Study On Nitrogen And Phosphorus Resource Utilization Of The Rural Domestic Sewage

China is a large agricultural country. However, the annual water shortage of agricultural production reached 300x108m3, drought-hit area reached about 2×104km2. In recent years, annual villages and small towns sewage discharge in China exceeded 100×108t. Rural sewage has become potential agricultural irrigation water. The nature of rural sewage is relatively stable, with better biodegradability, without heavy metals and toxic substances. Nitrogen and phosphorus and other substances in wastewater are pollutants for water environment, but they are essential nutrients and valuable resources for agricultural production. However, long-term use of wastewater for irrigation of farmland causes soil compaction and soil anaerobic even soil degradation and plant rot and other problems because of high concentrations of suspended particles and organic matter.This study presented a new idea from "processing" to "resource-based":Sewage organic nitrogen and phosphorus were converted to inorganic constituents which were easy to be used by crops. At the same time, domestic sewage after treatment which completely met the national STANDARS FOR IRRIGATION WATER QUALITY (GB5084-2005) was used for irrigation safely. This approach solved soil degradation and plant rot and other problems, obtained safe water quality for irrigation and fertilizer and achieved sewage resource utilization.This study put forward a new style of nitrogen and phosphorus utilization reactor (short-range nitrogen and phosphorus inorganic reactor,SNPIR) which was consisted of an anaerobic biological filter and a short-time aerobic one after effectively taking natural, economic, social and other factors into account. The treatment system had the advantages of low investment, low energy consumption, easy maintenance and management and good effect. Conclusions of this study in nearly a year were as follows:1. The nitrogen and phosphorus resources effects and operating parameters of SNPIR in different seasons were studied. The feasible HRT of the anaerobic filter was 4h and the feasible HLR of short-range aerobic biological filter was 5.40m3/(m2-d). Now NH4+-N average concentrations of effluent in summer and autumn were 45mg/L and 5mg/L, respectively. PO43--P average concentrations were 6.5mg/L and 5.6mg/L, respectively. Both COD average concentrations were 60mg/L or less. Optimum operating parameters of SNPIR in winter were as follows:The best HRT of the anaerobic filter was 5h and the best HLR of short-range aerobic biological filter was 4.20m3/(m2·d). Now NH4+-N and PO43--P average concentrations of effluent were 88mg/L and 7.7mg/L, respectively, which providing a large number of inorganic nitrogen and phosphate for subsequent utilization. However, COD average concentration cannot met the national STANDARS FOR IRRIGATION WATER QUALITY (GB5084-2005).The influent COD average concentration was reduced to 250mg/ L or less after taking reflux measures. The COD removal efficiency increased around to 75% and effluent COD average concentration decreased to 60mg/L or less after taking warming measures. At this point, the effluent NH4+-N and PO43--P average concentrations were 70.95 mg/L and 5.8 mg/L, respectively.2. Substrate degradation kinetics model of SNPIR in different seasons was derived and established, which was used to guide reactor design, optimization and control. Organic substrate degradation of anaerobic biological filter in summer, autumn and winter all conformed first-order kinetics.In summer and autumn, organic substrate degradation of short-time aerobic biological filter conformed first-order kinetics. In winter, the degradation conformed second-order kinetics.NH4+-N degradation was mainly for short-time aerobic biological filter in summer and autumn, the degradation conformed first-order kinetics. Both absolute error and relative error were minor.The concentration of COD and NH4+-N could be well estimated within a certain error range.3. The performance of separate short-range aerobic biological filter process and that of SNPIR process were compared under the same hydraulic loading in different seasons. The separate short-range aerobic biological filter process had good nitrogen and phosphorus resources effects. However, the separate short-range aerobic biological filter process had lower shock load capacity. The average COD of effluent reduced to 60mg/L when the HLR was low. In the actual engineering design, smaller design hydraulic load can increase the filter area and result in the increase of construction cost. COD average concentration cannot met the national STANDARS FOR IRRIGATION WATER QUALITY (GB5084-2005) in winter. During the running period of nearly a year, the SNPIR process did not appear filler clogging. However, the case of filler clogging appeared repeatedly in separate short-range aerobic biological filter process. Therefore, SNPIR process was more conducive to the popularization and application.