In the coal chemical industry, semi-coke wastewater is widely recognized as "one of the most difficult industrial wastewaters to treat". Generated from the medium-low temperature pyrolysis of low-rank coal, coal gas purification and semi-coke steam quenching processes, this wastewater features three high indicators - high COD, high ammonia nitrogen and high phenol concentration. It contains inorganic pollutants including ammonia nitrogen, sulfides and thiocyanates, together with a large volume of highly toxic and refractory organic substances such as light/heavy coal tar, polyphenols and azo heterocyclic compounds. Conventional biochemical treatment processes cannot handle this wastewater effectively, incurring high operating costs and carrying a high risk of watershed pollution.
Against such challenges, Cycle Columbus has built an industry benchmark project on the Gobi Desert in Xinjiang. It realizes full-process, low-cost, resource-oriented and zero-liquid-discharge treatment of semi-coke wastewater. Meanwhile, pollutants are converted into valuable resources such as crude phenol, ammonia water and oil products, achieving "waste-to-value". Today we will take the Xinjiang Tianyu Coal Chemical Project as an example to break down the real technical solution.
1. Project Overview
This project serves as the wastewater treatment works for Phase I of a Xinjiang coal enterprise's 5 million t/a coal grading, clean and efficient comprehensive utilization project. It is also the first full-process zero-liquid-discharge system for refractory organic wastewater in the semi-coke sector.
Wastewater sources: coal conversion wastewater (semi-coke wastewater, tar hydrogenation process wastewater, etc.)
Commissioning: completed and put into operation in 2020
Treatment capacity: 5,232 m³/d
Influent water quality: COD: 35,000~40,000 mg/L | Ammonia nitrogen: 3,500~5,000 mg/L
2. Technical Route: Five-stage Full-process Zero Liquid Discharge
Cycle Columbus adopts a holistic pollution control approach of "Pretreatment → Biochemical Treatment → Advanced Treatment → Membrane Treatment → Evaporation & Crystallization", enabling resource recovery of water, crude phenol, ammonia water and heavy oil as well as wastewater zero liquid discharge.
Detailed process flow: Semi-coke wastewater → Phenol & ammonia recovery (demulsification & oil removal pretreatment + distillation for acid removal and ammonia stripping + synergistic extraction of phenol and oil) → Biochemical treatment (enhanced denitrification and carbon removal) → Advanced treatment (high-efficiency coagulation for cyanide removal + catalytic ozonation) → Membrane treatment (multi-stage membrane concentration) → Evaporation & crystallization (zero liquid discharge)
3. Environmental Benefits
Annual COD reduction: approx. 22,659 tons
Annual ammonia nitrogen reduction: approx. 2,814 tons
After deploying this treatment system, the Xinjiang project delivers direct environmental benefits of over RMB 34.85 million per year, with cumulative benefits exceeding RMB 210 million.
