Treatment of synthetic refinery wastewater in anoxic-aerobic sequential moving bed reactors and sulphur recovery

Treatment of petroleum wastewater contaminated with hydrocarbons and inorganics by anoxic-aerobic sequential moving bed reactors

The present study deals with the biotransformation of virulent petroleum refinery concoction with phenol (750 mg/L), emulsified crude oil (300 mg/L), S^2- (750 mg/L), NH₄⁺-N (350 mg/L) and NO₃^--N (1000 mg/L) in anoxic (A1) - aerobic (A2) moving bed reactors operated in series. The efficacy of the system was analysed through measurement of pollutant concentrations, GC-MS and FTIR peaks of the influent and effluent, and biomass activity studies. The system was able to eliminate the organics and inorganics with more than 99% efficiency at 80 h HRT and 64 h cycle time. GC-MS results revealed breakage of high molecular weight organics to smaller compounds after anoxic treatment. Further treatment of anoxic effluent by aerobic biomass reduced the number of peaks in the final effluent significantly. FTIR results were in accord with the GC-MS results. Heterotrophic activity (HA) of the aerobic biomass was higher than anoxic biomass due to its higher free energy change. Anoxic biomass showed chemolithotrophic activity (CA), suggesting survival in the absence of organics. Gas generated from anoxic reactor consisted of 91% nitrogen, 1% CO₂, 1% H₂S and rest was unaccounted.

Bioremediation of hydrocarbon containing wastewater in anoxic-aerobic sequential reactors

Anoxic-aerobic sequential moving-bed reactors were operated for the degradation of synthetic petroleum refinery wastewater containing phenol (750 mg/L), hydrocarbons (1250 mg/L), S^2- (750 mg/L), NH₄ ⁺-N (350 mg/L), NO₃ ^-N (1000 mg/L) and surfactant as nonylphenol-monoethoxylate (0.2 mmol/L). Kerosene, heavy oil and their mixture were used as hydrocarbon source. Anoxic reactor was a disc-bed reactor and aerobic reactor was moving-bed reactor operated at hydraulic retention times (HRT) of 48 and 16 h respectively at 27 ± 3°C. In anoxic reactor, removals of S^2- and NO₃ ^-N were more than 99% along with 50-60% removal of hydrocarbons and phenol. Removal of organics deteriorated in anoxic reactor with heavy oil in feed having higher density and viscosity. Residual organics and NH₄ ⁺-N were removed in aerobic reactor with more than 99% efficiency. Biomass activity decreased in anoxic reactor and increased in aerobic reactor with an increase in density and viscosity of hydrocarbon in feed. Abiotic study confirmed most of the removals were due to biodegradation.

Enhancing the removal of H2S from biogas through refluxing of outlet gas in biological bubble-column

Biological bubble-column (BBC) is beneficial for elemental sulfur recycle from H₂S, but it's difficult to remove high concentration of H₂S in biogas efficiently due to the mass transfer limitation of H₂S from gas to liquid. In this study, a novel method with refluxing outlet gas in BBC was investigated. The results showed that gas reflux greatly enhanced the removal of high concentration of H₂S (about 5000 ppmv) from biogas. The removal efficiency of H₂S was 88.0 ± 4.1% with the reflux ratio at 1.0, which was higher than those without gas reflux (58.4 ± 1.0%), when the inlet H₂S loading was 143.1 ± 4.5 g/(m³·h). Moreover, the removal capacity of H₂S improved significantly with the increase of the reflux ratios from 1.0 to 4.0 and achieved the maximum at 271.8 ± 2.4 g/(m³·h). This might mainly be attributed to longer residence time and enhanced the mass transfer of O₂ and H₂S from gas to liquid through gas reflux.

Influence of inoculum variation on formation and stability of aerobic granules in oily wastewater treatment

This study provides extensive information about oily wastewater treatment in aerobic granular reactors (AGR) using three different inoculums from sewage, refinery and brewery. Initially, sodium acetate was used for granule formation while AGR with brewery inoculum had maximum granule size (5.44 ± 0.05 mm) and extracellular polymeric substances (EPS: 471.22 ± 2.0 mg/g VSS). But, during emulsified diesel exposure, refinery sludge granules achieved maximum granule size of 3.49 ± 0.01 mm and EPS of 204.85 ± 2.01 mg/g VSS with maximum 67.39 ± 0.15% oil removal efficiency. AGRs achieved 99.9 ± 0.05% chemical oxygen demand (COD) and 91.67 ± 0.14% ammonia nitrogen (NH₄⁺-N) removal efficiencies. Refinery granules remained stable at maximum 310 ± 10 mg/L diesel concentration whereas, the stability thresholds for sewage and brewery granules were 170 ± 15 and 250 ± 10 mg/L, respectively. Brevibacterium paucivorans strain SG001, Micrococcus aloeverae strain SG002 and Staphylococcus hominis strain SG003 were identified as the major pollutant degraders isolated from sewage, refinery and brewery sludge. Micrococcus aloeverae strain SG002 exhibited maximum pollutant removal efficiencies (COD: 99.9 ± 0.01%, NH₄⁺-N: 99.9 ± 0.01%, oil: 61.34 ± 0.85%) among the three species. Re-addition of sodium acetate restored granule structure and stability.

Pitfalls of Wastewater Treatment in Oil Refinery Enterprises in Kazakhstan—A System Approach

The present article is an assessment of wastewater treatment processes in the oil refinery sector in Kazakhstan by comparing relevant experience of developed and developing countries. The legislation in this sphere, the treatment methods, the discharge process and the effect on the environment were evaluated following international and national regulations. In our study, the wastewater systems in three factories in Kazakhstan were assessed. Results show that, even though the environmental regulation in Kazakhstan promotes the polluter pays principle and follows the World Health Organization (WHO) recommendations, the oil refinery plants in Kazakhstan still contain exceeding concentrations of pollutants in their effluents. One issue is that the local legislation allows disposal of wastewater to natural or artificial ponds as long as the concentrations of pollutants in effluents are less than the already existing concentrations in the pond. Consequently, the factories can use ponds with an initially high concentration of contaminants. The high initial concentration of pollutants in the pond water is due to wastewater discharged before the implementation of current environmental regulations. This issue in the current legislation leads to the situation where there is no incentive for efficient wastewater treatment. The national law also lacks regulations regarding which methodology should be used to assess the pollutants in the wastewater. Thus, the control by national environmental office for each enterprise is negotiated separately between the factory and the governmental body. This gives the factory a strong position to define the parameters assessing the effluents. This has led to none of the factories measuring, e.g., heavy metals in discharged wastewater. Total petroleum hydrocarbons (TPH) concentration in wastewater is often exceeded at each factory and there is no analysis done for different hydrocarbon fraction. To overcome the issues described in the present study, we strongly recommended a unified and transparent methodology for the country’s oil refinery industry to assess important pollutants in discharged wastewater.