The Treatment Of The Low C/N Ratio Biogas Slurry Of Dairy Cow Farming By Using Two-stage A_N /O Process

In the rainy mountains of the south, because of topography, climate, limited land resources and other factors, biogas slurry which results of the Manure of dairy farming by anaerobic digestion treatment is easy to form the irrigation characteristics of large and short period when used for agriculture to field. Nitrate, phosphorus and heavy metals deposit in the soil, then lead to new non-point source pollution after the rain leaching. To choose a treatment process has been difficult as the slurry of high NH₃-N and low C/N. The effluent is either difficult to achieve the standards as the environmental requirements of high, or stable up to standard in conditions of high running costs. Combine with the specific circumstances of, it is imperative to Find a treatment which is high pollutant removal efficiency, low investment, high efficiency, low consumption and suitable for biogas slurry.AN/O technology is used more widely and efficiently as a nitrogen removal process. Two-stage AN/O combination makes the removal of nitrogen more thorough with high load, good water quality, Conservation area, etc. The test relies on the transformation of wastewater treatment plant in the Guangda (Group) Yuzui farm. The biogas slurry effluent water reach to the first emission standard "Integrated Wastewater Discharge " (GB 8978-1996). Studies include the acclimation of sludge, treatment effect of the process used directly for biogas slurry, treatment effect of the slurry adding undigested raw dairy farming wastewater, the appropriate adding ratio and the optimal operating conditions, which provide a scientific basis for design and operation of the process.Firstly inoculation method is used to develop sludge, then acclimated sludge by gradually increase the concentration of substrate– ammonia to a certain range when the sludge is mature. During this time, the water effects have been very well.The tests get some conclusions as following.For the high NH₃-N and high concentrations of dairy farming wastewater, there is a problem about out-of-step removal of BOD5 and COD, nitrogen and organic matter, as the easily degradable organic matter is always preferred to be removed in the anaerobic digestion process. The COD left in the slurry is mainly biodegradable organic matter, resulting in pH value of reaction O1 pool down to 6.7 and reaction O2 pool down to 6.36 (which is stable between 5.7 to 6.0 in the later) in the use of two AN/O combination processing for directly biogas slurry. It is seriously affected the growth and metabolism of nitrifying bacteria and the effectiveness of the matrix. The removal of NH₃-N is higher in the system (average removal rate of 83.2%), but the effluent is 52±10 mg/L, far more than the first emission standard "Integrated Wastewater Discharge " (GB 8978-1996) of 15 mg/L. The removal rate of SS is 91.1%, SS of the effluent is 29±8 mg/L, which meets compliance requirements. COD removal efficiency is 80.1%, COD of the effluent is 99±11 mg/L, which doesn't meet the stability standards requirements. To strengthen the system of the capacity of nitrogen, adding undigested raw dairy farming wastewater to the slurry can maintain the suitable habitat conditions of proper pH, so as to achieve the purpose of improving the removal of nitrification in the system. Nitrogen removal of two-stage AN/O combination for biogas slurry is significantly increased after adding the raw water. The average removal rate of NH₃-N is 94.2%,and the highest is 97.2%,when TN removal efficiency up to 79.1%. Under the conditions of NH₃-N in the influent of 302.6±8 mg/L, the average of the effluent is 12.5 mg/L, and Stable under the emission limits. Under the analysis of pollutant removal efficiency for different add-matching ratio, only in the raw water add-matching ratio of 20% to 25% (in this ratio the B/C value is stabilized at 0.52, and B/N value is 2.0), pH value of reaction AN1 pool, O1 pool, AN2 pool and O2 pool can be stabilized at 7.3,7.1,6.9 and 6.7, respectively. It is said that pH to the treatment system is significantly improved after adding the raw water, which create a favorable pH conditions for the removal of pollutants in the slurry.And pH of the systems whose water distribution ratio are less than 20% to 25% are low. it indicates that there may be a water distribution ratio threshold. Only above this threshold the pH maintain stability. The ratio reached the threshold required to achieve 20% to 25%, when the COD load is 0.45kgCOD/kg MLSS.d and NH₃-N load can be stabilized at 0.119 kgNH₃-N/ kg MLSS.d. In addition, adding the raw water in the slurry, COD of the influent gradually increased, but the system still maintained its high removal efficiency, which is stable at 80% to 90%, and averaging 84.6%, indicating that the system are strong to resist the impact of organic matter.Know from the significant analysis of Water distribution proportion, changes in the proportion of raw water to add have some influence on the SS, and significantly affected on the COD, TN, NH₃-N.By orthogonal test, the optimal operating conditions of two-stage AN/O combination are DO of 2.0 3.0mg/L, r of 200%, HRT of 36h. At this time COD, SS, TN and NH₃-N removal rates were 91%, 92%, 75.1% and 95%, respectively. Analysis along the way to decontamination effectiveness of two AN/O combination, it is clear that the contribution rate of the first- AN/O is about 95% of all, when the second-stage AN/O is mainly in the role of supplement and to ensure compliance.Using two-stage AN/O process treating biogas slurry, excepting COD, NH₃-N,SS and pH all can reach"the integrated wastewater discharge standard"(GB8978-1996) level 1 emission requirements that the process is suitable for low C/N Ratio Biogas Slurry of Dairy Cow Farming processing;...