Faculty of Applied Sciences

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Removal of selected heavy metals from wastewater using modified agricultural waste
(2023-09) Msimango, Maureen Nomaxhosa; Qwabe, L. Q.; Ntola, P.
This study explores the potential of utilizing inexpensive adsorbent materials derived from agricultural waste to eliminate Zn (II), Ni (II) and Cd (II) from water-based solutions. Sugarcane bagasse was chemically modified to extract cellulose and further functionalize extracted cellulose to prepare carboxymethyl cellulose which were used as biosorbents. The biosorbents were characterized using XRD, FTIR (ATR), and SEM for confirmation of physical and chemical properties and surface morphology of the adsorbents. In batch experiments, the effect of various parameters such initial concentration (10-300 mg/L), pH (2- 8), adsorbent mass (0.1-1.7 g), and contact time (5-150 min). Adsorption was poor for all metals below pH 4 and reached maximum removal efficiency at pH 6. The increase in initial concentration favoured the increase in removal efficiency but reaches a maximum beyond 100 mg/L. The increase in biosorbent mass shows favours increase in removal efficiency for Ni (II) and Cd (II) but a decrease was observed for Zn(II). The removal efficiency increased with contact time and reached equilibrium at 60 minutes for all metals and biosorbents. The maximum adsorption capacities of Zn(II), on SCB, SCBC, and CMC were 12.3, 20.9 , and 33.5 mg/g respectively. Ni (II) adsorption capacities on SCB, SCBC, and CMC, were 41.9, 25.4, and 125.7 mg/g respectively. The maximum capacities of Cd(II) on SCB, SCBC, and CMC, were 11.3, 20.8, and 21.6 mg/g respectively. The performance of CMC superseded SCB and SCBC. Kinetic experiments showed that the adsorption process followed pseudo second order whereas the equilibrium studies showed that the adsorption process followed the Langmuir adsorption isotherm
Assessment of heavy metals and pathogens removal from municipal wastewater using a constructed rhizofiltration system
(2018) Odinga, Christine Akinyi; Swalaha, Feroz Mahomed; Bux, Faizal; Otieno, Fredrick Alfred O.
Wastewater discharged from municipal treatment plants contain a mixture of organic contaminants, trace metals, enteric pathogens, viruses, and inorganic materials. The presence of such pollutants in wastewater poses a huge challenge to the choice and applications of the preferred treatment method. Conventional treatment methods are inefficient in the removal of some environmentally toxic pollutants and pathogens. This study evaluated the effectiveness of a constructed rhizofiltration system in the removal of heavy metals and enteric pathogens from municipal wastewater. The study was conducted at an eThekwini municipal wastewater treatment plant in Kingsburgh - Durban in the province of KwaZulu-Natal. The pilot-scale rhizofiltration unit included three different layers of substrates consisting of medium stones, coarse gravel and fine sand. The system had one section planted with Phragmites australis and Kyllinga nemoralis while the other section was unplanted and acted as the reference section. Influent and effluent, plant tissue and sediment from the rhizofilter were sampled bi-monthly for a period of two years and assessed for the presence and removal of selected enteric pathogens, trace heavy metals and changes in physicochemical and biological parameters using standard methods. Antibacterial potential of the two experimental plants was determined by the agar-well diffusion method using plant root exudates exposed to selected pathogenic bacteria. Observation of details of plant morphology, distribution and assessment of the metals attachment onto the various plant tissues was determined using images from scanning electron microscopy (SEM). The Langmuir model was used to assess the heavy metal adsorption of the plants. There was an increase in pH from 6.95 pH units to 7.55 pH units in the planted and 6.72 to 7.23 pH units in the reference sections. There was an average reduction in biochemical oxygen demand (BOD) by 79% and chemical oxygen demand (COD) by 75%. Suspended solids were reduced by 86% in the planted section and 59.8% in the reference section, Electrical conductivity was reduced by 7.7% in the planted section and 0.83% in the reference section, Total Dissolved Solids was reduced by 11.5% in the planted section and 3.5% in the reference section, temperature was reduced by 11.9% in the planted section and 1.2% in the reference section, while dissolved oxygen was raised by 10% in the planted section and 5% in the reference section. Turbidity was reduced by 9.7 NTU in the planted section and 9.1 NTU in the reference section, while alkalinity was reduced by 46.3% in planted and 45.5% on reference sections of the rhizofilter. There was a significant reduction in organic loading in the system which was statistically significant (phosphorous, p = 0.029; ammonia, p = 0.03).These average reductions and increases were observed after the system was fully established. The results indicate a comparatively better removal efficiency in the planted than the reference sections of the system. Considering the entire rhizofilter, heavy metals were accumulated at varying percentages of 96.69% on planted and 48.98% in reference sections for cadmium. Chromium was 81% and 24%, Copper was 23.4% and 1.1%, Nickel was 72% and 46.5, Lead was 63% and 31%, while Zinc was 76% and 84% in the planted and reference section of the rhizofilter respectively. The planted section had a much higher removal efficiency as compared to the reference section of the rhizofilter. The macrophytes were found to display some metals binding potential according to observations from SEM and EDX analysis. Significant amounts of Cu deposits were recorded on the roots of K. nemoralis at 0.31wt% with a peak at 0.6cps/eV than on P. australis which was at 0.31wt% with a peak at 0.6cps/eV. Further, higher deposits of Ni at 0.01 wt% with peak at 0.5 cps/eV and 0.0 wt% with peak at 0.2 cps/eV, Pb at 0.22 wt% with peak at 0.2 cps/eV and 0.21wt% with peak at 0.2 cps/eV were recorded on the roots of K. nemoralis and P. australis respectively. Kyllinga nemoralis was found to have greater metals adsorptive capabilities than P. australis. The planted and reference sections had varied removal capacities of between 45% and 98% for the various pathogens detected in the influent wastewater. For example, the concentration of coliphage was reduced by 94.6% in the planted section and 93.6% in the reference section, Candida spp. removal was 64.7% in the planted section and 62.5% in the reference section. Escherichia coli was reduced by 65%- 85% while Salmonella spp. was removed by 94% in the planted section compared to 78% in the reference section. Ascaris lumbricoides was reduced by 77% in the planted section and 53% in the reference section. Accordingly, higher pathogens reduction was achieved in the planted section as compared to the reference section of the rhizofilter. Root exudates from Kyllinga nemoralis were found to display a wider zone of growth inhibition at 9.97±0.19 mm compared to P. australis which had a zone of 8.63 ± 0.22 mm when exposed to cultured colonies of Escherichia coli.
An assessment of selected metal pollutants in Durban Harbour
(2001) Paul, Vimla; Moodley, K. G.
The purpose of this study was to determine the concentration of selected metals in Durban Harbour water and sediments. Four sites were selected for the investigation. The water and sediment samples were collected from July 1998 to July 1999 to accommodate seasonal changes
The accumulation of heavy metals by aquatic plants
(2003) Maharaj, Saroja; Moodley, Kandasamy Govindsamy; Southway-Ajulu, F. A.; Baijnath, Himansu
The pollution of water bodies by heavy metals is a serious threat to humanity. The technique known as phytoremediation is used to clean up these polluted water bodies. The accumulation of heavy metals by aquatic plants is a safer, . cheaper and friendlier manner of cleaning the environment. The aquatic plants -studied in this project are A.sessilis, P.stratiotes, R.steudelii and T.capensis. The accumulation of heavy metals in aquatic plants growing in waste water treatment ponds was investigated. The water, sludge and plants were collected from five maturation ponds at the Northern Waste Water Treatment Works, Sea Cow Lake, Durban. The samples were analysed for Zn, Mn, Cr, Ni, Pb and Cu using ICP-MS. In general it was found that the concentrations of the targeted metals were much lower in the water (0.002 to 0.109 mg/I) compared to sediment/sludge (44 to 1543mg/kg dry wt) and plants (0.4 to 2246 mg/kg dry wt). These results show that water released into the river from the final maturation pond has metal concentrations well below the maximum limits set by international environmental control bodies. It also shows that sediments act as good sinks for metals and that plants do uptake metals to a significant extent. Of the four plants investigated it was found that }t.sessi[ir (leaves, roots and stems) and }A.sessilis (roots and stems) are relatively good collectors of Mn and Cu respectively. These findings are described in the thesis. The concentration of heavy metals in the stems, leaves and roots of the three plants were compared to ascertain if there were differences in the ability of the plant at different parts of the plant to bioaccumulate the six heavy metals studied.

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