Greenhouse Canada

Features Structures & Equipment Water and irrigation
Looking to the land

August 26, 2013  By Chris Attema & Colin Ashbee

It has been a winding and sometimes tortuous path but with recent
progress there is reason for optimism as things appear to be heading in
the right direction.

It has been a winding and sometimes tortuous path but with recent progress there is reason for optimism as things appear to be heading in the right direction.

One of their recent projects in Ontario.



In January 2011, the Ontario Ministry of Environment (MOE) released a factsheet entitled “Greenhouses and Sewage.” Greenhouse-source sanitary sewage, storm water and process water were all classified as “sewage” requiring an Environmental Compliance Approval (ECA).  

While an Environmental Compliance Approval (ECA) process may fit with some greenhouse operations, in most cases the initial cost, ongoing operational cost and uncertainty of outcome due to the site-specific study requirement make it an unattractive choice. 

Depending on the size of operation, the initial engineering fees for an Environmental Compliance Approval (ECA) have been reported to be as high as $20,000 to $100,000. Application fees to the Ministry of Environment (MOE) can reach $5,000 or more. 

Ongoing operational costs have not been reported or estimated, but it is likely that most Environmental Compliance Approvals (ECA) would be linked to rigorous ongoing monitoring and reporting responsibilities. Of equal significance, with an Environmental Compliance Approval (ECA) approach, the Ministry of Environment (MOE) is using an industrial regulatory instrument to regulate agriculture. 

For several reasons it is important for the greenhouse sector to be classified and regulated as an agricultural rather than an industrial activity.


■ Over the past several months, the MOE has worked collaboratively with individual greenhouses, the Ontario Ministry of Agriculture and Food and others in order to examine alternatives to the current regulatory framework.

Individual greenhouse operations facing Ministry of Environment “Provincial Officer Orders” and the greenhouse growers’ associations have requested more flexibility and regulatory options other than an Environmental Compliance Approval (ECA) process.

While there has been positive progress since January 2011, one fundamental Ministry of Environment (MOE) principle remains unchanged. Currently, the regulatory compliance flexibility and options are available only to those greenhouse operations that completely separate storm water from process water and sanitary sewage. 

We will take a look at each of the greenhouse “sewage” categories and review the current status of each.

Sanitary sewage: No changes to the sanitary sewage policy are expected. In situations with less than 10,000 litres per day of sanitary sewage flow, the greenhouse facility will require a sewage system meeting the Ontario Building Code approval with a permit issued by the local municipality. In situations with a flow of greater than 10,000 litres per day, the greenhouse operation will require a sanitary sewage ECA issued by the Ministry of Environment.

Storm water: Not all of the details have been finalized, but our most recent information is that the MOE is considering interim guidelines for agricultural (greenhouse) storm water management.  The expectation is that under certain conditions, greenhouse operations will be permitted to discharge storm water from the greenhouse property without an ECA. 

Conditions of operation are expected to include a storm water self-assessment profile, periodic monitoring during discharge periods and meeting certain storm water discharge water quality standards. Our expectation is that most greenhouse operations that separate storm water from process water will be able to meet the proposed Ministry of Environment Interim Compliance Strategy standards for storm water.

Process water: Managing surplus nutrient water, including hydroponic recirculation water, will continue to be the most complex challenge for greenhouse producers. The term “greenhouse-source nutrient feedwater” is used to describe the surplus nutrient from greenhouse operations. (What is nutrient feedwater? The unusable greenhouse-generated feedwater from plant growing media [no longer needed in the greenhouse] is termed “nutrient feedwater.”)

The Discussion Paper on a Proposal for Land Application of Nutrient Feedwater in Ontario (February 2013) summarizes the current and proposed approaches for managing greenhouse discharge material.

The current requirements include discharge to septic or sanitary sewers. With a completed ECA land application or treatment with subsequent direct discharge to surface water may also be considered. The new opportunity (proposed) is the potential to land apply under the Nutrient Management Act rather than an ECA framework.


■ We have developed, obtained Ministry of Environment approval, and implemented a crop land spray irrigation system based on the Nutrient Management Act principles for a leading greenhouse operation in Ontario. At St. David’s Hydroponics, the spray irrigation concept has been in operation since 2011. The stormwater management and nutrient feedwater crop land application standards planned for 2013 growing season meet the most recent MOE and Ontario Ministry of Agriculture and Food requirements.

We can summarize the key features.

The hydroponic crop nutrients are recirculated inside the greenhouse as frequently as possible. However, due to a buildup of salts and other limiting factors, some surplus nutrient feedwater is generated at this location. 

The surplus nutrient feedwater collected throughout the year is separated and stored in a clay lined earthen pond with over 5,000 m3 storage capacity. The surplus nutrient feedwater is kept completely separate from the stormwater collection ponds.

The nutrient feedwater is applied to a growing soybean crop during the June 1 to September period.

Prior to land application, the nutrient feedwater is analyzed for beneficial nutrients, electrical conductivity (EC), boron and molybdenum. The receiving cropland soil is also analyzed.

The application rate is based on the principle of a beneficial use of nutrients, while not exceeding electrical conductivity (EC), boron or molybdenum levels that could be harmful to the soil or the growing crop. 

The current approved land application rate at this location is two separate irrigation applications of 150 m3/ha (each application .665 inches). In this initial stage we are being very conservative with our land application rates. It works out to be approximately one acre of “greenhouse” to one acre of “outdoor cropland,” with plenty of room to spare. 

If we pushed the application rate and nutrient application to the regulatory maximums currently permitted under the Nutrient Management legislation, we could apply the surplus nutrient feedwater from up to 7.5 acres of “greenhouse” to one acre of “cropland” at this location.

Proper precautions are followed during the land application period in order to ensure that the land-applied material actually benefits the receiving crop and does not run off into surface water. The “best management practices” include setbacks from surface water and wells, attention to soil moisture conditions and the weather forecast at the time of application, and monitoring or shut-off of the crop land tile drain outlets.

The operating cost for the spray irrigation is less than one cent per gallon of nutrient feedwater applied.

Nutrient feedwater analysis expense is limited to one sample for every 1,000 m3 of applied material.

There is no application fee for obtaining a Nutrient Management Act/MOE approval under the Interim Guideline process.

At this facility, greenhouse roof stormwater is used as the main water supply. Since there is seasonal discharge of stormwater, the MOE has requested quarterly sampling (once every three months) during periods of stormwater discharge. The facility currently meets the MOE greenhouse stormwater “Interim Compliance Strategy” standards.

This greenhouse operation has a septic system designed for up to a 20,000 litres/day design flow. There is an existing ECA from the MOE for the sewage works.


■ There is no “one-size-fits-all” water management approach that will be the best solution for all greenhouse producers. There is a great deal of variety in the way Ontario greenhouse operations collect and manage stormwater, apply nutrient and manage surplus nutrient feedwater. 

Each situation is unique, including the type of crop grown, the quality of the greenhouse source water, the type of collection, filtering and recirculation technology, and proximity to outdoor cropland being used.

However, regardless of the individual greenhouse operation situation, a few general conditions or circumstances emerge.

  • Separation of process (nutrient feedwater) from stormwater and sanitary sewage will increase the regulatory compliance options available to greenhouse producers.
  • Most greenhouse producers would prefer to maximize water and fertilize efficiency through recycling as much of the nutrient feedwater utilized in the greenhouse as possible. 

While emerging technologies hold promise in achieving the goal of 100 per cent recirculation, the current reality is that many greenhouse operations do generate some surplus nutrient feedwater due to buildup of salts and other recycling nutrient feedwater use limiters.

  • Nutrient feedwater that is left over may no longer have the proper nutrients for greenhouse growth, but there are still valuable nutrients that can be beneficial for crops grown outdoors on agricultural lands.
  • Greenhouse source nutrient feedwater contains a nutrient content that is much too high for discharge to surface water or stormwater. 

For example, typical nutrient feedwater could contain as much as 30 times the nitrate and up to 3,000 times the phosphorus concentration compared to the Provincial Surface Water Quality Objectives.

  • Many greenhouse operations may not own additional agricultural land where crops are grown outdoors. 

The proposed Nutrient Management Act standards allow the transfer of surplus nutrients from greenhouse operations to cropland receivers. 

Three types of sewage
Greenhouses commonly generate three types of sewage: stormwater, sanitary sewage and process wastewater.

Stormwater: rainfall, snowmelt, and roof and surface runoff.

Sanitary sewage: wastewater generated from showers, toilets and kitchens located on the greenhouse operation site.

Process wastewater: water with added nutrients; water that has been used for irrigation and washing of crops; recycled water; and water transported through floor drains located within the greenhouse operation, including water that mixes with stormwater.

Under the act, sewage works is defined as any works for the collection, transmission, treatment and disposal of sewage or any part of such works. Since stormwater is defined as sewage in the OWRA, stormwater management facilities are also sewage works under this definition.

Source:  Ministry of Environment (MOE), January 2011.
To see more information go to:


■ With this background and context, and in consideration of other current alternatives, separation and discharge of stormwater and spray irrigation of surplus greenhouse source nutrient feedwater to outdoor crop land based on Nutrient Management Act approval criteria may be a feasible and cost-effective solution for other Ontario greenhouse producers.

■ Chris Attema is a nutrient management consultant. For the past 12 years, he has worked extensively with livestock agriculture commodity organizations and has helped individual livestock producers manage the transition to compliance with Nutrient Management Act and Ministry of Environment regulatory standards.
Colin Ashbee is a greenhouse consultant as well as the Canadian technical sales manager for BioWorks Inc.
Visit their website at for additional details.

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