As a low-cost adsorbent, biochar can be used as a low-cost adsorbent for wastewater treatment, particularly with respect to treating heavy metals in wastewater. A number of studies have demonstrated effective removal of heavy metals from aqueous solutions by biochar and, in some cases, proven the superiority of biochars to activated carbons. Among several factors Downloaded by [University of Nebraska, Lincoln] at 19:41 29 September 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 affecting the sorption ability of biochars, feedstock materials play a significant role. This review incorporates existing literature to understand the overall sorption behavior of heavy metals on biochar adsorbents. Depending on the biochar type, heavy metal can be removed by different mechanisms such as complexation, physical sorption, precipitation and electrostatic interactions.Mathematical sorption models can be used to understand the efficiency of biochar at removing heavy metals, and promote the application of biochar technology in water treatment.

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There is lack of information available concerning the effect of humic substances (HS) applied via fertigation on plant growth in sandy soils. Therefore, a field experiment was carried out at El-Saff district (20 km southwest of Cairo), Egypt, to investigate the role of HS fertigation on water retention of a sandy soil, yield and quality of broccoli (Broccoli oleracea L.) as well as on soil nutrient concentration retained after harvest. The experiment consisted of six fertigation treatments (50%, 75%, and 100% of the recommended NPK-fertilizer rate for broccoli combined with and without HS application at 120 L ha -1 ) in a complete randomized block design with three replicates. Humic substances affected spatial water distribution and improved water retention in the root zone. Furthermore, application of HS increased total marketable yield and head diameter of broccoli as well as quality parameters (i.e., total soluble solids, protein, and vitamin C). Higher nutrient concentrations were found in the broccoli heads and concentrations of plant-available nutrients in soil after harvesting were also higher, indicating an improvement in soil fertility. In conclusion, HS fertigation can be judged as an interesting option to improve soil water and nutrient status leading to better plant growth.

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