Leaching and standing water characteristics of bottom ash and composted manure blends

Abstract

Coal burning electrical generating facilities produce roughly 91 million metric tons of ash byproducts annually. Typically, this ash is retained at the power plant sites, adding to the cost of managing wastes at the plants. Another waste material requiring significant management efforts and costs is manure. Repeated application of manure on small parcels of land can contribute to environmental problems such as impaired water quality due to nitrate (NO₃) leaching into the groundwater and phosphorus (P) runoff into surface water bodies. Alternative uses of bottom ash (BA) and composted manure (CM) such as a soil amendment for landscapes or potting media need to be explored. Before an alternative is adopted at a large scale, however, it must be evaluated for its effectiveness and environmental integrity. Two column studies were conducted to evaluate three blends of acidic and alkaline BA and CM, namely B1 (95:5%), B2 (90:10%), and B3 (80:20%). Samples from standing water (top) and leachate (bottom) were collected at weekly intervals to evaluate the effects of different blend ratios and time on chemical and physical properties. It was found that higher CM content in acidic and alkaline raw blends (no-de-ionized water added) resulted in significantly higher concentrations of total Kjeldahl nitrogen (TKN), P, and potassium (K). Generally, a higher CM content in acidic and alkaline blends resulted in higher leachate concentrations for total solids (TS), total dissolved solids (TDS), total volatile solids (TVS), total suspended solids (TSS), chemical oxygen demand (COD), TKN, NO₃-N, ammonium (NH₄-N), P, and K. Concentrations of nearly all chemicals were lower in standing water (top) compared to leachate (bottom) for acidic and alkaline blends. Alkaline blends had higher leachate and standing water TKN, NH₄-N, N0₃-N, P, and K compared to the acidic blends. After day 28, standing water TDS concentrations for all acidic blends were below the USEPA drinking water standard for TDS. Standing water for alkaline blends remained below the USEPA drinking water standard for TDS for the entire duration of the study. Leachate and standing water concentrations for all blends were below the USEPA drinking water standard for NO₃-N for acidic blends. Standing water and leachate for alkaline blends B1 and B2 were below the USEPA drinking water standard for NO₃-N while standing water was well below the standard for the entire duration of the study. P concentrations were low in leachate and nonexistent in standing water for both acidic and alkaline blends. Based on these findings, it is concluded that acidic and alkaline B1 (95:5%) and B2 (90:10%) may be considered as a soil amendment substitute.