Sewage Characteristics | Sewage Treatment Objectives | Sewage Treatment Methods | Sewage Treatment System | The Evolution Of Sewage Treatment

Sewage Treatment Systems

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.