Land treatment of sludge 473
9.7 EXERCISES
9.1 Discuss the advantages and limitations of agricultural utilization of
sludge, and compare them with aquacultural utilization (or fish
production) of sludge.
9.2 Why is it important to maintain the soil pH at 6.5 or greater in sludge
application on land? What should be done if the land for sludge
application has a pH lower than 6.5?
9.3 Objectionable odour of the sludge could result in unfavourable public
relations and reduced acceptance of land application options. Therefore,
all sludge management systems must consider objectionable odour as a
potential problem. What measures should be taken to reduce the odour
problems during sludge application on land?
9.4 A piece of land received anaerobically digested sludge containing 3
percent organic N at a rate of 15 dry tons/ha in 2003. In 2004, a
composted sludge containing 2% organic N was applied to the same land
at a rate of 10 dry tons/ha. Determine the available N in the Year 2005
from the sludge applications in the year 2003 and 2004.
9.5 An analysis of a composted sludge reveals the following information:
Production 100 tons/day
Dry solids 15 %
Total N 3.5 %
NO 3 -N 0.1 %
NH 4 -N 1.6 %
P 1.2 %
K 0.3 %
Zn 2000 ppm
Cu 1000 ppm
Ni 100 ppm
Cd 2 ppm
Pb 500 ppm
Determine the land area needed for application of this sludge for a period
of ten years and the amount of additional chemical fertilizers required.
The sludge is to be incorporated into cotton fields with a CEC of 8
meq/100 g soil. Nutrient uptake rates of cotton are given in Table 8.7.
