Table 1.

Overview of analytical protocols used for the determination of surfactant biodegradability

Type of surfactant	Microorganism(s)	Experimental setup	Initial concentration	Removal efficiency	Analytical method	Comment	Reference
Cationic surfactant—cetylpyridinium chloride (CPC)	Activated sludge	Fed-batch bioreactor	0.5 mg/L 0.05 mg/L	90% (0.05 mg/L) and 66% (0.5 mg/L) after 42 days	HPLC	Biomass was included during the recovery of the surfactant; sorption of the surfactant was taken into account.	Nguyen and Oh (2019)
Cationic surfactant—cocamidopropyl betaine (CAPB)	Activated sludge as well as Pseudomonas sp. and Rhizobium sp. strains	Aerobic flask experiments	200 mg/L (activated sludge), 300 mg/L (strains)	63% mineralization after 10 days (activated sludge), 90% after 4 days (strains)	CO2 respirometry (activated sludge), dissolved organic carbon (strains)	Sorption of surfactants is not an issue in case of mineralization studies; however, it was not taken into account during the determination of dissolved organic carbon. Measurement of dissolved organic carbon (DOC) is not a selective method and the results may be influenced by cell metabolites.	Merkova et al. (2018)
Cationic gemini surfactants	Activated sludge	CO2 headspace biodegradation test	12 mg C/L	2% after 28 days	CO2 respirometry	Due to the employed methodology the obtained results are not influenced by sorption of surfactants on the biomass.	Kaczerewska et al. (2018)
Cationic surfactants—quaternary ammonium compounds (QACs)	Activated sludge + Pseudomonas putida (ATCC 12633) and Aeromonas hydrophila MFB03 immobilized on alginate beads	Aerobic flask experiments	200 mg/L	90% after 24 h	Colorimetric method with the use of bromothymol blue	Sorption of surfactants on biomass, biomass immobilized on alginate beads and biomass-free alginate beads was determined. Due to the employed analytical method it is unclear whether the surfactant was mineralized or biotransformed.	Bergero and Lucchesi (2018)
Cationic gemini surfactants	River water microorganisms	OECD 301D	3 mg/L	72–77% after 28 days	Biochemical oxygen demand measurement	Sorption of surfactants is not an issue in case of mineralization studies; however, no control samples were included in the test, which would allow to exclude the presence of organic carbon.	Xu et al. (2017)
Anionic surfactants—sodium dodecylbenzenesulfonate (SDBS), sodium dodecyl sulfate (SDS), sodium lauryl ether sulfate (SLES)	3 monocultures: A. faecalis, E. cloacae, and S. marcescens	Aerobic flask experiments	10 mg/L	20–90% for SDBS, 25–95% for SDS, and 15–50% for SLES after 6 days	Methylene blue active substances (MBAS)	No data regarding surfactant recovery from biomass, no data regarding initial inoculum, the achieved OD values exceed the expected OD based on the amount of introduced carbon source by approx. 4 times.	Fedeila et al. (2018)
Anionic surfactant—sodium lauryl ether sulfate (SLES)	Soil microbial community	Soil microcosms (1 kg of soil)	75–100 mg/kg of soil	100% after 28 days	Pressurized liquid extraction + methylene blue active substances (MBAS)	It can be assumed that the issues associated with sorption were taken into account during the pressurized liquid extraction. Metabolites of SLES were not determined; hence, it is unclear whether the surfactant was mineralized or biotransformed.	Barra Caracciolo et al. (2019)
Anionic surfactants—linear alkylbenzene sulfonates (LAS)	Microbial community in commercial laundry wastewater and domestic sewage	Expanded granular sludge bed (EGSB) reactor	4 and 16 mg/L	79% after 98 days (4 mg/L) and 60% after 95 days (16 mg/L)	No detection method was given	The manuscript was focused on microbial community dynamics, whereas the analytical procedures associated with surfactant detection were not properly described. It is not possible to determine whether the removal of LAS results from degradation or sorption.	Centurion et al. (2018)
Anionic surfactants—sodium lauryl sulfate (SLS) and sodium lauryl ether sulfate (SLES)	Activated sludge	Anaerobic membrane bioreactor (AnMBR)	Approx. 110 mg/L (influent)	35–65% (effluent)	Methylene blue active substances (MBAS)	No data regarding surfactant recovery from biomass.	Cheng et al. (2018)
Anionic surfactant—sodium dodecyl sulfate (SDS)	Bacteria isolated from sediment and wastewater samples	Aerobic flask experiments	Approx. 29 g	37–51% after 10 days	HPLC	Biomass was not included in the determination of surfactants. It is plausible that the depletion of the surfactant concentration occurred due to sorption and not biodegradation.	Adekanmbi and Usinola (2017)
Anionic surfactants—linear alkylbenzene sulfonates (LAS)	Microbial communities from four freshwater and marine sediments	OECD 308	10 mg/L	0–63% after 160 days (depending on the sediment type)	Pressurized liquid extraction + UPLC-ToF-MS	Mass balance was carried out, based on the determination of LAS in aqueous and particulate phases.	Corada-Fernández et al. (2018)
Anionic surfactants—linear alkylbenzene sulfonates (LAS)	Activated sludge	Aerobic bottle tests	50–250 mg/L	54–100% after 10 days	Biochemical oxygen demand + HPLC	Biomass was not included in the determination of surfactants. Since LAS removal was based on HPLC results, it is plausible that the depletion of the surfactant concentration occurred due to sorption and not biodegradation.	Katam et al. 2018
Anionic surfactant—sodium lauryl ether sulfate (SLES)	Activated sludge	Aerobic and anoxic bottle tests	500 mg/L	78% (aerobic) and 41% (anoxic) after 14 days	Dissolved organic carbon test	Biomass was not included in the determination of surfactants. It is plausible that the depletion of the surfactant concentration occurred due to sorption and not biodegradation.	Paulo et al. (2017)
Non-ionic surfactant—nonylphenol polyethoxylate	Activated sludge, anaerobically digested sludge	Anaerobic semi-continuous digesters	3 mg/L	90% after 52 days	GC/MS	Biomass was included during the recovery of the surfactant	Kara Murdoch et al. (2018)
Non-ionic (amphoteric) surfactants—alkyl amine oxides	Activated sludge	OECD 314A and OECD 303A tests	25 and 50 μg/L	76% after 4 days (OECD 314A test) 97% after 36 days (OECD 303A test)	Liquid scintillation counting and radiolabelled thin layer chromatography	Comprehensive analysis of C14-labelled surfactant depletion was conducted and mass balance was carried out. Biomass was included during the recovery of the surfactant; Sorption of the surfactant was taken into account.	McDonough et al. (2018)
Non-ionic surfactants—alkyl ethoxylates (AEOs), nonylphenol ethoxylates (NPEOs) and polypropylene glycols (PPGs)	Groundwater and soil microorganisms	Anaerobic microcosms	Working concentration of 350 mg/L (after combination with groundwater)	90–99% after 15–19 days (AEOs), 100% after 19 days (NPEOs), 68% after 50 days (PPGs)	LC-ToF-MS, GC-MS	Sorption of the surfactant on biomass was taken into account. Mass balance was carried out and potential metabolites were analyzed.	Heyob et al. (2017)
Non-ionic (amphoteric) surfactants—alkyl amine oxides	Sludge from anaerobic digester	OxiTop Closed bottle test	100 mg organic carbon/L	60% after 22 days	CO2 and CH4 respirometry	Due to the employed methodology the obtained results are not influenced by sorption of surfactants on the biomass.	Rios et al. (2017)
Non-ionic surfactants—ethoxylated fatty alcohols and ethoxylated fatty acid methyl esters	Activated sludge	Small activated sludge plant unit	10 mg/L	84–94% after 21 days	Bismuth-active substance (BiAS) test	Biomass was not included in the determination of surfactants. It is plausible that the depletion of the surfactant concentration occurred due to sorption and not biodegradation.	Szwach and Lukosek (2017)