3.10 Example from Cox’s Bazar, Bangladesh

During the humanitarian response in Cox’s Bazar, Bangladesh, the International Federation of Red Cross and Red Crescent Societies (IFRC) implemented an aerobic treatment unit for faecal sludge with a capacity of 20 m³ daily substrate input per day.

Sludge was delivered manually in 50-litre drums and then screened into the aeration tank. The tank had a surface aerator and mixer to stabilise the sludge. After approximately 20 hours, the effluent was discharged to the settlement tank, where the flocs settled, and the liquid effluent was discharged.

Some sludge from the bottom was returned to the aeration tank. The liquid effluent passed through a glass bead filter to remove solids before being discharged to surface water. The effluent was further treated in a chlorination tank before being released.

The biosolids were homogenised and stabilised further at the nearby lime treatment site. The site was operating with a generator for 24 hours a day. The plant met DoE standards for nutrients, solids and helminth but not coliform. Therefore, the liquid portion had a final disinfection step to kill pathogens before discharge.

The plant was decommissioned and moved to a new location with a setup where faecal sludge from pit latrines and septic tanks is collected and screened in the collection chamber. The sludge settled in the primary settler, and the liquid part is further treated in an ABR, followed by an aeration tank, where bacteria consumed the organic content and produced carbon dioxide. The supernatant from the aeration tank is further settled in the settling tank, where solids are separated. The liquid part is further treated with a glass bead filter to remove parasites and eggs and disinfected with chlorine before discharge. According to the operator, the effluent meets national discharging standards.

The separated and settled sludge from the primary tank, ABR, and settling tank is transferred to the Flexigester for further anaerobic digestion and biogas recovery. The stabilised sludge was then dewatered in a drying bed for incineration. The incinerator ash was provided to the community as a soil conditioner and fertiliser.

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