Practitioner's Tool / Technology and Operation 2 Overview

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Secondary Treatment

Septic tanks alone are not sufficient to treat wastewater to the point where it can be safely discharged, so secondary systems are required. View a summary table of the secondary treatment technologies.

  • Constructed Wetlands: Constructed wetlands are gaining in popularity as the wastewater system of choice in the Philippines for many point sources of sewage pollution, including those from public markets, hospitals and slaughterhouses. Constructed wetlands come in many shapes, sizes and flow patterns.
  • Aerobic Systems
    • Activated Sludge: Activated sludge is a flow-through process during which wastewater passes through a series of tanks or basins where different processes treat the wastewater. After large solids and grit are removed through bar screens and grit traps, the wastewater undergoes primary settling to remove much of the settleable solids. Settled effluent then undergoes biological treatment in the next tank where oxygen and activated sludge containing billions of microbes act upon the organic material in the wastewater.
    • Extended Aeration: Extended aeration is a modification of the activated sludge process and was developed to provide a more stable treatment process for smaller and more variable flows for sources from schools, tourist facilities, shopping malls and similar facilities.
    • Sequencing Batch Reactors: A sequencing batch reactor (SBR) is an aerobic treatment process that is highly efficient in removing organic matter, suspended solids and even nutrients in wastewater. Unlike the traditional activated sludge method that uses multiple tanks, the SBR treats each batch individually in a single tank.
    • Oxidation Ditches: An oxidation ditch is a combination of extended aeration and activated sludge processes. An oxidation ditch is constructed as a large holding tank in a continuous oval-shaped ditch.
    • Fixed Activated Sludge Treatment: The Fixed Activated Sludge Treatment (FAST®) process employs a unique hybrid combination of attached and suspended growth in an aerobic, packed-bed bioreactor.
  • Rotating Biological Contactors: Rotating biological contactor (RBC), or biodisc, technology is a fixed-film aerobic treatment process that can be very effective in treating a variety of wastewaters.  It is a secondary treatment process, meaning that grit removal and primary settling are required before the RBC process.


Wastewater effluent exiting secondary treatment units may still have large quantities of pathogenic organisms, including bacteria, viruses, helminthes and protozoa. Disinfect effluent to ensure compliance with discharge requirements. Click here for a summary table of the disinfection methods available. For more detailed information, please click on any of the links below.

  • Natural Disinfection: Ultraviolet (UV) light is composed of high-energy rays that are found in the natural spectrum of sunlight and can also be emitted by certain specially designed lamps and bulbs.  The energy in UV light is powerful enough to kill bacteria in water or filtered effluent.
  • Chemical Disinfection: Chlorination is the most common form of disinfection as it is inexpensive to install and simple to manage. Chlorine is available in solid, liquid and gas forms. Large municipal treatment plants may choose gaseous chlorine due to the cost savings, but there are many special health and safety requirements.
  • Physical Disinfection: Ozonation

Reuse and Recycling

Biosolids (excess solids from treated sewage sludge) can make an important contribution to sustainable environmental management by returning organic material, trace elements, moisture and nutrients to soils. The Guidelines for Environmental Management: Biosolids Land Application (linked below) enables this beneficial use of biosolids by providing a management framework that ensures any chemical and microbiological risks are appropriately managed. The drafting of the guideline has been supported by a best practice review of International and Australian biosolids management approaches and broad consultation on proposed guidance in November 2002 and 2000. For more information: Biosolids - Land Application (.pdf)

Septage Management

Below is a step-wise explanation of the single steps in septage management. To help determine septage program costs, an interactive toolkit has been uploaded here. The toolkit is preloaded with actual information from the Dumaguete City Septage Management program. The toolkit is open source and free to download. It is in its Beta format, so still considered a work in progress and comments are being accepted.

  • Septage Collection: Septage collection refers to the removal of solids from septic tanks (usually by pumping), as opposed to transportation and treatment. As you will see from the link below, however, collection involves more than just pumping the tank. It also includes pre- and post-pumping inspections, coordinating with local officials, reporting, and customer interface.
  • Septage Transportation: Septage transportation includes all activities from the time a septic tank is pumped to the time the septage load arrives at the treatment facility. The driver and service providers are responsible for safe operation of the vehicle and equipment. Traffic rules shall be followed at all times. All accidents and citations shall be reviewed and investigated by management to ensure adequately trained and competent drivers are employed for septage and sludge transportation.
  • Septage Treatment and Reuse: Proper wastewater treatment is required to reduce pathogens and separate water from solids so that both may be safely disposed of or reused. All domestic sludge (waste from wastewater treatment plants) and septage (waste from septic tanks) requires processing and treatment before disposal. The treatment processes for domestic sludge and septage are presented at the link below to provide an overview of available technologies. Some of these technologies are cost effective and well suited for small communities or private treatment plant operators.
  • Lime Stabilization of Septage: Lime stabilization, or applying hydrated lime (calcium hydroxide) to septage as a treatment method is well documented. The United States Environmental Protection Agency (EPA) has endorsed this methodology as effective, and it has been used in that country to treat septage for many years. The full recommendations on use of lime stabilization from the US EPA can be viewed here. The link describes a demonstration project to determine the effectiveness of lime stabilization as a method of treating domestic septage in the Philippines.
  • Septage tool (.xls) (click here (.pdf) for a guide on how to use the Septage Management Tool)

Best On-Site Practices

The following links guide to Best DEWATS Practices files which give practical guidance for Decentralized Wastewater Treatment Systems (DEWATS).


The SuSanA factsheet on Operation and maintenance of sustainable sanitation systems gives an introduction into the topics of funding, development, responsibilities and reasons for failure of operation and maintenance. It also gives six short case studies as examples for successful implementation.