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Judged by their negative nutrient balances, low soil cover and low productivity, the predominant agro-pastoral farming systems in the Sudano-Sahelian zone of West Africa are highly unsustainable for crop production intensification. With kaolinite as the main clay type, the cation exchange capacity of the soils in this region, often less than 1 cmolc kg−1soil, depends heavily on the organic carbon (Corg) content. However, due to low carbon sequestration and to the microbe, termite and temperature-induced rapid turnover rates of organic material in the present land-use systems, Corg contents of the topsoil are very low, ranging between 1 and 8 g kg-1 in most soils. For sustainable food production, the availability of phosphorus (P) and nitrogen (N) has to be increased considerably in combination with an improvement in soil physical properties. Therefore, the adoption of innovative management options that help to stop or even reverse the decline in Corg typically observed after cultivating bush or rangeland is of utmost importance. To maintain food production for a rapidly growing population, targeted applications of mineral fertilisers and the effective recycling of organic amendments as crop residues and manure are essential. Any increase in soil cover has large effects in reducing topsoil erosion by wind and water and favours the accumulation of wind-blown dust high in bases which in turn improves P availability. In the future decision support systems, based on GIS, modelling and simulation should be used to combine (i) available fertiliser response data from on-station and on-farm research, (ii) results on soil productivity restoration with the application of mineral and organic amendments and (iii) our present understanding of the cause-effect relationships governing the prevailing soil degradation processes. This will help to predict the effectiveness of regionally differentiated soil fertility management approaches to maintain or even increase soil Corg levels.

Abstract Dolomite, a naturally occurring Ca-based sorbent, shows superior recycling stability in carbonation/calcination cycles for CO2 capture. However, the separation between Ca and Mg in sorbent during recycling weakens the resistance for sintering from MgO, leading to a drastic reduction in the CO2 carrying activity (spent sorbent). This paper presents a novel method for the reactivation of spent dolomite sorbents. Notable activity recovery is achieved by ball milling of the spent sorbent with H2O and dry ice. Powder X-ray diffraction (XRD) results confirm the transformation from oxide (CaO/MgO) to carbonate (CaCO3/CaMg(CO3)2), so that the segregated Ca and Mg in spent sorbent are re-mixed at the atomic level, which is mainly responsible for this effective reactivation. Water plays an irreplaceable role in this process by providing a liquid environment to accelerate the diffusion of the reactants and ionic reactions. In addition, thermogravimetric analysis was carried out on a series of samples with different ball-milling times to determine the suitable reactivation conditions for CO2 capture.

Abstract Synthetic hyperaccumulator biomass (SHB) impregnated with Ni, Zn, Cu, Co or Cr was used to conduct 11 experiments in a lab-scale fluidized bed reactor. Two runs with blank corn stover, with no metal added, were also conducted. The reactor was operated in an entrained mode in a oxygen-free (N2) environment at 873 K and 1 atm . The apparent gas residence time through the lab-scale reactor was 0.6 s at 873 K . The material balance for the lab-scale experiments on N2-free basis varied between 81% and 98%. The presence of a heavy metal in the SHB decreased the char yield and increased the tar yield, compared to the blank. The char and gas yields appeared to depend on the form of the metal salt used to prepare the SHB. However, the metal distribution in the product streams did not seem to be influenced by the chemical form of the metal salt used to prepare the SHB. Greater than 98.5% of the metal in the product stream was concentrated in the char formed by pyrolyzing and gasifying the SHB in the reactor. The metal concentration in the char varied between 0.7 and 15.3% depending on the type of metal in the SHB. However, the metal concentration was increased 4 to 6 times in the char compared to the feed.

The study evaluated the effect of environmental conditions and morphometric parameters on lake water temperature changes. The analysis was carried out on the basis of 14 lakes located in northern Poland. The assessment was based on the daily water and air temperatures from 1972 to 2016. It took into account the location of lakes (latitude, longitude, altitude) morphometric parameters (surface area, maximum and mean depth, volume), hydrological processes (rate of water exchange, course of ice phenomena), and trophic status (water transparency) as factors that can modify lake water temperature changes. Direction and rate of air and water temperature changes were analysed by means of Mann–Kendall’s and Sen’s tests. Cluster analysis (CA) was applied to group lakes characterised by similar water temperature changes. The effect of climatic and non-climatic parameters on a lake’s water temperature was assessed on the basis of principal component analysis (PCA). Water temperatures in the lakes in the years 1972–2016 were characterised by a higher rate of increase of 0.43 °C·dec−1 than the air temperature decrease of 0.34 °C·dec−1. The analysis showed a faster rate of heating of waters in western Poland. This can be explained by shorter duration of ice cover. Moreover, the changes of water temperature were affected by other factors, including the location of the lakes, their morphometric parameters, wind speed, water transparency and water exchange time.

Biomethane production from processed industrial food waste (IFW) in admixture with sewage sludge (primary and waste activated sludge: PS and WAS) was evaluated at a range of C:N ratios using a standard biochemical methane potential (BMP) test. IFW alone had a C:N of 30 whereas for WAS it was 5.4 and thus the C:N ratio of the blends fell in that range. Increasing the IFW content in mix improves the methane potential by increasing both the cumulative biogas production and the rate of methane production. Optimum methane yield 239 mL/g VSremoved occurred at a C:N ratio of 15 which was achieved with a blend containing 11 percent (w/w) IFW. As the fraction of IFW in the blend increased, volatile solids (VS) destruction was increased and this led to a reduction in methane yield and amount of production. The highest destruction of volatile solids of 93 percent was achieved at C:N of 20 followed by C:N 30 and 15. A shortened BMP test is adequate for evaluating optimum admixtures.

Wastewater treatment plants (WWTPs) exhibit significant energy consumption and produce large amounts of Greenhouse Gas emissions (GHG emissions). Energy efficiency and reduction in GHG emissions in WWTPs have become important issues, especially in view of the climate crisis. The core objective of this work is to assess the energy and carbon footprint of Greek WWTPs and to propose methods to improve energy efficiency and reduce GHG emissions. Data were collected from 31 Greek WWTPs with an average treatment capacity between 250 and 3,650,000 population equivalents (PE). The total population served by the 31 WWTPs was over 6,000,000, which is more than half of the population in Greece with access to WWTPs. Based on the results, the annual average energy consumption for small, medium and large WWTPs equals 137 kWh/PE, 48 kWh/PE and 32 kWh/PE, respectively. Accordingly, annual average GHG emissions, both biogenic and non-biogenic in small, medium and large WWTPs are equal to 207 kgCO2e/PE, 144 kgCO2e/PE and 89 kgCO2e/PE, respectively. Annual average on-site GHG emissions are equal to 56.5 kgCO2e/PE, while the average off-site GHG emissions account for 16.9 kgCO2e/PE. Based on the results, acceptable and attainable targets for WWTPs energy consumption and GHG emissions are proposed.

Microbe-assisted phytoremediation is emerging as one of the most effective means by which plants and their associated rhizosphere microbes degrade organic contaminants in soils. A pot study was conducted to examine the effects of inoculation with Rhizobium meliloti on phytoremediation by alfalfa grown for 90 days in an agricultural soil contaminated with weathered polycyclic aromatic hydrocarbons (PAHs). Planting with uninoculated alfalfa (P) and alfalfa inoculated with R. meliloti (PR) significantly lowered the initial soil PAH concentrations by 37.2 and 51.4% respectively compared with unplanted control soil. Inoculation with R. meliloti significantly increased the counts of culturable PAH-degrading bacteria, soil microbial activity and the carbon utilization ability of the soil microbial community. The results suggest that the symbiotic association between alfalfa and Rhizobium can stimulate the rhizosphere microflora to degrade PAHs and its application may be a promising bioremediation strategy for aged PAH-contaminated soils.

Microbial fuel cell (MFC) is an emerging biotechnology to convert the organic substrates in wastewater to electricity by anaerobic electrogenic bacteria. The main challenge for MFC research is to elucidate the fundamental mechanisms of electron generation and transfer and to apply these mechanisms to improve the power production in the engineering operation. This study extensively investigated the effects of three inocula (Geobacter sulfurreducens, soil, and wastewater) on the power production and electrochemical characteristics (i.e., internal resistances, Coulombic Efficiency) of MFCs. The results showed that the extents of bacterial adhesion varied between mixed cultures (soil) and pure cultures (G. sulfurreducens). The voltage output increased 30% when bacterial adhesion was well-developed in the soil inocula. Meanwhile, the inoculum types clearly affected the internal resistance (R(in)) and power production of MFCs. Pure culture inoculum (G. sulfurreducens) had the lowest R(in) (165 Omega) and the highest Coulombic Efficiency (CE, 25.8%) and Energy Conversion Efficiency (ECE, 7.2%), while the mixed culture inocula (soil) with the high concentration of nonelectrogenic bacteria, exhibited the highest R(in) (620 Omega), lowest CE (9.2%) and lowest ECE (2.4%). Additionally, a second-order correlation was established between the anode potential (P(A)) and power output while an exponential correlation was established between the difference between anode and cathode potentials (DeltaP(C-A)) and power output.