Advanced Materials Research Vols. 20-21

Abstract: It has been postulated that bacterial sulphate reduction is related to pH-values above 5.5 (e.g. [1]). First investigations for the 80-year old dump Plessa in the Lower Lusatian mining district (East Germany) show evidence for active sulphate reduction. Mining dump waters from the Plessa site have pH values of 2.4 to 4.9 and pe values between 2 and 6. Measured sulphide concentrations range from 50 to 1200 -g/L. The influence of bacterial sulphate reduction on the development of sulphate concentrations in the dump waters is supported by increasing δ34S and δ18O values with decreasing sulphate concentrations. These findings document that sulphate reduction under natural conditions is not exclusively related to neutral pH values and strongly reducing conditions. Furthermore the tertiary organic matter contained in the dump sediments is the main carbon source for sulphate reducing bacteria.

Abstract: Water draining a waste dump at the Hartenstein site of the former uranium mining company SDAG Wismut is characterised by an uranium concentration between 1mg/L and 3 mg/L and a nitrate concentration from 30 mg/L to 120 mg/L. A microbiological process was developed between 2001 - 2003 under laboratory conditions and, after this time, the process was scaled up to a technical plant. The water was treated continuously by a controlled microbiological process under anaerobic conditions with methanol as the sole carbon and energy source. The reduction plant is a basin filled with about 540 m³ of gravel and with a free water volume of about 200 m³. The plant was foreseen for the treatment of a drainage water flow rate of 2 m³/h – 5 m³/h. The residence time of the treated water in the plant comprises 40 h– 100 h according to the water flow. The continuous process started in 2004. The Uranium concentration decreased to values lower than 0.5 mg/L. The arsenic concentration varied in a range from 60 to 80 .g/L after reaching stable anaerobic conditions. The plant worked also during deep temperatures in the wintertime.

Abstract: Piles and dumps in mining sites of lignite and ore mines very often generate drainage water with a low pH value. Furthermore they are contaminated with heavy metals or radionuclides. A comprehensive sustainable remediation and / or a water treatment process requires an assessment of the water quality and the determination of the future development thereof. This, in turn, requires prediction of the microbial processes which are responsible for the release of heavy metals and radionuclides. The paper deals with the demonstration of a suitable method for the prediction of these reactions and water quality.

Abstract: Sludge, a natural, uncalled for byproduct of aerobic/ anaerobic biological digestion of organic matter present in wastewaters, also known as biosolids, is a thick, black and viscous substance comprising of dead and degraded microbial cells that digested the influents. This dead microbial material, accumulates on the bottom of anaerobic lagoons/ reactors, is organic in nature and rich in plant nutrients such as nitrogen, phosphorus and essential trace elements. It must be removed periodically. Therefore, the objective is to use the sludge as a fertilizer on agricultural land. It is an environmentally acceptable and economical method of sludge disposal. The application of organic wastes to farmland has increased over the years as it contributes to the preservation of the environment and results in an improvement of chemical, biochemical and physical properties of soil, although there is an increased risk of soil and ground water being contaminated by pollutants. Sewage sludge may contain heavy metals whose presence in soil may reduce enzyme activities and affect microbial communities in soil. They accumulate in soil and are taken up by crop plants thus posing health hazard. The study was conducted to characterize anaerobic sludge and quantify the concentration of heavy metals in it, to determine the suitability of the sludge as fertilizer for crops. Physicochemical and biochemical analyses showed that anaerobic sludge produced at Upflow Anaerobic Sludge Blanket (UASB) sewage treatment plant at Faridabad (an industrial town), Haryana, India, contained total organic C 15.714 percent, total Kjeldahl N 0.795 percent, available P 8 3g g-1and heavy metals Zn 1500 3g g-1, Ni 226 3g g-1, Fe 3000 3g g-1 and high activity of enzymes like alkaline phosphatase and dehydrogenase in the sludge. These enzymes are important for soil fertility and nutrient cycling. The toxic heavy metals have been accumulated by bacteria from sewage waters. The ideal C/N ratio, P and enzyme activities show its suitability as fertilizer but presence of heavy metals is a matter of concern. Therefore its application as crop fertilizer or onto land has to be carefully managed.

Abstract: An enhanced entry of heavy metals and metalloids into ground and surface water was observed in the historical hard coal mining areas of the districts of Zwickau and Lugau/ Oelsnitz in Saxonia, Germany. Heavy metals and metalloids like Mn, Co, Ni, Zn, As and Cd are enriched in the surface waters of the district. This environmental impact is observed even though a recultivation of some of the dumps occurred partially already 50 years ago. In this study, preliminary microbial and geochemical characterizations of samples from drilling cores in different depths of a dump site, of surface and ground water samples, and of sediments are described. Thiobacillus denitrificans appeared to be a dominating species in these moderately acidic environment especially where there is nitrate infiltration and inflow, respectively, due to agricultural use of the adjacent area. Some of the sediment samples also contained high counts of iron- and sulfate-reducing bacteria due to the organic detritus on the sediment surface.

Abstract: An Environmental Risk Management methodology was developed for the Toka catchment area, an abandoned base metal mining site in Gyöngyösoroszi, Hungary. The postmining activities on the Hungarian site require the management of both the point and diffuse sources. The mobile Cd and Zn content of the mine waste, soil and sediment transported by water pose the highest environmental risk in the area. The approach is „GIS based” (Geographical Information System) and „catchment scale”, using a three tiered, iterative Environmental Risk Assessment methodology. The model parameters of the metal transport were determined in leaching microcosms. The risk reduction concept aims at reducing the runoff water quantity and contamination by removal of the point sources and chemical & phytostabilisation of the residual and diffuse pollution. The planning of the field application was based on the results of the stabilisation microcosms.

Abstract: Mining activities have deleterious impacts on the environment, such as the formation of acid mine drainage (AMD), which occurs by the action of acidophilic bacteria in tailing deposits, generating diverse types of pollution. Hence it is important to examine the potential of mining waste material to produce acid solutions. Currently, the determination of the net potential of neutralization considers the criteria of the Enviromental Protection Agency of the United States. It was concluded from experiments carried out with diverse samples from Mexico that the tailing samples studied have a high capacity of autoneutralization; although the drainage waters from the tailings and the aqueous extracts from tailing samples react acidic. It is obvious that this method of determination of the neutralization potential and the criteria accepted at the moment do not reflect the reality of the problem. The sulfide analysis in aqueous solution consists of an indirect titration of the excess iodine in two phases (water/ CCl4) with a thiosulfate solution using starch as indicator. Since the iodine is insoluble in water, the equivalent point can be uncertain because part of the iodine can be retained by the starch. Thus, the XOCHIQUETZALLI method for the sulfide ion titration, has been developed. It covers the chemical aspects of the titration procedure, such as the suitable reagents and the maximum permissible concentrations, based on the law of Lambert and Beer. This titration procedure was successfully applied to determine dissolved sulfides extracted from tailing samples.

Abstract: An upflow fixed-bed sulphate-reducing reactor has been set up and monitored for the treatment of metal-bearing wastewater. Zinc has been chosen as the target metal to be sequestered from influent water stream at initial concentrations ranging from 50 to 400 mg/l and initial pH values ranging from 3 to 5. Main operating parameters of the reactor, such as the composition and content of electron donor, electron acceptor, sulphate and metal removal capacity, have been monitored during ten months of continuous operation. The results obtained have shown that the reactor has a considerable capacity of completely reducing sulphates for initial concentrations up to 7,200 mg/l, completely removing soluble zinc for initial concentrations up to 400 mg/l and completely removing Total Organic Carbon (TOC), for initial concentrations up to 1,500 mg/l.