Organic Waste Recycling

474 Organic Waste Recycling: Technology and Management

9.6 The Chiang Mai Municipality in northern Thailand produces septage (or

anaerobically digested sludge) with the following characteristics:

Total weight = 100 tons/day

Total solids (TS) = 15 tons/day

Organic N = 20,000 mg/kg of TS

Cd = 20 mg/kg TS

The septage is to be applied by incorporation into a land for growing

soya bean, whose N uptake rate is 250 kg/(ha-year). Assuming N loss via

volatilization and runoff is negligible.

a) If all the septage is to be used to grow soya bean, based on N

requirement alone, determine the land areas for growing soya bean

in years 1 and 2. Data on N mineralization rate is given in Table

9.14.

b) If the Cadmium application rate to the soya bean field should not

exceed 0.5 kg/(ha-year), determine the land areas, based on Cd limit

alone, for growing soya bean in years 1 and 2.

Compare the results of a) and b) and recommend to the Chiang Mai

Municipality the best option for applying septage to grow soya bean.

9.7 A cattle farm in southern China produces animal manure (raw sludge)

with the following characteristics;

Total weight = 2 tons/day

Total solids (TS) = 0.2 tons/day

Organic N = 20,000 mg/kg TS

Arsenic (As) = 10 mg/kg TS

1,000 kg = 1 ton

This animal manure is to be applied as fertilizer to grow sunflower crops

whose N uptake rate is 200 kg/(ha-year). Assume N losses via

volatilization and runoff is negligible.

a) If the farmer has only 1 ha of farm land to grow sunflower crops,

determine the amounts of animal manure the farmer should apply to

this farm land in years 1 and 2 to obtain maximum crop yields and

minimum impact on the environment. Data on N mineralization is

given in Table 9.14.