ABR – constructed wetland – ponds – drying beds – December 2019

ABR – constructed wetland – ponds – drying beds – December 2019
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Location of the case study

Myanmar - Rakhine - Sittwe camps


Main treatment objectives

BOD/COD reduction, Pathogen reduction, Solid/liquid separation, TSS and TDS reduction

Opex per real input flow


Required space


Description of the treatment process

The dumping station is the first module of the Sludge Treatment Site (STS), where the tractors empty the barrel. It is composed of two emptying tanks where the barrel is emptied and its volume measured, with a screen to remove the solid waste, of a channel and of an outlet tank where the scum is trapped.

Two Hopper Bottom Tanks (HBT) are the second module of the STS. It provides mechanical primary treatment which consists mainly of sedimentation and flotation of inorganic material (biological degradation of settled solids occurs partly).

The Anaerobic Baffled Reactor (ABR) is the first module of the STS wastewater treatment line. It provides biological secondary treatment that is the biodegradation of organic material by the micro-organisms contained in the settled sludge.

The horizontal flow constructed wetlands are the second module of the STS wastewater treatment line. It consists of two large gravel and sand-filled basins (that are planted with wetland vegetation). As wastewater flows horizontally through the basin, the filter material filters out particles and microorganisms degrade the organics.

The maturation ponds are the third module of the STS wastewater treatment line. It consists of two large, man-made water bodies in which fecal sludge is treated by natural occurring processes and the influence of solar light, wind, microorganisms and algae.

Infiltration basins are the final module of the wastewater treatment line of the STS. The wastewater infiltrates into the ground through two infiltration basins that are filled alternatively.

The drying beds are the first module of the STS sludge treatment line. They are shallow unplanted filter beds with media consisting of sand and gravels. The drying process is based on drainage of the liquid through the sand and gravels to the bottom of the bed and evaporation of water from the surface of the sludge to the air.

The secondary constructed wetland is the second module of the sludge treatment line of the STS. It treats the leachate from the sludge drying beds.

The infiltration basins are the third module of the sludge treatment line of the STS. The wastewater infiltrates into the ground through two large basins filled with sand.

The dried sludge storage is the fourth module of the sludge treatment line of the STS. The sludge from the drying beds is stored to further dry.

The incinerator is the fifth module of the sludge treatment line of the STS. The dried sludge is incinerated and the ashes are given to farmers as amendment.

Description of the emergency context

About 100 000 IDPs live in Sittwe camps. They exist since 2012, when a resurgence of tensions and violence between Muslims and Buddhists groups resulted in several hundreds of deaths and the displacement of more than 140,000 people.

The access to the camps are restricted by the government, and a Travel Authorization is needed to enter and exit the camps, for international staff as well as for Myanmar staff.

The IDP camps are all located within the same restricted area, which includes also some existing villages from different ethnicities.

It is a rural context, located on the coastal line at about 10 kilometers from the main city and on the coastal line.

Hygiene promotion is carried out through Community Mobilization and behavioral change approach. Water supply is from borehole with hand pumps. Solid waste management is ongoing as well as drainages maintenance and cleaning.

Oxfam and SI are the main WaSH focal agencies in Sittwe camps, working in a Consortium. DRC is in the process of ending over the WASH service provision of two camps to Save the Children.



Lessons learned

The design hypotheses were not available.

Steel is stronger than wood for the roof structures, due to the exposure to monsoon coastal winds and the risk of cyclones.

The concrete and bricks were damaged over time and numerous cracks appeared, possibly due to the bad quality of the sand (salty?).

Hiring our own staff instead of working with contractors usually resulted in higher control of the quality of work.

By providing and enforcing the use of protection equipment and providing training explaining the risks associated with faecal sludge to our staff.

The authorities are currently not involved in the management of the plant and the financial balance of the plant is guaranteed by international donors. The spare parts are available locally, except for the laboratory, for which some consumables are shipped from France. The HR skills for daily operation can be found locally, and a partnership with Veolia Foundation ensures regular technical visits for improvements and to verify the proper operation of the plant.

The design documents were not available, which resulted in problems in the operation. SI had technical support from the Veolia Foundation to fill this gap with design calculations. SI construction team provided the design drawings.

The constructed wetlands were not properly designed and thus sludge was very quickly surfacing. They have been redesigned into 2 anaerobic ponds with an additional facultative pond, construction will start in 2020 or 2021.

The operation of the first retention tank was not easy, so it had to be replaced with hopper bottom tanks.
The pipes are regularly clogged by the sludge.

Insects are biting the workers when they are removing the dry sludge from the drying beds.

Basic and regular analyses of the sludge should be done from the beginning, as it is important to design the plant and ensure its proper operation.

The solid content measurement (evaporation of the water and weight of the remaining solid) is easy to do and gives a good indication of each treatment step solids removal capacity.

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