Nitrogen removal from coke making wastewater through a pre-denitrification activated sludge process

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Industrial Microbiology

Background:

• Coke production generates wastewater with high nitrogen content, requiring treatment to meet stringent environmental regulations like the Industrial Emissions Directive (IED).
• The IED mandates a total nitrogen (TN) concentration below 50 mg/L in treated effluent from coke production facilities.
• Conventional treatment methods may struggle to efficiently remove nitrogenous compounds and other pollutants from this complex wastewater.

Purpose of the Study:

• To investigate the optimal operational parameters for an anoxic-aerobic activated sludge pilot plant treating coke production wastewater.
• To determine the conditions necessary to achieve an effluent TN concentration below 50 mg/L as required by the IED.
• To assess the removal efficiency of key pollutants, including ammonia, phenol, and thiocyanate (SCN⁻), and identify factors affecting denitrification.

Main Methods:

• A 1 m³ anoxic-aerobic activated sludge pilot plant was operated with coke production wastewater.
• Loading rates for soluble chemical oxygen demand (sCOD) and total nitrogen (TN) were varied.
• Alkalinity was added to facilitate ammonia removal.
• Effluent quality, including TN, ammonia, phenol, and SCN⁻ concentrations, was monitored.
• The soluble chemical oxygen demand to total nitrogen (sCOD:TN) ratio was analyzed for its impact on treatment performance.

Main Results:

• Ammonia (NH₄⁺-N) removal efficiency reached 96% after alkalinity addition.
• Phenol and SCN⁻ removals were consistently high (96% and 100%, respectively), with both utilized as carbon sources for denitrification.
• A soluble chemical oxygen demand to total nitrogen (sCOD:TN) ratio greater than 5.7 was identified as essential for achieving an effluent TN below 50 mg/L.
• Nitrite accumulation was observed, indicating potential disruptions in the denitrification process under tested conditions.

Conclusions:

• The anoxic-aerobic activated sludge process is a robust and reliable technology for treating coke production wastewater to meet IED requirements.
• Maintaining an influent sCOD:TN ratio above 5.7 is critical for effective nitrogen removal, or alternatively, the addition of an external carbon source should be considered.
• Monitoring influent conditions to ensure an adequate sCOD:TN ratio is necessary for optimizing the denitrification pathway and preventing process disturbances.