Treatment of septage in constructed wetlands in tropical climate: lessons learnt from seven years of operation

Abstract

In tropical regions, where most of the developing countries are located, septic tanks and other onsite sanitation systems are the predominant form of storage and pre-treatment of excreta and wastewater, generating septage and other types of sludges. The septage is disposed of untreated, mainly due to lack of affordable treatment options. This study presents lessons that have been learned from the operation of pilotscale constructed wetlands (CWs) for septage treatment since 1997. The experiments have been conducted by using three CW units planted with narrow-leave cattails (Typha augustifolia) and operating in a vertical-flow mode. Based on the experimental results, it can be suggested that the optimum solids loading rate be 250 kg TS/m2 yr and 6-day percolate impoundment. At these operational conditions, the removal efficiencies of CW units treating septage at the range of 80-96% for COD, TS and TKN were achieved. The biosolid accumulated on the CW units to a depth of 80 cm has never been removed during 7 years of operation, but bed permeability remained unimpaired. The biosolid contains viable helminth eggs below critical limit of sludge quality standards for agricultural use. Subject to local conditions, the suggested operational criteria should be reassessed at the full-scale implementation.

Sludge drying reed beds for septage treatment: Towards design and operation recommendations

“…Process performance is based, on the one hand, on ability to dewater sludge by two combined mechanisms (i) percolation through filter media (physical effect of reeds) (ii) evapotranspiration of water from sludge to atmosphere. Reeds play an important role in both mechanisms, thanks to their roots they improve infiltration of free water and they enhance dewatering due to evapotranspiration (Koottatep et al, 2005). On the other hand, organic matter mineralization occurs thanks to biological activity (microorganisms, earthworm…), which mean depending on aerobic conditions.…”

“…As a consequence, the few experiences done on septage differ greatly according to geographical context. For example Koottatep et al (2005) in Thailand suggest once-a-week 250 kgTS/m 2 /y application as operational condition. In France Liénard et al (2008) apply 50 kgTS/m 2 /y loading rate, with a feeding/resting period of 3.5/17.5 days as it is done when treating activated sludge.…”

Constructed Wetlands

“…Constructed wetlands have been used to treat on-site and centralized collected wastewater (Decamp and Warren, 2000;Stewart, 2005), septage (Koottatep et al, 2005), greywater (Morel and Diener, 2006), stormwater runoff , organic waste streams (Cronk, 1996), agricultural wastewater (Kantawanichkul and Somprasert, 2005), landfill leachate (Headley et al, 2004), acid mine drainage (Batty et al, 2005), and food processing and tannery wastewaters (Burgoon et al, 1999;Calheiros et al, 2007). Pre-treatment is recommended for waste streams such as domestic wastewater when there is a large amount of particulate matter (i.e., suspended solids) or organic matter (i.e., COD, BOD) (Cronk, 1996, Williams et al, 1999.…”

The flower and the butterfly constructed wetland system at Koh Phi Phi—System design and lessons learned during implementation and operation

“…The approach of the rehabilitation project was therefore to focus on constructed wetland systems, which are known to fulfil many of these requirements as they are generally reliant and costefficient (Brix and Schierup, 1989;Koottatep et al, 2005;Vymazal et al, 2006;Kadlec and Wallace, 2009). In addition, constructed wetlands can facilitate biological, aesthetical and social synergies in the built environment (Brix, 1999;Brix et al, 2007;Zurita et al, 2009;Konnerup et al, 2009;Dreiseitl and Grau, 2009).…”