Shortcut Nitrification-denitrification For Biogas Slurry Of Low Carbon Nitrogen Ratio In Pig Farms

Piggery wastewater is a kind of wastewater with high ammonia nitrogen,high turbidity and high COD_Cr concentration.The methods of cleaning manure has been changed from the previous flushing of manure and blisters into a dry and wet separation with a recyclable carbon source.The piggery wastewater is generally treated with traditional anaerobic digestion.However,the degradation of pollutants is not synchronized with the removal of ammonia nitrogen in the process of anaerobic digestion,which decrease the biodegradability of anerobic effluent(BOD₅/COD_Cr),destruct the ratio of carbon to nitrogen seriously,and increase the difficulty of subsequent aerobic treatment.The swine biogas slurry with low ratio of carbon to nitrogen is difficult to treat by traditional biological denitrification process,because of the disadvantages such as high energey consumption,poor denitrification effectioncy,carbon complemented and alkali solution added.However,the new short-cut nitrification and denitrification technology can save 25.0%of the oxygen demand and even not need extra alkali solution in the aerobic section.It can also save 40.0%of the organic carbon demand in anoxic secton.Besides,sludge production is greatly reduced;and the nitrite denitrification reaction rate is 1.5 to 2.0 times of nitrate denitrification rate,which makes up for the defects of traditional biological denitrification.Therefore,in this paper,short-cut nitrification and denitrification technology is used to treat low-carbon-nitrogen-ratio biogas slurry.The experimental water quality,biodegradability of biogas slurry,and carbon-nitrogen ratio are very low.To achieve efficient removal of total nitrogen,external carbon sources must be added.In addition,agricultural wastes such as pig manure,corn cobs,and corn stalks were selected as the external carbon sources near the experimental site in accordance with local conditions.The effect of the removal of various contaminants from the system was investigated,and the effluent was subjected to advanced flocculation treatment.Experimental results were shown in the following:?1?At room temperature,activated sludge from domestic sewage treatment plants was used as inoculation sludge to control the reactor dissolved oxygen to 4.0mg/L-6.0mg/L,pH was 7.7±0.2,and a short-run nitrification reactor was successfully started in 15days.During the start-up period,the ammonia nitrogen conversion rate was above80.5%,and the nitrous oxide accumulation rate was stable at over 70.4%,which enabled short-cut nitrification system to be stable.?2?In this experiment,the removal efficiency of pollutants was studied from three aspects:HRT,ammonia nitrogen loading,and reflux ratio.The experimental results showed that the removal efficiency of TN and ammonia nitrogen can meet the emission standards in the conditions of the reflux ratio was 400.0%,HRT was 12 days,and the ammonia nitrogen load was 0.2-0.3kg_NH3-N/kg_MLSS/d and the removal rate of ammonia nitrogen,TN and COD_Cr is 96.4%,78.1%and 77.4%.the average ammonia nitrogen,total nitrogen and COD_Cr of effluent were 40.9mg/L,305.8mg/L and352.8mg/L.?3?The experiment of adding pig manure to optimize the denitrification test showed that the pig manure as the external carbon source,the ammonia nitrogen,total nitrogen and COD_Cr concentration of the effluent were 92.5mg/L,456.9mg/L and 605.3mg/L respectively,and the removal rates were 91.8%,66.7%and 51.1%respectively.The removal rate of COD_Crr was reduced,because some of the pig manure contained some difficult bio-degradation.The COD_Crr increased and the total nitrogen removal rate increased by 13%and the total nitrogen concentration of effluent was lower after HRT extension.In view of the high concentration of COD_Cr and TP in the effluent,the effluent depth coagulation test was carried out,and four kinds of flocculants were treated with polymerized aluminum ferric sulfate,polyaluminosilicate,aluminum chloride and PAC.The results showed that the removal of COD_Crr and TP was best by aluminum chloride.When the dosage was 0.5g/L,the effluent COD_Cr and TP were all reachable.The discharge indicated that the biogas slurry of pig farms could reach the discharge standard of livestock and poultry pollutants?GB18596-2001?after anoxic aerobic coagulation treatment.?4?The optimal experiments of straw enhanced nitrogen and nitrogen ratio denitrification showed that adding straw could enhance the removal efficiency of total nitrogen in the short range nitrification and denitrification system,and the ammonia nitrogen,total nitrogen and COD_Crr concentration in the effluent were 52.3mg/L,230.2mg/L and 490.5mg/L respectively,and the removal rates were 94.6%and 72.1%respectively.52.1%.The ammonia nitrogen,total nitrogen and COD_Cr concentration in the effluent of the system were 45.4mg/L,200.2mg/L and 570.8mg/L respectively,and the removal rates were 95.4%,83.8%and 52.1%respectively.Comprehensive analysis shows that the addition of corn stalk in the regulation/anoxic tank can enhance the removal of ammonia nitrogen and total nitrogen in the system.Low carbon and nitrogen ratio;shortcut nitrification-denitrification;slow release carbon source;sustained-release carbon source...