Characteristics of nitrogen and phosphorus content and analysis of its influencing factors in feces and wastewater of livestock farms in Beijing suburb

Abstract: With the increasing demand of meat products, animal husbandry industry had been rapidly developed in China in the past decade, especially the intensive livestock farms, increased from 16% to 52% in the total amount, from the year 1999 to 2015. Large amount of animal manures have been produced at the same time, which would be serious pollutant sources to the soil and water if they were discharged without any appropriate treatment. However, there is no suitable technology to deal with these wastes to realize recycling of nutrients, e.g. nitrogen (N) and phosphorus (P) in feces livestock farms, which must lead to serious environmental pollution. Because of the increasing amount of feces and shortage of treatment methods, it is meaningful to assess their potential impacts and the influencing factors in the intensive livestock farms, together with the research of treatment methods. Based on the questionnaire inquiry and samples collection, this study collected 41 questionnaires and 218 examples from 19 scale pig farms and 22 scale cattle farms in different districts of Beijing suburb. Then the concentrations of N and P in 86 wastewater samples and 132 manure samples were analyzed. And taking one of the pig farms as an example, the main influencing factors that changed the nutrients content were analyzed. The results indicated that, in the livestock farms investigated in this study, the average contents of the total N (TN) in manures from pig livestock farms and cattle livestock farms were 29.1 and 17.8 g/kg, respectively; the total P (TP) were 15.1 and 6.8 g/kg, respectively. It also suggested that more variation of TN and TP contents were observed in pig manure than that in cattle manure. The average contents of TN in wastewater of pig livestock farms and cattle livestock farms were 892 and 540 mg/L, and the TP were 82.4 and 53.3 mg/L, respectively. That was similar with the manure nutrient content, more variation of TN and TP contents were observed in wastewater from pig livestock farm. The TN and TP contents in pig manure in the large-scale pig farm were mainly attributed to the feed formula. TN and TP contents of manures had less effect on TN and TP contents of wastewater under the current methods of feeding and disposal of manure due to the fodder and water usage. For the solid manure selected in pig farms, content of TN and TP were more influenced by their feed formulas, rather than other factors. While for the wastewater in pig farms, the content of TN and TP were more influenced by their manure management process and feed formulas rather than solid manure even though most of N and P in the wastewater come from solid manure. The seasonal variation of N and P in wastewater were observed in the large-scale pig farms with more than ten thousand pigs and the proportion of inorganic P was increased with the time of wastewater storage. Results of this study provide reference for not only land use of manures and wastewater, but also decision-making on regional gross control of animal feeding and distribution of livestock farming.