In 2017, a study was conducted into using activated carbon for the purification of crop protection agents in discharge water from greenhouse horticulture. The research project was called 'Technology for treatment of discharge water in glasshouse horticulture'. This is because no expertise was available at the start of the project and it was expected that this could be an interesting technique in terms of cost. Meanwhile, thanks to this project, the use of activated carbon for greenhouse horticulture is an option.
Two types of activated carbon are available for water purification: granular (GAC) and powder activated carbon (PAC). Laboratory tests have shown that both the GAC (GAC 400 and HPC Super 830) and PAC (SAE Super and Pulsorb WP235) can achieve the desired purification efficiency of at least 95% per active substance from standard water, depending on the dosage and the contact time.
Research into PAC installation
An installation based on PAC was developed in the study. A PAC installation consists of a dosing unit for PAC, a (stirred) reactor vessel for achieving the contact time and a post-filtration. Various filters have been investigated for naphtholation. A cloth filter seems most suitable in a simple, robust system for removing PAC from the treated water. Then a pilot installation was built. For SAE Super and Pulsorb WP235 the purification efficiency has been determined for three doses and three contact times. Both types of PAC showed an increasing purification efficiency with increasing dosing and contact time. However, the desired purification efficiency was not achieved for all active substances. This effect was possibly caused by a relatively low turbulence in the reactor vessel, as a result of which the transport of the active substances from the liquid phase to the adsorption sites of the PAC progressed more slowly than on lab scale. Another cause may lie in the dosing of the flocculant, which may cause desorption of the active substances from the PAC. In addition, particle counts have shown that even the post-filtration of the PAC from the treated water with flocculant and a cloth filter requires optimization.
As a spin-off of the project, project partner WaterQ has now developed an installation based on PAC approved by the BZG, in which ultrafiltration is used as naphthiltration.
Calculation tool to help in choosing purification techniques
In addition, a calculation tool has been developed in Excel and is available online for growers. The tool contains information about the investment costs, operating costs and maintenance of the installations. The calculation tool can also be supplemented with the more recently approved treatment plants outside of the project duration. The suppliers can provide information for this.
View the final report here (in Dutch).
For more information:
Glastuinbouw Waterproof
www.glastuinbouwwaterproof.nl
water@ltoglaskracht.nl