| Direct discharge of the pig biogas slurry can caused serious water pollution problems due to the high content of nitrogen and phosphorus in the wastewater.Thus,it is extremely urgent to search for an effective and eco-friendly pig wastewater disposal technology.As a new type of wastewater utilization technology,biological purification process is widely used in wastewater treatment with the advantages of strong ability of wastewater purification,low energy consumption and excellent adaptability.Chlorella with strong ability to resist pollutant can achieve the sufficient removal of nutrients in the pig biogas slurry by absorbing the nutrients and reducing the major pollution indicators such as nitrogen and phosphorus.At the same time,the value-added algal biomass is obtained.Due to the high contents of ammonia nitrogen in the biogas slurry,this study established the zeolite column adsorption and stripping two-step pretreatment method.With the pretreatment method,deep purification of the biogas slurry with high strength ammonia using Chlorella vulgaris was established.The main results are as follows:The optimum NaCl modification conditions of zeolite were obtained via orthogonal experimental design.The results showed that the optimum modification condition of Na Cl was 0.8 mol/L of Na Cl concentration,24 h of modification time and 120 min of treatment time.The impact of these conditions on the adsorption capacity of zeolite were in the order of: processing time>modification time>Na Cl concentration.Based on these inforamtion,the effects of the column height on the removal of ammonia nitrogen from the biogas slurry were studied.The results showed that the removal efficiency of ammonia nitrogen were in the order of: 10 cm>20cm>40 cm,there was no significant difference between 10 cm and 20 cm column heights.However,considering the treatment capacity,the higher one was used to treat the biogas slurry.Furthermore,the effects of connection types on the removal efficiency of the ammonia nitrogen were studied,using combined two 20 cm zeolite columns or one 40 cm zeolite column,the removal rates of ammonia nitrogen were55.18% and 51.53%,respectively.The results showed that the multi-column connection was better than that of the single column.The zeolite column adsorption and air stripping two-step pretreatment method was established to remove ammonia nitrogen from the pig biogas slurry.For zeolite column adsorption: when connect six 20 cm zeolite columns in series as the first step to treat the pig biogas slurry,and ammonia nitrogen concentration of biogas slurry was decreased from 598.04 mg/L to 379.58 mg/L after 45 min.For air stripping: the ammonia nitrogen concentration of the biogas slurry after the first processing was decreased from 379.58 mg/L to 338.02 mg/L when pig biogas slurry was air stripped for 1 h with the aeration rate of 0.273 m3/h and p H value of 11.0 in 30 C of water bath.The effects of different inoculation amounts(5%,15%,25% and 35%,v/v),light intensities(500 Lux,1500 Lux and 2500 Lux),and acidification degree of the biogas slurry(p H4.0,p H5.0 and p H6.0)on the deep purification of pig biogas slurry with high strength ammonia using Chlorella vulgaris were evaluated.The results indicated that the 25% experimental group had the best purification effect,and the removal rates of NH4+-N,TN and TP were 54.14%,29.06% and 60.51%,respectively.2500 Lux was the optimum light intensity.The removal rates of NH4+-N,TN and TP were the highest in 2500 Lux experimental group,which were 55.05%,29.44% and66.51%,respectively.With the increase of the acidity in the biogas slurry,the purification effect was getting worse.The ammonia nitrogen removal rates for p H4.0,p H5.0 and p H6.0 experimental groups were 35.09%,39.83%,50.61%,respectively.The removal rates of TN and TP were the highest in the p H6.0 experimental group,reaching 25.35% and 77.85%,respectively.OD680 in p H4.0,p H5.0 and p H6.0experimental groups were 1.05 times,1.60 times,and 1.73 times as much as that of the 25% experimental group with no acidification.In other words,OD680 after acidification was significantly higher than that of the non-acidification group.The results of this study showed that algae in all the experimental groups were able to survive in as high as 338.02 mg/L ammonia nitrogen slurry and could remove nitrogen and phosphorus in the biogas slurry.The feasibility of treating high ammonia nitrogen biogas slurry by Chlorella was confirmed. |
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