Enhanced Petroleum Hydrocarbons Biodegradation and Sulfuric Odor Mitigation from Contaminated Marine Sediment

The petroleum hydrocarbon contamination and offensive odor problem induced by the reduced sulfur compounds are inter-related and should be considered in unison during marine sediment decontamination. Denitrification is considered to be an attractive option for remediating contaminated sediment, since the co-existence of autotrophic and heterotrophic denitrification processes can result in the reduction of reduced sulfur compounds such as acid volatile sulfide (AVS) and thus suppression of odor generation, as well as the biodegradation of total petroleum hydrocarbons (TPH, C10 -- C40). In this study, NO3- was injected into sediment to facilitate the denitrification process. The results revealed that the injection of NO3- was effective in oxidizing AVS through autotrophic denitrification. It was further found that the migration behavior of the injected NO3- was dissimilar in sediments with different AVS contents. In addition, the reduction of NO3- resulting from autotrophic denitrification can influence its preferential migration path in sediment and the possibility of its release into seawater.;The low solubility of petroleum hydrocarbons especially the high molecular weight fractions is one of the key factors that limit its degradation. Thus, this study investigated the feasibility of using microemulsion to increase TPH solubility and enhance TPH degradation during the nitrate-induced bioremediation. Desorption tests revealed that microemulsion could effectively desorb TPH from the sediment phase into aqueous phase. However, the enhancing effect of microemulsion on TPH degradation was still not satisfactory, since the injected NO3- tends to participate in autotrophic denitrification for AVS oxidation instead of heterotrophic denitrification for organic degradation.;Apart from denitrification, sulfate reduction has also been reported to be an important terminal electron-accepting process for regulating TPH degradation in marine sediment. In this study, acetate and methanol were selected as co-substrates to facilitate sulfate reduction and enhance TPH degradation under sulfate reducing condition. It was shown that acetate can effectively facilitate sulfate reduction in the presence of SO42-. And the addition of acetate exhibited a better enhancing effect than the addition of methanol on TPH degradation. After 30 weeks of incubation, approximately 64% of TPH removal efficiency was achieved in the sediment dosed with 10 mmol of acetate. The 16S rRNA clone library-based analysis revealed that the addition of different co-substrates led to distinct structures of the microbial community.;A novel sequential sulfate reduction-denitrification combined with akaganeite (beta-FeOOH) was developed based on the results aforementioned, which demonstrated a promising potential for both TPH degradation and sulfuric odor mitigation from contaminated marine sediment. Results revealed that about 72% of TPH and more than 90% of reduced sulfur compounds (i.e., AVS and S0) were removed after 20 weeks of treatment, and no S2- was released into the overlying seawater throughout the experiment. Sulfate reduction and denitrification were sequentially facilitated by adding acetate in the first treatment phase (i.e., Phase I) and injecting NO3- in the second treatment phase (i.e., Phase II). The integration of sulfate reduction and denitrification led to an effective TPH degradation at broader carbon number ranges. The release of S2- into overlying seawater was effectively controlled by adding akaganeite in Phase I. The injection of NO3- in Phase II was effective in inhibiting sulfate reduction and in oxidizing AVS. The 16S rRNA clone library-based analysis revealed a distinct shift of microbial community structure in the sediment over different treatment phases.