Effect of submerged and exposed aeration on dissolved oxygen in soaking water and germination of paddy grains

Abstract

Rice is the staple food grain in Sri Lanka and therefore 34% of the total cultivated land is under paddy. About 70% of people in Sri Lanka consume parboiled rice and the cold water soaking in parboiling process utilizes about 1,300 L of water per tonne of paddy. Paddy soaking water has higher BOD values (950-1300mg/L), and usually millers discharge it into environment without treatment causing environmental pollution and the traditional submerged cold water soaking produces anaerobic conditions in the soaking tank leading to bad odours in rice as well as in the environment. Therefore, introduction of a simple aerated soaking method is vital to resolve this issue. Aeration, under exposed or submerged conditions, would increase paddy hydration and Dissolved Oxygen (DO) concentration in the soaking water, which in turn could stimulate paddy germination. Therefore, this experiment was conducted to study the effect of aeration, under exposed and submerged conditions, on DO concentration and paddy germination and to compare it with conventional cold water soaking process. Two simple water circulation units were made for the exposed and submerged aeration tests and similar unit was used without water circulation to represent conventional cold soaking. Water circulation and aeration was done using a 12V DC pump at a frequency of 10 minutes operation and 20 minutes resting based on the results of observation trials. After 30 hours of soaking, the DO level in soaking water in exposed aeration reduced to 1.4 mg/L, 1.1 mg/L in submerged aeration and O.lmg/L in submerged traditional soaking. Paddy samples were taken after 36 hours of soaking and kept for standard germination test. Highest percentage of paddy grain germination (50%) was found in exposed aeration, 2% for submerged aeration and 0% for conventional soaking within 30 minutes after taking samples. Therefore, aeration had an impact on DO, which in turn affects paddy grain germination.