• Energy Research
• 6. Clean water close
• IT close
• University Federico II of Naples close

AbstractFloating photovoltaic system for reservoirs is a recent innovative technology that is highly advantageous in reducing evaporation while generating solar power. In addition, the integration of floating photovoltaic systems with the existing hydroelectric power plants will increase renewable power production. The present study aims to assess the electrical performance of floating photovoltaic systems in major reservoirs with existing hydroelectric power plants in India. The reservoirs with large water surface area were selected for the study, and a model floating photovoltaic system with a 5-MW capacity was designed for the selected reservoirs. The numerical analysis showed that installing floating photovoltaic systems will result in an annual energy yield of 160 GWh. Further, the systems also save 1.40 million cubic meters of water per day and also help in generating additional energy of 514.80 MWh/day from the saved water through its integration with hydroelectric power plants. A single-axis tracking mechanism to the floating photovoltaic systems will increase the annual energy generation by 11%. The detailed cost analysis and carbon emission analysis were also carried out. The results indicate that the tracking mechanisms increase the total installation cost of the systems. The annual carbon emission reduction from the floating photovoltaic systems accounts for about 3.30 million tons of CO2. The obtained results highlight the suitability of this innovative technology for installation in Indian reservoirs and its effectiveness in reducing evaporation and carbon emission. Graphic abstract

Syngas (CO, CO2, and H2) has attracted special attention due to the double benefit of syngas fermentation for carbon sequestration (pollution reduction), while generating energy. Syngas can be either produced by gasification of biomasses or as a by-product of industrial processes. Only few microorganisms, mainly clostridia, were identified as capable of using syngas as a substrate to produce medium chain acids, or alcohols (such as butyric acid, butanol, hexanoic acid, and hexanol). Since CO plays a critical role in the availability of reducing equivalents and carbon conversion, this work assessed the effects of constant CO partial pressure (PCO), ranging from 0.5 to 2.5 atm, on cell growth, acid production, and solvent production, using Clostridium carboxidivorans. Moreover, this work focused on the effect of the liquid to gas volume ratio (VL/VG) on fermentation performances; in particular, two VL/VG were considered (0.28 and 0.92). The main results included—(a) PCO affected the growth kinetics of the microorganism; indeed, C. carboxidivorans growth rate was characterized by CO inhibition within the investigated range of CO concentration, and the optimal PCO was 1.1 atm (corresponding to a dissolved CO concentration of about 25 mg/L) for both VL/VG used; (b) growth differences were observed when the gas-to-liquid volume ratio changed; mass transport phenomena did not control the CO uptake for VL/VG = 0.28; on the contrary, the experimental CO depletion rate was about equal to the transport rate in the case of VL/VG = 0.92.

Nitrogen is an element present on Earth in different forms, such as gaseous in the air, dissolved in water, immobilized in the soil, as well as biologically bound in all living organisms. The transition from one form to another constitutes the nitrogen cycle. Current agricultural systems rely on nitrogen fertilizers, which represent the reactive or biologically available nitrogen in soil. The excessive presence of reactive nitrogen in the environment has become a threat to soil, water, and air. The increasing demands for food in the world are associated with significant increase in nitrogen fertilizers inputs which threatens the environment and living organisms. The quantities of nitrogen used per capita in developed countries exceed those in developing countries. However, developed countries are regulated by restrictions of fertilizers inputs in agriculture, whereas such regulations do not exist in most of the developing countries. The need to resort to alternative and eco-sustainable strategies to mitigate the pollution related to human activities, is increasingly evident. This review aims to highlight the fate of nitrogen through the main agricultural practices in modern agriculture. Special attention was given to rocket (Eruca sativa) which is considered a nitrate hyper-accumulator and was used as a case study in the present review. Finally, some eco-sustainable solutions, useful for mitigating or preventing the excessive release of harmful forms of nitrogen into the environment, were also discussed.

The co-production of biohydrogen and methane from the organic fraction of municipal solid waste was investigated using a two-stage AD system, composed of a pilot scale dark fermenter (DF) and a continuous methanogenic biofilm reactor. From the DF process, a biohydrogen yield of 41.7 (± 2.3) ml H2/gVSadded was achieved. The liquid DF effluent (DFE) was rich in short chain volatile fatty acids, i.e., mainly acetic and butyric acid. The DFE was valorized by producing methane in the methanogenic biofilm reactor. Two methanogenic biofilm reactors were used to assess the biotic and abiotic role of the DFE on the performance of the reactors. Regardless of the different DFE feeding (i.e., biotic and abiotic), similar and stable operational performance of the two methanogenic biofilm reactors were observed with a respective methane yield and COD removal efficiency of 280–300 ml CH4/gCODremoved and 80–90%. Both methanogenic biofilm reactors showed significant resistance toward organic shock loads and recovered fast after reactor disturbance. The total estimated energy recovered in the form of hydrogen and methane gas was, respectively, 28 and 72%, of the initial COD.HIGHLIGHTSSimultaneous production of biohydrogen and methane from OFMSW was investigated.A pilot scale dark fermenter and methanogenic biofilm reactor were used for, respectively, biohydrogen and methane production.The biotic and abiotic role of the dark fermentation effluent on the methanogenic biofilm reactor was assessed.Anaerobic biofilm reactors demonstrated a high tolerance toward an increased OLR.H2 and CH4 was 28 and 72%, respectively, of the total energy recovery from the OFMSW.

Reservoir silting is an unavoidable issue. It is estimated that in Italy, the potential rate of silting-up in large reservoirs ranges from 0.1% to 1% in the presence of wooded river basins and intensive agricultural land use, respectively. In medium and small-sized reservoirs, these values vary between 0.3% and 2%. Considering both the types of reservoirs, the annual average loss of storage capacity would be of about 1.59%. In this paper, a management strategy aimed at sediment productive reuse is presented. Particularly, the main engineering outcomes of an extensive experimental program on geopolymer binder synthesis is reported. The case study deals with Occhito reservoir, located in Southern Italy. Clay sediments coming from this silted-up artificial lake were characterized, calcined and activated, by means of a wide set of alkaline activating solutions. The results showed the feasibility of this recovery process, optimizing a few chemical parameters. The possible reuse in building material production (binders, precast concrete, bricks, etc.) represents a relevant sustainable alternative to landfill and other more consolidated practices.

Abstract We propose an optimal control problem to determine the best aeration strategy for aerobic biodegradation in a composting cell. The goal is to minimize the deviation of the oxygen level from its reference value for the entire duration of the biodegradation process. The mathematical model includes several chemical phenomena, like the aerobic biodegradation of the soluble substrate by means of a bacterial biomass, the hydrolysis of insoluble substrate and the biomass decay. The oxygen and the optimal mechanical aeration time profiles are obtained and discussed. Finally, the plant performance is evaluated in absence and presence of external aeration by means of several specific indices.

The anaerobic digestion is a well-established process for the treatment of organic solid waste, pursuing its conversion into a methane rich gas destined to energy generation. Research has largely dealt with the enhancement of the overall bioconversion yields, providing several strategies to maximize the production of bio-methane from the anaerobic processing of a wide variety of substrates. Nevertheless, the valorization of the process effluents should be pursued as well, especially if the anaerobic digestion is regarded in the light of the circular economy principles. Aim of this work is in identifying the state of the art of the strategies to manage the digestate from the anaerobic processing of the organic fractions of municipal solid waste. Conventional approaches are described and novel solutions are figured out in order to highlight their potential scale up as well as to address future research perspectives.