Environmental Engineering Reference
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over a 48 h period. Nitrite and NO 3 -N concentrations were reduced from 0.197 to
0.024 and 0.029 mg L -1 and from 21.4 to 17.4 and 17.9 mg L -1 in aquaria containing
water lettuce and water hyacinth, respectively.
A number of investigators have examined use of hydroponics for improving
water quality of municipal or factory effluents [75-78]. DeBusk et al. [75] evaluated
the use of a water hyacinth based treatment system for nutrient removal from sec-
ondarily treated municipal wastewater and reported an average plant productivity of
16gm -2 day -1 . Over a three month period the water hyacinth reduced the NH 4 -N,
NO 2 -N, and NO 3 -N concentrations in the wastewater from 2.57 to 0.03 mg L -1 ,
1.32 to 0.08 mg L -1 , and 4.12 to 0.26 mg L -1 , respectively.
Nuttall [76] examined the ability of parrot's feather for nutrient reduction from
a secondarily treated municipal wastewater over a 13 month period and reported
suspended solids removal efficiencies ranging from 12.8 to 65.0%. John [77] inves-
tigated the use of water hyacinth for TS removal from rubber factory and palm oil
mill effluents. They reported TS reductions of 16.9, 39.4 and 57.0% at hydraulic
retention times (HRTs) of 5, 10, and 15 days when the water hyacinths were grown
on undiluted raw rubber factory effluent and 32.4, 42.9, and 44.7% at HRTs of 10,
20 and 25 days when they were grown on an anaerobically treated palm oil mill
effluent.
From rubber factory effluent John [77] reported COD reductions of 69.0, 80.2,
and 88.7% at hydraulic retention times of 5, 10, and 15 days. When water hyacinths
were grown on an anaerobically treated palm mill effluent, COD reductions of 76.7,
83.1 and 87.3% were observed at HRTs of 10, 20 and 25 days, respectively.
Dedes and O'Shaughnessy [78] investigated the use of duckweed ( Lemna minor )
for treatment of domestic wastewater over 74 days under 5 different hydraulic reten-
tion times (2.0, 2.7, 5.5, 5.6 and 11.7 days) and reported that the fraction of NH 4 -N
removed remained relatively constant at approximately 54-58% despite changes in
hydraulic retention time. The fraction of NO 3 -N removed ranged from 17 to 36%
and increased with longer retention times.
Awuah et al. [79] evaluated the potential use of water lettuce for pollutant
removal from a low-strength, anaerobically treated domestic sewage and reported
NO 3 -N reductions of 70% after 6 months of operation. Cloris and Araujo [80] exam-
ined the use of a water hyacinth based system for tertiary treatment of domestic
sewage and reported a PO 4 -P reduction of 88% over a 4 month period. Xu et al.
[81] evaluated the ability of a water hyacinth based treatment system for removal
of nutrients from domestic wastewater and reported PO 4 -P reduction of 75-95%.
Jing et al. [82] investigated the use of water lettuce for nutrient removal from an
artificially prepared wastewater over a 30 day period and reported average PO 4 -P
removal efficiencies in the controls and in the compartments containing water let-
tuce of 8.0, 33.3, 42.3, and 31.6%, and 14.3, 53.9, 73.2, and 55.6 % at hydraulic
retention times of 1, 2, 3 and 4 days, respectively.
Tripathi and Shukla [83] used a three stage system in the laboratory to treat
wastewater from Varanasi city, India (city sewage mixed with industrial effluents).
Their system had water hyacinth in the first and third stages and algal culture in the
second stage. Their three stage system resulted in very high reductions of BOD
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