Abstract
In urban and peri-urban areas of developing countries decentralized wastewater treatment using septic tanks as pretreatment is common. One challenge of decentralized wastewater treatment systems (DEWATS) is handling and utilization of the generated sludge. Sludge drying reed beds (SDRBs) are a robust method for dewatering and stabilization of sludge. Constructed wetlands (CWs) and SDRBs can be integrated to treat both wastewater and sludge. SDRBs require more area than most other sludge treatment options, but have low operational cost and energy requirements. The land area required for SDRB’s can be optimized by the selection of an appropriate loading rate, sludge application frequency and resting phase. This paper gives a review regarding the use of SDRB’s as well as presenting a pilot scale experiment comparing planted and unplanted sludge drying beds in Kathmandu. The planted beds showed a higher dewatering capability and higher reduction of volatile solids (VS). A short-term pilot-scale experiment can give valuable input to the design and operation of full-scale systems and for sub-tropical climate as that of Kathmandu Nepal, an initial sludge loading rate (SLR) of 100 kg total solids (TS)/m2/year is suggested with a gradual increase to up to 250 kg TS/m2/year.
Highlights
The management of sludge generated in decentralized wastewater treatment systems is a huge challenge in developing countries
In a decentralized sludge treatment facility where the incoming sludge is expected to vary considerably, homogeneous mixing of sludge in a buffer tank is recommended, as this will equalize the total solids (TS) concentration of the sludge [28]
Since the activated sludge is younger, the readily degradable part of the volatile solids (VS) can be expected to be higher in the activated sludge, for the same amount of TS load the mineralization rate of organic matter can be expected to be higher for the plants receiving activated sludge
Summary
The management of sludge generated in decentralized wastewater treatment systems is a huge challenge in developing countries. The challenges of using SRDB’s are: long startup time due to conditioning of the reeds, sensitivity to the loading regime, wilting of plants and lack of design criteria for different sludge types and climate zones [2] [13]. In Ghana a SLR of 100 - 200 kg TS/m2/year has been used to treat fecal sludge in unplanted sludge drying beds. The aim of the short-term study presented is to examine the dewatering performance of planted and unplanted drying beds treating septic tank sludge.
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