Fecal sludge management
Fecal sludge is defined very broadly as what accumulates in onsite sanitation systems (e.g. pit latrines, septic tanks and container-based solutions) and specifically is not transported through a sewer.
[2][3] In low-income countries, the majority of fecal sludge is discharged untreated into the urban environment, placing a huge burden on public and environmental health.
[4] A variety of mechanized and non-mechanized processing technologies may be used, including settling tanks, planted and unplanted drying beds, and waste stabilization ponds.
[1]: 2 The incorporation of the entire sanitation management service chain in the Sustainable Development Goal (SDG) 6, as opposed to just providing access to toilets, has further established acknowledge of the importance of FSM.
Some have the potential to alter the existing service chain, such as container-based sanitation, decentralized options, and innovations developed through the Bill & Melinda Gates Foundation 'Reinvent the Toilet Challenge' since at least 2012.
Another factor is that the transporting fecal sludge has a real cost to vacuum truck operators and there is thus an incentive to dispose of the untreated waste into the environment (primarily into waterways, but also directly onto the land.)
Fecal sludge management (FSM) requires safe and hygienic septic tank and pit latrine emptying services, along with the effective treatment of solids and liquids and the reuse of treated produce where possible.
[16] Citywide FSM programs may utilize multiple or one treatment facility, use stationary and mobile transfer stations, and engage with micro, small and medium-sized enterprises that may conduct some or all of the services.
Rural areas with low population density may not need formal FSM services if the local practice is to cover and rebuild latrines when they fill up.
Also sharing decentralized FSM services and sludge treatment between nearby villages, or direct safe removal burial of waste could be considered and organized.
[18] Organized larger scale FSM programs may be able to provide the service more cheaply and more hygienically than the independent private operators working on an ad hoc basis.
San Fernando City, La Union, Philippines is an example of a local government that has contracted out the treatment facility construction and collection program to the private sector.
[21] FSM services can be provided as demand based (often called on-request, on-call, on-demand, ad-hoc or non-scheduled) or scheduled (also known as regular) desludging, or a combination of both.
A number of low-cost pumping systems exist to remove this hardened sludge hygienically from the ground surface, although many of them are still in the experimental stage (e.g. Excravator, Gulper, e-Vac).
Some advanced transfer stations and vacuum trucks can dewater fecal sludge to some extent, and this water may be placed in sewer lines to be treated in wastewater treatment plants.
Fixed transfer stations are dedicated facilities installed strategically throughout the municipality that serve as drop off locations for collected fecal sludge.
Mobile transfer stations work best for scheduled desludging programs where there are no traffic restrictions or truck bans, and a relatively large number of homes that are inaccessible to the larger vehicles.
[1]: 4 The result of the demographic, environmental, and technical factors that influence characteristics of fecal sludge is a high level of heterogeneity that complicates characterization.
[28] Performing a waste characterization study helps to understand local conditions and provides data that factors into treatment plant sizing.
[31] Grasses with adventitious roots may also be planted in drying beds, allowing for reduction of odor, collection over longer periods, production of forage, and more decomposition of the final biosolids by the time they are extracted.
[33] The Water Sanitation and Hygiene Institute of India has developed a truck based mobile treatment unit[34] that is able to treat fecal sludge on site.
Six mobile septage treatment units have been built to date using readily available filters and membranes (mesh fabric, sand, granular activated carbon (GAC), microfilter, ultrafilter) and installed on the bed of a small truck.
With support from a USAID grant, the WASH Institute is working to scale the MTU solution as the preferred option over traditional vacuum trucks that discharge wastes into the environment.
However, the high strength of septage and fecal sludge means that relatively small volumes of both can have a large impact on the organic, suspended solids, and nitrogen loads on a wastewater treatment plant.
Even where co-treatment is not an option, existing wastewater treatment plants may provide land in strategic locations, close to areas of demand for septage management services.
Solids-liquid separation will reduce both the overall load and the proportion of digested material in the liquid fraction and will thus lessen the possibility that it will disrupt wastewater treatment processes.
A formal and transparent process for developing appropriate plans and designs for wastewater and fecal sludge treatment plants will achieve local buy-in and ownership of technology decisions, which is critical for the long term success and sustainability of the program.
[citation needed] Resource recovery from fecal sludge can take many forms, including as a fuel, soil amendment, building material, protein, animal fodder, and water for irrigation.
For fecal sludge, the heat deactivates the pathogens while the digestion process breaks down the organic matter into a humus-like material that acts as a soils amendment, and nutrients that are broken down into a form that is more easily taken up by plants.
Such programs may include tariffs or user fees, promotions campaigns to raise the willingness to pay for the service, and local ordinances that define the rules and regulations governing FSM.
