Temporal variation in bacterial and methanogenic communities of three full-scale anaerobic digesters treating swine wastewater

Linking the shifts in the metabolically active microbiota in a UASB and hybrid anaerobic-aerobic bioreactor for swine wastewater treatment

Due to the high concentration of pollutants, swine wastewater needs to be treated prior to disposal. The combination of anaerobic and aerobic technologies in one hybrid system allows to obtain higher removal efficiencies compared to those achieved via conventional biological treatment, and the performance of a hybrid system depends on the microbial community in the bioreactor. Here, we evaluated the community assembly of an anaerobic-aerobic hybrid reactor for swine wastewater treatment. Sequencing of partial 16S rRNA coding genes was performed using Illumina from DNA and retrotranscribed RNA templates (cDNA) extracted from samples from both sections of the hybrid system and from a UASB bioreactor fed with the same swine wastewater influent. Proteobacteria and Firmicutes were the dominant phyla and play a key role in anaerobic fermentation, followed by Methanosaeta and Methanobacterium. Several differences were found in the relative abundances of some genera between the DNA and cDNA samples, indicating an increase in the diversity of the metabolically active community, highlighting Chlorobaculum, Cladimonas, Turicibacter and Clostridium senso stricto. Nitrifying bacteria were more abundant in the hybrid bioreactor. Beta diversity analysis revealed that the microbial community structure significantly differed among the samples (p < 0.05) and between both anaerobic treatments. The main predicted metabolic pathways were the biosynthesis of amino acids and the formation of antibiotics. Also, the metabolism of C5-branched dibasic acid, Vit B5 and CoA, exhibited an important relationship with the main nitrogen-removing microorganisms. The anaerobic-aerobic hybrid bioreactor showed a higher ammonia removal rate compared to the conventional UASB system. However, further research and adjustments are needed to completely remove nitrogen from wastewater.

Anaerobic co-digestion of landfill leachate and acid mine drainage using up-flow anaerobic sludge blanket reactor

A laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor was developed and constructed for the treatment of landfill leachate and acid mine drainage (AMD). The removal of chemical oxygen demand (COD), sulfate, and metal ions was studied. The maximum COD and sulfate removal efficiency reached 75% and 69%, respectively, during the start-up phase of the UASB. The hydraulic retention time (HRT) had a significant influence on the system. The maximum removal efficiency for COD and sulfate reached 83% and 78%, respectively, at an HRT of 20 h. The methane production process competed with the sulfate reduction process in the UASB. The fractionation of metals in the sludge was analyzed to facilitate metal recovery in a later processing stage. The most abundant sulfate-reducing bacteria was Desulfobulbus, and the methanogen archaeal community in the reactor was mainly composed of Methanobacterium.

Methanogenic Microorganisms in Industrial Wastewater Anaerobic Treatment

Over the past decades, anaerobic biotechnology is commonly used for treating high-strength wastewaters from different industries. This biotechnology depends on interactions and co-operation between microorganisms in the anaerobic environment where many pollutants’ transformation to energy-rich biogas occurs. Properties of wastewater vary across industries and significantly affect microbiome composition in the anaerobic reactor. Methanogenic archaea play a crucial role during anaerobic wastewater treatment. The most abundant acetoclastic methanogens in the anaerobic reactors for industrial wastewater treatment are Methanosarcina sp. and Methanotrix sp. Hydrogenotrophic representatives of methanogens presented in the anaerobic reactors are characterized by a wide species diversity. Methanoculleus sp., Methanobacterium sp. and Methanospirillum sp. prevailed in this group. This work summarizes the relation of industrial wastewater composition and methanogen microbial communities present in different reactors treating these wastewaters.

Evaluation of the factors limiting biogas production in full-scale processes and increasing the biogas production efficiency

Biogas production from sewage sludge volatile solids (VS) by anaerobic digestion slows down towards the end of the process, among inhibitory factors being pH increase upon ammonia accumulation, poorly digestible biomaterials, and high fixed solid (FS) content. The possibility of concentrating the digested sludge VS (41.7-56.6% on a dry weight basis) by surface and bottom layer separation with biogas post-production was studied. Furthermore, the potential to recycle concentrated VS and digested sludge back to the process after adjusting pH 7.0 to optimal for biogas-producing microbes and after acid, alkali, thermal, and sonolytic treatments was examined. In general, pH 7.0 control alone improved biogas production from the recycled digested sludge the most. An equally good improvement in biogas production was achieved by recycling the digested sludge, which had been heated until ammonia had evaporated and the pH dropped to 7.0 (1-2 h, 75 °C), and at the same time, VS was degraded. The biogas production from the sonicated and recycled sludge was almost as good as from the pH-adjusted, or heat-treated recycled sludge. After the acid and base treatments of the digested sludge, the recycled sludge yielded often the lowest biogas volume, as the added chemicals increased the FS concentration, which proved to be a more important inhibitory factor than poorly degradable VS. The high FS content significantly reduced the benefits of the treatments. By separating the surface and bottom layers with biogas post-production, the surface layer of VS was concentrated to 51.6-61.8%, while different compositions of the layers affected the biogas production.

The correlation between antibiotic resistance gene abundance and microbial community resistance in pig farm wastewater and surrounding rivers

Antimicrobial resistance gene (ARG) abundance and microbial resistance (MR) are often used as important indicators of pollution risk; however, the relationship between ARGs abundance and MR in pig farm wastewater remains unknown. In this study, the raw pig farm wastewater, effluent water, upstream river water, domestic wastewater and downstream river water samples were collected. The concentration of 20 subtypes of ARGs and 2 integrons, minimal inhibit concentration (MIC), and bacterial communities were investigated. In this study, 20 subtypes of ARGs and integrons were detected in all sampling sites. The highest abundance of 17 of the 20 subtypes of ARGs was detected in raw pig farm wastewater, and ermA had the maximum average abundance of 10⁸ copies/mL, with up to 2.41 ± 0.12 × 10⁸ copies/mL. There was no significant correlation between MR to three antibiotics (ciprofloxacin, streptomycin and tetracycline hydrochloride) and the abundance of their corresponding ARGs (P > 0.05), and a large difference was detected between the types of ARGs co-occur bacteria and resistance co-occur bacteria in the 5 sampling sites. And the pig farm wastewater treatment (WWT) could effectively reduce the ARGs and MR to the 3 antibiotics. The results presented here show that there may be no obvious correlation between ARGs and MCR in pig farm wastewater and surrounding rivers, which may be due to various environmental factors, highlighting the urgent need for a comprehensive evaluation of relationship between ARGs abundance and MR.

Contribution of electrodes and electric current to process stability and methane production during the electro-fermentation of food waste

Electro-fermentation is used as an alternative to conventional anaerobic digestion to enhance system stability and methane production from food waste. In particular, the contributions of electrode materials and an electric current are analyzed separately. The results showed that the introduction of electrodes (conductive carbon brushes without applied voltage) rapidly decreased the average concentration of volatile fatty acids (VFAs) from 6617 mg/L to 174 mg/L quickly, accelerated stabilization of digestion system, and improved methane production by 13.5%. When low voltage was supplied, the VFAs concentration declined to 129 mg/L, and methane production increased by 26.3%. Electric current stimulated the growth of hydrogenotrophic methanogens, but acetotrophic Methanosaeta still made up 27.6-61.9% of archaeal community. Geobacter occurred at the cathode with a low abundance. The energy contained in incremental methane was 4.55 times the consumption of electric energy, indicating the enhanced methanogenesis was mainly attributed to the improved digestion environment.

Single and combined inhibition of Methanosaeta concilii by ammonia, sodium ion and hydrogen sulfide

Single and combined inhibition of lag time λ and specific methanogenic activity R_CH4 of Methanosaeta concilii by NH₃, Na⁺ and H₂S were investigated using inhibition tests with a single inhibitor and a 3³ full-factorial experiment of NH₃, Na⁺ and H₂S concentrations (1.5 ≤ total ammonia nitrogen (TAN)/L ≤ 4.5 g, 1 ≤ Na⁺/L ≤ 4.3 g, 14.2 ≤ total hydrogen sulfide sulfur (THSS)/L ≤ 836 mg). All three inhibitors significantly increased λ and reduced R_CH4 of M. concilii. The half-maximal inhibitory concentrations of NH₃, Na⁺ and H₂S for M. concilii were 6.4 g TAN/L, 5.2 g Na⁺/L and 1.6 g THSS/L. Partial cubic models adequately approximated the corresponding response surfaces of λ and R_CH4 from the 3³ full-factorial experiment. The inhibitors inhibited R_CH4 synergistically, but inhibited λ in a complex manner. The combination of NH₃ and Na⁺ showed the strongest synergistic inhibition of both λ and R_CH4.

Evaluating the effect of biochar addition on the anaerobic digestion of swine manure: application of Py-GC/MS

The anaerobic digestion process of swine manure was studied when char was used as supplement for improving performance. The use of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was proposed for assessing the organic matter degradation. The assessment on biogas production was carried out using samples of swine manure (SM) supplemented with char in one case and pre-treated by microwave irradiation in the other. This experimental set-up allows for the comparison of the biological degradation observed under these two different configurations and therefore aids in understanding the effect of char particles on the process. Results showed similar performance for both systems, with an average improvement of 39% being obtained in methane production when compared to the single digestion of SM. The analysis of digestate samples by Fourier transform infrared (FTIR) spectroscopy and Py-GC/MS showed improved degradation of proteins, with the Py-GC/MS technique also capable of identifying an increase in microbial-derived material when char was added, therefore highlighting the relevant role of carbon conductive particles on biological systems. Py-GC/MS along with the use of FTIR spectroscopy has proven to be useful tools when evaluating anaerobic digestion.