International Journal of Environmental Research and Public Health Review Bioaugmentation: An Emerging Strategy of Industrial Wastewater Treatment for Reuse and Discharge Alexis Nzila 1,*, Shaikh Abdur Razzak 2 and Jesse Zhu 3 1 Department of Life Sciences, King Fahd University of Petroleum and Minerals (KFUPM), P.O. Box 468, Dhahran 31261, Saudi Arabia 2 Department of Chemical Engineering, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran 31261, Saudi Arabia; [email protected] 3 Department of Chemical and Biochemical Engineering, University of Western Ontario, London, ON N6A 5B9, Canada; [email protected] * Correspondence: [email protected]; Tel.: +966-13-860-7716; Fax: +966-13-860-4277 Academic Editors: Rao Bhamidiammarri and Kiran Tota-Maharaj Received: 12 May 2016; Accepted: 9 July 2016; Published: 25 August 2016 Abstract: A promising long-term and sustainable solution to the growing scarcity of water worldwide is to recycle and reuse wastewater. In wastewater treatment plants, the biodegradation of contaminants or pollutants by harnessing microorganisms present in activated sludge is one of the most important strategies to remove organic contaminants from wastewater. However, this approach has limitations because many pollutants are not efficiently eliminated. To counterbalance the limitations, bioaugmentation has been developed and consists of adding specific and efficient pollutant-biodegrading microorganisms into a microbial community in an effort to enhance the ability of this microbial community to biodegrade contaminants. This approach has been tested for wastewater cleaning with encouraging results, but failure has also been reported, especially during scale-up. In this review, work on the bioaugmentation in the context of removal of important pollutants from industrial wastewater is summarized, with an emphasis on recalcitrant compounds, and strategies that can be used to improve the efficiency of bioaugmentation are also discussed. This review also initiates a discussion regarding new research areas, such as nanotechnology and quorum sensing, that should be investigated to improve the efficiency of wastewater bioaugmentation. Keywords: bioaugmentation; biodegradation; bioremediation; industrial wastewater; pollution; bacteria; quorum sensing; nanotechnology; protozoan grazing; bacteriophage; cell-immobilization; transfection and plasmid transfer 1. Introduction Industries require a supply of clean water, while at the same time, they generate huge amounts of wastewater that is contaminated with various toxic compounds. In the past, such a situation (high demand of clean water and production of wastewater) only occurred in the developed world, but is now becoming a burgeoning problem in the developing world too, as the result of growing industrialization. For instance, China, one of the fastest growing industrial countries in the world, has generated more than 20 billion m3/year of wastewater in the recent years [1]. This need to supply a large amount of clean water for industrial activities compounds the challenges that human beings face for providing the same clean water to the ever-increasing human population. Because the supplies of freshwater is limited, especially in countries with a limited rainfall pattern, including North Africa, the Middle East, Southern Europe, Australia, and the Southern and Western states of the USA [2], the reuse of both domestic and industrial wastewater, remains the most feasible long-term solution to this problem [3]. Int. J. Environ. Res. Public Health 2016, 13, 846; doi:10.3390/ijerph13090846 www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2016, 13, 846 2 of 20 Int. J. Environ. Res. Public Health 2016, 13, 846 7 of 19 The contaminated wastewater needs treatment(s) to remove or lower the concentration of pollutants to acceptable acceptable levels levels prior prior to to its its reuse reuse or or discharge discharge to to the the environment. environment. With With the the increase increase in thein the awareness awareness of ofpollutants’ pollutants’ consequences consequences on on hu humanman health health and and the the environment, environment, all all over the world, legislations on the discharge of pollutantspollutants are beingbeing tightened.tightened. As th thee result, strategies to improve thethe efficiency efficiency of of treatment treatment plants plants to clean to clean industrial industrial wastewater wastewater are being are developed. being developed. Figure1 Figuresummarizes 1 summarizes a generic a industrial generic industrial treatment treatmen plant. Thet plant. first stepsThe first involve steps physico-chemical involve physico-chemical treatment treatmentfor the removal for the of removal organic of or organic inorganic or pollutants, inorganic po and/orllutants, biological and/or treatmentsbiological treatments (removal of (removal organic pollutants),of organic pollutants), followed by followed a secondary by a treatment.secondary Thistreatment. secondary This treatmentsecondary leadstreatment to the leads generation to the generationbackwash effluents,backwash sludge effluents, and membranesludge and concentrates. membrane concentrates. Backwash effluents Backwash can beeffluents discharged can be or dischargedsent to a local or sent sewage to a treatment local sewage plant treatment if the discharge plant if criteriathe discharge are met. criteria Depending are met. upon Depending the type uponof contaminations, the type of contaminations, the products ofthe physico-chemical products of physico-chemical and biological and treatments biological will treatments be subjected will be to purificationsubjected to andpurification disinfection and priordisinfection to reuse prior [4]. to reuse [4]. Figure 1. Generic flow of industrial wastewater treatment plan (adapted and modified from [4]). Figure 1. Generic flow of industrial wastewater treatment plan (adapted and modified from [4]). In the physico-chemical treatment, approaches including advanced oxidation, nanofiltration, reverseIn theosmosis physico-chemical filtration, and treatment, activated carbon approaches filtration including are used advanced in removing oxidation, pollutants; nanofiltration, however thesereverse processes osmosis still filtration, remain and costly, activated especially carbon in the filtration context are of used full scale in removing treatment pollutants; [5–7]. In addition, however somethese of processes these approaches still remain generate costly, especiallyby-products in thethat context are toxic of to full the scale environment. treatment [5–7]. In addition, someBiological of these approaches treatment is generate based on by-products the biodegra thatdation are toxic of organic to the environment. pollutants by microorganisms presentBiological in wastewater treatment or isactivated based on sludge the biodegradation (AS, Figure 1). of However, organic pollutants many pollutants, by microorganisms especially presenthighly complex in wastewater compounds, or activated are not sludge efficientl (AS,y Figurebiodegraded1). However, by microorganisms; many pollutants, they especially may be resistanthighly complex to biodegradation, compounds, and are consequently not efficiently pers biodegradedist in the wastewater, by microorganisms; thus compromising they may water be quality.resistant To to overcome biodegradation, these limitations, and consequently bioaugmentation persist in strategies the wastewater, may be thus used. compromising Bioaugmentation water is quality.the addition To overcome of microorganisms these limitations, that have bioaugmentation the ability to strategiesbiodegrade may recalcitrant be used. Bioaugmentationmolecules in the pollutedis the addition environment. of microorganisms This approach that is have less-costl the abilityy and tofriendlier biodegrade to environment recalcitrant compared molecules to in the pollutedphysico-chemical environment. approaches. This approach The literature is less-costly has reported and friendlier many examples to environment of this approach compared for to the physico-chemicalremoval of contaminants approaches. in soil, The and literature we refer hasthe reportedreaders to many the following examples excellent of this approach reviews on for this the topicremoval [8–14]. of contaminants Bioaugmentation in soil, approaches and we refer have the been readers reviewed to the recently, following with excellent an emphasis reviews on operational challenges and wastewater plant management [15]. The current review focuses on the use of bioaugmentation on industrial wastewater exclusively, with an emphasis on microbiological Int. J. Environ. Res. Public Health 2016, 13, 846 3 of 20 this topic [8–14]. Bioaugmentation approaches have been reviewed recently, with an emphasis on operational challenges and wastewater plant management [15]. The current review focuses on the use of bioaugmentation on industrial wastewater exclusively, with an emphasis on microbiological aspects of bioaugmentation, and the biodegradation of recalcitrant organic pollutants found in industrial wastewater. We also intend to identify knowledge gaps for future research efforts. The pollutants discussed are chlorinated molecules, quinolines, dyes, polyaromatic compounds, gycol-ether, cyanide and nitrogen heterocyclic compounds. The pollutants commonly found in domestic wastewater such as carbohydrates, lipid and proteins, and nitrate are excluded from this review. In addition, limitations of bioaugmentation strategies are presented,