Microconstituents in Biosolids Treatment: A Canadian Field Study

A field sampling program involving eleven sites from across Canada was completed for the Canadian Council of Ministers of the Environment. The study involved analyses of 57 pharmaceutical and personal care products in sludges and biosolids collected during three sampling campaigns. Eleven metals were also analyzed in one of the sampling campaigns. Samples of feed sludge, treated sludge and where applicable, liquid sidestreams were collected to allow calculation of mass balances around the processes. The processes examined included composting, anaerobic digestion, autothermal thermophilic aerobic digestion, alkaline stabilization, geotextile bag dewatering, thermal drying, and mechanical dewatering. Only four of the 57 pharmaceutical compounds (triclocarban, carbamazepine, diphenhydramine and miconazole) were found in detectable concentrations in all 31 samples of treated sludges and biosolids, as were two polycyclic fragrance compounds, HHCB and AHTN. The antibacterial compounds triclosan and triclocarban, the antibiotic ciprofloxacin, and the fragrance compound HHCB were the compounds most frequently detected (9 or more of 11 sites) above 1000 ng/g TS dw. For the most part, the frequency of occurrence and concentrations of the corresponding compounds were found to be comparable to that of the U.S. EPA's Targeted National Sewage Sludge Survey (TNSSS). Biosolids stabilisation processes using some form of biological treatment were found to be more efficient at reducing the organic microconstituent (MC) concentrations than non-biological processes. Of the biological treatment processes, the composting process (aerobic) appeared to be more effective in overall reduction (in number and degradation) of MC than mesophilic anaerobic digestion. While many of the MC remained associated with the solid phase of the sludges or biosolids, a number of compounds were found to be lost in any aqueous process sidestreams (e.g., dewatering filtrate, leachate, digester supernatant). The MC concentration data in sludges and biosolids produced in this sampling program were insufficient alone, without applying formal risk assessment methods, to determine human health or environmental risks of managed biosolids land application, land reclamation, and production of commercial and soil amendments.