Feasibility of Biological Elimination of COD, Ammonia-Nitrogen and Total Nitrogen from HTS Molecular Sieves Wastewater Using SBR Processes

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 possiHow to cite this paper: Ali, I. L., Karimou, D. H., & Jun, L. (2020). Feasibility of Biological Elimination of COD, Ammonia-Nitrogen and Total Nitrogen from HTS Molecular Sieves Wastewater Using SBR Processes. Journal of Geoscience and Environment Protection, 8, 156-171. https://doi.org/10.4236/gep.2020.82011 Received: December 26, 2019 Accepted: February 22, 2020 Published: February 25, 2020 Copyright © 2020 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
Nowadays, the special development of catalysts used in oil refining processes results in a great economic benefit. Among these catalysts, Hollow Titanium Silicate (HTS) zeolite is a new catalyst (Xia et al., 2016), which is widely used in various oil refining operations. However, 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). Moreover, they are also full of organic pollutants which are not easy to biodegrade (Cao et al., 2019;Boethling & Lynch, 1992). In fact, the persistence of high organic pollutant concentrations may be due to HTS zeolite's physicochemical structure and proprieties which for example do not favor the accessibility of bulk organic molecules to inner tetrahedral framework Ti sites (Boethling & Lynch, 1992;Xia et al., 2017). Thus, 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).
Since wastewaters coming from the production of catalysts have been subjected to strict regulations, several technologies for organic matter removal have been proven to be relatively effective (Herney-Ramirez et al., 2010). Among them are the following methods: physical (adsorption), chemical (micro-electrolysis, photoelectric Catalytic oxidation), photocatalytic degradation, Fenton reagent (Fongsatitkul et al., 2004;Pan et al., 2001), potassium tetraoxo ferrate (II) reagent, and cationic surfactant method, biochemical (aerobic, anaerobic, and aero-I. L. Ali et al. DOI: 10.4236/gep.2020.82011 158 Journal of Geoscience and Environment Protection bic-anaerobic combination process) (Scott & Ollis, 1995;Zheng et al., 2013). However, because of their high energy consumption, their affinity for certain dangerous reagents and therefore their high pollution and complex functioning, most of these methods are sometimes considered as pre-treatment methods. It is also estimated that these methods have high overall costs as much as the quality of their effluents does not always meet discharge standards. In comparison, and as they provide less costly and environmental-friendly solutions, biological treatment methods seem to be more appropriate (Kargi & Dinçer, 1997;Morsyleide et al., 1998;Ren & Zhang, 2010). Moreover, such HTS-sieve wastewaters have low and sometimes high concentrations of ammonia species, and therefore special attention should be paid on them. In fact, SBR nitrification and denitrification, biofilms and other biological treatment processes used to treat this type of ammonia species has shown the difficulty of their effective removal (Morsyleide et al., 1998;Ren & Zhang, 2010). Despite a number of studies on wastewater containing QACs materials (Xiang et al., 2016;Li, 2011;Zhu & Xiao, 2000), it should be noted that very little attention has so far been paid to the biological disposal of HTS type catalysts used by petroleum refineries.
The main objectives of this study are to investigate: 1) whether the HTS molecular sieves wastewater COD can be biodegraded; 2) whether the ammonia-nitrogen (NH 3 -N) and the total nitrogen (TN) removals are efficient; and 3) whether the HTS molecular sieves wastewater COD can be used as a carbon source for denitrification.

Quality of HTS Molecular Sieve Wastewaters
Quality and biochemical properties of HTS molecular sieve wastewaters have been measured using China National Environmental Protection Agency's methods from factory as given by Table 1.
Effects of sample softness and biodegradation are particularly pronounced for the No. 2 wastewater such as BOD/COD ratio is less significant (0.06) in No. 1 wastewater than the No. 2 (BOD/COD ratio = 0.30).

Chemical Parameters and Analytical Methods
During the whole process, the wastewaters' chemical parameters characterized and determined were COD (Chemical oxygen demand), NH 3 -N (Ammonia-nitrogen), TN (Total nitrogen), Cl − (Chlorine ions), and 2 4 SO − (Sulfate ions). Technical details of analyzed parameters and analytical methods are presented in Table 2.

SBR Reactor 1) Experimental apparatus
The main parts of SBR bioreactor ( Figure 1) are made with transparent plexiglass. During this study, the SBR processes involved 3 L and 9 L total volumes reactors both made with transparent plexiglass.  Air stone diffuser is installed in the reactor, and the aeration amount (dissolved oxygen DO) is controlled by adjusting the intensity of the aerator (DO-meter).
The bioreactor is also equipped with related temperature and pH control equipment, and continuous online dissolved oxygen analyzer. An automatic control device, allows the regular schedule of water outlet, water inlet, aeration and idle processes.

Domestication of Municipal Sewage Plant's Sludge
The activated sludge from one municipal sewage plant was selected for SBR experiments. First, the sludge was recovered after precipitation and supernatant removal. Thereafter, water with a small amount of glucose and ammonia-nitrogen was injected into the reactor for stuffy exposure of 2 days. After supernatant removal, the remaining sludge was added to 9 L total volume SBR reactor.
In the early stage of domestication, only glucose water was used in order to facilitate sludge domestication. Then, for each cycle the feed (or intake) water was composed by reducing gradually the glucose concentration while increasing the HTS molecular sieves wastewater concentration. A solution of trace elements nutrient was added, and sodium bicarbonate or phosphoric acid was used to maintain the pH neutral around 7. Each cycle was composed of 4 L feed water and the operation consisted of 8 h aeration phase and 2 hours anoxic phase. The Hydraulic Residence Time (HRT) and the settle steps were both of 2 hours. At the end of each cycle, the supernatant was discharged in respect with a liquid exchange ratio of 44%. For each cycle, feed water and effluent characteristics of COD as well as sludge's SV 30 , MLSS and SVI were tested.

Treatment of HTS-Sieves Wastewater by SBR Domesticated Sludge
At the end of domestication processes, processes of COD removal from the HTS molecular sieves wastewater were tested during three months. The feed water was entirely composed of HTS molecular sieves wastewater, pH was maintained between 6 and 8. Feed water's COD concentrations were changed by cycle and were between 400 and 2900 mg/L. Operational conditions were those adapted to sludge domestication. For each cycle, feed water and effluent characteristics of COD as well as sludge's SV 30 , MLSS and SVI were measured.

Nitrification and Denitrification Properties of HTS-Sieves Wastewater by SBR Processes
To perform nitrification and denitrification processes, and contrary to the previous water quality data, another HTS molecular sieves wastewater with high ammonia-nitrogen concentration was studied by SBR system.

1) Nitrification process
The process involved 9 L effective volume SBR reactor. At the beginning, 3 L of activated sludge and 2 L of HTS molecular sieves wastewater were poured into

Municipal Sludge Domestication by SBR Process
SBR process summary of COD removal rate, sludge properties and the specific parameters are summarized in subsequent Table 3 while Figure 3 and Figure 4 illustrate the results of COD removal efficiency and the sludge performance, respectively.
According to this variability scheme (Table 3,  and 70%, respectively. Thereafter, the sludge domestication continued, and from the 3 rd to the 7 th day, when the ratios were increased gradually by 0.08:1, 0.08:1, 0.15:1, and 0.25:1, respectively, COD removal rate remained stable at 69%. This indicates that sludge domestication started. On the 9 th and 10 th days, the ratio was increased by 0.35:1 and 0.45:1 with appropriate increase of HTS-COD.
The COD removal rate records from mixed wastewater were 85% and 89%, respectively, and the sludge domestication was relatively smooth. The sludge domestication continued and from the 11 th to 15 th day the HTS-COD concentrations were increased with related gradual ratios of 0.5:1, 0.6:1, 0.7:1, 0.8:1 until 1:1 and then the average removal rate of COD in wastewater became 86% which means that the biochemical properties of sludge are good. From 16 th day to 23 rd day, I. L. Ali et al.   the HTS-COD concentrations were gradually elevated than that of glucose-COD with the ratios of 1.2:1, 1.6:1, 2:1, 3:1, 5:1, 5.5:1, 8.3:1 until 16:1, respectively. At the end of reactions, the recorded average of COD removal rate was 83%. Thereafter, the HTS-COD concentrations were increased again and the average removal rate of COD was between 83% up to 92% which indicates that the sludge domestication is effective. This stage achieves the adaptation period of sludge's microbial community to the high organic matter of HTS molecular sieves wastewater.
From above Figure 3, it is also noted that on the 23 rd day, the rate of removal of COD was 92%; on the 24 th day, glucose was no longer added, and 614 mg/L HTS-COD was supplemented. At the end of this step, effluent showed 80 mg/L COD concentration corresponding to 87% COD removal rate. Following some early evidence based on better sedimentation index of the domesticated sludge, we show here (Figure 4) that the degradation of COD is better biochemical treatment performance. This implies enhanced the COD removal rate in HTS molecular sieves wastewater is significantly improved, and an increased contri-

HTS Molecular Sieves Wastewater Treatment by Domesticated Sludge
Some of the specific parameters of feed water, the treatment efficiency and the sludge's properties are summarized in Table 4. The capability of the SBR has been evaluated by following the process of COD removal from HTS molecular sieves wastewater and conducting experiments during three months overall to acquire data.
While the effluent's COD concentration is greater than that of feed water's COD, the initial treatment effect is abnormal in the first few days (Table 4 and Figure 5). In fact, the previous stage of water shortage has caused the sludge to self-decompose which was resulted to an increase of effluent's COD. Thereafter, on 11.05, the COD removal rate began to increase. At the 25 th day, the COD removal efficiency remained more stable reaching about 50%. From the 25 th day to the end of operations, the COD removal rate fluctuated between 47% to 67%. In addition, unlike the case where glucose was a carbon source, and because of the low C/N ratio of wastewater, the COD removal rate can be considered as moderate justifying the difficult biodegradation of COD of this kind of wastewaters.
In fact, this situation is particularly related to the proprieties of high salinity and refractory to treatment of high salt organic wastewater (Cao et al., 2019).
Moreover, the persistence of high organic pollutants concentrations is also favored by HTS molecular zeolite cavities which do not promote the accessibility of bulk organic molecules to inner tetrahedral framework Ti sites (Xia et al., 2017).
In addition, HTS molecular sieves like QACs species have high surface activity and moderate-high activity which are proved to be harmful to microorganisms even at low concentration (Xiang et al., 2016). Furthermore, such species have great influence on the bioavailability and mobility of the other coexisting pollutants (Xiang et al., 2016). Hence, the COD removal rate is an average value which can be considered acceptable knowing that such organic matters, even after pretreatment by physicochemical methods, are very difficult to manage (Herney-Ramirez et al., 2010).
These results could be useful for the petroleum and petrochemical industries in the design of further COD treatment processes of high COD and high salinity wastewaters. In fact, they could be useful to determine additional procedures which can consider the fact to decompose or to reduce HTS surfactants from such wastewaters prior to any COD removal.

SBR Nitrification Process
The results of nitrification process are detailed in Table 5 and Table 6 below.
There are some fluctuations of COD concentrations while the changes of ammonia-nitrogen, nitrate-nitrogen and total nitrogen concentrations are fairly  (Table 5). The slow nitrification reaction can be probably attributed to low temperature. In fact, the registered high sludge concentration can be explained by the death of certain microorganisms due to low temperature conditions. Thereafter, 3 L of wastewater (1.5 L HTS molecular sieves raw water +1.5 L deionized water) and heating rods were added into the reactor. The following analysis of sludge proprieties gave MLSS of 4.6 mg/l and MLVSS/MLSS ratio of 0.9. The aeration was continued at room temperature with dissolved oxygen (DO) of above 2 mg/L and the results of COD, ammonia-nitrogen, nitrate-nitrogen and total nitrogen tests are shown in the following Table 6.     (Chapman, 1996) and this has probably an impact on dissolved oxygen

Denitrification Process
All over the experiment, the results of COD, nitrate-nitrogen and total nitrogen for denitrification were determined as shown in Table 7. In Table 7, the left data are the experimental results without glucose, and the right data are the experimental results with the initial addition of 500 mg/L glucose. For both cases, the COD concentrations decrease somewhat at the beginning from 0 h to 3.5 h, and then increase gradually. The removal rates of ammonia-nitrogen (ammonia-N), nitrate-nitrogen (nitrate-N) and total nitrogen (total N) concentrations were fairly small. The possible reason is that microorganisms in the presence of high concentrations pollutants are hibernated, and eventually some of them are disintegrated so that pollutants and nitrogen species concentrations remain high in the system. Furthermore, the persistence of high organic pollutants concentrations is also favored to HTS molecular zeolite cavities which do not promote the accessibility of bulk organic molecules to inner tetrahedral framework Ti sites (Xia et al., 2017). According to the data of the two situations (i.e. with and without glucose addition), neither case allows the promotion of the denitrification reaction. Therefore, the specific characters of the HTS molecular sieves wastewaters have a great effect on the denitrification efficiency.

Conclusion
SBR intermittent domestication tests of sludge were successfully performed with wastewater from one municipal sewage treatment plant giving 87% COD removal rate. The results of HTS molecular sieves wastewater's COD treatment showed partial efficiency with a removal rate fluctuating around 47% to 67%. In addition, unlike the case where glucose is a carbon source, the COD removal rate can be considered as passable.
The nitrification process showed no changes in NH 3 -N and TN concentrations. Under temperature below 10˚C (winter condition), less than 16% TN was removed. When temperature was increased to 40˚C, TN removal efficiency remained worse. These observations mean that the change in temperature had no effect on the TN elimination. Problems still exist in the choice of suitable operational conditions along with the impact of HTS molecular sieves on activated sludge's surface which hinders the nitrification reaction. Suitable operational conditions such as pH, temperature, DO and low C/N ratio should be redefined after reducing the salinity of this wastewater which probably disturbed activated sludge's efficiency. The renewal of activated sludge capable of oxidizing TN in salty conditions should be an option.
Regarding the denitrification process, changes in NH 3 -N, NO 3 -N and (TN) concentrations were fairly small. This can be the result on one hand of the hibernation of microorganisms because of high concentrations of contaminants which lead to their disintegration and an increase of nitrogen, and one the other hand due to the lack of specific activated sludge which could be capable to oxidize nitrogen species. It can be also concluded that this HTS molecular sieves wastewater's salinity had a great effect on the nitrification and denitrification reactions.
Further studies should be directed towards the choice of specialized activated sludge along with suitable operational parameters which could improve TN removal. Experimental conditions should be changed and additional physicochemical pretreatment on HTS molecular sieves wastewater could help reduce their impact on activated sludge.