Removal of Cr (â ¢) from aqueous solution by using bauxite residue (red mud): Identification of active components and column tests.

Bauxite residue is the by-product of the aluminium industry with an annual output of more than 200 million metric tons in China. Its treatment is still a big problem because more than 96% of that is stockpiled on land causing environmental pollution and threatening the human health. This study used bauxite residue to remove Cr (Ⅲ) from aqueous solution and analyzed the removal mechanism. The removal time was dependent on the initial concentrations of Cr (Ⅲ) and different active components acted on different reaction period. Reaction time increased from <5 min to >2 h with an increase of Cr (Ⅲ) concentration from 5 to 100 and 170 mg/L. The existing forms of adsorbed-Cr were iron oxide-bound Cr (40.80%-87.85%), sulfide-bound Cr (4.04%-20.28%) and residue (6.60%-33.72%). All the components started to react as soon as bauxite residue was added. Cr did not precipitate in the presence of high alkalinity bauxite residue due to the slow release of alkalinity maintaining pH < 6, thus producing Cr(OH)2+, Cr2(OH)24+ and Cr3(OH)45+ by hydrolysis without precipitation. Fe2O3 and Al-containing components were the main active phases for Cr (Ⅲ) removal, with the reaction time lasting more than 2 h and producing Ca6Al4Cr2O15, AlCr2, (Si, Al)2O4, Fe(Cr, Al)2O4, FeCr2Si3O12, MgCr0·1Fe1·9O4 and MgCr0·4Fe1·6O4. Finally, bauxite residue was granulated and used for column tests. Cr (Ⅲ) wastewater (1 and 50 mg/L) was treated and the effluent can meet the first level of the Shanghai standard (0.1 mg/L) defined by Integrated Wastewater Discharge Standard (DB 31/199-2009).

Analysis of bauxite residue components responsible for copper removal and related reaction products.

Bauxite residue is a solid waste produced during alumina production process, and the storage of that in China reached 0.6 billion tons with an increase of more than 70 million annually. Bauxite residue can be used to remove heavy metals from water. This study analyzed components of bauxite residue responsible for copper removal, removal process and accompanying reaction products. Calcite (CaCO3), hematite (Fe2O3) and sulfur-Fe are main components contributing to copper removal. Sulfur in bauxite residue works with iron to remove copper. All these components reacted with copper immediately as bauxite residue was added. Reaction time of sulfur-Fe and carbonate was 5 min and 1 h, respectively. And hematite reacted until complete removal of copper (>2 h). Sulfur quickly reacted with coexisting iron to remove copper, producing chalcopyrite (CuFeS2), cubanite (CuFe2S3) and bornite (Cu5FeS4). Carbonate in bauxite residue reacted with copper, producing tenorite (CuO), copper hydroxide (Cu(OH)2), malachite (Cu2(OH)2CO3), carbonate cyanotrichite (Cu4Al2(CO3,SO4)(OH)12·2H2O), chalconatronite (Na2Cu(CO3)2·3H2O), nakauriite (Cu8(SO4)4(CO3)(OH)6·48H2O) and callaghanite (Cu2Mg2(CO3)(OH)6·2H2O). Copper precipitated through reaction with hematite to produce delafossite (CuFeO2). After removal reaction, the existing forms of copper in bauxite residue comprised carbonate-bound (73.6%-85.7%), iron oxide-bound (5.6%-23.8%), organic matter/sulfide-bound (0.5%-9.0%) and residual forms (0.9%-2.0%). In conclusion, removal of copper using bauxite residue features a more complex reaction than adsorption.

Urban eutrophication and its spurring conditions in the Murchison Bay of Lake Victoria.

The efficiency of Lake Victoria in providing its ecosystem services to riparian states, both immediate and along the Nile river basin, is strongly related to its water quality. Over the past few decades, eutrophication has increased in the lake arising from increased inflow of nutrients. This study was carried out in the Murchison Bay area of Lake Victoria with the aims of assessing the progress of eutrophication nutrient enrichment into the lake between 1990 and 2014. Using Landsat satellite floating algae index (FAI) products and data from laboratory analysis of water samples, the study revealed that floating algae reoccurred periodically with coverage varying between 1 and 18 km(2). The findings also indicated that the range of nitrate-nitrogen concentrations increased greatly with maximum concentrations recorded at 31.2 mg l(-1) in 2007 from 0.084 mg l(-1) in 1990. The soluble reactive phosphorus concentration range showed a maximum of 1.45 mg l(-1) in 2007 from 0.043 mg l(-1) in 1990. The chlorophyll levels increased from an average of 17 µg l(-1) in 1992 by threefold in 1996 but had however declined and halved in intensity by 2011. The eutrophication that has occurred in Lake Victoria over the past decades has been due to pollution from industrial, residential, and agricultural areas within the catchment.

Impacts of population growth and economic development on water quality of a lake: case study of Lake Victoria Kenya water.

Anthropogenic-induced water quality pollution is a major environmental problem in freshwater ecosystems today. As a result of this, eutrophication of lakes occurs. Population and economic development are key drivers of water resource pollution. To evaluate how growth in the riparian population and in the gross domestic product (GDP) with unplanned development affects the water quality of the lake, this paper evaluates Lake Victoria Kenyan waters basin. Waters quality data between 1990 and 2012 were analyzed along with reviews of published literature, papers, and reports. The nitrate-nitrogen (NO3-N), soluble phosphorus (PO4-P), chlorophyll a, and Secchi transparencies were evaluated as they are key water quality indicators. The NO3-N increased from 10 µg l(-1) in 1990 to 98 µg 1(-1) in 2008, while PO4-P increased from 4 µg l(-1) in 1990 to 57 µg l(-1) in 2008. The population and economic growth of Kenya are increasing with both having minimums in 1990 of 24.143 million people and 12.18 billion US dollars, to maximums in 2010 of 39.742 million people and 32.163 billion US dollars, respectively. A Secchi transparency is reducing with time, indicating an increasing pollution. This was confirmed by an increase in aquatic vegetation using an analysis of moderate resolution imaging spectroradiometer (MODIS) images of 2000 and 2012 of Kenyan waters. This study found that increasing population and GDP increases pollution discharge thus polluting lakes. One of major factors causing lake water pollution is the unplanned or poor waste management policy and service.

Efficient degradation of lube oil by a mixed bacterial consortium.

A laboratory study was performed to assess the biodegradation of lube oil in bio-reactor with 304# stainless steel as a biofilm carrier. Among 164 oil degrading bacterial cultures isolated from oil contaminated soil samples, Commaonas acidovorans Pxl, Bacillus sp. Px2, Pseudomonas sp. Px3 were selected to prepare a mixed consortium for the study based on the efficiency of lube oil utilization. The percentage of oil degraded by the mixed bacterial consortium decreased slightly from 99% to 97.2% as the concentration of lube oil was increased from 2000 to 10,000 mg/L. The degradation of TDOC (total dissolved organic carbon) showed a similar tendency compared with lube oil removal, which indicated that the intermediates in degradation process hardly accumulated. Selected mixed bacterial consortium showed their edge compared to activated sludge. Scanning electron microscopy (SEM) photos showed that biofilms on stainless steel were robust and with a dimensional framework constructed by EPS (extracellular polymeric substances), which could promote the biodegradation of hydrocarbons. The increase of biofilm followed first-order kinetics with rate of 0.216 microg glucose/(cm2-day) in logarithm phase. With analysis of Fourier transform infrared spectroscopy (FT-IR) and gas chromatography-mass spectrometry (GC-MS) combined with removal of lube oil and TDOC, mixed bacterial consortium could degrade benzene and its derivatives, aromatic ring organic matters with a percentage over 97%.

Chemically enhanced primary treatment (CEPT) for removal of carbon and nutrients from municipal wastewater treatment plants: a case study of Shanghai.

With Chemically Enhanced Primary Treatment (CEPT) as the short-term process, the capacity of Bailonggang Wastewater Treatment Plant accounts for almost 25% of the total capacity of wastewater treatment in Shanghai, China. However, shortly after this plant was placed in operation in 2004, it was found that the effluent of CEPT couldn't meet the new national discharge criteria. Although the removal of phosphate is almost 80%, chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) in the effluent is frequently found to exceed the standards. The primary goal of this research is to investigate the possibility of optimizing the CEPT to make it meet the discharge criteria before it is upgraded to a secondary treatment. An oxidant is adopted to remove NH3-N, and a high performance polyaluminum chloride (HP-PACl) is synthesized to enhance the removal of COD. It is found that HP-PACl improves the removal of COD, and the oxidant enhances NH3-N removal effectively. However, to meet the requirement of a newly implemented stricter discharge standard, it is necessary to upgrade this CEPT to a secondary treatment. The results of this study provide scientific evidence for the upgrade of the Bailonggang Wastewater Treatment Plant.