Migration And Transformation Of Organic Phosphorus In Make-up Water Of Circulating Cooling System

In the circulating cooling system,the use of urban reclaimed water as make-up water has gradually become one of the important measures to save water.However,the reclaimed water is mostly derived from the secondary effluent treated by domestic sewage treatment plant and the water quality is complex.Because foods,beverages and daily chemical products are rich in organic phosphates,organic phosphorus is an important part of nutrient elements in reclaimed water.Phosphorus is one of the important factors causing problems such as scaling,corrosion and microbial growth.Its form and content have certain influence on the safe operation of the system.At present,there are few reports on the migration and transformation of organic phosphorus in reclaimed water in the circulating cooling system and its influence on scaling and corrosion,and there is no consensus.In this paper,a simulated circulating cooling system device was set up,and the organic phosphorus in urban reclaimed water as make-up water was studied as the object.Based on the phosphorus spectrum nuclear magnetic resonance(³¹P-NMR)method,the extraction method of particulate organic phosphorus was established and optimized from extraction agent types,extraction time and extraction amount.Using this method,the migration and transformation of organic phosphorus in reclaimed water from the dissolved state of the aqueous phase to the particulate state of the scaling layer under different operating conditions?temperature,flow rate and concentration ratio?and different water quality conditions?hardness and organic phosphorus concentration?were studied,and the effects of migration and transformation on scaling and corrosion were investigated.The optimization results of the extraction method of particulate organic phosphorus in the scale layer showed that the extractant was a mixed solution of0.25mol/L NaOH and 0.05mol/L EDTA;the extraction time was 20h;the extraction amount was 0.4g.The results of different operating conditions showed that the temperature,flow rate and concentration ratio?COC?had a great influence on the migration and transformation of organic phosphorus.With the increase of temperature and concentration ratio,the migration and transformation rate of organic phosphorus increased gradually.With the increase of flow rate,the migration and transformation rate of organic phosphorus increased first and then decreased.When 50°C,COC6 and0.6m/s,the migration rates of organophosphorus were 3.62%,7.52%and 3.29%,respectively,and the transformation rates were 58.95%,68.49%and 59.28%,respectively.The organic phosphorus mainly decomposed and transformed.The results of ³¹P-NMR showed that the main forms of particulate phosphorus were orthophosphate,phosphonate and phosphate monoester,indicating that the phosphorus in scaling is all the orthophosphate decomposed by organic phosphorus except for the migration of organic phosphorus.The migration and transformation rates of organic phosphorus were higher,the scaling and corrosion rates were greater.Considering comprehensively,the optimal operating conditions of system were 40°C,0.5 m/s and COC4.The results of different water quality conditions showed that the hardness was higher,the migration and transformation of organic phosphorus was greater.When the hardness was TH6,the migration and transformation rates of organic phosphorus were as high as 6.69%and 52.21%.The migration and transformation rates of organic phosphorus decreased with the increase of organic phosphorus concentration.When the concentration of organic phosphorus was 12 mg/L,the migration and transformation rates were only 2.96%and 33.82%.The organic phosphorus mainly decomposed and transformed.The results of ³¹P-NMR showed that the main forms of particulate phosphorus were orthophosphate and monophosphate,and the content of orthophosphate was the highest,indicating that the decomposition and conversion products of organic phosphorus were mainly orthophosphate.The migration and transformation rates of organic phosphorus were higher,the scaling and corrosion rates were greater.Considering comprehensively,the optimal water quality conditions of system were hardness TH4 and organic phosphorus concentration of 12 mg/L.The research results provide data reference for the safe and efficient operation of actual power plant,and lay a theoretical foundation for the wide application of reclaimed water in circulating cooling system,which has important social and economic value.