Performance assessment of aquatic macrophytes for treatment of municipal wastewater
© Shah et al.; licensee BioMed Central Ltd. 2014
Received: 21 July 2013
Accepted: 9 July 2014
Published: 16 July 2014
The objective of the study was to evaluate the performance of three different aquatic macrophytes for treatment of municipal wastewater collected from Taxila (Pakistan). A physical model of treatment plant was constructed and was operated for six experimental runs with each species of macrophyte. Every experimental run consist of thirty days period. Regular monitoring of influent and effluent concentrations were made during each experimental run. For the treatment locally available macrophyte species i.e. water hyacinth, duckweed & water lettuce were selected to use. To evaluate the treatment performance of each macrophyte, BOD5, COD, and Nutrients (Nitrogen and Phosphorus) were monitored in effluent from model at different detention time of every experimental run after ensuring steady state conditions. The average reduction of effluent value of each parameter using water hyacinth were 50.61% for BOD5, 46.38% for COD, 40.34% for Nitrogen and 18.76% for Phosphorus. For duckweed the average removal efficiency for selected parameters were 33.43% for BOD5, 26.37% for COD, 17.59% for Nitrogen and 15.25% for Phosphorus and for Water Lettuce the average removal efficiency were 33.43% for BOD5, 26.37% for COD, 17.59% for Nitrogen and 15.25% for Phosphorus. The mechanisms of pollutant removal in this system include both aerobic and anaerobic microbiological conversions, sorption, sedimentation, volatilization and chemical transformations. The rapid growth of the biomass was measured within first ten days detention time. It was also observed that performance of macrophytes is influenced by variation of pH and Temperature. A pH of 6-9 and Temperature of 15-38°C is most favorable for treatment of wastewater by macrophytes. The option of macrophytes for treatment of Municipal sewage under local environmental conditions can be explored by further verifying the removal efficiency under variation of different environmental conditions. Also this is need of time that macrophyte system should be used for treatment of wastewater because their performance is comparable to conventional wastewater treatment plants and also the system has very low O&M costs.
Wastewater is any liquid that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, or agriculture and can encompass a wide range of potential contaminants and concentrations. In the most common usage, it refers to the municipal wastewater that contains a broad spectrum of contaminants resulting from the mixing of wastewater from different sources. Urban wastewater contains 99% water, and other materials make up the portion. The potential pollutants include pathogens, oil and grease, metals, organic matter (OM), solids and nutrients such as Nitrogen (N) and Phosphorous (P). The actual proportion of each constituent within any given wastewater varies depending on the spatial and temporal differences .
In recent years, the amount of wastewater produced from several activities has increased as a result of the rapid improvement of living standards . Although some communities treat their wastewater in a suitable way, others lack convenient treatment systems, thus discharging untreated wastewater into the natural environment. Pollutants (e.g. heavy metals) enter aquatic systems via numerous pathways, including effluent discharge, urban and agricultural run-off. Contaminants present in sewage commonly include a wide range of metallic and organic compounds .
Wastewater treatment technology needs to be appropriate and sustainable. It also needs to be less costly, easy to operate and maintain, and very efficient in removing both organic matter and heavy metals. In developing countries natural treatment systems, are more suitable. Natural treatment systems are considered one of the best treatment options, particularly in warm climates . Wetlands with macrophytes are one of the many types of natural systems that can be used for treatment of municipal wastewater. According to Trepanier, a wetland specifically constructed for the purpose of pollution control and waste management, at a location other than existing natural wetlands” is known as constructed wetland. Wetlands have many unique benefits as a wastewater treatment process, including the ability to operate on ambient solar energy, self-organize and increase treatment capacity over time, rich in biodiversity, produce oxygen and consume carbon dioxide, and achieve high levels of treatment with minimum maintenance . Macrophytes have been used effectively to treat different types of wastewaters. This is mainly due to their nutrient absorbing capacity, simplicity, low construction/operation and maintenance cost, low energy demand, process stability, potential benefits of the harvested materials .
The macrophytes have several properties in relation to the treatment processes. The most important effects of the macrophytes in relation to the wastewater treatment processes are the physical effects of the plant tissues give rise to filtration effect and provide of surface area for attached microorganisms. The pollutants removal of macrophytes by plant uptake and oxygen release affects the wastewater treatment processes in different extends. The macrophytes provide habitat for wildlife .
Zhang et al.  conducted investigation regarding the efficiency of macrophytes based treatment system in China for Municipal Wastewater Treatment. According to his findings Large-scale centralized wastewater treatment systems often prevail in industrial countries and have been regarded as a successful approach during the last century .
According to Mayo et al.  the removal of faecal coliforms was investigated in pilot-scale water hyacinths ponds. The investigation was conducted to evaluate the role of solar intensity, pH, dissolved oxygen, temperature, sedimentation, and attachment of faecal coliforms on Eichhornia crassipes on disappearance of bacteria in water hyacinths ponds. The results showed that environmental factors such as solar intensity and pH were the key factors when water hyacinths ponds have a large exposed surface area .
Water pollution is becoming a serious issue of the entire world due to the rapid population growth, unsuitable treatment technology and inadequate management. In Pakistan untreated municipal wastewater is indiscriminately discharged into water bodies. Rapid urbanization and industrialization have resulted in increased pollution load in the rivers and streams. In large cities municipal wastewaters from almost whole city along with commercial/industrial effluents is being discharged into water bodies in the immediate vicinity of the city (i.e. rivers, surface drains & canals). As a result pollution level in the water bodies is ever increasing due to the increase in the population and commercial/industrial development. There are several sophisticated treatment systems available, such as activated sludge process, rotating biological contactor, and aerated lagoon, but they require high capital, operational, and maintenance costs. In Pakistan treatment plant based of trickling filter was installed in Karachi while other based on activated sludge process was installed in Islamabad but both the treatment plant are non functional now a days due to high maintenance and no skilled staff availability. Waste stabilization ponds are currently functioning in Peshawar. due to the experience of wastewater treatment plants, biological treatment system with low operational and capital costs is preferred especially for developing countries like Pakistan, with warm climate all year round. Pakistan has sufficient land for natural wastewater treatment technology in the outskirts of cities. Thus, the maximum advantages of climate and land availability should be taken for wastewater treatment purpose. The attractive method is combination of waste stabilization pond along with macrophytes. The mechanism of treatment in this system is same as in constructed wetland. This method has been used as the effective low-cost technologies that require minimum energy to operate that are suitable for urban as well as for rural areas in Pakistan.
Though, the treatment of wastewater by macrophyte plants has been started long before. The question how low aquatic plants can decrease the wastewater quality indicators still remain unanswered. Mainly macrophytes treat wastewater by organic matter uptake from the wastewater. at the roots of macrophytes small zones exist which arrest organic matter from wastewater. It is of interest to determine the lower bounds of pollutant contents that can reached because of their removal by aquatic plants and under what condition removal occur. This reflects on the range of application of aquatic plants (macrophytes) for wastewater treatment. Therefore, a physical Macrophyte based treatment plant model was constructed to treat municipal wastewater from University of Engineering& Technology (UET), Taxila. Wastewater was discharged into physical model containing Macrophytes. The objectives of the study aimed to evaluate the removal performance of pollutants as COD, BOD5 and nutrients (N&P) by different macrophytes species.
Material and methods
The municipal wastewater for the study was collected from the municipal sewer of UET Taxila containing wastewater of university and university colony.
Selection of species of macrophytes
The selection of macrophytes for the study was done on the availability of macrophytes locally as well as the environmental conditions of the area. Keeping in view of all the factors three macrophytes i.e. Water Hyacinth, Duckweed & Water Lettuce were selected.
The study was carried for 18 months in physical model. The BOD5, COD, and ammonia, Phosphorus were analyzed according to Standard Methods for the Examination of Water and Wastewater.
Results and discussions
The removal of pollutants by macrophytes may occur through a number of processes, including sedimentation, filtration, plant uptake/removal efficiency, adsorption, formation of solid compounds, and microbial-mediated reaction.
Raw wastewater characteristics
Characteristics of raw wastwater
Ammonia nitrogen (NH3-N)
Factors affecting the performance
Plants (Macrophyte) height measurement
Plant height (ft)
Plants biomass productivity
The results showed that the optimum period for harvesting can be found to be 8-10 days. At the optimum point, the growth rate of the plant is lowest.
As far removal efficiencies are concerned Water Hyacinth is found most effective while considerable removals of pollutants were also found with Duckweed and Water Lettuce. Performance of Water Hyacinth based system was found to be 50.61% for BOD5, 46.38% for COD, 40.34% for Nitrogen and 18.76% for Phosphorus. For Duckweed based system the efficiencies were 33.43% for BOD5, 26.37% for COD, 17.59% for Nitrogen and 15.25% for Phosphorus. Similarly for Water Lettuce 33.43% for BOD5, 26.37% for COD, 17.59% for Nitrogen and 15.25% for Phosphorus. The mechanisms of pollutant removal in the system include both aerobic and anaerobic microbiological conversions, sorption, sedimentation, volatilization and chemical transformations. pH for the wastewater affect the performance of macrophytes and it was found that macrophytes gave optimum performance at pH 6-9. Temperature is another factor that severely affect macrophytes performance and it was found a Temperature below 10°C macrophytes were unable to perform treatment and the favorable temperature for treatment is 15-38°C. the growth of macrophytes is more in first ten days of an experimental run because in first ten days maximum treatment to wastewater is provided by macrophytes by up-taking the organic matter. Pre-treatment of wastewater before the plant acclimatization could be potentially effective. The option of macrophytes for treatment of Municipal sewage under local environmental conditions can be explored by further verifying the removal efficiency under variation of different environmental conditions. Also this is need of time that macrophyte system should be used for treatment of wastewater because their performance is comparable to conventional wastewater treatment plants and also the system has very low O&M costs.
The authors acknowledge the financial and scientific support provided by Department of Civil and Environmental Engineering, University of Engineering and Technology, Taxila, Pakistan.
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