This research study undertakes to evaluate the efficiency of Dandora Estate Sewage
Treatment Works which is located in Nairobi County by analysing the influent and effluent
characteristics of the wastewater. The plant capacity is 160000 ??⁄??? which it treats
compared to the approximately 400000??/??? of wastewater produced in Nairobi thus the
plant is of paramount importance. The plant has eight series consisting of 55 ponds whose
treatment in the ponds is achieved by waste stabilization. Grab samples were taken from the
inlet and outlet of the plant as well as the inlet of each pond along series three. The
parameters studied included pH, Biological oxygen demand after five days (BOD5),
Chemical Oxygen Demand (COD), Total Suspended Solids (TSS) and Total Dissolved Solids
(TDS).The treated effluent was also analysed to determine its conformity to the required
Kenyan standards for discharge into the environment.
The results obtained were as follows: for BOD5 values were 148 mgO2/l, 108.75 mgO2/l, 53.2
mgO2/l, 48.6 mgO2/l, 45.85 mgO2/l and 32.15 mgO2/l from the inlet, anaerobic pond,
facultative pond, maturation ponds and the outlet respectively. The removal efficiency was
78.277%.The COD values were 960 mgO2/l, 792 mgO2/l, 396 mgO2/l, 316 mgO2/l, 228
mgO2/l and 207 mg/l respectively at the ponds along series three. The removal efficiency was
78.438%. The TSS values were 300 mg/l, 80 mg/l, 40 mg/l, 40 mg/l, 60 mg/l and 80 mg/l
respectively along series three. The TSS removal efficiency ranged from 70% to 86.667%.
The Biological Oxygen Demand (BOD5), Chemical Oxygen Demand (COD) and Total
Suspended Solids (TSS) in the final effluents did not meet the design expectation of 20
mgO2/L, 280 mgO2/L and 30 mg/L respectively. The pH values were 6.85, 7.45, 7.48, 7.65,
7.53 and 7.62 respectively along series three.
The treated effluent did not meet the standards for discharge into the environment thus
measures have to be taken to improve the quality of the final effluent. Some of these
measures include regular maintenance of the machines to prevent frequent breakdowns and
strict regulation of industries to treat their waste to acceptable levels before discharging to
public sewers etc.