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.

中文翻译：

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膜生物反应器中高温条件下含盐苯酚废水的厌氧转化

关闭化学工业中的水回路会产生高温和高盐度的残留水流，通常具有高强度和难熔或有毒化合物的特点。如果化合物是可生物降解的，这些流对厌氧技术很有吸引力。然而，在如此恶劣的条件下，生物质的有效固定很困难，限制了常用污泥床反应器的使用。在本研究中，我们评估了在 55°C 和高盐度 (18 gNa+.L–1) 下运行的实验室规模厌氧膜生物反应器 (AnMBR) 的长期苯酚转化能力。在超过 388 天的时间里，使用特定产甲烷活性 (SMA) 测定、苯酚转化率测定、挥发性脂肪酸渗透特性和 Illumina MiSeq 分析 16S rRNA 基因序列。苯酚在反应器中积累到超过 600 mgPh.L-1 的浓度会显着降低不同操作阶段的产甲烷量，同时应用 0.12 gPh.L-1.d-1 的苯酚体积加载率。稳定的 AnMBR 反应器性能可以通过应用约 20 mgPh.gVSS–1.d–1 的污泥苯酚负载率来实现。实现了 21.3 mgPh.gVSS–1.d–1 的原位最大苯酚转化率，而在操作结束时在非原位批量测试中评估了 32.8 mgPh.gVSS–1.d–1 的转化率。不存在作为中间体的己酸表明苯酚转化途径可能通过羧化为苯甲酸而发生。引人注目的是，0.34 gCOD-CH4.gVSS–1 的氢营养型 SMA。AnMBR 生物量的 d-1 显着超过了乙酸营养型 SMA，仅达到 0.15 gCOD-CH4.gVSS-1.d-1。我们的结果表明，在实验过程中，乙酸盐转化逐渐从乙酰碎屑产甲烷转变为乙酸盐氧化与氢营养产甲烷相结合。相应地，甲烷微生物类的氢营养产甲烷菌，连同协同菌、嗜热菌和梭菌类，在微生物群落中占主导地位，并在三个运行阶段中富集，而醋酸甲烷菌则显着减少。我们的研究结果清楚地表明，高盐酚类废水可以在嗜热 AnMBR 中得到令人满意的处理，并且特定的苯酚转化能力限制了处理过程。