Current technologies and future perspectives for the treatment of complex petroleum refinery wastewater: A review.

Petroleum refinery wastewater (PRW) is a complex mixture of hydrocarbons, sulphides, ammonia, oils, suspended and dissolved solids, and heavy metals. As these pollutants are toxic and recalcitrant, it is essential to address the above issue with efficient, economical, and eco-friendly technologies. In this review, initially, an overview of the characteristics of wastewater discharged from different petroleum refinery units is discussed. Further, various pre-treatment and post-treatment strategies for complex PRW are introduced. A segregated approach has been proposed to treat the crude desalting, sour, spent caustic, and oily wastewater of petroleum refineries. The combined systems (e.g., ozonation + moving bed biofilm reactor and photocatalysis + packed bed biofilm reactor) for the treatment of low biodegradability index wastewater (BOD5/COD < 0.2) were discussed to construct a perspective map and implement the proposed system efficiently. The economic, toxicity, and biodegradability aspects are also introduced, along with research gaps and future scope.

Effect of mixing intensity on biodegradation of phenol in a moving bed biofilm reactor: Process optimization and external mass transfer study.

In this work, an effort has been made to design the process variables and to analyse the impact of mixing intensity on mass transfer diffusion in a moving bed biofilm reactor (MBBR). A lab-scale MBBR, filled with Bacillus cereus GS2 IIT (BHU) immobilized-polyethylene biocarriers, was employed to optimize the process variables, including mixing intensity (60-140 rpm), phenol concentration (50-200 mg/L), and hydraulic retention time (HRT) (4-24 h) using response surface methodology. The optimum phenol removal of 87.64 % was found at 100 rpm of mixing intensity, 200 mg/L of phenol concentration, and 24 h of HRT. The higher mixing intensity improved the substrate diffusion between the liquid phase and the surface of the biofilm. The external mass transfer coefficients were found in the range of 1.431 × 10-5-1.845 × 10-5 m/s. Moreover, the detection of catechol and 2-hydroxymuconic semialdehyde revealed that the Bacillus sp. followed the meta-cleavage pathway during the biodegradation of phenol.

Biodegradation of Congo red dye using polyurethane foam-based biocarrier combined with activated carbon and sodium alginate: Batch and continuous study.

Dyes are an important class of organic pollutants and are well known for their adverse effects on aquatic life and human beings. In this work, an effort has been made to treat the dye-containing wastewater using modified biocarriers in packed bed bioreactors (PBBRs). Lysinibacillus sp. immobilized polyurethane foam combined with activated carbon and sodium alginate was used for the biodegradation of Congo red dye. The optimum values of process time, glucose concentration, and dye concentration were obtained to be 4.0 days, 2.0 g/L, and 50 mg/L, respectively. The maximum dye removal efficiency (RE) of 92.63 % was obtained at the optimized conditions. The continuous PBBR offered a maximum RE and elimination capacity of 90.73% and 10.89 mg/L. d, respectively, at an inlet loading rate of 12 mg/L. d. Moreover, the growth kinetic of Lysinibacillus sp. was well predicted by the Andrew-Haldane model with a regression coefficient of 0.98.

Construction of integrated system for the treatment of Acid orange 7 dye from wastewater: Optimization and growth kinetic study.

In this work, an effort has been made to develop an integrated system (ozonation followed by biodegradation) for the treatment of Acid orange 7 (AO 7) dye. The process parameters such as pH (3.0-11) and ozone dosage (5-25 mg/L) were optimized and obtained as 3.0 and 25 mg/L, respectively to treat the AO 7 by ozonation. Similarly, the process parameters, namely pH (5.0-9.0) and temperature (25-45 °C) were optimized and found to be 7.0 and 35 °C, respectively by biological treatment. Bacillus sp. was found to be the most effective bacteria to remove the AO 7. An integrated system obtained an overall 98.7% removal of AO 7 under optimum conditions. Andrews-Haldane model was best to predict the experimental data and the bio-kinetic constants; µmax: 0.1875 day-1; Ks: 49.53 mg/L; Ki: 133.32 mg/L were obtained. The developed integrated system can be a promising option for the treatment of azo dye containing-wastewaters.

Application of Arjuna (Terminalia arjuna) seed biochar in hybrid treatment system for the bioremediation of Congo red dye.

In the present study, a hybrid treatment system (biological and ozonation) was developed and used in the decolorization of Congo red (CR) dye. The biological treatment was performed in packed bed bioreactor (PBBR) containing Arjuna (Terminalia Arjuna) seeds biochar immobilized with Providencia stuartii, whereas ozonation was carried out in an ozone reactor. The process variables such as temperature, process time, and inoculum size were optimized and found to be 30 °C, 2 48 h, and 3 × 105 CFU/mL, respectively with 92.0 ± 5.0% of dye decolorization. Furthermore, biologically treated effluent was subject to ozone treatment for the decolorization of the remaining CR dye. The hybrid approach reveals almost complete decolorization of Congo red (CR) dye. The kinetic study of microbial growth was examined by Monod model. In addition, the cost analysis estimation for the removal of CR dye was done, and removal per liter was found to be economic.