Organic Waste Recycling

Algal production 243

between 1.25 and 1.75. The deviation of value for p from theoretical value, 1.58,
was due to various reasons. In practice, all Lt cannot be oxidized even though
enough O 2 is present; therefore low value for p is observed. Or a strong wind
blow can increase the surface re-aeration, increasing the value of O 2 produced;
therefore high p value can be obtained.

Example 5.2

An agro-industry in Thailand is producing wastewater at a flow rate of 500
m^3 /day and its COD or Lt is 400 mg/L. Determine the size of HRAP to be used
to produce algae from this wastewater. The following information are given:

H = unit heat value of algae = 6 kcal/g

p = 1.5

F = efficiency of energy conversion = 0.1

Tc = temperature coefficient = 0.9

Io or Ii = visible solar energy irradiance = 400 gcal/(cm^2 -day) or 11100 ft-

candle, respectively

Į = specific light absorption coefficient = 1.5x10-3

From Equation 5.9, algal concentration in HRAP may be theoretically
estimated.

Ca = Lt/p = 400/1.5 = 266.7 mg/L

Pond depth can be estimated from Equation 5.2.

ln Ii ln 11,100

z = = = 23.3 cm

CaĮ 266.7(1.5x10-3)

Select a ‘z’ value of 25 cm.

HRT of the pond is estimated from Equation 5.3

Ca .h.z

HRT =

1000 F.Io.Tc.

266.7×6×25

HRT = = 1.11 days

1000×0.1×400×0.9