constructed wetlands for septage treatment

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  • 8/6/2019 Constructed Wetlands for Septage Treatment


    Constructed Wetlands for Septage Treatment Towards Effective faecal Sludge Management 1

    Thammarat Koottatep*, Chongrak Polprasert*, Nguyen Thi Kim Oanh*, NarongSurinkul*, Agnes Montangero** and Martin Strauss**

    * Urban Environmental Engineering and Management Program (UEEM),School of Environment, Resources and Development (SERD)Asian Institute of Technology (AIT),P.O. Box 4, Klong Laung, Pathumthani 12120, Thailand

    ** Department of Water and Sanitation in Developing Countries (SANDEC),Swiss Federal Institute for Environmental Science and Technology (EAWAG)P.O. Box 611, CH-8600 Dbendorf, Switzerland

    Author to whom correspondence should be addressed: Thammarat Koottatep at [email protected] (Tel. +66-2-524 61 88 Fax +66-2-524 56 25) or: Martin Strauss at [email protected] (Tel. +41-1-823 50 20 Fax +41-1-823 53 99)

    ABSTRACTThe majority of urban dwellers in Africa depend on on-site sanitation (OSS) systems for excreta disposal.There is a considerable gap-in-knowledge on strategies for sustainable management and on treatment optionsfor faecal sludges evacuated from OSS, which are appropriate for developing countries. The authors providean overview of the situation, challenges, and selected strategies in handling FS. Treatment options are

    presented. The authors describe in detail pilot-scale investigations on using constructed wetlands (CW) for the treatment of septage. The experiments are being conducted at AIT, Bangkok since 1997. The plantconsists of three beds planted with cattail ( Typha ). A loading rate of 250 kg TS/m 2.yr was found optimum for the type of septage treated. Intermittent percolate impoundment is required to prevent cattail wilting duringdry weather. 65 % of the septage liquid passes through the underdrain and 35 % is evapotranspirated. The

    beds have been operated for nearly four years with unimpaired bed permeability. Accumulated solids are lowin viable helminth eggs and satisfy expedient sludge quality standards for agricultural use. Compared withconventional sludge drying beds, CW require a much-reduced frequency at which dewatered biosolids needto be removed from the bed.


    Cattails; constructed wetlands; faecal sludge; septage; management; treatment; on-site sanitation


    1 Paper presented at the IWA 8 th Int. Conference on Weetlands Systems for Water Pollution Control, Arusha,Tanzania, Sept. 15-19.

    BOD Biochemical oxygen demandCW Constructed wetlandsFS Faecal sludge

    N Nitrogen NH 4 Ammonium NO 3 NitrateOSS On-site sanitation

    SLR Solids loading rateSS Suspended solidsTCOD Total (unfiltered) chemical oxygen demand

    TKN Total Kjeldahl nitrogenTS Total solidsTVS Total volatile solidsWWTP Wastewater treatment plant


    Situation and Challenges

    In urban areas of developing countries, on-site sanitation (OSS) systems predominate over water- borne, sewered sanitation (Table 1). They comprise unsewered family and public toilets, aqua

    privies and septic tanks. In sub-Saharan Africa, > 75 % of houses in large cities and up to 100 % in

  • 8/6/2019 Constructed Wetlands for Septage Treatment


    Table 1 Proportion of urban populations served byon-site sanitation systems (OSS)

    City or country % of inhabitants served by on-site sanitation systems

    Ghana 85Bamako (Mali) 98

    Tanzania > 85Manila 78Philippines (towns) 98Bangkok 65Latin America > 50

    towns are served by on-site sanitationfacilities (Strauss et al. [1 ]). These willcontinue to play an important role for excreta disposal as area-wide sewerageis not affordable. In the USA, 25 % of

    dwellings are served by septic tanks.The collection of the faecal sludges fromOSS installations and their haulage in largecities in Asia are faced with immense

    problems. In the absence of long-termurban planning and/or failing

    enforcement of existing zonal plans have lead to a lack of feasible landfilling or treatment sites atreasonable haulage distance. Emptying services are poorly managed and often hardly affordable tocustomers, due also to the lack of entrepreneurial competition or due to cartelization byentrepreneurs. A minor fraction (< 10 % ?), only, of the faecal sludges accumulating in on-sitesanitation installations are formally collected and discharged or treated. Where treatment schemesexist, charges are usually levied for each load of FS delivered to the plant by private collectors. As

    a consequence, faecal sludge is often dumped at non-designated sites to avoid fee paying. This maygo unavenged due to lack of competition among collection entreprises, lack of adequateenforcement and corruption. Innovative incentive, fee levying and licensing procedures wouldcontribute considerably to avoiding such problems and to rendering FS management moresustainable.

    FS Management Planning

    Current FS management has resulted from the historical development in excreta handling (which,often, is linked to agricultural practices), general socio-economic developments and purposeful

    planning efforts, which indirectly or directly affect the choice of sanitation systems. Improving onand finding appropriate strategies and solutions in FS management must, thus, be dealt with inconjunction with both unplanned and planned urban and peri-urban development, institutionalsettings, jurisdictional conditions, and expected future sanitation infrastructure and service


    In short, an FS management concept should be based on the assessment of:

    Existing sanitary infrastructure and trends Current FS management practices and their shortcomings Stakeholders customs, needs and perceptions regarding FS management and use Environmental sanitation strategy Prevailing socio-economic, institutional, legal and technical conditions, and The general urban development concept

    (Klingel [2 ]; Klingel et al. [3 ]). Based on an FS management concept, FS treatment objectives maythen be formulated and, consequently, feasible treatment options be evaluated.

    In most places, a large array of technical, economic and institutional/organizational measures arerequired to improve the FS management situation. Given the difficulties in collecting FS and inhauling it across cities to designated disposal and treatment sites, decentralizing FS management isall-important. The devising of modest-scale satellite treatment plants (Fig.1) and of neighbourhood or condominial septic tanks (Fig.2) may contribute significantly to reducingindiscriminate dumping of FS and, hence, to reducing health and pollution risks. However, everycity has to be taken at its own merits, given the great variability of spatial settings, sanitationinfrastructure and planning mechanisms.

  • 8/6/2019 Constructed Wetlands for Septage Treatment


    Making sure that collected FS will actually be hauled to the designated treatment sites is one of thegreatest managerial and institutional challenges. It is now a widely accepted paradigm thatsustainable environmental sanitation may be achieved or enhanced only by applying appropriateincentive and sanctioning structures. Where fees are payable by private entrepreneurs for discharging FS to designated treatment or disposal sites, municipalities must devise an effectivesanctioning system in case FS is discharged at non-designated points, e.g., by not renewing servicecontracts with violators. Alternatively, such fee structures and cost recovery/financial proceduresshould be developed, by which entrepreneurs will receive reimbursement for FS delivered to thelegally designated treatment or disposal site. Jeuland (2002) [4 ] has proposed such alternative

    procedures to secure sustainability of FS management and treatment in the planned manner for thecity of Bamako, Mali.


    Per-capita quantities

    Table 2 contains the daily per capita volumes and loads of organic matter, solids and nutrients in faecal sludges collected from septic tanks and pit latrines, as well as from low or zero-flush,unsewered public toilets. Values for fresh excreta are given for comparative purposes. The figuresare overall averages and may be used for planning and preliminary design. Actual quantities may,however, vary from place to place.

    Table 2 Daily per capita volumes; BOD, TS, and TKN quantities of different types of faecal sludges(Heinss et al. 1998) [5 ]

    Where nematode infections are not endemic and, hence, eggs may be found at insignificantconcentrations only in excreta and FS, bacterial pathogens (e.g. Salmonellae spp. ) or

    bacteriophages might be used as indicators-of-choice.

    Communal instead of individual septic tanks

    Allows to cater for better access to septic tanksand, hence, for more effective FS management

    Fig. 2 The use of communal septic tanks astrategic tool to facilitate effective FS collection

    What scale for FS treatment:

    centralized or semi-centralized ?


    minimize overall cost for collection, haulage and treatmentwhile guaranteeing safety in FS handling, use or disposal


    Fig. 1 Satellite FS treatment a strategic tool tominimize cost, indiscriminate dumping, healthrisks and water pollution

    Parameter Septage 1 Public toilet sludge 1 Pit latrine sludge 2 Fresh excreta

    BOD g/capday 1 16 8 45

    TS g/capday 14 100 90 110

    TKN g/capday 0.8 8 5 10

    Volume l/capday 1 2(incl. water for toilet cleansing)

    0.15 - 0-20 1.5(faeces and urine)

    1 Estimates are based on a faecal sludge collection survey conducted in Accra, Ghana.

    2 Figures have been estimated on an assu