Investigation into suitability of duckweed-treated wastewater for multipurpose use in Bangladesh

Abstract

Current mainstream technologies for wastewater treatment, such as activated slndge and tertiary nutrient removal, are too costly to provide a satisfactory solution for the increasing wasrewater problems in developing countries. Besides, these technologies do not allow for re-use of valuable energy and nutrients contained in the wastewater. This study investigated the suitability of duckweed-treated wastewater for mnltipwpose use, e,g, pisciculture, agricu1ltIre, recreation, ero. This study also assessed the feasibility of a (;ommunity based application of a duckweed-based integrated system for wastewater treatment, pismculture and co-cr-ops, This study was conducted in a duckweed-based wastewater treatment facility at Mirzapur, Tangail. Suitability of the duckweed-treated wastewater was assessed by monitoring the water quality at several locations of the system, and the feasibility of a community-based duckweed-treated wastewater reuse facility for rural areas was assessed from socio-economic analysis of secondary data collected in a previous household survey. Retention time in the pond was varied by varying the influent pumping rate into the system. To determine the optimum retention time, three retentions times, 22 days, 27 days and 19 days were tested during the field experiment From analysis of the water quality monitoring results, it was found that 22 days retention time is optimum for treating domestic wastewater by a duckweed-based system wbere polyrhiza is the predominant species. The study demonstrated that duckweeds can efficiently reduce coliform count (almost 100% removal), TDS (79.06% removal), BOD (98.08% removal), NH1-N (99.15% removal), P04 (98.30% removal), Fe (64.80% removal), Mn (58,64% removal), and As (99% removid) in the wastewater after a retention time of 22 days, The DO concentration was observed to increase consistently from raw sewage (0.45 mgIL) to effluent (4,67 mglL) for 22-day retention, This study also shows that duckweed-treated effiuent may be suitable for pisciculture and recreation as per the water quality standards and guidelines. However, the effluent may not be suitable as a drinking water source since it contams a few fecal coliforms, Co-erops grown on the pond embankment may provide additional financial return while they provide shade to the duckweed mat in the waste stabilization pond. Duckweed grown in the pond may be also used for other purposes such as fish and poultry feed. However, thc adverse effects of such use should be carefully analyzed.