MANAGING GREENHOUSE ORGANIC WASTES: A HOLISTIC APPROACH

Abstract

During the last decade, several sustainable management practices have been proposed by researchers and extension services. For greenhouse production, three main factors should be considered to reduce environmental burdens: 1) waste management, 2) nutrient emission, and 3) fossil energy use. Organic waste represents a significant source of biomass production for protected crops. Wastes such as 4.5 t tomato leaf biomass ha-1 week-1 are usually discarded in sanitary landfills or directed to other waste management sites such as composting sites or accumulated near the production facility thus constituting a phytosanitary problem. When drainage water from producing greenhouse vegetables is not recycled, nutrient emission into the groundwater may represent a major environmental impact (up to 3000-4500 m3 per ha of tomato wasted nutritive solution containing 4-10 t of nutrients such as nitrogen and phosphorus). Greenhouse culture production also uses a significant quantity of fossil fuel energy, in the form of heat (10-40% of production costs), CO2-enrichment, and fertilizers. Thus, management of significant quantities of organic solid and liquid waste produced by greenhouse crops as well as the use of renewable energy constitute a challenge that can be partly solved by more sustainable production systems. Our integrated closed-loop process recycles both solid and liquid organic waste, and converts the waste into renewable energy (CH4), CO2, and liquid and solid fertilizers. Organic waste products and drained water are then reintroduced into the irrigation system. This ensures minimal risks using biological processes such as anaerobic digestion and nitrifying bioreactor, artificial wetlands and passive bioreactors to reduce nutrient pollutants and sulfate content as well as risks associated to pathogens. The proposed integrated production system uses organic growing media or soil with organic fertilizers as well as liquid organic culture, and constitutes a sustainable organic production system achieving productivity levels as high as conventional growing systems.