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
Why Focus on Water Disinfection? Singular critical control point capable of amplifying an error in sanitation or hygiene management during production, harvest, or postharvest
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
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
ph o T 0 (32) 5 (41) 5 Effect of ph and o T on % HOCL (41) 10 10 20 25 30 30 (78) 99.85 99.68 6 7 8 9 10 98.53 96.92 87.04 Desired target ph 75.90 40.18 23.95 6.29 Balance of Effectiveness 3.05 0.67 Corrosiveness Worker safety 0.31 Worker comfort
Postharvest Water Disinfection Monitor, Control, Document UC Davis Western Precooling CA DHS / FDB Pulse Instruments Primuslabs.com Boskovich, Capuro,, Cal-West Cooling Mann Packing
Effect of ph on ORP (mv) ORP of 3 ppm NaOCl from ph 6-9 800 ORP (mv) 700 600 8.0 7.5 7.0 6.5 6.0 ph ORP o T Disc Dataport IRMA 500 400 9.0 8.5 0 1 2 3 [HOCl] (ppm) 250A Quikchek 250A - Pulse Instruments ORP probe Quikchek - Orion Instruments Pocket Probe
ORP Strong Oxidizers pull electrons away from platinum probe creating a small voltage differential to the reference probe. Platinum Electrode Reference Electrode Embedding matrix
ORP mv 875 850 825 800 775 50 ppm NaOCl ph = 6.5 750 0 20 40 60 80 100 120 140 Time (min)
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
CLOH interactions with bacterial membranes causes ruptures at high doses and disrupts metabolic functions at lower doses. ClOH ClOH ClOH
ORP = 350 mv Pectobacterium = Erwinia ORP = 650 mv
Relative Conidia Survival 1.25 1 0.75 0.5 0.25 0 1.25 1 0.75 0.5 0.25 0 5 10 15 20 25 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 850 0 0 5 10 15 20 25 Time (min)
5.5 5 4.5 Efficacy of HydroVac Reservoir Chlorination in Suppressing Microbial Load Accumulation 4 3.5 3 2.5 2 No Chlorine Chlorine @ ORP 650 First celery load. ORP dropped to 315mV Cooling Cycle
HOCL Needed to Maintain ORP 750 mv 500 12.5 400 10 FAU 300 200 100 Turbidity (FAU) Free Cl 7.5 5 ppm 0 2.5 0 0.25 0.5 0.75 1 1.25 Soil g/l Chualar Loamy Sand
Hyperchlorination May Increase Undesirable Disinfection By-Products Trihalomethanes chloroform, bromodichloromethane Ozone < Chlorine Dioxide < Chlorine S. Richardson, EPA
Maintain a "Window" of ORP Residual 850 4.5 ORP (mv) 750 650 550 450 350 4 3.5 3 CFU/g (log) ORP 350 ORP 650 ORP 750 Load 350 Load 650 Load 750 250 Beginning End 2.5 10 min Batch Wash
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
Variance in ORP Readings with Different Hand-held Meters ORP (mv) 850 800 750 700 650 Orion Pocket OakTon PRC 650 Orion 250A 600 1 3 5 7 9 11 13 15 17 19 21 Sample Sequence
Variance in ORP Readings with Different Hand-Held Meters ORP (mv) 850 800 750 700 650 Orion 250A-1 Orion 250A-2 Orion Pocket 600 1 3 5 7 9 11 13 15 17 19 21 Reading Sequence
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
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
Commercially Available Sanova Stabilized ClO 2 Acidified Sodium Chlorate forms ClO 2 on acid activation Biocide International Oxine Purogene Sanogene
Typical Reported Use Rates of ClO 2 Produce mist (potable water only) 5 ppm Produce wash (clean water rinse) 25-35 ppm Water disinfection (flumes) 25-50 50 ppm Biofilm removal (flumes and lines) 100 ppm Clean out (tanks, trays, bins) Storage (tanks, trays, bins) 100-200* ppm Storage room walls and floors 200-500 ppm* * Requires ClO 2 protective mask
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
http://anrcatalog.ucdavis.edu/ Water Disinfection: A Practical Approach to Calculating Dose Values for Preharvest and Postharvest Applications ANR # 7256