VG99005 Quality wash water

Washing vegetables is an essential part of the postharvest treatment to remove soil adhering to root vegetables and to clean the product ready for sale.

It has been estimated that Australia-wide, the process requires 4.4 million megalitres of water annually.

Wash water reuse has the potential to significantly reduce the demand for water from our rivers and catchments and to alleviate water restrictions in our drier vegetable producing regions.

Saving water has a direct financial benefit to growers in lower water costs and in having the ability to utilise waste water for washing soil off product or for irrigation.

The re-use of waste water has not been widely practiced due to fears that the water could harm the crop by recirculating plant pathogens or because the water may be contaminated with agrochemicals or excessive salts.

This project examined the quality of water used for washing vegetables before and after the washing process and examined treatment methods aimed at improving water quality to a standard suitable for re-use on farm.


Martin Mebalds

Andrew Hamilton

Quality Wash Water for Carrots and Other Vegetables - 2002
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Summary :

  • This project has found that if basic precautions are adopted, waste water from vegetable washing sheds can be re-used, saving many millions of litres of water annually.

  • Very few growers are willing to re-use the water for fear that it may contain plant pathogens, human pathogens such as E. coli or significant residues of agrochemicals.

  • Growers are most concerned about the re-use of waste water used to remove soil from root crops as it is highly coloured and often produces foul odours.

  • Australia-wide surveys of vegetable farm waste-water derived from washing root crops showed that there were very few cases of excessive agrochemical residues but there was a slight increase in levels of plant pathogens, E. coli, nitrates and phosphorus.

  • The water was shown to be unsuitable for discharge into rivers and streams but could be treated economically and effectively on farm for re-use.

  • The most common agrochemical residues were residual pre-emergent herbicides. Consideration should be given to recent herbicide application history and if recent applications were made, then the water should be tested for herbicide residue concentrations.

  • In some instances, excessive linuron levels in waste water had the potential to harm sensitive crops.

  • A set of guidelines were developed to assist growers in designing effective waste water treatment systems to remove excess organic matter, plant and human pathogens and nutrients.

  • Safe re-use of waste water has the benefit of reducing farm costs and the requirement of water from rivers and bores.

  • A system of settling pits and ponds can adequately reduce excessive loads of organic matter provided that the capacity of the system can allow for a sufficient holding time to improve water quality.

  • However, some larger packing houses have insufficient holding capacity in their settling ponds to cope with the volumes of water used by the washing system.

  • The end result is thus little improvement of water quality after settlement pond treatment. Improvements in waste water treatment such as aeration and constructed wetland treatment may overcome the short-comings of existing water treatment methods for the removal of organic matter and nutrients.

  • If waste water is to be re-used to wash harvested crops, it should be disinfested considering it is highly likely to have elevated levels of human pathogens.

  • The waste water is highly coloured and so is unsuitable for disinfestation by UV light, however, micro-organisms in the water may be best controlled using chlorine dioxide, which works more effectively than other forms of chlorine treatments in water with high levels of organic matter.

Recommendations :

  • The project examined a range of existing water treatment strategies, as it was considered that an evaluation of the existing facilities has not been previously assessed.

  • Once treatment strategies have been examined and analysed, recommendations could be made to improve water treatment processes within the vegetable industry.

  • This approach has the best chance of adoption, as modifications of existing technologies are less expensive than installing new facilities.

  • The pond systems were shown to reduce organic matter content if they were not overloaded with large volumes of wash water, reducing hydraulic retention time.

  • The systems have a capability to reduce agrochemical concentrations in water however, in practice, there was little beneficial effect in existing systems when overloaded.

  • Further work needs to be undertaken in studying alternative and complimentary water treatment systems that may overcome current system inadequacies.

  • In particular, extra aeration of water in settling ponds, and the addition of subsurface or surface horizontal constructed wetlands similar to those developed by Headley et al. (2001), have the potential to further reduce nitrates, phosphates, agrochemical concentrations and coliform bacteria levels with minimal additional cost.

  • Further work on irrigation of crops with waste water over a period of years would help resolve the issue of cumulative effect of introduction of a range of pathogens at low concentration and plant disease development.

Acknowledgments :

This project was commissioned by Horticulture Australia Limited with funds frrom the Vegetable R&D levy and the Victorian State Government..

The Australian Government provides matched funding for all HAL’s R&D activities.

Many growers supported the project but in particular we are indebted to Mr Rocky Lamatina who provided advice and support for the project in the development stage.

We acknowledge the support of Dr Elaine Davison for the provision of Pythium cultures and the identification of isolates from waste water.

Dr Davison and Dr Alan McKay also helped collecting water samples, arranged a grower’s seminar in Perth and showed us carrot farms in the region.

We thank Fawzia Tawfik and Maresa Connell of the State Chemistry Laboratories, Werribee for her work on agrochemical detection in all water samples.

We acknowledge the work done by our collaborators in this national project. Their work was a key to the projects success.

The Industry Development Officers in each state contributed to the project, in particular Patrick Ulloa (Victoria) who helped with grower meetings and our technology transfer plan.

NSW Vegetable IDO Dr Alison Anderson assisted in planning the grower workshop in Cowra and provided transport from Sydney.

Craig Feutrill SA Vegetable IDO organised the Virginia grower workshop.

Judy Skilton, Executive Officer, Bundaberg Fruit & Vegetable Growers helped with the Bundaberg workshop.

SallyAnn Henderson provided transport and drove us to carrot growers along the Murray River from Swan Hill to Mildura.

Dr Alison Anderson, NSW vegetable IDO and Joe Napoli of the Lachlan Valley Horticultural Network helped to organised the Cowra workshop and Samantha Hertiage and Julia Telford vegetable JDOs for Queensland help organise the Bundaburg workshop.

The grower workshops were held in conjunction with a Mr Paul Harrup and Dr Robert Holmes who presented finding of their work on Clean and Safe Handling Systems for Vegetables and consequently, we shared the work load associated with the technology transfer package.

This project was largely dependant on the good will of the participating vegetable growers for access to farms and samples of their source and waste waters and to those that allowed detailed analysis of the performance of their waste water treatment systems.

We thank all participating growers, their participation was vital for the advancement of the industry through research and especially for the development of methods for the conservation of water within the vegetable industry.

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