An activated sludge process which produces no excess sludge was developed. The process is very simple as a small amount of return sludge is ozonated and then returned to the aeration tank. The ozonation enhances biodegradability of activated sludge, which is biologically oxidized in the aeration tank.
A full-scale plant for treating 450m3/d of municipal wastewater was constructed and has been operated successfully for 9 months. The amount of excess sludge eliminated is directly proportional to the amount of ozone dosed to the sludge. At the ozone dosing rate of 0.034 kg/kg-SS, complete elimination of excess sludge has been achieved when 4 times more amount of sludge is ozonated than that of the excess sludge expected in the treatment without ozonation. After 5 months of operation without any withdrawal of excess sludge, small amount of inorganic substances like sand and silt accumulated in the sludge. On the other hand, inert organic substances does not seem to accumulate. As for effluent quality, BOD and nitrogen were kept good. Although effluent SS was 2–15 mg/l higher compared to a control without ozonation, it has been well below the discharge limit.
Newly isolated Pseudomonas sp. KWI-56 produced an extracellular thermostable lipase. The enzyme was purified 13.9-fold by acetone precipitation and gel filtration by HPLCwith 2.9 % recovery. The purified enzyme, which showed a single band on SDS-PAGE,had a molecular weight of 33,000. The thermostability was very high, such that more than 96% of initial activity remained after incubation at 60°C for 24 hr. The optimum temperature was 60 C and the maximumhydrolysis of beef tallow reached 95 % at the reaction temperature of 50°C.
A lipase gene (lip) and its activator gene (act) on a 2.9 kb BglII-EcoRI fragment from Pseudomonas sp. KWI-56 were cloned in Escherichia coli using pUC19 as a vector plasmid. From the sequencing results, the open reading frames of the lip and the act were found to contain 1092 and 1032 nucleotides, respectively. The act existed downstream of the lip with the same orientation. When the lip was expressed in E. coli using the lac promoter on the pUC plasmid vector, the lipase activity of E. coli carrying both the lip and the act was 200-fold greater than that carrying only the lip. This result suggested the act was important in the expression of the lip in E. coli.
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