Faecal Sludge Management for Disaster Relief - Technology Comparison Study

On behalf of Oxfam, Arup have conducted a technical comparison study on Faecal Sludge Management at the Rohingya camps close to Cox’s Bazar (CXB), Bangladesh. The aim of the study is to draw conclusions on best practice FSM for disaster relief, from evidence gathered through practical experience. The study used existing available data to inform the analysis and in many cases these datasets are limited. The findings from the report should therefore be treated as provisional and are relevant to the particular context of the situation at CXB.

Over 20 operational FSM sites were visited in CXB, constructed by eight different NGOs and using eight different technologies. The eight FSM technologies were:

1. Constructed Wetlands

2. GeoTubes

3. Lime (Three main types; lagoons, in barrel and three tanks)

4. Anaerobic Lagoons

5. Aerobic Treatment

6. Upflow Filters (Two main types; with and without pre-settlement)

7. Biogas

8. Anaerobic Baffled Reactors (ABR)

The FSM technologies were compared against a set of indicators including; cost, footprint area, speed of construction and commissioning, operation and maintenance issues, pathogen inactivation and resilience to natural disasters. A scoring of 1 (most effective) to 5 (less effective) has been given to each technology for each indicator. For longer term i.e over 2 years, decentralised FSM technology, the Upflow Filters score well against a number of the key indicators and are therefore considered an effective ‘all round’ FSM technology. The Aerobic Treatment and Anerobic Lagoons scored similar for centralised treatment. The lagoons scored slightly better as the technology is simpler operate and maintain. Although these technologies have the lowest/best scoring they still have limitations and selection should be informed by site conditions.

It is considered that in the immediate phase of an emergency Lime treatment is still the appropriate FSM technology choice due to its speed of set up, stability of the treatment process and effluent quality. However due to the high OPEX of Lime it is not appropriate to use it as a longer-term solution i.e. after one or two years.

Footprint area and costs were two indicators of interest in this study. The footprint area comparison showed that, the technologies that provide full FS treatment and have the lowest footprint area, are the Lime treatment sites. The costs comparison includes capital expenditure (CAPEX in $ per m3 treated), operational expenditure (OPEX in $ per m3 treated) and the Whole Life Costs (WLC in $), assuming a 10-year design life. The lowest WLC FSM plant are the decentralised Upflow Filters and the ABR. This is due to the low OPEX of these systems and longevity of materials used. Lime had a relatively high WLC due to the high OPEX (cost of hydrated Lime). The centralised systems (biological and aeration) had a relatively high CAPEX due to the size of the infrastructure, so a higher WLC.

Another key finding from CXB was that adequate allowance (cost, area, operational skills etc) should be made for the full treatment train. This must include liquid and solids management and final disposal.

Some sites visited did not have a full treatment chain, this is noted in the technology review section.