## 1 Introduction  
A large amount and high concentration of heavy metals in industrial wastewater, mainly from mining, metal processing, tanneries, pharmaceuticals, pesticides, organic chemicals, rubber and plastics, lumber, and wood products, has been discharged into water bodies without adequate treatment [1]. Heavy metal concentrations exceeding the permissible standards in drinking water and wastewater have often been observed in many countries [2]. Heavy metals are toxic to humans and other animal predators because they accumulate in the body through the food chain [3, 4]. These can, accumulated in the body, cause toxic effects such as cancer and gastrointestinal disease, as well as neurological and renal disturbances [5, 6, 7]. Therefore, it is vital to develop methods and technologies to remove heavy metals before being discharged into the aquatic environment [8]. Various methods, including ion exchange [9], coagulation/precipitation [10], membrane separation [11], adsorption/filtration [12, 13], and electrochemical treatment [14], have been applied to industrial wastewater contaminated with heavy metals. However, most of these methods have limitations for use in the field because of the generation of large amounts of sludge from the chemical process as well as the cost for build-up and management, and low technical maturity [15, 16, 17]. For these reasons, the attraction for environmentally friendly technologies as low cost, effective, and easy-to-apply alternatives has been increased by many researchers [18, 19, 20]. The adsorption process is preferable for heavy metal removal because of the relatively low cost for build-up and maintenance, simple implementation, easy operations, availability of a number of adsorbents, environment friendly, high removal efficiency, and ability to remove a variety of pollutants present in wastewater [8; 21; 22]. The use of living or dead biomass has been considered one of the most effective, economical, and promising bioadsorbents for removing toxic metals from contaminated water [23; 24]. Biomass from bacteria, fungi, and algae is also considered a promising adsorbent for removing heavy metals from wastewater because of the abundance of this biomass in nature and its rapid growth, and ease of cultivation [25; 26; 27]. Among the types of naturally occurring biomass, marine algae, in particular, are a renewable source and easily obtainable in large quantities [28; 29]. A statistical review on biosorption [5] reported that algae had been widely used as raw material for biosorbents 15.3% more than other types of biomass (activated carbon or activated sludge) and 84.6% more than fungi and bacteria. Marine algae also have a high affinity for metals because the polysaccharides, proteins, or lipids on the outer cell wall of the algae provide adsorption sites for the metals via complex formation and ion exchange [30]. Both live and dead algae can be used as adsorbents for heavy metals, and dead algae have several advantages over living algae in terms of utilization. Dead marine algae may be even more cost-effective than living algae because inactive algae require neither food nor essential elements for biological growth [5]. Moreover, dead biomass is not affected by the toxicity of metal ions, and the chemical and physical modification of the biomass can be applied to enhance the adsorption capacity [5; 31]. Acid or base modification is the most common method of enhancing the bioadsorption of heavy metals to algae, which results from exposure of active metal-binding sites contained in the cell wall or chemical modification of cell wall components [32]. Therefore, in this study, we evaluated the feasibility of marine algae as bioadsorbents for removing heavy metals from contaminated water.