Treatment of spent filter backwash water using dissolved air flotation

2001 ◽  
Vol 43 (8) ◽  
pp. 59-66 ◽  
Author(s):  
A. Eades ◽  
B. J. Bates ◽  
M. J. MacPhee
Keyword(s):  
Design Parameters ◽  
Water Recovery ◽  
Raw Water ◽  
Dissolved Air Flotation ◽  
Water Recycle ◽  
The Usa ◽  
Air Flotation ◽  
Pathogenic Agents ◽  
Dissolved Air ◽  
Filter Backwash Water

There is increasing interest in treating recovered spent filter backwash water in the drinking water industry. In the USA the Filter Backwash Recycling Rule will come into effect in the near future. The purpose of the Rule is to prevent the concentrated pathogenic agents, potentially in the filter backwash water, from being returned to the head of the water treatment works without some form of treatment or dilution. By treating this flow both public health and financial liability can be better managed by the operating utility. Dissolved Air Flotation (DAF) was investigated as a possible technology alternative to simple or advanced sedimentation techniques. This application is not widespread but sits somewhere in between the two normal applications of DAF as a high solids sludge thickener and a low turbidity clarification system. Given this a pilot plant program, supported by jar testing, was undertaken to determine the process capability and the design parameters for this application. DAF proved to be very suitable for backwash water recovery. DAF effluent turbidities of <1.0 NTU could be easily obtained, when raw water turbidities were in excess of 50 NTU. Chemical requirements were low with only a single low dose of polymer required to bind the floc particles to form a solids matrix suitable for flotation. Flocculation contact times ranged from 0–10 minutes depending on the nature of the raw water. Recycle rates as low as 5% performed satisfactorily with no significant improvement when increased to 20%. Sludge solids of 3.5–9.6% dry solids were found and very low volumes of sludge, <0.1% of the incoming flow make the DAF solids handling system very compact.

Treatment Spent Filter Backwash Water using Dissolved Air Flotation (DAF) in Isfahan WTP

2008 ◽  
Vol 3 (3) ◽  
Author(s):  
Mohammad Hassan Mahmoodian ◽  
Mohammad Mehdi Amin ◽  
Mohammad Reza Shahmansouri ◽  
Mohammad Ghasemian
Keyword(s):  
Low Dose ◽  
Saturation Pressure ◽  
Raw Water ◽  
Dissolved Air Flotation ◽  
Air Flotation ◽  
Recycle Rate ◽  
Polyaluminium Chloride ◽  
Significant Concentration ◽  
Dissolved Air ◽  
Filter Backwash Water

Recovering spent filter backwash water is currently receiving a great deal of attention. EPA published the Filter Backwash-Recycling Rule (FBRR) in 2001. Recycle stream may contain significant concentration of pathogens, such as, cryptosporidium and Giardia. Dissolved Air Flotation (DAF) was investigated as a possible technology alternative to simple or advanced sedimentation technology. In this study with using a pilot of DAF effluent turbidities of >20NTU could be easily obtained, when raw water turbidities were in excess of 800 NTU. Chemical requirements were low with only a single low dose of polyaluminium chloride (PACl) required binding the floc particles to form a solids matrix suitable for flotation. The results showed that the efficiency of continuous flow DAF with using PACl as coagulant for removal of Turbidity, COD, HPC, SS and MPN were 97, 72, 75, 95 and 100 percent, respectively. The statistical analyses indicated that the optimum saturation pressure is 4-5 atm, during recycle rate of 20-25 percent. The removal efficiencies of turbidity and bacteria in coagulation with sedimentation were reported up to 70 and 65 percent, while in this study using DAF with coagulant PACl could remove turbidity, COD, SS and bacterial up to 97,72, 95 and, 72 percent respectively.

High-rate dissolved air flotation for water treatment

2001 ◽  
Vol 43 (8) ◽  
pp. 43-49 ◽  
Author(s):  
M. A. P. Raeli ◽  
M. Marchetto
Keyword(s):  
Reynolds Numbers ◽  
Pilot Scale ◽  
Water Velocity ◽  
High Rate ◽  
Raw Water ◽  
Parallel Plates ◽  
Dissolved Air Flotation ◽  
Removal Efficiencies ◽  
Air Flotation ◽  
Dissolved Air

This paper presents the results of an experimental investigation about the performance of a horizontal flow high-rate pilot scale Dissolved Air Flotation (HRDAF) unit containing inclined parallel plates for treating a coloured and low turbidity raw water. Experiments were performed with the DAF unit in order to verify the influence on flotation of : (i) the water velocity (Vh) between the plates, in the range 18 to 96.5 cm.min−1 with corresponding Reynolds numbers between 240 and 1060; (ii) the supplied air (S*) value ranging from 2.2 to 8.5 g of air/m3 of water ; (iii) the angle of the plates (60° or 70°). The best pilot plant operational condition was obtained applying only 4.0 g/m3 (S*) with Vh around 18 cm.min−1 for treatment of water coagulated with a Al2(SO4)3 dosage of 40 mg.l−1. In these conditions, the unit presented very good removal efficiencies of colour (90%, residual of 10 uC), turbidity (88%, residual of 0.8 NTU ) and TSS (94%, residual of 1.8 mg.l−1). Furthermore, the unit could operate at higher Vh values up to 76 cm.min−1 and still present good results. The DAF unit thus behaved as a high rate unit presenting good performance with low air requirement.

scholarly journals The evaluation of polymeric organic coagulants for potable water treatment by dissolved air flotation

2001 ◽  
Author(s):  
◽  
Rachigan Rajagopaul
Keyword(s):  
Water Treatment ◽  
Ferric Chloride ◽  
Potable Water ◽  
Raw Water ◽  
Dissolved Air Flotation ◽  
Air Flotation ◽  
Potable Water Treatment ◽  
Dissolved Air

Historically inorganic coagulants were the coagulants of choice for OAF treatment of potable water. Water treatment practitioners using OAF technology preferred ferric chloride, an inorganic coagulant. Ferric chloride formed light, floatable floes at relatively low flocculation intensities and detention times. The inorganic coagulant was also more forgiving during incidents of overdosing and raw water and pH variability

Recent applications of dissolved air flotation pilot studies and full scale design

1995 ◽  
Vol 31 (3-4) ◽  
pp. 327-340
Author(s):  
Steven R. Arnold ◽  
Thomas P. Grubb ◽  
Peter J. Harvey
Keyword(s):  
Water Treatment ◽  
Potable Water ◽  
The United States ◽  
Wastewater Sludge ◽  
Design Parameters ◽  
Dissolved Air Flotation ◽  
Pilot Studies ◽  
Air Flotation ◽  
Potable Water Treatment ◽  
Dissolved Air

The use of Dissolved Air Flotation (DAF) as a solids/liquid separation process in water treatment has been an effective alternative to sedimentation for 70 years. The process was initially applied for removal of materials which had a specific gravity less than water, such as fats, oils, fibers, and grease. DAF installations expanded in the late 1960s to wastewater and potable water treatment. Today, Dissolved Air Flotation is utilized for a wide variety of water and wastewater applications. DAF is applied extensively for wastewater sludge thickening and it is widely accepted in Scandinavia and the United Kingdom for potable water treatment. It has also gained a foothold in the United States with the start up of a 7.5 mgd (28.4 Ml/d) potable water flotation plant at New Castle, New York. The goal of this paper is to present recent applications of Dissolved Air Flotation technology on a variety of raw water sources. Descriptions and general design parameters of a typical flotation and a proprietary combined flotation and filtration process will be discussed.

The treatment of algae-laden raw water with compact flofilter of dissolved air flotation and GAC deep bed filtration

2004 ◽  
Vol 4 (5-6) ◽  
pp. 35-41
Author(s):  
X. Zhang ◽  
S. Zhang ◽  
Y. Liu
Keyword(s):  
Conventional Treatment ◽  
Good Alternative ◽  
Raw Water ◽  
Deep Bed Filtration ◽  
Dissolved Air Flotation ◽  
Chl A ◽  
Air Flotation ◽  
Filtration Unit ◽  
Advanced Treatments ◽  
Dissolved Air

Compact flofilter of dissolved air flotation and GAC deep bed filtration is a good integrated procedure, having the following characteristics: flotation and filtration are integrated in one tank, the flotation unit is above the filtration unit, filtration is GAC deep bed, and conventional and advanced treatments are integrated in one tank. During the treatment of algae-laden raw water with compact flofilter of dissolved air flotation and GAC deep bed filtration, the general performance was good: the outlet algae-count was 1.21×105–1.26×106 cell/l, the average removal of algae was 95.4%, the outlet chl-a was 0.68 μg/l, the removal of chl-a was 92.2%, the outlet turbidity was 0.16–0.20 NTU, the outlet had no odor, the outlet color was 3, the removal of color was 86.4%, the outlet Al-residual was 0.011 mg/l. Good removal of organics can be achieved: the average removal of UV254 was 54.3%, the outlet UV254 was 0.016–0.018 cm−1, the removal of DOC was 29.6%, the outlet DOC was 1.608 mg/l, the removal of BDOC was 42.6%, the outlet BDOC was 0.120 mg/l, the removal of AOC was 72.2%, the outlet AOC was 52 μg/l. Filter run period and UFRV were 36 h and 504 m3/m2. The results show that flofilter is a good alternative process for conventional treatment plus GAC adsorption.

Pretreatment considerations for dissolved air flotation: water type, coagulants and flocculation

1995 ◽  
Vol 31 (3-4) ◽  
pp. 63-71 ◽  
Author(s):  
Donald Q. Bunker ◽  
James K. Edzwald ◽  
Jan Dahlquist ◽  
Lars Gillberg
Keyword(s):  
Chemical Properties ◽  
Water Type ◽  
Raw Water ◽  
Dissolved Air Flotation ◽  
Mixing Intensity ◽  
Flotation Performance ◽  
Air Flotation ◽  
Favorable Conditions ◽  
Flocculation Time ◽  
Dissolved Air

Pretreatment considerations of coagulant selection, flocculation time and flocculation mixing intensity were studied for two different water supply types, aquatic humic and non-aquatic humic waters of low turbidity. Alum, ferric salts, and various polyaluminium chlorides (PACs) with different chemical properties were all effective in dissolved air flotation (DAF) when used under favorable conditions of dosage, pH, and flocculation time. A stoichiometry was found for the aluminium coagulants between coagulant dose and raw water DOC. Si and sulfate PACs were effective in treating cold waters with short flocculation times of 2.5 to 5 minutes. Flotation performance improved slightly with increasing flocculation mixing intensity. The results suggest that flocculation tanks be designed to produce strong, “pinpoint” size floc particles.

Fate and removal of Cryptosporidium in a dissolved air flotation water plant with and without recycle of waste filter backwash water

2002 ◽  
Vol 2 (2) ◽  
pp. 85-90 ◽  
Author(s):  
J.K. Edzwald ◽  
J.E. Tobiason
Keyword(s):  
Water Production ◽  
Dissolved Air Flotation ◽  
Water Plant ◽  
Cryptosporidium Oocysts ◽  
Model Predictions ◽  
Particle Counts ◽  
Air Flotation ◽  
Recycle Rate ◽  
Dissolved Air ◽  
Filter Backwash Water

Pilot plant research focused on the removal of Cryptosporidium oocysts by dissolved air flotation (DAF) clarification and by dual media filtration and on the impacts of the recycle of waste filter backwash water containing oocysts. No impacts from recycle of filter backwash (10% rate) were found for turbidity, particle counts (2-15 μm), and UV254 on DAF and filtration performance. DAF achieved Cryptosporidium log removals of 1.6 to 2.2 without or with recycle of filter backwash. No impacts of recycle were found on filtration, and cumulative (DAF plus filtration) log oocyst removals exceeded 4 log. Model predictions show that the fate of Cryptosporidium and the build-up of oocysts in the plant influent depend on: DAF performance, the percent of filtered water production used for backwashing, and the percent of filter backwash recycle flow. A DAF plant using 2.5% of filtered water production for backwashing and achieving 1.6 log removal or greater of oocysts by DAF clarification will not have a build-up of oocysts in the plant influent regardless of the recycle rate.

scholarly journals Dissolved Air Flotation: A Review from the Perspective of System Parameters and Uses in Wastewater Treatment

TecnoLógicas ◽  
2021 ◽  
Vol 24 (52) ◽  
pp. e2111
Author(s):  
Jeimmy Adriana Muñoz-Alegría ◽  
Elena Muñoz-España ◽  
Juan Fernando Flórez-Marulanda
Keyword(s):  
Climate Change ◽  
Wastewater Treatment ◽  
Biogas Production ◽  
Clean Energy ◽  
Design Parameters ◽  
Wastewater Reclamation ◽  
Dissolved Air Flotation ◽  
Flotation Process ◽  
Air Flotation ◽  
Dissolved Air

The current issues of climate change and high freshwater demand worldwide have promoted the implementation of wastewater reclamation technologies. This study aims to review the efficiency of the dissolved air flotation (DAF) technique in a wide variety of applications in the agricultural, industrial, domestic, and municipal sectors, which have high freshwater consumption worldwide. We made a systematic review of the DAF technique in wastewater treatment in 2015-2021. We reviewed six indexed databases and governmental statistical reports; we used the keywords: dissolved air flotation, microbubbles, wastewater treatment, and the main operating and design parameters involved in the effectiveness of the flotation process. Additionally, we conducted a review of the most common synthetic coagulant studies used with DAF, as well as natural coagulants that promise to mitigate current climate change. Finally, we discussed advantages, disadvantages, and potential future studies. DAF to have considerable potential for wastewater treatment, as well as for waste utilization. The generation of large quantities of DAF sludge is a breakthrough for clean energy production, as it allows the use of this waste for biogas production.

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