Organic Waste Recycling

414 Organic waste reuse and recycling: technology and management

Example 8.3

A sandy soil with an infiltration capacity of 90 cm/day will be used for
wastewater treatment and renovation through the rapid infiltration (RF) process.
Based on a laboratory study and Figure 8.1, the following wastewater
application modes were found suitable for the RI operation.

Average wastewater application rate = 30 m/yr

Application period = 4 days

Resting period = 10 days

Determine whether this RI operation will create flooding condition or not.

Wastewater cycle time = 4 +10 = 14 days

Number of cycle per year = 365/ 14 = 26

Wastewater application per cycle = 30/26 = 1.15 m/cycle

Wastewater application rate = (1.15 m/cycle)/ 4 days

= 0.29 m/day-cycle

= 29 cm/day-cycle

The wastewater application of 29 cm/day is less than the soil infiltration
capacity of 90 cm/day, so flooding will not occur.
Note: Suppose 1 ha land is used for this RI unit, the wastewater flow would
be 822 m^3 /day. Since the wastewater application rate of 29 cm/day is equivalent
to a wastewater flow rate of 2,900 m^3 /day, for the application period of 4 days, a
storage reservoir of 11,600m^3 capacity should be built to store the wastewater
sufficient for the above RI operation.

8.4.3 Overland flow or OF system

Wastewater application rate

Overland flow is a form of a fixed-film biological reactor. The application rate
should therefore be predictable on the basis of the kinetics of treatment and the
required treatment levels. For example, high-quality effluent has been produced
in research projects using these application rates: raw wastewater, 10 cm/week;
primary effluent, 15 to 20 cm/week; and secondary effluent, 25 to 40 cm/week.
With all three application rates, the runoff contained less than 10 mg/L BOD 5 on
the average. Slopes of the land were 2 to 4% and 36 m long (Tucker and Vivado
1980).