Chemical-free DAF flotation wastewater treatment equipment treats most TSS in wastewater, taking advantage of this TSS recovery to increase economic benefits, save chemicals, suitable for use for plant groups . paper production and cream milk production.

What is a Dissolved Air Flotation?

Dissolved Air Flotation in wastewater treatment has the function of separating and removing Total suspended solids (TSS) from the liquid based on the solubility of the barometric pressure.

The smaller the particles suspended in the water, the longer the settling time. Solids can settle by gravity naturally, differing only in the time it takes to settle. With some types of suspended particles, the flotation time will be faster than the settling time due to the size and specific gravity of the particles, for example: mineral oil particles, fiber particles, cellulose, …

The principle is to dissolve the air in the wastewater under pressure, then release the air at atmospheric pressure in the tank. The air released forms small bubbles that cling to the matter that float to the surface of the water and are easily removed.

DAF equipment can be installed in different locations of the water/wastewater treatment line depending on the nature and design of each project.

(PICTURES) Chemical-free Dissolved Air Flotation, Chemical-free DAF equipment for paper mills, post-treatment water quality of Dissolved Air Flotation  for milk/cream factory




Types of suspended solids, particles suspended in water

Size of suspended particles (Diameter –m)

Type of particles

Time for sedimentation

10 -2


0.3 seconds

10 -3

Coarse sand

3 seconds

10 -4

Fine sand

38 seconds

10 -5

Alluvial seeds

33 minutes

10 -6

Bacteria, microbial mud

35 hours

10 -7

Clay particles

230 days

10 -8

Colloidal particles

63 years

Suspended solid particles work in the absence of chemicals

Most of the solid particles suspended in water carry Negative (-) charges and are in a STABILITY by electrostatic repulsion, when in STABILITY, the particles will not coagulate with each other and remain suspended in the water.

Particles with no charge will freely collide and coagulate with each other

Particles with the same electric charges will repel each other.


Solid particles suspended in paper wastewater

In the food and paper industry, the waste stream from pulp and paper mill produces a large amount of coarse waste such as pieces of adhesive tape, etc. or cellulose fibres, suspended pulp, etc.

Buffered cellulose powders tend to float and should be removed from the water by flotation.

Other solid particles such as sand, which are often very heavy and tend to sink, should be removed by settling.

The purpose of the flotation method or the settling method is the same, both to separate the suspended SOLID from the water.. However, depending on the nature of the particle, our NGO company decides the appropriate method of removal.

Effects of PAC, Polymer

PAC: can break the STABILITY of particles to facilitate the particles to coagulate together.

POLYMER: has the effect of accelerating the coagulation of the flocs together and the formation of large flocs

=> The effect of CHEMICAL (PAC, Polymer) is to REDUCE the coagulation and flocculation time of particles suspended in water, thus assisting to REDUCE the flotation or settling time.

(Image) PAC addition, stability break, particles coagulate



Principle of using NGO’s DAF WITHOUT CHEMICALS

DAF specifications are based on:

  • Amount of Dissolved Gas (Gas Capacity) and Gas Rate Required for flotation
  • Hydraulic retention time for TSS to float to the surface with micro gas from which the DAF Diameter and Height Decision is made
  • Design the TSS removal performance of each DAF until the post-processing output TSS requirements are met

Based on the wastewater characteristics of each plant, NGO will design measuring equipment for each project, ensuring optimal treatment efficiency without the use of chemicals.

The solution of NGO International Co., Ltd. is beneficial for food and paper production enterprises

  • It can treat most of TSS in wastewater, and utilize and recover these TSS to increase economic benefits (for example, recover cellulose fibers in the paper industry, …)
  • No chemicals are used, thus bringing great economic benefits to businesses. Considering the cost of chemicals used for traditional flotation equipment only, using NO CHEMICALS Flotation has an exceptionally fast payback period (6 months – 1)

Article published in the Journal of the Vietnam Pulp and Paper Association, 3rd issue in 2021

Link to article: http://vppa.vn/wp-content/uploads/2021/08/TAP-CHI-CONG-NGHIEP-GIAY-32021.pdf

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Nguồn: NGO