Water, energy, air and hygiene solutions specialist ImproChem believes that a critical contributor to a healthy population is a well- managed sewerage process. Owing to this, the company has designed membrane bioreactors (MBRs) for the treatment of sewage at plants in rural municipalities.

The MBRs can manage domestic effluent with biological oxygen demand (BOD) ranges of between 200 mg/ℓ and 600 mg/ℓ. For a conventional wastewater treatment plant, the secondary clarifier limits the mixed liquor suspended solids (MLSS) to between 1 500 mg/ℓ and 5 000 mg/ℓ. The MBR replaces the secondary clarification step.

MBRs separate biologically treated effluent from the mixed liquor, using membranes to perform the separation. The membranes allow the purified water to pass through the pores – filtrate – while creating a complete barrier to the passage of any solids greater than 0.4 μm, which includes almost all bacteria and suspended solids. In an MBR, the membranes create a solids barrier and, therefore, the process is not subjected to gravity settling solids limitations, as in conventional clarifiers. Typically, MLSS concentrations in MBR systems are 10 000 mg/ℓ to 12 000 mg/ℓ.

The characteristics of the MBR system make it ideal for a small community that needs effluent water for discharge or reuse. The MBR produces water from domestic effluent with less than 10 mg/ℓ BOD and total suspended solids of less than 2 mg/ℓ. Since the membranes provide a barrier, the process is not subject to upsets that can lead to effluent being discharged that does not meet environmental regulations.

“The system is very simple to operate, with a minimum of pumps and controls. Typical daily maintenance includes monitoring of performance parameters. Cleaning takes place about four times a year. These low-maintenance requirements can be performed by people from local communities,” the company notes.

Historically, the production of drinking water and the treatment of sewage were done at large, centralised plants using long pipelines to outlying rural areas. The MBRs offering allows a decentralised strategy to be applied to sewage, which is much more suitable for South Africa.