การหาสภาวะสำหรับการกวนผสมที่เหมาะสมด้วยระบบอากาศยกตัวในถังปฏิกรณ์ผลิตก๊าซชีวภาพจากมูลโคนม

Abstract

Dairy manure is an important waste generated from dairy farm activities. This waste presents both in the liquid and solid forms, which comes from different parts of the farm, such as wastewater from the stable or the milking part. Dairy manure contains high concentrations of organic substances, which can impact the environment if it is not properly managed. Anaerobic treatment of dairy manure is the appropriate approach as it can both treat and utilize the waste for biogas production. This study was conducted to determine the suitable operation, i.e. biogas flowrate and installation position, of the air-lift system used as the mixing system for the Modified Covered Lagoon Digester (MCL). This system is needed in order to improve the digester performance and prevent the clogging problem of the pipe in the digester. The suitable mixing conditions were determined via the mixing regime simulation using ANSYS Student 2019 program and results were shown in the form of 2-dimentional models. It was found that at the biogas flowrate of 20 L/min (provided through 2 pipes at the flowrate of 10 L/min-pipe), complete mixing was achieved inside the reactor. At this condition, the dead zone of velocity vector at the front and middle parts of the reactor was the least. For determination of the suitable installation position and performance of the pilot-scale reactor, three MCLs (each had the working volume of 8 m3 and named as R1, R2 and R3) were utilized. R1 was the controlled reactor, in which the air-lift system was turned off. Both air-lift systems at the front and rear parts were turned on in R2, while only that at the front part was turned on in R3. All reactors were used for the treatment and biogas production from dairy waste generated at Darunee farm, Doi Lo District, Chiang Mai, Thailand and operated up to the organic loading rate (OLR) of 2.0 kg VS/m3-d. Results showed that R2 performed better than R1 and R3, considering from the system stability and efficiency in treating and producing biogas from dairy farm. R2 had the organic substance removal efficiencies of 51±16.5% and provided the specific methane yield of 156 ±51 ml/g VS, both of which were significantly higher than those obtained from other reactors. This work showed that simulation of the mixing pattern by computer program and experiments with real reactor could help to determine the suitable operational conditions for mixing system used in the treatment and biogas production from dairy waste. The suitable conditions achieved from this approach for MCL was the installation of the air-lift system only in the front part at the biogas flowrate of 2.0 L/min.