Application of Microalgae in Wastewater Treatment

Due to changed land use, population pressure, and consumption pattern, the pollution load on environment is posing threats to ecosystem health and human welfare. The need to search for environmental friendly cleanup techniques for removal or reduction of pollutants has brought phycoremediation into focus which is a global natural phenomenon in maintaining ecological balance. The agents of phycoremediation (micro- and macroalgae) have already been established for their remarkable capacity to detoxify/remove pollutants from environment along with providing a very good platform for production of food supplements, biofuels, and so on. Algae possess a number of desirable properties which help in sequestration of various pollutants from the environment. As a green technology for clean environment and the biomass production, phycoremediation can serve as an appropriate technology. In this chapter, an overview of algae-based bioremediation, its status, and challenges toward global sustainability have been discussed.

Diatoms are heterokonts which are highly diverse and have significant evolutionary differences when compared with green algae and vascular plants. Diatoms drive primary production in all photic zones from the equator to arctic. Diatoms have great potential as bioindicators as their population diversity reflects the environmental conditions of their oceanic or riverine ecosystems. The ease of their detection and versatility across different ecosystems complements to their sensitivity to many physicochemical and biological changes. Diatom importance in marine and fresh water ecosystems is attributed to their primary role in aquatic food webs. Mass cultivation of microalgae for biodiesel and high-value products needs enormous supply of growth medium. Meeting this need from fresh water and fertilizers is not environmentally and economically sustainable. Hence, growing diatom algae utilizing the nutrient contents of wastewater will offer a natural wastewater treatment option with revenue generation potential. Constructed wetland-based decentralized wastewater treatment when followed by diatom treatment can reduce their footprint and increase their revenue generation potential. Performance monitoring of decentralized wastewater treatment facilities through standard physicochemical methods remains a challenge for remote locations as the time lag between sampling and analysis often diminishes the quality of performance evaluation. In this chapter we explore the enormous potential of diatom to augment the feasibility of constructed wetland as a sustainable wastewater treatment technology with simultaneous biomonitoring.

Various types of medicines, including nonsteroidal antiinflammatory drugs and quinolone antibiotics, have been used to treat infections caused by microorganisms. Consequently, most of these medicines, undigested, and with their metabolic intermediates, are released through excretion into the ecosystem. In addition, hormones, especially steroid hormones, are observed in the ecosystem, which because of their long-term persistence (even at trace levels) in the environmental surroundings might pose a risk to living systems. Hence, various research groups have studied the fate of such contaminants. To avoid the high risk of micropollutants, various remediation techniques have been proposed to remove such contaminants from the environment. One of these methods is removal of the contaminant(s) by microalgae. In this book chapter, we briefly summarize the occurrence of some of these microcontaminants in the ecosystem and their detoxification as well as elimination by microalgae (alone or combination with other processes), as reported in the published literature.

In the present investigation, the algal community and developed consortia in aquatic as well as terrestrial environments are shown to provide numerous genetic resources and vast biodiversity. Thus, microalgae consortia have the capability to provide biofuel, bioethanol, and bioactive products. The development of microalgae consortia has been widely evaluated for their unique role in greenhouse gas mitigation. The biomass production of microalgae consortia is less well studied, although microalgae consortia currently are significant in bioenergy and biofuel production. Global climate changes resulting from increasing atmospheric carbon dioxide could minimize carbon sequestration and mitigation by microalgae consortia. Developed microalgae consortia have a future role in carbon capture and cost-efficient industry demands. Microalgae consortia produce several products, such as chemicals, that can increase cost-effectiveness. Increase in production of edible algae has proved to be commercially viable, and using microalgae consortia for wastewater treatment is now feasible. In this chapter, we discuss the future demand of fuels and sustainable development approaches for industrial production, keeping in mind current environmental issues.

Microalgae can be applied for wastewater treatment (WWT) because of their potential to assimilate nutrients. The recent interest in using wastewater as a medium for algae biomass generation is considered as a promising biological process from environmental and economic points of view. Despite the promising research findings on microalgae for WWT at the laboratory scale, the large-scale microalgae-based WWT process is reliable only in outdoor systems that still need further investigation. In this book chapter, we provide an overview and the most up-to-date information on outdoor cultivation of microalgae for WWT, discussing the progress and the important operational factors in outdoor culture.

Removal of increasing level of EDCs from wastewater has become a major concern nowadays. Since EDCs are known to cause interference in the activities of endocrine system of the body affecting almost all types of organisms including human beings, their removal from wastewater is of prime importance. Minimal growth requirements, broad spectrum of mechanisms and widespread occurrence make microalgae an economic and ecofriendly option for removal of EDCs from wastewater. Recent studies showed increased use of microalgae in removal of endocrine disruptors like 17β-estradiol, PAHs, PCBs, phenols and heavy metals. Among several parameters significant in an algal remediation process, strain selection is of prime importance, i.e. to select an alga with maximum capacity to treat the contaminants. This chapter reviewed recent literature pertaining to the application of microalgae for remediation of EDCs and various practical avenues of this technology in the area of wastewater treatment.

Rapid urbanization has resulted in an increase of municipal sewage discharge, which, in turn, has added load and cost to the conventional water treatment processes. The composition of municipal sewage mostly contains natural inorganic and organic minerals as well as synthetic compounds. Microalgae utilize these wastes as nutritional sources and hence could be used as an interesting step to improve the quality of sewage. Though there are some natural algal flora existing in sewage, few selective and efficient strains could be used in this purpose. They are non-pathogenic and have the potential to eliminate pathogens by competitive growth. Moreover, they could reduce biological and chemical oxygen demand of water as well as remove heavy metals by algal metabolism. Unlike conventional methods, it requires low operational and maintenance cost and no use of hazardous chemicals for water treatment. Additionally, the biomass could be utilized to generate value-added products such as bioenergy, pharmaceuticals, nutraceuticals, etc. However, land requirement, difficulties in the growth of pure strains, variation in environmental factors, eutrophication, self-shading and difficulties in the harvesting of biomass are some of the bottlenecks of this process. With recent advances in scientific knowledge, sophisticated techniques and environmental awareness, microalgae could offer a sustainable, environment-friendly solution to treat wastewater which could be further enhanced by the addition of other organisms and aquatic plants.

Impoverished communities everywhere in the world face challenges with respect to the treatment of wastewater. In particular, rural areas and remote communities with low socioeconomic conditions may lack conventional centralized wastewater treatment systems. As a result, in many instances, wastewater may be disposed without appropriate treatment, thus contaminating drinking water resources. Even if the communities choose a minimal effort and cost system for wastewater treatment, existing decontamination techniques do not provide complete reduction in biodegradable organic materials, pathogens, nutrients, etc., from the wastewater. Particularly, wastewater containing petrochemical hydrocarbons is of major concern under varying climatic conditions because of their high sensitivity to subsurface variability, which enables the pollutants to spread widely. Thus, engineered bioremediation is a promising cost-effective technique that is widely used to accelerate degradation and biotransformation of different pollutants. Phycoremediation is a technique using algae through various mechanisms for pollutant removal or biotransformation that includes nutrients, heavy metals, hydrocarbons, and pesticides. In addition to the removal of pollutants, this mechanism yields algal biomass as an interesting raw material for a diversity of valuable products and biofuel. In this book chapter, we give a comprehensive compilation of existing knowledge and future prospects of algal application in remediation of petrochemical hydrocarbon pollution. Further, this chapter discusses the biogeochemical pathway leading to degradation of petrochemical-polluted soils and groundwater using phycoremediation techniques. The emphasis of the chapter is on present practical applications and the technological constraints to employing sustainable methods. The knowledge pool of this chapter will help in applying decontamination techniques to petrochemical-polluted wastewater and the soil–water system.

Algae could be utilized in bioremediation and wastewater treatment to decrease nitrogen and phosphorus contents in agricultural wastes. Algae can also be used to remove the toxic metals from industrial wastewater through taking up heavy metals from the environment and stimulating a heavy metal stress response, thereby producing heavy metal binding factors and proteins. Additionally, genetic modifications and transgenesis technologies which improve the physiological characteristics and optimize the production systems of algae could further enhance the potential utilization of algae in wastewater treatment and bioremediation. Therefore, this chapter discusses the genetic transformation and transgenesis technologies that could be applied for algae and highlights the potential use of transgenic algae in wastewater treatment and bioremediation.

Presence of pharmaceutical compounds in wastewater streams is a matter of great concern as the persistence nature of these chemicals affects the terrestrial and aquatic organisms. Conventional effluent treatment plants from pharmaceutical industries are not efficient enough to remove the pharmaceutical compounds released along with the waste products. Therefore, more effective and cost-effective waste treatments procedures are required for removal of these chemicals. Nowadays, microalgal-based waste treatment systems are drawing huge attention due to their potential advantages like efficient, low-cost removal of hazardous chemicals, generation of valuable products, sequestering of greenhouse gases, etc. This chapter discusses various microalgal-based systems for removal of pharmaceutical compounds and their challenges and future prospects.

Persistent organic pollutants (POPs) are the most widespread pollutants having toxicity, mutagenicity, and carcinogenicity. Countless amounts of POPs are introduced into our environment as an outcome of myriads of anthropogenic activities. Pollution caused by POPs is a severe problem throughout the world. To solve the problem, extensive research efforts have been focused worldwide to implement sustainable technologies for the treatment of POPs present in the environment. There are various chemical and biological remediation methods which are well documented and are in practice for removal of diverse forms of POPs from soil and aquatic system. Microbial remediation process is an economical way to remediate POPs as compared to the chemical process and has been studied well over a period of more than three decades. Recently, interest has gathered in phycoremediation of POPs into harmless organic pollutants, which are adaptive, ubiquitous, and thriving in different ecosystems. The objective of this chapter is to review and discuss the bioremediating and biodegradative competencies of microalgae on persistent organic pollutants, viz., PAHs, PCBs, pesticides, OCPs, phenolics, PHCs, and antibiotics. This chapter will concisely incorporate studies which have examined and scrutinized the oxidation, transformation, and accumulation of these compounds by algal species. A detailed analysis of the molecular mechanisms involved in bioremediation and biotransformation of POPs has also been reviewed. the limitations and various approaches to enhance phycoremediation and its perspective are discussed in detail.

Various anthropogenic activities continuously affect the quality of water adversely leading to its transformation into wastewater. The wastewater comprises a wide range of heavy metals, xenobiotic substances, pathogens (bacteria, viruses, protozoans, fungi, and helminths), and contaminants like organic and inorganic materials from industrial, domestic, and agricultural sources. Thus, the infelicitous disposal of wastewater into the environment, apart from producing various pollution problems (eutrophication or depletion of oxygen in water bodies), results in public health issues including waterborne diseases. Therefore, treatment of wastewater is imperative. Microalgal cultures render an elegant way out for wastewater treatment as they offer a tertiary biotreatment coupled with the production of potentially beneficial biomass that can be utilized for various purposes like biofertilizers and biofuel production. Microalgae play a pivotal role, directly or indirectly, in the removal of fecal bacteria from domestic wastewater. Some indirect algae governed modes of pathogen removal include starvation, sedimentation, and photooxidation. Algae-based processes constitute viable and cost-effective biological processes that are capable to eliminate pathogens at a reduced energy cost. This chapter presents a comprehensive overview on the feasibility of application of microalgae in pathogen removal from wastewater. It is focused on mechanisms involved in pathogen removal from wastewater, factors affecting pathogen elimination, and algal technologies feasible for pathogen removal. Lastly, it highlights the utilization of algae grown from the wastewater.

Microalgae are widely used for wastewater treatment. Microalgae offer several advantages over other microbial culture used in wastewater treatment. Some of these advantages are (i) low-cost cultivation at large scale without external supply of nutrient and carbon, (ii) ability to sequester CO₂ from waste gases, and (iii) production of biochemical-rich biomass which can be used for biofuel production or as animal feed. Further, research reports revealed that algal-bacterial co-culture has number of advantages over pure algal cultures in wastewater treatment. Microalgae and bacteria in wastewater systems usually have synergistic relation, resulting in improved remediation and enhanced biomass production. However, these interactions are affected by several operational conditions such as nutrient profile, pH, and temperature. Indeed, the algal-bacterial synergies are situation based and may change significantly even with a slight change in the operational conditions. In the recent years, in-depth research and development has been carried to overcome the process limitations particularly for wastewater treatment using algal-bacterial co-cultures. Moreover, attempts have also been made for coupling the algal-bacterial treatment process with bioenergy production. The present chapter shall systematically cover the various aspects related to utilization of algal-bacterial interaction in wastewater remediation from laboratory-scale to pilot-scale studies.

The textile industry has flourished tremendously in response to increasing customer demands for its products. This is naturally accompanied by increasing amounts of wastewater. These effluents contain high levels of synthetic dyes, detergents, stain repellents, waxes, biocides, etc. The dyes are often non-biodegradable and carcinogenic. When released into waterbodies, the intense colour apart from impairing water aesthetics drastically deters sunlight penetration thereby affecting aquatic photosynthesis. The other pollutants in the effluents are capable of giving rise to several human disorders. Treatment of the effluent before release into the environment is thus imperative, and environmental regulations have imposed definitive standards. Several physico-chemical treatment methods have been identified to help conform to these standards. The methods are however cost intensive. The use of algae in remediating textile effluents has been suggested as a cost-effective alternative. Algal biomass have demonstrated adsorption properties superior to its chemical counterparts. Some studies have even reported biomass generation in addition to effluent treatment thus inviting interesting prospects for other applications such as carbon sequestration and biofuel production. The current chapter thus discusses the possibilities and constraints of phycoremediation of textile effluents.

Increased production of industrial wastewaters is an inevitable part of the present developing world, but majority of these waters are highly toxic to not only humans but to other biota, if they are released as such into ponds, streams, rivers, and oceans. Although it is obligatory to remove certain nutrient and other chemicals from industrial effluents before their release, this practice is overlooked by many industries especially in developing countries. This practice can be attributed to nonavailability of low-cost eco-friendly alternatives to the present chemical-based technologies. The diatom algae possess enormous potential in removal of pollutants like organic chemical toxins and heavy metal pollutants and rather than N and P from predominantly industrial wastewaters. The industrial wastewater is characterized by the low concentration of nitrogen and phosphorous, poor light penetration in colored effluents, and elevated concentrations of metals, which are not favorable for algal growth rates. So it is paramount to select right kind of algae to treat industrial wastewaters. Diatoms are unique class of algae with tremendous diversity and are significantly different in cellular and metabolic potential from other algae. Diatoms are responsible for about 20% of the total photosynthetic CO₂ fixation. Diatom algae are pioneers in controlling and biomonitoring of organic pollutants, heavy metals, hydrocarbons, PCBs, pesticides, etc. in aquatic ecosystems. Heavy metal resistance was shown in several diatoms like Cyclotella cryptica, Skeletonema costatum, Cylindrotheca fusiformis, Phaeodactylum tricornutum, and Thalassiosira pseudonana. Although diatoms are extensively studied for their role as bioindicators of water pollution, their application in phycoremediation of polluted water bodies has just started. This chapter reviews the current research on the potential advantages and lacuna pertinent to the utilization of diatoms for sustainable approach of industrial wastewaters remediation.

The widespread use of agricultural chemicals has dramatically increased crop production while simultaneously controlling disease vectors associated with pest vectors for more than half of a century. While the use of these pesticides differs by region, the current levels of use, due to exponential population increase, have led to the contamination of groundwater, surface water, and soils worldwide. Pesticides and the associated residues have led to significant contamination of entire terrestrial ecosystems potentially leading to loss of diversity associated with bio-concentration of aquatic systems. Many of these pesticide pollutants are toxic to humans and even accumulate and transfer vertically through food webs leading to a litany of health problems. The removal of these pollutants through microalgal bioremediation has proven to be efficient, inexpensive, and environmentally friendly. In this chapter, we review the common industrial, agricultural, and domestic pesticides leading to soil and water contamination while outlining a variety of remediation approaches to treating these wastewaters. Furthermore, this chapter includes a discussion on the factors affecting both bioaccumulation and biodegradation efficiencies, including limitations, as associated with approach, environment, and microbial consortium.

All the advancement and development witnessed since the industrial revolution has also brought broad spectrum of problems, and water pollution is one of them. Although 70% of the earth is covered by water, keeping freshwater clean is an issue of survival. The industrial pollution, a major reason for freshwater pollution, is a major growing concern. The measures taken to treat this wastewater with primary and secondary treatments are of less help, by just removing less harmful primary dischargeable effluents. However, more harmful secondary wastes loaded with inorganic nitrogenous and phosphorus compounds along with heavy metals are sometime left in open ecosystems leading to long-term permanent damages. The usage of blue-green algae (BGA) started in early twentieth century, but recent understandings of cellular and metabolic diversities of BGA have given a new hope in wastewater treatment. BGA has got extraordinary flexibility in use of large-scale chemicals as energy sources, producing biomass and biofuel through both organic and inorganic photosynthetic processes. BGA can also stabilizes the water ecosystems by outperforming the growth of pathogenic coliforms as well as microorganisms, which can oxidize organic and inorganic materials using dissolved oxygen, leading to lowering of biological oxygen demand (BOD) and chemical oxygen demand (COD). BGA has been widely used as water quality indicator, for animal/aquaculture food, composting and production of useful chemicals like methane. However the use of BGA for wastewater treatment has started to gain popularity in the last few decades. This chapter summarizes recent reports of BGA usage in wastewater treatment and its future aspects in phytoremediation.

The application of microalgae for wastewater treatment is attracting increasing attention of researchers because of the added potential of harvesting the generated algal biomass for deriving numerous useful products. The conventional systems, viz., algal ponds, are historically used for both wastewater treatment and biomass production at field scale. However, such systems are dependent on the prevalent environmental conditions and do not provide a sufficient level of control over the process, thus achieving a sub-optimal performance. Photobioreactors provide a better process control and optimization due to their design. However, their large-scale application is constrained by the overall economics, in addition to the increased complexity of the operation. The recent advancement in the technology, however, has addressed many of the associated difficulties in the large-scale photobioreactor application. This chapter provides an overview of the photobioreactor technology, the inherent complexity of their application, and the current technical advances leading to their large-scale application.

Algal systems offer a promising solution for wastewater remediation via the uptake of nitrogen and phosphorus species as well as organic pollutants. The obtained biomass can be utilized for the extraction of value-added products such as lipids, protein, and carbohydrates. Algal cells are influenced by several environmental factors making the design of culture systems an essential procedure. Open ponds are considered as a low-cost option for biomass growth; however, they suffer from the limited control of environmental conditions. Alternatively, enclosed photobioreactors have been developed for the enhancement of biomass quality and productivity. However, the expensive construction and maintenance items, as well as the high energy requirements, are the main drawbacks of this system. This chapter provides an overview of the design and basic limiting factors of algal cultivation systems. The design considerations included light irradiance/distribution, culture mixing/agitation, air-CO₂ mixture supply, heat and gas-liquid mass transfers, and energy inputs. The factors were emphasized along with the description of several algal growing systems, viz., facultative waste stabilization ponds, shallow ponds, raceway, tubular photobioreactors, flat panel photobioreactors, and airlift photobioreactors.