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Introduction

Client A one of the largest wholesale suppliers of hardy perennial plant stock in the United Kingdom. Annually, they supply two million plants to their customers, over fifteen hundred varieties. These include garden designers, local authorities, garden centres, landscapers and other wholesale nurseries.

For nearly 30 years, the client used borehole water to feed their existing irrigation system. Initially this system was sufficient to their needs due to them being a small acre site of around 4 acres to begin with. Over time they expanded to over 150 acres.
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The Challenge

Their borehole water presented several problems for them from the off. Firstly, it was naturally very cold with iron deposits. This shocked plant roots and stunted plant growth. Further problems become more apparent over time and the quality of their water declined over the years. They were faced with a number of issues before 4i Water Services Ltd. offered their services. As you can see below, it was essentially a 'snowball effect' with one issue leading to the other. 

• Salinity - the salts in the water reduced water availability to the pots affecting the water infiltration rate. 
• Water infiltration rate - sufficient water could not be infiltrated to supply the plant stock adequately from one irrigation to the next which meant continuous watering was needed. 
• Continuous watering to achieve infiltration due to salinity then lead to - crusting of peat, excessive weeds, nutritional disorders and drowning of the plant stock, rotting of seeds and poor crops. One serious side effect of the infiltration problem was the potential to develop disease. 
• Due to continuous watering this then lead to toxicity - chloride and sodium primary ions were taken up by the plant through the leaves and to high enough concentration levels leading to damage, this became more rapid during hot parts of the year. 
• Corrosion - poor quality water also damaged irrigation equipment. 
• Sedimentation - caused problems in irrigation systems through the clogging of pumps and sprinkler heads. 

The bore hole water was also riddled with biofilm. This flourishes in horticultural operations; in particular within irrigation systems and pipe work. It is often completely unbeknownst to the operator until it is too late and you suffer irreparable crop damage or loss as a result of incorrect biocide management. Biofilm will sustain harmful plant disease organisms, including waterborne plant pathogens; pythium, mildews, phytophthora etc. 
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â €Testimonial

"4i was able to offer a solution to a clients existing irrigation problem as well as introduce a water treatment system into a horticultural environment due to it being an excellent suppressor of harmful plant pathogens." Container Manager

Furthermore, the client was also not aware that by using liquid fertilizer through their irrigation system that they were in fact sustaining and/or enhancing the growth of biofilm and therefore also the potential for harmful plant pathogen growth. 

These issues and repeated plant stock failures as a result, led to a review of their current irrigation system and Client A acquired the services of 4i Water Services Ltd to provide a solution. 

During the hot summer of 2006, the above issues manifested beyond Client A's expectations. Following advice from 4i Water Services Ltd. to their ever increasing demands for water and to improve the quality of their plants, they invested in the construction of a two million cm³ reservoir. 

Considerations 
• The client could not have any down time with their water supply due to the ever increasing demand of their plant stock, particularly during the summer period. 
• Due to the reservoir water being aerated through the clients current irrigation system in glasshouse, polytunnels and in the presence of employees, it required treatment. 
• The water that was being treated and supplied could not have any negative effects on the quality of their plant stock. 
• Solution had to be safe, robust and easily monitored. 

The supplied package had to be cost effective as budgets were strained. 
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The Solution

Create a long term strategy and engineering solution that is not only effective and compliant.

4i Water Services considered various water treatment methodologies with regard to the water being stored in the reservoir and aerated through the irrigation systems. 

• UV is an excellent method of disinfection but requires pre-filtration and has no residue. This was cost-prohibitive. 
• Ozonolysis, an excellent method of disinfection, ozonolysis is a very effective disinfecting agent in very dirty situations with a residual for direct real time measurement. However, it is also quite expensive to run the electrical generation plant and the aggressive oxidising nature of ozone was expected to drastically 
shorten the life of the system. 
• Chlorine dioxide. When produced in sufficiently high purity, chlorine dioxide is an online biocide, meaning that it can be dosed directly into all water, including drinking. It also has a noticeably less corrosive effect than ozone. Any potential chlorine dioxide unit must be able to ensure that the total chlorine dioxide, chlorites and chlorates produced as byproducts of its generation remain below 0.5 mg/L. 

The final approach were deemed as the most appropriate. 4i Water Services Ltd would use the Februus Agri-Sentinel Chlorine Dioxide Unit, specifically designed to cope with the high flow rates and water usage that our clients site demanded. Alongside this it would provide suppression of harmful waterborne plant pathogens present in biofilm. 

The Februus Agri-SentineI system has engineered out issues that required water treatment and the suppression of harmful plant pathogens in the past. 

• Remotely monitored and operated, this means that onsite and offsite personnel can be alerted to problems or check the operation of the unit through a smartphone app
• Highly accurate water meter 99.998%, this means that rather than dosing 50 mg/100L like a K100 mechanical water meter, it doses 0.5 mg/L avoiding the issues of "slugs" of treated and untreated water
• High purity dosing of chlorine dioxide, this means that the chemical is used efficiently and the customer is not paying for waste
• BMS Link-up option to manage other plant through our PLC Operating System, this can be used as another safety measure, or as a control, putting control into the site manager's hands
• DWI-Approved method of continuous disinfection of drinking water which means statutory compliance
• BS 8558:2011 Approved method of continuous disinfection which means compliance with the approved code of conduct 
• Water authority approved installations which means compliance with the Water Supply Regulations (1999)

Monitoring the Solution 
Along with the dosing system a monitoring regime was put in place to ensure efficacy as detailed below. 

This process was agreed by the client director and 4i Water Services. 
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The Results

Due to the efficacy of the Februus Agri-SentineI Chlorine Dioxide Unit dosing system, the client no longer suffers from plant stock loss through disease and poor quality borehole water on a massive scale. This has resulted in an average saving of between £45,000-65,000 depending on plant variety and stock levels per annum. 

Furthermore, due to chlorine dioxide not reacting with water, it only penetrates bio film and harmful micro organisms that are present. It is non-toxic to any plant varieties the client wishes to now grow. This has allowed the client to expand it's catalogue to varieties that it would not normally have attempted to propagate in the past. 

The client also no longer needs to 'blanket spray' it's plant stock for harmful plant pathogens such as Pythophthora, Pythium and various mildews as a direct result of the dosing system. Client A now only 'spot sprays' specific varieties that suffer from disease that Chlorine Dioxide cannot suppress e.g. Red Spider Mite. This has resulted in an average saving of between £4,000-7,000 per annum on spray chemicals. 

Additionally, as it does not lose it's efficacy over time, the client can irrigate all year round at both evening and during the day if required. 

The Februus Agri-SentineI Chlorine Dioxide Unit dosing system has proven to be a reliable, robust, cost effective chlorine dioxide system. The unit is frequently incorporated into site visits as a 'showpiece' for Client A's customers and offered as a solution to any issues that they also could possibly be having 
with water treatment. 

Chlorine Dioxide
These samples were carried out by both 4i Water Services and the site maintenance staff. Over 500 chlorine dioxide samples were taken. The vast majority of samples fell into the 0.1-0.5 ppm range. This means that 
zero overdosing took place and under dosing took place on 0% of samples in 24 months, achieving a correct dosing rate 100% of the time. 

Legionella
150 random legionella samples were taken according to the latest standards in microbiological sampling and sent to a UKAS accredited laboratory for culturing and analysis over a two year period. Not one sample showed the detection of legionella spp. in the system. 
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Conclusion

The system has been in place for twelve years. Due to it's effectiveness, alongside profitable years as a direct result of the System, the Client has added a second reservoir of four million m³ in size that the system also provides water treatment for. 

"We have found a robust and cost effective engineering solution to water treatment and the suppression of harmful plant pathogens in the past. In turn this has delivered year on year savings, increased yield and ensured that our Client has consistantly delivered the very best product colminating in winning Gold at the Royal Chelsea Show". 

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