Washwater sampling from carrot operations showed it may be a good source of potassium, and under study the risk of transferring plant diseases

Ontario vegetable growers with post-harvest washwaters are looking for answers to water quality needed before discharging, and what will it all cost? Water authorities may not provide adequate advice for solutions for washwater discharge compliance from Ontario root crop producers. If settling ponds are suggested, many of the current carrot facilities are constrained for space to build them. That?s why Deanna Nemeth, OMAF and MRA?s nutrient management lead for horticulture, is evaluating how land application of washwaters could be an alternative option. Nemeth released results of studies from three carrot operations in the Holland Marsh at the 62nd Muck Vegetable Growers? Conference in Bradford, Ontario. The toplines offer some insight. During harvest 2012, OMAF and MRA completed a wastewater characterization study. For each of the carrot operations, washwater was sampled twice during harvest season and standard washwater characteristics were analyzed for water quality (total suspended solids, biological oxygen demand), pathogens (E. coli, coliform, salmonella), nutrients (nitrogen, phosphorous, potassium), and heavy metals. ?This is high-volume, low-nutrient water,? says Nemeth, but it?s not irrigation water per se.? Results from the washwater sampling from carrot operations showed the washwater may be a good source of potassium with levels ranging from 1.4 lbs K2O per 1000 imperial gallons in carrot root washing water, to levels of potassium at 9.5 lbs K2O per 1000 imperial gallons washwater from carrot processing operations. A second washwater study is in progress in the Holland Marsh conducted by the Univeristy of Guelph Muck Crops Research Station. Due to the physical characteristics of carrots, washwater has high soil sediments. This project is to determine if land application of wash water and washed off soil poses a risk of transferring plant diseases: Sclerotinia sclerotiorum, Sclerotinia cepivorum and pathogenic fusarium. They are testing survival of sclerotia in the ponds over time. The environmental issue becomes what are the best management practices for disposing of the water. Measurements are now being taken to see if discharging that washwater may impact the water quality of the receiving river or stream. In the future, it may need to be treated before release, or land applied to other crops as a nutrient source. Several observations are clouding the issue. Production and therefore washwater quality is not consistent. For example, a limited amount of soil is on cauliflower and broccoli whereas root pieces readily come off root vegetables such as carrots and parsnips. That means washwater quality can change dramatically depending on the crop. Also, the volume of water can change depending on the crop being washed. ?The challenge for growers is to know what washwater treatment or land application options fit their operations best,? says Nemeth. The best option is to reduce the amount of soil on the carrots when they come out of the field by dry brushing or mud removal before the carrots are washed. After the carrots are washed, washwater treatment options to separate solids from the washwater are settling basins, aerobic ponds, or mechanical screens to separate sediment from the water. Land application options are spreading or irrigating onto crops, keeping in mind food safety and water quality requirements if overhead irrigating onto fresh market horticulture crops (examples such as lettuce, spinach, celery or herbs). Nemeth said more work is required to understand operational characteristics. She emphasized that solutions need to have minimal operator input. ?Water treatment is not your main business,? she said, ?Solutions need to be as simple as possible.? Original title and sources:Vading through washwater options for root vegetablesThe Grower, May 2013Photo by Glenn Lowson ? ? ? ? ? ? ? ?