Subsurface flow reedbeds using alternative media for the treatment of domestic greywater in Monteverde, Costa Rica, Central America S. Dallas* , ** and G. Ho* *UNEP-IETC Environmental Technology Centre, Murdoch University, Perth 6150, Western Australia (E-mail: s.dallas@murdoch.edu.au) **Monteverde Institute, Apdo 69-5655, Monteverde de Puntarenas, Costa Rica, Central America Abstract This paper describes the performance of reedbeds using plastic (PET) bottle segments as an alternative low-cost media for the treatment of domestic greywater in Monteverde, Costa Rica, Central America. Twelve reedbeds consisting of four sets of triplicates were monitored through wet and dry seasons in order to determine the effect of media type (PET versus crushed rock) and the effect of plants. In both seasons, performance of the planted reedbeds with PET media, for BOD and fecal coliform removal, was either comparable to, or better than, that of the crushed rock systems. The planted PET reedbeds achieved fecal coliform removal rates .99.9% in all cases equating to reductions of between 3 and nearly 5 log, with an average BOD outflow of 12.9 mg/L over both seasons. The hydraulic loading rate varied between 1.33 and 2.67 cm/day and hydraulic retention times (HRT) ranged from 3.5 to 7.5 days. The six reedbeds planted with Coix lacryma-jobi proved to be significantly more effective in pathogen removal and BOD reduction than the unplanted reedbeds. The planted PET reedbeds also increased their biomass by twice that of the planted crushed rock reedbeds during the study period. The majority of this increase was shown to be due to root growth. This paper discusses the implications of the above results for developing countries and identifies potential areas for further research. Keywords Constructed wetlands; Coix lacryma-jobi; developing countries; greywater; reedbeds; media Introduction It is estimated that less than 14% of all wastewater generated in Latin America receives any form of treatment (PAHO, 2001b) and in Costa Rica this figure is estimated to be less than 4% (PAHO, 2001a). In rural areas it is common practice to dispose of all house- hold greywater untreated directly into the environment. This is the situation in the rapidly growing tourist destination of Monteverde in northwest Costa Rica, where greywater runs freely through the streets and into the streams of a once pristine environment. The potential for constructed wetlands (CWs) in developing countries for wastewater treatment has been described as enormous and yet the uptake of this technology has been slow (Denny, 1997; Haberl, 1999; Kivaisi, 2001). This assessment was made on the basis of their low cost, ease of operation and maintenance when compared to conventional treatment systems, and that they represent an appropriate and sustainable technology for wastewater treatment – properties which have been widely documented. The warm tropi- cal and subtropical climates found in many developing countries are also ideal for pro- ductive biological systems such as constructed wetlands. It is also in many tropical regions, such as Central America, however, that mosquito-borne diseases such as malaria and dengue are endemic. The sub-surface flow wetland (SSF), or reedbed, is one form of constructed wetland which has no exposed water surface, thus preventing mosquitoes from using it as a breeding site. While operation and maintenance costs are generally low, unfortunately the media (usually gravel) required to form the SSF wetland substrate is typically the single most expensive component (Kadlec and Knight, 1996; Crites and Water Science & Technology Vol 51 No 10 pp 119–128 Q IWA Publishing 2005 119 Downloaded from https://iwaponline.com/wst/article-pdf/51/10/119/433464/119.pdf by guest on 12 November 2019