The efficiency of the treatment plant is affected mainly by:

• The operation and maintenance of the plant
• The burden of the amount of waste arriving at the treatment plant on the designed capacity of that plant

Data about this can be found from:

• Municipality plans, design and budget
• Key Informant Interviews with the operators of the plant
• Registers from the treatment plant (vacuum tanker arriving)
• Observations
• National standards and effluent measures

Based on this, the efficiency can be determined regarding the standard parameters and effluent quality; if the effluent does not meet the national standards the efficiency cannot be considered 100%. If the facility is well maintained and it is not working under capacity, the treatment could be considered to be at least partially treated (50%). If the effluent is not monitored then assumptions regarding operation and based on expert opinion can be made as long as the report shows all the assumptions made by the author. For instance, in Kumasi, where effluent is not being monitored, it was assumed that the plant was partially treating the waste due to the following observation: although there was a lack of maintenance and the amount of waste arriving was close to the treatment capacity limit (working some days over capacity), the treatment plant was still working and the effluent was of a nationally accepted quality.

Where possible, authors must agree on the percentage of waste being treated with the relevant stakeholders. In the absence of specific data the following three percentages can be used as a guiding principle: 0% where there is no treatment, 50% where there is “some” level of treatment, and 95% where almost all the waste is being treated.