Optimization of slurry flocculation and dewatering based on electrokinetic and rheological phenomena

Dentel, Steven K.; Abu-Orf, Mohammad; Walker, Carol

doi:10.1016/s1383-5866(00)00078-2

Cited by 70 publications

(29 citation statements)

References 14 publications

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“…Inorganic coagulants have been found to act as skeleton builders and reduce the solids compressibility. Therefore, it is especially beneficial when a high pressure dewatering method, such as using a filter press, is adopted, as high porosity of the solids cake needs to be maintained under high pressure (Dentel et al, 2000;Qi et al, 2011).The most commonly inorganic coagulants in water and wastewater treatment are aluminum salts and iron salts. PACl has many advantages over conventional coagulants including less sludge production, insensitive on change of temperature and pH and high charge neutralization property (Matsui et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Correlation of physicochemical properties and sludge dewaterability under chemical conditioning using inorganic coagulants

Niu

Zhang

Wang

et al. 2013

Bioresource Technology

284

110

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h i g h l i g h t sWaste sludge conditioned with inorganic coagulants. Change in physicochemical properties of sludge floc was investigated. Chemical conditioning process included rapid aggregation and floc densification. SRF correlated well with the change in content of soluble EPS, LB-EPS and TB-EPS. Compression of EPS structure was a major mechanism of dewaterability improvement. This study investigated the effects of chemical conditioning with three representative inorganic coagulants (FeCl 3 , polyaluminum chloride (PACl) and high performance PACl (HPAC) on sludge dewaterability. We monitored the particle size, kinetic viscosity (KV), fractal dimension (D F ) and extracellular polymeric substances (EPS) located in different layers of sludge floc (soluble, loosely-bound (LB), tightly-bound (TB)) to understand the correlation of dewaterability and physicochemical properties of sludge under chemical conditioning. The conditioning process included the rapid aggregation of sludge particles induced by charge neutralization and bridging followed by floc densification caused by double electric layer compression. The floc size and D F were increased after chemical conditioning, indicating that larger and more compact floc formed. The floc conditioned with FeCl 3 was smaller but denser than that of PACl and HPAC. Furthermore, sludge dewaterability correlated well with the change in concentration of soluble EPS, LB-EPS and TB-EPS, but not with KV, D F , floc size.

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Section: Introductionmentioning

confidence: 99%

Correlation of physicochemical properties and sludge dewaterability under chemical conditioning using inorganic coagulants

Niu

Zhang

Wang

et al. 2013

Bioresource Technology

284

110

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“…Numerous suppliers offer an assortment of these water-soluble organic polymers by altering the molecular weight, charge density, structure (e.g. linear, branched, comb), and degree of cross-linking [3]. For example, SNF Floerger sells over forty different versions of their FLOPAM cationic poly(acrylamide) flocculant; the offerings differ in their charge density (low, medium, high, or very high), molecular weight (low, medium, fairly high, high, or very high) and structure (linear, branched).…”

Section: Introductionmentioning

confidence: 99%

“…This leads to two important considerations: first, it is generally understood that there is no workable algorithm to relate flocculant properties to dewatering performance [3]. Secondly, wastewater sources from different treatment plants have diverse dewatering characteristics.…”

Section: Introductionmentioning

confidence: 99%

“…In our previous work, we found that the dewatering performance of twenty-four different flocculants from three suppliers varied considerably [4]. Notably, for anaerobic wastewater treatment, the cost of the polymer flocculant is the greatest component in the biosolids treatment operation [5].This leads to two important considerations: first, it is generally understood that there is no workable algorithm to relate flocculant properties to dewatering performance [3]. Secondly, wastewater sources from different treatment plants have diverse dewatering characteristics.…”

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confidence: 99%

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The microscale flocculation test (MFT)—A high-throughput technique for optimizing separation performance

LaRue

Cobbledick

Aubry

et al. 2016

Chemical Engineering Research and Design

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In this work, a new microscale flocculation test (MFT) method was developed that is ideally-suited for optimizing separation performance. A critical and complicated task in wastewater treatment is to identify the flocculation conditions that yield the optimal separation of water from suspended solid materials. The standard 'jar test' method is inadequate for conducting a full process optimization because a typical set-up only allows for a maximum of 6 tests to be conducted at once, and fairly large volumes of materials (approximately 1 to 2 litres) are needed for each individual test. The microplate-based, parallel processing format of the MFT method allows for many dozens of flocculation tests to be conducted simultaneously, with each test requiring only a few millilitres of material. As a demonstration of the MFT method, ten cationic polymer flocculants were evaluated with various digestate types. The optimal separation performance, as determined by the lowest capillary suction time (CST) measurement, was found by rigorously evaluating the effect of flocculant type (including molecular weight and charge density) and dosage conditions (including total amount added and single versus staged addition).For example, the dose-dependent profiles for certain flocculants exhibited a nearly 10-fold greater decrease in CST compared to other flocculants. Process optimization in environmental separations is not trivial, but rather, is a complicated task that requires an extensive amount of experimental work for which the MFT method is ideally suited. For any dewatering process, an ongoing challenge involves selecting, from the vast number of possible flocculants, the 'best' one in terms of economics and performance. In our previous work, we found that the dewatering performance of twenty-four different flocculants from three suppliers varied considerably [4]. Notably, for anaerobic wastewater treatment, the cost of the polymer flocculant is the greatest component in the biosolids treatment operation [5].This leads to two important considerations: first, it is generally understood that there is no workable algorithm to relate flocculant properties to dewatering performance [3]. Secondly, wastewater sources from different treatment plants have diverse dewatering characteristics. So, the exact flocculant type and the optimum dose must be determined on a case-by-case basis for different treatment applications. Yet, the selection of the 'best' flocculant has been described as "one of the most demanding, frustrating, and time-consuming experiences for many operations personnel" [6].The benefit of optimizing the flocculant dose extends beyond the operating costs for a given treatment facility. Water-soluble polymers have been found to be toxic to aquatic lifeforms, even at low concentrations [7]. Thus, there are valid concerns about the effect of flocculant 'overdosing' in dewatering processes, given the potential for discharge into the aquatic environment, either directly via the liquid fraction, or indirectly via leachin...

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“…In dewatering operations the main objective is to produce the driest sludge at the optimum chemical conditions, which is most often a water-soluble organic polyelectrolyte usually termed a polymer. The flow properties and variability, mixing intensity, and time allowed for mixing all effect the optimal dosing of the flocculation process (Dental et al, 2000). Örmeci (2007) links the optimal sludge dewatering operation, in terms of polymer dose and mixing intensity, to the rheological properties of wastewater sludge, and a reduction of 50% polymer consumption was achieved with the off-line methods used for both conditioned and unconditioned sludges.…”

Section: Introductionmentioning

confidence: 99%

A feasibility study of in-line rheological characterisation of a wastewater sludge using ultrasound technology

Kotze¹,

Haldenwang²,

Fester³

et al. 2014

WSA

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The rheological characteristics of sludge affect transportation, treatment and the disposal processes involved in sludge system design and management operations such as dewatering, including flocculation and filtration. The concentration of solid matter in the sludge has an effect on rheological parameters such as yield stress and viscosity. These rheological properties of sludge are almost exclusively obtained today using commercially available instruments, such as conventional rotational rheometers or tube (capillary) viscometers. Since these methods are time-consuming and unsuitable for realtime process monitoring, the ultrasonic velocity profiling coupled with pressure drop (UVP+PD) methodology becomes very attractive for in-line flow behaviour monitoring for quality control and process optimisation. The main objective of this research work was to evaluate the UVP+PD technique in a concentrated sludge as found in a wastewater treatment plant. A portable pump test rig with tube viscometer fitted with a UVP+PD system was used to determine the rheological parameters. Conventional UVP installation techniques were tested as well as a new delay line UVP transducer. The results obtained from different installation techniques and transducers are compared. Finally, rheological parameters obtained using UVP+PD compared within 15% of that obtained using the tube viscometer. The results showed that UVP+PD is a feasible and promising technique for in-line real time flow visualisation and rheological characterisation for treated wastewater sludge which, when used as in-line process control, could lead to significant savings in chemicals and will optimise processes producing drier sludges and filter cakes.

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Optimization of slurry flocculation and dewatering based on electrokinetic and rheological phenomena

Cited by 70 publications

References 14 publications

Correlation of physicochemical properties and sludge dewaterability under chemical conditioning using inorganic coagulants

Correlation of physicochemical properties and sludge dewaterability under chemical conditioning using inorganic coagulants

The microscale flocculation test (MFT)—A high-throughput technique for optimizing separation performance

A feasibility study of in-line rheological characterisation of a wastewater sludge using ultrasound technology

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