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Faecal Sludge Management

Oxfam is developing significant in dealing with the significant amounts of faecal sludge that sometimes needs to be dealt with in emergencies.

Faecal Sludge Management in Bangladesh

In response to the refugee influx in Bangladesh significant innovations were made. The below report was written in conjunction with Arup, and compares some of the technologies used.

Download the full report, or read the executive summary below.

Technical Assessment of Faecal Sludge Management in the Rohingya Response

Executive Summmary

Objectives

On behalf of Oxfam GB and the Cox's Bazar WASH sector, Arup have conducted this Technical Assessment study of different Faecal Sludge Management (FSM) methods in the Rohingya camps in Cox’s Bazar (CxB), Bangladesh. This is a phase 2 study, following completion of phase 1 in 2019. This phase of the study builds on existing FSM technical information and monitoring and evaluation (collected by others since 2019), broadens to include whole FSM chain, wider range of stakeholders and camp areas covered and focuses on current challenges of sustainability and environmental impact, space requirements and costs. The WASH sector will use findings of this study to inform development of a (longer term) FSM Strategy for the camps. To this end, this study aims to provide a technical assessment to answer the following questions, where costs and operational robustness are the key criteria:

  1. Does the FSM chain meet the need? i.e., does each stage in the FSM chain have capacity to manage the sludge generated, what are the bottlenecks and inefficiencies, and how can these be addressed?
  2. Which type of FSTP is performing best against most assessment parameters? This should include reasoning for improving or decommissioning FSTPs.
  3. Which mode of FS transfer/transport is most cost effective and resilient?
  4. Does the containment type influence the sludge chain, and which containment is best?
  5. Is the centralised or decentralised approach of FSM more cost effective and sustainable?

Methods

A core team of FSM experts was formed from the CxB WASH sector group, to guide and support the project. Arup, Oxfam, and the core team identified a wider stakeholder group (eight NGOs operating FSM in the camps) to include in the study and to provide the evidence/data for analysis and FSTPs to visit. Review meetings where also held with DPHE and other technical experts when appropriate.

A series of ‘camp wide’ and ‘detailed field’ assessments were completed to draw conclusions on the whole FSM chain and inform the discussion on centralised and decentralised FSM systems. Camp wide assessments are based on existing data provided by the sector and stakeholder data collected on operational cost and performance of containment, desludge and transfer. The FSTP assessments are based on the field visits covering 20 FSTPs and eight technology types, conducted during this study by technical partner Oxfam Bangladesh. The FSTPs types (Lime, Anaerobic lagoons (centralised), Aerobic treatment (aeration), Biological multi-stage (central), Anaerobic baffled reactor (ABR). Waste Stabilisation Ponds (WSP), Anaerobic Digester System (ADS), Upflow filters (UFF) and Decentralised Wastewater Treatment System (DEWATs)) were compared against a set of indicators to summarise performance, including: cost; footprint area; speed of construction and commissioning/decommissioning; operation and maintenance issues; pathogen inactivation and environmental impact.

In many cases the existing or collected datasets are limited e.g. do not cover the whole camp area or all parameters required, some assumptions and extrapolation of data has been undertaken. The findings from the report should therefore be treated as provisional and relevant to the particular context in CxB.

Findings

The camp wide review of desludge and transport data gave an approximate ‘total volume of sludge generation (at point of desludging)’ and the wet season variation, this was extrapolated to give an estimation of 1.1 l/h/d and a total monthly production of 29,718m3 of FS. Wet season impact resulted in approximately 26% more volume generated (at point of desludging).

The analysis of the containment systems showed a wide range of latrines are used and the current dataset records many more types than the sectors ‘Unified Standard Design for Latrines’. Latrines are desludged more often either because of insufficient capacity for the number of users, mixed use (black and grey water), operational defects and/or poor infiltration.

Analysis of the transport and transfer systems showed that IFSTN (permanent pipe networks) have a lower cost to operate and can transport increased volumes of sludge throughout the year. Their construction comes with an initial higher Capex but (based on available data) this investment can pay off within nine years when compared against other transport modes. The FS volume in transit during the wet season was noted as impacted by: poor access conditions to desludge and/or transfer, limited infiltration capacity (hence treatment capacity) at the receiving FSTP, and accessibility or overflowing of latrines in low land/flood prone areas.

Review of camp wide treatment performance data and the detailed review of parameters for the 20 FSTPs visited, showed that generally the centralised plants were operating well and had the lowest overall cost for the volume treated. The WASH sector infrastructure data (2021) set shows the total FSTP daily treatment capacity of 879m3 across the camps. For a population in RCs of 904,639 and a sludge generation rate of 1.1 l/h/day we get a daily sludge production of 995m3. It is fair to consider that there is some sludge retention in the camps’ latrines and tanks, and that some people might still practice open defecation, so this slightly lower treatment capacity might accommodate for the sludge produced in camp. However, during the wet season the volume of sludge in transit increases and this treatment capacity might not be enough.

Eight out of the 20 FSTPs visited were not utilising their full design capacity at the time of the study, leaving a nominal 196m3 of underutilised capacity in total. Reasons stated as: site was under commissioning or decommissioning, poor final effluent quality, and variable volumes of incoming sludge depending on the season. If FSTPs not investigated in this study (included in the WASH sector infrastructure data) have a similar underutilisation, again this shows that the available treatment capacity is slightly below the demand (sludge generation). Across the 20 FSTPs visited the Capex of treatment per m3 ranged from approximately $1,000 to $14,000 USD and Opex from $1 to $44 USD. Several types of decentralised FSTPs were not achieving the DoE effluent standards but the WSPs, ABR and DEWATs showed potential for good performance, with some passing results from certain FSTPs or in certain months. The Aeration plant performs best against the effluent standards (passing COD, pathogen, pH and nutrient requirements). Centralised FSTPs showed generally a better performance than the smaller decentralised FSTPs. Lime FSTPs had high pH and generally poor performance for COD/BOD and nutrients removal. Lime sites are not appropriate for this stage of the emergency, given their high Opex and low treatment performance, and a majority are being decommissioned. GeoTubes and Constructed Wetlands (assessed in phase 1 and not phase 2) are poorly performing and not appropriate for use as a standalone technology and should be decommissioned.

FSTPs that are not meeting DoE effluent standards for most parameters, can pose a risk to human health and the environment. Most of the site visited use infiltration via soak pit or infiltration field as the final disposal for liquid, perhaps negating the need to meet the DoE (discharge to surface water) standards, it is likely that larger or additional treatment units, and hence a larger areas, would be required for these FSTPs to achieve better effluent quality. Where infiltration is the final disposal route for FSTP liquid effluent (and DoE pathogen standards are not achieved), risk assessments to ground water are required to properly design the infiltration area and upstream FSTP and define the capacity of the treatment and associated FSM chain.

Final solids products from FSTPs are generally being stored at sites and are not being widely reused or recycled. There is a need to understand the market and acceptability for sludge products (compost, gas etc) to understand if additional solids handling could be made cost efficient i.e., offset Capex and Opex costs by selling fertiliser or compost in local areas. Consolidation/centralisation of final solids handling can help move solids off FSTP sites, allowing for an efficient treatment to be established and a better use of FSTP area. Review would be required of if final solids require further ‘rewetting’ or ‘drying’ to facilitate process to produce saleable products, this may prove cost or logistically prohibitive.

In the shorter term e.g., next 5 years, improving the existing FSTP infrastructure is likely to have the lowest Capex and environmental impact (from materials use etc). However most existing sites do not have space for additional process stages required to achieve DoE effluent standards or accommodate population growth, therefore this is unfeasible. In the ‘longer term’ i.e., 5 to 10 years most FSTPs in this study will have reached their design life, it would be most cost effective, looking at whole chain cost, to provide a centralised FSTP with permeant pipe as transfer system.

The phase 1 report is also available: FSM for Disaster Relief - Phase 1 Technical Comparison