Experimental Study On Induced Crystallization-ion Exchange Technology For Recovery Of Ammonia Nitrogen In Domestic Wastewater

Nitrogen recycling is one of the fundamental concepts of an ecologically sustainable civilization.Researchers have often proposed nitrogen recycling in domestic sewage.However,due to a much larger ratio of volume of domestic sewage to concentration of pollutants,the lack of cost-effective recycling methods is prominent.The ion exchange(IE)method has a wide range of applications in water softening,but it is rarely used in domestic sewage.This article proposed the utilization of induced crystallization as a pretreatment,due to low concentrations of calcium and magnesium ions in sewage,and induced crystallization-IE to remove and enrich low concentration ammonia nitrogen in domestic sewage.This research studied the technical feasibility of induced crystallization-powder resin covered filter/ion exchange resin fluidized bed process,and explored the feasibility of struvite crystallization method and freezing crystallization method for ammonia nitrogen recovery in ammonia nitrogen enrichment solution.The results showed that:Firstly,through static experiments,Na-type powder resin,H-type powder resin,natural zeolite,001×7 and D113 ion exchange resins were selected,and Na-type powder resin and 001×7 ion exchange resin were selected as the preferred ion exchange agent.Na-type powder resin has the advantages of faster ion exchange rate and higher ion exchange capacity compared with 001×7 ion exchange resin.In addition,experiments on factors influencing the removal of ammonia nitrogen by Na-type powder resin revealed that both pH and divalent cations had a great effect on the ion exchange of ammonia nitrogen.Secondly,a small test was carried out on a filtered covered by powder resin,and the results showed that the maximum ion exchange capacity of the Na-type powder resin can be achieved when the film thickness was about 1.5 mm.The pilot test of ion exchange column and the pilot application of ion exchange fluidized bed 100 L·h-1 were conducted and results showed that ion exchange resin fluidized bed process in domestic sewage is feasible.A laboratory test was carried out on the two processes of induced crystallization-powder resin covered filter/ion exchange fluidized bed,and the results showed that the pretreatment of induced crystallization increased the treatment water volume of the ion exchange column by about 50 BV,which was an increment of 62.5%.The increase rate of the treated water volume of the powder resin was only 15.4%.The feasibility analysis of the two processes was carried out.The induced crystallization-ion exchange fluidized bed technology was more practical and mature compared with the powder resin covered filter.Finally,the feasibility of ammonia nitrogen enrichment solution with struvite crystallization method and freezing crystallization method was discussed.The results showed that when the pH was adjusted to 10,struvite crystals with higher purity can be produced.The freezing crystallization method can produce ammonium chloride crystals when the temperature is reduced,but the required ammonia nitrogen concentration was high,and its feasibility still needs further experimental analysis.