Recovery of Free Ammonia from Dirty Cooling Water at Effluent Treatment Plant

Abstract

Ammonia is a highly irritating gas which is corrosive in nature and causes perilous effects both on environment and human health if its amount increases the safe limit. Upon contact with humans by either inhalation or ingestion, it causes damage to skin, eyes and the respiratory system. It causes eutrophication, soil acidification and disturbs the eco-system if discarded in environment. Therefore, its removal from the effluent water streams of all industries is a pressing need. Our aim is to reduce the amount of Ammonia from 800 to 20 ppm in the effluent water stream of NP Plant of Pak-Arab Fertilizers. By doing so, the effluent water composition matches the standards set by the Environment Protection Agency. Firstly, the dissolved Phosphate and Fluoride impurities are removed by the addition of CaO in water, settling of hence formed insoluble salts takes place in a set of clarifiers, sludge thickener and filter press are installed to dewater the sludge and obtain a solid cake. A heat exchanger is employed to increase the temperature of supernatant water stream, in order to meet the desired stripper conditions. An air stripper, with counter-current flow type, reduces the amount of ammonia in effluent water to 20 ppm. After that, the stripped ammonia moves to an absorber column in which Sulphuric acid is used as an absorbent, resulting in a lean solution of Ammonium Sulphate. The effluent air stream from absorber column has 12 ppm of Ammonia. Hence, by the use of this Ammonia removal and recovery process the amount of ammonia in both effluent air and water streams meets the restriction of EPA and falls well within the safe limits.