Investigation of biotic degradation of hexabromocyclododecane (HBCDD)

---

Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Çevre Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2018

Öğrenci: İREM KARAHAN

Danışman: İPEK İMAMOĞLU

Özet:

Hexabromocyclododecane (HBCDD), a brominated flame retardant, is used in heat insulation materials, and in furniture, textile, etc. for incombustibility. HBCDD is listed among the persistent organic pollutants (POPs) by the Stockholm Convention in 2013. In this study, anaerobic biodegradation of HBCDD was investigated in laboratory sediment microcosms and mesocosms. The microcosms set up as natural attenuation, biostimulation, contaminant control and sterile set were operated for 20 days. HBCDD biodegradation rate tripled (degradation rate constants were 0.069 day1 vs. 0.221 day-1) with the addition of a carbon source and electron donor in biostimulation (100% removal), when compared to natural attenuation (75% removal). No HBCDD was detected in contaminant control and no trend observed in sterile microcosms, though lower than target concentration was measured initially. Larger scale mesocosm reactors were set up similarly as four sets and operated for 49 days. Biodegradation rate observed for biostimulation was more than triple that of the natural attenuation (rate constants of 0.048 day-1 vs. 0.157 day-1). The order of diastereomer degradation rates was found as β-HBCDD > γ-HBCDD > α-HBCDD. Mesocosm results indicate biotransformation of γ- and/or β- into α-HBCDD at some stage in incubation. Degradation was observed in sterilized mesocosms, indicating a breach of sterility. Sterilization method was found to affect HBCDD, both in terms of loss of total-HBCDD and shift in diastereomers. Results of sterilization control microcosms indicated that addition of mercuric chloride and autoclaving result in unwanted degradation of HBCDD at initial time, with no further degradation taking place throughout incubation period.