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Ammonia increases buffer capacity of methanogenic medium in mesophilic anaerobic reactor thus increasing the stability of anaerobic digestion process. Optimal ammonia concentration ensures sufficient buffer capacity while not inhibiting the process. It was found out in this paper that this optimum depends on the quality of anaerobic sludge under investigation. The optimal concentrations for methanogens were 2.1, 2.6 and 3.1 g/L of ammonia nitrogen in dependence on inoculum origin. High ammonia nitrogen concentration (4.0 g/L) inhibited methane production, while low ammonia nitrogen concentration (0.5 g/L) caused low methane yield, loss of biomass (as VSS) and loss of the aceticlastic methanogenic activity. It was found out that negative effect of low ammonia nitrogen concentration on biomass is caused not only by low buffer capacity but also by insufficiency of nitrogen as nutrient. It was also found out that anaerobic sludge with higher ammonia nitrogen concentration (4.2 g/L) tolerates even concentration of volatile fatty acids (160 mmol/L) which causes inhibition of the process with low ammonia nitrogen concentration (0.2 g/L).

This paper describes anaerobic thermophilic sludge digestion (55 °C) in a continuously stirred tank reactor (CSTR) on a pilot-plant scale (150 L). The experimental protocol was defined to examine the effect of the increase in the organic loading rate on the efficiency of the digester and to report on its steady-state performance. The reactor was subjected to a programme of steady-state operation over a range of solids retention times (SRTs) of 75, 40, 27, 20 and 15 days and organic loading rates (OLR) in the range 0.4–2.2 kg VS/(m3 day). The digester was fed with raw sludge (containing approximately 35 kg/m3 volatile solids (VS)) once daily during the 75-day SRT period, twice daily during the 40-day SRT period and three times a day during the 27-, 20- and 15-day SRT periods. The reactor was initially operated with an organic loading rate of 0.4 kg VS/(m3 day) and an SRT of 75 days. The volatile solids removal efficiency in the reactor was found to be 73%, while the volumetric methane production rate produced in the digester reached 0.02 m3/(m3 day). Over a 338-day operating period, an OLR of 2.2 kg VS/(m3 day) was achieved with 49.1% VS removal efficiency in the pilot sludge digester, at which time the volumetric methane production rate content of biogas produced in the digester reached 0.4 m3/(m3 day). The chemical oxygen demand (COD) mass balance obtained indicated that COD used for methane generation increased when the SRT was decreased or when the influent organic loading rate was increased. This implies that the amount of COD used in the anabolism route decreased with SRT due the microbial population becoming adapted to new operational conditions and more COD being used to generate methane.

This study classifies Mediterranean marine protected areas (MPAs) according to the combined result of pressure level and protection. Six major marine environment pressures were considered: pressures from fish farms, fishing, marine litter, pressures from marinas, pollution from maritime transport, and climate change. MPA protection was assessed through legal protection and management effort. Most MPA area in the Mediterranean is under relatively high pressure level and afforded low protection. Inshore areas show higher pressure levels. Five marine ecoregions, nine countries and nineteen MPA designation categories have over 50% of their MPA area under major concern. The mean number of cumulative pressures occurring in priority MPAs ranges between three and four, although the mean combined intensity of those pressures is low. However, these figures are most likely underestimated, especially for the southern Mediterranean. The most concerning pressures to MPAs regarding extent and intensity were: climate change, fishing and pollution from maritime transport.

Abstract Biofuels are considered as an alternative to partially replace fossil fuels and mitigate climate change effects. A life cycle assessment of second generation ethanol, derived from banana agricultural wastes, was developed to assess its environmental sustainability and demonstrate its capacity of reducing greenhouse gas emissions. The methodological approach was conducted in a Well-to-Wheel perspective, using as functional unit 1 MJ of energy released in the combustion of bioethanol in a passenger car from different bioethanol blends. Primary and secondary information sources were used for the assessment; mass balance and ethanol yield data came from laboratory experimentation. The environmental assessment was carried out using SimaPro 8.0.4.30 with the ReCiPe midpoint (H) impact assessment methodology. The quantified impact categories were climate change (CC), terrestrial acidification (TA), freshwater eutrophication (FE), photochemical oxidant formation (PO), particulate matter formation (PM), and fossil depletion (FD). In addition, net energy value and energy ratio (ER) were analyzed to ensure a positive energy balance. Compared to using pure gasoline, blended gasoline reduced CC, PO, PM, and FD impacts, but increased FE and TA impacts. The obtained energy balance was positive, with an ER of 2.68 MJ/MJ. Wastewater treatment is the process that presented the greatest energy consumption. Since Ecuador is the world's largest exporter of bananas, and a great amount of agricultural waste is available, a case study in this country was analyzed. This case study indicated that Ecuador could use banana residue for ethanol production, considering its positive and negative impacts. In conclusion, second generation ethanol derived from banana agricultural waste has potential to reduce greenhouse gas emissions and fossil depletion and has a positive energy balance.

Biomass gasification processes generate large amounts of solid. The aim of this work is to characterize the particles produced at a demonstration scale downdraft multi-stage gasification plant running on pinewood. The results have been used to understand their formation mechanism, evaluate potential applications and determine their hazardousness to human health and the environment. Chemical, physical, morphological and textural analyses suggest that most of the particles are formed via gas phase condensation reactions, with a very limited proportion resulting from direct carbonization of the original biomass feedstock. This is confirmed by a very limited micropore structure, surface area and adsorption capacity, making the particles unsuitable for use as an adsorbent in gas and water treatment applications. The particles exhibit superior fuel properties in terms of carbon content, heating value and thermal stability, which may be associated with the high temperatures at which they are generated. Due to their biomass origin, the particles contain a high proportion of calcium, potassium, magnesium and other plant micronutrients that could be beneficial if the material is used for soil conditioning and fertilizing. Regarding particle size distribution, most of the particles fitted in the range between 100 and 250 μm, with only 0.5 wt% smaller than 30 μm. This is too large for a carbon black surrogate but minimizes health risks associated with exposure to the lower regions of the respiratory tract. The concentration of biologically active PAH is sufficiently low to represent no hazard to the environment or human health.

The identification of species-rich areas and their prognosticated turnover under climate change are crucial for the conservation of endemic taxa. This study aims to identify areas of reptile endemicity richness in a global biodiversity hot spot (Morocco) under current and future climatic conditions and to investigate the role of protected areas in biodiversity conservation under climate change. Species distribution models (SDM) were performed over the distribution of 21 endemic reptiles, combined to estimate current species richness at 1 × 1 km resolution and projected to years 2050 and 2080 according to distinct story lines and ensemble global circulation models, assuming unlimited and null dispersion ability. Generalized additive models were performed between species richness and geographic characteristics of 43 protected areas. SDM found precipitation as the most important factor related to current species distributions. Important reductions in future suitable areas were predicted for 50 % of species, and four species were identified as highly vulnerable to extinction. Drastic reductions in species-rich areas were predicted for the future, with considerable variability between years and dispersal scenarios. High turnover rates of species composition were predicted for eastern Morocco, whereas low values were forecasted for the Northern Atlantic coast and mountains. Species richness for current and future conditions was significantly related to the altitude and latitude of protected areas. Protected areas located in mountains and/or in the Northern Atlantic coast were identified as refugia, where population monitoring and conservation management is needed.

Abstract The residual circulation of the Ria de Muros, a large coastal embayment in NW Spain, are studied using a three-dimensional baroclinic finite-difference model. The driving forces considered by the model include the tide, winds, river inflows and density forcing at the open boundary. In situ data of current velocity and direction, water level, wind velocity and direction, river discharge, and temperature and salinity are used for model validation. Simulated and observed time series of water level and current velocity are in good agreement. Once validated, the model is applied to compute the residual circulation induced by the relevant agents of the ria hydrodynamics—the tide, an upwelling-favourable wind characteristic of spring and summer, a downwelling-favourable wind typical of winter, and freshwater inflows associated with high river runoff. The resulting residual circulation differ notably. The tide does not generate significant residual flows except in the inner ria. By contrast, winds and river discharges induce important residual flows throughout; in the middle and outer ria they generate a 3D residual circulation pattern which renders the conventional two-layer scheme of estuarine circulation too simplistic in this case. Thus, this first application of a 3D numerical model to the Ria de Muros sheds new light on its fundamental hydrodynamics.

AbstractClimate change globally affects soil microbial community assembly across ecosystems. However, little is known about the impact of warming on the structure of soil microbial communities or underlying mechanisms that shape microbial community composition in subtropical forest ecosystems. To address this gap, we utilized natural variation in temperature via an altitudinal gradient to simulate ecosystem warming. After 6 years, microbial co‐occurrence network complexity increased with warming, and changes in their taxonomic composition were asynchronous, likely due to contrasting community assembly processes. We found that while stochastic processes were drivers of bacterial community composition, warming led to a shift from stochastic to deterministic drivers in dry season. Structural equation modelling highlighted that soil temperature and water content positively influenced soil microbial communities during dry season and negatively during wet season. These results facilitate our understanding of the response of soil microbial communities to climate warming and may improve predictions of ecosystem function of soil microbes in subtropical forests.