Identification of microbial inhibitions and mitigation strategies towards cleaner bioconversions of palm oil mill effluent (POME): A review

Flourishing oil palm agroindustry inevitably produces voluminous pollutant-laden palm oil mill effluent (POME), which often treated by obsolete open ponding. By introducing foreign microbes, POME bioconversions confer simultaneous valorization and remediation of POME; however, environmental-sensitive microbes are prone to microbial inhibitions, which can upset the bioconversion. Herein, up to eight possible microbial inhibitions of POME bioconversions are identified and detailed after holistic review of multitudinous bioconversion routes. Potential microbial inhibitions include oil encapsulation, chemical inhibition, physical disruption, strict oxygen preference (O-2 toxicity/deficiency), extreme temperature (cold/thermal denaturation), extreme pH (acid/alkali toxicity), extreme salinity, and photoinactivation. To lessen microbial inhibitions in POME bioconversions, constructive mitigation strategies are classified into three aspects, viz substrate aspects (debris removal, supplementation, dilution, pretreatments, & co-substrates addition), microbial aspects (mixed cultures, immobilization, granulation, & gradual acclimation), and process aspects (thermophilic anaerobic/mesophilic aerobic pairs, continuous operation, pH control/adjustment, biosludge recycling/entrapment, & additional bioreactor). In authors' opinion, genetically modified microbes (GMM) application in POME bioconversions might be a promising research direction. Aforesaid superbugs can be engineered for efficient bioremediation, rapid proliferation, and high adaptability, which likely resolve all the aforesaid microbial inhibitions via genetic engineering. (C) 2020 Elsevier Ltd. All rights reserved.