Experimental Study On Nutrient Recovery And Tail Water Purification From Tannery Sludge Leachate

The tanning industry is a traditional advantageous industry in our country,which occupies an important position in the development of our country's economy.But a large amount of tanning sludge has also been produced during its development.Tannery sludge will produce high-concentration sludge leachate during the storage and treatment process.Due to the high concentration of ammonia nitrogen,a large amount of refractory organic matter and a certain concentration of heavy metal ions,traditional biological methods are difficult to directly treat and the cost is high.The treatment and disposal of tannery sludge leachate is a difficult problem currently studied at home and abroad.Based on the analysis of the water quality characteristics of the tannery sludge leachate,this thesis proposes to use the magnesium ammonium phosphate precipitation(MAP)method to couple the plant ecology to treat the leachate.Through studying the influence of different reaction conditions on the MAP,and applying the response surface methodology design optimizes the process parameters to determine the best reaction conditions.Uses the phosphogypsum leachate as a substitute for the reagent as the phosphorus source,determines the best process parameters for the MAP method of the phosphogypsum leachate to treat ammonia nitrogen.Combines the chemical equilibrium model Visual MINTEQ and the corresponding the stability constant draws the ion dominant component and the p H diagram of the solution.Selects the tail water after MAP chemical precipitation under different reaction conditions to study the purifying effect of Iris pseudacorus L.on tail water pollutants.The main findings are as follows:(1)Single factor experiment and response surface methodology design are used to study the removal of ammonia nitrogen in tanning sludge leachate by MAP method,including reaction p H value,reaction time,precipitation time,and chemical precipitant dosage ratio,etc.Explore the influence of the above-mentioned influence factors.The influence law of ammonia nitrogen removal rate in wastewater.The best reaction parameters in the MAP experiment were obtained: temperature 25?,p H=9.5,Mg: N:P=1.2: 1: 0.8,stirring rate 200 r/min,reaction time 25 minutes,precipitation time 30 minutes.Under this operating condition,the initial concentration of ammonia nitrogen in leachate decreased from 3000 mg/L to 283.6 mg/L.The removal rate of ammonia nitrogen in the leachate can reach 74.50%.The response surface method was used to methodology and optimize the MAP method to remove the ammonia nitrogen parameters of the leachate.It can be concluded that when p H=9.5,Mg: N: P=1.19: 1:0.8,the ammonia nitrogen removal rate can reach the maximum value of 73.35%,and the phosphoric acid recovery rate is close to 99% in the system.(2)Using phosphogypsum leachate as a source of phosphorus,the MAP method of phosphogypsum leachate was used to study the best parameters of ammonia nitrogen in the tanning sludge leachate through single factor experiments.The effect of different conditions on the removal rate of ammonia nitrogen in the leachate was explored and analyzed.The influence law is combined with the chemical equilibrium model Visual MINTEQ and the corresponding stability constant to draw the diagram of ion dominant components and solution p H.Obtain the best reaction parameters in the MAP method experiment of phosphogypsum leachate: temperature 25?,p H=8.5,Mg: N: P=1.2: 1:1,reaction time 25 minutes,precipitation time 30 minutes.Under these conditions,the ammonia nitrogen removal rate of the sludge leachate can reach 59.7%,and the phosphate recovery rate can reach 79.5%.Compared with the traditional MAP method,the ammonia nitrogen removal rate is reduced by 13.65%,but economic costs are saved.In the study of the recycling performance of the tanning sludge leachate using the MAP pyrolysis method.When the precipitation product was recycled for 5 times,the removal rate of ammonia nitrogen was reduced from 59.8% to 37.5%.While the phosphate in the solution,the remaining concentration is basically maintained in the range of 3.5mg/L to 5.1 mg/L,this method can further reduce the experimental cost.(3)The leachate tail water obtained based on the MAP method still contains a certain concentration of pollutants.The tail water treated under different reaction conditions is selected to study the purification ability of the tail water pollutants in the form of Iris pseudacorus L.The experimental results show that the Iris pseudacorus L.has a good effect on the treatment of nitrogen,phosphorus and heavy metals in the tail water.And the concentration of nitrogen,phosphorus and Cr in the tail water after the treatment basically reaches the pollutant emission limit of tannery enterprises(GB30486-2013).Among them,Iris pseudacorus L.has the highest removal rate of heavy metal Cr,which can reach 87.5%.The developed root system,good adaptability and growth characteristics of Iris pseudacorus L.have good purification ability,and the removal rate of different concentrations of ammonia nitrogen and total phosphate not much differences.