Towards Sustainable Use of Algae as Adsorbents for Wastewater Treatment

Introduction

One of the primary issues in the twenty-first century is access to clean water (Al-Amshawee et al., 2019). Water quality is deteriorating rapidly as a result of growing anthropogenic activities, unplanned development, and increased industrialization. Increased human population also increases the strain on access to clean water. The principal pollutants found in wastewater effluent are various types of dyes, micro- and macronutrients and metal ions, which cause harm to the aquatic environments (Varghese et al., 2019; Saravanan et al., 2021). However, in the past decade, several studies have reported the occurrence of new classes of water contaminants with no regulatory status. These pollutants are generally knowns as chemicals of emerging concern (CEC) or emerging contaminants (Shikuku, 2020). Among these contaminants are pharmaceutical and personal care products (PPCPs). The ubiquitous presence of PPCPs in the environment is of scientific concern due to their ecological toxicity such as inducing the development of drug resistant bacterial strains, mutagenicity and causing endocrine disruption. Conventional wastewater treatment plants (WWTPs) are point sources for both heavy metals (Shikuku et al., 2017) and PPCPs (Kimosop et al., 2016; Muriuki et al., 2020) loading into the recipient water bodies. The physical, chemical and biological methods of wastewater treatment have intensively been discussed in literature and textbooks, and their details will not be reiterated in this chapter. Adsorption still remains the widespread method for removal of the aforementioned contaminants from the wastewater. Various materials have been reported as possible sorbents for sequestration of water pollutants. Biochars (Ng’eno et al., 2016; Achieng’ and Shikuku, 2020), clays (Shikuku and Mishra, 2021), zeolites (Ng’eno et al., 2019), and geopolymers (Tome et al., 2021; Dzoujo et al., 2021) are among the common materials, of geological, industrial, and agricultural origin, that are used in this respect. The search for alterative adsorbents is a subject of ongoing research due to the expensiveness of activated carbon. Biomass-based adsorbents are an emerging class of water purification approach due to their eco-friendliness, low-cost, and good surface characteristics. This chapter highlights the recently published information about the biosorption of PPCPs, phenols, dyes, nitrates, phosphates and heavy metals using various algal species, as well as the sorption mechanisms, and their comparative adsorptive capacities. As shown in Figure 1, the adsorption performance of the algal-based adsorbents will be dependent on the pre-treatment method of the algal biomass, which determines the type of sorbent generated, the type of pollutant and the environmental or experimental conditions.

Figure 1.

Algal biomass-based adsorbent preparation approaches (Lee et al., 2022)