Biological Treatment Processes

The waste flow from a parathion production unit undergoes activated sludge treatment (Coley and Stutz 1966) with a residence time of 7-10 days, providing nearly complete breakdown of parathion and paranitrophenol as well as over 95% reduction in organic matter as measured by chemical oxygen demand (COD).

Studies were also conducted in designing a wastewater treatment facility for production of organic phosphorus pesticides (Lue-Hing and Brady 1968). Although treata-bility studies showed the waste to be biodegradable, shock loads caused stresses at up to 6000 mg/l solids. Consequently, a two-stage activated sludge system was chosen in which the first stage is a dispensable, low-solids, detoxification unit. Removal of dissolved organic matter measured as biochemical oxygen demand was 90-98% in the pilot plant.

The oxidation of Sevin carbaryl insecticide by an activated sludge culture is depicted in Figure 8.2.12. No adverse effects on bacteria, protozoa and rotifers were noted. Biological degradation studies (Leigh 1969) of lindane indicated no significant removal of this pesticide from mi-crobial activity following 28 days of acclimatization in sta-

0 20 40 60 80 100

TIME, HOURS

FIG. 8.2.12 Oxidation of Sevin carbaryl insecticide by acclimated bacteria.

0 20 40 60 80 100

TIME, HOURS

FIG. 8.2.12 Oxidation of Sevin carbaryl insecticide by acclimated bacteria.

tically aerated cultures. Removals in unseeded controls (reference samples) were approximately 46% while biological removals averaged only 41%. The biodegradabil-ity of heptachlor could not be deduced from similar studies because analyses of aqueous solutions of this pesticide indicated partial degradation to 1-hydroxyl chlordene and an undetermined compound. Removals of as high as 99.4% were attained within four days for heptachlor, but volatilization losses were considered significant.

The degradation of chlorinated hydrocarbon pesticides was studied under anaerobic conditions (Hill and McCarty 1966) such as lake and stream bottoms, lagoon treatment systems, and digestion systems. Lindane and DDT were rapidly decomposed, the latter to DDE which degraded more slowly. Heptachlor and endrin also formed intermediate degradation products within short periods. The rate of decomposition of aldrin was similar to that for DDD; only slight degradation of heptachlor epoxide occurred, and dieldrin remained unchanged. Anaerobic conditions were more favorable than aerobic conditions for pesticide degradation. Sorption of chlorinated hydrocarbon pesticides was found to be greater on algae than on bentonite or fine sand; the process was partially reversible and the degree of sorption was inversely related to the solubility of the pesticide.

Lindane was degraded anaerobically in pure culture; only 0.5% of the lindane present after 1 hr incubation was found in the reaction mixture after 27 hr incubation (MacRae, Raghu and Bautista 1969). The covalently linked chlorine of the lindane molecule was released. A detected intermediate product reached a maximum level after about 4 hr incubation and diminished to undetectable levels after 27 hr incubation.

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