Continuous dechlorination of tetrachloroethene in an upflow anaerobic sludge blanket reactor

Study on the community structure and function of anaerobic granular sludge under trichloroethylene stress

Trichloroethylene (TCE) is one of the most common groundwater pollutants. It is carcinogenic, teratogenic, mutagenic and poses a serious threat to human health and the environment. Therefore, reducing the environmental toxicity of TCE is of great significance. Anaerobic sludge was cultured and acclimated in an upflow anaerobic sludge blanket (UASB) reactor in this study. The Chemical Oxygen Demand (COD) concentration of the influent was approximately 2500 mg L^-1, and the TCE concentration of the influent ranged from 1.46 mg L^-1 to 73 mg L^-1. After biodegradation of the anaerobic microflora, the COD removal rate was approximately 85%, and the TCE removal rate was over 85%. The microbial community of anaerobic sludge was analysed by 16 S rDNA clone libray and 454 high-throughput sequencing. Through analysis of the sequencing results, we found that there were a variety of acid-forming bacteria, anaerobic dechlorinating bacteria, and methanogenic bacteria. Based on the analysis of microflora function, it was speculated that the TCE metabolic pathway took place in UASB reactors. Desulfovibrio and Syntrophobacter provided an anaerobic environment, and acid-forming bacteria metabolise organic compounds into hydrogen. With Dehalobacter and Geobacter, TCE as an electron acceptor is dechlorinated and reduced under the anaerobic environment, in which hydrogen acts as an electron donor. By this, we clarified the metabolic pathway for improving TCE bioremediation.

Characterisation and cleaning of biogas from sewage sludge for biomethane production

This study investigates the conversion of sewage sludge from wastewater treatment plants (WWTP) into biomethane for automotive fuel or grid injection. A prototype plant was monitored in Northern Italy, based on vacuum swing adsorption (VSA) on synthetic zeolite 13×: this biogas upgrading method is similar to pressure swing adsorption (PSA) and commonly used for other kinds of biomass. Measurements of biogas inlet, biomethane outlet and off-gas were performed including CH₄, CO₂, CO, H₂, O₂, N₂, HCl, HF, NH₃, H₂S and volatile organic compounds (VOCs). Critical levels were observed in the biogas for of H₂S and HCl, whose concentrations were 1570 and 26.8 mg m^-3, respectively. On the other hand, the concentration of halogenated VOCs (including tetrachloroethylene and traces of perfluoroalkilated substances, PFAS) and mercaptans were relatively low. A simultaneous and reversible adsorption on 13× zeolite was achieved for H₂S and CO₂, and carbon filters played a minor role in desulfurisation. The presence of HCl is due to clarifying agents, and its removal is necessary in order to meet the required biomethane characteristics: an additional carbon-supported basic adsorbent was successfully used to remove this contaminant. This study also highlights the interference of CO₂ towards HCl if sampling is performed in compliance with the new EU standard for biomethane. High total volatile silicon (TVS) was confirmed in sewage sludge biogas, with a major contribution of siloxane D5: the suitability of this compound as an indicator of total siloxanes is discussed. Results demonstrate that volatile methyl siloxanes (VMS) do not represent a critical issue for the VSA upgrading methodology.

Coupling Bioflocculation of Dehalococcoides mccartyi to High-Rate Reductive Dehalogenation of Chlorinated Ethenes

Continuous bioreactors operated at low hydraulic retention times have rarely been explored for reductive dehalogenation of chlorinated ethenes. The inability to consistently develop such bioreactors affects the way growth approaches for Dehalococcoides mccartyi bioaugmentation cultures are envisioned. It also affects interpretation of results from in situ continuous treatment processes. We report bioreactor performance and dehalogenation kinetics of a D. mccartyi-containing consortium in an upflow bioreactor. When fed synthetic groundwater at 11-3.6 h HRT, the upflow bioreactor removed >99.7% of the influent trichloroethene (1.5-2.8 mM) and produced ethene as the main product. A trichloroethene removal rate of 98.51 ± 0.05 me^- equiv L^-1 d^-1 was achieved at 3.6 h HRT. D. mccartyi cell densities were 10¹³ and 10¹² 16S rRNA gene copies L^-1 in the bioflocs and planktonic culture, respectively. When challenged with a feed of natural groundwater containing various competing electron acceptors and 0.3-0.4 mM trichloroethene, trichloroethene removal was sustained at >99.6%. Electron micrographs revealed that D. mccartyi were abundant within the bioflocs, not only in multispecies structures, but also as self-aggregated microcolonies. This study provides fundamental evidence toward the feasibility of upflow bioreactors containing D. mccartyi as high-density culture production tools or as a high-rate, real-time remediation biotechnology.

Dehalococcoides as a Potential Biomarker Evidence for Uncharacterized Organohalides in Environmental Samples

The massive production and improper disposal of organohalides resulted in worldwide contamination in soil and water. However, their environmental survey based on chromatographic methods was hindered by challenges in testing the extremely wide variety of organohalides. Dehalococcoides as obligate organohalide-respiring bacteria exclusively use organohalides as electron acceptors to support their growth, of which the presence could be coupled with organohalides and, therefore, could be employed as a biomarker of the organohalide pollution. In this study, Dehalococcoides was screened in various samples of bioreactors and subsurface environments, showing the wide distribution of Dehalococcoides in sludge and sediment. Further laboratory cultivation confirmed the dechlorination activities of those Dehalococcoides. Among those samples, Dehalococcoides accounting for 1.8% of the total microbial community was found in an anaerobic granular sludge sample collected from a full-scale bioreactor treating petroleum wastewater. Experimental evidence suggested that the influent wastewater in the bioreactor contained bromomethane which support the growth of Dehalococcoides. This study demonstrated that Dehalococcoides could be employed as a promising biomarker to test the present of organohalides in wastestreams or other environmental samples.

Performance of an anaerobic, static bed, fixed film bioreactor for chlorinated solvent treatment

Anaerobic, fixed film, bioreactors bioaugmented with a dechlorinating microbial consortium were evaluated as a potential technology for cost effective, sustainable, and reliable treatment of mixed chlorinated ethanes and ethenes in groundwater from a large groundwater recovery system. Bench- and pilot-scale testing at about 3 and 13,500 L, respectively, demonstrated that total chlorinated solvent removal to less than the permitted discharge limit of 100 μg/L. Various planned and unexpected upsets, interruptions, and changes demonstrated the robustness and reliability of the bioreactor system, which handled the operational variations with no observable change in performance. Key operating parameters included an adequately long hydraulic retention time for the surface area, a constant supply of electron donor, pH control with a buffer to minimize pH variance, an oxidation reduction potential of approximately -200 millivolts or lower, and a well-adapted biomass capable of degrading the full suite of chlorinated solvents in the groundwater. Results indicated that the current discharge criteria can be met using a bioreactor technology that is less complex and has less downtime than the sorption based technology currently being used to treat the groundwater.

Effect of hydraulic retention time (HRT) on the biodegradation of trichloroethylene wastewater and anaerobic bacterial community in the UASB reactor

This study utilizes the unique merits of an 8-L laboratory upflow anaerobic sludge blanket (UASB) reactor for treating synthetic wastewater containing trichloroethylene (TCE). The reactor was operated at different hydraulic retention times (HRT) of 25, 20, 15, 10, and 5 h. TCE removal efficiency decreased from 99 to 85 % when the HRT was lowered down from 25 to 5 h, as well as chemical oxygen demand (COD) removal efficiency (from 95 to 84.15 %). Using Illumina 16S rRNA gene MiSeq sequencing, we investigated the evolution of bacterial communities in the anaerobic sludge under five different conditions of HRT. In total, 106,387 effective sequences of the 16S rRNA gene were generated from 5 samples that widely represented the diversity of microbial community. Sequence analysis consisting of several novel taxonomic levels ranging from phyla to genera revealed the percentages of these bacterial groups in each sample under different HRTs. The differences found among the five samples indicated that HRT had effects on the structures of bacterial communities and the changes of bacterial communities associated with the effect of HRT on the performance of the reactor. Sequence analyses showed that Bacteroidetes and Firmicutes were the dominant phyla. It is notable that the class Dehalococcoidia was found in the samples at HRT of 5, 10, 20, and 25 h, respectively, in which there were some dechlorination strains. Moreover, a tremendous rise of TCE removal efficiency from HRT of 5 h to HRT of 10 h was found.

Performance of UASB reactor in the biotreatment of 1,1,2-Trichloroethane

This article aims to examine the performance of bench-scale Upflow Anaerobic Sludge Blanket (UASB) reactor operated under varying operating conditions, during the treatment of simulated wastewater containing 1,1,2-Trichloroethane (TCA). Initially, reactor R1 (control) and reactor R2 (test) containing TCA were operated at 5 different Hydraulic Retention Times (HRTs) of 36, 30, 24, 18 and 12 hours. TCA removal decreased from 99.8% to 96.5%, when the HRT was reduced from 36 to 12 hours in discrete steps. Later, when the OLR was varied periodically from 1.5 to 3.1 kg COD/m(3).d to obtain a different substrate: co-substrate ratios; lower TCA removal efficiencies were observed at an OLR of 2.5 kg COD/ m(3).d and above. The average effluent concentrations of TCA and COD were 0.12 and 79 mg/L, respectively, at the optimum HRT of 24 hours; whereas the effluent TCA and COD concentrations at the substrate: co-substrate ratio of 50:1 was 0.06 mg/L and 48 mg/L, respectively.