Domestic wastewater treatment using vertical flow constructed wetlands planted with Arundo donax, and the intermittent sand filters impact

Abstract

Plant filtering techniques have proved to be appropriate solutions in the treatment of wastewater. In addition, the effluents can be re-used in water-deficient areas, in urban settings as well as in rural agricultural areas. The influent from the secondary black water pilot scale filtration basins (RALBI) was treated during a six-month study. The study shows the elimination of different pollutants from black water effluents with the effectiveness of 46.9–63.26% COD and 31.72–60% of the NH₄⁺ concentrations. We also tested the performance of Arundo donax on the adsorption of nitrogen compounds. The rate of COD removal for the control was 0.0185 gCOD/m²/d and 0.012 gCOD/m²/d for the planted filters, while the mean loading rate of the influent was 0.317 g/d. The rate of NH₄-N removal for the control was 0.0152 gNH₄-N/m²/d and 0.0127 gNH₄-N/m²/d for the planted filters, while the mean loading rate of the influent was 0.271 g/d. Then, a concentration of 101.77–176.44 mg/L of nitrate was measured in the treated effluent. In addition, meaningful reduction of fecal coliforms and streptococci was achieved and reached over 95%. The quality of treated effluents has shown that the use of planted filters as a post-treatment stage is an efficient and inexpensive technology for the treatment of wastewater in small urban and rural communities.

Introduction

The elimination of poorly treated wastewater from on-site systems serving households and small communities can result in hydraulic failure, leading to infiltration of pollution into groundwater and surface water contamination. This poses risks to human health, the environment and soil (Tanner et al., 2012). In Morocco, as in other developing countries, increasing urbanization has led to a significant increase in the quantities generated from urban wastewater (Lamghari Moubarrad and Assobhei, 2007). However, without having high-performance or very expensive treatment systems in their operation, constructed wetlands (CWs) have been recognized as cost-effective alternatives or useful compliments to conventional wastewater treatment systems (Brix and Arias, 2005, Tsihrintzis and Gikas, 2010, Vymazal, 2009; Schlz and Lee 2005). CWs are effective treatment systems for decreasing concentrations of the total suspended solids (TSSs), biological oxygen demand (BOD), nitrogen, bacteria (Escherichia coli, total coliforms) and metals (Kadlec and Knight, 1996, IWA, 2000; ).

However, in most applied horizontal subsurface flow CWs, oxygen transport to saturated media is limited, with only a small quantity of net release via macrophyte roots (1–8 g/m²/d) (Kadlec and Wallace, 2009, Garcia et al., 2010). Artificially aerated CWs can increase the oxygen transfer rate to 160 g/m²/d by compressing air from the atmosphere into the wetland bed through a blower (Kadlec and Wallace, 2009) thus, the oxygen transfer rate reaches up to 450 g/m²/d (Wu et al., 2011b), and the treatment capacity of ammonium and organic matter significantly improves (Hu et al., 2012, 2014), facing the standards of wastewater discharge which are strictly controlled due to severe eutrophication and environmental pollution (Liu and Qiu, 2007). Nitrogen compounds, such as ammonium, are among the main nutrients coming from different types of wastewater, which must be treated before being discharged directly into waterbodies (Kadlec and Wallace, 2009). Nitrification of ammonium also allows the production of other nitrogen compounds such as nitrite and nitrate in wastewater. However, nitrate and phosphorus are responsible for an intensification of biological productivity in the natural environment (eutrophication), due to their elevated contributions brought in by the action of the man.

In addition, the use of treated wastewater for irrigation and crop planting is becoming a common practice in the world (Angelakis et al., 1999, Lubello et al., 2004). Hence CWs could be effective solutions for the quality and quantity control of treated effluents for the purpose of their reuse or release into the environment in a safe and responsible manner.

Our aims were to test the effectiveness of two tertiary wastewater treatment systems consisting of sand filter and a constructed wetland based on sand filter planted with Arundo donaxin reducing levels of organic matter (COD, TSS), nitrogen (NH₄⁺, NO₂⁻, and NO₃⁻) and fecal contaminants (coliforms and streptococci). The pre-treated wastewater was comeing from the experimental RALBI blackwater treatment system installed in Faculty of Sciences El Jadida, Chouaî Doukkali University, Morocco. Arundo donax,The impact of the nature of the sand was also investigated.