Anaerobic Co-digestion Of Waste Activated Sludge Research Articles

Microbial community changes and metabolic pathways analysis during waste activated sludge and meat processing waste anaerobic co-digestion

Waste activated sludge (WAS) and meat processing waste (MPW) were acted as co-substrates in anaerobic co-digestion (AcD), and biochemical methane potential (BMP) test was carried out to investigate the methane production performances. Microbial community structure and metabolic pathways analyses were conducted by 16S rRNA high-throughput sequencing and functional prediction analysis. BMP test results indicated that AcD of 70% WAS+30% MPW and 50% WAS+50% MPW (VS/VS) could significantly improve methane yield to 371.05 mL/g VS and 599.61 mL/g VS, respectively, compared with WAS acting as sole substrate (191.87 mL/g VS). The results of microbial community analysis showed that Syntrophomonas and Petrimonas became the dominant bacteria genera, and Methanomassiliicoccus and Methanobacterium became the dominant archaea genera after MPW addition. 16S functional prediction analysis results indicated that genes expression of key enzymes involved in syntrophic acetate oxidation (SAO), hydrogenotrophic and methylotrophic methanogenesis were up-regulated, and acetoclastic methanogenesis was inhibited after MPW addition. Based on these analyses, it could be inferred that SAO combined with hydrogenotrophic and methylotrophic methanogenesis was the dominant pathway for organics degradation and methane production during AcD. These findings provided systematic insights into the microbial community changes and metabolic pathways during AcD of WAS and MPW.

Taking Advantage of Waste Heat Resource from Vinasses for Anaerobic Co-digestion of Waste Activated Sludge under the Thermophilic Condition: Energy Balance and Kinetic Analysis.

Vinasses are not only an easily biodegradable substrate but also a heat energy resource. In this study, the energy balance and kinetic model of anaerobic co-digestion of waste activated sludge (WAS) with vinasses have been investigated in semicontinuous reactor experiments at 55 °C. Herein, the maximum energy balance value, the ratio of energy to mass, and the kinetic constants μmax and K of anaerobic digestion of WAS were −33.44 kJ·day–1, −5.72 kJ·VS–1·day–1, and 0.0894 day–1 and 0.7294, respectively, at an organic loading rate (OLR) of 1.17 VS·L–3·day–1; when the mixture ratio of WAS to vinasses was 2:1 (dry VS) for co-digestion, the maximum energy balance value, the maximum ratio of energy to mass, and the kinetic constants μmax and K of anaerobic co-digestion of WAS and vinasses were +39.73 kJ·day–1, 8.1 kJ·VS–1·day–1, and 0.2619 day–1 and 1.9583, respectively, at an OLR of 1.73 VS·L–3·day–1. The positive energy balance was obtained for two reasons: one is for making the best use of the high-temperature heat energy resource of vinasses and the other is for enhancing the amount of biogas yield. The bottleneck of the negative energy balance of thermophilic digestion of WAS can be broken by anaerobic co-digestion of WAS and vinasses. The results indicate a promising future in the application of anaerobic thermophilic co-digestion of WAS and vinasses. Methane production from digestion and co-digestion was also predicted by the Chen–Hashimoto kinetic model.

Fat, oil, and grease (FOG) deposits yield higher methane than FOG in anaerobic co-digestion with waste activated sludge

The formation of fat, oil, and grease (FOG) deposits in sewers is a global challenge for the maintenance of sewer collection systems. Tons of FOG deposits (FDs) are removed from sewer systems every year and present an opportunity for increased methane production via anaerobic co-digestion with waste activated sludge (WAS) at water resource recovery facilities with existing anaerobic digesters. We hypothesized that FDs have higher biomethane potential than that of FOG (e.g., FOG collected in grease interceptors), because of the reduction of inhibition of long chain fatty acids due to saponification. In this study, substantially enhanced methane production was found in anaerobic co-digestion of WAS with FDs within the substrate to inoculum (S/I) ratio range of 0.25–1.2, and the maximum ultimate methane production (685.7 ± 24.1 mL/gVSadded, at S/I = 0.5) was 4.0 times higher than in the control (with WAS only) after 42 days of incubation. Although the lag phase period was longer in FD co-digestion (S/I = 0.5) than in FOG co-digestion (S/I = 0.5) under the same organic loading (gVS) and two times the COD loading, the daily methane production rate became higher after Day 15 in FD co-digestion. Significantly higher cumulative methane production (10.2%, p < 0.05) was obtained in FD co-digestion than in FOG co-digestion after 42-days. Microbial community analysis revealed higher levels of Geobacter in FD co-digestion, possibly suggesting a role for direct interspecies electron transfer (DIET) between Methanosaeta and Geobacter. This work provides fundamental insights supporting anaerobic co-digestion of FDs with WAS, demonstrating the advantages of FDs compared to FOG as co-substrate for enhanced biomethane recovery.

Biogas production from anaerobic co-digestion of waste activated sludge: co-substrates and influencing parameters

Anaerobic digestion is a versatile biotechnology to treat waste activated sludge (WAS), the main by-products of biological wastewater treatment, because it can achieve simultaneously energy recovery (biogas) and pollutant reduction (organic matter, pathogens). However, the potential of biogas production from mono-digestion of WAS is usually limited by the imbalance carbon to nitrogen (C/N) ratio of WAS and ammonia accumulation. Anaerobic co-digestion, simultaneous digestion of two or more substrates, should be a feasible option to resolve these disadvantages. The abundant organic wastes from municipal, industrial, and agricultural field have been the ideal co-substrates because they not only can balance the substrate nutrient to obtain the optimal C/N ratio, but also can adjust pH and dilute the toxic materials to mitigate the inhibition to methanogens, consequently improving the yield of biogas, especially methane. This paper classified the main organic co-substrates according to their source and reviewed their application in anaerobic co-digestion of WAS. Then the influence of temperature, pH, organic loading rate, hydraulic retention time, C/N ratio, digester type and pretreatment method on biogas production was extensively discussed. Finally, this review brought forward the challenges and outlooks of anaerobic co-digestion in the future.

Smart Approaches to Food Waste Final Disposal.

Food waste, among the organic wastes, is one of the most promising substrates to be used as a renewable resource. Wide availability of food waste and the high greenhouse gas impacts derived from its inappropriate disposal, boost research through food waste valorization. Several innovative technologies are applied nowadays, mainly focused on bioenergy and bioresource recovery, within a circular economy approach. Nevertheless, food waste treatment should be evaluated in terms of sustainability and considering the availability of an optimized separate collection and a suitable treatment facility. Anaerobic codigestion of waste-activated sludge with food waste is a way to fully utilize available anaerobic digestion plants, increasing biogas production, energy, and nutrient recovery and reducing greenhouse gas (GHG) emissions. Codigestion implementation in Europe is explored and discussed in this paper, taking into account different food waste collection approaches in relation to anaerobic digestion treatment and confirming the sustainability of the anaerobic process based on case studies. Household food waste disposal implementation is also analyzed, and the results show that such a waste management system is able to reduce GHG emissions due to transport reduction and increase wastewater treatment performance.

Multi-hydrolytic enzyme accumulation and microbial community structure of anaerobic co-digestion of food waste and waste-activated sludge

ABSTRACTThe accumulation of multi-hydrolytic enzyme through anaerobic co-digestion of waste-activated sludge (WAS) and food waste (FW) was studied by regulating temperature, pH and the mass ratio of FW to WAS (F/W). Experimental results showed that temperature had a profound effect on the activity of the enzyme and the most suitable temperatures for the accumulation of amylase and protease were 37°C and 50°C, respectively. The highest activity of amylase and protease accumulated reached 10.29 and 19.23 U/mL at an F/W ratio of 2:1. The addition of anaerobic co-digestion solution enriching protease and amylase had positive effects on the hydrolysis of WAS. In addition, the Illumina high-throughput sequencing demonstrated that the bacterial diversity decreased, but the bacterial abundance increased during the co-digestion process of WAS and FW. The predominant strains for secreting amylase were Lactobacillus and Clostridium-sensu-strito-1, and Aeromonas was the dominant strain for secreting protease.

Effect of enhancing nutrient balance in anaerobic digester feedstock by co-substrate addition on the microbial diversity and energy production from municipal sewage sludge

Enhancement of methane production during anaerobic digestion of waste activated sludge (WAS) could improve the energy self sufficiency of the municipal wastewater treatment plants (WWTPs). Therefore, mixing WAS with organic wastes improved process performance and stability. In this work, the anaerobic co-digestion of WAS combined with the olive processing wastewater (OPW) was investigated and associated with the energetic benefits and microbial populations shifts. The bio-methane potential (BMP) of various WAS and OPW mixtures corresponding to increased phenols concentrations were tested. The anaerobic digestion of better proportions (90%/10% and 80%/20%) was performed in anaerobic sequencing batch reactors (ASBRs). The biodegradation of phenols at concentrations up to 0.76g/L was confirmed by Sephadex gel filtration showing that ASBR, which is suspended growth reactor, can handle much higher concentration of toxic compounds. Microbial analysis showed that phenols induced significantly the archaea community dynamic, which showed highly richness and diversity in the well performed reactor. The dominant bacteria and archaea phylotypes were affiliated to Proteobacteria and Methanosarcinales, respectively. Therefore, OPW addition increased total energy production from 24.6kWh/ton to 64.7kWh/ton, which would provide 0.43M€/year net benefits only from the electric power. In addition it brings a payback time on investment of 2 years for WWTPs modification, which was considered interesting.

Two-Stage Start-Up to Achieve the Stable via-Nitrite Pathway in a Demonstration SBR for Anaerobic Codigestate Treatment

The supernatant effluent from full scale anaerobic codigestion of waste-activated sludge and the organic fraction of municipal solid waste was treated by a demonstration sequencing batch reactor for short-cut nitrogen removal. After inoculation with conventional municipal activated sludge, the strategy of two-stage start-up allowed us the fast speciation of ammonia oxidizing bacteria (achieved within 20 days), then the achievement of the maximal treatment potential (0.8 kgN m–3 d–1) for nitritation–denitritation. By automatic indirect control of the free ammonia and the free nitrous acid concentrations, the via-nitrite pathway was fully and stably achieved under aerobic conditions (DO of 1.5 mg L–1) and T of 15 °C. Under ordinary operation, the specific nitritation rates were 15–20 mgN gMLVSS–1h–1, while the denitritation rate was 45–50 mgN gMLVSS–1h–1. In-situ and ex-situ respirometry and gene-based molecular techniques demonstrated the stable presence of a dominant, restricted ammonia oxidizing bacteria...