Organic Waste Recycling

168 Organic waste recycling: technology and management

pH 7.4 7.4 7.4

Total Kjeldahl nitrogen (mg/L) 890 900 880

Chemical oxygen demand (g/L) 46 48.7 49.6

Total volatile solids (g/L) 36.1 37.7 37.2

Influent mixture

Total solids (g/L) 46.9 49.0 48.1

Wet weight basis 3.1: 3.2: 4.3 - 3.0: 9.5: 11.5 5.5: 3.8: 1.3 - 8.3: 1.4: 2.1 6.1: 2.2: 1.3 - 5.6: 3.1: 1.3

Approximate proportion of raw materials (nightsoil/ rice

straw/ water hyacinth)

Dry weight basis 1.0 : 5.6: 3.0 - 1.0: 8.0: 8.0 1.0: 3.4: 1.0 - 1.0: 0.9: 1.0 1.0: 2.0: 1.0 - 1.0: 2.8: 1.0

Total solids to water ratio 8: 92 8: 92 8: 92

Carbon to nitrogen ratio (C/N ratio) 25 25 25

Hydraulic retention time (days) 30 50 70

In a study conducted at the Asian Institute of Technology (AIT), Bangkok,
Thailand, four pilot small-scale digesters (size = 3.5 m^3 ) were fed with

Table 4.7 Proportions of raw materials used to obtain the desired C/N ratio of 25, and characteristics of influent mixture