Study On Fe-Mn Oxygen Catalyst And Oxidative Removal Of Ammonium

Excessive ammonia nitrogen is a water pollution problem that cannot be underestimated in the process of urbanization and industrialization.At present,nitrification and denitrification biological methods are mainly used in sewage treatment plants to reduce ammonia nitrogen and total nitrogen.However,the biological methods for ammonia nitrogen removal mainly have shortcomings such as incomplete deammonium removal,poor low temperature effect and large area.Short-range nitrification and denitrification technology（Ammonia nitrogen→Nitrite nitrogen→Nitrogen）has obvious advantages in theory,but how to continuously convert ammonia nitrogen into nitrous nitrogen with high selectivity is still a technical problem to be overcome.In recent years,there have been many reports on the catalytic oxidation of ammonia nitrogen to nitrate nitrogen using air and catalysts,but there has been no report on the catalytic oxidation of ammonia nitrogen to nitrous nitrogen using catalysts and air.In this paper,a precipitation method was used to prepare an iron-manganese oxide-based ammonium oxidation catalyst（hereinafter referred to as"Ammonium catalyst"）,which can catalyze the oxidation of ammonia nitrogen to nitrous nitrogen with high selectivity using air.The ammonium catalyst is used in combination with the ammonium ion sieve developed by the project team for efficient adsorption,enrichment and catalytic oxidation of ammonia nitrogen.The following results were achieved:1.Test the performance of the iron-manganese oxide-based ammonium catalyst.The results show that the ammonium catalyst can catalyze the oxidation of 40 mg/L ammonia nitrogen to nitrous nitrogen with a conversion rate of 75%,and can run normally and stably for nearly 300 h（If the proportion of nitrate nitrogen in the oxidation product is>10%,it means that the material is denatured）.At the same time,SEM,TEM,XRD,XPS and other characterization analysis of the ammonium catalyst were carried out,and the structure-activity relationship between the microscopic morphology,structural properties,elemental composition and catalytic performance of the ammonium catalyst was explored.In addition,a multi-cycle systematic study on the recycling of ammonia nitrogen for more than 150 h was carried out on each factor and level such as sodium bicarbonate concentration,feed ratio,dissolved oxygen,and inlet water temperature.The results showed that when the concentration of sodium bicarbonate in the test system is 6 mmol/L,the feeding ratio is 20 g/L,the dissolved oxygen concentration is 8 mg/L,and the inlet water temperature is 30℃,the iron-manganese oxide-based ammonium catalyst can convert 40 mg/L ammonia nitrogen with a high conversion rate of 85.5%.It can be catalyzed and oxidized to nitrous nitrogen at a high rate,and it can operate normally and stably for nearly 750 h,and the degradation rate of ammonia nitrogen in the whole cycle is up to 0.023 g NH₄⁺-N/day.2.After mixing ammonium catalyst powder with ammonium ion sieve powder in the ratio of 10:1,the performance test shows that the composite material can catalyze and oxidize 40 mg/L ammonia nitrogen to nitrite nitrogen with a high conversion rate of 90%,and it can run normally for nearly 840 h,and the degradation rate of ammonia nitrogen in the first 8 h is increased to0.075 g NH₄⁺-N/day.3.The ammonium catalyst and ammonium ion sieve were formed in a ratio of 2:1 as a composite catalyst.The above materials were filled into the reaction column and passed through a 40 mg/L ammonia nitrogen water body in a continuous flow.When the hydraulic retention time was 5.2 h,the composite catalyst was formed.The catalytic oxidation of ammonia nitrogen to nitrous nitrogen with a conversion rate of 80%can be performed normally for nearly950 h,and the degradation rate of ammonia nitrogen in the first 8 h is increased to 0.105 gNH₄⁺-N/day.