Analysis On Flow Characteristic Of Urban Food-nitrogen Consumption In China

With the growing of urbanization, food consumption structure of China changes significantly, consequently the change of nitrogen flow model has led to tremendous pressure of ecological environment and serious pollution problems in urban regions. Therefore, nitrogen flow characteristics were analyzed useing the method of material flow analysis, analyzing the statistical data, survey data, experiment data and literatures. Main research results were shown as follows.Food consumption is one of the important processes of household metabolism, contributing to the cause of resource consumption and pollution emission. The trend of urban food-nitrogen consumption from 1981 to 2007 based on national statistical data was analyzed. The results showed that, urban food-nitrogen consumption per capita underwent the multiple-periodic change of rise first then fall finally rise again. With the rapid development of economy and urbanization, food-nitrogen consumption per capita will be increasing continuously and has not yet reach a stable level.In order to estimate the nitrogen loss discharged into domestic sewage, analytical study on the Chinese cuisine by simulation test method was introduced. The results showed that there were significant differences among the nitrogen loss of different kind of food discharged into domestic sewage. The proportion of nitrogen loss of rice, vegetable, meat, egg and aquatic products was 16.00%.17.00%.5.00%.7.00%. All these provided the theoretical guidance for making pollutants producing coefficient and optimizing on the process for the Chinese cuisine.Nested design was performed in order to execute experiment on excretion of human, in which mainly related factors affecting the excretion coefficients were examined. The results showed that excretion coefficients of TN,TP were higher than that of COD,BOD5, suggesting that the absorption rates of N, P were lower, and there would be more excretion of TN and TP than that of COD and BOD5 in human excreta when equivalent amount of pollutants were .ingested. Except for COD excretion coefficient, excretion coefficients in female group were higher than those in male group with significant difference (P<0.05), possibly related to gender differences in weight, digestive ability and physical output. Besides, dietary pattern and food arrangement were also important factors affecting excretion coefficient, possibly associated with the levels and existing forms of COD, BOD5, TP, TN in different kinds of food. Therefore, environmental problems induced by the change of dietary pattern should be paid much attention to. The metabolic pathway of nutrients and regulation mechanism of trace elements and exogenous enzymes in different foods in human metabolism should be further studied.The effect of N excreteion for age and BMI of human excreta was investigated. The excretion rate of N element found in urine was 9.16 g/cap/day and 1.33 g/cap/day in faeces. As age increased, it presented with progressive tendency for the N excretetion both in urine and faeces. When BMI gone up, it also led to the increase on N excretetion in urine, but no significant variation was found between the results for human faeces at different BMI groups. The model gave a comprehensive consideration of age, BMI and their interaction effect.Taking urban household as the research object, relationships between household scale, household structure and emission characteristics of domestic sewage were investigated. The results showed that emission characteristics of domestic sewage were closely related to household scale and household structure. As household scale increased, it presented with progressive tendency for pollutant indicators of COD and BOD, due to scale economic effect. While the results of TN,TP were mainly influenced by individual factors. According to some special relationships between pollutants emission and household type, a simple approach of equivalence factor in reference household was proposed for estimating wastewater discharge in different urban household.Based on the systematical analysis of the main factors which affects nitrogen flow in urban household, a model frame of nitrogen flow was established and nitrogen flow in the different scenarios were analyzed. The results showed that food consumption structure was a important factor affecting nitrogen output. Return field rate, sewage treatment rateand nitrogen removal efficiency had different contribution to nitrogen loss discharged into water environment. When return field rate, sewage treatment rate and nitrogen removal efficiency increased by 10 percentage points respectively, nitrogen discharged into water environment would decreases by 11.65%,3%,12.14%.