Environmental Engineering Reference
In-Depth Information
Appropriate Standards
As shown in Figure 4.3, the target for DC sewage systems should be not the IC
target of point C, but point B. This is all that is needed for environmental protec-
tion in the DCs, and it will require several decades to achieve this. Unfortunately,
the international media releases nowadays feature point C concerns, leading to
confusion rather than help to DC practitioners.
A few years ago the IWA sponsored a major international conference at
Bangkok on the subject of controlling eutrophication in rivers and lakes and
other waterways in DCs by removal of nutrients. But this is quite expensive
and hardly ever needed in DCs, where problems of eutrophication are scarcely a
priority issue.
Some examples relating to appropriate standards for sewage treatment devel-
oped by ADB 112
are included here as Figures 4.8, 4.9, and 4.10.
Marine Sewage Disposal
As indicated by Figure 4.10, treatment/disposal of municipal sewage for discharge
to marine waters can be categorized into two types, (1) disposal to confined
marine waters (bays, shallow nearshore waters) for which DO is the controlling
parameter, hence treatment requirements are the same as for inland waterways,
and (2) disposal to open ocean waters, which requires use of a submarine out-
fall extending far enough offshore to reach unconfined open ocean water, for
which removal only of floatables is really required, together with point source
controls to prevent discharge of toxics/hazardous substances into sewer systems.
Influent (typical)
Affluence level as indicated by
per capita GNP
Sus. Solids
Grease / Oils
240 mg/l
300 mg/l
30 mg/l
Advanced Waste Treatment
Eff Sus. Solids
Eff Grease/Oils
10 mg/l
10 mg/l
1 mg/l
Eff Phosphorus reduced to levels obtained
with chemical precipitation
Complete Treatment
Eff = Effluent
Eff Sus. Solids
20 mg/l
30 mg/l
5 mg/l
Primary Treatment
(The Ten States Standard)
Effluent BOD
Effluent Sus. Solids
Effluent Grease/Oils
160 mg/l
200 mg/l
10 mg/l
FIGURE 4.8 Drawing showing effluent standards requirements for disposal of munic-
ipal sewage to receiving waters where DO is a salient ambient parameter (inland waters
and confined coastal waters including estuaries and semi-enclosed bays).
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