ISSN:
1573-5117
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. Impounding of sewage in holding and percolating ponds, called solar drying beds, of less than one acre to 1.7 acres in area and with depths of 1 to 2 feet, has been practised as a distinct treatment process since 1932 for a portion of the sewage admixture with textile mill wastes in Ahmedabad. 2. The solar drying beds have been used as holding ponds for the sewage that is not required for irrigation; and also as leaching ponds for evaporating and percolating the liquid wastes into the sandy soil on the banks of the river Sabarmati. 3. Two distinct processes have been taking place simultaneously in broad day light in these solar drying beds: (i) Synthesis of fresh organic matter in the form of millions of blue-green algae making use of the fertilising elements found in the sewage admixture with textile mill wastes; and (ii) the concomitant release of oxygen which is being used for stabilizing the old decomposing organic matter of sewage by bacterial action which results ultimately in the formation of carbon dioxide, ammonia, phosphates etc. 4. The organic loading in these drying beds varies from about 70 to 140 lbs. per acre per day, and the depth/detention ratio from 1.7 to 3.4. The 5 day at 30°C B.O.D. removal is 85 to 90% with an annual average figure of 87.4%. Thus the drying beds accomplish a very high degree of purification or rather stabilization at practically no cost by means of biological oxidation; and also produce thousands of planktonic algae, principally of the blue-green variety, though limited to a few species in all. These algae being mostly larger and filamentons as compared to Chlorella can be easily harvested. The beds do not have effluents but dispose of the water by seepage and evaporation. 5. Chlorides and dissolved solids are found to be greater than the corresponding figures for the raw sewage. 6. The solar drying beds resemble the Type II oxidation pond of Oswald & Gotaas (1957) in their smaller size with a detention period of one week, where stabilization of sewage is brought about essentially by the photo-physiological action of certain species of blue-green planktonic algae.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00142270
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