Challenges and development trends of emulsified oil removal technology from semi-coking wastewater

Abstract

As the world's largest coal producer and consumer, China actively promotes efficient clean coal use to achieve its “dual carbon” goal. Semicoke, a high-value product from low-temperature pyrolysis of low-rank coal, effectively replaces loose coal and industrial coke. This enables clean low-rank coal utilization while reducing terminal carbon emissions. However, production generates high-concentration organic wastewater with complex components where oil forms highly stable emulsions using micron/nanometer carbon powder as emulsification cores. Emulsified oil typically exceeds 1 g L⁻¹, making it unsuitable for traditional physical separation. Persistent emulsified oil clogs phenol ammonia recovery equipment, causing pipeline scaling and process interruptions that lead to frequent cleaning and maintenance shutdowns. It also significantly inhibits downstream biological treatment, becoming a key near-zero emissions bottleneck. Existing reviews only discuss traditional processes like air flotation and gravity sedimentation. They lack a systematic review of emulsified oil stability mechanisms or removal strategies, nor do they summarize recent applications of advanced functional materials. This review examines current status and development trends of emulsified oil removal from semi-coking wastewater while exploring main sources and distinct formation mechanisms. It comprehensively evaluates novel adsorption materials, membrane separation technologies, and efficient reverse-phase demulsifiers, focusing on removal mechanisms, recent breakthroughs, and key challenges. Ultimately, the analysis aims to facilitate emulsified oil removal technology innovation. Further, this work supports the development of cost-effective treatment systems. Such advancements are vital to promote the industry's green transformation and to aid China's environmental and carbon neutrality objectives.