Energy valorisation of the residual biomass from greenhouses in the framework of a circular economy

Abstract

Thrace Greenhouses S.A. cultivates 5000 t y−1 cucumbers and 3500 t y−1 tomatoes hydroponically on 170,000 m2 of land. During cultivation (from February to November), suckers and leaves are removed regularly, producing 7,000 – 8,000 t y−1 residual green biomass. The anaerobic digestion technology was applied at laboratory scale, to explore the potential of valorising the generated residues for biogas production. The latter ranged between 18 and 30 NL methane per kg of fresh biomass (suckers or leaves, respectively). Considering a typical mixture of suckers and leaves produced during the cultivating season, the methane produced annually was estimated at 140,000 m3. The biogas can be used as a fuel in a combined heat and power (CHP) system (cogeneration). CHP was considered the central unit in a hybrid energy system (HES) integrated with batteries, aiming to provide energy autonomy to the greenhouses. Moreover, the flue gas from the CHP containing 10% CO2 and 9% O2 could be used as a source of CO2 in the greenhouses. In this case, trace gases (NOx: 401±37 ppm, NO:168±15 ppm, NO2: 150±18ppm, CO: 401±60, SO2: 1.4±2.2) present in the flue gas should be removed and/or diluted with air before entering the greenhouses.

Method and Simulation of a Power Supply System Operation Based on Methane Generator Supported by Energy Storage System, to Cover High Fluctuation Electrical Loads: Greenhouse Case Study

“…The present study focuses on the use of a natural gas or biomethane generator to meet the energy needs of the GHU. The choice of this fuel is based on a recent study by the company concerning its estimation of Greenhouse residues' biogas production [13,14]. The possibility of using constant generator power in the three load-demand areas will be studied.…”

“…A percentage of the required amount of fuel, according to Table 5, could be covered by biogas production, utilizing the produced biomass of the greenhouse [13,14]. The rest will be covered by the supply of natural gas from the network.…”

“…An additional investment that the company could proceed concerns the exploitation of residues from crops for energy production, thus adopting the principles of the circular economy. In particular, 75 tons of greenhouse waste (biomass) [12] could, with proper treatment, lead to the production of biogas [13,14]. This article studies the management strategy of the electricity produced from methane (biogas or biomethane) based generators in conjunction with ESS.…”

Greenhouse Residues’ Potential for Biogas Production

“…In the same line, Jagadabhi et al [46] stated that greenhouses could use their crop residues for biogas production and, in turn, meet their energy demand. Gioulounta et al [47] evaluated the potential of tomatoes' and cucumbers' leaves and suckers generated in a greenhouse to provide energy autonomy to the greenhouse via a CHP unit combined with a battery system. The hybrid renewable energy system could partially cover the facility's energy demands.…”

“…Studies on biogas production from tomato and cucumber crop residues are limited to wastes from industrial processing or from green parts of the plant that are uprooted at the end of the growing season (such as stems), which, in addition to the plant, may have fruits. On the other hand, many leaves and stems are removed during the growing season, especially in hydroponic greenhouses [47], since the regular removal of leaves and suckers is necessary to promote plant growth. Therefore, there is a massive production of biomass throughout the cultivating period.…”