Septage treatment using vertical-flow engineered wetland: A critical review

Abstract

Septage, which is a mixture of sludge, scum and liquid, is a type of faecal sludge that is specifically removed from an individual septic tank. Their biochemical stability and high concentration of solids and nutrients are the major technical challenges towards effective treatments in the existing wastewater treatment systems. A subsurface vertical-flow engineered wetland (VFEW) is, therefore, introduced as a feasible decentralized septage treatment option for small or medium communities due to its abilities in achieving excellent treatment and energy efficiency and reasonable cost through a simple operation. In general, the VFEW removes suspended solids, organic matter and nitrogenous components constituted in raw septage efficiently and sustainably. This paper presents a critical review on the state-of-the art of septage treatment using vertical-flow engineered wetland with regards to their characteristics and operation. The system-factor such as substrate profile and operational factors such as solid loading rate (SLR) and frequency of loading have been generally agreed as major factors governing the effectiveness of VFEWs. The selection of substrates is crucial to ensure a long-term usability of the VFEW with regards to the clogging phenomenon. The SLR, which ranged from 30 to 250 kg TS m-2 y-1, is of great importance to the treatment capability. The frequency of loading determines the rate of oxygen renewal, microbial growth and mineralization of the accumulated sludge deposit within the VFEW system. Future research directions and recommendations are also outlined.