Global NEST Journal

The major environmental impact of discharge of excessive quantities of sulfate is the pollution of the surface and ground water supplies which can be harmful to life forms and therefore the need for an efficient treatment system arises. Biological sulfate reduction offers the advantage of less sludge production, less operational cost and efficiency in comparison to the physicochemical processes. Depending upon the feeding and operating conditions as well as microbes used, a number of intermediates are formed that may greatly affect the overall performance of bioreactor. This article extensively explores the bacterial community, formation of intermediates and desirable end products, theoretical and practical aspects of various environmental and operating conditions, and performance of bioreactors used for treating sulfate rich wastewater along with process biokinetics involved in biological sulfate reduction.

This study investigated optimum operating conditions of supercritical water oxidation (SCWO) for octol and compared the degradation of its components TNT (2,4,6-trinitrotoluene) and HMX (octahydro-1,3,5,7- tetranitro-1,3,5,7-tetrazocine, octogen) under the same conditions. Pilot scale experiments were conducted at various temperatures, reaction times and oxidant amounts. Removal efficiency, by-product analysis and toxicity tests were selected as the performance criteria for the SCWO. Optimum conditions were determined as a temperature of 500 C, 120 s of oxidation time and an oxidant ratio of 150%. Removal of octol was achieved at a rate of 99.99%, while TNT and HMX were removed individually at a rate of ~85% when they existed in the wastewater. No toxicity was observed at the end of the octol oxidation, whereas toxicity was found in the TNT and HMX oxidation due to the formation of TNT isomer and aniline. Higher initial organic material concentrations promoted the removal rates. These results demonstrated that SCWO can be effectively used for the degradation of ammunition wastewater even when concentrations are high.

New challenges for industrial microbiology and biotechnology of algae are to increase the efficiency of microalgae growth rates and decrease the cultivation costs. Algae could be cultivated in fresh water as well as in salty sea water or wastewater. Microalgae biomass can be used as a sorbent to remove microcontaminants (e.g. heavy metals, biogens) from wastewater. The obtained results showed that there is a possibility of application of a cheap and universal growing medium (Bf) despite common fertilizers: Bristol or BG-11 to cultivate Chlorella vulgaris and Scenedesmus armatus. The mixotrophic condition can be useful for cultivation of Chlorella vulgaris and Scenedesmus armatus. The highest concentrations of algal biomass for both species were determined after the application of the Bf medium, lower after the BG-11 medium and the lowest after the Br medium in autotrophic as well as mixotrophic conditions. The number of C. vulgaris cells in mixotrophic conditions was higher than S. armatus. The utilization of cheap growing media will lowering the production costs of algal biomass on a large scale.

Due to the intermittent and fluctuating nature of wind and other renewable energy sources, their integration into electricity systems requires large-scale and flexible storage systems to ensure uninterrupted power supply and to reduce the percentage of produced energy that is discarded or curtailed. Storage of large quantities of electricity in the form of dynamic energy of water masses by means of coupled reservoirs has been globally recognized as a mature, competitive and reliable technology; it is particularly useful in countries with mountainous terrain, such as Greece. Its application may increase the total energy output (and profit) of coupled wind-hydroelectric systems, without affecting the availability of water resources. Optimization of such renewable energy systems is a very complex, multi-dimensional, non-linear, multi modal, nonconvex and dynamic problem, as the reservoirs, besides hydroelectric power generation, serve many other objectives such as water supply, irrigation and flood mitigation. Moreover, their function should observe constraints such as environmental flow. In this paper we developed a combined simulation and optimization model to maximize the total benefits by integrating wind energy production into a pumped-storage multi-reservoir system, operating either in closed-loop or in open-loop mode. In this process, we have used genetic algorithms as the optimization tool. Our results show that when the operation of the reservoir system is coordinated with the wind farm, the hydroelectricity generation decreases drastically, but the total economical revenue of the system increases by 7.02% when operating in closed-loop and by 7.16% when operating in open-loop mode. We conclude that the hydro-wind coordination can achieve high wind energy penetration to the electricity grid, resulting in increase of the total benefits of the system. Moreover, the open-loop pumped-storage multi-reservoir system seems to have better performance, ability and flexibility to absorb the wind energy decreasing to a lesser extent the hydroelectricity generation, than the closed-loop.