ABSTRACT
In wastewater treatment plants a hard scale consisting of struvite crystals can be formed, in pipes and recirculation pumps, during anaerobic digestion of wastewater. This study was conducted to evaluate the effect of airflow rate and substrate nature on nucleation type, induction period and supersaturation coefficient during struvite precipitation. A crystallization reactor similar to that designed for calcium carbonate precipitation was used. The pH of synthetic wastewater solution was increased by air bubbling. Experimental results indicated that the airflow increased heterogeneous precipitation of struvite. The susceptibility to scale formation was more important on polyamide and polyvinyl chloride than on stainless steel. In all cases, X-ray diffraction and infrared spectroscopy showed that the precipitated solid phase was solely struvite. No difference in crystal morphology was observed. However, at similar experimental conditions, the particle size of struvite was higher for stainless-steel material than that for plastic materials.
Subject(s)
Magnesium Compounds/chemistry , Nylons/chemistry , Phosphates/chemistry , Polyvinyl Chloride/chemistry , Stainless Steel/chemistry , Water Purification/methods , Chemical Precipitation , Crystallization , Hydrogen-Ion Concentration , StruviteABSTRACT
In the present work, struvite precipitation was provoked by the dissolved CO(2) degasification technique where precipitation occurred following the degassing of the CO(2) by atmospheric air. The impact of the airflow rate and initial solution pH on struvite precipitation were assessed. For initial solution pH<6.5, no precipitation was observed. For initial solution pH>6.5, the phosphorus removal through struvite precipitation could be improved by increasing the airflow rate up to 25 L min(-1), or by increasing the initial pH for higher airflow rates. Compared to traditional techniques of struvite precipitation such as stirring and aeration, the dissolved CO(2) degasification technique is promising since a high amount of phosphorus (approximately 78%) could be removed at relatively short experiment time.
