The feasibility of using spent sulfidic caustic as alternative sulfur and alkalinity sources in autotrophic denitrification

Batch experiments using acclimated sludge to sulfur utilizing autotrophic denitrification were performed to determine the applicability of spent sulfidic caustic in autotrophic denitrification as alternative sulfur and alkalinity sources. Fluorescence insitu hybridization (FISH) analysis showed that the microbial community of β-proteobacteria/ Eubacteria increased from 45% to 69% during enrichment period and nitrate removal reached up to 84% under this enriched sludge condition. In thiosulfate utilizing autotrophic denitrification, the initial condition at a sulfur/nitrate (S/N) ratio of 1.5 showed higher nitrate removal with 95.9%, and nitrate removal could be expressed by a first-order function of biomass concentration if all parameters such as pH, alkalinity and S/N ratio were in the optimum range. In spent sulfidic caustic utilizing autotrophic denitrification, the sulfate formation ratios to nitrate reduction were lower than those in thiosulfate utilizing autotrophic denitrification with a range of 2.65 to 2.78, and nitrate removal was over 95% at 1.0 and 1.5 S/N ratios. For S/N ratios of 1.0 and 1.5, initial alkalinities were sufficient to maintain optimum pH range of autotrophic denitrification. Furthermore, well enriched seeding sludge showed good activity of autotrophic denitrification at pH over 10. Therefore, spent sulfidic caustic could be effectively applied to autotrophic denitrification as an alternative sulfur source and an alkalinity source     

Simultaneous autotrophic & heterotrophic denitrification by the injection of reformed spent sulfidic caustic (SSC) in a pilot-scale sewage treatment plant

Spent sulfidic caustic (SSC), produced from petroleum plants, contains high levels of H₂S and alkalinity. It can be used to denitrify nitrate-nitrogen via a biological nitrogen removal process, as both the electron donor and buffering agent for sulfur-based autotrophic denitrification. However, SSC also contains some recalcitrant organic compounds such as BTEX, so it has to be refined. To remove BTEX, air stripping was conducted in a laboratory scale, and as a result, over 93% of the BTEX were removed within 30min. For the reformation of the refined SSC, Na₂S₂O₃ · 5H₂O, methanol and organic material, produced from a biodiesel production plant, were supplemented, and referred to as new sulfidic caustic I (NSCI), II (NSCII), III (NSCIII), respectively. Thereafter, these products were applied to a modified Ludzack-Ettinger (MLE) process to evaluate their effects on the effluent COD and TN concentrations. As a result, there was no increase in the COD level on the injection of NSC due to the removal of BTEX via air stripping. In addition, compared to no NSC injection, 44.0% more TN was removed with an injection of NSC III, which were the most effective conditions. Thus, the application of NSC to the biological nitrogen removal process was successfully performed. These results may contribute to the development of resource recovery technology.     

Use of spent sulfidic caustic for autotrophic denitrification in the biological nitrogen removal processes: Lab-scale and pilot-scale experiments

Caustic is utilized in petrochemical plants for the removal of hydrogen sulfide (H₂S) from a variety of hydrocarbon streams. Because spent sulfidic caustic (SSC) harbors a high level of H₂S and high alkalinity, it was injected into the anoxic zones of the biological nitrogen removal process as the electron donor and buffering agent for sulfur-based autotrophic denitrificaton. In order to determine the optimal SSC dosage, a modified Ludzack–Ettinger (MLE) process was first conducted at laboratory scale. As the result of the lab-scale experiments, the chemical oxygen demand (COD) increment of effluent and nitrification failure were observed, because SSC harbors barely biodegradable matter, and the caustic content was high, in accordance with the requirements. Thus, during the pilot-scale experiments, a hybrid Bardenpho process was designed and the SSC was neutralized from pH 13.3 to 11.5. These strategies were successful because no COD increment of effluent was observed and the pH of the unit process was stable. The heterotrophic and autotrophic denitrification ratios at each condition were calculated and, as the end product of sulfur-based autotrophic denitrification, the sulfate concentration was monitored.     

乙烯废碱液处理技术研究进展

对乙烯废碱液综合治理过程中油类物质(包括悬浮物)的去除、剩余碱的综合处置及硫化物的处理等几个方面的研究进展进行了综述,指出乙烯废碱液的再生回用是其治理的发展趋势,针对乙烯废碱液的脱硫、脱碳再生技术存在的问题提出了解决方案.     

萃取-吸附法处理辛醇废碱液

辛醇废碱液中含有大量有机物,为此开展了萃取-大孔树脂吸附法处理辛醇废碱液、高效回收有机物的实验研究,实验结果表明:当辛醇废碱液的ρ(COD)为104651mg/L时,以辛醇为萃取剂,在pH=3、辛醇与辛醇废碱液的体积比为0.5、萃取级数为2等条件下,出水ρ(COD)可降至6453mg/L以下,COD去除率达到93.8%以上,萃取剂辛醇可以通过精馏再生循环利用;采用HYA-106大孔吸附树脂对辛醇二级萃取出水进行吸附处理,HYA-106大孔吸附树脂较佳的吸附流速为1BV/h、温度为40℃,此时出水ρ(COD)平均在155~183mg/L之间,COD去除率在97.1%~97.4%之间,单位体积树脂的废水处理量为34BV以上,树脂吸附量在213~215mgCOD/mL树脂之间,吸附-解吸效果稳定;萃取-吸附工艺的COD总去除率达到99.8%以上,最大程度地实现了辛醇废碱液中有机物的回收。     

两步沉淀法处理乙烯废碱液的实验研究

采用苛化及化学沉淀两步工艺对乙烯裂解废碱液的再生进行了研究,考察了影响再生效果的各种条件因素.结果表明苛化反应温度大于80℃,反应时间超过120min,n(CuO)n(Na2CO3)为1.11,CuO沉淀反应温度为80℃,反应时间30min,n(CuO)n(Na2S)为1.451等条件下,再生后的NaOH含量可在8%以上,并且再生碱液的物性以及再生碱液对CO2吸收速率上与新鲜碱基本相同.     

乙烯装置废碱液处理的现状与展望

废碱液的处理是乙烯生产的难点之一。介绍了部分国内外乙烯装置废碱液的处理方法，并对废碱液处理的发展方向提出了看法。     

乙烯碱洗废液处理工艺研究进展

本文介绍了乙烯碱洗废液的产生和组成，分别介绍了目前普遍采用的中和法、氧化法、综合利用法等几类碱洗废液处理工艺的处理过程，比较了几种工艺的优缺点，提出了废碱液处理的研究方向。     

Insight into spent caustic treatment: on wet oxidation of thiosulfate to sulfate

Oxidation of thiosulfate to sulfate is often the rate controlling step during wet air oxidation (WAO) of spent caustic from the refinery and petrochemical industry and exhibits high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). The kinetics of WAO of thiosulfate was studied in the absence and presence of a heterogeneous copper catalyst. Wet oxidation of thiosulfate to sulfate is a free radical reaction exhibiting an induction period. In non‐catalytic oxidation, almost complete conversion of thiosulfate to sulfate was observed in 12 min at 150 °C and in 8 min at 120 °C in the presence of a heterogeneous copper catalyst at 0.69 MPa oxygen partial pressure. The presence of phenol accelerated thiosulfate oxidation. © 1999 Society of Chemical Industry     

化学沉淀法处理乙烯裂解废碱液中的硫化物

采用化学沉淀方法处理乙烯裂解废碱液中的硫化物,寻求到了一种较合适的沉淀剂CuO,并考察了影响沉淀效果的各种因素。结果表明：在沉淀反应温度20℃,反应时间30min,CuO：S=1．5：1(摩尔比)等条件下,S^2-的去除率可达到96．78％,CODCr的去除率达到73．83％。沉淀剂CuO再生后可以循环使用,满足处理要求。     

裂解装置废碱液湿式氧化处理技术的工业应用

介绍了湿式氧化技术处理大庆石化乙烯装置废碱液的工艺原理及开发运行结果。     

催化氧化法处理废碱液中硫化物的工程应用研究

采用催化氧化法处理陕北某煤化工企业乙烯废碱液中的高浓度硫化物,在实验室小试基础上在现场进一步研究了脱硫剂种类、投加量、反应温度、反应时间、曝气量及pH值对硫化物脱除的影响。结果表明,采用脱硫剂3且其投加量5‰,曝气量7 500 m3/h,在60~65℃下反应75 h时,硫化物的脱除率达96%。对硫化物的转化规律进行了初步研究。     

催化氧化法处理废碱液中硫化物的工程应用研究

采用催化氧化法处理陕北某煤化工企业乙烯废碱液中的高浓度硫化物,在实验室小试基础上在现场进一步研究了脱硫剂种类、投加量、反应温度、反应时间、曝气量及pH值对硫化物脱除的影响。结果表明,采用脱硫剂3且其投加量5‰,曝气量7 500 m3/h,在60⁶5℃下反应75 h时,硫化物的脱除率达96%。对硫化物的转化规律进行了初步研究。     

碱渣废水湿式氧化催化剂的研究

选择了Cu、Mn、Cu-Mn-Ce、Cu-Mn、Mn-Ce、Cu-Zn和Cu-Mn-Co七种活性组分,负载于-γAl2O3上,试验制备催化剂并对其用于碱渣废水湿式氧化的活性和稳定性进行了研究,结果表明MnOx/-γAl2O3在反应温度为200℃,室温下氧分压为1.0 MPa,反应搅拌速率为200 r/min,反应时间为2 h的试验条件下具有良好的催化性能;对COD、硫化物、挥发酚的质量浓度分别为16 149、19、3 326 mg/L,pH值为10.0的碱渣废水,经过酸化预处理的中和水通过该催化剂的催化湿式氧化处理,COD的去除率可达86.6%;同时,对MnOx/-γAl2O3负载型催化剂的制备条件也进行了研究和优化,并通过X射线衍射、BET比表面分析和孔径分析等对催化剂性能作了进一步研究,结果表明,550℃的焙烧温度下催化剂的活性成分是呈自发单层分散状态的不同价态的氧化锰,随着反应的进行,5～11 nm范围内的孔体积有较明显的减少,比表面积和孔总体积都有所下降,活性组分有部分溶出。     

乙烯废碱液的苛化法再生工艺研究

采用苛化法对乙烯裂解废碱液进行处理，Na2CO3的苛化转化率在80％以上(平衡反应液的苛化率在90％以上)；废碱液的反复再生和利用对碱液的吸收性能无显著影响，再生碱液可满足吸收裂解气中CO2等酸性气的要求。     

滴流床反应器催化湿式氧化法处理碱渣废水

在自行研制的滴流床反应器中,以MnOx/γ-Al2O3为催化剂,研究了反应温度、进水有机物浓度、液体流率等主要工艺参数对酸化中和预处理后的碱渣废水催化湿式氧化效果的影响。结果发现反应温度和液体流率对氧化反应效果的影响显著:温度升高,反应速率加快;液体流率越慢,反应效果越好。在滴流床处理碱渣废水最开始连续运转的15 h中出水中金属离子溶出现象比较严重,但随后趋于稳定,催化剂的活性并没有受到影响。由于滴流床中高的催化剂-液相比,废水在滴流床中表现出高的降解速率。     

废碱液催化氧化脱硫工艺研究

以硫酸亚铁、硝酸锰为活性物制备铁锰复合催化剂,对乙烯废碱液进行常压空气催化氧化脱硫,考察了反应温度、反应时间、曝气量、催化剂浓度等因素对脱硫效率的影响。结果表明,在反应温度50℃,反应时间20 min,曝气量40 L/h,催化剂浓度10 mg/L条件下,复合催化剂具有很好的催化活性,S2-的转化率达99.7%。     

废碱液催化氧化脱硫工艺研究

以硫酸亚铁、硝酸锰为活性物制备铁锰复合催化剂,对乙烯废碱液进行常压空气催化氧化脱硫,考察了反应温度、反应时间、曝气量、催化剂浓度等因素对脱硫效率的影响。结果表明,在反应温度50℃,反应时间20 min,曝气量40 L/h,催化剂浓度10 mg/L条件下,复合催化剂具有很好的催化活性,S2-的转化率达99.7%。     

化学沉淀法再生乙烯裂解废碱液的研究

采用化学沉淀技术对乙烯裂解废碱液进行再生研究,考察了影响再生效果的各种条件因素。研究结果表明,在反应温度20℃、沉淀反应时间超过30min、沉淀剂CuO与乙烯裂解废碱液中的S2- (以Na2S计)的摩尔比为1 45∶1等条件下,S2-的去除率可达98%以上。沉淀剂CuO经再生后可循环使用,且再生碱液的物性及对CO2 的吸收速率与新鲜碱液基本相同。     

乙烯废碱液再生回用的可行性研究

采用过渡金属氧化物沉淀法和苛化法处理乙烯裂解废碱液得到再生碱液,考察了再生碱液循环使用的可行性.结果表明再生后乙烯废碱液的腐蚀性、结垢趋势以及发泡性能都在允许范围之内,同时循环再生试验结果表明其吸收性能可以满足裂解气碱洗的需要.