Zero liquid discharge in horticulture

The global environmental awareness, the focus on water pollution and the reduction of water consumption have resulted in increasingly stringent legislation and regulations for the use and discharge of waste water. “Zero liquid discharge” (ZLD) is a treatment process that has been developed to filter all liquid waste from a water system. The technology was developed to enable industry and the horticultural sector - among others - to clean and recycle their process water. In 2013, Witteveen+Bos and chain partners participated in the Zero Liquid Discharge Horticulture project initiated by the “Top Consortium Knowledge and Innovation” (TKI). This project aimed to develop knowledge and stimulate innovations regarding the recycling of liquid waste flows in horticulture.

The “Zero liquid discharge for agriculture” project focused on the development of sustainable and circular glasshouse systems for the horticultural industry. The recycling of waste flows has become increasingly important in this business line, due to increasingly stringent legislation and regulations. This has also resulted in a substantial increase in the costs of discharge and/or deposition. 

Witteveen+Bos provide insight into the benefits and disadvantages of purification techniques

Witteveen+Bos have worked out various purification techniques and combinations of techniques in response to these challenges. In addition, we described the benefits and disadvantages for each option. Research has demonstrated that two purification concepts meet the purification requirements that have been set. The first concept was a combination of a fine sieve, active carbon filtration and advanced oxidation using hydrogen peroxide and UV. The second concept consisted of a fine sieve, followed by an ozone treatment and an active carbon filter.

Both technical concepts complied with the following criteria:

• The complete removal of crop protection products from the waste flows
• The extensive removal of organic matter and suspended particulate.

These two pre-purification techniques are followed by concentration techniques, which enable the recycling of water and result in a significant reduction of the waste flow. All this combined results in a severely reduced liquid waste flow for this form of horticulture. This method provides the horticultural industry with a relatively cost-efficient process for the removal of nutrients, crop protection products and salts from water flows and - where possible - the recycling of waste flows in a useful manner.