Problem:

High levels of Iron and magnesium are found in the borehole water supply.  These levels need to be reduced to ensure ideal water quality.  Secondly, high levels of bacteria counts are also present in the pack house process.  One of the post harvest factors that influences decay is proper sanitation in the packing stage.  It is important to maintain sanitary conditions in all areas where produce is packed.  Organic matter (culls, extraneous plant parts and soil) can act as substrates for decay-causing pathogens.  Chlorine readily kills microorganisms suspended in dump tanks and flumes if the amount of available chlorine is adequate. Organic matter in the water inactivates chlorine, and levels of chlorine must be constantly monitored.

Solution:

Plant and packing material washing

At a post harvest washing facility, the first step is ensuring proper free chlorine levels are maintained in the incoming water stream with HTH® Chips (calcium hypochlorite).  During this phase of the operation the free chlorine level on the incoming water is controlled via the HTH® Controller.  The controller sends a signal to an automatic valve on the PULSAR® 3 unit, which activates the water flow.  The HTH® Chips are dissolved and the chlorine solution is sucked via a venturi into the water stream.  When the control limit on the free chlorine is reached the automatic valve is closed and chlorine dosage suspended until the free chlorine readings drop below the set point. The HTH® Controller also regulates the pH level of the incoming water.  Iron and Magnesium is sensitive to pH as it precipitates out of solution when the pH level exceeds 7.2, thus reducing the Iron and Magnesium to acceptable levels.

Pulsar 3 on the recirculating line           

HTH® Controller, regulating the dosage of the incoming water

Pre – refrigeration treatment

The vegetables get transported in ambient conditions from the farms to the pack house.  Since temperature increases decay rate, the vegetables are water cooled before refrigeration.  The addition of chlorine to the water at this stage kills bacterial growth and retards decay.  The pH and chlorine levels need to be maintained to ensure that adequate chlorination takes place.  A recirculating line was installed on the hydro cooling bath and the venturi for the Pulsar 1 was fitted to this line.  On the sprayer line a sample of water is routed to the HTH® Controller.  The HTH® controller measures and controls the free chlorine and pH levels to the required levels.  The free chlorine level is being maintained at 5ppm with a pH level of 7.

Pulsar 1 on Hydro cooler                                               

HTH® Controller, by night

Washing bath chlorination and pH control

Controlling adequate chlorine levels while at the same time maintaining pH levels between 6.8 and 7.2 in the washing bath proved to be a challenge, due to the fact that the volume in the bath is around 1000 liters and any dosing by hand proved inaccurate.  A recirculating line was installed on the bath, and the Venturi for the PULSAR 3 was fitted to this line. 

A HTH® controller was installed to monitor the bath.  The dosing of the HTH® Chips is regulated via the HTH® controller which controls an automatic valve feeding the Pulsar 1.  The HTH® controller also activates a small acid dosing pump based on a pH set point entered into the controller. 

Recirculating system with the Pulsar 1 on the air rated bath

Acid dosing point and venture on the assembly

Benefits

The benefits in controlling the free chlorine and pH levels proved to be the following:

• Significant reduction of bacterial counts on produce (40% improvement to 70% in spec, 70% of the time compares to 50% in spec, 50% of the time)
• Longer shelf life of fresh packed produce ( 3 days)
• Safer and less handling of chemicals (hoppers are filled once in two weeks)
• Improved efficiencies due to correct washing water standard at all times
• Higher productivity
• Reduced chemical and water costs