In order to apply the intermittent aeration technique to sewage disposal in agricultural communities, an automatic control system with high rate removal of nitrogen and organic substances from wastewater was designed and tested. Basing on settleability of sludge which depends on aerobic or anaerobic conditions of water the light-beam sensor had detected a time spent to settle to given depth of water, then the time was transferred to an aeration time within a given pair of on-off aeration time.
A columu used as the test tank had 20cm in diameter and 21
l in volume. The test had been run in 3 batches per day and hydraulic retention time was 1 day. During almost 50 days test under the same influent load of total nitrogen as 35.3mg-N/
l and COD as 237mg/
l, effluent total nitrogen and COD had fluctuated in 1.34-5.92mg-N/
l and 6.8-31mg/
l, respectively. Mean removal rates of nitrogen and COD were 91 and 95%, respectively.
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