Cecil Lue-Hing

Mercury in Soils and Crops from Fields Receiving High Cumulative Sewage Sludge Applications: Validation of U. S. EPA’s Risk Assessment for Human Ingestion

The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) has owned and operated a 6320 ha Dedicated Beneficial Sludge Utilization Site in Fulton County, Illinois since 1971. The site consists of calcareous strip mine spoil intermingled with placed land. Sewage sludge from Chicago is barged to the site, located approximately 185 miles southwest of the city, and utilized to reclaim the strip mined soils and to fertilize the corn and wheat crops grown on them. Fields have received as much as 1317 dry Mg ha−1 of sewage sludge since 1971. Sludge Hg concentrations have ranged from 1.1 to 8.5 mg Hg kg−1 with mean concentration of 3.31 mg Hg kg−1, and maximum cumulative Hg loading rates are approximately 4 kg ha−1. Sludge applications have significantly increased extractable soil Hg concentrations, and regression analysis indicates that from 80 to 100% of the Hg applied to soils in sewage sludge since 1971 still resides in the top 15 cm of soil. Since 1985 the MWRDGC has been monitoring Hg concentration in corn leaf and grain, wheat grain and soils at the Fulton County site. Monitoring data indicate that 98.8% of the corn grain samples, 93.0% of the wheat samples and 50.7% of the corn leaf samples collected from 1985 through 1992 had Hg concentrations below detectable limits (<25μg kg−1). Cumulative Hg loading rates are utilized along with crop tissue concentrations to compute crop uptake response slopes (UC) for Hg into plant tissues at the Fulton County site. The UC for corn and wheat grain was zero and for corn leaf was −0.0014 (mg Hg/kg tissue)/(kg Hg/ha soil), which indicate that sewage sludge additions did not increase plant tissue Hg concentrations at the Fulton County site. The negative UC obtained for corn leaf may actually indicate that sewage sludge applications decreased Hg uptake from mined soils possibly due to organic carbon and sulfides in the anaerobically digested sludge binding native Hg. The United States Environmental Protection Agency (U. S. EPA) has recently promulgated their 40 CFR Part 503 regulation for sewage sludge use and disposal. The rule sets risk based limits on ten metals, including Hg, in sludges that are land applied. Exposure pathways involving plant uptake of Hg are briefly discussed and it is shown that the UC used in U. S. EPAs risk assessment models for these pathways overpredict uptake of Hg by crops when compared with the UC derived from the MWRDGCs monitoring data at Fulton County.

VOC Emissions from Wastewater Treatment Plants : Characterization, Control and Compliance

This book provides comprehensive information on Volatile Organic Compound (VOC) emissions from publicly owned treatment works (POTWs). It describes models of emission factors so that readers will know what to expect when models need to be used for the estimation of VOCs from their specific wastewaters. The authors provide a road-map approach for air pollution abatement compliance so that managers can determine their human resource needs. POTW professionals will find information on VOC emissions from various unit processes such as sewers, preliminary and secondary clarifiers, activated sludge and attached growth systems, sludge treatment, and combustion devices.

Class A biosolids production by a low-cost conventional technology

Encouraged by a finding that the pathogen analyses of numerous samples of the final product of the Metropolitan Water Reclamation District of Greater Chicago, Illinois (District), met the U.S. Environmental Protection Agency (U.S. EPA) Class A criteria, the District optimized and codified the operation of its sludge processing trains (SPTs), submitted a petition to the U.S. EPA Pathogen Equivalency Committee for obtaining certification of its SPTs as equivalent to a process to further reduce pathogens, and conducted a 3-year full-scale study. The objective of the study was to determine whether or not the Districts SPTs consistently produced a Class A biosolids final product. The primary conclusion drawn from this optimized and codified operation study was that all batches of the final air-dried product complied with the Class A criteria as specified by U.S. EPA in the Part 503 regulations.

Statistical evaluation of pathogen inactivation for a conventional low-cost technology Class A biosolids process

Statistical methods were developed for analyzing the results of a study of pathogen densities for sludge samples taken over the four stages of the solids processing trains (SPTs) operating at the Stickney and Calumet Water Reclamation Plants of the Metropolitan Water Reclamation District of Greater Chicago, Illinois (District). These methods also apply to pathogen density studies for other biosolids processes. Analysis of covariance models were used to estimate expected pathogen densities for individual solids processing stages. Cross-validation was used to select appropriate analysis of covariance models. Nonparametric methods were used to estimate distributions for pathogen density reductions between solids processing stages and to assess the effect of hypothetical surges and expansions in initial stage pathogen densities on final stage pathogen densities. These statistical analyses demonstrate that the Districts SPTs achieve target reductions in enteric virus and viable helminth ova densities with high probabilities. Furthermore, the Districts SPTs would still meet U.S. Environmental Protection Agency Class A restrictions for these pathogens with high probabilities, even if the initial stage pathogen densities observed in the study undergo extreme hypothetical surges or extreme hypothetical uniform expansions, that is, exceptionally large isolated bursts of pathogens or exceptionally large sustained increases in pathogens in the feed to the SPTs.