Contaminants In Sludge Research Articles

The effect of three sludge processing operations on the fate and leachability of trace organics in municipal sludges

Abstract The effect of three sludge treatment processes (heat treatment, anaerobic digestion and anaerobic digestion with polymer addition) on the fate (i.e., mass in the solid and liquid fractions) and leachability of trace organic contaminants in a municipal wastewater treatment plant sludge was evaluated. In general, heat treatment was found to be the most effective method for reducing both total contaminant mass and leachability, whereas digestion with polymer addition was the most effective for reducing contaminant mass in the liquid fraction.

Heavy Metals and Persistent Organics at a Sewage Sludge Disposal Site

AbstractThere are problems associated with the utilization of sewage sludge as an agricultural fertilizer. One of the more pressing problems is the question of heavy metals and persistent organics. There is concern that indiscriminate disposal of sewage sludges on agricultural lands may lead to decreased crop yields, and/or may endanger the human food chain through excessive accumulation of some of these metals in edible portions of crops.The effects of sewage sludge disposal on agricultural land, and possible transmission of sludge contaminants into the food chain is a possible environmental problem. Soils, plants, and sewage sludge from the Metro Denver sewage sludge disposal site were examined for trace elements and persistent organics content. Concentrations of Zn, Cu, Ni, Cd, Pb, and Hg in soils increased when sludge was applied, whereas concentrations of As, Se, Mo, and 22 refractory organics were unaffected. Forage crops grown on these soils showed increased concentrations of Zn, Cu, Cd, and Ni; however, these metals were not elevated to a phytotoxic level or above ranges that would be considered normal for forage tissues. Concentrations of As, Se, and Hg in forage tissues were unchanged, while Pb concentrations decreased as a result of sludge applications. None of the forage tissues examined contained detectable levels of any of the 22 organics that they were analyzed for.Soil metals (Zn, Cu, Ni, Cd, and Pb) extracted with DTPA (diethylenetriaminepentaacetic acid) did not correlate with plant concentrations of these metals. Results indicated that the DTPA soil test could be used as a reliable index as to the total metal concentration of a soil, but not as an indication of heavy metal availability for crop uptake.Heavy metals and P remained within the depth of sludge incorporation. Nitrate concentrations, while decreasing with soil depth, showed that substantial amounts had leached to a 91‐cm depth.

Adherence of Spray‐applied Liquid Digested Sewage Sludge to Tall Fescue

AbstractLiquid anaerobically digested sewage sludge was spray‐applied on field plots of mowed and unmowed tall rescue (Festuca arundinacea Schreb) at rates of 0, 51, and 103 m3/ha in mid‐September 1975. Forage samples were periodically cut to a 7‐cm height following rainfall events for 80 days, and again the following spring. The concentrations of Fe, Cu, Zn, Pb, Cd, and Ni were markedly increased by sludge spraying, with a greater increase at the higher sludge rate. The levels of Fe, Pb, and Cu in samples of healthy plants were so high (37,800 mg Fe, 140 mg Pb, and 115 mg Cu/kg dry forage) that absorption‐translocation by the roots could not have supplied them. The %‐sludge in/on the forage was calculated for each element based on the proportion of increased metal content in/on the forage to the metal content of the sludge. The %‐sludge estimates for six elements were in close agreement, confirming sludge contamination rather than metal uptake from soil. Adhering sludge was not removed by washing in 0.1% Na lauryl sulfate. Adhering sludge comprised 22 to 32% of the forage on the day of application; sludge content decreased with time but was not related to rainfall events (27 cm during 15 days following sludge application). Sludge content declined more rapidly in the mowed treatment, apparently because less forage was contaminated and rapid growth diluted contaminated forage. Sludge was no longer found in/on forage samples grown after spring mowing. Adhering sludge could increase exposure of forage consumers to heavy metals and other sludge constituents.