An experimental study of heating tail water treatment of the Lindian geothermal fields in the Northern Songnen Basin

Direct discharge of geothermal tail water mixed with pollutants and impurities to surface water bodies will cause water and soil environmental pollution and waste of water resources. In order to effectively reduce pollutants in geothermal tail water and realize the harmless discharge of geothermal tail water, this paper takes the geothermal heating tail water of the Huayuan Town in Lindian County to the south of Daqing as an example to carry out the experimental study of tail water treatment. Laboratory and pilot tests are conducted on heating tail water treatment by coagulation sedimentation, ultrafiltration and nanofiltration processes. The operating parameters of the geothermal tailwater treatment process are obtained through continuous monitoring. During the stable operation of the combined process, TDS is detected from 5824.7 mg/L to 432.40 mg/L, chloride from 3010.13 mg/L to 194.16 mg/L, fluoride from 1.57 mg/L to 0.31 mg/L, and boron from 4.04 mg/L to 1.62mg/L. The best combined process for determining the geothermal tail water treatment in this area is to use the coagulant PAC with an ultrafiltration operating pressure of 0.1 MPa. The filter membrane Dow NF90 is employed, the operating pressure is 0.60 MPa, and the inflow is 0.8 m³/h. In this study, the TDS removal rate in the laboratory experiment is between 90.21% and 92.49%, the chloride removal rate between 91.63% and 93.02%, the fluoride removal rate is 96.81%, and the boron removal rate is 55.20%−55.69%. The TDS removal rate in the pilot test is 92.62%, the product water chloride is 200 mg/L, the chloride removal rate is 92.57%, the product water boron is 1.77 mg/L, and the boron removal rate is 55.7%. The above experimental results have reached the relevant standard. The test results confirm that the process of treating tail water in the Lindian geothermal field in southern Songnen Basin is feasible. The treatment solves the technical problems of resource waste and tail water recycling in tail water treatment, and it provides a new way for geothermal resource utilization.