Zhangbei Yili Dairy Wastewater Treatment Upgrade, Zhangjiakou (biofilm process plus scum digestion; sludge cut by over 95% at source)

Zhangbei Yili Dairy is a dairy products base of the Yili Group in Zhangbei County, Zhangjiakou, Hebei, producing 41 kinds of dairy products. Cleaning between product changeovers generates high-strength organic wastewater. Under conventional activated sludge treatment the biomass multiplies as it degrades organics, and the plant produced about 4,000 tonnes of sludge a year, all of which had to be hauled off site for compliant disposal at considerable cost and with residual risk of secondary pollution. In 2024 the company invested more than RMB 30 million in upgrading its wastewater treatment system, with the aim of digesting all sludge inside the plant and sending none off site. The upgrade had two pillars: a new scum digestion system, and replacing the activated sludge aerobic stage with a pure biofilm process, in which the micro-organisms that degrade pollutants are immobilised on carriers to form biofilm, cutting surplus sludge at the source. In the upgraded treatment area the floor is clean and there is no sharp odour; equalisation, acidification, sedimentation and aeration tanks run in tandem, and the aeration tank surface is free of the heavy sludge blanket seen before. Operating data show the effect: sludge generation at source is cut by more than 95%, and effluent COD falls below 50 mg/L, low enough for direct discharge to the municipal sewer. The company no longer pays to haul away thousands of tonnes of sludge each year. The small remainder does not leave the site either. It is piped to a scum digestion tank, where anaerobic maturation turns it into highly active biomass that is returned to the treatment system, closing the loop inside the plant. Biogas output has risen alongside the sludge reduction. The project was listed in Hebei's first batch of methane emission control pilots in January 2024: new treatment facilities and a 1 t/h biogas boiler capture gas from the digestion tank, collecting about 305,000 m3 a year, and technical adjustments raised the gas yield from 62% to 82%. The biogas replaces natural gas in steam generation for the workshop, cutting both energy costs and methane emissions. For a sector where dairy wastewater is highly biodegradable but sludge disposal is a hidden burden, the combination of biofilm-based sludge prevention, scum digestion with biomass return and biogas substitution turns waste from the treatment stage into recyclable biomass and energy on site. Sources: Hebei Daily, "Dairy firm re-engineers its process to squeeze the last drop out of sludge" (9 September 2026, by Guo Xiaotong); Zhangjiakou Municipal People's Government, "Zhangbei County advances its carbon-peaking pilot" (https://www.zjk.gov.cn/content/gzbs/239745.html). Image: aeration tank in the wastewater treatment area of Zhangbei Yili Dairy, with technicians sampling at the tank edge and digestion tanks behind (source: Hebei Daily, photo by Guo Xiaotong).