Performance evaluation of hybrid constructed wetlands for the treatment of municipal wastewater in developing countries (original) (raw)
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Despite the demonstrated ability of subsurface flow constructed wetlands to treat effectively domestic and agricultural/industrial sewage wastewater, this ecotechnology has not been applied as widely as it deserves considering the great added value such systems offer. Some of the reasons are lack of awareness of this option, lack of experience and/or availability, especially in countries where the technology has not been previously developed. While having limitations, especially in their need for land, constructed wetlands are appropriate ecologically-based solutions, particularly for treating and reusing residential sewage, and especially for small, decentralized systems in remote or developing regions. Sewage treatment systems must be low-tech, low maintenance and minimal in their energy requirements to be affordable and easy to maintain in such applications, attributes which constructed wetland systems exemplify. Typical "package plant" or municipal sewage plant requires high capital investment, technical expertise and are energy-intensive to operate, while often a great nuisance for neighbours. Subsurface wetlands use little or no electricity and technology and require little technical supervision once installed. Previous studies of subsurface flow wetlands for sewage treatment have demonstrated their advantages in situations of small on-site sewage loading and in situations where avoidance of malodour and mosquito-breeding are important. A well-designed subsurface flow wetland can not only provide inexpensive and highly effective sewage treatment, but also great added value though the creation of additional green zone, biodiversity and productivity such a system enables. Constructed wetlands can also be conceived as buffer zones between human activity and natural green spaces. Sewage treatment can and should do far more than simply preventing pollution and the degradation of natural ecosystems occasioned by the incomplete treatment and discharge of wastewater. Wastewater treatment should also accomplish the return of nutrients and water to productive use. Nutrient recycling is just as central to the challenge of transforming human economic activities in Earth's vaster biospheric life support system to a sustainable basis. As Wastewater Gardens systems have been developed around the world, it has become evident that the next step beyond sewage water treatment however is to come as close as possible to total productive use of water and nutrients -not simply removal of sewage water "pollutant/nutrients". This has changed our conception from the old paradigm of "final disposal, e.g. leachdrains" to incorporating greywater recycle/irrigation where possible via subsoil irrigation of the treated effluents and designing robust systems with a plant diversity as wide as possible and as productive as possible (fruit trees, medicinal plants, animal fodder, flowers, wood, … etc), depending of local need and wishes. The interdisciplinary nature of the knowledge base behind constructed wetlands however -from ecology to engineering to botany/agronomy -however often makes the technology more difficult for specialized government and institutions to deal with ; in addition, like any ecological system, constructed wetlands are complex, living systems and unlike mechanical systems respond and evolve in response to local conditions and climate. Numerous parameters must be considered to ensure successful design and implementation as well as generalized sizing/treatment formulas. This paper will examine general issues and challenges illustrated by a few case studies from our work around the world.
Advances in Civil and Architectural Engineering, 2023
Water contamination is the greatest hazard to public health. Addressing water scarcity and protecting accessible water sources necessitates the effective treatment of wastewater. This makes the use of sustainable solutions such as constructed wetlands (CWs) essential. CWs leverage natural processes involving wetland vegetation, soils, and microbial communities. This study evaluates the efficiency of a horizontal sub-surface flow CW, established with local plants at Hudiara drain, in removing pollutants such as Biochemical Oxygen Demand (BOD), Turbidity, Nitrates, Phosphates, and pH, across different months. The study reveals that while temperature and precipitation rates influence the CW's efficacy, the linear regression model indicates a strong correlation between phosphorus and BOD levels with precipitation. However, nitrates are sensitive to temperature, and turbidity is influenced by both temperature and precipitation within certain limits. Additional factors impacting CW performance include wastewater characteristics, design flow, and wetland location. When compared with Pakistan Environmental Quality Standards (PEQS), it is concluded that CWs are effective in wastewater treatment. By constructing CWs along the banks of wastewater drains, treated water from the outlet chamber can be collected and redirected, offering a viable solution to water scarcity challenges.
Ecological Engineering, 2011
Hybrid constructed wetland systems have recently been used to treat wastewaters where high demand for removal of ammonia is required. However, these systems have not been used too often for small onsite treatment systems. This is because in many countries ammonia is not limited in the discharge from small systems. Hybrid systems have a great potential to reduce both ammonia and nitrate concentrations at the same time. In our study we employed a three-stage constructed wetland system consisting of saturated vertical-flow (VF) bed (2.5 m 2 , planted with Phragmites australis), free-drained VF bed (1.5 m 2 , planted with P. australis) and horizontal-flow (HF) bed (6 m 2 , planted with Phalaris arundinacea) in series. All wetlands were originally filled with crushed rock (4-8 mm). However, nitrification was achieved only after the crushed rock was replaced with sand (0-4 mm) in the free-drain wetland. Also, original size of crushed rock proved to be too vulnerable to clogging and therefore, in the first wetlands the upper 40 cm was replaced by coarser fraction of crushed rock (16-32 mm) before the second year of operation started. The system was fed with mechanically pretreated municipal wastewater and the total daily flow was divided into two batches 12 h apart. The evaluation of the results from the period 2007 to 2008 indicated that such a system has a great potential for oxidation of ammonia and reduction of nitrate. The ammonia was substantially reduced in the free-drained VF bed and nitrate was effectively reduced in the final HF bed. The inflow mean NH 4-N concentration of 29.9 mg/l was reduced to 6.5 mg/l with the average removal efficiency of 78.3%. At the same time the average nitrate-N concentration rose from 0.5 to only 2.7 mg/l at the outflow. Removal of BOD 5 and COD amounted to 94.5% and 84.4%, respectively, with respective average outflow concentrations of 10 and 50 mg/l. Phosphorus was removed efficiently despite the fact that the system was not aimed at P removal and therefore no special media were used. Phosphorus removal amounted in 2008 to 65.4%, but the average outflow concentration of 1.8 mg/l is still high. The results of the present study indicate very efficient performance of the hybrid constructed wetlands, but optimal loading parameters still need to be adjusted. The capital cost of the experimental system is comparable to the conventional on-site treatment plant but the operations and maintenance costs are about one third of the conventional plant.
Performance evaluation of constructed wetlands in a tropical region
Ecological Engineering, 2009
Constructed wetland is widely used in developed countries and temperate climate for the stormwater quality improvement. However, constructed wetland in Malaysia can be considered as a new innovation and not widely implemented in all over Malaysia. The aim of this paper is to evaluate the efficiency of constructed wetland in Malaysia through the two experiences of constructed wetland at Universiti Sains Malaysia Engineering Campus, Malaysia and Humid Tropic Centre Kuala Lumpur, Malaysia. The data collected from these wetland systems used to treat stormwater runoff or runoff-impacted surface waters were examined and compared in order to identify any obvious trends that may aid future stormwater treatment wetland design efforts. The parameters measured and discussed in this paper were Turbidity, Total Phosphorus, Biological Oxygen Demand and Chemical Oxygen Demand. The result for USM Engineering Campus constructed wetland showed that the average removal efficiency of pollutant removal for BOD was range from 9.7% to 80%, COD was 5.7% to 62.9%, turbidity was 25.9% to 30.0% and TSS was 50% to 100%. While for HTC constructed wetland, the result showed that the average removal efficiency for BOD was range from 4.55% to 36.67% and COD was 9.1% to 88%, turbidity was 9.76% to 66% and TSS was 12.5% to 45%. Generally, the results obtained show that the constructed wetland under tropical climate is capable to improve stormwater quality before discharging to the nearest water ways. The efficacy of these constructed wetlands to treat stormwater from different sources varied, and modified wetland designs or active management may be necessary to improve water quality even further. The findings can be used significantly to enhance the knowledge in constructed wetland under tropical climate where it can serve effectively for managing urban runoff using control at source approach.
E3S Web of Conferences
In recent years, an increase in interest in hybrid constructed wetland systems (HCWs) has been observed. The aim of the paper is to compare different HCW configurations in terms of mass removal rates and efficiency of pollutants removal. Analysed data have been collected at multistage constructed wetlands in Poland, which are composed by at least two beds: horizontal subsurface flow (SSHF) and vertical subsurface flow (SSVF). The evaluation was focused on hybrid constructed wetlands performance with HF+VF vs. VF+HF configuration, where influent wastewater of the same composition was treated. In analysed HCWs, the effective removal of organic matter from 75.2 to 91.6% COD was confirmed. Efficiency of total nitrogen removal varied from 47.3 to 91.7%. The most effective removal of TN (8.3 g m-2 d-1) occurred in the system with VF+VF+HF configuration.
COMPARISON OF TREATMENT PERFORMANCE BETWEEN CONSTRUCTED WETLANDS WITH DIFFERENT PLANTS
Constructed wetlands have gained much importance for treating domestic, industrial and agricultural wastes and are considered as an effective secondary or tertiary treatment method. The main characteristics affect the removal efficiency of constructed wetland are the vegetation type, hydraulic residence time and substrate. The aim of the present study is to examine effect of vegetation type on organic and nutrient removal under varying hydraulic residence time in constructed wetlands. With this in mind, we have designed, constructed and operated two pilot-scale horizontal subsurface flow constructed wetlands having two different wetland vegetation plants in our open-air laboratory receiving pre-treated domestic wastewater by varying hydraulic residence time as 2, 4, 6 and 8 days. The influent wastewater is rich in orgnic matter with high variability presence of nutrients. In the first unit, the removal efficiency of COD, BOD, TN, and TP was increased from 39 to 69%, 29 to 56%, 23 to 45% and 25 to 75% when there was an increase in HRT from 2 days to 8 days respectively. In the second unit, the removal efficiency of COD, BOD, TN, and TP was increased from 31 to 68%, 25 to 52%, 26 to 36% and 40 to 77% when there was an increase in HRT from 2 days to 8 days respectively. It was found that vegetation type influenced concentration reduction. A 6-day hydraulic residence time is suggested for an acceptable level of treatment in these systems.
Ecological Engineering, 2020
The universalization and decentralization of wastewater treatment is one of the greatest challenges faced in Brazil. In this context, Constructed Wetlands (CWs) may be considered environment friendly and economically viable alternative for geographically remote locations, having fewer financial resources and infrastructure. During the last years, studies have investigated different configurations aiming to increase the capacity of CW to remove nutrients, mainly phosphorus (P) and reinforced its importance in ecological and landscape contexts. Thus, the present study evaluated the performance of a hybrid system combining Floating, Vertical and Horizontal Flow CWs to treat urban wastewaters. A removable adsorbent barrier was developed to improve the removal of P and a polyculture with ornamental plants was used to add landscape potential. The obtained results showed a promising nutrients removal capacity of the hybrid system, with mean removal rates of 94.0% for total P, 93.8% for ammonium nitrogen (N−NH 3), 93.8% for total nitrogen (N), 80.0% for dissolved organic carbon (DOC), 84.0% for biochemical oxygen demand (BDO 5), 77.0% for chemical oxygen demand (COD) and 99.7% for turbidity. The integrated system kept its ability to remove pollutants during the 11 months of operation (January to December 2019), without substrate saturation, and also maintaining P values within the limits allowed by current Brazilian (CONSEMA Resolution 355/17 (3 mg L −1)) and international legislation (UWTD 91/271/EEC (2 mg L −1)). The landscape benefits were extremely positive mainly due to the flowering of Canna generalis and its greater biomass production. By crossing the biomass data and the accumulation of nutrients in the tissues of the aerial part it was possible to verify that the contribution of the plants in the N removal from the system reached 8.08% while the P decrease attained 17.92% in the horizontal sub-surface flow constructed wetland (HSSFCWs). Therefore, the developed system enabled an efficient removal of nutrients throughout the monitoring period, enhancing the wastewater quality and potentializing its reuse for different purposes. Witthayaphirom et al., 2019; Lin et al., 2020). Thus, it is necessary to use processes that make it possible to reduce the eutrophic potential and encourage the reuse of water. In this sense, CWs have been considered interesting options for decentralized
Natural and constructed wetlands for wastewater treatement: Potentials and problems
Water Science and Technology, 1999
Wetlands are being considered increasingly important for wastewater treatment because of the ability of many wetland plants to absorb large amounts of nutrient and a variety of toxic substances . The paper highlights the physical , chemical and biological processes which contribute to the improvement of water quality, and the distinction between natural and constructed wetlands. The impacts of long-term wastewater disposal on the biotic changes , reduction in treatment efficiency, and wetland processes such as production of trace gases, arc pointed out. Constraints in usmg wetlands, for wastewater treatment, such as poor understanding of the natural wetland functions and responses of native plants and animals to wastewater, particularly in developing countries, are briefly discussed. It IS suggested that while the possibil ities for using constructed wetlands based on native species for small communmes are explored, greater emphasis should be laid on the restoration of lost and degraded wetlands, especially the river floodpla ins, lake httorals and coastal wetlands, which can help check pollution from non-point sources . ()