Abstract
The wastewater from hollow titanium silicate (HTS) zeolite consists essentially of high concentrations of COD and salt, and low ammonia-nitrogen concentrations (or high, sometimes). These chemical pollutants are produced in very large quantities during oil refining and are very difficult to manage on site. In addition, they can be very harmful to the environment when released without any treatment. The aim of this study is to evaluate, on the one hand, the feasibility of removing the COD from HTS wastewater using a sequencing batch reactor (SBR) and, on the other hand, to test the combined effect of nitrification and denitrification under different conditions of treatment on the elimination of Total Nitrogen (TN) from HTS wastewater containing a high concentration of ammonia-nitrogen. SBR intermittent domestication tests of sludge have been successfully carried out with wastewater from a municipal treatment plant with a COD removal rate of 87%. Subsequently, HTS wastewater containing high concentrations of COD was treated by this SBR system. After three months of operation, the efficiency of COD elimination fluctuated between 47% and 67%. Therefore this result could serve as a precursor to a possible second COD bioprocessing. The results obtained during nitrification of the same HTS molecular sieves wastewater with low C/N ratio gave, under an operating temperature below 10°C (winter conditions), less than 16% of total nitrogen (TN) removal. When the temperature was increased to 40°C, the TN removal efficiency remained worse. These observations make it possible to affirm that the change in temperature solely had no effect on oxidation of TN. Thereafter, two SBR devices were used for the denitrification process: one containing HTS wastewater, activated sludge and glucose as carbon source, and the other only HTS wastewater and activated sludge. In both cases, the elimination of TN still low even with an increase in the amount of glucose. These situations show that the TN removal was not only depended on type of carbon source. Based on the results of nitrification and denitrification tests, it may turn out that the activated sludge microorganisms’ activities were affected by the HTS molecular sieves wastewater high concentration as well as the salinity (about 3%) of this kind of wastewater.
Highlights
Nowadays, the special development of catalysts used in oil refining processes results in a great economic benefit
The aim of this study is to evaluate, on the one hand, the feasibility of removing the COD from hollow titanium silicate (HTS) wastewater using a sequencing batch reactor (SBR) and, on the other hand, to test the combined effect of nitrification and denitrification under different conditions of treatment on the elimination of Total Nitrogen (TN) from HTS wastewater containing a high concentration of ammonia-nitrogen
The results obtained during nitrification of the same HTS molecular sieves wastewater with low C/N ratio gave, under an operating temperature below 10 ̊C, less than 16% of total nitrogen (TN) removal
Summary
The special development of catalysts used in oil refining processes results in a great economic benefit. The production and the use of these catalysts generate a large amount (thousands tons/year) of toxic and harmful wastewaters (Cao et al, 2019; Boethling & Lynch, 1992; Xiang et al, 2016) These wastewaters generally consist of high salt, low (or sometimes high) ammonia-nitrogen and high COD concentrations. Their structures contain tetrapropylammonium hydroxide (referred to as TPAOH) which are similar to that of quaternary ammonium salt compounds (QACs) (Tezel et al, 2006; Xia et al, 2017). The external drainage from HTS molecular sieves production device wastewaters should contain a large number of TPAOH and a very high COD concentration in the effluent which are not environmental-friendly (Friedel, 1994; Shon et al, 2011)
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