Swine Waste Treatment

A swine farm discharged wastewater with supernatant COD of 4200-6000 mg/L and NH3-N of 450-850 mg/L. The following three processes were used to treat the waste: (a)

aerobic treatment; (b) anaerobic treatment followed by aerobic treatment; and (c) coagulation, air stripping for nitrogen removal, and aerobic treatment.

The characteristics of the influent and effluent, together with the operational parameters, are demonstrated in Table 6. As shown, the third process provides the best treatment results.

Table 6 Water Quality of Effluent by the Three Treatment Processes for Swine Waste Treatment

Process

Loading (kg/m2-day)

Influent (mg/L)

Effluent (mg/L)

COD

NH3-N

COD

NH3-N

COD BODs NH3-N

1

0.6-0.7

0.08-0.10

4,000

570

700-800 21-25 300-500

2

1.5-2.0*

0.23-0.31*

5,600

850

700-800 23-25 900-1,000

0.8-0.9**

0.5-0.55**

3

2.0-3.0

0.16-0.18

3,600

180

<400 18-21 5-28

Note: 1, Aerobic treatment; 2, Anaerobic+aerobic treatment (*anaerobic treatment, **aerobic treatment); 3, Coagulation+air stripping+aerobic treatment.

Note: 1, Aerobic treatment; 2, Anaerobic+aerobic treatment (*anaerobic treatment, **aerobic treatment); 3, Coagulation+air stripping+aerobic treatment.

Through the coagulation, most of the suspended solids could be removed, which resulted in some COD removal. The solution pH, at the same time, was increased, which provided a favorable operating condition for NH3-N removal by the air stripping process. This nitrogen removal reduced the operating cost for the subsequent biological nitrogen treatment.

In the coagulation process, lime [Ca(OH)2] was used. When dissolved in a water solution, it forms a floc, which can remove the suspended solids by various mechanisms, such as adsorption. A linear relationship was found between the COD removal efficiency and the dosage of lime:

COD removal %=0.01xC

where C is the concentration of lime (mg/L). The concentration of lime ranges from 2000 to 4000 mg/L.

It was found that the solution pH increased from 8.5 to 10.5 when the lime dosage was increased from 500 to 6000 mg/L. A higher pH can significantly enhance the percentage of NH3 in the solution, which can be more easily removed by the air stripping. At pH 8, the NH3-N removal was almost zero; however, it increased to 90% when the pH was increased to 10.5. The operating condition in the coagulation process was then set at lime of 3000-6000 mg/L (dependent on the temperature of the wastewater). In the air stripping process, the aeration time was set at 2-3 hours, pH was at 10-10.5, and the air to water ratio was 10:1.

After coagulation and air stripping treatment, the wastewater had a COD of 26003500 mg/L and NH3-N of 140-180 mg/L. It was then treated by a sequencing batch reactor, whose mixed liquid suspended solids was 3500-4500 mg/L. The sludge loading was 0.5-0.7 kg COD/m2 day. As shown in Table 6, the effluent was quite acceptable.

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