Organic Waste Recycling

420 Organic waste reuse and recycling: technology and management

perennial rye grass, annal rye grass, orchard grass, and tall fescue grass. The tall
fescue grass was predominant.

BOD 5 and TOC removal

Removal of BOD 5 and TOC from wastewater and primary effluent after the first
9 m of travel down the overland flow slope followed the first-order removal
model:

Cz/Co = A.exp(-K.z) (8.7)
Where:
z = distance down-slope, in m (z > 9 m)
Cz = organic concentration (BOD 5 or TOC) at a distance (z) down-slope, mg/L
Co = initial organic concentration (BOD 5 or TOC), mg/L
K = empirically determined overall rate constant
A = empirically determined coefficient

It has been shown that BOD 5 concentrations in the runoff from overland flow
slopes approach a nonzero value in the range of 3 to 5 mg/L. Effluent BOD 5 and
TOC concentrations approach average values of 5 mg/L and 7 mg/L, respectively,
after 64 m of down-slope travel. Hence the removal models were modified to
account for this as follows:

BOD 5 removal model:

(C - 5)/Co = A.exp (-K.z) (8.8)

TOC removal model:

(C - 7)/Co = A'.exp (-K'.z) (8.9)

Where:

C = required effluent BOD 5 or TOC concentrations at distance z

K and K' = empirical rate constants for BOD 5 and TOC removal, respectively

A and A' = empirical coefficients for BOD 5 and TOC removal, respectively

The overall rate constants K and K' in Equations 8.8 and 8.9 vary as a function
of application rate q, according to the following equation:

K or K' = k/qn (8.10)

Where, k and n are empirical coefficients and q is wastewater application rate
whose unit is m^3 /(hr-m of slope width).