Bacterial ecology of abattoir wastewater treated by an anaerobic digestor

Identification of protein-degraders in an anaerobic digester by protein stable isotope probing and metagenomics

Presence of carbohydrates hampers protein degradation in anaerobic digesters. To understand this phenomenon, we used proteogenomics to identify the active protein-degraders in the presence of low and high carbohydrates concentrations. Active metabolic pathways of the identified protein-degraders were investigated using proteomics with 13C-protein substrates (protein stable isotope probing). Results showed that 1) Acinetobacter was the active protein-degraders under both protein-fed and protein-glucose mixture-fed conditions, 2) the relative abundance of Acinetobacter was not affected by the presence of carbohydrates, 3) the incorporation of the 13C-labelled protein substrate was predominantly observed in outer membrane-bound proteins and porin proteins, which are associated with proteinases or the transportation of amino acids across the cell wall. The Acinetobacter metabolic model and the incubation conditions suggested that glucose and proteins were degraded through anaerobic respiration. The negative impact of carbohydrates on protein biodegradation was attributed to Acinetobacter's preference for carbohydrates. This work highlights that efficient degradation of protein and carbohydrate mixtures in anaerobic digesters requires a staged or time-phased approach and enrichment of active protein-degraders, offering a new direction for process optimization in anaerobic digestion systems. KEY POINTS: • Acinetobacter identified for the first time as main anaerobic protein-degrader • Metabolic model revealed protein degradation via anaerobic respiration • Metabolic pathway analysis indicated SO42- or Fe3+ as terminal electron acceptors.

Effect of operational parameters on the performance of an anaerobic sequencing batch reactor (AnSBR) treating protein-rich wastewater

Treating protein-rich wastewater using cost-effective and simple-structured single-stage reactors presents several challenges. In this study, we applied an anaerobic sequencing batch reactor (AnSBR) to treat protein-rich wastewater from a slaughterhouse. We focused on identifying the key factors influencing the removal of chemical oxygen demand (COD) and the settling performance of the sludge. The AnSBR achieved a maximum total COD removal of 90%, a protein degradation efficiency exceeding 80%, and a COD to methane conversion efficiency of over 70% at organic loading rates of up to 6.2 g COD L-1 d-1. We found that the variations in both the organic loading rate within the reactor and the hydraulic retention time in the buffer tank had a significant effect on COD removal. The hydraulic retention time in the buffer tank and the reactor, which determined the ammonification efficiencies and the residual carbohydrate concentrations in the reactor liquid, affected the sludge settleability. Furthermore, the genus Clostridium sensu stricto 1, known as protein- and lipids-degraders, was predominant in the reactor. Statistical analysis showed a significant correlation between the core microbiome and ammonification efficiency, highlighting the importance of protein degradation as the governing process in the treatment. Our results will provide valuable insights to optimise the design and operation of AnSBR for efficient treatment of protein-rich wastewater.

Environmental impacts of an unlined municipal solid waste landfill on groundwater and surface water quality in Ibadan, Nigeria

Environmental and public health concerns grow on the interaction of municipal solid waste (MSW) leachates from unlined waste disposal sites with aquifers in many developing countries. This study investigated the environmental pollution impacts of an unlined MSW landfill at Ajakanga area, Ibadan, southwest Nigeria. Analytical studies indicated that the concentrations of NO₃^-, SO₄^2-, PO₄^3-, NH₄^-, Cl^-, Na, Fe, Mn, Cr, and Mo in the leachate samples exceeded the WHO wastewater discharge limits. Hydrochemical parameters of the groundwater and surface water were within WHO allowable thresholds, except for EC, TDS, Fe, Mn, and Pb in the groundwater and Pb, Cd, and Cu in the surface water, indicating major geogenic and minor MSW leachate impacts on the groundwater and surface water chemistry. Bacteria found in the leachate include Enterobacter cloacae (16.67%), Pseudomonas spp. (14.28%) and Bacillus spp. (9.52%). The geoelectrical imaging data indicated substratum leachate infiltration greater than 10 m deep, which is consistent with the low resistivity values of the topsoil-weathered basement layers. The health risk assessment showed high hazardous index values, indicating health risks of Mn, Cd and Pb in the surface water for the residents around Ajakanga landfill. Hydrochemical data indicated greater impact of the MSW leachates on the surface water than the groundwater, while geophysical data showed greater propensity of the surrounding aquifer to leachate interaction through fractured basement zone with increasing abstraction. Waste site closure and hydrochemical monitoring are suggested measures to mitigate environmental pollution in the study area.

The Microbial Genetic Diversity and Succession Associated with Processing Waters at Different Broiler Processing Stages in an Abattoir in Australia

The high organic content of abattoir-associated process water provides an alternative for low-cost and non-invasive sample collection. This study investigated the association of microbial diversity from an abattoir processing environment with that of chicken meat. Water samples from scalders, defeathering, evisceration, carcass-washer, chillers, and post-chill carcass rinsate were collected from a large-scale abattoir in Australia. DNA was extracted using the Wizard^® Genomic DNA Purification Kit, and the 16S rRNA v3-v4 gene region was sequenced using Illumina MiSeq. The results revealed that the Firmicutes decreased from scalding to evisceration (72.55%) and increased with chilling (23.47%), with the Proteobacteria and Bacteroidota changing inversely. A diverse bacterial community with 24 phyla and 392 genera was recovered from the post-chill chicken, with Anoxybacillus (71.84%), Megamonas (4.18%), Gallibacterium (2.14%), Unclassified Lachnospiraceae (1.87%), and Lactobacillus (1.80%) being the abundant genera. The alpha diversity increased from scalding to chilling, while the beta diversity revealed a significant separation of clusters at different processing points (p = 0.01). The alpha- and beta-diversity revealed significant contamination during the defeathering, with a redistribution of the bacteria during the chilling. This study concluded that the genetic diversity during the defeathering is strongly associated with the extent of the post-chill contamination, and may be used to indicate the microbial quality of the chicken meat.

The reliability of evaporation ponds as a final basin for industrial effluent: Demonstration of an environmental risk management methodology

Recognizing and assessing environmental risk are key components of every industry management strategy. Projects need to make sure that a detailed environmental risk management strategy is applied by methodically recognizing and addressing threats from internal and external influences to comply with regulatory standards for environmental preservation and safeguarding. This study's goal is to use a novel technique to assess the impact of environmental risks related to the use of evaporation ponds as final basins for industrial effluents. It employs qualitative and statistical methodologies to identify areas where engineering and managerial safeguards' structure, functioning, and lines of defense have flaws that might result in an ecologically hazardous occurrence. Additionally, it will offer a risk evaluation based on the gravity of the impact and the likelihood that the environmental occurrence would happen by using evaporation ponds to store industrial effluents. While the environmental threat would be entirely removed, it must be capable of reducing it to ALARP. The environmental risk assessment matrix will serve as a key factor in determining whether the environmental risk level linked with an evaporation pond is acceptable, as determined by the likelihood and impacts. The result of this research allows industrial units to recognize and control potential environmental risks associated with effluents by practically implementing a new environmental risk matrix based on several environmental and ecological effects with probability factors.•This study aims to assist industrial operators, especially power plants, manage environmental risk by combining ALARP concepts with other factors to evaluate risk acceptance and tolerance levels.•The Physico-chemical characteristics of effluent collected in the evaporation pond reveal that evaporation has a deleterious impact on such industrial effluent, as evidenced by a large increase in various effluent properties, some of which exceed the limit values.•A risk evaluation found that effluent collected in the evaporation pond has a detrimental negative impact on industrial effluents. This was evidenced by a significant rise in associated activities. This could increase the expense of operating and managing evaporation ponds, which could harm the ecosystem.

Biogas production and nutrients removal from slaughterhouse wastewater using integrated anaerobic and aerobic granular intermittent SBRs - Bioreactors stability and microbial dynamics

Slaughterhouse wastewater (SWW) was effectively treated in sequential anaerobic and aerobic granular intermittent sequencing batch reactors (ASBR+ISBR) for 665 days at different HRTs (48 h, 32 h, 24 h, and 12 h). The ASBR was stable at each HRT but performed relatively well at 12 h (OLR - 7.8-9.8 kg COD/m³-d) in terms of pollutants removal and biogas production than previously conducted research. The average biogas production was about 17.3 L/day having 70-76 % of CH₄ which could subsidize around 52 % of electricity demand while saving 103 US dollars/day if installed at full scale. In the case of post aerobic granular ISBR, carbon and nutrients removal (N&P) was achieved by enriching granules (1.7-2.2 mm) at low DO (0.5-0.8 mg/L) via the nitrite pathway. The ISBR was also well stable at 12 h HRT (average OLR of 2.1 kg COD/m³-d) and met the effluent discharge guidelines recommended by the Central Pollution Control Board of India. During steady-state conditions (12 h HRT), the average removal efficiencies for COD, TSS, O&G, TN, and PO₄-P were 98.8 %, 96.4 %, 98.7 %, 93.4 %, and 86.6 % respectively from combined ASBR and ISBR. The microbial analysis confirmed Euryarchaeota, Proteobacteria, Firmicutes, Chloroflexi, Bacteroidetes, Planctomycetes, and Synergistetes as the dominant phyla in ASBR. Methanosaeta (21.56 %) and Methanosarcina (6.48 %) were the prevailing methanogens for CH₄ production. The leading phyla observed in ISBR were Bacteroidetes, Proteobacteria, Firmicutes, Armatimonadetes, Verrucomicrobia, Chloroflexi, and Planctomycetes. Heterotrophic AOB (Thauera, Xanthomonadaceae, Pseudomonas, Sphingomonadaceae, and Rhodococcus) were mainly detected in the system for ammonia oxidation besides common autotrophic AOB. Similarly, a known PAO (Accumulibacter) was not identified but other PAO (Rhodocyclaceae, Dechloromonas, Pseudomonas, Flavobacteriaceae, and Sphingobacteriaceae) were prevalent inside aerobic granular ISBR that contributed to both carbon and nutrients removal. The results obtained would help implement the investigated reactor configurations at the pilot and full scale for SWW treatment.

Biogas Production and Microbial Communities of Mesophilic and Thermophilic Anaerobic Co-Digestion of Animal Manures and Food Wastes in Costa Rica

Biomass generated from agricultural operations in Costa Rica represents an untapped renewable resource for bioenergy generation. This study investigated the effects of two temperatures and three mixture ratios of manures and food wastes on biogas production and microbial community structure. Increasing the amount of fruit and restaurant wastes in the feed mixture significantly enhanced the productivity of the systems (16% increase in the mesophilic systems and 41% in the thermophilic). The methane content of biogas was also favored at higher temperatures. Beta diversity analysis, based on high-throughput sequencing of 16S rRNA gene, showed that microbial communities of the thermophilic digestions were more similar to each other than the mesophilic digestions. Species richness of the thermophilic digestions was significantly greater than the corresponding mesophilic digestions (F = 40.08, p = 0.003). The mesophilic digesters were dominated by Firmicutes and Bacteroidetes while in thermophilic digesters, the phyla Firmicutes and Chloroflexi accounted for up to 90% of all sequences. Methanosarcina represented the key methanogen and was more abundant in thermophilic digestions. These results demonstrate that increasing digestion temperature and adding food wastes can alleviate the negative impact of low C:N ratios on anaerobic digestion.

Hydrogen Sulfide Production with a Microbial Consortium Isolated from Marine Sediments Offshore

Hydrogen, electric energy production, and metal toxic bioremediation are some of the biotechnological applications of sulfate-reducing organisms, which potentially depend on the sulfide produced. In this study, offshore of Yucatan, the capacity to produce hydrogen sulfide using microbial consortia from marine sediment (SC469, PD102, SD636) in batch reactors was evaluated. Kinetic tests were characterized by lactate oxidation to acetate, propionate, CO2 and methane. The inoculum SC469, located in open-ocean, differed strongly in microbial diversity and showed better performance in substrate utilization with the highest hydrogen sulfide production (246 mmolg−1 VSS) at a specific hydrogen sulfide rate of 113 mmol g−1 VSS d−1 with a 0.79 molar ratio of sulfate/lactate. Sulfate-reducing microbial consortia enriched in the laboratory from marine sediments collected offshore in Yucatan and with a moderate eutrophication index, differed strongly in microbial diversity with loss of microorganisms with greater capacity for degradation of organic macromolecules. The sulfate-reducing microorganisms were characterized using Illumina MiSeq technology and were mainly Desulfomicrobium, Clostridium and Desulfobacter.

Effects of different amino acids and their configurations on methane yield and biotransformation of intermediate metabolites during anaerobic digestion

Anaerobic digestion (AD) comprises a series of biochemical reactions, with methane as one of the target products. Amino acids (AAs) are important molecular and primary intermediate products when protein is the main component of organic waste/wastewater. The L (levorotatory, left-handed)-configuration is natural for AAs, while D (dextrorotatory, right-handed) -AAs also widely exist in the natural environment and can be generated by racemization. However, the effects and underlying mechanisms of natural AAs and their enantiomers on the methane yield and the underlying mechanisms remain unclear. In this study, the effects of certain widespread L-AAs and their enantiomers on two-stage AD and the mechanisms therein were investigated. The AAs enantiomers showed variable or even opposite effects on different processes. The methane yield from a model monosaccharide (glucose) decreased by 57% with D-leucine addition. The butyrate generation and the methane yield from propionate were sensitive to the AA configuration and were inhibited by D-leucine by 80% and 61.8%, respectively, with D-leucine addition, while the volatile fatty acids concentration was slightly increased with the addition of L-leucine. The related mechanisms were further investigated in terms of key enzymes and microbial communities. The addition of D-Leucine decreased acetic acid production from homoacetogens by 30.2% due to the inhibition of key enzymes involved in hydrogen generation and consumption. The transform of butyryl CoA to butyryl phosphate was the rate-limiting step, with the related enzyme (phosphotransbutylase) was inhibited by D-leucine. Furthermore, the bacteria related to butyric acid generation and organic matter degradation were inhibited by D-leucine, while the methanogenic archaea remained stable irrespective of leucine addition. The effect of D-AAs on microorganisms is related to the type of sludge. In this study, the methanogenetic seed sludge was granular and did not dissociate after treatment; however, the D-AAs could trigger biofilm disassembly and reduce the stability of the sludge floc. The study provides a novel method for regulating AD by adding specific AAs with L or D configuration.

Characteristics of microbial community in EGSB system treating with oxytetracycline production wastewater

In order to realize the efficient and stable operation of anaerobic digestion for oxytetracycline (OTC) production wastewater which contains high concentration refractory organic matters and antibiotic residues, two laboratory-scale EGSB reactors (the experimental reactor and the control reactor) were constructed for pre-treating OTC production wastewater and the complex characteristics and connections among anaerobic fermentative bacteria, methanogens and fungi were analyzed. The experimental reactor gradually increased OTC doses of 0-200 mg/L by four phases compared with the control reactor which was fed without OTC addition during 280 days' operation. The average COD removal efficiency of 91.44% with the average OTC removal efficiency of 27.90% was achieved at OTC concentration of 200 mg/L. The addition of OTC did not affect the preponderant methanogen type, and Methanosaeta, a strict aceticlastic methanogen genus, was dominant both in working and controlling reactors on day 280. Redundancy analysis revealed that OTC and VFAs were the main environmental factors affecting the microbial communities and molecular ecological networks analysis indicated that the key genera principally belonged to Methanosaeta, Proteobacteria and Apiotrichum. Additionally, the fungi genus Apiotrichum might be related to the degradation of complex organic contaminants in OTC production wastewater treatment system.

Microbial Communities and Sulfate-Reducing Microorganisms Abundance and Diversity in Municipal Anaerobic Sewage Sludge Digesters from a Wastewater Treatment Plant (Marrakech, Morocco)

Both molecular analyses and culture-dependent isolation were combined to investigate the diversity of sulfate-reducing prokaryotes and explore their role in sulfides production in full-scale anaerobic digesters (Marrakech, Morocco). At global scale, using 16S rRNA gene sequencing, Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Synergistetes, and Euryarchaeota were the most dominant phyla. The abundance of Archaea (3.1–5.7%) was linked with temperature. The mcrA gene ranged from 2.18 × 105 to 1.47 × 107 gene copies.g−1 of sludge. The sulfate-reducing prokaryotes, representing 5% of total sequences, involved in sulfides production were Peptococcaceae, Syntrophaceae, Desulfobulbaceae, Desulfovibrionaceae, Syntrophobacteraceae, Desulfurellaceae, and Desulfobacteraceae. Furthermore, dsrB gene ranged from 2.18 × 105 to 1.92 × 107 gene copies.g−1 of sludge. The results revealed that exploration of diversity and function of sulfate-reducing bacteria may play a key role in decreasing sulfide production, an undesirable by-product, during anaerobic digestion.

Response of an aerobic granular and conventional flocculated reactors against changing feed composition from simple composition to more complex

This research evaluated the effect of changing feed composition on the performances of a conventional activated sludge (CAS) and an aerobic granular sludge (AGS) reactor operated simultaneously. Both reactors were initially fed with 100% synthetic feed. In a stepwise manner, the feed composition was slowly changed to real primary effluent collected from a local wastewater treatment plant. After an initial stabilization period, both reactors could achieve more than 90% NH₄⁺-N removal. However, PO₄^3--P removal eventually reached to a maximum of 92% in the AGS and 88% in the CAS. COD removal in both reactors was least affected, with the lowest percent removal of 81 ± 3% achieved in AGS and 62 ± 4% in CAS respectively when fed with 100% real wastewater. Despite granule breakage the AGS reactor was able to remove the pollutants (COD, N, P). The abundance of Candidatus Accumulibacter, a polyphosphate accumulating organism, in the AGS system increased over the operational phases: II (6.2%), III (10.32%), and IV (11.9%). While in CAS, it increased from phase I to phase II (12.6%), but decreased in phase III to 9.9%. Genus-based classification revealed a successive increase in the relative abundance of Nitrospira to 11.05% during Phase III and 10.3% during Phase IV in the AGS. In contrast with its presence in the CAS, which was, 3.4% during Phase III and 9.5% during Phase IV.

Assessment of groundwater pollution near Aba-Eku municipal solid waste dumpsite

Municipal solid waste (MSW) dumpsite constitutes a major anthropogenic point source of leachate contamination to the ambient groundwater and poses a significant threat to the geo-ecosystem. This study investigated the pollution of groundwater by leachate emanating from Aba-Eku MSW dumpsite in Ibadan, Nigeria, using bacteriological, hydrochemical, and geophysical techniques. There is a diversity of bacteria in the leachate and the dominant phyla being proteobacteria (83%) and firmicutes (17%). The mean concentrations (mg/L) of Mn, Fe, Al, Cu, Mo, and Cr in the leachate samples were above the World Health Organization wastewater discharge limits. The hydrochemical parameters of the groundwater samples around the dumpsite were generally within the permissible limits, except for K and Cl^-; which invariably indicate major inputs from water-rock interaction and minor contributions from the dumpsite. Three geoelectrical layers were indicated from the vertical electrical sounding data, which are the topsoil, the lateritic clay layer, and the weathered basement. Low resistivity values of 5-33 Ωm and 3-24 Ωm were obtained within 2 m and 5.5 m depths for the topsoil and the lateritic layer, respectively; while the 2-D subsurface model reveals leachate plume beyond 5 m. Although the MSW leachate is heterogeneous, the hydrochemical data show that the aquifer around the dumpsite has not been seriously polluted with the leachate, but there is a continuous percolation of leachate into the soil subsurface, based on the geophysical findings. Discontinuing waste dumping and groundwater extraction, which would over time reduce the leachate plume, are measures to enhance the groundwater quality in the area.

Anaerobic digestion of aqueous phase from pyrolysis of biomass: Reducing toxicity and improving microbial tolerance

Among the products of pyrolysis is an aqueous phase (AP), which contains a significant fraction of carbon but is too dilute to make recovery of this organic content cost-effectively. This study was to explore the use of AP for anaerobic digestion. Different treatment methods including overliming, Fenton's reagent oxidation, bleaching and activated carbon adsorption were investigated to reduce toxicity of AP. Overliming treatment increased biogas production up to 32-fold compared to non-treated AP. Enhancing the tolerance of the bacterial and archaeal community to the AP toxicity was also attempted with a directed evolution method, resulting the microbes' tolerance to AP from 5% to 14%. Directed evolution resulted a major bacterial taxa as Cloacimonetes, Firmicutes, and Chloroflexi, while shifted the predominant archaea shifted from acetoclastic to hydrogenotrophic methanogens. Collectively, the results demonstrated that combining feedstock treatment and directed evolution of the microbial community is an effective way for AP anaerobic digestion.

Biological wastewater treatment (anaerobic-aerobic) technologies for safe discharge of treated slaughterhouse and meat processing wastewater

Slaughterhouse industry generates considerable amount of wastewater rich in proteins, lipids, fibres, and carbohydrates. Numerous technologies such as electrocoagulation, membrane separation, advanced oxidation, physico-chemical processes, and biological treatment have been implemented for reducing the concentrations of these compounds. Nevertheless, this review aims to provide extensive information solely on the biological treatment (anaerobic and aerobic) of slaughterhouse wastewater. The advantages of anaerobic treatment are excellent organic matter removal, less sludge production, low energy requirement, execution of higher loading rates, and considerable production of biogas. Aerobic treatment on the other hand is a less sensitive process, possess lower start-up period, and efficient nutrient removal process. Numerous case studies are described to bestow maximum understanding of the wastewater characteristics, kind of treatment employed, and complications involved in managing and treating of slaughterhouse effluent. Additionally, role of microbial community involved in the treatment of slaughterhouse waste is also discussed. Sequential anaerobic and aerobic reactors are also reviewed in order to present their advantages over single bioreactors. Intermittent sequencing batch reactor is a promising technology than other high rate digesters in the removal of carbon, nitrogen, and phosphorous.

Comparison of microbial and physicochemical behavior of expanded granular sludge bed system during methylparaben and triclosan removal

Methylparaben and triclosan are antimicrobial agents widely used as preservatives in a variety of personal care and pharmaceutical products. Wastewater is considered the main source of these compounds in the environment. Expanded granular sludge bed (EGSB) reactors are a high rate technology for wastewater treatment based on biological processes and have been shown to be efficient in removing different types of compounds; however, little is known about the effect of contaminants such as methylparaben and triclosan on their behavior and effectiveness. In this study, we evaluate and compare the microbial and physicochemical behavior of EGSB systems during methylparaben and triclosan removal. The presence of different concentrations of pollutants had an influence on the cluster organization of microbial communities, especially bacteria. However, this did not affect the stability and performance of the EGSB systems. The banding patterns of the denaturing gradient gel electrophoresis of archaea demonstrated the constant presence and abundance of Methanosaeta concilii throughout all stages of operation, showing that this microorganism played a fundamental role in the stability of the reactors for the production of methane. The type of compound and its concentration influenced the expression of the mcrA and ACAs genes; however, these changes did not alter the stability and performance of the EGSB systems.

Improved methane production from sugarcane vinasse with filter cake in thermophilic UASB reactors, with predominance of Methanothermobacter and Methanosarcina archaea and Thermotogae bacteria

Biogas production from sugarcane vinasse has enormous economic, energy, and environmental management potential. However, methane production stability and biodigested vinasse quality remain key issues, requiring better nutrient and alkalinity availability, operational strategies, and knowledge of reactor microbiota. This study demonstrates increased methane production from vinasse through the use of sugarcane filter cake and improved effluent recirculation, with elevated organic loading rates (OLR) and good reactor stability. We used UASB reactors in a two-stage configuration, with OLRs up to 45gCODL^-1d^-1, and obtained methane production as high as 3LL^-1d^-1. Quantitative PCR indicated balanced amounts of bacteria and archaea in the sludge (10⁹-10¹⁰copiesg^-1VS), and of the predominant archaea orders, Methanobacteriales and Methanosarcinales (10⁶-10⁸copiesg^-1VS). 16S rDNA sequencing also indicated the thermophilic Thermotogae as the most abundant class of bacteria in the sludge.