Organic Waste Recycling

Introduction 9

pollution occurs when the organic waste load is mild and little DO is utilized by the
bacteria in waste decomposition. At higher organic waste load (type 2 pollution),
more oxygen is utilized by the bacteria, causing a greater DO sag and consequently
a longer recovery time or distance of flow before the DO could reach the normal
level again. Type 3 pollution has an over-loading of organic waste into the stream,
resulting in the occurrence of anaerobic condition (zero DO concentration). This is
detrimental to the aquatic organisms; the recovery time for DO will be much longer
than those of the types 1 & 2 pollution. Although DO is an indicator of stream
recovery from pollution discharge, other parameters such as the concentrations of
pathogens and toxic compounds should be taken into account in the reuse of the
stream water.

Figure 1.3 DO sag profile in polluted stream

Similarly, raw or partially treated wastewater can be injected into wells
upstream and, through the processes of filtration, straining, and some microbial
activities; good quality water can be deducted from wells downstream. The subject
of groundwater recharge is presented in Chapter 8.

1.3 INTEGRATED AND ALTERNATIVE TECHNOLOGIES

Depending on local conditions, the above-mentioned technologies can be
implemented individually or in combination with each other. For optimum use of
resources, the integration of various waste recycling technologies in which the
wastes of one process serve as raw material for another should be considered. In
these integrated systems, animal, human and agricultural wastes are all used to

Type 3 pollution

Saturated DO concentration

DO concentration

Organic waste discharge

Type 1 pollution

Distance of flow

Type 2 pollution

Waste decomposition

zone

DO recovery zone

0