Title: Fate of microconstituents in biosolids composted in an aerated silage bag Authors
Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 20, 2014
Publication Date: February 17, 2014
Citation: Lozano, N., Andrade, N., Deng, D., Torrents, A., Rice, C., McConnell, L.L., Ramirez, M., Millner, P.D. 2014. Fate of microconstituents in biosolids composted in an aerated silage bag. Journal of Environmental Science and Health. 49(A):720-730. DOI:10.1080/10934529.2014.865461. Interpretive Summary: Wastewater plants generate large amounts of carbon and nitrogen-rich solids, sometimes called biosolids, which can be beneficially used by farmers to improve the quality of their soils and increase crop yields. However, biosolids sometimes contain low levels of pollutants that enter the wastewater stream from a variety of consumer products. Two types of pollutants that are of concern are anti-microbial additives present in soaps and other household products and flame retardant compounds that are present as additives in fabrics and electronics. In this project we tested composting as a way to reduce the amount of these pollutants in the biosolids prior to application to soils. We used large plastic bags that were about 200 feet long to compost batches of a biosolids and wood chip mixtures in a process that took 7 to 8 months. We found that one of the anti-microbial compounds, triclosan, was greatly reduced by composting while another anti-microbial and a flame retardant compound were not reduced by composting. The results of this work are important since we have identified compounds that resist degradation and may build up in soils over time. This work is also important because many wastewater plants are considering composting as a means to reduce risks from their biosolids application programs.
Technical Abstract: The use of silage bags for composting was evaluated as a means to produce Class A Biosolids while minimizing vector attraction and odor emissions. While most composting studies report pathogen concentrations, little is known about the fate of Endocrine Disruptor Chemicals (EDCs) during composting. In this study, a positively aerated polyethylene bag composting system was filled with a mixture of woodchips and limed biosolids from a large WWTP to study the removal efficiency of two different groups of EDCs. Two antibacterial compounds, Triclocarban (TCC) and Triclosan (TCS), and a TCS byproduct, Methyltriclosan (MeTCS), as well as flame retardants known as PBDEs (Polybrominated Diphenyl Ethers) were studied during two phases of composting: 1) a thermophilic phase, in which positive mechanical aeration, pushing air into and through the materials matrix, is conducted for two months; and 2) a curing and stabilization phase in which no mechanical aeration was provided, and the bag was opened to ambient passive aeration to simulate storage conditions for seven months. Our results illustrate that while TCC did not undergo significant degradation, TCS degradation took place during both phases. The degradation of TCS was corroborated by the formation of MeTCS in both phases. The TCS concentrations decreased from 18,400 ± 1,880 to 12,000 ± 290 ng g-1 dry wt. by the end of the thermophilic phase and then, declined from 12,000 ± 290 to 7,200 ± 910. ng g-1 dry wt. during the curing phase. Thus, slightly greater TCS transformation occurred during the second phase as compared to the first phase (35.1 vs 39.4 %). The MeTCS concentrations increased from 190 ± 8.6 to 360 ± 73 ng g-1 dry wt. during the first phase and reached 590 ± 95 ng g-1 dry wt. at the end of the second phase. The PBDEs were measured at the end of the first phase and were comparable to initial concentrations. No removal of the two major congeners analyzed was observed.