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Chemical and Biological Phenomena Observed with Sewage Sludges in Simulated Soil Trenches¹

ABSTRACT

Chemical and biological observations were made on sewage sludge in a simulated trenching system in the greenhouse. Limed and unlimed raw and digested sludges were placed in simulated trenches in soil profile boxes in which corn (Zea mays L.) was sown. During the 160-day growth period, roots penetrated entrenched digested sludge and root growth proliferated throughout the sludge. Root penetration into the raw sludges was severely restricted. Gas analysis showed that anaerobic conditions prevailed for extensive periods during the 160 days in raw sludge. Methane and CO₂ levels reached 45 and 25%, respectively. The levels of CH₄ and CO₂ were < 3 and 21%, respectively, in the digested sludge boxes. Nitrate nitrogen, adjacent to and beneath the sludge, was generally higher with digested than with raw sludge. Zinc and copper did not move from the sludge into the surrounding soil. The increase of these metals in corn leaves was relatively low, reaching only 131 µ/g Zn and 5.9 µ/g Cu as compared with 79 µ/g Zn and 3.8 µ/g Cu in the controls. Although low levels of fecal coliforms survived in the sludge, none were found in the soil surrounding the sludge. Total coliform numbers in the sludge after 160 days were negatively correlated with NH₃-N concentrations, suggesting that NH₃, generated on dissociation on NH₄⁺, may be important in reduction of human pathogens.

Key Words: waste • sludge entrenchment • methane • carbon dioxide • nitrate • ammonia • zinc • copper • total coliforms • fecal coliforms

¹ Contribution from the Agric. Environ. Qual. Inst., SEA-USDA, Beltsville, MD 20705. This research was supported in part by the U.S. Environ. Prot. Agency, under Interagency Agreement EPA-IAG-D4-0510.

² Plant Physiologist, Soil Scientist, Soil Microbiologist, Plant Physiologist, Soil Microbiologist, and Research Chemist, respectively.

Received for publication March 22, 1978.