Practical solutions for water reuse

Introduction

Increased emphasis on resource use and preventing pollution, together with the potential for climate change to make water an increasingly scarce (or even costly) resource, means that growers are looking to maximize water use efficiency. In controlled environments, such as greenhouses and indoor farms, one option is to treat, clean and re-use drain water for crop irrigation and fertigation.

While the idea is not new, challenges remain about the potential for the build-up of disease, nutrients and crop protection pesticides. Priva offers solutions to enable water reuse and recycling to be carried out effectively and efficiently.

Kathryn Smethurst, Business Development Manager at Priva continues: “There has been movement in recent years from government authorities to tighten up the use of natural resources and where we get our water from, and the next logical step would be further legislation in this area. Many growers are seeing these signals and the interest in investment for this technology is growing rapidly. There is also pressure on the industry to show green credentials and sustainable responsibility to the supply chain and ultimately the consumer.”

Savings on fertilizers

She also points out that as well as the ‘push’ factors, there are also benefits for growers when it comes to recycling water: “The good news is that there is also a financial case for reduction in water and fertilizer use by using recirculation technology, particularly in these times where fertilizer can be hard to get hold of and increasingly expensive.”

“You always need fresh water from your primary supply. Drain water is only about 30% of the water you give your crop, so roughly 70% still comes from a fresh source. That fresh water also tops up the fertilizers your crop has taken out,” points out Kathryn. “Recirculation technology can be used on any growing system but the more water that has to be treated then the bigger that system needs to be. The main options include thermal disinfection, ultra-filtration, ozone and UV disinfection and there are pros and cons for each technology.”

Approved by Wageningen University

Priva has developed products using UV disinfection which has a relatively inexpensive operational expenditure, no harmful pesticides or toxic by-products, and a highly controlled process with multiple safeguards and feedback to the customer. “The products have been independently tested with Wageningen university and Priva can advise on the level of dose required for each crop,” adds Kathryn.

Industrial climate control equipment installed in a technical room with piping, control units and pumps.

How does UV disinfection work?

The Priva system collects the drain water, which is filtered and then stored in the ‘dirty’ drain water basin. As a precautionary measure, the drain water is then disinfected by the Priva Vialux M-line. UV disinfection systems, which can remove moulds, bacteria and nematodes, and make viruses inactive – including specific viruses such as the Tomato Brown Rugose Fruit Virus (ToBRFV). “This allows continuous recirculation of irrigation water in a safe way,” says Kathryn. “As a result, expensive fertilizers are not flushed down the drain and do not contaminate the environment. Your fertigation unit can then be fitted with EC pre-mixing which allows you to reuse the drain water to the greatest possible extent; here the recirculated drain water is mixed with the necessary ratio of fresh water before fertilizers are added. This means that you are not only looking after the environment but saving money on your water and fertilizer costs.”

Taken from an original article by Richard Crowhurst for the Greenhouse Yearbook and Buyers Guide in 2022 and updated in 2026