Final Report: Combination of Chlorine-Free Electrolytic and Photochemical Methods for Sterilization of Contaminated Waters

EPA Contract Number: EPD11052
Title: Combination of Chlorine-Free Electrolytic and Photochemical Methods for Sterilization of Contaminated Waters
Investigators: Barashkov, Nikolay
Small Business: Micro-Tracers Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: March 1, 2011 through August 31, 2011
Project Amount: $73,433
RFA: Small Business Innovation Research (SBIR) - Phase I (2011) RFA Text |  Recipients Lists
Research Category: SBIR - Water and Wastewater , Small Business Innovation Research (SBIR)

Description:

Micro-Tracers, Inc., has performed a study on the combined electro/photochemical disinfection of water contaminated with Salmonella typhimurium (S. typhimurium) and E. coli. The main results of the project are summarized below. Micro-Tracers has:

  1. Found that the application of low voltage and low AC current to screen electrodes within a specially designed laboratory apparatus that circulates water containing various chloride-free electrolytes (sulfates, nitrates, carbonates, phosphates, and benzoates) is an effective method for sterilizing water contaminated with bacteria.
  2. Determined that hydroxyl radicals are the reactive species responsible for the sanitizing effect of the above-stated electrolytic treatment in the presence of chloride-free electrolytes. This has been confirmed by the well-established spin trap method. Additionally, Micro-Tracers has recorded and evaluated the rates of bacterial elimination by hydroxyl radicals in both inoculated distilled water and inoculated poultry chiller water.
  3. Designed two types of polymer-based active photolayers containing water-insoluble forms of fluorescent dyes. These photolayers have been used successfully for the disinfection of contaminated water through their generation of singlet oxygen when irradiated with low intensity visible light.
  4. Found the experimental conditions that provide the most effective combinations of singlet oxygen generation and chlorine-free electrolytic processes for the purpose of sterilizing contaminated water, superior to each applied individually (see Table 1).

Summary/Accomplishments (Outputs/Outcomes):

Parameters presented in Table 1 are evaluated in terms of equation (1), where the initial number of bacteria no, and current number of bacteria n, at time t is described as follows:

Log n = log no - k t (1)

where k is a constant depending on the current density for a constant volume of treated water and a constant surface area of electrodes. The time td in which the straight lines intersect the time axis (Log n = 0) is considered as the minimum time needed for complete disinfection.

Table 1. Results for the combined electrolytic treatment and photochemical treatment of DI water and poultry rinse water (both containing 0.2% electrolyte) inoculated with S. typhimurium*

Type of treatment

Nature of electrolyte

Disinfection

media

Log no

[cfu/ml]

k

min-1

td,

min

Photochemistry** (layer I)

Phosphate Buffer

DI water

5.85

0.0613

95.4

Poultry water

5.93

0.0567

104.6

Electrochemistry***

Phosphate Buffer

DI water

6.20

0.0640

96.8

Poultry water

6.11

0.0579

105.5

Photochemistry (layer I) & Electrochemistry

Phosphate Buffer

DI water

5.85

0.1275

45.9

Poultry water

5.97

0.1204

49.6

Photochemistry** (layer III)

Ammonium sulfate

DI water

6.03

0.0658

91.7

Poultry water

5.95

0.0604

98.7

Electrochemistry***

Ammonium sulfate

DI water

6.13

0.0565

108.5

Poultry water

5.63

0.0472

119.2

Photochemistry (layer III) & Electrochemistry***

Ammonium sulfate

DI water

6.10

0.1586

38.4

Poultry water

6.13

0.1396

43.9

*) 2000 ml of DI or poultry rinse water contaminated with S.Typhimurium was placed in the apparatus consisting of a pump, flow meter, and two types of cells: an electrochemical cell containing 10 screen electrodes; and a photochemical cell, containing a transparent window that allows for visible light to irradiate the active photolayer.

**) Photosensitive layer I and III contain different fluorescent dyes encapsulated into polymer films; irradiation was provided by non-filtered light from a source with a 35 Watt Halogen Bi-Pin Bulb Q35GY8.

***) 10 stainless steel electrodes; current ~0.2 A, current densities ~60 ma/cm2.

In a series of experiments with different natured electrodes, it was determined that there was no significant difference in the sanitizing efficiency of the electrolytic cell when using nickel or titanium electrodes. When using stainless steel electrodes, however, an increase in the rate of sterilization was observed; this effect was especially noticeable when utilized with the phosphate buffer solution.

It was determined that the AC electrolysis of the phosphate buffer solution was leading to the formation of hydrogen peroxide, which has been confirmed using Hochanadel’s colorimetric method. It is known that hydrogen peroxide can easily react with ferrous ions resulting in the creation of very active hydroxyl radicals (Fenton reaction). The experimental proof for hydroxyl radical generation was obtained by the addition of ferrous sulfate (0.05%) to the phosphate buffer during electrolysis of the aqueous S.Typhimurium solution with titanium electrodes: complete water disinfection time td in this case was decreased from 105.1 min (the same system, but with no ferrous sulfate addition) to 89.3 min. It was shown that in the case of using stainless steel electrodes the decrease in population of bacteria is proportional to the concentration of H2O2 formed.

Micro-Tracers' results show that separately both singlet oxygen generation and chlorine-free electrolytic processes are able to achieve the complete disinfection of S. typhimurium and E. coli. For both methods, the treatment of poultry water requires about 20 percent more time than the treatment of DI water. This difference is because poultry rinse water contains blood cells, fat micelles, and other organic substances that can coat the cells of bacteria and thus protect them from the effects of radicals or singlet oxygen.

Conclusions:

The positive results of the combined electro/photochemical treatment indicate the proposed technology may have market value for the disinfection of scalding water and/or poultry chiller water. Currently, USDA regulations permit the use of up to 50-ppm chlorine in chiller bath water to reduce the risk of pathogenic microorganisms adhering to chilled poultry products. Chlorine generally is effective for this purpose but is hazardous to store and handle in the processing plant. Concern exists because chlorine reacts with organics and may yield potentially carcinogenic trihalomethane (THM) compounds. The THM compounds adsorbed by the carcasses during chilling present a potential food-safety risk. Recovery and reuse of spent chiller water can save energy and reduce total water usage, but may tend to concentrate such undesirable residues. Besides, chlorination is not proven to be a reliable treatment to eliminate Campylobacter.

Additionally, the chlorine-containing ingredients used as part of a pathogen reduction treatment are not approved for any foods in the European Union (EU) and Russia, significantly reducing the export market for U.S. poultry.

Therefore, chlorine-free technologies, including the proposed electro/photochemical treatment, may have a high potential value for the poultry industry. The possibility of scaling up the technology for use at university pilot poultry processing plants will be a subject of Phase II proposal.