| As a subsidiary product of sewage treatment,sludge output has increased gradually in recent years,and the treatment difficulty has increased gradually.However,according to the development requirements of national economy and environmental protection,sludge treatment needs to achieve the effect of resource utilization while reducing,which undoubtedly brings more severe challenges to sludge treatment.Among the existing sludge,industrial sludge treatment is the most difficult and intense,industrial sludge has a wide range of sources,large output,complexed components and easy to enrich toxicity,which has always been the difficulty and pain point of sludge treatment.In industrial sludge,paper-making sludge is the most representative of this kind of characteristics.The treatment and disposal of paper-making sludge are mainly composting and incineration,but its resource treatment needs further study.The bioleaching method can not only effectively realize the conditioning,dehydration and reduction of paper-making sludge,but also has a high content of organic matter in the treated sludge cake,which can be composted directly to realize the resource utilization.However,for the sludge of food waste after anaerobic fermentation,the ordinary conditioning method can't achieve the function of promoting its dehydration,and the inherent high concentration of ammonia nitrogen in the original biogas slurry,even after conditioning,the biochemical treatment of the filtrate is extremely difficult and the nitrogen and phosphorus elements in the cake will be wasted,which is not conducive to the recycling of resources.The process of struvite crystallization(MAP)can remove ammonium and phosphate from wastewater in the form of struvite crystallization,and has the advantages of rapid chemical reaction and simple operation.After MAP reaction,the supernatant can be easily separated from the sediment,and the biochemical treatment ability can be greatly improved.The dosage of the supernatant in the biological precipitation treatment is nearly 50%lower than that in the lower sediment,and the combined treatment effect is excellent.There are abundant nitrogen,phosphorus and magnesium elements in the bottom sediment after MAP reaction.If the nitrogen element is removed by pyrolysis method,and then magnesium and phosphorus are added into the food waste slurry,the effect of ammonia nitrogen removal can be realized by the re-use of struvite crystal.Therefore,the denitrification conditions of direct calcination pyrolysis and alkali addition pyrolysis are optimized,and the number of times to realize recycling is determined under the optimal conditions,and the reasons for the low sum times under the effect are analyzed.The struvite crystal material which can not be recycled can be used as agricultural slow-release fertilizer,and the reuse of magnesium and phosphorus and the resource utilization of kitchen biogas liquid can be realized at the same time.The conclusions are as follows:(1)The paper-making sludge is treated by conventional conditioning methods,such as iron salt PFS,aluminum salt PAC,ferric iron activated persulfate,etc.the effect of conditioning methods is not good;such treatment methods as ferric chloride combined with calcium oxide and Fenton oxidation can achieve the function of promoting dehydration,but the cost of dosing is high and the utilization of sludge cake resources cannot be realized.Conventional conditioning methods regulate paper-making sludge The effect is not suitable for selection;(2)In addition,20%of inoculum,1%of nutrient and 4h of bioleaching reaction were inoculated under the optimal condition of bioleaching,high efficiency and low cost of paper-making sludge treatment can be achieved;the engineering application potential of bioleaching can be verified under the optimal condition by using the incremental operation mode(pilot test,small plate and frame).The results show that the dewatering performance of paper-making sludge after bioleaching is greatly improved,and the color of filtrate is clear,in which cod is greatly reduced and the water quality is better,The moisture content of sludge cake can be as low as 50%,and the organic matter content is high;(3)When the pH is 9,the reaction time is 90 minutes,and the molar ratio of Mg/P/N is 1.76:1.6:1,the removal rate of ammonia nitrogen is 93.2%,and the content of ammonia nitrogen is reduced from 3005 mg/L to 210 mg/L.Under the best reaction condition,the settling performance of MAP reaction is very excellent,the results showed that COD/TN increased from 5.12 to 38.23,the biochemical property of the supernatant was greatly improved;the supernatant and sediment after MAP reaction were treated by bio precipitation,dehydration and slag removal,and the most important dosage of bio coagulant and coagulant aid was optimized.Adding 0.8%bio coagulant and 1.2%coagulant aid can achieve good dehydration effect.However,for the sediment in the lower layer,the biological coagulant should be increased to 1%and coagulant aid to 2%in order to achieve a relatively close dehydration and slag removal effect;(4)The denitrification rate of struvite crystal can reach about 80%at 150? and 2 h.The ratio of OH-to NH4+ is 1.0,and the temperature and time of alkali heat are controlled at 90? and 2 h,respectively The denitrification rate of struvite crystal can be close to 95%at least,and the removal efficiency of ammonia nitrogen is only 65%when calcined and pyrolyzed twice under the optimal conditions respectively,while the removal efficiency of ammonia nitrogen can still reach more than 70%after four cycles of alkali pyrolysis.The recycling of struvite crystal can be realized by alkali pyrolysis,which can greatly reduce the cost of adding magnesium and phosphorus,and realize the sustainable and resource utilization of MAP reaction. |
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