Evaluation of bottom ash and composted manure blends as a soil amendment material S. Mukhtar * , A.L. Kenimer, S.S. Sadaka, J.G. Mathis Biological and Agricultural Engineering Department, Texas A&M University, 201 Scoates Hall, College Station, TX 77843-2117, USA Received 20 May 2002; received in revised form 6 March 2003; accepted 6 March 2003 Abstract The long-term goal of this project was to find alternative uses for bottom ash (BA) and composted dairy manure (CM), by- products of coal combustion and livestock production, respectively. The study discussed in this paper focused on potential water quality impacts associated with using blended BA and CM as a soil amendment. The constituents of BA and CM include heavy metals and other chemicals that, while essential nutrients for plant growth, also pose a potential threat to water quality. Four blends (BA:CM, v/v) namely, B1 (100%:0%), B2 (70%:30%), B3 (50%:50%) and B4 (0%:100%), were subjected to flow-through water table management and two blends, B2 (70%:30%) and B3 (50%:50%), were subjected to constant head water table management using de- ionized water. Leachate and standing water from saturated and flooded blends of BA and CM were examined for total solids (TS), volatile solids (VS), COD, pH, total Kjeldahl nitrogen (TKN), NO 3 -N, total P, total K as well as selected metals over a 5 and 7 week period for flow-through and constant head watertables, respectively. The results showed that higher CM content resulted in higher TS, VS, TKN, P and K concentrations in the leachate and standing water. Concentrations of these constituents were higher in leachate than in the standing water. Even though, marked reductions of most chemicals in the leachate and standing water were realized within one to three weeks, initially high concentrations of chemicals in leachate and standing water from these particular blends made them unsuitable as soil amendment material. Based upon these results, it was concluded that additional column studies of BA and CM blends with reduced CM content (5%, 10% and 20%) should be performed to further assess the feasibility of BA and CM blends as an environmentally safe soil amendment material. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Bottom ash; Compost; Leachate; Manure; Nutrients; Water table 1. Introduction Bottom ash (BA) and fly ash (FA) are produced at rates of 12–20% by weight of the original coal (Chen et al., 1991) when coal is burned to produce steam for electricity generation. Texas consumes approximately 38 million tons of coal annually to generate electricity (PUCT, 1998), and therefore generates significant quan- tities of BA and FA. Bottom ash represents 13–20% of the total ash remaining in the bottom of a coal-fired boiler after combustion. Right et al. (1998) reported that only 20% of the ash by-products are recycled while 80% are retained at the power plant site. The total cost of managing coal combustion wastes ranged from $2.20 to $34.14 per metric ton in 1988 (USEPA, 1988a), and, according to Right et al. (1998), this cost will continue to rise in the future. Bottom ash is a relatively coarse, gritty material in contrast to FA, which consists of very fine particles. Bottom ash has a particle size generally within the range of 0.1–10 mm (Korcak, 1995). The chemical constituents of BA can vary greatly depending on the coal type, source, and plant operating parameters. Major constit- uents include calcium (Ca), aluminum (Al), iron (Fe), magnesium (Mg), potassium (K), silicone (Si), sodium (Na) and titanium (Ti). These constituents typically constitute up to 95% of the mass of the ash. Of these materials, Ca, Fe, Mg, K and Si are essential plant nu- trients (Korcak, 1995). Zhang and Lei (1998) used some of these constituents (Ca, Fe, or Al ions) to precipitate soluble phosphorus (P) to reduce eutrophication of surface water. Studies conducted in laboratory green- houses and experimental fields, indicated that BA has potential as an agronomic soil additive that will not be * Corresponding author. Tel.: +1-979-458-1019; fax: +1-979-845- 3932. E-mail address: mukhtar@tamu.edu (S. Mukhtar). 0960-8524/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0960-8524(03)00085-3 Bioresource Technology 89 (2003) 217–228