferred for treating dilute wastewaters but the retention of adequate active biomass, in successive-cycles, is always a challenge. This research investigated the efficacy of using a cationic polyacrylamide (PAM) flocculant for enhanced sludge retention in an ASBR treating flushed dairy manure, operated under psychrophilic conditions. Three PAM doses (10, 25, and 50 mg [PAM] l−1) were tested in duplicate reactors. At 6 d hydraulic retention time (HRT) and dosing of the feed-manure, steady state specific biogas yield for the 50 mg [PAM] l−1 treatment was 491 ± 7 ml g−1 [TCOD] (56% greater than control). At 4 d HRT the 50 mg [PAM] l−1 dose resulted in 465 ± 8 ml g−1 [TCOD] (20% higher than the control) at steady state conditions. The ratio of total volatile fatty acid to alkalinity was 0.29 ± 0.08 during the 6 d HRT and 0.14 ± 0.02 during the 4 d HRT, which were both below the trigger point for digester souring. This study shows that the use of PAM for high sludge retention in ASBR is a viable approach for, not only enhancing biogas yield, but also for improved and high-rate treatment of flushed dairy manure under psychrophilic conditions.

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.

Preparation and characterization of a soy protein based bio-adhesive crosslinked by waterborne epoxy resin and polyacrylamide.

A simple and useful approach by using non-toxic and water-soluble raw material to improve the bonding properties of soy protein adhesive has attracted much attention recently. The objective of this research was to provide a simple and environmentally friendly approach for preparing a high adhesion performance soy protein adhesive in aqueous solution by using waterborne-epoxy resin, soy protein and water-soluble polyacrylamide (PAM). The chemical structure and curing characteristics, as well as the initial viscosity and adhesion performance of the resulted soy protein adhesive were characterized by 1H nuclear magnetic resonance (1H-NMR), differential scanning calorimetry (DSC), a rotary viscosity meter and a plywood panel test. The 1H-NMR analysis results confirmed that epoxy resin was successfully crosslinked with the –NH2 groups of the soy protein molecule to form a water-resistance network structure, and the resulting adhesive contains active epoxy groups. It was found that the addition of PAM can decrease the apparent viscosity, lower curing temperature, and enhancing the wet shear strength of soy protein adhesives effectively, which were capable of facilitating their application as wood adhesives. The resulting soy protein adhesive containing 4% epoxy resin and 0.05% PAM dosage had a reasonable viscosity and lower cure temperature, and showed good water resistance and wet shear strength, which met the requirement for interior use plywood of the Chinese Industrial Standard. These results suggested that waterborne-epoxy resin can be used to prepare high-performance environmentally friendly soy protein adhesives, which might provide a feasible methodology to prepare bio-adhesive adhesives for plywood industrial applications.

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.

Continuous low dosing of cationic polyacrylamide (PAM) to enhance algal harvest from a hectare-scale wastewater treatment high rate algal pond

ABSTRACTCationic polymers (e.g. polyacrylamide) having a high molecular weight require a much lower dose than inorganic metal salts (e.g. AlCl3, FeCl3, or Al2(SO4)3) to produce dense compact flocs with good settling characteristics. This study investigated the effect of a continuous low dosing of cationic polyacrylamide (PAM) to achieve efficient algal removal from a 1-ha High Rate Algal Pond (HRAP) treating domestic wastewater in New Zealand. Firstly, standard jar tests were conducted in laboratory conditions. A wide range of PAM dose rates (0.25–9 mg/L), mixing periods (60–250 s) and settling times (0–120 min) were tested on HRAP effluent samples to determine optimal operational parameters for the 1-ha HRAP in terms of TSS and turbidity removal. PAM addition effectively promoted flocculation of the wastewater algal biomass, removing 78% of TSS (from 135 to 30 mg/L) and 70% of turbidity (from 41 to 12 NTU) at a dose of only 4 mg/L. The jar tests determined that ∼120 s of vigorous mixing followed by 15-min of settling were sufficient to promote the formation of dense/settleable algal flocs. Continuous addition of PAM to the hectare-scale HRAP effluent at the 4 mg/L laboratory determined dose rate was found to improve TSS removal in the Algal Harvest Pond (AHP) by ∼55% (from 13% to 68%). The TSS concentration and turbidity of the AHP effluent were consistently maintained <50 mg/L and <18 NTU respectively. Furthermore, a ∼1-log E. coli removal (from 1 × 105 to 1 × 104 MPN/100 ml after settling) was also achieved in the AHP as a result of the algal floc formation and removal. Overall, this study demonstrated that addition of low levels of the chemical flocculant (e.g. cationic polyacrylamide) to the HRAP effluent can greatly improve algal solid removal (at least 50%) with a minimum chemical cost (∼$0.05 NZD/m3 of wastewater).

Evaluation of dynamic behavior of coagulation-flocculation using hydrous ferric oxide for removal of radioactive nuclides in wastewater

Coprecipitation using hydrous ferric oxide (HFO) has been effectively used for the removal of radionuclides from radioactive wastewater. This work studied the dynamic behavior of HFO floc formation during the neutralization of acidic ferric iron in the presence of several radionuclides by using a photometric dispersion analyzer (PDA). Then the coagulation-flocculation system using HFO-anionic poly acrylamide (PAM) composite floc system was evaluated and compared in seawater and distilled water to find the effective condition to remove the target nuclides (Co-60, Mn-54, Sb-125, and Ru-106) present in wastewater generated in the severe accident of nuclear power plant like Fukushima Daiichi case. A ferric iron dosage of 10 ppm for the formation of HFO was suitable in terms of fast formation of HFO flocs without induction time, and maximum total removal yield of radioactivity from the wastewater. The settling time of HFO flocs was reduced by changing them to HFO-PAM composite floc. The optimal dosage of anionic PAM for HFO-anionic PAM floc system was approximately 1–10 ppm. The total removal yield of Mn-54, Co-60, Sb-125, Ru-106 radionuclides by the HFO-anionic PAM coagulation-flocculation system was higher in distilled water than in seawater and was more than 99%.

Application and mechanism of nucleation-induced pelleting coagulation (NPC) in treatment of fracturing wastewater with high concentration of dissolved organic matter

To improve the separation efficiency of fluffy flocs during coagulation of fracturing wastewater with high concentration of dissolved organic matter, a novel nucleation-induced pelleting coagulation (NPC) process is proposed based on pelleting coagulation in this study. In the NPC process, nucleation agents were added to act as pellet seeds to generate high-density pellet flocs. The results implied that the necessary condition for the NPC process was to control the metastable state, i.e. zeta potential around −10 mV after addition of the coagulant, polyaluminium chloride (PAC). Diatomite, which was added after rapid mixing, was used as the nucleation agent, and its optimal dosage was about 100 mg/L with particle size 100–200 μm. In addition, the dosage of the coagulant aid, polyacrylamide (PAM), significantly affected the performance of the NPC process, and the optimal PAM dosage was 10 mg/L in this study. It was found that 60 rpm (G = 55.1 s−1) was the optimal hydraulic condition for pellet growth during slow mixing. The pellet floc settling velocity reached 14.9 mm/s and the particle size (d50) reached 4.6 mm with an effective density of 0.021 g/cm3 at the optimal condition, which was one order higher than that of conventional aluminium flocs.