Anaerobic Conversion of Saline Phenol-Containing Wastewater Under Thermophilic Conditions in a Membrane Bioreactor

Abstract

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-CH 4. gVSS −1. d −1 of the AnMBR biomass significantly exceeded the acetotrophic SMA, which only reached 0.15 gCOD-CH 4. 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

Directional Selection of Microbial Community Reduces Propionate Accumulation in Glycerol and Glucose Anaerobic Bioconversion Under Elevated pCO2

“…Secondary metabolites in the liquid medium (acetate, propionate, butyrate, and valerate) were measured by gas chromatography (7890A GC; Agilent Technologies, United States) according to the method described by Muñoz Sierra et al (2020) . The gas composition of samples stabilized at atmospheric conditions was determined via gas chromatography (7890A GC; Agilent Technologies, United States) using a thermal conductivity detector operated at 200°C and oven temperature ramping from 40 to 100°C.…”

Steering the product spectrum in high-pressure anaerobic processes: CO2 partial pressure as a novel tool in biorefinery concepts

“…Secondary metabolites, i.e., acetate, propionate, butyrate and valerate were measured from filtered (0.45 μm) liquid samples by gas chromatography (7890A GC, Agilent Technologies, US) according to [ 97 ]. The detection limits for these compounds were 12, 16, 18 and 23 mg L −1 , respectively.…”

Syntrophic acetate oxidation having a key role in thermophilic phenol conversion in anaerobic membrane bioreactor under saline conditions

“…The membrane module was operated with a cross-flow velocity of 0.8 ± 0.1 m⋅s − 1 and a constant flux of 4.0 LMH (Q = 1 L/d). The inoculum biomass was obtained from a full-scale UASB reactor treating petrochemical wastewater (Shell Moerdijk, The Netherlands), and it was acclimated and used in previous experiments [29]. The reactor was mixed thoroughly by biomass recirculation at a rate of 200 d − 1 .…”

“…Previous research showed the feasibility of phenol degradation under saline and thermophilic conditions [29]. Nevertheless, there is a lack of understanding of the process, which is needed for guaranteeing process stability.…”