| The drilling wastewater is one of the main pollutants produced in Oil & Gas drilling fields. It has the water quality characteristics of changeability and complexity of component, and it also has the characteristics of dispersing and movability of drilling operation. Usually its CODcr, chroma and suspended solids are higher than those regulated in standard, and it also contains oil component. According to the characteristics of the drilling wastewater and the implementary conditions in the well, experimental studies on drilling wastewater treatment have been made by a combined method of acidification, neutralization, coagulation and oxidation under various conditions, then the feasibility of the further treatment with cinder used as adsorption has been discussed, and the mechanism of the major process have also been studied.Experimental results show: ⑴Acidification can reduce the CODcr value and the content of suspended solids, and it also can play a good role in demulsification. Neutralization can improve the treatment. Under the experimental conditions, when pH is been adjusted to 2, its CODcr value has been reduced from 1086~10900 mg/l to 211~1399mg/l, whose removal rate is 80.6~87.3%, its content of suspended solids has been reduced from 1.8×103~2.3×104 mg/l to 30~579mg/l with the removal rate of 97.5~98.6%, And the chroma and oil elimination is 95.0~97.8% and 78.0~86.6% respectively. When pH is adjusted to 9, its CODcr value has been lowered by 99～1267mg/l. The oil elimination is 41.7~80.0%. And over 61.8% suspended solids and 40.0~76.9% oil can be removed. ⑵The acidification and neutralization process is effective on the drilling wastewater treatment of high CODcr and suspended solids. And the viscosity has been decreased after the treatment, which helps to the coagulation. And the dosage of flocculants may be reduced greatly. ⑶Coagulation, acidification and neutralization can be done in the same tank. The selection of the flocculants indicates that PFS and PAC are both the perfect flocculants. The removal efficiency of suspended solids, CODcr, oil and chroma can be increased greatly following adequate technique conditions. The wastewater of sludge content <6% is mixed with proper amount of PAC only and the sedimentation proceeds in 15~20min, the wastewater of sludge content about 10% is mixed with PAC and PAM and sedimentates for 20~25min, and wastewater of sludge content 15% need be centrifuged. ⑷After coagulation treatment, those that can not come up to the national drainage standards have been oxidized by Fenton reagent. When the molar ratio of H2O2 and Fe2+ is 8.7:1,their dosage is 6ml/l and 0.5g/l, and the oxidation time reaches 3h, the CODcr removal rate can reach 54%. ⑸The adsorption capacity of cinder is 8.3mg/g in the statistic experiment. The adsorption experiment has showed that the dosage is 25g/l when the wastewater with original CODcr 341mg/l can meet the discharged criteria. ⑹CaO has good demulsification effect. When the dosage exceeds 1.0g/l, the oil removal is increased. And PAC, PFS and CaO have good synergism in coordination.Based on the results of the experimental research, a combined process that can change with the water quality and the requirements of the effluents has been proposed. And the major parameters are also provided. In the end, the elementary process design has been finished, which has practical applied meaning to the treatment of the drilling wastewater.
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