University of Brescia
Institute for Microbiology
Laboratory for virology
and microbiological tests
General Director: Professor Adolfo Turano
assigned professor: Nino Manca
assigned professor: Arnaldo Caruso
Testing of the air cleaning done by the
DELPHIN DP 2001 system (Abstract)
Institute for Microbiology at the University of Brescia
Microbes can be found everywhere in our atmosphere. They are usually found in our domestic environment and workplace. Therefore, they can represent a source of infection. In our environment, these microorganisms are mainly spread by people and animals; and become airborne either due to skin peeling or droplet transmission. Up to a certain size ( >10-20µm diameter), the microbes cling to microscopically small particles whereas smaller sizes float in the surrounding air. Keeping this information in mind, it is obvious why it is important to have an active air-cleaning system that is able to suck in as much dust as possible and contain the existing microbial load in the air.
The appliance DELPHIN DP 2001 is a system to clean the air that binds the dust in the air with the aid of water. Our goal was to analyse the effectiveness of the appliance regarding the reduction of the microbial load that might be found in the dust in the air.
The DELPHIN was used in the rooms of the institute, in which the day-to-day laboratory work is conducted.
In order to have a more accurate evaluation, the tests for the DELPHIN DP 2001 system were divided into two parts.
Stage one: Checking the appliance and determination of the method
During tests, the following circumstances for said tests are sensible:
- Thorough cleaning of the appliance and the water tank of the DELPHIN with a 5 percent sodium hypochlorite solution for at least 30 minutes.
- As a precaution, the water for the air cleaning was sterilized in an autoclave.
- Regarding the speed with which the air is sucked in, a minimum rotational speed of ½ m³ of air per minute is seen as ideal in terms of sufficient intake of dust and good simultaneous extraction of microbes.
- The air was cleaned in a closed room without any air exchange and also in an open room, which was entered by laboratory staff. In both cases the system has proven effective regarding an increase in microbes in the extracted water after the cleaning process.
- Extraction of a water sample (100 ml) before and after using the appliance.
- Application of suspension on Petri dishes with cultures of blood agar.
- The test for moulds was conducted in a special filtering area with the goal to prove their possible existence in the surrounding air.
The Petri dishes set up for this stage, showed an increase in microbes although mainly gram-negative bacteria (Pseudomonas), gram-positive cocci (Staphylococci) and moulds (Penicillin, Aspergillus, Dematiaceae) were found.
Stage two: Experiments with the appliance and application of the method
The obtained results of the first stage directed our attention to the application of the methodology that is able to show the effectiveness of the appliance regarding the cleaning of a closed room, not entered by people, and the reduction of the microbial load after its application.
a) 6 Petri dishes with blood agar are set up in a closed room for six hours in order to give the particles in the air a chance to settle.
b) Time 0: 100 ml of water are extracted from the water tank of the appliance and then the DELPHIN is activated for 15 hours in the constantly closed room.
c) Time 15 hours: Switching off of the DELPHIN and extraction of 100 ml of water from the water tank.
d) In order to test the remaining microbial load, another 6 Petri dishes with blood agar are set up for 6 hours after the room has been cleaned by the DELPHIN for 15 hours.
Information on how the bacterial colonies were analysed:
The Petri dishes are incubated at room temperature for 4 days and at 37 centigrade for 48 hours. Afterwards the counting takes place.
Information on how the water was analysed:
- Centrifugation of the extracted sample at 3500 rotations per minute for 15 minutes;
- Extraction of floating particles and dissolve again the sedimented particles with 1 ml of natural saline solution;
- Spread 10 µl on Petri dish with blood agar in order to be able to count;
- Incubation of the Petri dishes at ambient temperature for several days and at 37 centigrade for 24 - 48 hours;
- Reading of the number of increased colonies.
a) Analysis of the microbial load in the surrounding air via open blood agar cultures and 6 hours of sedimentation of air in a closed room, before the use of DELPHIN: (see diagram no. 2)
Petri dishes incubated at room temperature: 24 bacterial colonies 6 mould cultures
Petri dishes incubated at 37 centigrade: 12 bacterial colonies 2 mould cultures
b) Time 0: Extraction of 100 ml of clean water and activation of DELPHIN (see diagram no. 1)
Petri dishes incubated at room temperature: no increase
Petri dishes incubated at 37 centigrade: no increase
c) Time 15 hours: Switching off of the DELPHIN and extraction of 100 ml of water with dust exposure (see diagram no. 1)
Petri dishes incubated at room temperature: 1950 bacteria/ml 200 mould cultures/ml
Petri dishes incubated at 37 centigrade: 1775 bacteria/ml no mould cultures
d) Analysis of the microbial load in the surrounding air via open Petri dishes with blood agar and 6 hours of sedimentation of air in a closed room, after the use of DELPHIN:
(see diagram no. 2)
Petri dishes incubated at room temperature: 10 bacterial colonies 4 mould cultures
Petri dishes incubated at 37 centigrade: 7 bacterial colonies no mould cultures
Diagram no. 1: Analysis of microbial load in the water depending on the amount of time the DELPHIN was used.
Diagram no. 2: Analysis of microbial load in the surrounding air depending on the amount of time the DELPHIN was used.
Clearly the DELPHIN DP 2001 system for air cleaning achieves a great efficiency regarding the reduction of the microbial load in closed rooms. The appliance managed to reduce the bacterial load by 50 – 60 % and the mould load by 40 – 50 % (see diagrams no. 1 and 2). This makes the DELPHIN ideally usable in domestic environments and at the workplace, especially for people, who require a high air quality. Though this is not only applicable to people with a good state of health but also to people with symptoms such as dust or pollen allergies, bronchitis in general or in stages of convalescence. Furthermore, it is advisable to use the appliance in closed rooms, where a lot of people stay and therefore need a constant exchange of air in order to keep the microbial load in the air as small as possible.
It is also advisable to thoroughly clean the appliance, especially the water tank, with a surface-active cleansing agent that is neither ionic nor anionic or to carefully clean the DELPHIN with a diluted sodium hypochlorite solution. On top of that, it is important to change the water after each use of the appliance.
Professor Adolfo Turano