Sanitation and Wastewater Atlas of Africa

6.3.3. CEA 3: Treated wastewater for aquaculture

Table 6.3. Status of wastewater treatment and reuse for aquaculture in Ghana and Bangladesh

Country and wastewater treated

Main wastewater treatment pond processes in the country

Products

In this CEA, sewered wastewater is treated to quality standards suitable for fish, fingerling and livestock feed production.

Ghana 225 m 3 /d

Waste stabilization ponds (1 ha)

• 40 tons of African catfish • Fingerlings • Broodstock

6.3.3.1. Case examples

Bangladesh 300 m 3 /d

Waste stabilization ponds (1ha) + duckweed canals (0.6 ha)

• 6.5–15 tonnes carp • Fish feed • Fruit

Table 6.3 presents the status of treated wastewater reuse for aquaculture in selected countries. Waste stabilization ponds are transformed into fish ponds for fish species that can survive under such conditions (Drechsel and Hanjra 2018a; Drechsel and Hanjra 2018b). Studies (IWMI2018) showthatpathogensmay accumulate on the skin and in the gut of the fish, so it is important that fish ready for harvesting spend the days prior to the harvest in clean water. Post-harvest processing techniques such as smoking should be carried out on the fish harvested from wastewater ponds. The preferred fish-processing method depends on the local context and market demand. Rearing of broodstock for fingerling production helps to minimize the negative perception of using wastewater for aquaculture. Since the use of treated wastewater for aquaculture is not consumptive, it can still be used for other activities, such as irrigation of crops or fruit trees (Drechsel and Hanjra 2018d). Conventional revenue sources (Box 6.3) include household sanitation fees for wastewater discharged into sewers, either collected as part of the water bill or separately, and government subsidies reflecting the treatment service benefits for society and nature. Another key revenue source comes from fish and fish feed sales. In some cases, fingerlings are also produced and sold. 6.3.3.2. Sources of revenue

Source: Amoah et al. (2018); Drechsel et al. (2018)

is moderate compared with other CEAs, as the addition of fish feed to treating ponds may increase the nutrient content of the treated wastewater. 6.3.4. CEA 4: Recycling of wastewater for industrial use Recycling wastewater for industrial use is critical in regions affected by high water stress. In Durban, South Africa, a private company treats the city’s wastewater for local industries to reuse.

Box 6.3. S ources of revenue, conventional and non-conventional

Conventional sources of revenue: • Household sanitation fees • Government subsidies • Fish sales • Fish feed and fingerling sales

Non-conventional sources of revenue: • Sludge recycling • Reuse of treated wastewater for irrigation • Carbon credits

Main resources: Wastewater

Treatment technology: Multiprocess treatment of municipal waste- water with activated sludge and ozonation

Figure 6.9 presents the typical financial flow from a recently implemented model in Kumasi, Ghana. The main sources of revenue are from sales of African catfish, which exceed the operation andmaintenance costs of the wastewater treatment plant. Treated wastewater can also be reused on-site to irrigate crops and fruit trees or for several other purposes. The volumes of sludge in small plants may not be attractive enough to engage in sludge recycling and commercialization. Also, carbon credits may be considered if the scale of implementation of this CEA and related savings are sufficient. The main benefit of using treated wastewater for aquaculture is the high profitability potential of fish farming and the low operation and maintenance costs of the treatment plant. The environmental impact of treated wastewater for aquaculture

Typical geography: Urban, peri-urban

6.3.4.1. Case example

Main resources: Treated water for aquaculture

Durban is the third biggest city in South Africa, a water-scarce country. During the 1990s, Durban faced constraints in its sewage capacity and management. The existing infrastructure could not cope with the city’s growing population and economic development. The municipality therefore had to invest in new infrastructure to increase wastewater collection in order to avoid negative impacts on its citizens and the environment. Durban’s first option was to invest in a new marine outfall pipeline to discharge the treated wastewater

Treatment technology: Pond stabilization systems or any process involving the use of ponds or enabling the construction of fish ponds

Typical geography: Urban, peri-urban

CapVal project financial flows CapVal project financial flows

Wastewater

Treated wastewater Treated wastewater

Wastewater

Sell broodstock

Sell fingerlings

Sell table fish

Sell broodstock

Sell fingerlings

Sell table fish

Fish broodstock culture in ponds

Regular/normal fish ponds Regular/normal fish ponds

Consumers

Fingerling production Fingerling production

Fish broodstock culture in ponds

Consumers

$

Revenue

Source: IWMI, 2018.

GRID-Arendal/Studio Atlantis GRID-Arendal/Studio Atlantis

$

Revenue

Source: IWMI, 2018.

Figure 6.9. CapVal project financial flows

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SANITATION AND WASTEWATER ATLAS OF AFRICA