Aerated soaking of paddy for rice parboiling and its effect on effluent kinetics
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Date
2001-11-16
Authors
Senanayake, S. S.
Basnayake, B. F. A.
Mowjood, M. I. M.
Journal Title
Journal ISSN
Volume Title
Publisher
Unviersity of Peradeniya, Peradeniya, Sri Lanka
Abstract
Parboiling is practiced to increase the milling performance and cooking quality of rice.
The main steps in parboiling process are soaking, steaming and drying of paddy. Traditional cold
soaking is one of the methods used for soaking in which the paddy is submerged in water for a
period of 48- 72h. The effluent from this method is in poor quality and has the potential to
pollute the environment, water bodies and lands. This study was carried out to find a solution to
reduce the environmental impact of effluent release from parboiling process.
The effluents (traditional parboiling method - T 1) from five mills in Anuradhapura were
collected and the colour, odour, turbidity, temperature, pH, Biological Oxygen Demand (BOD),
Chemical Oxygen Demand (COD), Total Solids (TS), and Total Suspended Solids (TSS) were
measured. Alternatively two laboratory models were developed and tested for aerated soaking. In
the first model (T 2) the water was trickled over the paddy at the rate of 1000ml/min and drained
water was re-circulated to reduce the amount of water needed for soaking In the second model
(T,) a charcoal filter was introduced before the re-circulation of water to study the effect of
charcoal treatment in the effluent The effluent samples from 11, 12 and 13 were incubated at
20°C and Dissolved Oxygen (DO) was measured in 12h intervals for 5 days to calculate BOD
values. DO was measured using Winkler titration method The rate constants were estimated from
the BOD curve developed for the three treatments.
Average temperature, pH, COD, TS and TSS values of the eftluent of T 1 were 38°C , 6.1,
2548 mg/l, 150 mg/l and 50 mg/l, respectively. The effluent from T 1 also had the highest mean
BOD value (2452 mg/I) at the end of 5 days, unpleasant colour and odour though the degree of
contamination varied among the mills These results indicate the potential of the effluent of the
traditional method as a pollutant. Effluents of the laboratory models (T2 and T3) recorded much
lower BOD values at the end of 5 days (356 and 128 mg/l, respectively) with no unfavorable
colour or odour T3 recorded the lowest rate constant (0.07 per day) when compared with T, and
T2 (0.28 and 0.15 per day, respectively).
In the aerated soaking methods (T2 and 13) tested, water can be recycled. In addition, the
soaking time needed to absorb water up to optimum moisture content was less in T2 and T3
compared to that of traditional method. Eating quality of rice was also observed to be high with
the aerated models than with the traditional method.
Power requirements and cost - benefit analysis have to be studied to improve the aerated
soaking system in mills. Further studies are necessary to identify carbonaceous and nitrogenous
demand in the BOD curves of the models considered Further understanding on the kinetics of
effluent can lead to design more efficient aerated soaking and effluent treatment reactors.
Description
Keywords
Agricultural , Aerated , Soaking , Paddy , Rice , Parboiling , Kinetics
Citation
Proceedings & abstracts of the Annual Research Sessions 2001,Unviersity of Peradeniya, Peradeniya, Sri Lanka,pp.12