MICROBIAL LEACHING OF CHROMIUM FROM SOLIDIFIED WASTE FORMS – A KINETIC STUDY

In this study, Thiobacillus thiooxidans (T. thiooxidans) was used to study the microbial stability / degradation of cement-based waste forms. The waste forms contained a chromium salt (CrCl3·6H2O), cement and other additives viz., lime and gypsum in two different proportions. The experimental samples of all the simulated waste forms showed evidence of microbial growth as indicated by substantial increase in sulfate. Chromium leached from the waste forms was found to be lowest in cement – lime solidified waste forms (0.061 mg·l-1) and highest in cement gypsum waste forms (0.22 mg·l-1) after 30 days of exposure. These values were lower than the toxicity characteristic leaching procedure (TCLP), regulatory limit (5 mg·l-1). Model equations based on two shrinking core models (acid dissolution and bulk diffusion model), were used to analyze the kinetics of microbial degradation of cement based waste forms. The bulk diffusion model was observed to fit the data better than the acid dissolution model, as indicated by good correlation coefficient

Microbial water desalination and bio-electricity generation - Role of biomass carbon

Microbial desalination cells (MDCs) are modified microbial fuel cells (MFC) that are energy-sustainable. They use organic matter in wastewater as the energy source for desalination. The electric potential gradient is caused by exoelectrogenic bacteria. A typical MDC has a middle compartment for water desalination between the anode and cathode chambers. Our study reports lab-scale desalination, for evaluating the role of carbon from biomass waste. Control experiments were performed in the absence of activated carbon. Different initial salt concentrations (25 and 35 gl–1 ) were investigated. MDC produced a maximum voltage of 460 13 mV simultaneously removing about 83.3 1.3% of Na+ and 57.8 1.1% of Cl– , in the desalination cycle. The control MDC produced a maximum of 260 8 mV and 69.3 2% of Na+ removal and 51 1.5% Cl– removal. These results explain the role of using activated carbon for improved power production and water desalination. The SEM image of the biofilm shows pili (nanowires) with rod-shaped microorganisms. EDAX confirmed the presence of minerals such as Al, P, K, O, N, which may be due to chemical scale formation (especially P, Na and Ca

Solidification and stabilization of chromium laden wastes in cementitious binders

Solidification/stabilization (S/S) technology was applied to a simulated sludge containing chromium. Leaching tests such as toxicity characteristic leaching procedure (TCLP), ANS 16.1 and multiple TCLP tests conducted on stabilized blocks showed that chromium was immobilized by the binder studied. A linear relationship was obtained between the cumulative fraction of chromium leached and time1/2 in the stabilized samples proving that chromium is leached by diffusion. The leachability indices obtained for the solidified materials satisfy the guidance value as per US Nuclear Regulatory Commission. Chromium concentrations in the TCLP leachates were well within the regulatory levels of the United States Environmental Protection Agency. Microchemistry and morphology of the stabilized samples were studied using Fourier transformation infrared (FTIR) technique and scanning electron microscopy (SEM). FTIR confirms the presence of ν2 CO3 band and O–H stretching of Ca(OH)2 and SEM shows uniform dense crystalline morphologies in all the samples. X-ray diffraction indicates the presence of bentorite, which proves that Cr replaces Al in the ettringit

A NOVEL BIO-WASTE INCORPORATED ALGINATE SORBENT FOR DE-FLUORIDATION OF WATER

This study evaluates the feasibility of using tamarind (Tamarindus indica) seed powder for de-fluoridation of fluoride contaminated water. Batch study confirmed that tamarind seeds in dry powder form could remove 87% of fluoride from water. This bio-sorbent can be used effectively in areas where fluoride concentrations are above the permissible limits of 1.5 mg-l-1 as per WHO Standard, 1984. Tamarind seed powder was incorporated in a matrix of sodium alginate and made into gel-beads. The beads were tested for de-fluoridation efficiency by conducting column studies. The effect of various factors, such as flow rate, retention time, and the number of runs on the efficacy of fluoride removal was also studied. The results revealed that flow rate did not seem to have much effect on the percentage fluoride removal but the fluoride concentration decreased drastically upon greater retention time and multiple run

Synthesis of nano-porous carbon from cellulosic waste and its application in water disinfection

The present study deals with the preparation of new cellulosic catalyst materials, viz. paper and textile industry waste. Activated nano-carbons were prepared from these waste materials using thermo-chemical method. Nano-silver particles (AgNP) were embedded into the synthesized carbons to incorporate antimicrobial properties. The catalyst materials were characterized using FESEM-EDX, XRD, FTIR, etc. The characterization results showed that the materials were nanoporous and silver was uniformly distributed throughout the catalyst. The suitability of the catalyst as an antimicrobial agent was studied using pour plate technique. The main advantages of the disinfecting materials over conventional materials were: (i) only small quantities (mg) of catalysts are required to deactivate microorganism for up to 1 litre of water; (ii) time required for more than 99% disinfection is less (60 min); (iii) carbon has been synthesized from cellulosic wastes which otherwise would pollute the environment, hence it is a waste recycling process. The carbons exhibited more than 99% E. coli removal within 60 mi

From the lab to the field: Self-stratifying microbial fuel cells stacks directly powering lights

The microbial fuel cell (MFC) technology relies on energy storage and harvesting circuitry to deliver stable power outputs. This increases costs, and for wider deployment into society, these should be kept minimal. The present study reports how a MFC system was developed to continuously power public toilet lighting, with for the first time no energy storage nor harvesting circuitry. Two different stacks, one consisting of 15 and the other 18 membrane-less MFC modules, were operated for 6 days and fuelled by the urine of festival goers at the 2019 Glastonbury Music Festival. The 15-module stack was directly connected to 2 spotlights each comprising 6 LEDs. The 18-module stack was connected to 2 identical LED spotlights but going through 2 LED electronic controller/drivers. Twenty hours after inoculation the stacks were able to directly power the bespoke lighting system. The electrical energy produced by the 15-module stack evolved with usage from ≈280 mW (≈2.650 V at ≈105 mA) at the beginning to ≈860 mW (≈2.750 V at ≈300 mA) by the end of the festival. The electrical energy produced by the LED-driven 18-module stack increased from ≈490 mW at the beginning to ≈680 mW toward the end of the festival. During this period, illumination was above the legal standards for outdoor public areas, with the 15-module stack reaching a maximum of ≈89 Lx at 220 cm. These results demonstrate for the first time that the MFC technology can be deployed as a direct energy source in decentralised area (e.g. refugee camps)

Microbial fuel cells: From fundamentals to applications. A review

© 2017 The Author(s) In the past 10–15 years, the microbial fuel cell (MFC) technology has captured the attention of the scientific community for the possibility of transforming organic waste directly into electricity through microbially catalyzed anodic, and microbial/enzymatic/abiotic cathodic electrochemical reactions. In this review, several aspects of the technology are considered. Firstly, a brief history of abiotic to biological fuel cells and subsequently, microbial fuel cells is presented. Secondly, the development of the concept of microbial fuel cell into a wider range of derivative technologies, called bioelectrochemical systems, is described introducing briefly microbial electrolysis cells, microbial desalination cells and microbial electrosynthesis cells. The focus is then shifted to electroactive biofilms and electron transfer mechanisms involved with solid electrodes. Carbonaceous and metallic anode materials are then introduced, followed by an explanation of the electro catalysis of the oxygen reduction reaction and its behavior in neutral media, from recent studies. Cathode catalysts based on carbonaceous, platinum-group metal and platinum-group-metal-free materials are presented, along with membrane materials with a view to future directions. Finally, microbial fuel cell practical implementation, through the utilization of energy output for practical applications, is described

Reduction of chromium(VI) with energy recovery using microbial fuel cell technology

A simple microbial fuel cell (MFC) method for the reduction of hexavalent chromium (Cr6+) at an abiotic cathode by using an exoelectrogenic biofilm on the biotic anode, has been established. Two different Cr6+-containing effluents were synthetically prepared in the laboratory (4 and 8 mg l−1). The chromium effluents were used as catholyte and anaerobic microorganisms as anodic biocatalyst. 4 mg l−1 of Cr6+ was reduced 95% while, 8 mg l−1 reduced 86% during 456 h reaction in the MFC systems investigated. The MFC system with 4 mg l−1 of chromium exhibited a maximum power density of 89 ± 3 mW m−2 and a maximum voltage of 931 mV. A power density of 69.5 ± 2.1 mW m−2 and voltage of 700 mV was obtained by 8 mg l−1 chromium containing MFC cell. This work verifies the possibility of current production and simultaneous cathodic Cr6+ reduction. The novelty and significance of this system is that it uses an uncomplicated and economical salt bridge which replaces costly membranes like Nafion and an abiotic cathod

Assessment of the mechanical stability and chemical leachability of immobilized electroplating waste

The effectiveness of cement based treatment technology, in immobilizing chromium laden electroplating sludge was assessed by conducting toxicity characteristic leaching procedure (TCLP). The mechanical stability of the blocks was tested by measuring the compressive strength. Other leaching tests such as NEN 7341 test, ANS 16.1 and multiple TCLP (MTCLP) test conducted on select solidified blocks showed that chromium was immobilized by the binder studied. A linear relationship was obtained between the cumulative fraction of chromium leached (CFL) and square root of time in the solidified samples proving that diffusion is the controlling mechanism for leaching of chromium. The leachability indices (LI) obtained for the solidified materials using cement and cement-fly ash system (EPC6, EPFC6A and EPFC6B) satisfy the guidance value as per US NRC, which clearly indicates that chromium is well retained within the solid matrix. Chromium concentrations in the TCLP leachates of the above mix ratios were well within the regulatory level of United States Environmental Protection Agency (USEPA). Molecular characterization of the solidified material was carried out using Fourier transformation infra red (FTIR) technique