Autotrophic denitrification and inhibitory effect caused by the injection of spent sulfidic caustic in a modified Ludzack-Ettinger process

Abstract

As spent sulfidic caustic (SSC) from petroleum plants contains a high concentration of alkalinity and sulfur compounds, SSC can be applied in sewage treatment system as an electron donor for autotrophic denitrification. In our previous study, the reuse of SSC in the biological nitrogen process was successful, and some neutralization may be required for stable treatment performance. In this study, the pH of SSC was neutralized to 12.0 from 13.3, and the modified Ludzack-Ettinger process was conducted for 90 days with the municipal wastewater. Some toxic effects of SSC on microorganisms were tested via a specific oxygen uptake rate (SOUR) assay. According to the SOUR assay, as compared with no SSC injection condition, SOUR was reduced by approximately 5.4% when 4 mL SSC/L was injected and the effective concentration of a toxicant causing 50% inhibition of the microorganism's activity (EC 50 ) was 22.6 mL/L. During the days of operation, the COD removal and nitrification efficiency were over 53.0 and 98.2%, respectively. The TN removal efficiency was 56.6% and the nitrogen removal rate (NRR) was 0.15 kg/m 3 ½d when the hydraulic retention time (HRT) in the anoxic tank was 3 h. The ratio of nitrifying bacteria was unaffected by the HRT, and Nitrobacter spp. and Nitrospira genus existed at similar ratios. The ratio of T. denitrificans increased after the injection of SSC and was approximately 6.5%. © KSBB

Microbial community structures in conventional activated sludge system and membrane bioreactor (MBR)

“…It suggests that other nitrite-oxidizing bacteria, such as Nitrospira, played an important role for nitrification. In the future study, another probe specified for Nitrospira will be used for a detection of nitrite oxidizing bacteria [16,17].…”

Evaluation of Sulfide-driven Autotrophic Denitrification in a Moving Bed Biofilm Reactor

“…Spent sulfidic caustic (SSC) could also be a potential source of both sulfide and alkalinity for autotrophic denitrification. SSC is a waste product from petroleum refining process and has been studied in few denitrification applications Byun et al, 2008;Park et al, 2008). Neither of these sulfide-generating methods were investigated for this study; however they are discussed in some detail later.…”

“…SSC is a waste product from petroleum refining processes and contains high concentrations of sulfur compounds and alkalinity, as well as some non-biodegradable organics including phenols, benzene and toluene Byun et al, 2008;Park et al, 2008). Biological treatment of SSC was initially proposed by Ragjanesh et al (1995) using Thiobacillus denitrificans for the neutralization and removal of the active sulfides.…”

“…The U.S. Resource Conservation Recovery Act (RCRA) classifies SSC as a hazardous waste, which initially sparked some concerns for microbial inhibition . However, Park et al (2008) suggested that with the small amount of SSC required for autotrophic denitrification, less than 4 mL SSC/L influent, that SSC could be used without meaningful microbial inhibition. Byun et al (2008) demonstrated 90 percent NO 3 -N removal using SSC in an upflow anoxic hybrid growth reactor (UAHGR) and an upflow anoxic suspended growth reactor (UASGR).…”