Tertiary treatment of wastewater for reuse in China

Abstract

China has water shortage problems, especially in its northern region. The accelerated industrialization in the country further compounds the issue. A drastic corrective measure is the South-North Water Diversion Project which will transfer 40 billion m/year of water from the south to the north. Other less dramatic abatement measures are water pollution control and wastewater reuse practices. Severn Trent Services has participated in three projects in China that involve tertiary treatment of wastewater for reuse. One project in Dalian utilizes a fixed-film biological treatment technology (SAF) and a deep bed sand filter (DeepBed) for upgrading a municipal secondary effluent for various industrial reuses. The other two projects employ the same treatment technologies for potential recycle of wastewater for internal reuses in two petrochemical complexes. The SAF treatment technology and DeepBed filter system were proven to be technically efficient and cost effective for upgrading secondary effluent for reuse. The Dalian reuse plant with a capacity of 20,000 m/day flow is producing a high quality reusable effluent with NH4-N at <1 mg/L, TSS < 1 mg/L and COD < 40 mg/L. The treatment plant owner is satisfied with an investment return of less than 3 years payback period. The end users realize about 60% cost savings by using the tertiary treated wastewater in place of potable water. The City of Dalian preserves the precious drinking water for domestic consumption and has sufficient fresh water to entice foreign investments to Dalian. It is a perfect model of a win-win policy. The treatment technology is also applicable to the upgrade of industrial wastewater for reuse. The pilot study at PetroChina Jinxi Petrochemical Plant No. 5 demonstrated that the technology was able to produce a high quality effluent for reuse with less than 1 mg/L of NH4-N, 5 mg/L of TSS and 80 mg/L of COD. If a COD standard of 40 mg/L is absolutely required for cooling water makeup, a physical/chemical treatment would have to be added. PetroChina Harbin Petrochemical Plant has an existing secondary activated sludge process and a tertiary treatment facility, which consists of chemical coagulation, sedimentation, granular filtration and granular activated carbon adsorption. The existing treatment plant cannot effectively remove ammonium nitrogen from the wastewater; plant effluent has an average ammonium nitrogen concentration of about 150 mg/L. The SAF process was able to nitrify the ammonium nitrogen to meet the reuse requirement of 1 mg/L or a discharge limit of 50 mg/L.