Removal of heavy metals from wastewater is of special concern due to the persistence of heavy metals in the environment. The industrial discharge of heavy metals adversely affects soil and water resources, aquatic organisms, and ecosystem integrity. In addition, high concentrations of heavy metals are detected in solid waste landfill leachate in many developing countries due to non-segregated waste dumping. At present, various kinds of adsorbents such as activated carbon, biomass resources, geomaterials, and industrial waste products are used to treat heavy metal-contaminated water. However, the use of construction and demolition waste (CDW) and its recycled materials to treat heavy metal-contaminated water has not been fully examined. Because the generation of CDW is increasing due to rapid urbanization and a high demand for construction, the wise use of CDW and its recycled materials is necessary. This paper reviews journal articles published from 2004 to 2016 that studied the applicability of low-cost CDW adsorbents to remove heavy metals from wastewater. In particular, it summarizes results on using CDW and recycled materials such as cement, concrete, and brick compared to those from various other adsorbents such as biosorbents, geomaterials, and their industrial products. The potential applicability of CDW and its recycled materials as heavy-metal adsorbents was examined based on a comparison table listing material properties, test conditions, and measured adsorption properties.
The number of presently operating small tanks in the Kurunegala district is 4,482 of which 2873 tanks have less than 6 ha of command area. Capacity of these tanks is low and the amount of water stored is not sufficient to fulfil the water requirement of the rice crop throughout the cropping season. Many farmers in Udakadawala area in the Kurunegala district adopts to start land preparation (LP) after filling tanks and start LP using tank water. This situation results in the delaying of the cultivation and limiting the use of rain water during the initial stages of the crop. On the other hand, due to high variability of rainfall, severe crop damages are frequently experienced. The objectives of this study were to identify the factors affecting low water productivity and to introduce and evaluate a new land and water management approach to increase rice yields. A trans-disciplinary research methodology was used employing participatory research tools. Seedling broadcasting (parachute) method with proper LP technology, time of cultivation, water management practices and use of good quality seed paddy were applied to five separate plots in the field while other fields were under their normal activities. Yield components data were collected and were analyzed. According to the results obtained, farmers delayed LP until water issue from the tank and cultivation is mainly done by rotavators mounted to two wheel tractors. In treatment, early LP with onset of rainfall using four wheel tractors save water up to 66% of the total water requirement. LP using tine tiller compared to rotavator reduces the amount of water required for the LP and increase the access to more water and nutrients by increasing the root depth. Tank water productivity was 1.93 and 0.28 kg/m 3 in treatment and control, respectively. The effect is more useful in Yala than in the Maha season. "Parachute" method and other agronomic practices such as recommended seeds, using organic matter, proper weeding is important along with land and water management. Conjunctive use of rainfall and tank water in combination with other management techniques was successful in increasing water productivity in small tank irrigation system.
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