Emission Standards for Wastewater from Thermal Power Plants

Thermal power plants — including coal-fired, oil-fired, gas-fired, and cogeneration facilities — generate a wide variety of wastewater streams throughout their operations. These include circulating cooling water blowdown, chemical water treatment regeneration wastewater, boiler acid-cleaning wastewater, flue gas desulfurization (FGD) wastewater, oily wastewater, and ash transport water. 

If discharged untreated into natural water bodies, these effluents pose significant threats to aquatic ecosystems and public health. To address these risks, regulatory frameworks worldwide have established comprehensive, multi-tiered systems of emission standards governing wastewater discharge from the thermal power sector.

The Chinese Regulatory Framework

In China, the primary legal basis for thermal power plant wastewater discharge is the Integrated Wastewater Discharge Standard (GB 8978-1996), which specifies maximum permissible concentration limits for 69 water pollutants based on the discharge destination and applicable tier. For wastewater discharged into municipal sewers, the Wastewater Quality Standard for Discharge into Municipal Sewers (GB/T 31962-2015) imposes additional requirements. 

Furthermore, FGD wastewater from wet limestone-gypsum desulfurization systems must comply with the Water Quality Control Indicators for Wastewater from Limestone-Gypsum Wet FGD in Coal-Fired Power Plants (DL/T 997-2020). Boiler wastewater discharges are also subject to the Environmental Quality Standard for Surface Water (GB 3838).

The selection of applicable standards depends critically on the discharge destination. For direct discharge into surface waters, local standards take precedence where they exist; in their absence, GB 8978-1996 applies. Discharges into sea areas must meet the Sea Water Quality Standard (GB 3097-1997), while discharges into municipal sewers are governed by GB/T 31962-2015. Notably, local standards are generally more stringent than national ones, often imposing lower concentration limits and additional control parameters such as total nitrogen.

Key Pollutants Under Control

The primary pollutants subject to discharge limits include pH, suspended solids, chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD₅), ammonia nitrogen, total phosphorus, petroleum oils, sulfides, fluorides, volatile phenols, total dissolved solids, and priority heavy metals such as total mercury, cadmium, arsenic, and lead. Concentration limits for these parameters vary according to discharge destination and the applicable standard tier.