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Dead leaves of seagrass Posidonia oceanica were activated by using one mol L −1 acetic acid and used as an eco-adsorbent for the removal of methylene blue (MB) and Pb 2+ from aqueous solutions. The seagrass was characterized by chemical and physical measurements that confirmed the acid-activation of seagrass. The favourable conditions for MB and Pb 2+ adsorption onto the activated seagrass (SG a ) were determined to be a pH range of 2–12 and ≥6, an adsorbent dosage of 3.0 and 0.5 g L −1 , respectively, and a shaking time of 30 min, which are suitable for a wide range of wastewaters. The equilibrium data were analysed using the Langmuir, Freundlich and Dubinin-Raduskavich-Kaganer (DRK) adsorption isotherm models. The Freundlich and DRK models best describe the adsorption processes of MB and Pb 2+ , on SG a with capacities of 2681.9 and 631.13 mg g −1 , respectively. The adsorption isotherm fitting and thermodynamic studies suggest that the adsorption mechanism of MB may combine electrostatic and physical multilayer adsorption processes, in which MB may be present as monomers as well as dimers and trimers which were confirmed from UV spectroscopy whereas Pb 2+ is chemically adsorbed onto SG a . The pseudo-2 nd -order kinetic model was utilized to investigate the kinetics of adsorption processes. The removal process was successfully applied for MB-spiked brackish waste water from Manzala Lake, Egypt, with removal efficiencies of 91.5–99.9%.

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Lake Manzala is the largest and most productive lake of Egypt's northern coastal lakes and has socio-economic impacts. Pollution by heavy metals is the most significant type of pollution worldwide, particularly in Lake Manzala, which receives mixed discharges from densely populated areas. Water samples were collected at twelve sites around the lake in winter and summer of 2015. Samples of Eichhornia crassipes were collected in the winter, and Oreochromis niloticus samples were collected at two sites (8 and 10). V, Cr, Mn, Fe, Co, Ni, Cu, and Zn were analysed in these samples using inductively coupled plasma-mass spectrometry. The average metal concentrations were below the internationally accepted upper permissible limits and are improved compared to those in previous studies. However, the metal concentrations at the eastern and southeastern sites were higher than the allowable limits due to multiple waste discharges. Pollution assessment using pollution risk indicators indicated low to moderate concentrations of metal enrichment in the sediment and biota of the lake, except at sites near the eastern and southeastern drains; these latter sites were considered to be hazardous and should be taken into account in the current development efforts of the lake. Complete removal of floating plants transported by drains is recommended .

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