Hw. Pearson et al., PERFORMANCE OF THE PHASE-II DANDORA WASTE STABILIZATION PONDS THE LARGEST IN AFRICA - THE CASE FOR ANAEROBIC PONDS, Water science and technology, 33(7), 1996, pp. 91-98
Citations number
11
Categorie Soggetti
Water Resources","Environmental Sciences","Engineering, Civil
This paper describes the performance of the Dandora Waste Stabilisatio
n Pond System which treats the industrial and domestic sewage from the
City of Nairobi, Kenya and is the largest pond system in Africa. The
ponds have the capacity to treat a dry weather flow of 80,000m(3)/d bu
t currently treat only half this flow. Increased sewage strengths over
and above the design value mean that although the hydraulic load is h
alved the organic surface load on the primary facultative ponds is onl
y 37% below the design loading of 190kg BOD5/ha/d. The results of the
ongoing monitoring programme show that effluent quality is good and me
ets WHO guidelines for unrestricted irrigation. Extrapolation of the e
xisting results show that the system is performing to predictable effi
ciencies for the existing organic load and retention times (>90% BOD5
removal and >6 log reduction in FC) and will continue to do so as desi
gn flows and loads are reached. A pilot anaerobic pond study with what
turns out to be full size anaerobics, showed BOD5 removal in excess o
f 80% in the single celled anaerobic ponds at design loadings of 240g/
m(3)/d against a design prediction of 53% removal. Most importantly an
aerobic pond loadings as low as 17-26% of the permissable volumetric l
oading maintained their efficiency without odour problems. This allows
anaerobic ponds to be operated at flows well below design levels with
out risk of odour and without the need therefore to by-pass the anaero
bics during commissioning and low initial flows. The benefits of land
saving in the tropics by including anaerobic ponds in the system desig
n is discussed as are the benefits of detailed monitoring programmes f
or large pond systems. Copyright (C) 1996 IAWQ. Published by Elsevier
Science Ltd.