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Excessive use of phosphorus (P) based fertilizers for improved agricultural productivity has resulted in nutrient enrichment and consequent deterioration of surface and ground waters. Naturally, available soil microbes in an agricultural set-up are capable of mineralization of organic P and/or solubilisation of inorganic P thus making it bioavailable to the crop systems. As an alternative to conventional P based fertilizers, wastewater rich in nutrients can be cheap and economic P sources ensuring phosphorous recycle and reuse. However, the treatment of these waters to check pathogens, heavy metals and other toxicants; conveyance and storage are practical constraints that limits the usage of wastewaters directly to croplands. Wastewater grown algae as proficient biofertilizer can be potentially used to immobilize P and channelize P to croplands. Such algal biomass abundantly growing in natural waters as well as in treatment ponds can be rich sources of nutrients due to their higher P uptake abilities, growth rate and productivity. Although there are huge opportunities for using algae as a bio-filter to recover P from wastewater streams. However, their use for tapping valuable P with present day technologies are still evolving and are in infancy. Efforts on understanding the mechanism of P uptake, immobilization in algal cells and subsequent P transport to agricultural soil systems are important. This can provide global solutions in stocking wastewater P and its sustainable reuse as algal-based P rich biofertilizer.

Current perturbations in the agrarian economies and the agro-environment have sparked concerns regarding the future food security and a dire need for sustainable agricultural practices without jeopardizing the environmental assets. One such major requirement for an agrarian society is a resilient nutrient source for agriculture. In this regard algal cells that are cosmopolitan in nature with unparalleled characteristics of high biomass productivity, high photosynthetic efficiency and ability to grow in barren and non-arable lands are attractive. They grow in a wide range of water systems especially the ones that are highly enriched with salts (saline) and nutrients (eutrophied) and in numerous contaminated and polluted systems as urban wastewaters. Apart from these primary benefits, the algal route also offers important byproducts that can be further used as value-added products in industries and as C neutral commodities that help to evade climate change by negating greenhouse gas emissions. The most important aspects are its efficiency as a biofertilizer that dynamically improves the soil health and its physicochemical behaviour. The wastewater-grown algal microflora is exceptional in imparting the appropriate mineral nutrient mix with essential vitamins and plant growth promoters together with increasing the water holding capacity of the soil. Algal communities from wastewaters with optimal NPK ratio and secondary nutrients are therefore model biofertilizers. They can be substitutes of the conventional chemical fertilizers due to its ubiquity, enhanced metabolic flux, short generation time and inherent capabilities to transform inert N into plant-available N (N fixation). All the above-mentioned characteristics, techno-economic feasibility and environmental benefits make algae the most beneficial and demanding bioresource of the twenty-first century.

Globally, treatment and management of wastewater are a serious challenge. Voluminous wastewaters are generated on a day-to-day basis that is being either partly treated or untreated finds its ways into surface and groundwater thus enriching the systems with nutrients, pollutants and pathogens. In purview of the increasing water scarcity, rapid water deterioration, higher primary productivity in surface waters due to nutrient enrichment, towering wastewater production and complications related to its treatment, the understanding of water footprint, underlying mechanisms of wastewater treatment and transformation of terrestrial nutrients into value-added products and various downstream processes for their recovery needs to be understood. In this context, the algal treatment systems not only provides a simple and economical solution to wastewater treatment but also aids in the production of many valued bio-based products like lipids as feedstock for biofuels, single-cell proteins, Omega 3 fatty acids, carotenoids as astaxanthin and β-Carotene. The present chapter throws light on various mechanisms and strategies of wastewater transformations into value-added products while evaluating the techno-economics and feasibility of such systems for assessing its potential to be a bio-based industry. Various strategies for algal species selection targeting specific wastewater pollutants grown either as natural population or as engineered consortia with numerous wastewater treatment approaches until the production of valorized biomass is being discussed. Lastly, key techno-economics, environmental challenges and the scope of wastewater transformations into bio-based products are enumerated.

The concept of gazing trash or waste as a worthwhile resource is augmenting exponentially. Despite its worthiness, there are distinct factors which affect the profitability of a plant which processes waste to worthwhile products such as fuels, fertilizers, energy, or chemicals. There is the adequate literature of different processing methods of wastes; however, the majority of the studies do not consider economic perspective. This chapter focusses on the economics of handling wastes including collection and transportation and processing it into value-added products such as compost, electricity, or fuel. Different countries have different legislation for waste handling, and this chapter addresses the waste handling costs in different countries. Furthermore, the profitability of different processing methods was discussed. The critical factors affecting the profitability of waste treatment and handling were identified, and workable solutions or directions were provided to the scientific community to address the problems with an industrial outlook including profitability.