Flocculant Addition Research Articles

Settling velocity distribution of microalgal biomass from urban wastewater treatment high rate algal ponds

The aim of this study was to evaluate the settling velocity distribution of microalgal biomass with and without flocculant (Tanfloc SG). Microalgal biomass was obtained from two experimental wastewater treatment high rate algal ponds (HRAPs) operated with 4 and 8days of hydraulic retention time. Two sets of dynamic sedimentation tests were carried out using a water elutriation apparatus. In the first set, most of the biomass of the 8days-HRAP (63%) had settling velocities between 16.5 and 4m/h, while most of the biomass of the 4days-HRAP (65%) had settling velocities between 16.5 and 1m/h. In the second set, most of the biomass from both HRAPs (60% from the 8days-HRAP and 80% from the 4days-HRAP) had settling velocities between 6.5 and 0.4m/h. In this second set, settling velocities of <0.4m/h were reached by 20% and 40% of the biomass from 4days-HRAP and 8days-HRAP, respectively. The addition of flocculant at optimal doses ranging from 20 to 40mg/L had impressive effects on the settling velocity distribution in this second set. 70% and 84% of biomass reached velocities of >6.5m/h, compared to 10% and 14% of microalgal biomass without flocculant for the 8days- and 4days-HRAPs, respectively. With flocculant, a very small amount of biomass (3% for the 4days-HRAP and 8% for the 8days-HRAP) had settling velocities of <0.4m/h. Microscopic examination of samples from sedimentation tests showed how an important amount of microalgae settled in the system. Indeed, <1500microalgaeindividuals/mL were found in all outlet samples from the elutriation apparatus (inlet samples of >105microalgaeindividuals/mL). According to our results, a settler designed with a critical settling velocity of 1m/h would reach biomass recoveries as high as 90–94% with flocculant compared to 77–88% without flocculant.

Sedimentation behavior of flocculant-treated soil slurry

ABSTRACTSoil slurry dredged from seabed is becoming more widely used in land reclamation projects. A major problem encountered is that soil slurry is very high in water content and the dewatering process is difficult and time consuming. In this paper, the use of chemical flocculant for the dewatering of soil slurry is proposed and experimentally tested. Polyacrylamide (PAM) with different charge types/charge densities was tested in preliminary slurry dewatering tests. The results showed that the most effective flocculant, cationic PAM (CPAM) with +15 charge density, can reduce the volume of soil slurry (500% water content) by around 60% in 10 minutes. In contrast, the volume of pure soil slurry was almost unchanged. Slurry sedimentation tests on slurries with different flocculant contents and water contents were conducted. It is shown that, by adding flocculant into soil slurry, the rate of settlement under self-weight can be considerably increased in the tested range of water contents (100.7–879.5%). But the water content at the final state increases with flocculant additions. Slurry sedimentation curves displayed different characteristics with different flocculant contents as well as water contents. It is evidenced by particle size analysis that the addition of flocculant into soil slurry can attract soil particles and form large flocs (assemblage of particles), which explains the faster settlement rate in flocculant-treated soil slurry as compared with pure soil slurry. Scanning electron microscopic analysis revealed that flocculant-treated soil particles are more randomly oriented, while soil particles with no flocculant addition deposit in a more paralleled manner. This could explain the higher water content of flocculant-treated soil slurry at the final state.

Tensile strengths of flocculated compacted unsaturated soils

Flocculating agents can be introduced to soils through a number of natural or anthropogenic processes. This paper investigates the effect of flocculant addition (aqueous calcium chloride (CaCl2)) on the tensile strengths of two soils of differing flocculation susceptibility. Tensile strengths were found using the Brazilian (direct splitting) test for a range of suction values. A decrease in tensile strength was found for a soil with high clay content, which was consistent with previous findings in the literature. However, the strength of the soil with lower clay content unexpectedly increased. Results were interpreted using the extended Mohr–Coulomb (EMC) yield criterion fitted to data above the residual suction value. Changes in EMC parameters were used to infer changes in material behaviour on calcium chloride addition. Results have important implications for the design of geotechnical structures, for example engineered cover systems, exposed to flocculating conditions.

Phase behavior near and beyond the thermodynamic stability threshold.

The phase behavior of stabilized dispersions of macromolecules is most easily described in terms of the effective interaction between the centers of mass of solute particles. For molecules such as polymer chains, dendrimers, etc., the effective pair potential is finite at the origin, allowing "particles" to freely interpenetrate each other. Using a double-Gaussian model (DGM) for demonstration, we study the behavior of the system as a function of the attraction strength η. Above a critical strength η(c), the infinite-size system is Ruelle unstable, in that it collapses to a cluster of finite volume. As η(c) is approached from below, the liquid-vapor region exhibits an anomalous widening at low temperature, and the liquid density apparently diverges at the stability threshold. Above η(c), the thermodynamic plane is divided in two regions, differing in the value of the average waiting time for collapse, being finite and small on one side of the boundary line, while large or even infinite in the other region. Upon adding a small hard core to the DGM potential, stability is fully recovered and the boundary line is converted to the spinodal line of a transition between fluid phases. We argue that the destabilization of a colloidal dispersion, as induced by the addition of salt or other flocculant, finds a suggestive analogy in the process by which a strengthening of the attraction pushes a stabilized-DGM system inside the fluid-fluid spinodal region.

Optimizing the addition of flocculants for recycling mineral-processing wastewater

Mineral processing requires large volumes of water, but water is limited at mining sites. Therefore, techniques to recycle mineral-processing wastewater without negative effects on recovery and flotation grade are critical. Among a number of technologies to recycle water, flocculation using an anionic polymer was tested for recycling mineral-processing wastewater, as a major issue in mineral-processing wastewater recycling is to reduce suspended particles. A batch cylinder test was employed to evaluate the optimum amount of flocculant to add and settlement rate, turbidity, and floc size were measured as indications of dewaterability. Adding increasing amounts of flocculant increased the sedimentation rate due to the increased floc size. However, turbidity did not improve by increasing the concentration of flocculant because the polymer coating on the particle surface prevented efficient bridging of particles. In addition, excess use of flocculant may degrade water quality and produce unnecessary costs. Therefore, it is important to identify the optimum flocculant concentration for treating mineral-processing wastewater based on the properties of the water.

The utilization of forward osmosis for coal tailings dewatering

The feasibility of dewatering coal tailings slurry by forward osmosis (FO) membrane process was investigated in this research. A prototype cell was designed and used for the dewatering tests. A cellulosic FO membrane (Hydration Technology Innovations, LLC, Albany, OR) was used for the dewatering studies due to its high fouling resistance. Representative samples of coal tailings slurry were collected from the thickener outflow at American Coal Company (Galatia, Illinois). Characterization studies were conducted to obtain particle size distribution (PSD), total dissolved solids (TDS) and the solids content of the slurry. The impact of the slurry properties such as solids weight percent, osmotic pressure, and particle size on the dewatering rates was determined. Furthermore, the impact of slurry conditioning by the addition of flocculant and gypsum on the rate and extent of dewatering was also investigated. Dewatering to a total solids content of more than seventy weight percent from an initial solids content of approximately thirty percent was achieved in all cases. The dewatering rate and extent were found to be a function of particle size, particle shape, TDS content, and mixing. The membrane material was shown to withstand repeated use over a period of thirty trials without deterioration of performance. The results obtained from this research suggest that osmotic dewatering of coal refuse slurry is feasible.

Cultivating and harvesting of marine alga Nannochloropsis oculata in local municipal wastewater for biodiesel

The feasibility of using the mixture of seawater and municipal wastewater; (1) the wastewater before activated sludge tank, just after primary settling (BAS) and (2) the wastewater after activated sludge tank, just before addition of polymer flocculants (AAS); as culture medium for the cultivation of marine microalgae Nannochloropsis oculata was investigated.10% BAS, 20% BAS and 10% AAS, 20% AAS, 50% AAS, 70% AAS, 100% AAS effluent loadings were well adapted to used wastewater. Sufficient dry weights obtained (345–406mgL−1) with growth rates 0.37–0.45 for aerated cultures. High TN and TP removals (∼74–90%) were achieved. Harvesting technique for grown cultures was also studied with natural sedimentation and pH induced flocculation. By alkalinity induced flocculation, at pH values of 10.50, high recovery of the cells (∼80%) achieved with high sedimentation rates in 10min. The flocculation efficiencies decreased, sedimentation rates increased with the increase of the cell concentration.

An intelligent control strategy for thickening process

Through the online measurement of the thickener operation parameters including feed flow rate, mud bed level, and underflow concentration, an intelligent control strategy for thickener underflow and flocculant addition is proposed based on the mass balance model and expert rules. Based on the strategy, some guidelines concerning controllers tuning are provided. The application of thickener modeling and optimization software in the wastewater treatment plant of mineral processing illustrates an optimal control operation with stable underflow concentration.

Effect of coagulant and flocculant addition scheme on the treatment of dairy farm wastewater

Our group was approached by a manufacturer of treatment trains to recycle wastewater from dairy farm manure. Company X treatment trains consist of microscreening, sedimentation and filtration units attached to a reverse osmosis (RO) membrane. To enhance screening, a coagulant and a flocculant are added to the stream feeding the microscreen. However, their customers experience foaming on the microscreen as well as frequent fouling of the RO membranes. This study aimed to identify the source of foaming and to optimize the performance of the treatment train. Results show that interactions between the alum coagulant, the polymer flocculant and the contaminants are the cause of foaming. Addition of silicon polymer antifoam A effectively reduced foaming, while maintaining the same removal of total suspended solids (TSS) and total organic carbon (TOC). Alternatively, we proposed a new reagent addition scheme which circumvents back-to-back addition of the polymer flocculant and the alum coagulant. The proposed scheme resulted in significant reduction in foaming and ∼50% increase in TSS and TOC removal, even at the 40% lower dose of the cationic polymer. In addition to the economic benefit, a low concentration of left-over polymer should alleviate the fouling of the RO membrane.

Local treatment of coal-water slurries from thermal power plants with the use of coagulants

The coagulation of coal particles in a coal-water slurry from the Novo-Irkutsk thermal power plant was studied. The advisability of the application of highly basic aluminum hydroxochloride of grade B for the treatment of contaminated water with a concentration of suspended particles of 30 g/dm3 was shown. The granulometric analysis of coal particles was performed. The application of the reagent was revealed to be efficient for the coagulation of both coarse particles and a finely dispersed fraction. Carbonate hardness values of up to 1.5 mmol-equiv/dm3 and pH ≤ 7.8 were shown to be typical for the contaminated water from the fuel supply shop. They were the most optimal parameters for hydrolysis and efficient flocculation and did not require the addition of sodium bicarbonate and flocculants. The process flowsheet of the separate purification of a coal-water slurry was developed for the fuel supply shop. Among the advantages of this purification method are the return of rather highly purified water for thermal power plant needs, and also the production of additional fuel in the form of recovered coal particles. The product was characterized by improved engineering parameters in comparison with the initial fuel, i.e., had a higher calorific value and a lower sulfur content. The purified water corresponded to the normative requirements to the content of residual aluminum. This technology of purification was resource-saving, environmental-friendly, and economically profitable.

Effect of Disc Filtration with and without Addition of Flocculent on Nano- and Micro-Particles and Their Associated Polycyclic Aromatic Hydrocarbons in Stormwater

Many municipalities in Denmark and around Europe currently work towards separating stormwater and sewage. In existing urban areas this may imply disconnecting stormwater from the old combined sewer systems suffering from hydraulic overloading and discharging directly to nearby surface waters. Stormwater runoff may, however, be heavily polluted and Best Available Technologies (BAT) are therefore needed to treat the stormwater before discharge. The aim here was to determine the sizes of particles found in stormwater from roads and to evaluate the use of a cationic organic flocculant to increase the size of the particles and thereby increase the removal efficiency of a 10 µm woven polyester disc filter. The samples were collected in connection with a project testing a pilot scale disc filter for treating stormwater runoff. The micro-sized particles were found to be mainly below 10 µm (6.9–19 µm) and nano-sized particles were also observed (ca. 76–228 nm). The flocculent increased the observed particle micrometer sizes by 46% and the removal of particle-associate Polycyclic Aromatic Hydrocarbons (PAHs) was confirmed. The majority of the particles were, however, still below 10 µm after addition of flocculant, which shows that application of flocculants with the woven disc filter technology for stormwater treatment needs further refinement.

Lignin Removal From Aqueous Solution Using Calcium Lactate: The Effect Of Polymers And Magnesium Hydroxide As A Flocculant Aids

Palm oil mill effluent (POME) which is mainly associated with lignin has becoming a major concern due to its highly coloured appearance. The main colourant, i.e. lignin particles are difficult to be degraded in oil palm conventional biological ponding system. Coagulation/flocculation could remove the lignin prior to biological treatment and is considered vital to minimize the recalcitrance nature of palm oil mill effluent particles. In this study, the coagulation/flocculation process was investigated to remove lignin particles from aqueous solution. A non-toxic and biodegradable chemical i.e. calcium lactate was utilized as a destabilizer for the removal of lignin with an addition of several flocculants aid i.e. anionic polyacrylamide (APAM), polydimethyldiallylammonium chloride (polyDADMAC) and magnesium hydroxide. The effect of coagulant and flocculant aids dosage was investigated. From this study, it was found that the optimum condition was at 0.7g/L of calcium lactate and 0.5-1.0mg/L of APAM with ~64% of lignin removal. At concentration of 4 mg/L, the removal of lignin for APAM and polyDADMAC is similar. This result shows that the calcium lactate has potential as a coagulant and the efficiency can be enhanced with an addition of polymeric flocculant aids.

Mineral paste production from phosphate rock tailings

The dewatering stage is among the most important industrial unit operations, and is widely adopted in many different industries. Nowadays, mineral processing tailings disposal is a big problem due to the environmental degradation it causes. The phosphate rock processing in Anglo American Phosphate Brazil, situated in Catalão/ Go/Brazil, generates around 180 t/h of tailings for a plant feed of 480 t/h (approximately 37.5% of the processing plant feed), with 5 to 10% of solids and approximately 14% of P2O5. Nowadays, the tailings are sent directly to the tailings dam. The present work proposes paste production using the tailings from the phosphate rock processing plant. Through decantation of a tailings sample, a clarified liquid was obtained and drained. The decanted pulp then went through a second stage consisting of vacuum filtration. Flocculant addition in this stage generated a faster sedimentation rate and a higher dewatering performance in next stage of dewatering, because the flocculated material was retained by the filter medium instead of passing through it. The results were satisfactory for paste tailings production with a solid percentage of around 65%.

Efficient Application of Automation Technology in Thickener Process

The text mainly introduced the thickener’s front technology and also talked about the process of using flocculent addition and the emissions of underflow density presenting a more optimal automatic control scheme on the basis of the original automatic project. Using automatic control components like PLC programmable logic controller and the control elements of the inverter make the thickener in a whole closed-loop system for the flocculant addition and the density of the ore and the process of discharge. It will bring a positive side for our economic, social and ecological environment.

Using polyaluminum chloride and polyacrylamide to control membrane fouling in a cross-flow anaerobic membrane bioreactor

The objective of this study is to determine the feasibility of using flocculants to control membrane fouling in anaerobic membrane bioreactors (AnMBRs), which has not been previously reported. The effects of two typical polymeric flocculants, polyaluminum chloride (PAC) and polyacrylamide (PAM), on the properties (filterability, soluble microbial products (SMP), zeta potential and floc size) of anaerobic sludge were studied by batch experiment. The addition of either PAC or PAM can improve the filterability of the mixed sludge liquor but with different mechanisms and dosages. PAC mainly decreases the SMP, while PAM enlarges the floc size. The recommended PAC dosage is 500mg/L because a higher dosage would cause significant inhibition to anaerobic digestion. The effects of three flocculant addition methods on membrane fouling were tested in two lab-scale anaerobic membrane bioreactors. PAC at a dosage of 500mg/L was shown to be more effective than PAM in the control of membrane fouling through the reduction of TMP and the rate of TMP increase by facilitating the decrease in SMP and the improvement of sludge filterability. The addition of PAC at the beginning of the operation was the best way to control membrane fouling as the running period could be effectively extended.

Evaluation of flocculation behavior of marble powder suspensions

In this study, flocculation of marble powder suspensions was investigated depending on a polymer type and dosage. Polyacrylamide was used as a synthetic polymer, while starch was used as a natural polymer. The effect of polyacrylamide type was also examined using anionic, cationic and nonionic polyacrylamides. Flocculation of suspensions was ascertained by turbidity measurements. It was found that anionic and especially non-ionic polymers flocculated the marble powder suspension more strongly than starch and cationic polymer. On the other hand, it was observed that the sequential addition of starch and polymer did not improve flocculation of suspension. On contrary, sequential addition of flocculants caused re-dispersion of the flocculated suspension. When a non-ionic polymer was used as the flocculant, the reached minimum turbidity of suspension was measured to be 38 NTU (nephelometric turbidity unit).

Ferric biogenic flocculant produced by Acidithiobacillus ferrooxidans enable rapid dewaterability of municipal sewage sludge: A comparison with commercial cationic polymer

Dewatering of sludge at wastewater treatment plants is an essential and costly step in the subsequent sludge processing. Prior to dewatering, sludge is conditioned by addition of expensive organic and inorganic conditioners. The present study aimed at developing an effective biological process for sludge dewatering in comparison with commercial polyacrylamide polymers. A complex ferric biogenic flocculant produced by Acidithiobacillus ferrooxidans was used for dewatering of sludge generated after the Chemically Enhanced Primary Treatment process from municipal sewage. Within 1 h of treatment, the ferric biogenic flocculant reduced the capillary suction time (CST) and specific resistant to filtration (SRF) of sludge by 92 and 91%, respectively, as compared to the 89 and 72% respectively achieved by using polymer. The acidification of the sludge after the addition of ferric biogenic flocculant caused charge neutralization of sludge particles and led to enhanced dewaterability. It also enhanced the floc structure of sludge with much bigger sized flocs as compared to the control, which facilitate its dewatering capacity. Ferric biogenic flocculant treatment improved the calorific value of the sludge by 27% due to improved settlement of organic matter into the sludge pellet. The small scale mechanical filter press study confirmed that the ferric biogenic flocculant is effective in reducing sludge moisture content to 69% as well as improving the effluent quality in terms of total suspended solids and total dissolved solids removal compared with polymer treatment.

Pretreatment of Scenedesmus sp. Biomass as a Potential Anaerobic Digestion Substrate

<abstract><title><italic>Abstract.</italic></title> Algal biomass can be a potential substrate for anaerobic digestion. However, raw algae cells show a resistance to biological degradation, resulting in a slower methane production rate. Varying thermal and chemical pretreatments of algal biomass were investigated in an attempt to increase soluble organic matter (SOM) yield, which would result in enhanced methane production during subsequent anaerobic digestion. Scenedesmus sp. was harvested using three different procedures: with flocculation, with flocculation and drying, and without flocculation or drying. For all pretreatments and algae types, fluorescence micrographs were obtained to visually confirm the degradation of the algal cell walls. A complete 2×3×4 factorial design was applied for the algal biomass pretreatment study, including two heating temperatures (50°C or 90°C), three heating durations (10, 30, or 60 min), and four NaOH concentrations (0%, 3%, 6%, or 12% g NaOH g^-1 DW of algae). For algae cells with no flocculant addition, SOM yield increased by 15% with a moderate pretreatment of heating at 50°C in 3% NaOH for 60 min. For dried algae, the baseline SOM yield was higher than in the other algae, such that there was only a noticeable increase with the more severe pretreatments. For flocculated algae, the most severe pretreatment increased SOM yield by 17.2%, but overall the SOM increase was less than with fresh algae. Flocculation appears to inhibit cell wall disruption, but thermal chemical treatment can hydrolyze some flocculant polymers, which eases the flocculation and facilitates cell destruction.

Scale-down characterization of post-centrifuge flocculation processes for high-throughput process development.

AbctractFlocculation unit operations are being revisited as a strategy to ease the burden posed on clarification and purification operations by the increasingly high cell density cultures used in the biopharmaceutical industry. The purpose of this study was to determine the key process parameters impacting flocculation scale-up and use this understanding to develop an automated ultra-scale down (USD) method for the rapid characterization of flocculation at the microliter scale. The conditions under which flocculation performance of a non-geometrically similar vessel three orders of magnitude larger can be mimicked by the USD platform are reported. Saccharomyces cerevisiae clarified homogenate was flocculated with poly(ethyleneimine) (PEI) to remove the residual solids remaining in the centrate. Flocculant addition time modulated flocculation performance depending on the predominant mixing time scale (i.e. macro-, meso- or micromixing). Particle growth and breakage was mimicked at the two flocculation scales by the average turbulent energy dissipation (εavg) and impeller tip speed (vtip) scale-up bases. The results obtained were used to develop an USD method. The USD method proposed uses constant εavg as the scale-up basis under a micromixing controlled regime. These conditions mimicked the STR flocculation performance within a ±5% error margin. Operation in the mesomixing regime led to particle size deviations between the flocculation scales of ≤50 %. These results, in addition to the microscopic observations made, demonstrate the USD system presented in this work can produce process-relevant flocculated material at the microliter scale under the correct operating conditions.

Nanoclay for Micropollutant Removal in Wastewater-Effective Alternative?

The effluent of wastewater treatment plants (WWTPs) is an important source of priority substances and is, therefore, one of the bottlenecks in achieving the European Water Framework Directive (WFD) objectives. At various locations in the Netherlands, standard for priority substances are exceeded. The current concern regarding the cost and treatment method of these micropollutants in receiving waters may call for new approaches in wastewater treatment. In this study, a new treatment alternative is developed to remove micropollutant and wastewater parameter effectively and in a more cost effective way. A potential solution is the used of clay coupled with biodegradable polymer flocculants. Clay is naturally abundant and relatively inexpensive compared to currently conventional used adsorbent which can also act as coagulants. Experimental studies were carried out with four different nanoclay to select the best nanoclay for further optimisation. The atrazine removal percentage archived is in the range of 10-99% based on the nanoclay concentration of 0.01-50 g/L. Optimisation of best nanoclay performer leads towards atrazine reduction of &gt;99% with dosage of 0.1 g/L. The best and underperformed nanoclay then tested in other experiments with the addition of cationic starch flocculants. In this experiment, the addition of polymer increased the atrazine removal for the underperformer nanoclay to 46% with only 0.01 g/L clay dosages. This new approach in dealing with both micropollutant and wastewater parameter is promising and might help in reducing the compound concentration and the operational cost. However, further analysis and optimisation is required before any conclusion can be made.