Significance of pressure and recirculation in sludge thickening by dissolved air flotation

1997 ◽  
Vol 36 (12) ◽  
pp. 223-230 ◽  
Author(s):  
Hak Chung Tai ◽  
Yeon Kim Doo
Keyword(s):  
Separation Efficiency ◽  
Reliable Operation ◽  
Dissolved Air Flotation ◽  
Efficient Operation ◽  
Recirculation Flow ◽  
Operating Variable ◽  
Solids Separation ◽  
Air Flotation ◽  
Sludge Thickening ◽  
Dissolved Air

An experimental study was conducted to identify the effect of each operating variable on the liquid-solids separation efficiency using a bench scale batch flotation system and waste activated sludge. Interpretation of the experimental results was performed by use of the characteristic constants of an empirical equation proposed. Minimum A/S ratio for reliable operation of dissolved air flotation should be greater than 0.009. However, unstable sludge rising took place at the initial clarification stage due to excessive shear and turbulence when the pressure was high in spite of high A/S ratio. The efficiency increased as the A/S ratio increased except a case of high pressure coupled with high A/S ratio. High recirculation flow with a saturator pressure less than 5 atm is recommended for stable and efficient operation. The pore size of a diffuser did not affect the thickening efficiency significantly. Concentration gradient of the float solids became larger as flotation continued. Skimming of a top layer or a long skimming interval is desirable for high thickening efficiency.

Innovative use of dissolved air flotation with biosorption as primary treatment to approach energy neutrality in WWTPs

2015 ◽  
Vol 10 (1) ◽  
pp. 133-142 ◽  
Author(s):  
H.-B. Ding ◽  
M. Doyle ◽  
A. Erdogan ◽  
R. Wikramanayake ◽  
P. Gallagher
Keyword(s):  
Biogas Production ◽  
Primary Treatment ◽  
Anaerobic Sludge ◽  
Excess Sludge ◽  
Dissolved Air Flotation ◽  
Biogas Yield ◽  
Air Flotation ◽  
Sludge Thickening ◽  
Plant Capacity ◽  
Dissolved Air

This paper presents two types of dissolved air flotation application together with biosorption (the ‘Captivator® system’) as primary treatments. In the first instance, the Captivator® system is the sole primary treatment for a new plant installation and helps to gain 65% more biogas while requiring only 44% of aeration for COD oxidation, compared to a conventional process with a primary clarifier. In the second application, the Captivator® system is used to enhance the existing primary treatment for plant capacity expansion. With digested anaerobic sludge recycled as an additional adsorbent, the Captivator® system in the second application increases the biogas yield by 52% and only generates 59% excess sludge. Overall, the Captivator® system would help WWTPs to approach energy neutrality by diverting more organics for biogas production and reducing the energy requirements for aeration. In addition, it would help to reduce the installation footprint for primary treatment and save considerable capital cost by eliminating the sludge thickening process.

scholarly journals Application of dissolved air flotation process for industrial sludge thickening: A laboratory-scale study

2017 ◽  
Vol 4 (1) ◽  
pp. 22 ◽  
Author(s):  
MohammadBagher Miranzadeh ◽  
Ali Atamaleki ◽  
Gholamreza Mostafaii ◽  
Hossein Akbari ◽  
Leila Iranshahi ◽  
...  
Keyword(s):  
Laboratory Scale ◽  
Industrial Sludge ◽  
Dissolved Air Flotation ◽  
Flotation Process ◽  
Air Flotation ◽  
Sludge Thickening ◽  
Dissolved Air

Dissolved air flotation in Southern Africa

1995 ◽  
Vol 31 (3-4) ◽  
pp. 159-172 ◽  
Author(s):  
G. Offringa
Keyword(s):  
Southern Africa ◽  
Historical Development ◽  
Industrial Effluents ◽  
Water Reclamation ◽  
Current Application ◽  
Dissolved Air Flotation ◽  
Air Flotation ◽  
Sludge Thickening ◽  
Counter Current ◽  
Dissolved Air

A brief review is given of the historical development and current application of flotation technology in Southern Africa. Applications in water reclamation, sludge thickening, industrial effluents and water treatment are presented on the basis of some case studies and pilot investigations. Design philosophies followed are pointed out. Research and development performed and a few innovations by local engineers and scientists are highlighted. These include combination or integration of dissolved air flotation (DAF) with filtration, presettling and powdered activated carbon, a simple aeration nozzle, surface grids for float dewatering and stabilization, and a counter-current DAF.

Separation characteristics in dissolved air flotation - pilot and full-scale demonstration

2003 ◽  
Vol 48 (3) ◽  
pp. 89-96
Author(s):  
M. Ljunggren ◽  
L. Jönsson
Keyword(s):  
Particle Size ◽  
Contact Zone ◽  
Separation Efficiency ◽  
Particle Separation ◽  
Full Scale ◽  
Particle Sizes ◽  
Dissolved Air Flotation ◽  
Air Flotation ◽  
Practical Implications ◽  
Dissolved Air

This study presents practical implications for particle separation in Dissolved Air Flotation (DAF). The objectives were to localise where particles are separated from the water phase and to determine what particles, in terms of size, are removed by the DAF-process. Both pilot- and full-scale plants were investigated. Particle sizes were analysed with a light-blocking particle counter and an optical borescope was used for visualisation of particle-bubble aggregates. It was found that particles are preferably separated upstream in the process, i.e. close to the contact zone. Furthermore, separation efficiency for particles increased with increasing particle size.

Evaluation of dissolved air flotation process for water clarification and sludge thickening

1995 ◽  
Vol 31 (3-4) ◽  
pp. 137-147 ◽  
Author(s):  
Harish Arora ◽  
James R. DeWolfe ◽  
Ramon G. Lee ◽  
Thomas P. Grubb
Keyword(s):  
Pilot Study ◽  
Algal Blooms ◽  
Water Source ◽  
Complete Removal ◽  
Organic Content ◽  
Dissolved Air Flotation ◽  
Flotation Process ◽  
Air Flotation ◽  
Sludge Thickening ◽  
Dissolved Air

Dissolved air flotation was evaluated using pilot and bench tests for water clarification and sludge thickening. A DAF pilot study was conducted on one water source with low turbidity, high color, high organic content and algal blooms. For this water, coagulation with alum, cationic polymer and pH around 6.1 resulted in removal of turbidity, color and algae. THMFP and TOC were removed by approximately 25 and 50 percent, respectively. A river water source was used in another pilot study to identify limits on source water turbidity for the DAF process. Tests conducted with induced high turbidity values resulted in filtered water quality with low turbidity and complete removal of color. TOC was removed by approximately 35 percent, however, inconclusive results were obtained for THMFP removal. Based on these pilot test, DAF is a viable clarification process, especially for source waters with low turbidity (infrequent spikes upto 100 NTU), high algal blooms and high color. Bench-scale DAF assisted sludge thickening resulted in performance similar to gravity thickeners. High recycle ratios (around or greater than 100 percent) were required for effective sludge thickening.

scholarly journals Modeling the Separation of Microorganisms in Bioprocesses by Flotation

Processes ◽  
2018 ◽  
Vol 6 (10) ◽  
pp. 184 ◽  
Author(s):  
Stefan Schmideder ◽  
Christoph Kirse ◽  
Julia Hofinger ◽  
Sascha Rollié ◽  
Heiko Briesen
Keyword(s):  
Fluid Dynamics ◽  
Separation Efficiency ◽  
Algebraic Model ◽  
Balance Model ◽  
Separation Processes ◽  
Dissolved Air Flotation ◽  
Computational Fluid Dynamics Cfd ◽  
Air Flotation ◽  
Cell Size Distributions ◽  
Dissolved Air

Bioprocesses for the production of renewable energies and materials lack efficient separation processes for the utilized microorganisms such as algae and yeasts. Dissolved air flotation (DAF) and microflotation are promising approaches to overcome this problem. The efficiency of these processes depends on the ability of microorganisms to aggregate with microbubbles in the flotation tank. In this study, different new or adapted aggregation models for microbubbles and microorganisms are compared and investigated for their range of suitability to predict the separation efficiency of microorganisms from fermentation broths. The complexity of the heteroaggregation models range from an algebraic model to a 2D population balance model (PBM) including the formation of clusters containing several bubbles and microorganisms. The effect of bubble and cell size distributions on the flotation efficiency is considered by applying PBMs, as well. To determine the sensitivity of the results on the model assumptions, the modeling approaches are compared, and suggestions for their range of applicability are given. Evaluating the computational fluid dynamics (CFD) of a dissolved air flotation (DAF) system shows the heterogeneity of the fluid dynamics in the flotation tank. Since analysis of the streamlines of the tank show negligible back mixing, the proposed aggregation models are coupled to the CFD data by applying a Lagrangian approach.

Design parameters for dissolved air flotation in South Africa

1995 ◽  
Vol 31 (3-4) ◽  
pp. 203-212 ◽  
Author(s):  
Johannes Haarhoff ◽  
Lucas R. J. van Vuuren
Keyword(s):  
South Africa ◽  
Waste Water Treatment ◽  
Design Parameters ◽  
Clear Trend ◽  
Dissolved Air Flotation ◽  
Body Of Knowledge ◽  
Design Values ◽  
Air Flotation ◽  
Sludge Thickening ◽  
Dissolved Air

Dissolved air flotation has been used in South Africa for more than 25 years in the field of water and waste-water treatment, with practically all the development and verification done locally. This substantial body of knowledge and experience was recently condensed into a document titled A South African Design Guide for Dissolved Air Flotation. A general literature survey was combined with a detailed survey of 26 dissolved air flotation plants operating in Southern Africa, to arrive at suggested design parameters. Two broad categories of applications were covered in the guidelines - those of water clarification, and of activated sludge thickening. A clear trend emerged from the data collected. Drinking water clarification plants were generally designed within a fairly narrow range of the most design parameters, and the perception of operators and managers was that these clarification plants performed very efficiently. Sludge thickening plants, on the other hand, showed considerable variability in terms of most design parameters, and the general perception of its efficiency consequently varied from highly positive to negative. The paper includes summaries of the ranges of the actually surveyed design parameters, the suggested design values and a comparison with typical design values available from other countries.

Parameters Influencing Sludge Thickening by Dissolved Air Flotation

1993 ◽  
Vol 28 (1) ◽  
pp. 87-90 ◽  
Author(s):  
M. Sugahara ◽  
S. Oku
Keyword(s):  
Particle Size ◽  
Particle Sizes ◽  
Dissolved Air Flotation ◽  
Flotation Process ◽  
Sludge Characteristics ◽  
Factors Influencing ◽  
Air Flotation ◽  
Sludge Particle ◽  
Sludge Thickening ◽  
Dissolved Air

The purpose of this study was to investigate factors influencing sludge thickening in the dissolved air flotation process. Attention focused on the alteration of sludge characteristics as a result of coagulation and aeration. Batch thickening experiments showed that both coagulation and aeration enhanced sludge thickening. The most important parameter influencing sludge thickening appeared to be sludge particle size; larger particle sizes produced higher sludge solids concentrations in the float.

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