Study On Granulation Technology Of Struvite Crystal In Anaerobic Digestion Liquid From Train Toilet Wastewater

Phosphate recovery from wastewater is one of the major concerns for environmental protection and providing a new source of phosphorus fertilizer.Phosphorus is an essential nutrient for various life activities of animals and plants,and it is a valuable resource that cannot be regenerated.The rapid development of industry and agriculture has increased the demand for phosphorus.While the phosphorus resources are consumed in large quantities,a large amount of phosphorus in the wastewater is discharged into the water body,which not only causes the eutrophication of the water body,but also cannot be recycled.Therefore,it is of great practical significance to recycle phosphorus as a resource material from wastewater.The fluidized bed struvite crystallization method can not only remove phosphate,but also produce non-toxic phosphate fertilizer.However,the existing research lacks the research and discussion on the applicability of the technology of train collection wastewater.This study presents a comprehensive investigation on the treatment of train toilet wastewater via struvite precipitation using a fluidized bed reactor(FBR).Through the small test and model simulation to optimize the process parameters of the struvite crystallization method,the effect of the fluidized bed struvite crystallization method on the treatment of train collecting wastewater was studied,comparative analysis of the economics and feasibility of phosphorus removal by coagulation sedimentation and struvite crystallization.Jar-test experiments were first conducted to investigate effect of pH and molar ratio of Mg/P on the removal of phosphate.Results showed that the optimized removal efficiency of phosphate reached 98%at pH of 9 and Mg/P ratio of 1.3:1.Supersaturation index and precipitation potential was calculated using a geochemical software PHREEQC.The predicted removal efficiency of phosphate fitted well with the experimental values.Struvite had the highest potential to precipitate than the other possible precipitations.Furthermore,a long-term experiment was carried out at pH of 8.5-9,Mg/P ratio of 1.2:1,upflow of 400 cm/min for 4 months.The concentration of phosphate in the inflow ranged from 50 to 300 mg P/L.A high removal efficiency of phosphate was achieved which was approximately 85%.The struvite pellets obtained was sieved and about 75%of the pellets was larger than 1 mm.The pellets were mainly composed by struvite being characterized on a SEM-EDS and an XRD.The results showed that the removal of phosphorus by coagulation sedimentation required a certain cost,and the removal of phosphorus from the fluidized bed struvite crystallization could obtain considerable profits.The coagulant has no effect on the removal rate of nitrogen and phosphorus in the reaction of struvite crystallization,and the coagulant has poor effect on the removal of ammonia nitrogen and phosphorus in the wastewater,and the economic and feasibility of coagulation and phosphorus removal are all not as fluidized bed struvite crystallization.This indicates that phosphate recovery from the train toilet wastewater can be effectively achieved by struvite precipitation using a FBR.In summary,through process control,effective treatment of train toilet wastewater can be achieved and struvite pellets with sustained release properties can be recovered.