THERMAL EXCHANGES IN A COVERED LAGOON BIODIGESTER TREATING PIG FARM EFFLUENT HEATED BY SOLAR ENERGY

ABSTRACT Covered lagoon biodigesters are widely used in Brazil for treatment of agro-industrial effluents; however, under natural conditions, they operate at temperatures below the ideal. Thus, external sources for heating the effluent can enhance reactor performance and optimize thermal exchanges between the biodigester and the environment. This study aimed to evaluate the thermal exchanges in the internal and external environments of a covered lagoon biodigester from the influence of effluent heating through solar energy. Mathematical modeling (EnergyPlus software) was used as a tool to simulate thermal exchanges and obtain heat transfer rates. To do so, two scenarios were considered: with and without heated effluent. The results showed that solar radiation is the primary source of heating for anaerobic reactors and that the high thermal inertia of the soil contributes to a small variation in temperature of the resident biomass over the course of the day, even in the scenario with heated effluent. The temperature of the resident biomass reached and stabilized at 30°C, even after thermal exchanges with biogas and soil, in both hot and cold periods when heating was applied.

摘要：覆盖型泻湖式厌氧消化池（covered lagoon biodigester）目前在巴西广泛用于农业工业废水处理，但在自然工况下，其运行温度低于理想值。因此，采用外部热源对废水加热，可提升反应器运行性能，并优化消化池与环境间的热交换效率。本研究旨在评估太阳能加热废水对覆盖型泻湖式厌氧消化池内外环境热交换的影响，采用数学建模方法，借助EnergyPlus软件模拟热交换过程并获取传热速率。为此，本研究设置两组对照工况：废水加热工况与未加热废水工况。研究结果表明，太阳能辐射是厌氧反应器的主要加热热源；即便在废水加热工况下，土壤的高热惯性也可使池内留存生物质的单日温度波动幅度维持在极低水平。在实施加热的冷暖工况中，即便与沼气和土壤发生热交换，池内留存生物质的温度仍可达到30℃并保持稳定。