|
Various methods of sewage treatment
systems have been developed over the last fifty years to meet
the need to protect public health and the environment. For
urban centres where the population is concentrated and the
receiving environment is not able to cope with the waste discharge,
sophisticated treatment systems have evolved, which produces
a high quality effluent. Simpler systems have been used to
service small communities although ever increasing environment
standards means that even these areas must eventually install
better treatment systems. |
| |
| Sewage Treatment
Systems For Urban Areas |
Treatment processes
are divided into treatment, which utilises oxygen to breakdown
organic matter (aerobic) and treatment, which doesn't utilises
oxygen (anaerobic). The breakdown of organic matter can occur
while in suspension (suspended growth) or on the surface of
some type of media (attached growth). In addition, processes
using ponds are also sometimes used where large areas of land
are available. Treatment processes are categorised in this manner
as shown in Table 1. |
| |
| Table
1 Major Biological Sewage Treatment Processes |
| Aerobic
Processes |
Suspended
Growth |
Activated
Sludge |
| |
|
| - plug flow |
| - complete mix |
| - sequencing batch reactor |
| - extended aeration * |
| - oxidation ditch * |
| - deep shaft * |
| -Aerated Lagoons * |
|
| |
Attached Growth
|
Trickling Filters |
| |
|
| - low rate |
| - high rate * |
| - Rotating Biological Contactors
* |
| - Submerged Biological Contactors
* |
|
| |
Combines |
Biofilter Activated
Sludge |
| |
|
* Trickling
Filter Activated Sludge |
| Anaerobic Process |
Suspended Growth Attached Growth
|
| Anaerobic Contact |
| Anaerobic Filter |
| Expanded Bed |
|
| Pond Processes |
|
|
| |
|
| Aerobic Stabilization
(Oxidation) |
| Facultative |
| Anaerobic |
|
|
| |
| * Systems used in Malaysia. |
| |
| |
| Activated sludge, aerated lagoons,
rotating biological contactors and trickling filters are the
treatment systems most commonly used. |
| |
| Sewage Systems For Small Communities |
Because of their size, small communities
have traditionally faced the problems of high per capital
costs, limited finances and limited operation and maintenance
budgets for sewage treatment.
Where populations are less dense, the
receiving environment is able to cope with lesser level of
treatment, often only primary treatment will be provided.
However as population increases, these primary treatment systems
must be replaced with secondary treatment systems.
Sewage treatment plants for small communities
are now prefabricated before delivery to site and these are
commonly known as "package plants". They are only suitable
for small communities. Treatment processes are categorized
in this manner as shown in Table 2.
|
| |
| Table
2: Commonly Used Treatment Systems for Small Communities |
| Primary Treatment |
| |
| Individual Septic Tanks |
| Communal Septic Tanks |
| Imhoff Tanks |
| |
|
| Secondary
Treatment |
| |
| Package (pre fabricated) Plants |
| - activated sludge systems |
| - sequencing batch reactors |
| - contact stabilization |
| - rotating biological contactors
|
| |
| Individually Designed Plants |
| - activated sludge systems |
| - oxidation ponds |
| - sequencing batch reactors |
| - rotating biological contactors |
| - trickling filter |
| - facultation lagoons |
| - aerated lagoons |
| |
|
|
| |
The use of package plants will be
strictly controlled to ensure their long-term viability. In
urban areas Individual Septic Tanks (IST), Communal Septic Tanks
(CST) and Imhoff Tanks (IT) will be phased out. |
