A research collaboration between CSIR National Chemical Laboratory, Pune, India and Bernal Institute has demonstrated a cost-effective green methodology to remove ammoniacal nitrogen from effluent streams.

Ammoniacal nitrogen is a measure for the nitrogenous matter as ammonia, a toxic pollutant that can directly poison humans and upset the equilibrium of water ecology systems.  it cannot be treated using conventional biological and physico-chemical methods. Industries such as dyes and pigment, nitrogenous fertilizers and specialty chemicals generate wastewaters with high ammoniacal nitrogen (1500–3000 mg/L) which demand specific solutions for wastewater treatment. Similarly, industries such as fisheries also generate huge volumes of wastewaters with high ammoniacal nitrogen of the order of 400–600 mg/L.

The study demonstrated usefulness of hydrodynamic cavitation for removal of ammoniacal nitrogen with 4-amino phenol as model nitrogen containing organic pollutant. Hydrodynamic cavitation is a process of generation, growth and collapse of vapour cavities leading to intense shear, hot spots and OH radicals. The cavities are generated in a low-pressure region, which collapse when they travel to a high pressure region; resulting in intense shear, as well as very high pressure and temperature in localised regions near the location of collapse. This causes in situ generation of hydroxyl (OH•) radicals in the presence of water. This in situ generation of strong oxidants like OH• radicals, and local hot spots can be harnessed for wastewater treatment.

Initial concentration of ammoniacal nitrogen was found to have significant impact on the extent of removal. Significant improvement, almost of the order of magnitude in removal of ammoniacal nitrogen could be obtained by sparging air or oxygen. The removal of ammoniacal nitrogen by vortex based hydrodynamic cavitation devices was also found to be effective in the industrial wastewaters and results on two different effluent samples of distillery industry indicated up to 75% removal.  The vortex based cavitation devices and aeration may be used alone or in combinations with existing established effluent treatment processes to facilitate water recycling and reuse.

Further research on scale-up/ scale-out (numbering up instead of scaling up) of vortex based cavitation devices is in progress. Comprehensive multi-scale computational models are being developed to explore how the efficacy of vortex based cavitation device in terms of removal of ammoniacal nitrogen varies with scale of the device.

The findings of this study are published in ULTRASONICS SONOCHEMISTRY Journal and is available to read here; “Improving efficiency for removal of ammoniacal nitrogen from wastewaters using hydrodynamic cavitation”