Organic Waste Recycling

410 Organic waste reuse and recycling: technology and management

humid climate condition (as shown in Table 8.8), 36% more nitrogen can be
applied than in the arid climate.

The annual nitrogen balance is given by:

L'h = U + D + 0.1 W Cn (8.4)

Where,

L'h = wastewater nitrogen loading, kg/(ha-yr)

U = crop nitrogen uptake, kg/(ha-yr)

W = percolation rate, cm/yr

Cn = percolate nitrogen concentration, mg/L

D = denitrification rate, kg/(ha-yr)

The term 0.1 WCn on the right side of Equation 8.4 is the percolate N loading
or P'n whose unit is kg/(ha-yr).

Table 8.8 Comparison of nitrogen loadings in humid and arid climates (Olsen and
Kemper 1968)

Parameter Humid climate Arid climate
Applied nitrogen, mg/L 25 25
Precipitation minus evapotranspiration, m/yr 0.5 -0.5
Crop uptake, kg/ha 336 336
Denitrification, % of applied N 20 20
Hydraulic loading, m/yr 4.0 2.9
Wastewater nitrogen loading, kg/ha-yr 980 720

Example 8.2

Determine the nitrogen balance for a designed percolate nitrogen concentration
(Cn) of 10 mg/L for the following conditions.
Humid Arid

1. Applied N concentration, C'n, mg/L 25 25


2. Crop nitrogen uptake, U, kg/(ha-yr) 336 336


3. Denitrification, as % of applied N 20 20


4. Precipitation (Pp) – Evapo-transpiration (ET), cm/yr 50 -50

Assuming denitrification (D) is 20% of the wastewater nitrogen loading (L'n)

From Equation 8.3, the annual water balance is:

Lh + Pp = ET + W + R

or W = Lh + Pp - ET - O (assuming R is negligible)