Abstract
The multi-soil-layering (MSL) system primarily comprises two parts, specifically, the soil mixture layer (SML) and the permeable layer (PL). In Japan, zeolite is typically used as the permeable layer material. In the present study, zeolite was substituted with comparatively cheaper and more environmentally friendly materials, such as expanded clay aggregates, oyster shells, and already-used granular activated carbon collected from water purification plants. A series of indoor tests indicated that the suspended solid (SS) removal efficiency of granular activated carbon was between 76.2% and 94.6%; zeolite and expanded clay aggregates achieved similar efficiencies that were between 53.7% and 87.4%, and oyster shells presented the lowest efficiency that was between 29.8% and 61.8%. Further results show that the oyster shell system required an increase of wastewater retention time by 2 to 4 times that of the zeolite system to maintain similar chemical oxygen demand (COD) removal efficiency. Among the four MSL samples, the zeolite system and granular activated carbon system demonstrated a stable NH3-N removal performance at 92.3%–99.8%. The expanded clay aggregate system present lower removal performance because of its low adsorption capacity and excessively large pores, causing NO3−-N to be leached away under high hydraulic loading rate conditions. The total phosphorous (TP) removal efficiency of the MSL systems demonstrated no direct correlation with the permeable layer material. Therefore, all MSL samples achieved a TP efficiency of between 92.1% and 99.2%.
Highlights
Urbanisation increases the population density of residential areas, increasing the production of domestic wastewaters in these areas, which without proper treatment may severely affect the natural environment
The main purpose is to investigate the effectiveness of wastewater purification using four kinds of permeable layer (PL) materials, zeolite, expanded clay aggregates, oyster shells, and already-used granular activated carbon; as a result, the same soil mixture layer (SML) material is used for each experiment
Achieved similar results to System A at hydraulic loading rate (HLR) = 1.0, 0.5–1.0, and 1.0–2.0 m3/m2/d, respectively. These findings suggest that the expanded clay aggregate, oyster shells, and granular activated carbon systems can achieve a similar chemical oxygen demand (COD) removal efficiency as that of the zeolite system when the wastewater retention time within the MSL system is extended
Summary
Urbanisation increases the population density of residential areas, increasing the production of domestic wastewaters in these areas, which without proper treatment may severely affect the natural environment. Because of the ever-increasing awareness of environmental protection and sustainable management in recent years has prompted the Taiwanese government to aggressively seek cost-effective solutions for sewage treatment. In this context, the economical and easy-to-construct natural treatment system (NTS) has gained considerable attention in recent years. Wastewater treatment using constructed wetlands is extremely time-consuming and requires a large area of land to achieve the desired treatment effects. This type of NTS becomes uneconomical in areas with high land costs
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