Critical review on sustainable bioreactors for wastewater treatment and water reuse

Rapid developments are habitually connected with substantial wastewater production (sources- municipal, textile, landfill, digester reject, saline industry, tannery, greywater, petroleum, pharmaceuticals, coal gasification, etc.), which contains different pollutants like nitrogen, phosphorous, carbon, heavy metals, emerging pollutants (pharmaceuticals, personal care products, endocrine disruptive compounds) and others. In this critical situation and rising water demand, biological techniques are the need of the hour for wastewater treatment and reuse, thereby protecting the environment. This paper highlights the most used bioreactors like Biofilter, Vermifiltration, MFC, MBBR, UASB, and MBR and their unique features. Additionally, details like intermediates, microbiology, operational conditions, mechanisms, implications, advantages, recent advancements, shortcomings, and removal efficiency of target pollutants (carbon, nitrogen, phosphorous- CNP; emerging contaminants- pharmaceuticals, personal care products, endocrine disruptive compounds) were discussed. The traditional and advanced versions of those bioreactors were also emphasized. Moreover, the review highlights different case studies related to the reuse scope of treated water that must be addressed for upcoming expansions and large-scale application of biological techniques in water reuse and the further development of hybrid systems. MFC is a well-known treatment technology for removing pollutants from wastewater when undertaken on a small scale; however, attempts should be made to make it successful on a larger scale. In Vermifiltration, further attempts must to be conducted to develop and design of robust systems as earthworms are sensitive to temperature and moisture.