Utilization of condensed sludge from rural sewage disposal on paddy rice [Oryza sativa]
2001
Ito, J. (Hiroshima-ken. Agricultural Experiment Station, Higashihiroshima (Japan)) | Matsuura, K. | Masuhara, T. | Uratochi, S.
The experiments were undertaken to evaluate for a method by which condensed sludge is incorporated into rice field with a machine in terms of reduction of environmental pollution and effective utilization of resources in a region. The results were as follows: 1. A condensed sludge was characterized by 98% water content and low potassium concentration. A population of Escherichia coli in the sludge was reduced below critical level by applying 0.5% (W/V) CaO. Nitrogen concentration decreased immediately after application of CaO but was not affected by the duration of the treatment. These results suggest that the condensed sludge could be safely used 3 days after CaO treatment. 2. The sludge after CaO treatment could be incorporated into soil without smell and sight of it by the machine because it had capability to pore the sludge to the lower soil strata. 3. Application of the sludge with new method twice a year in rice varieties 'Koshihikari' had equivalent grain yields to that by conventional agricultural practices. 4. Soil Cd concentration did not increase by application of the sludge twice a year during consecutive two years. Soil Zn concentration also increased gradually, but the values were within a permissible level. These heavy metals were not detected in rice grains by application of the sludge. These results demonstrated that the condensed sludge after treated with CaO could be applied safely to the rice fields with a machine, resulting in rice production without depression of grain yields and quality.
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