• Energy Research

Column biodesulphurization of coal is at the experimental stage and is influenced by many variables including temperature, pH, particle size, concentration of iron in solution, among others. Idle time in the washing process and the concentration of dissolved iron in the purged leachate are two variables with a definite effect on the yield of the desulphurization system. In the laboratory, several trials were run with columns packed with coal for different idle times: 1, 2, 3, 5, 6 and 7 days, and for different concentrations of iron in the purged leachate: 500 to 4,000 mg/l. The optimal values for the two variables; that is, those allowing for the highest desulphurization yields, were idle times of 3 and 5 days, which give an elimination of 56% and 49% of pyritic sulphur, respectively, and 3,000 mg/l of iron concentration in the purged leachate, giving a decrease in pyritic sulphur in coal of 57%.

Abstract To combust coal together with a small percentage (<10%) of sewage sludge may be an option for the management of these wastes. Combustion of two different sewage sludge, one semianthracite coal and several sludges-coal blends (containing different dried mass% of each of the two sewage sludges) were studied by simultaneous TG/MS dynamic runs carried out at 5C min–1 in the temperature range 100–800C. No interactions have been observed between coal and sludge during the blends combustion. Neither the combustion process, neither the studied emissions have changed appreciably for the mass% of sludge in the blends considered in this work.

The kinetics of the combustion of coal, two different sewage sludge and their blends (containing different dried weight percentages of sewage sludge) was studied by simultaneous thermogravimetric analysis. Once the weight percentage of sludge in the blend was 10%, the effects on the combustion of coal were hardly noticeable in terms of weight loss. The Arrhenius activation energy corresponding to the co-combustion of the blends was evaluated by non-isothermal kinetic analysis. This showed that, though differences between coal and sewage sludge, the combustion of their blends kept kinetically alike to that of the coal. This work illustrates how thermogravimetric analysis may be used as an easy rapid tool to asses, not only mass loss, but also kinetics of the co-combustion of sewage sludge and coal blends.

Combustion of sewage sludge may be a viable solution for its management in some cases and so is its co-combustion with coal. The aim of the present paper is to study the behavior of three different sludges during combustion and the modifications of combustion parameters that take place when sludges are mixed with coal, all measurements being done by thermogravimetry. The combustion of pyrolyzed sewage sludges has also been studied, related to the possibility of combining combustion with pyrolysis when trying to valorize sludges by producing active carbon. From the burning profile data it has been possible to observe that a rapid devolatilization occurs during sludge combustion compared to coal and previously pyrolyzed sludge. The exact temperatures of devolatilization and of maximum speed of weight loss have also been ascertained together with differential thermal analysis and measurements of gas emissions during combustion. The behavior of the sludges tested is qualitatively similar but quantitatively different, so tests have to be carried out before they are put in the furnace.

Globally, large amounts of electrical energy are spent every year for domestic wastewater (dWW) treatment. In the future, energy prices are expected to rise as the demand for energy resources increases and fossil fuel reserves become depleted. By using appropriate technologies, the potential chemical energy contained in the organic compounds present in dWWs might help to improve the energy and economic balance of dWW treatment plants. Bioelectrochemical Systems (BESs) in general and microbial electrolysis cells (MECs) in particular represent an emerging technology capable of harvesting part of this energy. This study offers an overview of the potential of using MEC technology in dWW treatment plants (dWWTPs) to reduce the energy bill. It begins with a brief account of the basics of BESs, followed by an examination of how MECs can be integrated in dWW treatment plants (dWWTPs), identifying scaling-up bottlenecks and estimating potential energy savings. A simplified analysis showed that the use of MEC technology may help to reduce up to ~20% the energy consumption in a conventional dWWTP. The study concludes with a discussion of the future perspectives of MEC technology for dWW treatment. The growing rates of municipal water and wastewater treatment markets in Europe offer excellent business prospects and it is expected that the first generation of MECs could be ready within 1-4 years. However, before MEC technology may achieve practical implementation in dWWTPs, it needs not only to overcome important techno-economic challenges, but also to compete with other energy-producing technologies.

Abstract This study investigates the potential opportunities of hydrogen evolution treating landfill leachate in a set of two microbial electrolysis cells (MEC-1 and 2) under 30 °C and 17 ± 3 °C temperatures, respectively. The system achieved a projected current density of 1000–1200 mA m−2 (MEC-1) and 530–755 mA m−2 (MEC-2) coupled with low cost hydrogen production rate of 0.148 L La−1 d−1 (MEC-1) and 0.04 L La−1 d−1 (MEC-2) at an applied voltage of 1.0 V. Current generation led to a maximum COD oxidation of 73 ± 8% (MEC-1) and 65 ± 7% (MEC-2) with ≥100% energy recovery. The system also exhibited a high hydrogen recovery (66–95%), pure hydrogen yield (98%) and tremendous working stability during two months of operation. Electroactive microbes such as Pseudomonadaceae, Geobacteraceae and Comamonadaceae were found in anodophilic biofim, along with Rhodospirillaceae and Rhodocyclaceae, which could be involved in hydrogen production. These results demonstrated an energy-efficient approach for hydrogen production coupled with pollutants removal.

Microbial electrolysis cells (MECs) have the potential to become a sustainable domestic wastewater (dWW) treatment system. However, new scale-up experiences are required to gain knowledge of critical issues in MEC designs. In this study we assess the ability of two twin membraneless MEC units (that are part of a modular pilot-scale MEC) to treat dWW. Batch tests yielded COD removal efficiencies as high as 92%, with most of the hydrogen (>80% of the total production) being produced during the first 48h. During the continuous tests, MECs performance deteriorated significantly (energy consumption was relatively high and COD removal efficiencies fell below 10% in many cases), which was attributed to an inadequate configuration of the anodic chamber, insufficient mixing inside this chamber, inefficient hydrogen management on the cathode side and finally to dWW in itself. Some alternatives to the current design are suggested.

Abstract Differential thermogravimetry (DTG) was used to obtain information about the effect of biological desulphurisation on the entire coal combustion process. Two coals of different rank, a semianthracite (HVL1) and a high volatile bituminous coal (HM1), were inoculated with autochthonous bacterial cultures isolated from natural mine sludge and from bacteria inherent in the coal. From the combustion profiles and the reactivity in air at 500°C of the chars produced after pyrolysis, several characteristic parameters were determined. The results indicated that the influence of the biological treatment on combustion performance and char reactivity is more significant in the higher rank coal. The overall process seems to cause a slight beneficial effect on the ignition properties, evaluated from the burning profiles, of the semianthracite treated samples.

Abstract This research explores the opportunities of combining energy production with a biochar soil management using a pyrolysis process. Real-world issues justify this approach: the need to provide sustainable production systems that minimize on- and off-site pollution and soil degradation; and the demand for solutions to global warming. The proposed technology is a pyrolysis process that yields gas, bio-oil and biochar. The composition and heating value of the gas makes it suitable for use as a fuel. The bio-oil obtained may be evaluated as an environmentally friendly green biofuel candidate. The biochar product is carbon-rich and a potential solid biofuel. Other ways it might be used as a C and N source in soil amendment. This is a key to securing environmental benefits: the production of a biochar which can be applied to soil.