Alexander Szabo and Oscar Engle - Svenskt Vatten

value of 4:1 in length/width ratio. Within each case it was reported that increasing the
length/width ratio and introducing baffles slightly increases the water velocity and DO in the
effluent water (Abbas et al., 2006). The conclusion drawn from these data simulations is that a
pond should have a length/width ratio of 4:1 and at least two baffles.
5.2 Facultative and maturation ponds in Sri Pulai, Johor Bahru,
Malaysia.
An analysis of the performance of a waste water stabilization pond in Sri Pulai, Johor Bahru was
done in 2002. The treatment system uses a primary facultative pond followed by a maturation
pond (Ujang et al., 2002). This is the same pond arrangement as used at UTM. The system in Sri
Pulai serves a population equivalent (P.E.) of 10 327 from a residential area of approximately 0.7
km 2 . The ponds together cover an area of 17.725 m 2 , with pond volumes of 16.275 m 3 for the
facultative pond and 10 115 m 3 for the maturation pond. The volume of the facultative pond
should result in a retention time of about 30 days. Around 40 % of the incoming water is assumed
to origin from infiltrating ground water (Ujang et al., 2002).
Table 5.2: Average waste water characteristics at Sri Pulai WSP. The influent results is based on 24
samples, the results from the effluent facultative pond and the effluent maturation pond is based on
14 respectively 7 samples. (re-drawn from Ujang et al., 2002)
COD (mg O 2 / SS (g/l) NH 4 -N (mg/l) NO 3 -N (mg/l)
l)
Influent
Effluent facultative pond
446
139
146
48
23.1
19.7
1.5
1.6
Effluent maturation pond
114
41 16.8
1.2
Removal in entire pond
system
74% 72% 27%
20%
Removal in facultative pond
Removal in maturation pond
69%
18%
67%
15%
15%
15%
- 7%
25%
Compared with the effluent standard for Malaysia, the treatment process was not sufficient, since
the total COD concentration of the effluent was on average 114 mg O 2 /l (see Table 5.2). The
Malaysian effluent standard B is set to 100 mg COD/l (Ujang et al., 2002).
The authors´ conclusion of the unexpected low treatment efficiency (the pond should be able to
meet standard B) could partly be caused by hydraulic short-circuiting. The low treatment
efficiency could also be caused by the specific growth rates of biological degrading bacteria not
being so temperature dependent as expected. The authors recommended aeration and installation
of baffles to improve the treatment.
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