The effect of land use type on selected soil physicochemical properties in Shihatig watershed, Dabat district, Northwest Ethiopia

Different land use practices have a substantial influence on soil quality. An inappropriate land use system in Ethiopia leads to extensive deforestation which aggravates the loss of soil fertility. Even though there are various studies conducted on the effect of land use type on soil physicochemical properties, it is inadequate in the northern highlands of Ethiopia, in particular in the Dabat district. Thus, this study aimed to assess the effect of land use type and soil depth on selected soil physicochemical properties in the Shihatig watershed, Northwest Ethiopia. A total of 24 undisturbed core and disturbed composite soil samples were collected from the four land use types (natural forest, grazing, cultivated, and Eucalyptus lands) and two depths (0-20 cm and 20-40 cm) with three replications. The physicochemical properties of the soil were determined using standard operating procedures. The two-way analysis of variances was conducted using SAS software, Version 9.4. The result showed that the texture and soil organic carbon were affected by land use type, soil depth, and the interaction of the two factors; while bulk density, soil moisture content, total nitrogen, available phosphorus, cation exchange capacity, and level of Mg²⁺ were significantly affected by both land use and soil depth, whereas pH and electrical conductivity were affected by only the land use type. The highest clay, pH, electrical conductivity, total nitrogen, cation exchange capacity, and exchangeable cations (Ca²⁺ and Mg²⁺) were recorded in the natural forest land, while the lowest values of the same parameters were found under cultivated land. The mean values of most of the soil properties were low in the cultivated and Eucalyptus lands. Therefore, adopting sustainable cropping systems such as crop rotation and the addition of organic manure, and minimizing planting the Eucalyptus tree is vital to improve the existing soil quality and enhance crop productivity.

Removal of Hg0 from simulated flue gas over silver-loaded rice husk gasification char

Mercury released into the atmosphere from coal combustion is harmful to humans and the environment. Rice husk gasification char (RHGC) is an industrial waste of biomass gasification power generation, which is silver-loaded to develop a novel and efficient sorbent for mercury removal from simulated flue gas. The experiment was carried out in a fixed-bed experimental system. The Hg⁰ adsorption performance of RHGC was improved significantly after loading silver. Hg⁰ adsorption capacity and mercury inlet concentration were found to be nonlinear. The adsorption capacity of RHGC decreased with the increase of reaction temperature. SO₂ inhibited mercury removal, NO and HCl promoted mercury removal; the Hg⁰ adsorption capacity in the simulated flue gas was higher than that in pure N₂. The silver-loaded rice husk gasification char (SRHGC) could be recycled about five times without significantly losing its removal efficiency. The SRHGC will not only reduce the cost of mercury removal but also save energy and reduce environmental pollution. At the same time, it provides a new way for the resource utilization of RHGC.

Nitrate removal and bioenergy production in constructed wetland coupled with microbial fuel cell: Establishment of electrochemically active bacteria community on anode

The constructed wetland coupled with microbial fuel cell (CW-MFC) systems operated at different substrate concentration and pH influents were evaluated for bioelectricity generation, contaminant removal and microbial community structure. Performance of CW-MFC was evaluated at organic loading rate of 75.3gCODm^-3d^-1 and pH gradients of (5.18±0.14, 7.31±0.13, and 8.75±0.12) using carbon fiber felt as electrodes. Peak power density was observed at slightly neutral influent condition. Compared with the open circuit CW-MFC, average COD and NO₃-N removal efficiency in CW-MFC increased by 8.3% and 40.2% respectively under slightly neutral pH of influents. However, the removal efficiency and bioenergy production have been inhibited with acidic influents. The relative abundance of beta-Proteobacteria, nitrobacteria and denitrifying bacteria was significantly promoted in closed-circuit CW-MFC. Using of CW-MFC as a biochemical method for nitrate removal and bioelectricity generation under slightly neutral and alkaline influent conditions was a promising technology.

Microbial community structure of different electrode materials in constructed wetland incorporating microbial fuel cell

The microbial fuel cell coupled with constructed wetland (CW-MFC) microcosms were operated under fed-batch mode for evaluating the effect of electrode materials on bioelectricity generation and microbial community composition. Experimental results indicated that the bioenergy output in CW-MFC increased with the substrate concentration; maximum average voltage (177mV) was observed in CW-MFC with carbon fiber felt (CFF). In addition, the four different materials resulted in the formation of significantly different microbial community distribution around the anode electrode. The relative abundance of Proteobacteria in CFF and foamed nickel (FN) was significantly higher than that in stainless steel mesh (SSM) and graphite rod (GR) samples. Notably, the findings indicate that CW-MFC utilizing FN anode electrode could apparently improve relative abundance of Dechloromonas, which has been regarded as a denitrifying and phosphate accumulating microorganism.