Water Disinfection for Produce Applications. Decay and Illness Prevention

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1 UC UC STATEWIDE Postharvest Quality and and Safety Water Disinfection for Produce Applications Decay and Illness Prevention Why water? Basics of chlorination ORP performance trials Practical use issues Trevor Suslow Dept. of Vegetable Crops University of California, Davis

2 Why Focus on Water Disinfection? Singular critical control point capable of amplifying an error in sanitation or hygiene management during production, harvest, or postharvest

3 The Predominant role of Disinfection is to prevent introduction and to minimize re-distribution of plant and human microbial pathogens in water Reduction of surface microbial load is secondary

4 Measure Free Chlorine to to Determine Antimicrobial Levels HOCl + OCl - Free Cl is a mix of forms HOCL hypochlorous acid is far faster acting Free chlorine balance is strongly impacted by ph

5 ph o T 0 (32) 5 (41) 5 Effect of ph and o T on % HOCL (41) (78) Desired target ph Balance of Effectiveness Corrosiveness Worker safety 0.31 Worker comfort

6 Postharvest Water Disinfection Monitor, Control, Document UC Davis Western Precooling CA DHS / FDB Pulse Instruments Primuslabs.com Boskovich, Capuro,, Cal-West Cooling Mann Packing

7 Effect of ph on ORP (mv) ORP of 3 ppm NaOCl from ph ORP (mv) ph ORP o T Disc Dataport IRMA [HOCl] (ppm) 250A Quikchek 250A - Pulse Instruments ORP probe Quikchek - Orion Instruments Pocket Probe

8 ORP Strong Oxidizers pull electrons away from platinum probe creating a small voltage differential to the reference probe. Platinum Electrode Reference Electrode Embedding matrix

9 ORP mv ppm NaOCl ph = Time (min)

10 Bacteria on leaves or in soil are washed off into water ClOH ClOH ClOH ORP reflects the oxidizing potential of HYPOCHLOROUS ACID (ClOH) CLOH is an oxidizer and metabolic poison

11 CLOH interactions with bacterial membranes causes ruptures at high doses and disrupts metabolic functions at lower doses. ClOH ClOH ClOH

12 ORP = 350 mv Pectobacterium = Erwinia ORP = 650 mv

13 Relative Conidia Survival ORP B. cinerea 350 B. cinerea 650 B. cinerea 750 B. cinerea 850 Time (min) ORP G. candidum 350 G. candidum 650 G. candidum 750 G. candidum Time (min)

14 Efficacy of HydroVac Reservoir Chlorination in Suppressing Microbial Load Accumulation No Chlorine ORP 650 First celery load. ORP dropped to 315mV Cooling Cycle

15 HOCL Needed to Maintain ORP 750 mv FAU Turbidity (FAU) Free Cl ppm Soil g/l Chualar Loamy Sand

16 Hyperchlorination May Increase Undesirable Disinfection By-Products Trihalomethanes chloroform, bromodichloromethane Ozone < Chlorine Dioxide < Chlorine S. Richardson, EPA

17 Maintain a "Window" of ORP Residual ORP (mv) CFU/g (log) ORP 350 ORP 650 ORP 750 Load 350 Load 650 Load Beginning End min Batch Wash

18 Key Practical Issues for ORP Systems ORP is a window of performance Probe maintenance is critical Overshooting CL needs recovery Separate acid and chlorine injection Always use a redundant manual back-up

19 Variance in ORP Readings with Different Hand-held Meters ORP (mv) Orion Pocket OakTon PRC 650 Orion 250A Sample Sequence

20 Variance in ORP Readings with Different Hand-Held Meters ORP (mv) Orion 250A-1 Orion 250A-2 Orion Pocket Reading Sequence

21 Characteristics of Chlorine Dioxide Effective on bacteria, fungi, virus Good effectiveness on biofilm penetration Very low impact of ph on efficacy Good stability in water (=HOCl HOCl; ; >O 3 ) Low off-gassing in soluble form Less corrosive than chlorine No chlorinated Disinfection-By By-Products Inactivated/decompose in sunlight

22 Methods of Production of ClO 2 On-site generation; typically for large operations Can t be shipped; > 10% is explosive!! Very toxic and strong irritant Engineer and restricted space controls required Stabilized (as Sodium Chlorite) Acid activation forms chlorine dioxide in batch Manual acid activation and proportion-pump pump feed Automated acid activation and in-line feed

23 Commercially Available Sanova Stabilized ClO 2 Acidified Sodium Chlorate forms ClO 2 on acid activation Biocide International Oxine Purogene Sanogene

24 Typical Reported Use Rates of ClO 2 Produce mist (potable water only) 5 ppm Produce wash (clean water rinse) ppm Water disinfection (flumes) ppm Biofilm removal (flumes and lines) 100 ppm Clean out (tanks, trays, bins) Storage (tanks, trays, bins) * ppm Storage room walls and floors ppm* * Requires ClO 2 protective mask

25 Some Reported Uses in FFV Potato storage : Controls Silver Scurf as fog/mist Carrot storage: Controls Botrytis, Sclerotinia, Thielaviopsis Carrot processing: Flume treatment for biofilm Banana and Mango: fungi control as fog Fresh-cut process water and equipment treatment Tomato: flume treatment for Geotrichum control

26 Water Disinfection: A Practical Approach to Calculating Dose Values for Preharvest and Postharvest Applications ANR # 7256