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Effect of retention time on fertilizer value
 of biodigester effluent

San Thy

University of Tropical Agriculture
Chamcar Daung, Phnom Penh, Cambodia
santhy@uta.edu.kh
santhysimon@yahoo.com

Hypothesis

The hypothesis is that increasing the retention time in the biodigester charged with pig manure will increase the proportion of the total nitrogen in the effluent that is in the form of ionized ammonia, which in turn will improve its fertilizer value.

Procedure

Three experiments will be carried out:

In experiment 1, the treatments in a 3*3 Latin square arrangements are retention times of 10, 20 and 30 days. The digesters are of tubular polyethylene 2m long., 0.6m diameter, with a liquid volume of 500 litres. Experimental periods will be 40 days and the loading rate (amount of pig manure added daily) is  constant, varying the retention time by the amount of added water. Measurements are made of gas production, total and ammonia N in the effluent, pH and BOD in the effluent

The second experiment will test the growth of water spinach fertilized with the three sources of effluent at 75kg N/ha as fertilizer. The design is a 3*3 Latin square and will measure the growth of water spinach according to height and number of leaves, and total biomass at the end of the experiment. DM, total N and Non-protein N will be measured.

 The third experiment will test the growth of fish (Tilapia) by culturing in a small pond of 6 m2 area with 1 m depth, fertilized with effluent from `10 and 30 day retention times with 3 replicates (total 6 ponds). Fish growth will be measured by recording length and weight every 20 days.

Photo 1: Collecting the effluent Photo 2: Measuring the gas production by displacement of water Photo 3: Preparing the fish ponds