DISCOVERY OF BIODEGRADATION OF ETHYLENEDIAMINETETRAACETIC ACID (EDTA) UNDER DENITRIFYING CONDITIONS

摘要

Meeting the water needs in the arid southwestern United States requires efficient reuse of treated municipal wastewater. Soil-Aquifer Treatment (SAT) is a potential reclamation/reuse process consisting of (1) percolation through the biologically active vadose zone and (2) subsequent horizontal transport in the groundwater aquifer. The overall project was to evaluate organics removal during SAT of secondary municipal effluent, as a function of depth and loading rate at the Sweetwater Recharge Facilities in Tucson, Arizona. The focus of this presented study was the removal of bulk dissolved organic carbon (DOC) and three groups of trace organic compounds- ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and alkylphenol polyethoxycarboxylates (APEC) during percolation in the vadose zone. At 3 m and 38 m below land surface (bls), average DOC removals were ～ 60 % and ～ 90 %, respectively. At the 3 m depth, trace organics removals were EDTA (0 %), APEC (～ 30 %), and NTA (～ 75 %); and at 38 m bls they were EDTA (～ 80 %), APEC (～ 93 %) and NTA (～ 98 %). Overall, SAT at the Sweetwater Recharge Facilities exhibited great potential for sustained biodegradation of the monitored organics. Among the substantial organics removals, biodegradation of EDTA was noteworthy. EDTA had been considered recalcitrant, and only its limited aerobic biodegradation had been reported. However, this study found significant EDTA attenuation not only in aerobic zones, but also in anoxic zones where nitrate was removed. Such anoxic EDTA removal was unexplained in terms of the known mechanisms, and EDTA biodegradation under denitrifying conditions was hypothesized. Biodegradation of EDTA under denitrifying conditions has been subsequently demonstrated in a laboratory batch culture study, using soil from a recharge basin at the Sweetwater Recharge Facilities. The results indicate the possibility of EDTA biodegradation in aquatic environments in the absence of oxygen.