Land treatment of sludge 461From the mass balance equation (Equation 9.1)
21.555 x 10-3 (X) = 2.75 x 10-3 (X) + 0 + 224 + 0
and X = 11,912 kg/ha
The amount of sludge to be applied to corn crop in the first year is 11,912
kg/ha (dry weight).
9.3.2 Sludge loading determination
The calculation for sludge loading on a nitrogen basis is a three-step procedure:
- Determine the plant-available nitrogen (Np) in the sludge during the
application year:
Np = (1,000) [NO 3 + Kv (NH 4 ) + f 1 (ON)] (9.2)Where,
Np = plant-available nitrogen in sludge during application year, kg/dry
ton of sludge
NO 3 = percent nitrate in sludge, as a decimal (e.g. 1000 mg/L = 0.1% =
0.001)
Kv = volatilization factor: 0.5 for surface applied liquid sludge, 1.0 for
incorporated (or injected) liquid sludge and dewatered digested
sludge applied in any manner
NH 4 = percent ammonia nitrogen in sludge, as a decimal
f 1 = mineralization factor for first year, as a decimal (Table 9.14)
ON = percent organic nitrogen in sludge, as a decimalEquation 9.2 will determine the plant-available N in sludge in kg/ton. To
convert the concentrations of NO 3 , NH 4 and ON into the same unit, the value of
each of these N constituents has to be in decimal term. For example, an NH 4
concentration of 1000 mg/L is equivalent to 0.1%, or sludge 100 kg contains
NH 4 0.1 kg. Therefore, sludge 1000 kg (or 1 ton) will contain NH 4 = 1000.
(0.1/100). The term in bracket is the decimal value.
- Determine the plant-available nitrogen (NPR) from mineralization of
the residual sludge in subsequent years:
NPR1 = 1,000 [f 2 (ON) 2 + f 3 (ON) 3 + ......] (9.3)
Where,
NPR1= plant-available nitrogen from mineralization of the first-year
sludge in subsequent years, kg/dry ton of sludge