Environmental Technology

Prasad, D.; Wai, M.; Bérubé, P.; Henry, J. G.

doi: 10.1080/09593332008616840pmid: N/A

Acid mine drainage (AMD) contains high concentrations of sulphates and metals at low pH. Biological treatment of AMD via the sulphate reduction pathway seems promising. To make this treatment method economical, the availability of a suitable low cost organic substrate in the vicinity of the mine site is essential. The objectives of this study were: (1) to try and predict the degradability of three organic materials using the Forage Fibre Analysis (FFA) technique, BOD/COD ratio, protein and carbohydrate contents and C/N ratio, and (2) to evaluate the suitability of these organic materials to provide substrate for the sulphate reducing bacteria (SRB) in the anaerobic treatment of AMD. All four tests indicated that activated sludge would be the most suitable material. However, the results of the tests for predicting the biodegradability of the other two materials, were inconsistent. The FFA method and the BOD/COD ratio indicated rabbit pellets as the second most suitable material followed by digested sludge. But, the protein and carbohydrate contents and the C/N ratio pointed to digested sludge as the second most suitable material followed by rabbit pellets. None of the four tests alone was found to be sufficient to predict the biodegradability of organic materials. To assess the degradability of the three materials a series of anaerobic reactors was operated at room temperature with the different organic materials spiked with potassium sulphate. For comparison, ethanol, a readily degradable substrate, was included in the anaerobic assessment process. Of the three organic materials examined, activated sludge was found to be the most suitable material to provide substrate for SRB followed by rabbit pellets and digested sludge. The disparity in predicted and actual assessment results is discussed.

Shanableh, A.; Ginige, P.

doi: 10.1080/09593332008616841pmid: N/A

The study presented in this paper aimed to evaluate the impact of bio-acidification on the leaching of ammonia (NH4-N) and phosphorus (PO4-P) from various types of digested and undigested sludges. Bio-acidification produced a highly acidic and digestive environment which, accompanied by shifting microbial populations, accelerated the mineralisation of organic nitrogen and the leaching of phosphorus and heavy metals. The bio-acidification process was capable of leaching significant quantities (7–98%) of Ni, Zn, Pb, Cr, Cd, and Cu from sludge, however nitrogen and phosphorus were also leached simultaneously. It should be emphasised however that bio-acidification by itself did not reduce the TKN, total phosphorus, or heavy metal contents of the sludge. The separation of supernatant containing the leached products resulted in a significant loss in the nutrient value of the sludge. The measured organic nitrogen mineralisation results were in the range of 10–43%. Similarly for phosphorus, the leaching results were in the range of 16–65%. The phosphorus leaching results in individual sludge samples were significantly higher than the nitrogen leaching results. This is because the digestion of organic matter is the main cause of TKN mineralisation, while in addition, phosphorus leaching is possibly increased by the leaching of phosphorus from inorganic sources and polyphosphates stored in sludge. This study confirmed that while bio-acidification can be used to reduce the heavy metal contents in sludge, the process can also reduce the nitrogen and phosphorus values of the product.

Brown, D. A.; Sherrief, B. L.

doi: 10.1080/09593332008616842pmid: N/A

Suitable subsurface repositories for spent nuclear fuel are presently under investigation at several national underground research laboratories that have been excavated for this purpose. However, since spent fuel storage canisters can be expected to break down after a period of time, engineered barriers have been proposed to prevent radionuclides, leached from the canisters by groundwater, from escaping into the environment. Serious investigation of the effect of microbial activity on these barriers and the surrounding geosphere has only been undertaken fairly recently. This research has now provided evidence that most subsurface groundwater environments are reducing, due to the presence of indigenous microbial ecosystems. If such a reducing environment can be maintained during excavation, emplacement and storage of the waste canisters it could ensure that most of the radionuclides are in the reduced state, in which case, as the majority are only slightly soluble, they are unlikely to be very mobile in the groundwater system. Geological analogues at Cigar Lake, Canada, and Oklo, Gabon demonstrate that uranium ore and its fission products can be retained in situ for more than a billion years. Furthermore excavation of the laboratory at Äspö in Sweden has shown that, although the subsurface environment was disturbed during excavation, the indigenous microbial community was able to maintain the environment in a reduced state. Thus it appears to be important to characterize the natural ecosystem as well as the hydrological regime present in the subsurface sites that are being considered for storage. Natural rock barriers, which contain the indigenous groundwater and microorganisms, may provide a more resilient protection to the movement of radionuclides than that of the proposed engineered barriers.

Poulios, I.; Aetopoulou, I.

doi: 10.1080/09593332008616843pmid: N/A

The photocatalytic degradation of Reactive Orange 16, a textile azo dye, has been investigated in aqueous heterogeneous solutions containing titanium dioxide TiO2 as photocatalyst. The disappearance of the organic molecule follows approximately a pseudo-first kinetic order according to the Langmuir-Hinshelwood model. CO2, NO3 −, NH4 + and SO4 2− ions have been identified as mineralization products. Various commercial photocatalysts were compared with respect to their decolorization efficiency, as well as the production of CO2. The effect of pH and H2O2 on the reaction rate was ascertained.

Jordão, C. P.; Pereira, J. L.; Jham, G. N.; Bellato, C. R.

doi: 10.1080/09593332008616844pmid: N/A

The State of Minas Gerais possesses one of Brazil's important smelting resources. Aquatic contamination produced from mining activities and smelting of ores in the region may be harmful to the human population. However, no studies on levels of heavy metal have been carried out in the area. Thus, to assess the extent of pollution resulting from the metalliferous industry, river water, sediment, plant and fish samples were collected up- and down-river from the smelters and mining areas in Conselheiro Lafaiete and Ouro Branco and analysed to detect metal inputs. Samples of mineralized, contaminated and non-contaminated regions were also collected in the State of Minas Gerais to obtain control values. The metals examined included Fe, Al, Mn, Pb, Cu, Zn, Co, Cd, Ni, and Cr and were selected due to their toxicity and occurence in ores. Metal inputs in the samples analysed appeared to be related to effluent discharges into the rivers. High concentrations (in µg l−1) of Mn (697), Pb (153) and Cd (12.7) were found in river water collected from the smelting region when compared with control areas. The river sediments showed high concentrations (in µg g−1) of Mn (32276), Cd (1.4), Cu (70.6), Ni (170), and Cr (174). The concentrations of Mn and Cr in the plants were higher than those normally found in these materials. Chromium concentration in fish was found to be five times higher than the Brazilian recommended value for human intake.

Cheeseman, C. R.; Batchelder, M.; Sechioti, P.

doi: 10.1080/09593332008616845pmid: N/A

The relative effects of different cations on permeant flow through two commercially available Wyoming bentonite clays have been assessed using a rapid filter press (RFP) test. The clays were exposed to test solutions of sodium, potassium, calcium, ammonium and zinc ions, all added as acetates at different molarities, so that the relative effects on flow rates could be determined. Results showed that ammonium and potassium had particularly deleterious effects on permeant flow for both clays, while solutions of sodium and zinc acetate permeated at much lower rates. Of the two materials tested, the modified bentonite, which had been treated with surface-active additives, had significantly improved performance compared to the untreated clay. XRD has been used to identify changes in interlayer spacing (d001) associated with exposure to the different acetate solutions.

Artan, N.; Tasli, R.

doi: 10.1080/09593332008616846pmid: N/A

A sequencing batch reactor (SBR) was used to carry out an experimental study under well defined conditions to investigate the effect of filling and aeration pattern on nutrient removal efficiency and settling characteristics. The SBR was operated with a cycle time of 8 hours under 4 different operational conditions. The filling time was increased while aeration time was gradually reduced during these four runs. When mixing time to process time ratio (TM/TP) exceeded 0.65, sludge settleability began to deteriorate. It seemed that deterioration in sludge settleability was not due to long fill time but to prolonged anaerobisis. The change in sludge characteristics did not have a major effect on nutrient removal. From the experimental results, it can be concluded that aerated time fraction is the most important operational parameter that influences nutrient removal efficiency. In nutrient removal SBR, filling pattern plays a significant part in the efficient utilization of external carbon source rather than in creating concentration gradient needed for kinetic selection. A predetermined MLSS concentration can be maintained in the reactor even at high SVI values by adjusting the duration of settling and V0/VT ratio.

Gerente, C.; Andres, Y.; Le Cloirec, P.

doi: 10.1080/09593332008616847pmid: N/A

Organic materials and especially humic substances are often present in natural waters. The influence of organic compounds on uranium removal onto chitosan is studied. The pH of the media is fixed at 6. In operating conditions, uranium major species present in solution are: (UO2)3(OH)5 +. and (UO2)4(OH)7 +. Capacity of fixation is found to be 450 mg g−1, considering precipitation phenomena. Experimental results show that chitosan offers a selective adsorption depending on the different organics used: the adsorption capacity is maximum with benzaldehyde, average with humic acids, limited with phenol and insignificant with benzoic acid. Phenol does not affect the fixation capacity of uranium significantly whereas benzoic acid and benzaldehyde have an average effect upon it and humic acids decrease it to 200 mg g−1 and less as the concentration of the acid increases.

Tedesco, M. J.; Teixeira, E. C.; Medina, C.; Bugin, A.

doi: 10.1080/09593332008616848pmid: N/A

Brazil's coal production is about five million tonnes per year, mostly on open mining operations. Mined land reclamation is difficult due to the high acidity generated by the suphur compounds' oxidation. In order to evaluate the feasibility to use bottom ash and lime for land reclamation of coal mining and processing refuse deposit areas, a field experiment was carried out in a coal waste dumping area over 20 m deep, that was previosly leveled off, located on the Butiá County Recreio mine, in Rio Grande do Sul state, Brazil in 1992 and 1993. Trenches 10m width and 50m length were dug in the coal refuse and filled with bottom ash covered with a layer of soil of different depths. Several summer and winter plant species were grown on 10 × 10 m subplots. A minimum of 0.1 m soil layer over 0.2 m bottom ash with proper liming and fertilization was required to promote plant growth. Low soil pH due to sulphur compounds' oxidation was the most limiting factor for plant growth. Heavy metals Cr, Cd, Ni and Pb concentrations in the plants' shoots were in the range usually determined for plants grown on uncontaminated soils.

Bouhamra, W. S.; Elkilani, A. S.

doi: 10.1080/09593330.1999.9618807pmid: N/A

Volatile organic compound contents of 20 Kuwaiti houses were measured by pumped sampling versus time and 17 predominant compounds (namely, benzene, toluene, xylene, styrene, trimethylbenzene, butylbenzene, propylbenzene, dichloroethylene, trichloroethane, dichloropropane, dibromomethane, chloroform, tetrachloroethane, tetrachloroethylene, chlorotoluene, dichlorobenzene and fluorobenzene) have been identified. Other related factors, such as the outdoor concentrations, the surface areas of the walls and the furnishings, and the previously measured air exchange rates were incorporated in a transient mass balance model which also took into consideration the phenomenon surface sorption and the source emission. An integrated form of this model was used to analyze the experimental time-averaged concentration data. A plot of indoor concentration versus outdoor concentration for a specific VOC gave a straight line from which the removal rate by adsorption and the source emission were obtained. It was found that the data correlated satisfactorily if the surface area for sorption was estimated based not only on the surfaces of walls, ceiling and floor (an approach often used by other workers in previous studies) but also those of all components of interior, such as those of furniture. The surface sorption rate constants for each VOC under study were evaluated and they varied between 0.2 to 0.96 m hr−1 depending on the chemical nature of the VOCs. These results showed also that the removal rates of aliphatic and aromatic VOCs by adsorption increased if they were attached to halogen and alkyl groups respectively. On the other hand, relatively low removal rates were observed when unsaturated alkyl and phenyl groups were attached to a halogen.