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.
