Electrochemical treatment of wash water combats E.coli, allows reuse

13 Mar 2012

Electrochemical treatment of wash water in fresh produce processing shows real potential to combat E.coli contamination and cut in-plant water consumption, according to recent research.

The study, by a team of Spanish scientists, claims to demonstrate the efficacy of an electrochemical treatment in water disinfection, through the use of boron-doped diamond electrodes.

The group, from universities of Murcia and Cordoba, recorded reductions of E.coli 0157:H7 in wash water supplemented with sodium chloride (NaClW) reaching 5 log units when treated using the method for up to 24 minutes.

This was much faster than similar reductions in standard tap water – without NaCl – although the equipment still showed good disinfectant potential, they said.

The paper - Electrochemical disinfection: An efficient treatment to inactivate Escherichia coli O157:H7 in process wash water containing organic matter - was published in the journal Food Microbiology.

Water as vehicle for cross contamination

The method was investigated in the wake of several foodborne outbreaks linked to E.coli-contaminated leafy vegetables in the last three decades. Previous research had shown the bacteria could attach itself to lettuce leaves. While the scientist admitted there was little knowledge on how the pathogen is transmitted through food processing, “it seems cross contamination during washing at the factory could have an important role”.

They identified the disinfection of process water as “a critical step” but said chlorinated water and the currently widely-used sodium hypochlorite were not fully effective in tackling the pathogen – hence the need for alternatives.

Sustainability and cost issues also mean any process should ideally allow water to be reused. “Such technologies should be powerful enough to provide water that does not contain microorganisms or toxic substances in amounts that can influence food safety and that could be used without affecting the wholesomeness of the product, but that would not need to be necessarily of potable quality,” said Ana Allende et al.

Sanitizers can maintain the microbial safety of water but the chlorine content can react with organic matter in the liquid and lead to the formation of “potentially harmful chlorinated by-products”, said the study.

However, electrochemical treatment “has shown potential for the disinfection and improvement of physiochemical quality of different types of water” – including drinking, industrial and waste waters, they added.

Method and results

Tap water (TW) and tap water with sodium chloride (NaClW) containing different levels of organic matter – known as Chemical Oxygen Demand (COD) were obtained from lettuce. The levels of the COD ranged from around 60, 300, 550 ± 50 and 750 ± 50 mg/L.

These were inoculated with a cocktail of E.coli O157:H7 at 105 cfu/mL. The study examined range of measurements including changes in levels of E. coli O157:H7, as well as free, combined and total chlorine, pH, oxidation–reduction potential, COD and temperature.

They found that in NaClW, free chlorine was produced more rapidly than in TW and, as a consequence, reductions of 5 log units of E. coli O157:H7 were achieved faster than in tap water alone.

In NaClW the five log reduction was achieved in 0.17 minutes, 4 minutes 15 minutes and 24 minutes for water with 60, 300, 500 and 750 mg/L of COD, respectively. In TW alone the reductions were recorded as 0.9, 25, 60 and 90 minutes for water with 60, 300, 600 and 800 mg/L of COD, respectively.

Potential

The results demonstrate the treatment has “potential for disinfection and for reducing COD of process washing water containing lettuce organic matter”.

The group suggests the technology could be used in the fresh produce industry to “maintain the microbiological and physicochemical quality of washwater, reducing chlorination by-products formation with respect to sodium hypochlorite use”.

It could also be used after vegetable washing “to improve the water quality in order to allow its reuse or to recondition the wastewater before discharge”.

Source: Food Microbiology