Lime treatment, Geotube and filtration

Organisation : NC

 

Objective

Excreta containement, Solid/liquid separation, Sludge drying, Stabilisation of sludge, Sludge volume reduction, Reduction of odour/flies, Reduction of pathogens, BOD reduction, TSS and TDS reduction

Required space

0.15 m2/person

Short description of the emergency context

The project site – Unichiprang is a hilly area and is currently hosting an estimated 21,300 Rohingya refugees (ISCG Full Situation Report, 11 March 2018). Refugees are continuing to cross the border into Bangladesh, with a total of 3,236 new arrivals reportedly entering the country in February 2018 alone, bringing the number to over 5,000 newly arrived refugees so far in 2018. The population is predominantly Muslim. The latrines provided for the refugees are simple pit latrines. Pits are emptied approximately every 4 to 8 weeks depending on the number of users.

Objective

Excreta containement, Solid/liquid separation, Sludge drying, Stabilisation of sludge, Sludge volume reduction, Reduction of odour/flies, Reduction of pathogens, BOD reduction, TSS and TDS reduction

Life expectancy and reliability

Short term (months)

Skill level required for design

Low (easy design)

Technology suitable for context with high water table

No

Source of sludge

From public toilet, From septic tank, From pit latrines affected by groundwater infiltration

Required space

0.15 m2/person

Topography

Mountains and hills

Design input flow

4 m3/day

Type of outputs

Sludge, Effluent

Using locally available material

yes

Fencing

Yes

Drainage implemented

Yes

Flood risk

Yes

Real input flow

4 m3/day

COD reduction

97%

pH variation

-4

Exclusively communitarian operation

yes

Safety and hygiene: washing capacity availability

No

Safety and hygiene: PPEs availability

Yes

Skill level required for upgrading & decommissioning

Low skilled: general WASH officer and local labour required

The Lime treatment is carried out in 50 L barrels. Prior to the collection and transport of faecal sludge, 15 g/l lime (CaOH2, 2 kg per barrel) is added to the empty barrels. The faecal sludge from the pit latrines is removed from different ways: manual using buckets, manualy pumped using submersible pump and pumping with dedicated Oxfam trash/sludge pumps, which facilitates the mixing of the lime and the faecal sludge. Bucket desludging is used in place where it’s difficult to access with the heavy Oxfam pump. The lime creates a highly alkaline environment, which results in the inactivation of pathogens and stabilizes the sludge (if the alkaline environment of pH>12 is sustained for at least 1 hour).

From the barrels, the sludge is poured through a screen (to remove any solid waste) and into the Geotube. The time the leachate filters into the sand portion of the filtration unit still need to be determined. The primary filtration units are comprised of three layers of filter media. The bottom layer is 17 cm of coarse gravel 1’’ the second layer is 14 cm of medium size gravel ½’’, topped off by a 20 cm of 2.5 fineness modulus (FM) sand appropriate for filtration. After this filtration phase, the liquid drains through a 6’’ pipe installed below the filtration media and flows through gravity force to a secondary filtration unit comprised of a 20 cm layer of medium size gravel ½’’. The effluent from the secondary filtration phase is then discharged into the environment. The Geotube and primary filtration unit are protected with a roof to keep rain water out of the system. The solid phase of the faecal sludge is retained in the Geotube and is then emptied after a time to be determined. The Geotubes are single use and a new one must be installed after it is emptied. For the final disposal, two options are planned, depending on the final characteristics of the sludge. The first one is direct disposal of the remaining dried sludge into onto land in a nearby area and the second is, incineration of the dried sludge with basic equipment.

Hydrated Lime Treatment requires a barrel to prepare the the lime slurry (e.g. a 50 L plastic barrel). For an even distribution of hydrated lime throughout the sludge, constant mixing is required (either manually or with a mixing pump). The Geotubes are made from membrane material that is either woven and non-woven material. The project team initially piloted the non-woven membrane as it is easily available in Bangladesh and shipping time for woven material is expected to be time consuming (material pictures below). However, woven membranes have been successfully tested and may therefore be preferred, if available. Non-woven materials have mainly been used for dewatering purposes and have less been used for the treatment of sludge. Further materials required are all available in the local market such as; sand, gravel, cement, drainage pipes, bamboo, roofing, tarpaulins and fitting materials.

The overall operation and maintenance of the system is simple. However, in the hilly terrain of Cox’s Bazaar, the transportation of the sludge is challenging and time consuming. The pit latrines are desludged by trained operators using a Oxfam pump (Atalanta Pelican 351 Diaphragm sludge pump with Lombardini 15LD225 diesel engine) with a capacity of approximately 10 min for a 500 L pit. The sludge is transported in a 50 L barrel fixed to a pole and jointly carried by two emptiers (manual transport, see Figure 2 below). Due to potential health risks when handling Lime (see below Health and Safety section), and removal of the dewatered sludge, the process requires trained personnel following health and safety protocols and wearing proper personal protective equipment (PPE). Daily washing and disinfection of all used equipment is required.

Strengths

  • Low complexity and cost of the system,
  • Non-permanent infrastructure,
  • Rapid implementation,
  • Possibility of scaling up of capacity by adding more geotextile tubes and filter units.

Weaknesses


NC

Gallery

Geotube
FSM Bangladesh 2018 (3)
Sludge treatment unit using Geotubes
fig4

SI FSM Sludge transportation

SI FSM Geotextile membrane

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Valentina

Hello, I would like to check with you the management cost. As of 21 February 2019 is reported: 70 USD/month/person.
What is this cost including? If “person” is considered number of beneficiaries, it seems not realistic or not sustainable.
Thanks in advance for the clarification

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Indicators notice

Unit/value

Excreta containment
Solid/liquid separation
Urine/faeces separation
Sludge drying
Stabilisation of sludge
Sludge volume reduction
Reduction of odour/flies
Reduction of pathogens
BOD reduction
TSS and TDS reduction
Nutrient removal
Nitrification
Nutrient recovery
Biogas recovery
Water recovery
Biomass production
Other

How to measure or calculate it ?

If possible, revise design document and ask to the design team or consultants: the objective should have been considered to design and dimension the faecal sludge treatment site. Usually, the objective is related to the quality of input sludge and the environmental conditions of disposal sites or the desired reusing methodology

This is very important to design the faecal sludge treatment site and to evaluate the efficacy of the treatment

References, tips, examples

Why it is important to measure it
This is very important to design the faecal sludge treatment site and to evaluate the efficacy of the treatment

Unit/value
Short term (months)
Long term (years)

How to measure or calculate it ?

Identify immediate and long term needs. Analyse population growing and movements trends (see design beneficiary indicator), donors and implementing actors commitments for the future.

References, tips, examples

The size of the population today might be 1,000 persons (often referred to as ‘capita’), but in 1 year this may double and in 5 years this might increase ten-fold; moreover it is important to know how long the facility will need to last to determine the building materials to use

Why it is important to measure it ?
It is important to know the design period as this will help to calculate the designed beneficiary population (see indicator) by the faecal sludge treatment site. Moreover, it is important to know how long the facility will need to last to determine the building materials to use

Unit / value

Low skilled: general WASH officer
Skilled: FSM specialist

How to measure or calculate it ?

The indicator is determined by assessing the design process and understanding if specialists were involved or not

References, tips and/or examples

Example of different design skills in the same context: Design of large scale faecal sludge treatment site of Oxfam in Cox Bazar was implemented in collaboration with Borda (sanitation experts). The small lime stabilization faecal treatment site of Oxfam was implemented by the ‘regular’ WASH officers.

However it’s always preferable to check designs with FSM specialists as in practice the law of Murphy rules: anything that can go wrong, will go wrong.
So for example also during the design of a simple facility as septic tank the following mistakes are common:
– inlet and outlet are mixed up;
– plans and cross-sections are mixed up;
– capacity of the facility is far too large;
– absence of ventilation pipes;
– absence of infiltration facilities;
– leaking tanks;
Etc., etc. etc.

Why it is important to measure it ?

Faecal sludge is a potential dangerous material: a simple mistake impacts the lives of many people
This indicator is important for actors interested in implementing faecal sludge treatment for planning reasons.

Unit / value
yes
no

How to measure or calculate it ?
Check, at the end of rainy season, the groundwater table at the faecal sludge site by digging a pit and/or checking dug wells nearby (in the early morning before water is taken and water level drops).
If it’s not possible to do it at the end of rainy season, ask information to local population about water level in the wells during the year.

References, tips, examples

In areas with high water tables, it might be a challenge to dig pits/ tanks as pumps for keeping the pit dry might be absent. Even if pumps are available, care must be taken to avoid floating of empty tanks. Floating can be avoided by adding enough weight (stones, concrete) to the tank to prevent floating. Hence, above ground / raised facilities are advised such as raised Oxfam tanks.

Why it is important to measure it ?

Faecal sludge is potentially dangerous material and when in contacts with water, contaminants will spread easily and quickly. Moreover, construction in areas with high ground water table requires extra measures and more complex structures (expensive)

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