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MONITORING MICROBES, ALKYL PHENOLS, AND SOIL TOXICITY AFTER LAND APPLICATION OF ANAEROBICALLY DIGESTED BIOSOLIDS
Citation:
ACHESON, C. M., R. F. HERRMANN, L. ZINTEK, R. C. BRENNER, T. DAHLING, E. FOOTE, M. GRAVES, J. L. HECKMAN, S. J. STOLL, T. STROCK, J. TOMPKINS, S. VONDERHAAR, AND S. WRIGHT. MONITORING MICROBES, ALKYL PHENOLS, AND SOIL TOXICITY AFTER LAND APPLICATION OF ANAEROBICALLY DIGESTED BIOSOLIDS. Presented at WEF Residuals and Biosolids Management Conference, Covington, KY, March 12 - 15, 2006.
Impact/Purpose:
To inform the public.
Description:
A common disposal practice for municipal biosolids is to spread this material on agricultural fields as a soil amendment. For example, over 3 million dry tons of treated sewage sludge (or biosolids) are applied on agricultural lands in the US. The regulations which govern the land application of biosolids in the U.S. were promulgated in 1993. Since that time, methods for treating and handling biosolids have evolved. In 2002, the National Research Council (NRC) advised that a new national survey of chemicals and pathogens in sewage sludge was needed to determine if additional chemicals should be regulated and to examine management practices (NRC, 2002. Biosolids Applied to Land : Advancing Standards and Practices). Specific recommendations of the NRC report were to study pathogens and surfactants used in cleaning products and laundry detergents. Surfactants, such as alkyl phenol ethoxylates (APEs), are produced and used in large volumes and have been reported to disrupt endocrine activity. The NRC report expressed concern about the persistence of organic compounds in environmental matrices and the potential for transport within soils and to other environmental media. Based on the NRC recommendations and concerns, a field-scale research project was conducted in 2004-2005 to evaluate land application of anaerobically digested biosolids at agronomic levels. Biosolids had not been applied to this land previously. For this study, biosolids were applied in a 100-m diameter circle by a side discharge manure spreader. The soil sampling portion of this study focused on fecal coliforms and APEs and their degradation products. Soil samples were collected from 3 replicate plots within the application area prior to biosolids application (2 sample events ) and for 4 months following application (7 sample events). Biosolids distribution for each replicate plot was determined by measuring the dry mass and volatile solids of applied material at more than 15 locations in each plot. Fecal coliforms were measured as indicators pathogenic bacteria. Phospholipid fatty acids (PLFA) were measured to characterize the size and diversity of the microbial community. APEs, including degradation products such as octylphenol (OP) and nonylphenol (NP), were measured. APEs concentrations and PLFA were measured at three soil depths. At each sample event, three replicate samples were taken from each replicate plot for fecal coliforms, PLFA, and APEs. Soil toxicity was screened using the 14-day earthworm mortality and 5-day seed germination and root elongation in lettuce and oats bioassays. Soil samples were screened for toxicity prior to, immediately after, and 4 months after biosolids application. In addition, supporting information such as soil agronomic characterization, temperature, and weather data were gathered. Analysis of variance (ANOVA) was used to compare dry mass and volatile solids data from biosolids distribution samples. Fecal coliforms and APEs were analyzed by ANOVA as a function of replicate plot, time, and depth (for APEs). Hierarchical cluster analysis was used to analyze PLFA data as a function of replicate plot, time, and depth. Statistical analysis of this data is ongoing; however, some preliminary conclusions are apparent. The data displayed significant variation which complicates data interpretation. This variability may be a function of many experimental factors including: biosolids application equipment, physical properties of the biosolids, sample numbers, sample size, sampling equipment, and homogenization techniques. Fecal coliform concentrations increased following application. The microbial community based on PLFA returns to pre-application stucture within 30 days of application. NP and OP were observed in the surficial samples after biosolids application. APEs and degradation products were not found in deeper samples. NPand OP persisted in the surficial samples with a half life considerably longer than the 5-17 days reported by Topp and Starratt (2000, Environmental Toxicology and Water Quality 19:313-318) for NP. It is possible that the biosolids matrix may have affected removal. Soil toxicity screening assays showed no effect of biosolids application. Based on this initial study, more detailed studies are planned to reduce: data variability; and uncertainties in the rates of fecal coliform survival, and NP and OP removal rates. In addition, more sensitive soil toxicity assays will be adapted from the literature.