TY - JOUR
T1 - Anaerobic Conversion of Saline Phenol-Containing Wastewater Under Thermophilic Conditions in a Membrane Bioreactor
AU - Muñoz Sierra, Julian D.
AU - Garcia Rea, Victor S.
AU - Cerqueda-Garcia, Daniel
AU - Spanjers, Henri
AU - van Lier, Jules B.
PY - 2020
Y1 - 2020
N2 - Closing water loops in chemical industries result in hot and highly saline residual streams, often characterized by high strength and the presence of refractory or toxic compounds. These streams are attractive for anaerobic technologies, provided the chemical compounds are biodegradable. However, under such harsh conditions, effective biomass immobilization is difficult, limiting the use of the commonly applied sludge bed reactors. In this study, we assessed the long-term phenol conversion capacity of a lab-scale anaerobic membrane bioreactor (AnMBR) operated at 55°C, and high salinity (18 gNa+.L–1). Over 388 days, bioreactor performance and microbial community dynamics were monitored using specific methanogenic activity (SMA) assays, phenol conversion rate assays, volatile fatty acids permeate characterization and Illumina MiSeq analysis of 16S rRNA gene sequences. Phenol accumulation to concentrations exceeding 600 mgPh.L–1 in the reactor significantly reduced methanogenesis at different phases of operation, while applying a phenol volumetric loading rate of 0.12 gPh.L–1.d–1. Stable AnMBR reactor performance could be attained by applying a sludge phenol loading rate of about 20 mgPh.gVSS–1.d–1. In situ maximum phenol conversion rates of 21.3 mgPh.gVSS–1.d–1 were achieved, whereas conversion rates of 32.8 mgPh.gVSS–1.d–1 were assessed in ex situ batch tests at the end of the operation. The absence of caproate as intermediate inferred that the phenol conversion pathway likely occurred via carboxylation to benzoate. Strikingly, the hydrogenotrophic SMA of 0.34 gCOD-CH4.gVSS–1.d–1 of the AnMBR biomass significantly exceeded the acetotrophic SMA, which only reached 0.15 gCOD-CH4.gVSS–1.d–1. Our results indicated that during the course of the experiment, acetate conversion gradually changed from acetoclastic methanogenesis to acetate oxidation coupled to hydrogenotrophic methanogenesis. Correspondingly, hydrogenotrophic methanogens of the class Methanomicrobia, together with Synergistia, Thermotogae, and Clostridia classes, dominated the microbial community and were enriched during the three phases of operation, while the aceticlastic Methanosaeta species remarkably decreased. Our findings clearly showed that highly saline phenolic wastewaters could be satisfactorily treated in a thermophilic AnMBR and that the specific phenol conversion capacity was limiting the treatment process. The possibility of efficient chemical wastewater treatment under the challenging studied conditions would represent a major breakthrough for the widespread application of AnMBR technology.
AB - Closing water loops in chemical industries result in hot and highly saline residual streams, often characterized by high strength and the presence of refractory or toxic compounds. These streams are attractive for anaerobic technologies, provided the chemical compounds are biodegradable. However, under such harsh conditions, effective biomass immobilization is difficult, limiting the use of the commonly applied sludge bed reactors. In this study, we assessed the long-term phenol conversion capacity of a lab-scale anaerobic membrane bioreactor (AnMBR) operated at 55°C, and high salinity (18 gNa+.L–1). Over 388 days, bioreactor performance and microbial community dynamics were monitored using specific methanogenic activity (SMA) assays, phenol conversion rate assays, volatile fatty acids permeate characterization and Illumina MiSeq analysis of 16S rRNA gene sequences. Phenol accumulation to concentrations exceeding 600 mgPh.L–1 in the reactor significantly reduced methanogenesis at different phases of operation, while applying a phenol volumetric loading rate of 0.12 gPh.L–1.d–1. Stable AnMBR reactor performance could be attained by applying a sludge phenol loading rate of about 20 mgPh.gVSS–1.d–1. In situ maximum phenol conversion rates of 21.3 mgPh.gVSS–1.d–1 were achieved, whereas conversion rates of 32.8 mgPh.gVSS–1.d–1 were assessed in ex situ batch tests at the end of the operation. The absence of caproate as intermediate inferred that the phenol conversion pathway likely occurred via carboxylation to benzoate. Strikingly, the hydrogenotrophic SMA of 0.34 gCOD-CH4.gVSS–1.d–1 of the AnMBR biomass significantly exceeded the acetotrophic SMA, which only reached 0.15 gCOD-CH4.gVSS–1.d–1. Our results indicated that during the course of the experiment, acetate conversion gradually changed from acetoclastic methanogenesis to acetate oxidation coupled to hydrogenotrophic methanogenesis. Correspondingly, hydrogenotrophic methanogens of the class Methanomicrobia, together with Synergistia, Thermotogae, and Clostridia classes, dominated the microbial community and were enriched during the three phases of operation, while the aceticlastic Methanosaeta species remarkably decreased. Our findings clearly showed that highly saline phenolic wastewaters could be satisfactorily treated in a thermophilic AnMBR and that the specific phenol conversion capacity was limiting the treatment process. The possibility of efficient chemical wastewater treatment under the challenging studied conditions would represent a major breakthrough for the widespread application of AnMBR technology.
KW - AnMBR
KW - high salinity
KW - hydrogenotrophic activity
KW - microbial community
KW - phenol
KW - thermophilic
UR - http://www.scopus.com/inward/record.url?scp=85092734173&partnerID=8YFLogxK
U2 - 10.3389/fbioe.2020.565311
DO - 10.3389/fbioe.2020.565311
M3 - Article
AN - SCOPUS:85092734173
SN - 2296-4185
VL - 8
SP - 1
EP - 12
JO - Frontiers in Bioengineering and Biotechnology
JF - Frontiers in Bioengineering and Biotechnology
M1 - 565311
ER -