Application of an active ventilation fermentation heating and supplemental gas system in asymmetric plastic greenhouse

Abstract: A thermal insulation plastic greenhouse has been widely used in China, due to the cost-saving, ease to build, and heat preservation. The original heat preservation can be maintained for the air temperature and CO2 concentration in the insulation plastic greenhouses with the large span double arch and double membrane. In this study, an active ventilation fermentation heating and supplemental gas system (AVFHSGS) was designed to control the ventilation time in the asymmetric insulation plastic greenhouse. The system included a fermentation tank (long × wide × height: 7.0 m × 2.0 m × 2.0 m), an air-permeable plate, filter, air replenishment, and sprinkler irrigation device. A field experiment was carried out, where the cow dung, wheat, corn, and tomato straw were taken as the raw materials, and the ratio of cow dung to straw was 3:1 for the active ventilation in aerobic fermentation. There was a large annual output of livestock and poultry manure, together with the straw in China, where the raw materials for biomass fermentation were cheap and accessible. Moreover, the biological oxidative fermentation was often accompanied by the generation and release of a large amount of heat and carbon dioxide. The released heat during composting was diffused into the environment in the form of waste heat, where CO2 was the raw material for photosynthesis. A high concentration of CO2 was selected to accelerate the net photosynthesis of tomato leaves and bloom, which was essential to the supplement gas fertilizer in the process of crop growth and development. An evaluation was made on the heat source and CO2 gas source for the thermal insulation plastic greenhouses, considering the temperature variation of composting fermentation in the shed, the CO2 supplement, and the diffusion of harmful gases, such as NH3, N2O, and CH4. The results showed as follows. 1) The reactor temperature in the AVFHSGS was above 50 ℃ for 30 days in total, and 55 ℃ for 17 days in total, which met the requirements of the Chinese standard for the harmless feces; 2) The air temperature increased by 1-3 ℃ at night in the experimental plastic greenhouses, indicating the better heat source, compared with the control; 3) The average CO2 concentration in the 182 m2 measurement area increased to 1 997 μmol/mol by the release of CO2 gas during composting, and the average CO2 concentration in the measurement area was 1 099 μmol/mol during the whole measurement period, the optimal concentration of CO2 increased in the tomato production was 1 000 μmol/mol, meeting the requirement of tomato concentration; 4) The concentrations of NH3, N2O, and CH4 varied from 5.7 to 18.5 μmol/mol, 1.0 to 2.4 μmol/mol and 115 to 315 μmol/mol in the test area, respectively, indicating that there was no outstanding influence or harm on the human health and crop growth. The AVFHSGS can be used as the heat source of insulated plastic greenhouse and CO2 source of crop growth.