Table 2.

Limitations of bioaugmentation and potential solutions to overcome these limitations for industrial wastewater treatment.

Main Objectives	Limitations	Potential Solutions	Remarks	References
Overcoming low growth or washout of bioaugmented bacteria	Low inocula can lead to limited survival of bioaugmented bacteria	Use of high inocula, at least 106–107 cells per mL. Monitoring of growth of bioaugmented bacteria (followed by the addition of new bacteria)	Has been tested with encouraging results in groundwater	[57]
	Lysis of bacteria by viral (bacteriophage) infections	Monitoring of growth of bioaugmented bacteria (followed by the addition of new bacteria)	Several approaches exist to monitor bacterial levels in wastewater	[15,57]
	Limited bacterial growth as the result of low quorum sensing (QS)	Use of QS inducers to increase bacterial growth. Monitoring of growth of bioaugmented bacteria	Has been evaluated in laboratory scale, but cost may be a limitation in full scale treatment	[78,79,80]
Increase of efficiency of bioaugmentation	Low biochemical ability of bioaugmented bacteria to biodegrade pollutants	Use of genetically modified organisms encoding catabolic efficient enzymes	Has been tested with encouraging results	[84,85,86,87,88,89]
		Use of plasmids encoding catabolic efficient enzymes	Potentially attractive, but so far, not clear evidence of success due to the uncertainty of incorporation of plasmids into receiving organisms	[96,97]
	Low ability of bioaugmented bacteria to biodegrade pollutants	Use of immobilized bioaugmented bacteria	Has been evaluated with encouraging results, but cost may be a limitation in full scale treatment	[72,73,74,75]
		Exploitation of nanotechnology with the use of nanomaterial (NM) along with bioaugmented bacteria to increase biodegradation	NM (at low concentration) increases bacterial growth and the rates of biochemical reactions. Approach is promising but more studies are still needed to ascertain this evidence.	[105,106,108,109]
		Use of functionalized bioaugmented bacteria by fixing NM on their surface to increase bio-availability of pollutants	Promising approach, based one study, thus more studies are needed to support this technology	[110]