Zero liquid discharge for greenhouse horticulture (phase 1)

The objective of this TKI project is the development of a concept to achieve zero liquid discharge (ZLD) in greenhouse horticulture. In light of the fact that discharge standards and environmental requirements will become steadily stricter into the future, it is important that a concept be developed for the reuse and/or neutralisation of greenhouse horticulture residual streams. This would involve making residual streams more ‘liquid’, so that they can be reused or discharged without problem. In this study the ZLD principle is given broader scope and zero pollution discharge is the ultimate aim.

Technology

The concept to be developed is directed at the treatment of discharge water and the reuse of the resulting residual streams. The concept will consist of several treatment techniques. To determine the right concept, the techniques are sub-divided into pre-treatment and desalination groups. The goal of pre-treatment is (I) the removal of plant protection products (PPPs), growth regulators and pathogens, and (II) the protection of the desalination processes through the removal of suspended solids and organic matter.

The goals of the desalination step are (I) the highest possible concentration level for a maximisation of water reuse, (II) an effective nitrate removal from the discharge water, and (III) the generation of an ultimate residual stream (concentrate) that can be used as a nutrient stream. High recoveries (>96%) in membrane installations are attainable through the combination of nanofiltration softening or reverse osmosis.

Solution

The initial objective is to develop a jointly-conceived integrated ZLD concept for greenhouse horticulture, which is potentially viable and demonstrable (phase 1); and subsequently (phase 2), to conduct a proof-in-principle of the concept.

A theoretical ZLD concept for the specific situation has been developed, in part on the basis of two workshops held with project partners. This theoretical concept will be used as the basis for a proof-of-principle research project in 2014/15. As planned, phase 1 of the project was completed during the first half of 2014.