Environmental Study of Khartoum Refinery Liquid Effluents

Abstract

The environment is considered as man’s important asset that must be protected for his life support. Unfortunately, the situation is different where oil refinery and petrochemical plants operate. Environmental pollution in these areas poses serious threat to the ecosystem, often with undesirable effects. This study, therefore, was undertaken in order to investigate the quality of the liquid effluents released from Khartoum Refinery and their potential impacts on the surrounding environment. The results of this study provide a better understanding of pollutants load in the effluents generated by Khartoum Refinery and the corresponding potential environmental consequences. Effluents and sediments sampling and subsequent laboratory analyses were performed to evaluate the pollutants levels in both the effluents and sediments. Geological, geographical, and topographic data collection and field survey were conducted to assess the potential environmental impact of the effluent. 9 composite effluent samples were collected from the monitoring pond (MP), which is the final station for the treated effluent inside the refinery, and analysed for physical parameters ( Temperature, pH, TS, TDS, TSS, conductivity, and turbidity), inorganics (alkalinity, hardness, chloride, sulfate, cyanide, and sulfide), nutrients (ammonia, nitrate, nitrite, ortho phosphate, and total phosphorus), and organics (BOD, COD, oil and grease, and phenols). Effluent samples were also collected from the oxidation ponds, (27 composite each from 15 grab samples), that receives the effluent from MP outside the refinery, and analysed for the same parameters in addition to heavy metals (Cr, Cd, Ni, Fe, Pb, Zn, Ba, Ag, Se and Cu), which were also measured in the sediment samples collected from the oxidation ponds A, B, and C (3 samples, each was a composite of 5 grab samples). Based on the results of MP effluent analyses, it was observed that the effluent was alkaline (pH 8.47) and characterized by high levels exceeded the national and international standard limits, for temperature increase (12C), TSS (56 mg/L), conductivity (746.6 µs/cm), turbidity (43.25 NTU), sulfide (9.07 mg/L), ammonia-nitrogen (83.17 mg/L), BOD (41.2 mg/L), COD (611.33 mg/L), and phenols (39.72 mg/L). The rest of the parameters ranged from low to relatively high concentrations. Effluent quality survey in the oxidation ponds demonstrated removal efficiencies of 50%, 55.9%, 71%, 98.9%, 98.6%, 92.6%, 87%, 45.46%, 46.4%, and 99.8% for temperature increase, turbidity, alkalinity, hardness, sulfide, ammonia, BOD, COD, oil/grease, and phenols, respectively. Despite the biodegradation capability of oxidation ponds, it was obvious that, the levels of many effective pollution parameters were increasd to be above the maximum permissible limits. pH, TS, TDS, TSS, conductivity, chloride, sulfate, cyanide, nitrate, nitrite, orthophosphate, and total phosphorus were increased by 16.8%, 574.6%, 638.9%, 278.6%, 289.6%, 1,045.7%, 2,197.6%, 7.7%, 149,200%, 18,323%, 900%, and 129.2%, respectively, besides high residual COD of 333.33 mg/L. Heavy metals were generally found in low concentrations in oxidation ponds effluents, but the sediment was heavily polluted with Ba, Cr, and Cu and moderately polluted with Ni, Zn, and Fe.

Through this research, it is concluded that Khatoum Petroleum Refinery discharge low quality effluent and did not comply with the national and international standard limits in terms of many pollution parameters which could adversely impact the surrounding environment, although some parameters were within the acceptable limits, and recommendations are made for the development of future policies with regard to effluent management and for further research as well.