NO removal by reducing agents and additives in the selective non-catalytic reduction (SNCR) process

The effect of the additives on the selective non-catalytic reduction (SNCR) reaction has been determined in a three-stage laboratory scale reactor. The optimum reaction temperature is lowered and the reaction temperature window is widened with increasing concentrations of the gas additives (CO, CH4). The optimum reaction temperature is lowered and the maximum NO removal efficiency decreases with increasing the concentration of alcohol additives (CH3OH, C2H5OH). The addition of phenol lowers the optimum reaction temperature about 100-150 degrees C similar to that of the toluene addition. The volatile organic compounds (VOCs: C6H5OH, C7H8) can be utilized in the SNCR process to enhance NO reduction and removed at the same time. A previously proposed simple kinetic model can successfully apply the NO reduction by NH3 and the present additives.     

Water quality decline in coastal aquifers under anthropic pressure: the case of a suburban area of Dakar (Senegal)

In recent years, the unregulated increase of the population in coastal areas of developing countries has become source of concern for both water supply and quality control. In the region of Dakar (Senegal), approximately 80% of water resources come from groundwater reservoirs, which are increasingly affected by anthropogenic pressures. The identification of the main sources of pollution, and thus the aquifer vulnerability, is essential to provide a sound basis for the implementation of long-term geochemically based water management plans in this sub-Saharan area. With this aim, a hydrochemical and isotopic survey on 26 wells was performed in the so-called Peninsula of Cap-Vert. Results show that seawater intrusion represents the main process affecting groundwater chemical characteristics. Nitrates often exceed the World Health Organization drinking water limits: stable isotopes of dissolved nitrate ( $\updelta ^{15}$ N and $\updelta ^{18}$ O) indicate urban sewage and fertilizers as a major source of contamination. Results depict a complex situation in which groundwater is affected by direct and indirect infiltration of effluents, mixing with seawater and freshening processes from below. Besides the relevance of the investigation at a regional level, it represents a basis for decision-making processes in an integrated water resources management and in the planning of similar monitoring strategies for other urban coastal regions.     

Time Series Forecasting of Cyanobacteria Blooms in the Crestuma Reservoir (Douro River, Portugal) Using Artificial Neural Networks

In this work, time series neural networks were used to predict the occurrence of toxic cyanobacterial blooms in Crestuma Reservoir, which is an important potable water supply for the Porto region, located in the north of Portugal. These models can potentially be used to provide water treatment plant operators with an early warning for developing cyanobacteria blooms. Physical, chemical, and biological parameters were collected at Crestuma Reservoir from 1999 to 2002. The data set was then divided into three independent time series, each with a fortnightly periodicity. One training series was used to “teach” the neural networks to predict results. Another series was used to verify the results, and to avoid over-fitting of the data. An additional independently collected data series was then used to test the efficacy of the model for predicting the abundance of cyanobacteria. All of the models tested in this study incorporated a prediction time (look-ahead parameter) equal to the sampling interval (two weeks). Various lag periods, from 2 to 52 weeks, were also investigated. The best model produced in this study provided the following correlations between the target and forecast values in the training, verification, and validation series: 1.000 (P = 0.000), 0.802 (P = 0.000), and 0.773 (P = 0.001), respectively. By applying this model to the three-year data set, we were able to predict fluctuations in cyanobacteria abundance in the Crestuma Reservoir, with a high level of precision. By incorporating a lag-period of eight weeks, we were able to detect secondary fluctuations in cyanobacterial abundance over the annual cycle.     

Photochemical production of organic matter triplet states in water samples from mountain lakes, located below or above the tree line

The production of triplet states (T(*)) of chromophoric dissolved organic matter (CDOM), reacting with the probe molecule 2,4,6-trimethylphenol (TMP) was measured upon irradiation of water samples, taken from lakes located in a mountain area (NW Italy) between 1450 and 2750 m above sea level. The lakes are located below or above the tree line and surrounded by different vegetation types (trees, alpine meadows or exposed rocks). The most photoactive samples belonged to lakes below the tree line and their fluorescence spectra and CDOM optical features suggested the presence of a relatively elevated amount of humic (allochthonous) material. The lowest (negligible) photoactivity was found for a lake surrounded by exposed rocks. Its CDOM showed an important autochthonous contribution (due to in-lake productivity) and considerably higher spectral slope compared to the other samples, suggesting low CDOM molecular weight and/or aromaticity. Among the samples, CDOM photoactivity (measured as the rate of TMP-reactive T(*) photoproduction) decreased with changing vegetation type in the order: trees, meadows, rocks. It could be connected with decreasing contribution from catchment runoff and increasing contribution from autochthonous processes and possibly precipitation.     

Persistent organic pollutants in plastic marine debris found on beaches in San Diego, California

Plastic debris were collected from eight beaches around San Diego County, California. Debris collected include: pre-production pellets and post-consumer plastics including fragments, polystyrene (PS) foam, and rubber. A total of n = 2453 pieces were collected ranging from <5 mm to 50 mm in size. The plastic pieces were separated by type, location, and appearance and analyzed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and its breakdown products, and chlordanes. PAH concentrations ranged from 30 ng g⁻¹ to 1900 ng g⁻¹, PCBs from non-detect to 47 ng g⁻¹, chlordanes from 1.8 ng g⁻¹ to 60 ng g⁻¹, and DDTs from non-detect to 76 ng g⁻¹. Consistently higher PAH concentrations found in PS foam samples (300-1900 ng g⁻¹) led us to examine unexposed PS foam packaging materials and PS virgin pellets. Unexposed PS foam contained higher concentrations of PAHs (240-1700 ng g⁻¹) than PS virgin pellets (12-15 ng g⁻¹), suggesting that PAHs may be produced during manufacturing. Temporal trends of debris were investigated at one site, Ocean Beach, where storm events and beach maintenance were found to be important variables influencing debris present at a given time.     

Distribution of potentially harmful elements in soils around a large coal-fired power plant

An understanding of the spatial distribution and contribution of a power plant to local soil contamination is important for the planning of soil use and prioritizing remedial actions for public safety. Consequently, the aim of this study was to map the spatial distribution of potentially hazardous elements (PHEs; Cu, Pb, Zn, Ni, Cr, Fe, Mn, Cd, As, and Se) in soils around a large (796 MW) coal-fired power plant in Brazil. For the purpose, 33 soil samples were collected in the area within a radius of approximately 17.5 km from the plant and subsequently analyzed for PHEs. The frequency and direction of winds were also obtained from a meteorological station in the region. The sampling area was divided into four quadrants (northwest: N-NW; northeast: N-NE; southeast: S-SE; southwest: S-SW), and there were significant negative correlations between the distance and the concentrations of Se in the S-SE quadrant and As in the S-SW and S-SE quadrants. There were positive correlations between distance from the plant and the concentration of Mn in the N-NE quadrant and the concentration of Cd in the S-SW quadrant. The dominant direction of the winds was N-NE. The indexes used in this study showed low-to-moderate enrichment factor, but detailed analysis of the dominant quadrant of the winds showed a correlation with higher concentrations in the soils closer to the power plant for at least seven of the PHEs analyzed, especially with regard to As. Therefore, we conclude that the distribution of the metalloid As can be used as a marker of the spatial distribution of contamination from the thermoelectric plant, but the dynamics of the other elements suggests that the presence of other sources of contamination may also compromise the quality of local soils.

     

Impact on soil quality of a 10-year-old short-rotation coppice poplar stand compared with intensive agricultural and uncultivated systems in a Mediterranean area

Bioenergy crops play an ecologically and economically fundamental role as an alternative to agri-food productions and as renewable energy sources. Little attention has been focused on soil quality following conversion of agricultural lands to biomass crops. Here, we assessed the impact of a 10-year-old short-rotation coppice (SRC) poplar stand on the main soil chemical parameters, microbial biomass carbon, soil respiration, and arbuscular mycorrhizal fungi (AMF), compared with intensive agricultural and uncultivated systems. Three different harvest frequencies of poplar SRC (annual T1, biannual T2 and triennial T3 cutting cycles) were evaluated. Multivariate analysis showed that poplar SRC improved soil quality compared with intensive agricultural and uncultivated systems. T1 and T2 positively affected AMF inoculum potential and root colonisation of a co-occurring plant species, while T3 improved the majority of soil chemical and biochemical parameters. Moreover, three different AMF morphospecies belonging to the genera Glomus and Scutellospora were found in poplar SRC, while morphospecies belonging exclusively to genera Glomus were recorded in intensive agricultural and uncultivated systems. Such aspects have agro-ecological implications, since the positive changes of soil nutrient availability and carbon content together with a high abundance and diversity of soil biota show clear soil sustainability of poplar SRC.