Organic Waste Recycling

Fish, chitin, and chitosan production 305

Williamson, G. and Payne, W.J.A. (1978) Animal Husbandry in the Tropics, 3rd edition,
Longman, London.
Wohlfarth, G.W. and Schroeder, G.L. (1979) "Use of manure in fish farming - a review",
Agricultural Waste, 1 , 279-299.
Wolf, K. (1957) "Blue-sac disease investigations, microbiology and laboratory
induction", Progressive Fish Culturist, 19 , 14-18.

6.10 Exercises

6.1 What are the health problems associated with fish farming in wastewater-
enriched pond? What would you suggest to solve these problems?

6.2 Calculate the ammonia concentration in a water sample at pH = 8 and NH 3 -
N + NH 4 -N = 10 mg/L. The following equilibria exist:

NH +HO NH +OH

+ -

3 2 → 4

=1.76x 10 (at 25 C)

[NH]

[NH][OH] - 5

3

=^4 °

Kb

Kw=[H+][OH-]= 10 -14 (at^25 °C)

The U.S. Committee on Water Quality Criteria (1972) has recommended

that, to safeguard fish, no more than 0.02 mg/L NH 3 be permitted in

receiving waters. Does the ammonia concentration in the above calculation

meet the Criteria? If not, suggest methods to make the water safe for the fish.

6.3 Compare the advantages and disadvantages of applying commercial fish
meal or cattle manure into fish ponds for the purpose of raising Tilapia for
use as animal feed.

6.4 You are to visit a commercial fish farm and obtain the following
information:

• fish species and stocking density


• type and amount of fish meal being fed to the fish ponds


• productivity of the fish ponds in unit of kg fish/(ha-yr)

From the above data, estimate the organic loading rate (in kg BOD or

COD/ha-day) and the percent fish mortality. Also suggest some

improvements, if any, to be made to increase the fish productivity in this

farm.