Ind. Eng. Chem. Prod. Res. Dev. 1801, 20, 567-574
587
SYMPOSIA SECTION
I.
Symposium on Municipal and Industrial Wastes as Potential Fertilizer Sources J. C. Barber, Chairman Second Chemical Congress, Las Vegas, Nevada, August 1980 (Continued from June 1981 and September 1981 Issues)
Florence Demonstration of Fertilizer from Sludge Michael R. Matthews,’ Fred A. Miller, 111, and George J. Hyfantls, Jr. Tennessee Valley Authority, Office of Natural Resources, Dlvislon of Water Resources, Chattanooga, Tennessee 3740 1
The Tennessee Valley Authority and the city of Florence, Ala., are participating in a joint project to demonstrate the feasibility of applying aerobically digested sewage sludge to agricultural land. The demonstration site consists of two watersheds-one receives sewage sludge and one serves as a control. Both watersheds are planted with midland Bermuda grass. Ground water monitoring wells have been installed and both watersheds are equipped with automatic flow recorders and water sampling devices. No significant difference has been found in the heavy metal concentration between the control watershed and application watershed runoff water. The mean value of conductivity, dissolved solids, TKN, N H , NO2 NO,, total phosphorus, and TOC increased significantly in the runoff water from the sludge application watershed. Due to changes in the runoff water quality in the control watershed, only the increases in NH,, NO2 NO,, and TOC may actually be related to the sludge application.
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Introduction Several years ago, Florence, Ala., was experiencing problems disposing of its sewage sludge because dewatering was impaired by insufficient drying bed capacity. As a possible answer to the city’s sludge management problem, additional sludge drying beds were being considered. The major drawback to this plan, however, was expense. The cost of building and operating extra beds was prohibitive for the small city. City officials asked TVA to help find a solution to the problem. Assisting local governments is one of the mandates given to TVA in its charter. Such assistance is not funded through revenues generated through its power system but by appropriations from Congress. TVA agreed to conduct jointly with the city a demonstration project designated to show how sewage sludge can be disposed of on agricultural land characterized by karst topography (a limestone region where numerous sinkholes and underground streams abound). This method of sludge disposal could help many other communities in the Tennessee Valley with similar problems (Miller, 1977). There are four main objectives in the demonstration project: (1)solving Florence’s sludge disposal problem; (2) demonstrating the feasibility of applying aerobically digested sewage sludge to agricultural land; (3) better defining where sewage sludge may be safely applied; and (4) ensuring that other local governments will benefit from this demonstration through technology transfer. To accomplish these objectives, the project was broken into two major studies: water quality studies and smallscale vegetation studies. The site for the water quality
studies was on part of a 173-acre land tract owned by the city of Florence. Part of this site was divided into two watersheds (see Figure 1): a 5.4-acre watershed received sewage sludge and a 2.35-acre watershed served as a control site. A test plot area for studying trace element uptakes by various crops has also been established on the western edge of the sludge application watershed. This paper will only deal with the watershed water quality aspects of this demonstration. The Alabama Water Improvement Commission granted approval to begin applying sludge to the site on Feb 21, 1979. Actual application of the sewage sludge began on Apr 30,1979. Site Characteristics In a detailed site investigation, the underlying rock in this area was found to be Tuscumbia limestone which overlays the Fort Payne chert (Miller, 1978). This combined bedrock unit comprises a major aquifer and is deeply weathered. Although many sinkholes exist on the property, both watersheds are located away from sinkhole areas. The soil associations on the site are deep, well-drained, cherty, silty, clayey, and loamy. The soils hold water only during wet periods. The surface slopes are less than 15%. Surface and subsurface drainage from the site is toward Pickwick Lake (a Tennessee River reservoir) about onehalf mile away. Sludge Characteristics and Method of Application The characteristics of the aerobically digested sewage sludge from the Florence, Ala., Cypress Creek Sewage Treatment Plant are shown on Table I. Because very few
This article not subject to US. Copyright. Published 1981 by the American Chemical Society
568 Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 4, 1981 Table I. Characteristics of the Aerobically Digested Sewage Sludge from the Florence, Ala., Sewage Treatment Plant date of sample characteristic moisture, % solids, % volatile solids, % (of total solids) ash, % (of total solids) organic acid, mg/L (as acetic acid) pH, standard units grease and fats, mg/L chemical oxygen demand, mg/L total organic carbon, mg/L alkalinity, mg/L (as CaCO,) elements, pg/g (dry wt) As B Cd
co Cr cu F Hg
K
Mg Mn Mo Na Ni NO, and NO, Pb Se Si Sn
so4
Zn elements, % (dry wt) A1 Cab Fe
9-30-76 12-21-76 2-14-77 5-12-77 5-17-78 7-23-79 97.4 97.5 98.5 98.7 96.4 95.7 2.5 2.7 3.4 4.3 1.5 1.3 53 48 59 47 65 42 41 47 53 52 58 35 67 NA NA NA NA 260 5.8 6.3 6.3 3.1 6.5 6.5 1400 5 60 NA NA NA NA NA NA NA NA" 29 000 56 000 NA NA NA 620 5900 7000 NA NA NA NA 900 0
