Managing Minor Phosphorus Leaks in Greenhouses


Factsheet - ISSN 1198-712X   -   Copyright Queen's Printer for Ontario
Agdex#: 731/215
Publication Date: August 2017
Order#: 17-021
Last Reviewed:
History:
Written by: V. Hilborn, P.Eng.

Table of Contents

  1. Introduction
  2. Sources of Nutrient-Rich Water Leaks
  3. Reducing Minor Phosphorus Losses from a Greenhouse
  4. Compliance with Environmental Regulations
  5. Obtaining the Right Environmental Approvals
  6. Summary

Introduction

This factsheet provides information on how to reduce minor phosphorus leaks in greenhouses by preventing nutrient-rich water from entering a stormwater-management pond. Reducing phosphorus leaks within a greenhouse is critical for reducing fertilizer costs, minimizing environmental impact and ensuring regulatory compliance.

Phosphorus is an essential macronutrient for healthy plant growth that contributes to root and fruit development. Many greenhouse operations feed nutrient-rich water, containing phosphorus, directly to the plants through drip irrigation (Figure 1). Approximately 25%-30% of the water fed to the plants is unused and collected by trough systems (Figure 2). In most cases, this nutrient-rich water is treated and recycled back to the plants.

This photo is taken inside a vegetable greenhouse and shows a close-up view of long white troughs that have a vegetable crop growing in them. The troughs are suspended above the floor. White tubes go to each trough to feed nutrient-rich water directly to the plants through drip irrigation.

Figure 1. A vegetable greenhouse crop grown in a suspended trough.

This is a photo taken inside a flower greenhouse showing a close-up view of a long grey metal trough that has flowers growing from it. Water is flowing directly into the trough from an elevated opening. Below the grey trough, a second tan trough collects water dripping from the metal trough. Both troughs are suspended above the floor.

Figure 2. A greenhouse flower crop grown in a trough.

For greenhouse operations collecting this nutrient-rich water, small leaks from the trough systems may result in phosphorus making its way to surface water through leaching to buried drainage tiles or stormwater lines. Excessive phosphorus in lakes and rivers can result in algae blooms, which can foul beaches, impact fish populations and, in certain circumstances, release toxic substances into potential drinking water sources.

Given the environmental concerns and cost of fertilizer, greenhouses would benefit by limiting the loss of nutrient-rich water from their operations. For recommendations on water and fertilizer use, greenhouse operators can access the OMAFRA publication, Self-Assessment and Best Management Practices for Water and Fertilizer Use in Greenhouse Vegetable Production, at ontario.ca/omafra.

Sources of Nutrient-Rich Water Leaks

Small leaks of nutrient-rich water can occur in a number of places within a greenhouse:

  • collection troughs that are bowed or unbalanced (Figure 3)
  • leaking or disconnected troughs
  • leaking irrigation lines, especially at the drippers

The nutrient-rich water leaking from the troughs or connections will collect on the floor of the greenhouse and may enter the drainage tiles or stormwater lines that lie buried below. As a result, there is the potential for nutrient-rich water to enter a stormwater-management pond.

Reducing Minor Phosphorus Losses from a Greenhouse

It is important for everyone working in the greenhouse to understand how small nutrient-rich water leaks can become a significant problem. Finding and fixing these small leaks is important and should be a team effort by everyone working in the greenhouse.

Immediate solutions for existing greenhouses include:

  • train staff to look for and report leaks
  • schedule regular weekly inspections of trough ends and connections for damage or leaks, and repair or replace as necessary
  • add a "task" to existing labour management systems to ensure staff are checking rows for any trough leaks (at the ends and along the sides) and report leaks to maintenance staff
  • ensure troughs are properly cleaned at the end of each crop to reduce the build-up of lime or other sediments
  • replace troughs if worn out, damaged or leaking
  • ensure tight connections/seals when installing troughs (Figure 4)
  • regularly replace sheets of plastic on the floor to prevent leaks of nutrient-rich water from entering the ground

This photo is taken in a vegetable greenhouse showing two long white troughs suspended from the ground supporting vegetable plants. Under the troughs there is a black plastic material that appears stained by leaks from the troughs above it.

Figure 3. This collection trough is bowed or unbalanced, resulting in water spilling onto the floor.

Long-term solutions for new or renovated greenhouses include:

  • Not installing stormwater lines under the growing floor (critical). For renovated greenhouses, move stormwater mains and drainage tiles outside the greenhouse and away from the growing floor.
  • Installing an impervious layer on top of the soil under the troughs and collect all leaked nutrient-rich water. Transfer the collected nutrient-rich water to a central basin, where it is filtered, treated and returned to circulation. Inspect this layer annually and repair or replace when needed.

This is a photo taken near the floor of a greenhouse that shows two white tubes exiting the bottom of a growing trough and entering the floor of the greenhouse. The greenhouse floor is covered with a white tarp-like material. There is no appearance of staining on the tarp, which indicates the connection in the tubes are tight and do not allow leaks of nutrient-rich water.

Figure 4. A drain line from a trough with a secure connection.

Compliance with Environmental Regulations

Greenhouses usually generate three types of wastewater (which may be categorized as sewage), depending on the circumstances at the greenhouse:

  • process wastewater (e.g., spent nutrient-rich water, produce washwater)
  • stormwater (e.g., water collected from the roof and paved areas on the site)
  • sanitary sewage (e.g., human waste)

Acceptable options for managing process water and/or stormwater include:

  • reuse of process or stormwater internally without discharge
  • application on land as a nutrient under the Greenhouse Nutrient Feedwater (GNF) Regulation
  • application on land for purposes of disposal under an Environmental Compliance Approval (ECA)
  • treatment on-site and discharge to the natural environment under an ECA
  • disposal off-site by a Ministry of the Environment and Climate Change (MOECC)-approved waste hauler
  • discharge to a municipal sanitary sewer
  • discharge to an approved sub-surface sewage treatment system (e.g., septic system)
  • separate process and stormwater and apply for a stormwater ECA

The management of sanitary sewage is beyond the scope of this factsheet.

Obtaining the Right Environmental Approvals

Many of the management options listed require approvals from the MOECC, OMAFRA or other agencies. Secure any required approvals for both process water and stormwater prior to discharge or land application.

An ECA must be obtained from the MOECC before using, operating, establishing, altering, extending or replacing new or existing sewage works discharging to the natural environment or when land applying for the purpose of disposal. The Ontario Water Resources Act, 1990, defines "sewage works" as any works for the collection, transmission, treatment and disposal of sewage or any part of such works. A sewage works does not include plumbing to which the Building Code Act, 1992, applies, including septic systems with a design flow rate less than 10,000 m3/day (approved by the local municipality).

To obtain a stormwater ECA, separate the stormwater and process water (including nutrient-rich water) streams. It is important to keep the clean water (e.g., rainwater) separated from the nutrient-rich water. Discharging process water and/or storm water into the natural environment (even after treatment) without the appropriate approvals is a violation of the Ontario Water Resources Act, 1990.

For more information on the requirements for ECAs for greenhouse stormwater and/or process water, contact the local MOECC district office.

Land application of greenhouse nutrient feedwater (GNF) under the Nutrient Management Act, 2002 (NMA), is an alternate use of spent nutrient-rich water, which has been removed from a closed circulation system. This approach allows the nutrients to be used by field crops under the right conditions. To better understand the requirements for land applying GNF under the NMA, contact a nutrient management consultant or review the information on the OMAFRA website.

Summary

Reducing minor phosphorus leaks is possible with staff training, regular inspections, well-maintained equipment with tight connections/seals and impervious plastic protecting the greenhouse floor. Finding and fixing any existing leaks of nutrient-rich water will decrease fertilizer costs and avoid phosphorus making its way to surface water through leaching into buried drainage tiles or stormwater lines.

It is critical to obtain all necessary approvals before discharging or land-applying process water and/or stormwater.

To learn more about different options for minimizing small leaks within a greenhouse, contact your sector's association.

This factsheet was written by Vicki Hilborn, P.Eng., Engineering Specialist, Civil Systems, OMAFRA, London, and reviewed by Shalin Khosla, Greenhouse Vegetable Specialist, OMAFRA, Harrow; Chevonne Carlow, Greenhouse Floriculture Specialist, OMAFRA, Vineland; Trevor Robak, Environmental Specialist, OMAFRA, London; Nathan Scaiff, Divisional Program Specialist, MOECC, London; and Dr. Justine Taylor, Science & Government Relations Manager, Ontario Greenhouse Vegetable Growers Association, Leamington, Ontario.


For more information:
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E-mail: ag.info.omafra@ontario.ca