The study investigated the preparation and characterization of biochars from water hyacinth at 300°C to 700°C for cadmium (Cd) removal from aqueous solutions. The adsorption process was dominated by oxygen-containing functional groups with irregular surfaces via esterification reactions. Furthermore, the mineral components in the biochars also contributed to Cd absorption through precipitation. Parameters such as the effects of solution pH, contact time, and initial concentration were studied. The optimum pH value was observed at 5.0, in which nearly 90% of Cd was removed. The maximum Cd adsorption capacities based on the Langmuir isotherm were calculated at 49.837, 36.899, and 25.826 mg g−1. The adsorption processes of the biochars followed the pseudo-second-order kinetics, with the equilibrium achieved around 5 h. The biochar from E. crassipes is a promising adsorbent for the treatment of wastewater, which can in turn convert one environmental problem to a new cleaning Technology.

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The concentrations of dissolved inorganic nitrogen (DIN; NO2− -N, NH3-N, and NO3 − -N), PO4 3− -P, dissolved oxygen (DO), chemical oxygen demand (COD), five-day biological oxygen demand (BOD5), oil, Si, and seven heavy metals (Hg, Cr, Cu, As, Zn, Pb, and Cd) in seawater from the Dongzhaigang National Mangrove Nature Reserve of China in 2013 were determined. Except for the concentrations of the COD, BOD5, Cr, Hg, Cu, As, and Cd, each index in seawater were found to be over the limits of I-Class seawater standards. The index of organic pollution showed that the pollution level in this study area reached level 6; eutrophication levels indicated that the nutritional level reached level 4. According to the water quality index model, the sea area was slightly polluted by heavy metals. In a genetic algorithm-based fuzzy comprehensive evaluation, the results for organic pollutants, nutrients, and heavy metal pollution can be combined to evaluate the OPEN ACCESSWater 2015, 7 4822 water quality as a whole. Results showed that the sea area in Dongzhaigang did not have a healthy water environment, but was seriously polluted by organic pollutants and nutrients.

Groundwater is an important source of drinking water in the coastal areas of Hainan Island. In order to fully understand the condition of groundwater and impact of seawater intrusion, chemical data of logging groundwater in the northeast coast of Hainan Island, which was acquired by continuous sampling tests for 25 hours in the spring and neap tide, was employed to comprehensively analyze chemical characteristics of groundwater and evaluate the water quality.The results indicate that type of groundwater is Cl-Na without being affected by tide period significantly and groundwater quality is relatively poor under the influence of seawater intrusion.