Effect of bidens pilosa L in sulfate removal from industrial wastewater in a hydroponic system
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Date
2018
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University of Zululand
Abstract
Water contamination from human activities such as discarding sulfate-rich wastes into
natural water resources leads to the introduction of sulfate and other toxic substances like
heavy metals. This poses as a threat to human health and the environment since consumption
of sulfate concentration greater than 250 mg/l causes diarrhoea and dehydration.
Accumulation of sulfate in water also leads to the death of aquatic species and when sulfur is
produced from sulfate, it may react with oxygen in the atmosphere and form sulfur dioxide
which causes acid rain when reacted with nitrogenous gases. Acid rain is detrimental to the
environment. Ion exchange chromatography is currently used in sulfate removal but it is
expensive and energy consuming. This has necessitated the development of an
environmentally friendly, cost-effective, and simple wastewater technique for sulfate
removal using wetland technologies. In order to remove sulfate from wastewater, two
hydroponic systems were constructed, and the first one was cultivated with Bidens pilosa L
and the other one was left unplanted (control section). Wastewater collected from Tendele
Coal Mine was introduced into both sections and the initial sample was collected. After every
24 hours the samples were collected at different hydraulic retention time, for 2 weeks. In all
samples physicochemical parameters were determined using a pH meter. Sulfate
concentration was determined using sulfate test kits and a spectrophotometer. The qPCR was
used to identify the microorganisms responsible for the removal of sulfate in the system.
Sulfate removal in the planted section was higher than in the control section. It was 2.9%,4.9%
after 24 hours 6.5%, 11% after 48 hours, 12%, 17% after 72 hours, 16.3%, 25.4% after 96
hours, 18.2%, 34.8% after 120 hours, 26.9%, 44.6% after 144 hours, 34.7%, 55.1% after 168
hours, 42%, 63.7% after 192 hours, 47.5%, 71.5% after 216 hours, 53.2%, 73.3% after 240
x
hours, 54.7%, 74% after 264 hours and 56%, 76.3 % after 288 hours over 2 weeks in the control
and planted sections respectively. Sulfate concentration in the macrophytes was found to be
110 mg/l before treatment, and 353 mg/l after treatment. There was a significant difference
between sulfate removal in the planted and control section and also in macrophytes before
and after treatment, indicated by p=0.0001. This indicated that the hydroponic system was
able to remove sulfate from wastewater using the combination of the mechanisms of plant
uptake and microbial degradation. Sulfate removal was also indicated by final concentration
of sulfate, which was 169 mg/l in the planted section which was below the acceptable
amounts of sulfate in water (by World Health Organization) while it was 309 mg/l in the
control section. Temperature had a moderate negative correlation on sulfate removal (-0.38
≤ r ≤-0.42) while COD had a very strong negative correlation (-0.94 ≤ r ≤-0.97). The dissolved
oxygen indicated weak positive correlation (0.29≤ r ≤0.37), and pH indicated a strong positive
correlation (0.80 ≤ r ≤0.79) in the planted and control section respectively. These correlations
indicated that physical and chemical parameters were had an effect on sulfate removal.
Microbial population of sulfate-reducing bacteria (Desulfobacter, Desulfovibrio) was present
in both systems. Desulfococcus was present in the control section but absent in planted
section due to its sensitiveness to oxygen. These findings shown that the hydroponic system
had an ability to remove sulfate from industrial wastewater using macrophytes and sulfate
reducing bacteria but the removal was dependent on physicochemical parameters.
Description
This dissertation is submitted in complete fulfilment for the Degree of Masters (Microbiology) in the Department of Biochemistry and Microbiology, Faculty of Science and Agriculture at the University of Zululand, 2018.
Keywords
Bidens pilosa L, Industrial wastewater, hydroponic system, sulfate removal