**2. Emerging interest on filamentous algae**

Research in the application of microalgae in wastewater treatment was initiated in the 1950s. It has been highlighted that phycoremediation can remove up to 99% of nitrogen (N) and phosphorous (P) and reduce these nutrients concentration below 1 mg/L [3]. Moreover, the produced algal biomass can be valorised from niche markets of special materials (e.g. biopolymers and coatings) to the large-scale uses of fertilizer [4]. Phycoremediation has been demonstrated to be technically possible at lab scale, pilot scale, and industrial scale, but not economically viable. Although the cost for microalgae cultivation can be subsidized to a large extent by recovering nutrients from wastewater and sequestrating CO2 released by WWTPs [5], harvesting microalgae cells is actually a premier obstacle to impede the popularity and scalability of phycoremediation [1]. It is an energy-intensive and expensive process. For an operational facility, this process can occupy over 90% of capital expenses [6] and above 20–30% of the overall production cost [7]. Meanwhile, it cannot be ignored that most fast-growing microalgae are vulnerable to the fluctuation of biotic and abiotic conditions in wastewater [1]. This is another inevitable challenge for those delicate microalgae cultivations, especially for the commonly proposed monoculture [4]. To address these inherent problems on phycoremediation, research attention has gradually shifted to filamentous algae in recent years, as they possess some unique traits that singular microalgae does not have.

Species from the genera *Oedogonium, Cladophora, Spirogyra, Klebsormidium*, and *Stigeoclonium* have been demonstrated as good candidates for wastewater treatment applications [4]. These filamentous algae have several impressive advantages for wastewater treatment, such as robust ability to uptake nutrients from wastewater to achieve about 60% increase in dry biomass per day [8], simplicity of harvesting, stronger resistance to a variety of aquatic grazers and competing organisms, as well as better adaptation to dynamic conditions [9]. Even in the environment with varying N:P

## *A New Insight of Phycoremdiation Study: Using Filamentous Algae for the Treatment… DOI: http://dx.doi.org/10.5772/intechopen.104253*

ratios, the filamentous algae still can remove 99% of N and P simultaneously [10]. Moreover, these filamentous algae can naturally grow and bloom in a broad spectrum of waste streams including ash dam water [11]. Although filamentous algae have been highly recommended for wastewater treatment [4], there is little information to investigate their potentials for the contemporary requirement of WWTPs. With the declined interest of algae bioenergy and increased knowledge on pragmatic algae potentials, there is a growing consensus that the appropriate phycoremediation should be implemented and aligned with realistic demand and specific wastewater conditions.
