Disinfection efficiency of fine bubbles generated by hydrodynamic cavitation in the water phase (ISO TC281/WG3 New Proposal)

Nicholas Young Cheol PARK ypark115@naver.com New Water Tec Co. Ltd., Rep. of KOREA

- Hydrodynamic cavitation methods: ⇒ Important water treatment facilities for water disinfection purposes. - Hydrodynamic cavitation: fine bubble generation method used by physical hydrodynamic structures and pressure

Background

- Hydrodynamic cavitation acts as a disinfectant

=> through 1) chemical mechanisms : Generation of OH radicals) and 2) physical mechanisms : Shock waves, Pressure gradients and Share forces).

Background

- To establish an IS about methodology to evaluate the disinfection efficiency of fine bubbles, under conditions which are configured by ISO TC281,

- To promote the relevant technology development and their industrial applications

Study Purposes

- Fine bubbles are generated by the test fine bubble cavitation unit in the test facility with the following characteristics:

• a 100L test tank: PVC with a methacrylate window, 50cm (diameter) ⅹ 70cm (height)

• a 6kW(220V, 60Hz) centrifugal multistage pump made of stainless steel

• PVC pipes (diameter: 32mm) and the test fine bubble cavitation unit

• Water flow rate: maximum 10ton/hr

- The control test line is set without fine bubble cavitation to compare with the disinfection efficiency of test fine bubbles.

Method 1 – Test facility

Method 1 - Hydrodynamic Cavitation

- The capacity of the pump is appropriately fixed to circulate the bacterial test suspension within the test facility.

- Test fine bubble cavitation unit shall be operated to produce fine bubbles.

- The bacterial activity shall be evaluated using following two test organisms:

Escherichia coli ATCC 15442 ; Staphylococcus aureus ATCC 6538.

- The test tank and test facility should be cleaned by

appropriate methods before the test.

- Bacterial test suspension(N) : adjust the number of cells in the suspension to 1.5ⅹ108 cfu/ml to 5ⅹ108 cfu/ml using the diluent, estimating the numbers of units by any suitable means.

☞ Maintain this suspension in the water bath at 20°C±1°C and use within 2hr. ☞ The total amount of bacterial test suspension used is a 100 liters.

Method 2 – Test Bacteria & Bacterial test suspension

- initial contact temperature and initial temperature of the bacterial test suspension: 20°C±1°C.

- maximum contact temperature: if the contact temperature in the test tank is over 50°C±1°C, stop the test facility immediately, and take samples. The last recorded contact time at the final sampling shall be the last contact time.

- contact time (operation time of the test facility) to be tested are 1min±10sec; 10min±10sec and 30min±10sec.

Method 3 - Experimental conditions

- A total of 100 liters bacterial test suspension shall be moved to the test tank within 20min.

- The produced fine bubbles shall be contacted the bacterial test suspension during the operation of the test facility => Test solution

- Replicates of each test tube : ≥2

- Test: Test solution 9ml+ Interfering substance 1ml (20°C±1, 2min±10sec)

=> Test mixture 1ml+Neutralizer 8ml+ water 1ml (20°C±1, 5min±10sec) => Neutralizer mixture 1ml+Patri dishes(2) +TSA(12~15ml) => incubate(36 or37°C±1, 24hr) => Count

Method 3 - Experimental procedures

Method 4 - Experimental design Table 1. Test levels of microbubbles generated by HC (experimental temperature range is 20°C±1; initial water temperature of bacterial test solution is 20°C±1)

size class of microbubbles

(mean) Test Level description

test water with fine bubbles

Test Level Ⅰ Test water generated by a fine bubble cavitation

unit

test water without fine

bubbles

Test Level Ⅱ (Control)

Test water without using fine bubble generator (i.e. the water circulation in the pipe generated turbulence can cause a potential decrease of

the bacteria count)

- only colony counts <300 cfu/ml & >15 cfu/ml

- viable counts should be calculated using at least one pair of plates

- For calculation of the weighted mean count in cfu/ml, use the following formula : c/(nⅹ10-1) where c : the sum of the colonies on all the plates taken into account n : the number of plates taken into account.

Method 5 – Calculation and results

For each test bacteria record the number of cfu/ml in the bacterial test suspension (N) and after the test procedure for bactericidal activity of the fine bubbles (Na). The bactericidal activity of the test facility is expressed as reduction in viability: - Reduction in viability R = (N ⅹ 10-1)/ Na

- Relative Disinfection efficiency of the test fine bubble(D) =R/Rc where R = the reduction in viability of test fine bubble mixture Rc = the reduction in viability of the control test

Method 5 – Calculation and results

Table 2. Relative Disinfection efficiency (D) of fine bubble test levels estimated by each test bacterial strain’s disinfection test

N= number of cfu/ml of the bacterial test suspension; Na = number of cfu/ml in the test mixture; R= reduction in viability of test fine bubble mixture; Rc = reduction in viability of the control test; D= disinfection efficiency of the test fine bubbles.

Test case Test bacteria Contact time Bacterial

test suspension 1 min±10sec 10min±10sec 30min±10sec

Test Level Ⅰ

Escherichia coli ATCC 10536

Na1; Na2 R: D:

Na1; Na2 R: D:

Na1; Na2 R: D:

N:

Staphylococcus aureus ATCC 6

538;

Na1; Na2 R: D:

Na1; Na2 R: D:

Na1; Na2 R: D:

N:

Test Level Ⅱ

(Control)

Escherichia coli ATCC 10536

Na1; Na2 Rc:

Na1; Na2 Rc:

Na1; Na2 Rc:

N:

Staphylococcus aureus ATCC 6

538;

Na1; Na2 Rc:

Na1; Na2 Rc:

Na1; Na2 Rc:

N:

Table 3. Relative Disinfection efficiency (D) of fine bubble (mean size: 26.53±3.21 µm; No. concentration: 12,987±5321/l) test : Exp.1 Normal air- micro bubble

N= number of cfu/ml of the bacterial test suspension; Na = number of cfu/ml in the test mixture; R= reduction in viability of test fine bubble mixture; Rc = reduction in viability of the control test; D= relative disinfection efficiency of the test fine bubbles.

Test case Test bacteria Contact time Bacterial

test suspension 1 min±10sec 10min±10sec 30min±10sec

Test Level Ⅰ

Escherichia coli ATCC 10536

Na1: 7.0*106

; Na2: 3.3*107

R: 4 D: 40.6

Na1: 2.6*106

; Na2: 9.5*106

R: 11 D: 113.8

Na1: 2.0*106

; Na: 8.7*106

R: 14 D: 112.5

N: 4.6*108

Staphylococcus aureus ATCC 6

538;

Na1: 4.6*107

; Na2: 6.2*107

R: 1 D: 6.1

Na1: 1.5*107

; Na2: 4.1*107

R: 2 D: 15.3

Na1: 1.8*107

; Na2: 3.2*107

R: 2 D: 15.6

N: 2.2*108

Test Level Ⅱ

(Control)

Escherichia coli ATCC 10536

Na1: 4.8*108

; Na2: 5.2*108

Rc: 0

Na1: 4.9*108

; Na2: 5.0*108

Rc: 0

Na1: 3.8*108

; Na2: 4.0*108

Rc: 0

N: 4.9*108

Staphylococcus aureus ATCC 6

538;

Na1: 3.3*108

; Na2: 3.9*108

Rc: 0

Na1: 2.8*108

; Na2: 4.3*108

Rc: 0

Na1: 3.4*108

; Na2: 4.4*108

Rc: 0

N: 4.0*108

Table 4. Relative Disinfection efficiency (D) of fine bubble (mean size: 26.53±3.21 µm; No. concentration: 12,987±5321) test; Exp.2 Ozone(10g/hr) - micro bubble(* CD: Complete disinfection)

N= number of cfu/ml of the bacterial test suspension; Na = number of cfu/ml in the test mixture; R= reduction in viability of test fine bubble mixture; Rc = reduction in viability of the control test; D= disinfection efficiency of the test fine bubbles.

Test case Test bacteria Contact time Bacterial

test suspension 1 min±10sec 10min±10sec 30min±10sec

Test Level Ⅰ

(Ozone-microbubble)

Escherichia coli ATCC 10536

Na1: 4.4*106

; Na2: 3.4*106

R:14 D: 3.8

Na1: 2.9*105

; Na2: 1.5*105

R:263 D: 18.5

Na1: 0

; Na2: 0

R:*CD D:*CD

N:5.2*108

Staphylococcus aureus ATCC 6

538;

Na1: 4.2*107

; Na2: 6.2*107

R:1 D: 1.2

Na1: 1.7*106

; Na2: 8.0*106

R:12 D: 6.4

Na1: 4.4*105

; Na2: 7.1*105

R:64 D: 12.3

N:3.5*108

Test Level Ⅱ

(Control : Just

Ozone)

Escherichia coli ATCC 10536

Na1: 1.2*108

; Na2: 1.6*108

Rc:4

Na1: 9.5*106

; Na2: 2.1*106

Rc:14

Na1: 8.8*104

; Na2: 1.5*103

Rc:17

N:4.9*108

Staphylococcus aureus ATCC 6

538;

Na1: 7.3*107

; Na2: 6.5*107

Rc:1

Na1: 1.8*107

; Na2: 2.4*107

Rc:2

Na1: 6.4*106

; Na2: 9.4*106

Rc:5

N:4.0*108

Application Test 1: Weate water of Slaughter house

미생물배양액

Application Test 2: Paint factory in Kuwait

• Current status of the standardization of fine bubble tech. in Korea

Domestic Standardization of Korea

Policy Projects (’14~’15) - Policy projects on Basic technology information & current tech. status - Development of national roadmap for standardization of fine bubble tech.(’15)

Establishment of domestic Tech. Comm. on fine bubble tech,(ISO/TC 281) (‘15)

Korea Standard ㉿ - “Finebubble terminology & definition (KSL 1628)” (‘15.12.29)

Establishment of Korea Fine Bubble Industry Association (KFBIA; 16. 3. 29)

Domestic Strategy of Standardization (‘15)

Activation of fine bubble industry and research

Establishment of ㉿ on finebubble technolgy

Support of international standardization activities

Establishment of domestic verification system on

finebubble tech.

3rd ISO TC281 Plenary meeting in Jeju Island

President (NWT)

BOD (NWT, Ilsung, Sewon E&E, SB E&E, Pimax)

Secretariat

Envronmental Water

Treatment C.

Cleaning C.

Agri/aquaculture C.

Medical C.

Measuremen

t C.

Inter-

Organization C.

Semiconductor C.

R&D C.

Technical Committee (10 experts)

KS-Verification Center

Consultants

KFBIA Organization structure (3.29, 2016)

Technical workshop: 3 times /yr