Marshall Foods Corporation of the United States is an internationally renowned multinational fast-moving consumer goods company that produces and sells various famous brands of chocolate, candies, and pet food worldwide. Mars Food (China) Co., Ltd. is a wholly-owned subsidiary of Mars in China, owning numerous well-known domestic and international brands, including Dove Chocolate, Snickers Chocolate, M&M’s Chocolate, Rainbow Juice Candy, Crispy Rice (Crispy Rice Milk Chocolate), Purina Dog Food, and Weijia Cat Food. Mars began producing pet food in 1935, making it the first company in the world to specialize in pet food production. In 1993, it entered China, becoming one of the earliest pet food manufacturers to enter the Chinese market. Mars China established its first pet food factory in Huairou in 1995. Today, Mars sells a wide range of pet care product brands across the national market, including Purina Dog Food, Weijia Cat Food, Xisha Dog Food, JiaBei Dog Food, MeowCare Cat Food, Yiwai Dog Food, and Jieshan Cat Cat Food. Its product categories include dry food, wet food (fresh packs and canned), snacks, and care products, offering the most comprehensive and diverse range of pet care products in China. The wastewater project in question is related to the food processing wastewater from the Huairou Mars pet food factory.

Mars Foods’ existing wastewater treatment plant employs a pretreatment-anoxic-aerobic process design. Current operations face challenges including inefficient sludge removal in oil separators, unstable UASB reactor startup, and suboptimal dissolved air flotation performance. The original process design shows significant operational discrepancies and no longer meets current requirements. Considering reclaimed water reuse needs and existing infrastructure conditions, we propose process upgrades to achieve compliant reclaimed water reuse standards. This comprehensive solution begins with collection wells and encompasses system-wide process design, equipment modifications, electrical upgrades, automation system enhancements, maintenance protocols, and equipment commissioning.

The designed wastewater treatment capacity is 80 t/d, with the designed influent water quality as shown in the figure on the right. The low temperatures in northern winters pose significant challenges to the stability of biochemical treatment. As an international enterprise, Mars (China) has imposed multifaceted requirements on our design and construction that exceed industry standards, and mandated that the treated water quality meet the provisions of China’s “Water Quality Standards for Landscape Environmental Use of Reclaimed Urban Sewage” GB/T18921-2002 and “Water Quality Standards for Landscape Environmental Use of Reclaimed Urban Sewage” GB/T18920-2002. The final treated water will be used for landscape irrigation and landscaping throughout the plant.

Through experimental studies and systematic evaluations, this project adopted multiple wastewater treatment methods—including anaerobic, aerobic, and anaerobic-aerobic processes—for food production wastewater. While these methods effectively reduced CODcr and BOD5 levels to varying degrees, they demonstrated limited efficacy in treating animal and vegetable oils. Given the high oil content in the wastewater from the enterprise, a pretreatment approach combining oil separation and high-efficiency dissolved air flotation was implemented to remove most oily contaminants before proceeding with aerobic biochemical treatment. Following system commissioning and trial operations, the wastewater treatment system achieved stable performance, with treated effluent meeting all discharge standards.