The Challenge
Rapid urbanisation is reshaping the demographic landscape of SubSaharan Africa (SSA). Between 2000 and 2020, the urban population grew from roughly 30% to more than 40% of the total population, adding an estimated 150million new city dwellers. This surge strains municipal services, especially wastewater collection and treatment. According to the World Health Organization, only 30% of urban residents in SSA have access to safely managed sanitation, and a significant share of the remaining waste is discharged untreated into surface waters, groundwater, and wetlands.
Key problems include:
- Inadequate infrastructure: Many cities lack an extensive sewer network; where pipes exist, they are often poorly maintained.
- Financial constraints: Capital costs for conventional treatment plants are prohibitive for many municipal budgets.
- Technical capacity gaps: Shortages of skilled engineers and operators limit the reliable operation of complex facilities.
- Policy fragmentation: Overlapping responsibilities among ministries, utilities, and local governments hinder coordinated action.
Consequences are severe: polluted waterways lead to outbreaks of cholera, typhoid, and diarrhoeal disease; eutrophication harms fisheries; and contaminated groundwater jeopardises drinkingwater supplies. The need for affordable, resilient, and locally appropriate wastewater solutions is therefore urgent.
Key Principles for Selecting Appropriate Technologies
When evaluating options for municipal sewage management in SSA, the following principles guide decisionmaking:
- Affordability: Capital and operating costs must align with local revenue streams and the ability to secure donor or private financing.
- Simplicity & Robustness: Systems should be operable with minimal specialist training and tolerate fluctuating loads, power interruptions, and variable influent quality.
- Scalability: Solutions should be expandable as populations grow, allowing phased investment.
- Resource Recovery: Turning waste streams into valuable outputsbiogas, fertiliser, reclaimed watercreates revenue and reduces environmental impact.
- Local Context Fit: Climate, cultural practices, and existing informal sanitation networks must be respected.
Appropriate Technologies
1. Decentralised Wastewater Treatment Systems (DEWATS)
DEWATS are communityscale, modular plants that combine a series of lowtech units such as settling tanks, anaerobic baffled reactors, and constructed wetlands. They are designed to treat 5000200000mday, making them wellsuited for rapidly expanding periurban areas.
- Advantages: Low energy demand, simple operation, and the ability to generate biogas for local cooking or electricity.
- Limitations: Require land for wetlands; performance can drop if hydraulic loading exceeds design values.
2. WastetoEnergy (WtE) Facilities
Smallscale anaerobic digesters coupled with combined heatandpower (CHP) units transform sewage sludge into biogas. In Ghana and Kenya, pilot projects have demonstrated 0.50.7kWhm of biogas production, which can offset municipal electricity costs.
3. UBasin and Pit Latrine Upgrades
Where sewer extension is unrealistic, upgrading existing onsite sanitation with sealed Ubasins equipped with overflow filters reduces pathogen discharge. Periodic emptying can feed anaerobic digesters, linking onsite and offsite treatment.
4. Constructed Wetlands (Horizontal Subsurface Flow)
These systems use gravel and planted reeds to remove organic matter, nutrients, and pathogens through filtration, microbial activity, and plant uptake. They are especially effective in warm climates and can be integrated into public parks or green belts.
5. Membrane Bioreactors (MBR) LowCost Variants
Traditional MBRs are expensive, but emerging lowpressure membranes and modular designs are becoming more affordable. When combined with solar energy, they can supply highquality reclaimed water for irrigation or industrial cooling, creating a closedloop system.
6. Smart Monitoring & MobileBased Management
Simple sensor packages (pH, dissolved oxygen, flow) linked to cloud platforms enable remote supervision. Mobile apps allow community operators to log maintenance activities, improving accountability and reducing downtime.
Figure 1 Typical DEWATS configuration (source: SEEDAfrica)
Illustrative Case Studies
Dar es Salaam, Tanzania DEWATS for the Mbezi Ward
Implemented in 2019, a 30000mday DEWATS plant serves 150000 residents. The project reduced BOD concentrations from 250mgL to 20mgL and supplied biogas to the local market, cutting household firewood consumption by 30%.
Source: WaterAid Tanzania, 2022.
Lusaka, Zambia SolarPowered MBR for Industrial Park
A 5000mday lowpressure MBR was installed in 2021, powered by a 250kW solar array. The reclaimed water meets WHO ClassA irrigation standards, allowing the adjacent agroindustrial zone to recycle 80% of its process water.
Source: ZESCO & UNDP, 2023.
Accra, Ghana CommunityScale Biogas Digesters
In the Ablekuma neighbourhood, 12 anaerobic digesters treat septic tank sludge from 4000 homes. The collected biogas fuels a community kitchen that serves 1200 meals daily, generating modest revenue that funds routine desludging.
Source: Ghana Renewable Energy Agency, 2021.
Recommendations for Policy Makers and Practitioners
- Adopt a Tiered Service Framework: Classify urban areas into core, intermediate and periurban zones and match technology intensity accordingly.
- Leverage PublicPrivate Partnerships (PPPs): Structure contracts that allow private operators to recover investment through waterreuse sales, biogas, or performancebased fees.
- Integrate Sanitation with Urban Planning: Reserve land for wetlands and treatment ponds in masterplan drafts; align sewer extensions with future growth corridors.
- Strengthen Capacity Building: Develop locally delivered training curricula for operation of DEWATS, wetlands, and digesters; use mobile learning tools for ongoing support.
- Mobilise Climate Finance: Position wastewater projects within climateresilient infrastructure portfolios to access Green Climate Fund and Adaptation Fund streams.
- Promote Resource Recovery Regulations: Enact standards that recognise biogas and reclaimed water as marketable products, encouraging investment.
- Implement Incremental Monitoring: Deploy lowcost sensors at critical points (influent, effluent) and establish a national datasharing portal to benchmark performance.
