Photocatalytic oxidation (PCO) is a rather new technology in horticulture. It can be applied to i) disinfect water, ii) remove both organic and some inorganic pollutants, iii) improve color, smell and taste of water flows, and much more. In PCO processes, inert, non-toxic, inexpensive catalysts titanium oxide (TiO2) are used in combination with oxygen (from the air), water, and solar light (or another source of UV-A light) to generate hydroxide (OH) radicals. The OH radicals have a strong oxidative effect and can purify water and break down germs and pesticides. TNO research, in collaboration with Productshap Tuinbouw, Priva, TTO, and WUR, has demonstrated that daylight-driven PCO can break down more than 90% of pesticides and removes 99% of pathogens. Restrictions for PCO mainly refer to the load of contaminants per m2 of the area with a photocatalytic coating. Also, light may be blocked by suspended particles or strong color. One of the main preconditions for the feasibility of PCO in horticulture is the availability of light in and around the greenhouse. The amount of natural light, and thus the amount of UV-A radiation, is decisive for the surface of TiO2 which is necessary for effecting the required/desired degradation. Conversion rates in PCO are relatively low, because both the amount of UV light in daylight and the Quantum Yield (the effective usage of UV light for one oxidation step of the pollutants) are low, a few percent respectively less than 1%.
Effectiveness and costs are competitive with conventional techniques. The costs for PCO utilizing daylight (Solar-PCO) for treating 10 m3 wastewater per day are preliminarily estimated between €1.10-3.60 per m3 water with a selected number of pesticides.