260 Organic waste recycling: technology and management
required and the annual algal production including the income that can be
earned from the sale of the algal biomass. Submit the schematic drawings of the
HRAP. The following information is given:HRT for HRAP = 2-5 days
Depth of HRAP = 0.2-0.4 m.
Average I 0 = 400 gcal/ (cm^2 -day).
Mean temperature = 25°C
Light saturation intensity (Is) is to be estimated from Table 5.7.
Cost of algal harvesting = US$ 0.2/m^3 of algal water
Algal density in HRAP = 300 mg/L
Price of algae = US$ 30/kg (dry weight)
5.6 A small community has a one-ha land available to treat its sewage with a COD
of 300 mg/L. It plans to build high rate algal ponds (HRAPs) on this piece of
land to treat the sewage. Determine the total treatment capacity of the HRAPs
and the optimum pond depth. Also estimate the daily algal and protein
production to be obtained from this piece of land. Additional information is
given below:
I 0 or Ii = visible solar energy irradiance = 500 gcal/(cm^2 -day) or
13,900 ft-candle
Į = specific light absorption coefficient = 1.5x10-3
Tc = temperature coefficient = 0.8
F = efficiency of energy conversion = 0.1
p = 1.6
h = unit heat of algae = 6 kcal/g
5.7 A municipality in Vietnam produces wastewater with the following
characteristics:
Flow rate = 2000 m^3 /day
BOD 5 = 100 g/m^3
NH 4 -N = 20 g/m^3
a) If this wastewater is to be treated in a high-rate algal pond (HRAP) to
produce algal density of 200 g/m^3 , determine the dimension (depth ×
width × length) of the HRAP to achieve this objective. Draw schematic
diagram of this HRAP.The following information about HRAP are given in Equation 5.2.