Design of a Reed Bed System for Treatment of Domestic Wastewater using Native Plants

The reed bed system is one types of phytoremediation technology for removing pollutants from the environment. This technology provides an environmentally friendly approach to treating contamination with competitive cost, compared to the physico-chemical treatment. The design of reed bed system is highly important in order to achieve the highest pollutant removal efficiency. The design of reed bed system affects the natural oxygen transfer from the environment. The reed bed system was proven to have a good efficiency in removing Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), Total Dissolve Solid (TDS), Total Nitrogen (TN) and a number of bacteria. In addition to the oxygen transfer from the environment, the interaction among pollutant-plants-medium-microbes also plays a vital role in the removal of pollutant using the reed bed system. It was suggested that the future related research should accommodate the importance of several environmental conditions to the interaction between pollutant, plants, medium and microbes as well as the impact of those interactions on the pollutant removal efficiency.


INTRODUCTION
Phytoremediation is one of the treatment technologies that utilize plants to remediate the pollutants in contaminated environments (Ismail et al., 2017;Purwanti et al., 2019). It improves the condition of environments following the removal of the contamination (Bolan et al., 2011). This technology is also considered to be low cost and environmentally friendly in terms of the real implantation (Kinidi and Salleh, 2017;Tien et al., 2018). The reed bed system is a man-made wetland planted with selected species of plants (reeds) which have a capability to take oxygen from the air and release it into the rhizosphere (Manios et al., 2002). As a result of this action, a very high population of micro-organisms is promoted and enhanced in the rhizosphere (Bolan et al., 2011;Safronova et al., 2006;Titah et al., 2018). The reed bed system is a combination of three interdependent key elements: the growing medium, the plants and the micro-organisms Manios et al., 2002;Zhang et al., 2013).
It is necessary to find the optimal reed bed design characteristics such as residence time in order to maximize the removal efficiency under the smallest-as-possible treatment area (Purwanti et al., 2018b). Understanding the behavior of reed beds treating wastewater is required to obtain the optimum condition for wastewater treatment processes. Typically, the domestic wastewater contains pathogens (bacteria), total solids (dissolve and suspended), nutrients (nitrogen and phosphorus), other organic pollutants and traces of heavy metals (Ahmad et al., 2016;Mtshali et al., 2014;Ning et al., 2017;Samer, 2015).
It was reported that up to 18% of rivers were polluted by organic compounds as the presence of high biochemical oxygen demand (BOD). Around 24% of rivers in Malaysia were also polluted by ammoniacal nitrogen (NH 3 -N) originated from sewage that may include the livestock farming activities and domestic wastewater (Katayon et al., 2008; Ministry of Science Technology and the Environment Malaysia, 2003). These pollutants need to be brought down to permissible limits before the disposal of effluent by maximizing removal of pollutants from domestic wastewater (Manju et al., 1998;Tangahu et al., 2019;Titah et al., 2019). Hence, this paper was aimed at discussing about the design of reed bed system for treatment of domestic wastewater. Additionally, the paper also aimed at investigating the effectiveness of native plants in treating domestic wastewater. The result of this study may provide a general design of a phytoremediation reactor, especially using a reed bed system and provide an alternative technology for treating the domestic wastewater. Figure 1 presents a schematic diagram for the reed bed system, which was designed for the domestic wastewater treatments. It consisted of four lines; each line has three identical beds made of fiberglass columns of 2 m length, 1 m width and 1 m height. The type of medium used for this reed beds mostly consists of gravel of different size and sand. The gravel of different size was employed as a medium in the system with an alternative arrangement (10-15 mm, 3-5 mm (river sand) and 30-35 mm respectively) instead of the conventional medium arrangement to form multiple layers in the reed beds ( Figure 2).

Design of Reed Bed System
This bed system was designed to provide oxygen on the surfaces in which other organisms can grow and proliferate. The beds were planted with treatment plants which are highly suggested to be native plants already proven to have good capability in removing pollutants (Imron et 2

Scirpus grossus and Typha angustifolia
The complete treatment plant consisted of anaerobic baffled reactor and constructed wetland showed removal of COD, BOD and nutrient up to 99.71%, 99.76%, and 98.9%, respectively.

Continuous effluent recirculation system
High strength domestic wastewater

Phragmites australis
The system achieved total removal of 77% for COD, 78% for BOD 5 , 66% for suspended solid, 62% for NH 4 -N, and 38% for phosphorus, which mean that effluent recirculation can be considered to be applied to improve the removal efficiency of reed bed by enhancing interactions between wastewater, plants, and microorganisms either on surface of the medium or in the rhizosphere.

Conventional and alternative medium arrangement system
Farm wastewater

Phragmites australis
Considerable removal of COD and BOD 5 was obtained in both systems. The total removal percentages of COD reaching up to 74.79% and BOD 5 up to 67.71% in the anti-sized system. These removal efficiencies were slightly higher compared to the progressively-sized system which only reach 71.71% for COD and 66.71% for BOD 5 .

Cyperus flabelliforis
Recirculation enhances oxygen transport by pumping and re-distributing the wastewater and increase its contact with air. The increasing contact between wastewater and air will enhance the respiration and activities of the aerobic microorganisms. It also increased the removal of total nitrogen from 71% to 85% and achieving final COD and TKN removal of 95% and 98%, respectively.
7 Sub-surface system Domestic wastewater

Lepironia articulata
A total removal of COD, TSS and total coliform up to 77%, 88%, and 99%, respectively, indicating that sub-surface system may also handle the high number of bacteria in wastewater.

Reed bed performance and selection of plants
The performance of reed bed in treating the domestic wastewater is remarkably good. The presented design might provide a better removal efficiency of some parameters in domestic wastewater by providing a better natural oxygen transfer. For additional reference, some studies mention the removal efficiency of the reed bed in treating wastewater, as tabulated oinn Table 1.
In addition to the reed bed system, the capability of the plants used is a non-separated contribution to the overall reed bed performance (Manios et al., 2002;Reed and Glick, 2005;Zhang et al., 2013). It is highly suggested that the involved plants should be native to the location, because it has a better adaptability to the surrounding environmental condition (Abdullah et al., 2020). Since this design will be applied in Malaysia, some Asian native plant species which had been proven to have a good capability in treating wastewater are summarized in Table 2.

Future research approaches
Further research in the reed bed topic may analyze the optimum environmental condition during the treatment period. The optimum environmental condition may include retention time (Koottatep and Polprasert, 1997), pH (Dakora and Phillips, 2002), temperature (Vlaev et al., 2011), and the flow system (Cossu et al., 2001;Yasmin et al., 2016). The analysis of the environmental condition is highly suggested to consider the interaction of plant-medium and also plantmicrobes during the reed bed treatment. The highest removal of pollutant is considered to be obtained by achieving the optimum condition for medium-plant-microbes interaction.

CONCLUSIONS
Reed bed is proven to be highly reliable in treating wastewater, especially from the domestic source. A good reed bed design will give a better chance to achieve higher removal efficiency of pollutants by providing higher natural oxygen exchange. The application of reed bed treatment was shown to have a capability in removing TSS, COD, BOD, Total Nitrogen, TKN and also bacteria. The performance of reed bed in removing pollutants cannot be separated from the capability of the involved plants species. The interaction between pollutant, medium, plants and also microbes plays an important role in treating wastewater using the reed bed system.