K. B. S. N. Jinadasa

Application of constructed wetlands for wastewater treatment in developing countries--a review of recent developments (2000-2013).

Inadequate access to clean water and sanitation has become one of the most pervasive problems afflicting people throughout the developing world. Replication of centralized water-, energy- and cost-intensive technologies has proved ineffective in resolving the complex water-related problems resulting from rapid urbanization in the developing countries. Instead constructed wetlands (CWs) have emerged and become a viable option for wastewater treatment, and are currently being recognized as attractive alternatives to conventional wastewater treatment methods. The primary objective of this review is to present a comprehensive overview of the diverse range of practice, applications and researches of CW systems for removing various contaminants from wastewater in developing countries, placing them in the overall context of the need for low-cost and sustainable wastewater treatment systems. Emphasis of this review is placed on the treatment performance of various types of CWs including: (i) free water surface flow CW; (ii) subsurface flow CW; (iii) hybrid systems; and, (iv) floating treatment wetland. The impacts of different wetland design and pertinent operational variables (e.g., hydraulic loading rate, vegetation species, physical configurations, and seasonal variation) on contaminant removal in CW systems are also summarized and highlighted. Finally, the cost and land requirements for CW systems are critically evaluated.

Batch versus continuous feeding strategies for pharmaceutical removal by subsurface flow constructed wetland

This study evaluated the effect of continuous and batch feeding on the removal of 8 pharmaceuticals (carbamazepine, naproxen, diclofenac, ibuprofen, caffeine, salicylic acid, ketoprofen and clofibric acid) from synthetic wastewater in mesocosm-scale constructed wetlands (CWs). Both loading modes were operated at hydraulic application rates of 5.6 cm day(-1) and 2.8 cm day(-1). Except for carbamazepine, clofibric acid and naproxen, removal in CWs was significantly (p < 0.05) enhanced under the batch versus continuous mode. For all compounds tested except naproxen, values for first-order decay constants (k) for drain and fill operation were higher than that for the continuous mode of operation. Correlation between the distribution coefficient (log D(ow)) and removal efficiencies of pharmaceutical compounds in the CWs, showed that pharmaceutical removal efficiency was significantly (p < 0.1) and inversely correlated with log D(ow) value, but not with log K(ow) value.

Developing effective vegetation bioshield for tsunami protection

To elucidate the effectiveness and limitations of coastal vegetation for tsunami protection, the impact of vegetation structure on drag forces was analysed using the observed characteristics of reference tree species. The drag coefficient, including the vertical stand structures of trees, C d−all , and the vegetation thickness per unit area, dN u (d, reference diameter of trees; N u , number of trees per unit area), varies greatly with different species. Based on data analyses, dense Casuarina equisetifolia and Pandanus odoratissimus grown in beach sand were found to be especially effective in providing protection from tsunami damage due to their density and complex aerial root structure. The breaking moment of trees was investigated as a function of tree diameter. The breaking moment equation of P. odoratissimus explains well the damage caused to trees by the 2004 Indian Ocean tsunami and the 2006 Java tsunami. Numerical simulation indicates that inertia is the dominant force (99.1%) in comparison with the drag force when a wave front collides with a vegetation face, but while the water depth is very shallow and the total force is 6% of the maximum. Drag resistance is the dominant force in reducing both water depth and current velocity, but inertia resistance is active in reducing current velocity only in front of the vegetation. The breaking condition of trees can be discussed by the drag-force moment alone because when the total moment reaches the maximum, the contribution of the inertia moment is in the range of 0.1–0.3%. Considering the limitations of P. odoratissimus in reducing tsunami water depth and the other roles that coastal vegetation can play in mitigating tsunami-related damage, a forest with two layers in the vertical direction of P. odoratissimus and dense C. equisetifolia was found to be effective for increasing drag and trapping floating debris.

Application of constructed wetlands for wastewater treatment in tropical and subtropical regions (2000-2013).

Constructed wetlands (CWs) have been successfully used for treating various wastewaters for decades and have been identified as a sustainable wastewater management option for developing countries. With the goal of promoting sustainable engineered systems that support human well-being but are also compatible with sustaining natural (environmental) systems, the application of CWs has become more relevant. Such application is especially significant for developing countries with tropical climates, which are very conducive to higher biological activity and productivity, resulting in higher treatment efficiencies compared to those in temperate climates. This paper therefore highlights the practice, applications, and research of treatment wetlands under tropical and subtropical conditions since 2000. In the present review, removal of biochemical oxygen demand (BOD) and total suspended solid (TSS) was shown to be very efficient and consistent across all types of treatment wetlands. Hybrid systems appeared more efficient in the removal of total suspended solid (TSS) (91.3%), chemical oxygen demand (COD) (84.3%), and nitrogen (i.e., 80.7% for ammonium (NH)4-N, 80.8% for nitrate (NO)3-N, and 75.4% for total nitrogen (TN)) as compared to other wetland systems. Vertical subsurface flow (VSSF) CWs removed TSS (84.9%), BOD (87.6%), and nitrogen (i.e., 66.2% for NH4-N, 73.3% for NO3-N, and 53.3% for TN) more efficiently than horizontal subsurface flow (HSSF) CWs, while HSSF CWs (69.8%) showed better total phosphorus (TP) removal compared to VSSF CWs (60.1%). Floating treatment wetlands (FTWs) showed comparable removal efficiencies for BOD (70.7%), NH4-N (63.6%), and TP (44.8%) to free water surface (FWS) CW systems.

Impact of harvesting on constructed wetlands performance - a comparison between Scirpus grossus and Typha angustifolia.

Three units of free water surface (FWS) constructed wetlands treating domestic wastewater under tropical conditions were examined in terms of water quality and biomass characteristics. One unit (L2) was planted with Scirpus grossus, one with Typha angustifolia (L3), and the unplanted third (L1) served as control. Influent and effluent quality parameters: biological oxygen demand (BOD5), nitrate (NO3 −-N), ammonium (NH4 +-N), phosphorus (P), total suspended solids (TSS) and fecal coliforms were regularly measured. The average BOD5 reductions were 37.0%, 58.5%, and 53.8% for units L1, L2, and L3, respectively. The planted units removed pollutants more effectively although there was no significant difference between the Scirpus grossus and Typha angustifolia units. Plant growth was monitored in marked quadrats by measuring shoot height and other growth parameters. The above-ground organs in L2 and L3 was harvested whenever the shoots reached maximum shoot height and formed flowers. Scirpus grossus had sustainable above-ground biomass production but Typha angustifolia could not sustain repeated harvestings with the above-ground biomass production declining significantly following four consecutive harvests.

Free water surface constructed wetlands for domestic wastewater treatment: A tropical case study

The performance of three free water surface constructed wetlands in treating domestic wastewater was examined. One unit was planted with Scirpus grossus (L2), one was planted with Typha angustifolia (L3), and the unplanted third (L1) was the control. Biological oxygen demand (BOD5), nitrate , ammonium (NH4-N), total phosphorus (TP), and total suspended solids (TSS) of influent and effluent were regularly measured. The average BOD5 removal efficiencies were 44%, 68%, and 54% for units L1, L2, and L3, respectively. The plant growth was continuously monitored in marked quadrats by measuring the shoot height and other growth parameters. The above-ground biomass of L2 and L3 was harvested 8 months and 11 months after the planting date when the plants reached the maximum shoot height and at the start of inflorescence formation. S. grossus was superior to T. angustifolia, with faster establishment, higher productivity, and higher removal of BOD5. However, the growth of S. grossus was possibly inhibited by continuously high concentrations, while T. angustifolia showed tolerance of high concentrations.

Effect of broken dead culms of Phragmites australis on radial oxygen loss in relation to radiation and temperature

The amount of oxygen released from the roots of Phragmites australis was quantified to examine the effects of airflow through dead culms, radiation, and temperature on radial oxygen loss (ROL). To investigate the effect of dead culms on ROL quantitatively, the ROL of individual plants with open dead culms was compared to that of plants with sealed dead culms as a function of light intensity and temperature. The relationship between ROL and plant morphology (aboveground biomass, shoot diameter, shoot height) was investigated. When exposed to 300, 600, and 900 μmol m−2 s−1 light, the ROL was 15.6, 22.5, and 30.9 μmol O2 g−1 dry root day−1, respectively, from plants with open dead culms and 11.0, 16.4, and 23.3 μmol O2 g−1 dry root day−1, respectively, from plants with sealed dead culms. The ROL from plants with open dead culms was obviously higher than that from plants with sealed dead culms in every condition. The ROL from plants with open culms was 37% and 30% higher than that from plants with sealed culms at 20°C and 30°C, respectively. The effects of plant-specific parameters such as leaf area and shoot diameter on radial oxygen loss were evident. From the point of view of rhizosphere oxidation during the growing season, the existence of open dead culms should be taken into consideration for optimal plant management in constructed wetlands. This study provides a theoretical understanding of the effects of open dead culms, light conditions, and temperature on radial oxygen loss.

Coastal vegetation planting projects for tsunami disaster mitigation: effectiveness evaluation of new establishments

Coastal vegetation acts as a natural barrier against extreme natural and anthropogenic activities, protecting infrastructure and human lives. Establishment of hard infrastructure for tsunami protection is not feasible in developing countries due to its cost-intensive nature. Coastal vegetation can therefore be a feasible alternative for tsunami and general coastal protection in developing countries. This study investigates the effectiveness of current coastal vegetation projects and reports a pilot-scale vegetation project, which provides insights into the management and sustainability of such projects. Thirty-seven establishments of coastal vegetation for tsunami protection were identified for the study from Hambantota to Colombo along the southern coast in Sri Lanka. Evaluation was carried out to assess whether the coastal vegetation establishments fulfilled the planning objectives, such as vegetation alignment to tsunami direction, tree density and tree species, and whether monoculture or mixed species are grown. The study also assessed continuous maintenance and awareness about coastal vegetation, community participation and long-term institutional support from government, nongovernment groups, academic institutions, and other institutions within an integrated framework. Approximately 50% of the sites were found to be effective in terms of fulfilling the above requirements and had reasonable protection against future tsunami-type events. Continuous maintenance is ensured only for 35% of sites with community participation. The survey also revealed the importance of adopting scientific and nonscientific methods of vegetation establishment and selecting appropriate species and structure of vegetation strips for tsunami protection. It is expected that this will lead to the development of coastal vegetation guidelines for local authorities.

Constructed Tropical Wetlands with Integrated Submergent-Emergent Plants for Sustainable Water Quality Management

Improvement of primary effluent quality by using an integrated system of emergent plants (Scirpus grossus in the leading subsurface flow arrangement) and submergent plants (Hydrilla verticillata in a subsequent channel) was investigated. The primary effluent was drawn from a septic tank treating domestic sewage from a student dormitory at the University of Peradeniya, Sri Lanka. Influent and effluent samples were collected once every 2 weeks from May 2004 through July 2005 and analyzed to determine water quality parameters. Both the emergent and submergent plants were harvested at predetermined intervals. The results suggested that harvesting prolonged the usefulness of the system and the generation of a renewable biomass with potential economic value. The mean overall pollutant removal efficiencies of the integrated emergent and submergent plant system were biological oxygen demand (BOD5), 65.7%; chemical oxygen demand (COD), 40.8%; ammonium (NH4 +-N), 74.8%; nitrate (NO3 −-N), 38.8%; phosphate (PO4 3−), 61.2%; total suspended solids (TSS), 65.8%; and fecal coliforms, 94.8%. The submergent plant subsystem improved removal of nutrients that survived the emergent subsystem operated at low hydraulic retention times. The significant improvement in effluent quality following treatment by the submergent plant system indicates the value of incorporating such plants in wetland systems.

Effectiveness of Scirpus grossus in Treatment of Domestic Wastes in a Constructed Wetland

ABSTRACT We examined the ability of Scirpus grossus planted in a constructed wetland to treat domestic wastewater. One unit was planted with S. grossus, and another unit was used as a control. Influent wastewater and effluent from each wetland were tested monthly for 10 physical, chemical, and biological parameters from May 2004 to July 2005. Better performance was obtained by the vegetated unit than by the control unit. Mean removal efficiencies observed with S. grossus were total suspended solids, 61%; NH4 +-N, 71%; NO3 −-N, 31%; total phosphorus 18%; fecal coliforms, 90%; and five-day biochemical oxygen demand, 69%. Plant growth was continuously monitored, and the above-ground biomass of S. grossus was harvested after eight months, 11 months, and 14 months, when plants reached their maximum shoot height and inflorescence formation started. S. grossus has great potential to remove pollutants in constructed wetlands in tropical regions, especially because above-ground harvesting would be a feasible plant management option by which nutrients could be subsequently removed.