Ilunga Kamika

Assessing the resistance and bioremediation ability of selected bacterial and protozoan species to heavy metals in metal-rich industrial wastewater

BackgroundHeavy-metals exert considerable stress on the environment worldwide. This study assessed the resistance to and bioremediation of heavy-metals by selected protozoan and bacterial species in highly polluted industrial-wastewater. Specific variables (i.e. chemical oxygen demand, pH, dissolved oxygen) and the growth/die-off-rates of test organisms were measured using standard methods. Heavy-metal removals were determined in biomass and supernatant by the Inductively Couple Plasma Optical Emission Spectrometer. A parallel experiment was performed with dead microbial cells to assess the biosorption ability of test isolates.ResultsThe results revealed that the industrial-wastewater samples were highly polluted with heavy-metal concentrations exceeding by far the maximum limits (in mg/l) of 0.05-Co, 0.2-Ni, 0.1-Mn, 0.1-V, 0.01-Pb, 0.01-Cu, 0.1-Zn and 0.005-Cd, prescribed by the UN-FAO. Industrial-wastewater had no major effects on Pseudomonas putida, Bacillus licheniformis and Peranema sp. (growth rates up to 1.81, 1.45 and 1.43 d-1, respectively) compared to other test isolates. This was also revealed with significant COD increases (p < 0.05) in culture media inoculated with living bacterial isolates (over 100%) compared to protozoan isolates (up to 24% increase). Living Pseudomonas putida demonstrated the highest removal rates of heavy metals (Co-71%, Ni-51%, Mn-45%, V-83%, Pb-96%, Ti-100% and Cu-49%) followed by Bacillus licheniformis (Al-23% and Zn-53%) and Peranema sp. (Cd-42%). None of the dead cells were able to remove more than 25% of the heavy metals. Bacterial isolates contained the genes copC, chrB, cnrA3 and nccA encoding the resistance to Cu, Cr, Co-Ni and Cd-Ni-Co, respectively. Protozoan isolates contained only the genes encoding Cu and Cr resistance (copC and chrB genes). Peranema sp. was the only protozoan isolate which had an additional resistant gene cnrA3 encoding Co-Ni resistance.ConclusionSignificant differences (p < 0.05) observed between dead and living microbial cells for metal-removal and the presence of certain metal-resistant genes indicated that the selected microbial isolates used both passive (biosorptive) and active (bioaccumulation) mechanisms to remove heavy metals from industrial wastewater. This study advocates the use of Peranema sp. as a potential candidate for the bioremediation of heavy-metals in wastewater treatment, in addition to Pseudomonas putida and Bacillus licheniformis.

Comparing the tolerance limits of selected bacterial and protozoan species to nickel in wastewater systems.

Heavy-metal resistant microorganisms play a significant role in the treatment of industrial wastewater. The detoxifying ability of these resistant microorganisms can be manipulated for bioremediation of heavy metals in wastewater systems. This study aimed at comparing the tolerance limit of selected wastewater protozoan species (Aspidisca sp., Trachelophyllum sp. and Peranema sp.) against Ni(2+) with that of selected bacterial species (Bacillus licheniformis-ATCC12759, Brevibacillus laterosporus-ATCC64 and Pseudomonas putida-ATCC31483) commonly found in wastewater systems. The isolates were exposed to various concentrations of Ni(2+) in mixed liquor and their tolerance to Ni(2+) assessed at different temperatures (25°C, 30°C, 35°C and 40°C) and pHs (4, 6, 7, 8 and 10). The physicochemical parameters such as chemical oxygen demand (COD) and dissolved oxygen (DO) of the media and the growth rates of the isolates were measured using standard methods. In terms of their minimum inhibitory concentrations (MIC), the results revealed that the isolates could tolerate Ni(2+) at concentrations ranging between 32 and 52ppm for protozoa and between 52 and 84ppm for bacteria. B. licheniformis-ATCC12759 was the most tolerant bacterial species (MIC: 84ppm-Ni(2+)) while Peranema sp. was the most tolerant protozoan species (MIC: 52ppm-Ni(2+)). At 10 and/or 20ppm-Ni(2+) the growth of B. licheniformis-ATCC12759 (6.30 days(-1) for 10 and 5.73 days(-1) for 20ppm-Ni(2+)), P. putida-ATCC31483 (6.02 days(-1) for 10 and 5.31 days(-1) for 20ppm-Ni(2+)) and Peranema sp. (2.15 days(-1) for 10ppm-Ni(2+)) was stimulated after one day of incubation. Statistical evidence showed significant differences (p=0.0065) between the MIC of the six isolates and positive correlations between COD and the growth rates of isolates (r=0.8999/0.8810 for bacteria/protozoa). The tolerance limit of all isolates was significantly dependent on the pH and the temperature. The study suggests that these isolates can be used for the bioremediation of nickel in industrial wastewater systems.

Mycological and aflatoxin contamination of peanuts sold at markets in Kinshasa, Democratic Republic of Congo, and Pretoria, South Africa.

Peanut (Arachis hypogaea L.) is an important food crop in sub-Saharan Africa. In this survey, the mycological and aflatoxin contamination of peanuts collected from Kinshasa, Democratic Republic of Congo, and Pretoria, South Africa, was assessed. Twenty peanut samples were purchased randomly at informal markets in the two cities and analysed for mycoflora and aflatoxins (AFB1, AFB2, AFG1 and AFG2) using standard methods. The results indicated that 95% of the Kinshasa samples and 100% of the Pretoria samples were contaminated with aflatoxigenic fungi in the ranges 20–49,000 and 40–21,000 CFU/g, respectively. Seventy-five per cent of the Kinshasa samples and 35% of the Pretoria samples exceeded the maximum limits of AFB1 as set by The Joint FAO/WHO Expert Committee on Food Additives. Residents of both cities are at a high risk of aflatoxin exposure despite their apparent cultural, socio-economic, geographic and climatic differences. Further work needs to be done to understand the supply chains of peanut trade in informal markets of the two countries so that interventions are well targeted on a regional rather than a national level.

Microbial diversity of Emalahleni mine water in South Africa and tolerance ability of the predominant organism to vanadium and nickel.

The present study aims firstly at determining the microbial diversity of mine-water collected in Emalahleni, South Africa and secondly isolating and characterizing the most dominant bacterial species found in the mine water in terms of its resistance to both V5+ and Ni2+ in a modified wastewater liquid media. The results revealed a microbial diversity of 17 orders, 27 families and 33 genera were found in the mine-water samples with Marinobacteria (47.02%) and Anabaena (17.66%) being the most abundant genera. Considering their abundance in the mine-water samples, a species of the Marinobacter genera was isolated, identified, and characterised for metal tolerance and removal ability. The MWI-1 isolate (Marinobacter sp. MWI-1 [AB793286]) was found to be closely related to Marinobacter goseongensis at 97% of similarity. The isolate was exposed to various concentrations of Ni2+ and V5+ in wastewater liquid media and its tolerance to metals was also assessed. The MWI-1 isolate could tolerate V5+ and Ni2+ separately at concentrations (in terms of MIC) up to 13.41±0.56 mM and 5.39±0.5 mM at pH 7, whereas at pH 3, the tolerance limit decrease to 11.45±0.57 mM and 2.67±0.1 mM, respectively. The removal of V5+ and Ni2+ in liquid media was noted to gradually decrease with a gradual increase of the test metals. A significant difference (p<0.05) between V5+ and Ni2+ removal was noted. Marinobacter sp. MWI-1 achieved the maximum permissible limit of 0.1 mg-V5+/L prescribed by UN-FAO at 100 mg/L, while at 200 mg/L only V5+ was removed at approximately 95% and Ni2+ at 47%. This study suggests that mine-water indigenous microorganisms are the best solution for the remediation of polluted mine water.

Prevalence of enteropathogenic bacteria in treated effluents and receiving water bodies and their potential health risks

The failure of wastewater treatment plants to produce effluents of a high microbiological quality is a matter of great concern in terms of water resource pollution. A more serious concern is that this water source is used by communities in developing countries for multiple purposes, which include drinking, recreation and agriculture. The current study investigated the prevalence and potential health risks of enteropathogenic bacteria (Salmonella typhimurium, Shigella dysenteriae and Vibrio cholerae) in the treated effluents of three selected South African Wastewater Treatment Works as well as their receiving water bodies. Culture-based and polymerase chain reaction techniques were used to detect and identify the pathogenic bacteria. The conventional methods revealed that of the 272 water samples collected, 236 samples (86.8%) tested presumptively positive for Salmonella spp., 220 samples (80.9%) for Shigella spp. and 253 samples (93.0%) for V. cholerae. Molecular test results indicated that out of the randomly selected presumptive positive samples (145), zero to 60% of samples were positive for S. typhimurium and S. dysenteriae and 20% to 60% for V. cholerae. For the health risk assessment, the daily combined risk of S. typhimurium, S. dysenteriae and V. cholerae infection was above the lowest acceptable risk limit of 10(-4) as estimated by the World Health Organization for drinking water. This study showed that the target treated wastewater effluents and their receiving water bodies could pose a potential health risk to the surrounding communities.

Bacterial profiling in brine samples of the Emalahleni Water Reclamation Plant, South Africa, using 454-pyrosequencing method.

A metagenomic approach was applied using 454-pyrosequencing data analysis for the profiling of bacterial communities in the brine samples of the water reclamation plant. Some physicochemical characteristics of brine samples were also determined using standard methods. Samples ranged from being lightly alkaline to highly alkaline (pH 7.40-10.91) throughout the various treatment stages, with the salinity ranging from 1.62 to 4.53 g L(-1) and dissolved oxygen concentrations ranging from 7.47 to 9.12 mg L(-1). Phenotypic switching was found to occur due to these physicochemical parameters. Microbial diversities increased from those present in Stage I reactor (six taxonomic groups) to those in Reverse Osmosis (RO) stage I (17 taxonomic groups), whereas in the second phase of the treatment, it increased in Stage II clarifier (14 taxonomic groups) followed by a decrease in RO stage II (seven taxonomic groups). Overall, seven phyla were detected, apart from many bacterial sequences that were unclassified at the phylum level. The most dominant phylum found was Proteobacteria accounting for 59% of the total sequences. A blastn sequence similarity search showed that the majority of the sequences (56%) were homologous to the uncultured bacterial species, underlining the vast untapped bacterial diversity.

Effect of vanadium toxicity at its different oxidation states on selected bacterial and protozoan isolates in wastewater systems

This study assesses and compares vanadium toxicity in its different oxidation states towards bacterial isolates (Pseudomonas putida and Bacillus licheniformis) and protozoan isolates (Peranema sp. and Trachelophyllum sp.). The isolates were exposed to various concentrations of V in mixed liquors and their tolerance to V was assessed at 30°C at a pH of 4. The results revealed that the increase in V oxidation state increased its toxicity to bacterial isolates, whereas its toxicity decreased for protozoan isolates. Among the bacterial isolates, P. putida was found to be more tolerant to V3+(24 h-median lethal concentration (LC50): 390 mg/l), V4+(24 h-LC50: 230–250 mg/l) and V5+(24 h-LC50: 180–200 mg/l), whereas for the protozoan isolates, Peranema sp. appeared to be more tolerant to V3+(24 h-LC50: 110–120 mg/l), V4+(24 h-LC50: 160–170 mg/l) and V5+(24 h-LC50: 160–200 mg/l). A comparison of both groups of organisms revealed Trachelophyllum sp. as the most sensitive organism to V at its various oxidation states. The visual and spectrophotometric methods used to assess V reduction revealed that P. putida was the only isolate able to reduce V5+, V4+ and V3+ to V2+ in mixed liquor media. Vanadium (+2) in concentrations of approximately 46.46 mg/l, 29.57 m mg/l and 38.01 mg/l found in the media was treated with V3+, V4+ and V5+, respectively, and inoculated with P. putida. This study revealed that the ability of V reduction, adopted with P. putida, can be an effective strategy to remove V from polluted environments. This study also showed that the toxicity of V, in terms of its oxidation states, differs from one species to another and in kingdoms.

The ability of consortium wastewater protozoan and bacterial species to remove COD in the presence of nanomaterials under varying pH conditions

ABSTRACT The aim of this study was to ascertain the survival limit and capability of commonly found wastewater protozoan (Aspidisca sp, Trachelophyllum sp and Peranema sp) and bacterial (Bacillus licheniformis, Brevibacillus laterosporus and Pseudomonas putida) species to remove COD while exposed to commercial nanomaterials under varying pH conditions. The experimental study was carried out in modified mixed liquor media adjusted to various pH levels (pH 2, 7 and 10) and a comparative study was performed to determine the difference between the cytotoxicity effects of commercial zinc oxide (nZnO) and silver (nAg) nanomaterials (NMs) on the target wastewater microbial communities using standard methods. The selected microbial communities were exposed to lethal concentrations ranging from 0.015 g/L to 40 g/L for nZnO and from 0.015 g/L to 2 g/L for nAg for a period of 5 days of incubation at 30°C (100 r/min). Compared with the absence of NMs in wastewater mixed liquor, the relevant environmental concentration ranging between 10 µg/L and 100 µg/L, for both nZnO and nAg caused no adverse effects, but the presence of 20 g of nZnO/L and 0.65 g of nAg/L significantly inhibited microbial growth. Statistical evidence showed that nAg was significantly more toxic compared to nZnO, but there was an insignificant difference in toxicity between microbial communities and pH variations. A significant decrease in the removal of COD by microbial populations was observed in the presence of NMs with a moderate correlation of r = 0.3 to r = 0.7 at all pH levels. It was evident that there was a physical interaction between commercial NMs and target wastewater microbial communities; although not quantitatively assessed, cell morphology and cell death were observed. Such phenomena suggest the high resilience of the microbial community, but it is the accumulation of NMs that will have adverse effects on the performance in terms of COD removal.

The Limpopo Non-Metropolitan Drinking Water Supplier Response to a Diagnostic Tool for Technical Compliance

Water services providers should supply water that is fit for human consumption, taking into account multi-barrier approaches and technical aspects such as design aspects, operation monitoring, final water quality compliance monitoring, plant monitoring practices, maintenance, and risk management practices. Against this background, this study focused on applying the diagnostic tool for technical compliance as well as assessing the compliance of water treatment plants with management norms. Six plants in the Vhembe District Municipality were selected; the Vondo, Malamulele, Mutshedzi, and Mutale plants (conventional), and the Dzingahe and Tshedza package plants. During the first assessment, four (Malamulele, Mutshedzi, Mutale and Dzingahe) plants scored between 44% and 49% and achieved Class 3 certification, revealing serious challenges requiring immediate intervention. Two water plants (Vondo and Tshedza, scoring 53% and 63%, respectively) were in the Class 2 category, revealing serious challenges requiring attention and improvement. During the second assessment, all plants scored between 63% and 87% (Class 2 category). The greatest improvement (30%) was noted for the Dzingahe and Tshedza plants, followed by the Malamulele plant, while the Mutale, Vondo, and Mutshedzi plants improved their scores by 20%, 17% and 14%, respectively. After corrective actions and re-measurement, no plant complied. It is recommended that Water Services Providers (WSPs) regularly apply the diagnostic tools and water safety plans as developed in order to comply with applicable standards.