Characteristics And Agriculture Utilization Potential Of The Domestic Sewage, Sludge, And Garbage In A County Urban Of Shanxi Province

The production quantities and properties of domestic sewage, sludge, and garbage in a county urban of Shanxi province were studied with a combining method of field investigation, sampling, analysis and determination, and data collection, then the utilization potential of the county urban sewage, sludge, and waste as agricultural resource was analyzed. The results are as follows:(1) The domestic sewage of the county sewage treatment plant increased with an annual increase rate of 7.2%～14.4% since its operation in June 2009 and now it has been overloaded. The sewage-treated quantity is from 53000 m3 to 58000 m3 every month from July to December and less than 50000 m3 every month from January to June in a year. The sewage treatment plant produced less amount of sludge at the stage of trial operation from June to December in 2009, but it increased sharply in 2010, and then increased with an annual growth rate of 3.1%～11.6%. The amount of sludge was from 51t to 59t every month from January to May and from 45t to 54t every month from June to December in a year. The domestic garbage amount of the county urban showed an increasing trend from 2009 to 2013, but the annual growth rate was less than 10%. The amount of domestic garbage generated less than 2000 t every month from January to July, but more than 2000t every month from August to December in a year.(2) The COD content of the domestic sewage showed a slight downward trend, the BOD5 and SS contents both changed slightly, NH3-N and TP contents both showed an upward trend, and TN content was special low in 2010 and also showed an upward trend in the other years from 2009 to 2013 in the county town. The COD content was higher from January to March, lower from April to October, and the lowest was in July. The BOD5 content was higher from January to March and lower from April to October. The TN and NH3-N contents were both higher in March and lower in September. The SS content was higher in January and February and lower in June. The TP content was higher in February and lower in September. According to the " the pollutant discharge standard of urban sewage treatment plant" (GB18918-2002), the COD, BOD5, and SS contents of the county domestic sewage were all over the third level standard, TN and TP contents both exceeded the first level standard, and NH3-N content was higher than the second level standard, therefore, the domestic sewage from the county urban must be treated and then can be discharged into the natural environment. Compared to the basic control project standard value in the "the farmland irrigation water quality standard" (GB5084-2005), the COD, BOD5, and SS contents in the county urban sewage were all over the related control standards, therefore, the domestic sewage from the county town should not be directly used in farmland irrigation.(3) The organic matter content of the county sewage sludge was higher and was between 453.0 g/kg and 502.0 g/kg. The contents of total nitrogen, total phosphorus, and total potassium were 18.9 g/kg-21.6 g/kg, 10.6 g/kg-11.3 g/kg, and 1.6 g/kg-1.8 g/kg respectively. They were all higher than the related nutrition index values in the " sludge disposal of urban sewage treatment plant-agricultural mud" (CJ/T 309-2009). The content of zinc was higher, followed by copper, and then chromium, the contents of cadmium and mercury which were more toxicity were both lower. But the contents of the heavy metals above were all lower than the related limit values of class A sludge in CJ/T 309-2009 standard. Therefore, according to the nutrition ingredient and the contents of heavy metals, the county’s sewage sludge can be safely used as organic fertilizer for farmland after proper pretreatment.(4) The survey results in 2009 and 2013 both showed that the major compositions of the domestic garbage in the county’s urban were animal and plant organic matter and residue soil and both accounted more than 80% of the total domestic garbage. The animal and plant organic matter increased 10.47% in 2013 than in 2009, but the residue soil decreased 11.60%in 2013 than in 2009. The quantities of fabric, metal, paper, wood and bamboo, and plastic increased in varying degrees and the glass decreased and brick and pottery were same. It showed that the recyclable substances and biological organic matter increased, the residue soil decreased in the county’s urban domestic garbage as the time want on. The organic matter content of the domestic garbage in the county’s urban was higher and from 92.7 g/kg to 125.2 g/kg and the contents of nitrogen, phosphorus, and potassium were between 2.45 g/kg and 5.25 g/kg,2.58 g/kg and 3.15 g/kg, and 9.25 g/kg and 12.16 g/kg respectively. These beneficial components were basically at or closed to the corresponding requirements in the " agricultural control standard value of urban waste " (GB8172-87). The contents of copper and zinc were higher, followed by lead and chromium, the contents of arsenic, mercury, and cadmium were lower. But the contents of the above heavy metals were all much lower than the corresponding control index values in the GB8172-87 standard. Therefore, according to the indicators above, the county’s urban domestic garbage can safely become organic fertilizer resource for agricultural utilization.