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Investigation on the application of biological and physicochemical methods for solid greenhouse waste treatment

Theodoraki Maria

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Summary

In many European countries as well as in Greece, agricultural and livestock by-products and residue from agriculture and livestock industries and activities are usually discarded as waste, often constituting serious problems of environmental pollution. In the meantime, a large part of them, after appropriate treatment, could be utilized as a new economic resource and at the same time conform to any regulations for environmental protection.The present study focuses on the treatment of plant and plastic residues resulting from the cultivation of the tomato plant in a closed greenhouse. The first method used to treat any waste was Anaerobic Digestion. The plastic residues, string plant support and greenhouse’s plastic films, were pretreated in a microwave oven at 150 °C and 6 bar for 5 minutes. In the anaerobic digestion process, biological sludge derived from a mesophilic anaerobic digester was used as an inoculum. The sludge was mixed with the substrates (plastic residues) in order to provide a sufficient amount of microbial mass.Initially, some basic parameters were assessed for the characterization of the two materials and the sludge, which affect the amount of biogas produced. Biochemical Methane Potential (BMP) tests were then carried out to determine the biodegradability of organic substrates during anaerobic digestion and the ability to produce methane from them. The aforementioned tests, which lasted 60 days, were conducted within mesophilic conditions (35 °C) in batch reactors. The experimental process demonstrated that the PEMW (Polyethylene MicroWave waste), PPMW (Polypropylene MicroWave waste), PE (polyethylene waste) and PP (polypropylene waste) samples produce values equal to 150, 138 and 127 mL of CH4, respectively.Subsequently, the possibility of degrading greenhouse residue was examined via Hydrothermal method. Within the context of the experiment, 25 mL steel reactors were sealed in an airtight manner. For an optimal examination of the tested materials, mixtures with different compositions were prepared and two different residence times in the oven were set; at 6 and 24 h.In calculating the higher heating value of the samples tested, it was observed that in the case of samples with a plastic content of 5%, their storage in the oven for more than 6 hours leads to a reduction in their higher heating value, whereas in all samples containing 1% plastic, the heating value is observed to remain relatively constant, despite any differences in residence time.

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