Impact of anaerobic digestion and centrifugation/decanting processes in bacterial communities fractions

Enhanced methane production from source-separated human feces (brown water) by single phase anaerobic co-digestion: Effects of different co-substrates

Based on the concept of source separation of brown water (BW, human feces with flushing water) and yellow water (urine) in rural area, anaerobic co-digestion of BW with agricultural waste is a promising and effective method for rural waste treatment and resource recovery. The purpose of this study was to investigate the performance of different agricultural wastes (peanut straw (PST), peanut shell (PSH), swine wastewater acting as co-substrate for anaerobic co-digestion with BW, and the relative mechanisms were explored. When the mixed ratio was uniformly set as 1:1 (mass ratio, measured by volatile solid (VS)) and initial VS load as 20 g/L, the maximum cumulative methane production obtained by co-digestion (21 days) of BW and PST was 688 mL/g-VS, which performed better than the individual substrates (341 mL/g-VS), as well as the average of the sole BW and sole PST groups (531.2 mL/g-VS). The most impactful advantage was ascribed to the promotion of hydrolytic and acidogenic enzyme activities. The addition of PST also reduced the production of endogenous humus, which is difficult for biodegradation. Microbial community analysis showed that different co-substrates would affect the microbial community composition in the reactor. The relative abundance of hydrolytic acidogens in the PST and PSH co-digestion groups were higher than that in the SW co-digestion and sole BW groups, and the methanogenic archaea were dominated by the acetate-trophic Methanotrichaceae. The overall results suggest that anaerobic co-digestion is a feasible method, and co-digestion of BW and PST can improve methane production potential.

Metagenomics insights into the effect of co-landfill of incineration fly ash and refuse for bacterial community succession and metabolism pathway of VFAs production

With the development of incineration technologies, incineration has become the most common treatment method of municipal solid waste in China. However, stabilized fly ash may enter landfills during the transition from landfill to incineration, which caused uncertain impact on landfill waste stabilization. Two simulated co-landfill columns were constructed based on different co-landfill methods (layer co-landfill and mixed co-landfill) to investigate the effect of stabilized fly ash co-landfilled municipal solid waste for bacterial community succession and change in metabolic pathways during hydrolysis-acidogenesis stage. The mixed co-landfill method resulted in higher degree of organic matter degradation, and the concentrations of volatile fatty acids (VFA) and chemical oxygen demand (COD) in leachate were higher. The dominant phyla were Firmicutes in the layered co-landfill column and Bacteroidetes in mixed co-landfill column. The dominant genera for the total bacterial composition and VFA production were different, Pseudomonas and Propionibacterium, Proteiniphilum and unclassified Bacteroides were the dominant genera responsible for VFA generation in the layered and mixed co-landfill columns. The genes for butyrate production were enriched in the layered co-landfill column, whereas those related to acetate production were enriched in mixed co-landfill column. However, the layered co-landfill inhibited the microbial metabolic activity at the end of the co-landfill process.

Particle size as a driver of dewatering performance and its relationship to stabilization in fecal sludge

Poor and unpredictable dewatering performance of fecal sludge is a major barrier to sanitation provision in urban areas not served by sewers. Fecal sludge comprises everything that accumulates in onsite containments, and its characteristics are distinct from wastewater sludges and from feces. There is little fundamental understanding of what causes poor dewatering in fecal sludge. For the first time, we demonstrate that particle size distribution is a driver of dewatering performance in fecal sludge, and is associated with level of stabilization. Higher concentrations of small particles (<10 μm) and smaller median aggregate size (D50) corresponded to poor dewatering performance (measured by capillary suction time (CST) and supernatant turbidity) in field samples from Kenya and Uganda and in controlled laboratory anaerobic storage experiments. More stabilized fecal sludge (higher C/N, lower VSS/TSS) had better dewatering performance, corresponding to lower concentrations of small particles. Samples with the largest aggregates (D50 > 90 μm) had higher abundance of Gammaproteobacteria Pseudomonas, and samples with the smallest aggregates (D50 ≤ 50 μm) were characterized by higher abundance of Bacteroidetes Vadin HA17 and Rikenellaceae. Contrary to common perceptions, stabilization, particle size distribution, and dewatering performance were not dependent on time intervals between emptying of onsite containments or on time in controlled anaerobic storage experiments. Our results suggest that the stabilization process in onsite containments, and hence the dewaterability of sludge arriving at treatment facilities, is not dependent on time in containment but is more likely associated with specific microbial populations and the in-situ environmental conditions which promote or discourage their growth.

Fate of Clostridia and other spore-forming Firmicute bacteria during feedstock anaerobic digestion and aerobic composting

Pathogenic spore-forming Firmicutes are commonly present in animal and human wastes that are used as fertilizers in crop production. Pre-treatments of organic waste prior to land application offer the potential to abate enteric microorganisms, and therefore reduce the risk of contamination of crops or adjacent water resources with pathogens carried in these materials. The inactivation and reduction of gram-positive spore formers such as Clostridium spp., Clostridioides spp. and Bacillus spp. from animal and human waste can be challenging given the recalcitrance of the spores these bacteria produce. Given the significance of these organisms to human and animal health, information concerning spore-forming bacteria inactivation during anaerobic digestion (AD) and aerobic composting (AC) is required as the basis for recommending safe organic waste management practices. In this review, an assessment of the inactivation of spore-forming Firmicutes during AD and AC was conducted to provide guidance for practical management of organic matrices of animal or human origin. Temperature and pH may be the main factors contributing to the inactivation of spore-forming Firmicutes during batch lab-scale AD (log reduction <0.5-5 log). In continuous digesters, wet AD systems do not effectively inactivate spore-forming Firmicutes even under thermopholic conditions (log reduction -1.09 - 0.98), but dry AD systems could be a feasible management practice to inactivate spore-forming Firmicutes from organic materials with high solid content (log reduction 1.77-3.1). In contrast, composting is an effective treatment to abate spore-forming Firmicutes (log reduction 1.7-6.5) when thermophilic conditions last at least six consecutive days. Temperature, moisture content and composting scale are the key operating conditions influencing the inactivation of spore-forming Firmicutes during composting. Where possible, undertaking AD with subsequent composting to ensure the biosafety of digestate before its downstream processing and recycling is recommended to abate recalcitrant bacteria in digestate.

Dark fermentative hydrogen production from hydrolyzed sugar beet pulp improved by nitrogen and phosphorus supplementation

The effect of nitrogen and phosphorous addition on hydrogen production from hydrolyzed Sugar beet pulp (SBP) was investigated using (NH₄)₃PO₄, NH₄Cl and K₃PO₄ as the supplements. In batch tests, the maximal hydrogen production of 279 dm³/kgVS was observed for K₃PO₄, which was added to SBP in a dose of 1 g/dm³. In semi-continuous experiments, the greatest hydrogen production of 36 dm³/kgVS was reported for the same supplement, and this value was twice higher than that of the control run. The analysis of microbiota revealed that the majority of bacteria was affiliated to the orders Clostridiales, Lactobacillales and Coriobacteriales. Moreover, a noticeable methane production was associated with the activity of Methanosphaera sp., which could grow in a low pH environment of dark fermentation.

Relative Weight of Organic Waste Origin on Compost and Digestate 16S rRNA Gene Bacterial Profilings and Related Functional Inferences

Even though organic waste (OW) recycling via anaerobic digestion (AD) and composting are increasingly used, little is known about the impact of OW origin (fecal matters and food and vegetable wastes) on the end products' bacterial contents. The hypothesis of a predictable bacterial community structure in the end products according to the OW origin was tested. Nine OW treatment plants were selected to assess the genetic structure of bacterial communities found in raw OW according to their content in agricultural and urban wastes and to estimate their modifications through AD and composting. Two main bacterial community structures among raw OWs were observed and matched a differentiation according to the occurrences of urban chemical pollutants. Composting led to similar 16S rRNA gene OTU profiles whatever the OW origin. With a significant shift of about 140 genera (representing 50% of the bacteria), composting was confirmed to largely shape bacterial communities toward similar structures. The enriched taxa were found to be involved in detoxification and bioremediation activities. This process was found to be highly selective and favorable for bacterial specialists. Digestates showed that OTU profiles differentiated into two groups according to their relative content in agricultural (manure) and urban wastes (mainly activated sludge). About one third of the bacterial taxa was significantly affected by AD. In digestates of urban OW, this sorting led to an enrichment of 32 out of the 50 impacted genera, while for those produced from agricultural or mixed urban/agricultural OW (called central OW), a decay of 54 genera over 60 was observed. Bacteria from activated sludge appeared more fit for AD than those of other origins. Functional inferences showed AD enriched genera from all origins to share similar functional traits, e.g., chemoheterotrophy and fermentation, while being often taxonomically distinct. The main functional traits among the dominant genera in activated sludge supported a role in AD. Raw OW content in activated sludge was found to be a critical factor for predicting digestate bacterial contents. Composting generated highly predictable and specialized community patterns whatever the OW origin. AD and composting bacterial changes were driven by functional traits selected by physicochemical factors such as temperature and chemical pollutants.

Physico-chemical pre-treatments of anaerobic digestion liquor for aerobic treatment

Centrifugation of anaerobically digested sewage sludge gives rise to a solid phase, which could be employed as a fertilizer, and a liquid fraction (ADL), which should be treated before being spilled out. This is not an easy task because this liquor is characterized for presenting high COD (~16000 mg O₂/L), high ammonium content (~4000 mg/L) and low biodegradability (BOD₅/COD ~0.2). With the objective to pre-treat this aqueous waste before its treatment by means of more traditional aerobic processes, different physico-chemical methods (ultrasound, ozonation, hydrolysis and wet air oxidation) were assessed in this work. Ultrasound and thermal hydrolysis gave solubilizations around 47% and 68% respectively. The best results in terms of total COD removal were obtained when wet air oxidation (8 h, 160 C-200 °C and 6.0 MPa) and ozonation (8 h, 25 °C, 12 g/h O₃) techniques were employed achieving COD degradations of 71% and 38%, respectively. The pre-treatment of ADL with the four assayed techniques improved considerably the biodegradability (BOD₅/COD) of the effluent, with values around 0.3-0.4, depending on the treatment. The experimental data were successfully fitted by kinetic models and the kinetic constants for the solubilization and degradation steps were obtained. Application of the proposed models can be of interest for the optimization and selection of the most suitable techniques and operational conditions, in each particular case.

Effect of magnetite on anaerobic digestion of distillers grains and beet pulp: Operation of reactors and microbial community dynamics

It has been previously shown that magnetite (Fe₃O₄) nanoparticles stimulate the anaerobic digestion process in several anaerobic reactors. Here we evaluate the effect of magnetite nanoparticles on the efficiency of anaerobic digestion of distillers grains with solubles and sugar beet pulp in mesophilic batch experiments. The addition of magnetite nanopowder had a positive effect on the anaerobic digestion process. CH₄ was produced faster in the presence of 50 mg of Fe₃O₄ per 1 g of added total solids than from treatments without addition of Fe₃O₄. These results demonstrate that the addition of magnetite enhances the methanogenic decomposition of organic acids. Microbial community structure and dynamics were investigated based on bacterial and archaeal 16S rRNA genes, as well as mcrA genes encoding the methyl-CoM reductase. Depending on the reactor, Bacteroides, midas_1138, Petrimonas, unclassified Rikenellaceae (class Bacteroidia), Ruminiclostridium, Proteiniclasticum, Herbinix, and Intestinibacter (class Clostridia) were the main representatives of the bacterial communities. The archaeal communities in well-performed anaerobic reactors were mainly represented by representatives of the genera Methanosarcina and Methanobacterium. Based on our findings, Fe₃O₄ nanoparticles, when used properly, will improve biomethane production.

Dark fermentative hydrogen production from hydrolyzed sugar beet pulp improved by iron addition

This study evaluated the impact of three different iron compounds (Fe₂O₃, FeSO₄, FeCl₃) on hydrogen production via mesophilic dark fermentation (DF) of hydrolyzed sugar beet pulp (SBP). In batch tests, the maximum hydrogen yield of over 200 dm³H₂/kgVS was achieved with the addition of 0.1 gFe₂O₃/dm³, which was twice greater than the control. In semi-continuous experiments, the highest hydrogen production of 52.11 dm³H₂/kgVS combined with 19.4 dm³CH₄/kgVS methane yield was obtained at a dose of 1 gFe₂O₃/dm³. Acetic, lactic and caproic acids were the main metabolic products of DF. Microbiological studies showed some balance between hydrogen producing microorganisms from the order Clostridiales and lactic acid producers (LAB) affiliated with the orders Lactobacillales and Coriobacteriales. Moreover, the presence of methanogens affiliated to the genera Methanobrevibacter and Methanosphaera was also documented. An interesting finding was the appearance of rare bacteria from the genus Caproiciproducens, which was responsible for increased caproic acid production.

Performance of a forward osmotic membrane bioreactor for anaerobic digestion of waste sludge with increasing solid concentration

A forward osmotic membrane bioreactor for sludge anaerobic digestion (ad-OMBR) could realize high-solid digestion via drawing moisture out by forward osmosis (FO). Methane production and microbial community evolution were monitored in an ad-OMBR as the total solids (TS) content was gradually increased. With magnesium chloride (MgCl₂) and cellulose triacetate (CTA) membrane as a draw solution and FO membrane, respectively, the ad-OMBR exhibited better performance than the conventional digester, with higher solid content, organic degradation and methane content in biogas. The conductivity of the ad-OMBR did not increase, potentially because of the formation of struvite crystals aided by the reverse-fluxed Mg²⁺ ions. Microbial diversity increased along with the increase in solid content based on the Shannon index, while the most operational taxonomic units were obtained in the 8% TS sludge Although phylum Firmicutes decreased when the TS content was raised to 11%, the relative abundance of Proteobacteria, Chloroflexi, Actinobacteria, and Bacteroidetes, which could also degrade organic matter, increased with increasing TS in ad-OMBR. FO membrane fouling in ad-OMBR was highly reversible.