Sludge Fermentation Research Articles

Efficient methane production from waste activated sludge and Fenton-like pretreated rice straw in an integrated bio-electrochemical system

Integrated microbial electrolysis cell-anaerobic digestion (MEC-AD) systems have demonstrated potential advantages for methane production in the presence of small amounts of residual inhibitors. In this study, a series of tests were conducted to analyse the acidification and methanogenesis performance of pretreated rice straw (RS) in anaerobic digestion (AD) and MEC-AD systems after the addition of Fenton-like reagents. The results indicated that the short-chain acids (SCFAs) accumulations reached 2284.64 ± 21.57 mg COD/L with a dosage ratio of 1/4 (g RS/g VSS sludge) in the MEC-AD system and that methane production increased by 63.8% compared with that of an individual AD system. In the interim, the net energy output reached 1.09 × 103 J/g TCOD, which was 1.23 times higher than that of the AD system. The residual Fe3+/Fe2+ in the pretreatment reagent was capable of promoting acidification and methanogenesis in sludge and RS fermentation. The RS hydrolysis products could constrain methanogenesis, which can be mitigated by introducing an MEC. The microbiological analyses revealed that the MEC strongly increased the enrichment of hydrogenotrophic methanogens, especially Methanobacterium (61.16%). Meanwhile, the Syntrophomonas and Acetobacterium abundances increased to 2.81% and 2.65%, respectively, which suggested the reinforcement of acetogenesis and methanogenesis. Therefore, the enhanced hydrogenotrophic methanogens might have served as the key for enhancing the efficiency of methanogenesis due to the introduction of an MEC.

ASPECTS REGARDING THE ENERGITICAL VALORIFICATION OF URBAN SLUDGE TREATMENT

This paper highlights through the issues addressed, the application aspects regarding the approach of the concept of recovery of sewage sludge from an urban wastewater treatment plant (SEAU), which is in a stage of technological expansion and modernization. Thus, it is considered the need to process the potential of biological mass generated by anaerobic stabilization in the SEAU, with a population of about 10,000 equivalent inhabitants, which requires on one hand, the technological design of activated sludge basins and on the other hand, the design of a sewage sludge fermentation tank, in order to produce biogas, necessary for its recovery for energy purposes.

Trends in Methane Fermentation Treatment System and Sludge Recycling Technology for Biomass Utilization

Recently, utilization of biomass (i.e. domestic waste, excess sludge, food processing waste, etc.) is getting an attention as a promising way to realize economical low-carbon society goal. This paper provides a summary of current trends in biomass utilization regarding methane fermentation and sludge recycling technology. Methane fermentation is the process involved the conversion of organic waste to methane gas, which is being used for electricity generation and as fuel. As a plentiful of excess sludge is generated from sewage and night soil treatment plants daily, the recycle technology for biomass utilization is developed. For example; excess sludge and night soil are efficiently dewatered by shaft sliding screw press (to achieve 70% or lower moisture content) and utilized as a combustion improver. In addition, phosphorus in the thickening filtrate generated from the dewatering system is recovered through phosphorus recovery system and utilized as an agricultural fertilizer.

Realization of partial nitrification and in-situ anammox in continuous-flow anaerobic/aerobic/anoxic process with side-stream sludge fermentation for real sewage

A continuous-flow anaerobic/aerobic/anoxic reactor with complete suspended activated sludge using sludge alkaline fermentation products as carbon source was utilized to strengthen nitrogen removal performance for low C/N ratio (<4) wastewater. Long-time performance indicated that the nitrite accumulation rate reached 60.40%, which strengthened the contribution of anammox. The average total inorganic nitrogen removal efficiency improved 19.40%. The abundance of ammonia oxidizing bacteria has not changed, but the abundance of nitrite oxidizing bacteria reduced from 5.79% to 0.69%. Quantitative PCR results demonstrated that the abundance of anammox bacteria has raised by 80.5 times. These results indicated that side-stream sludge alkaline fermentation promoted the mainstream partial nitrification, consequently accelerating the in-situ enrichment of anammox bacteria. No external carbon source dosing and short oxic hydraulic retention time (5.3 h) save energy and reduce consumption significantly in this system.

Effects of persulfate treatment on the fates of antibiotic resistance genes in waste activated sludge fermentation process and the underlying mechanism

The occurrence of antibiotic resistance genes (ARGs) in waste activated sludge (WAS) fermentation was investigated with persulfate (PS)-based treatment. ARGs affiliated with multidrug (mexP), macrolide (blaOXA-129), tetracycline (tetB), sulfonamide (sul1), and vancomycin (vanRG) types were significantly decreased by PS/Fe treatment. Mechanistic investigations revealed that PS/Fe possessed oxidating potential and exhibited devastating effects on WAS fermentation. First, PS/Fe promoted cell structure damage, which facilitated ARGs release from potential hosts. A co-occurrence network analysis indicated that Fe/PS suppressed the proliferation of potential host bacteria. In addition, the PS/Fe treatment induced the decreased abundance of certain functional genes involved in pathways associated with ARGs dissemination. Finally, variation partitioning analysis demonstrated that the microbial community structure exhibited more vital effects on ARGs fates than physicochemical factors (i.e., pH and ORP) and gene expression (i.e., two-component system). This work provided a deeper understanding of the critical factors used to determine ARGs fates during WAS fermentation.

Implications for mitigation of antibiotic resistance: Differential response of intracellular and extracellular antibiotic resistance genes to sludge fermentation coupled with thermal hydrolysis

Thermal hydrolysis pretreatment (THP) can effectively remove the antibiotic resistance genes (ARGs) from sewage sludge, but the rebounding effects in the subsequent anaerobic fermentation are often observed. The purpose of this study was to elucidate the distribution and fate of intracellular and extracellular ARGs (iARGs and eARGs) in the sludge acidogenic fermentation process coupled with THP. Our results revealed that THP significantly reduced the absolute abundance of total ARGs in raw sludge but increased eARGs by 0.3–1.4 log units under practical conditions (140 °C for 30 min). There is no significant difference in the removal of total ARGs between the two acidogenic fermenters receiving raw and hydrolyzed sludge, with iARGs prevailing in the produced biosolids. The succession of bacterial community and the co-occurrence relationships among ARG type, mobile genetic elements and bacterial taxa were observed, suggesting a phylogenetic basis for the iARGs patterns in fermented sludge. However, eARGs were susceptible to biodegradation with a half-life of 2.34 h and they contributed limitedly to the ARGs propagation through transformation. These findings suggest an emphasis on the mitigation of iARGs during the acidogenic fermentation of sludge, which would be achieved by lowering the richness and physicochemical destruction of potential hosts.

Enhancement of denitrification efficiency using municipal and industrial waste fermentation liquids as external carbon sources

The addition of external carbon source for nitrogen removal from wastewater is an essential step in wastewater treatment. In this study, various external carbon sources from the fermentation of primary sludge (PS), thickened waste activated sludge (TWAS), food waste (FW), bakery processing & kitchen waste (BP + KW), fat, oil, & grease (FOG), and whey powder (WP) were successfully employed for wastewater denitrification. Methanol and acetate were also used as controls due to their common use as external carbon sources for wastewater denitrification. The denitrification performance and kinetics such as the specific denitrification rate (SDNR), denitrification potential (PDN), and the biomass yield were studied at a constant TVFA as COD/N ratio of 5 for all substrates. Complete denitrification was achieved with a NO3−-N removal efficiency of 98–99%, and no NO2− accumulation was observed at the end of the experiments for all substrates. The results revealed that the liquid fermentation filtrates exhibited higher SDNRs than methanol and acetate. This indicates the high organic matter utilization efficiency and better denitrification ability of fermentation filtrates over conventional carbon sources. WP exhibited the highest SDNR of 17.6 mg NOx − N/g VSS/h, which is approximately four times that of methanol (4.6 mg NOx − N/g VSS/h). The other carbon sources had SDNRs two to three times higher than that of methanol. However, the fermentation filtrates exhibited higher biomass yields of 0.26–0.37 mg VSS/mg COD compared to methanol of 0.21 mg VSS/mg COD, which could lead to higher sludge handling costs. Moreover, methanol exhibited higher PDN of 0.25 g N/g COD compared to all the fermentation filtrates.

Advanced nitrogen removal from landfill leachate via a two-stage combined process of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA)

In this study, a two-stage combined process of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA) was established achieving advanced nitrogen removal from landfill leachate. The PNA sludge used to treat reject water adapted to the leachate in 37 days, resulting in fast start-up of the PNA process with a nitrogen removal rate (NRR) of 0.22 kgN/(m3·d). Partial denitrification (PD) was induced using sodium acetate and proceeded in a stepwise manner using sludge fermentation liquid (SFL), achieving a NO3−-N to NO2−-N transformation ratio (NTR) of 52.1 ± 1.1% within 16 days. PDA was established via the addition of mature Anammox biofilms. The nitrogen removal efficiency (NRE) of this system was 97.6 ± 1.5%, of which PNA and PDA contributed 74.8 ± 4.0% and 18.7 ± 4.1%, respectively. Nitrosomonas (2.6% in PNA), Thauera (16.0% in PDA) and Candidatus Brocadia (23.0% in PNA, 1.4% in PDA) were dominant in the two-stage system. This study provides valuable and novel insights, supporting the practical application of PNA-PDA processes in landfill sites.

Sludge disintegration and phosphorus migration in anaerobic fermentation of waste activated sludge by the addition of EDTA-2Na

ABSTRACT The effects of the addition of EDTA-2Na on sludge disintegration and phosphorus (P) migration during anaerobic fermentation (AF) of waste activated sludge (WAS) are investigated. The efficiency of sludge disintegration was positively correlated with the dose of EDTA-2Na from 0.5–2.0 g/g SS, and an enormous quantity of P was liberated into the aqueous phase, accompanied by sludge disintegration. The proper dose of EDTA-2Na for P release from WAS was 1.5 g/g SS, with an orthophosphate concentration of 394.72 mg/L. P release was more consistent with the pseudo second-order kinetic model. The migration of P species during AF with EDTA-2Na addition was also studied. Orthophosphate was the main species in both of the liquid phase and the loosely bound extracellular polymeric substances (EPS), but organic P (OP) was much more abundant in tightly bound EPS. Inorganic P (IP) was the dominant P speciation in the solid and was mainly distributed in the fraction of non-apatite IP, which accounted for more than 62.8% of IP in the presence of EDTA-2Na. In addition, both IP and OP in the solid contributed to the accumulation of P and the former was outperformed. Furthermore, the increased total dissolved P mainly came from cells. However, the fermented sludge tended to be smaller and to have low compressibility, which is detrimental to its further treatment.

Corncob ash boosts fermentative hydrogen production from waste activated sludge

With the increasing demand for sustainable development, the recycling and utilization of wastes has received widespread attention. This study proposed a green method of using one waste, corncob ash, to boost microbial the production of hydrogen from another waste, waste activated sludge, during anaerobic fermentation. The corncob ash dosage and the fermentative hydrogen production was positively correlated, and the maximum production of hydrogen reached up to 46.8 ± 1.0 mL/g VS, which was about 3.5 times that of the control group without corncob ash dosage (17.0 ± 0.9 mL/g VS). Mechanistic studies found that corncob ash was beneficial to the solubilization, hydrolysis and acetogenesis processes involved in fermentative hydrogen production process. The microbial community analysis indicated that corncob ash enriched more hydrolytic microorganisms (e.g., Bacteroides sp. and Leptolinea sp.), and has less impact on acidifying microorganisms, compared to the control group. The strategy of using corncob ash to boost the production of hydrogen during anaerobic waste activated sludge fermentation proposed in this study might provide a new waste-control-waste paradigm, making sludge disposal and wastewater treatment more sustainable.

Accelerating acidogenic fermentation of sewage sludge with ash addition

A statistically designed range of tests was used in order to map the impact of time, temperature and pH on the acidogenic fermentation of sewage sludge with the addition of wood fly ash. The main factors investigated were temperature (35, 55 and 65 °C), pH (7, 8 and 8.5) and retention time (1, 2 and 4 days). The initial pH was adjusted by adding ash. Up to about a third of the volatile solids could be solubilized in less than two days retention time. Higher temperatures (55 and 65 °C) and adjusted pH (7 and 8) favored hydrolysis whereas fermentation producing organic acids was faster at lower temperatures (35 °C). Sludge hydrolysis occurred fast at 55 and 65 °C, reaching a solubilized total organic carbon (TOC) concentration of 3.84 g TOC L−1 after one day. Thermophilic conditions (55 and 65 °C) resulted in a lower volatile fatty acids (VFA) concentration compared to mesophilic conditions (35 °C). At 35 °C, the highest VFA concentration was measured after 4 days and initial pH 7 (10.0 ± 0.2 g COD L−1). This study showed the potential of using a waste stream to increase and hasten the hydrolysis of particulate organics, resulting in higher TOC solubilized in 2 days, while promoting a higher VFA production presented as g COD L−1.

Metagenomic assembly deciphered the type-dependent effects of surfactants on the fates of antibiotics resistance genes during sludge fermentation and the underlying mechanisms

Waste activated sludge (WAS) is an important reservoir of antibiotic resistance genes (ARGs). However, the interactive effects of co-existed substances in WAS on ARGs fates have yet to be disclosed. This study demonstrated the type-dependent effects of surfactants (potentially effective chemicals for WAS disposal) on the reduction of ARGs during WAS fermentation, which followed the order of linear alkylbenzene sulphonates (LAS) > alkyl polyglucoside (APG) > hexadecyl trimethyl ammonium bromide (HTAB). Interestingly, the ratio of ARGs affiliated to efflux pump showed an upward trend in the surfactant-treated reactor. Mechanistic investigations revealed that the extracellular polymeric substances (EPS) destruction induced by surfactants increased the permeability of bacterial cells and caused the ARGs being released and susceptible for subsequent elimination. Besides, the surfactants significantly altered the microbial community, resulting in the ARGs reduction via changing the potential hosts. Also, the metabolic pathways participated in the dissemination of ARGs were remarkably down-regulated, thereby resulting in the reduction of ARGs abundances. This work broadened the understanding of ARGs fates during WAS fermentation and provided insights on the interactive functions of exogenous chemicals in multiple matrics.

Transforming waste activated sludge into medium chain fatty acids in continuous two-stage anaerobic fermentation: Demonstration at different pH levels

Bioenergy recovery in the form of medium-chain fatty acids (MCFAs) from waste activated sludge (WAS) is increasingly attractive, which are valuable building blocks for fuel production. This study experimentally demonstrated the long-term MCFAs (C6–C8) production from WAS in two-stage anaerobic sludge fermentation at different pH conditions, using continuously operated bench-scale anaerobic reactors. The WAS was continuously converted to short chain fatty acids (SCFAs, 3500–3800 mg chemical oxygen demand (COD)/L) at the first stage via alkaline anaerobic fermentation, which was directly fed into the second stage as both substrates and inoculum for MCFAs production through chain elongation (CE). The productions of MCFAs at the second stage were continuously studied under three different pH conditions (i.e., 10, 7 and 5.5). The results demonstrated that there was no significant MCFAs production at pH 10 during the steady state, whereas the MCFAs productions were clearly observed at both pH 7 and pH 5.5, with much higher MCFAs production from WAS at pH 7 (i.e., 10.32 g COD/L MCFAs) than that at pH 5.5 (i.e., 8.73 g COD/L MCFAs) during the steady state. A higher MCFAs selectivity of 62.3% was also achieved at pH 7. The relatively lower MCFAs production and selectivity at pH 5.5 was likely due to the higher undissociated MCFAs generated at pH 5.5, which would pose toxicity impact on CE microbes and thus inhibit the CE process. Microbial community analysis confirmed that the relative abundances of CE related microbes (e.g., Clostridium sensu stricto 12 sp. and Clostridium sensu stricto 1) increased at pH 7 compared to those at pH 5.5, which enabled more efficient MCFAs production from WAS.

Revealing the mechanisms of rhamnolipid enhanced hydrogen production from dark fermentation of waste activated sludge

Rhamnolipid (RL), as an environmentally compatible biosurfactant, has been used to enhance waste activated sludge (WAS) fermentation. However, the effect of RL on hydrogen accumulation in anaerobic fermentation remains unclear. Therefore, this work targets to investigate the mechanism of RL-based dark fermentation system on hydrogen production of WAS. It was found that the maximum yield of hydrogen increased from 1.76 ± 0.26 to 11.01 ± 0.30 mL/g VSS (volatile suspended solids), when RL concentration increased from 0 to 0.10 g/g TSS (total suspended solids). Further enhancement of RL level to 0.12 g/g TSS slightly reduced the production to 10.80 ± 0.28 mL/g VSS. Experimental findings revealed that although RL could be degraded to generate hydrogen, it did not play a major role in enhancing hydrogen accumulation. Mechanism analysis suggested that RL decreased the surface tension between sludge liquid and hydrophobic compounds, thus accelerating the solubilization of WAS, improving the proportion of biodegradable substances which could be used for subsequent hydrogen production. Regardless of the fact that adding RL suppressed all the fermentation processes, the inhibition effect of processes associated with hydrogen consumption was much severer than that of hydrogen production. Further investigations of microbial community revealed that RL enriched the relative abundance of hydrogen producers e.g., Romboutsia but reduced that of hydrogen consumers like Desulfobulbus and Caldisericum.

Metagenomic approach reveals the fates and mechanisms of antibiotic resistance genes exposed to allicins during waste activated sludge fermentation: Insight of the microbial community, cellular status and gene regulation

This work revealed the impacts of exogeneous allicins on the antibiotic resistance genes (ARGs) variations during waste activated sludge (WAS) fermentation process. The overall abundance of ARGs was respectively reduced by 4.84 and 9.42% in presence of 0.01 and 0.05 g allicin/g TSS. Allicins disrupted the EPS structure and increased the permeability of cell membranes, which resulted in the release of ARGs for subsequent removal. Allicins also reduced intracellular ATP levels, which was disadvantageous to ARGs dissemination. Besides, allicins affected the microbial community and decreased the abundance of potential hosts based on bacterial taxa-ARGs network analysis. Moreover, the metabolic pathways and genetic expressions (i.e., two-component system, quorum sensing, and SOS response) involved in ARGs propagation were down-regulated, which caused the ARGs alleviation in allicins-stressed reactors. Overall, the simultaneous responses of cellular status, bacterial host, and genetic regulation accounted for the effective ARGs reduction induced by allicins during WAS fermentation.

Response of VFAs and microbial interspecific interaction to primary sludge fermentation temperature

It's not clear how fermentation affects the succession and interspecific interaction of functional microorganism in primary sludge anaerobic fermentation system. So as to explore the decisive role of temperature on microorganisms to reveal the mechanism, four fermentation experiments groups (25, 35, 45, and 55 °C) were designed. Results indicated the promotion in proportion of acetic and iso-valeric acid with temperature increasing. High-throughput sequencing reflected that the dominant microbial groups in all samples were Proteobacteria, Firmicutes, Bacteroidetes, Synergetes, Spirochaetae, and then key microbial interspecific interaction changed significantly due to the adjustment of microbial temperature. In addition, amino acid metabolism was the lowest at 35 °C, but carbohydrate metabolism was the highest. The metabolic abundances of amino acids at different temperatures were the highest, but the differences among kind of amino acids were significant. This study could reveal the effect of temperature on VFAs production in terms of microbial interspecific interaction and lay a theoretical foundation for sludge fermentation.

Highly Selective Fermentation of Waste-Activated Sludge by Alginate-Degrading Consortia

Highly Selective Fermentation of Waste-Activated Sludge by Alginate-Degrading Consortia

Influence of volatile solids and pH for the production of volatile fatty acids: Batch fermentation tests using sewage sludge

The aim of this work was to study the effect of volatile suspended solid (VSS) and pH on volatile fatty acids (VFA) production from waste activated sludge (WAS) fermentation by means of batch tests. The final goal was to gain insights to enhance VFA stream quality, with the novelty of using WAS with high sludge retention time. Results revealed that the optimum conditions to maximize VFAs and minimize nutrients and non-VFA sCOD are a VSS concentration of 5.9 g/L and initial pH adjustment to pH 10. The WAS bacterial community structures were analysed according to Next Generation Sequencing (NGS) of 16S rDNA amplicons. The results revealed changes of bacterial phyla abundance in comparison with the batch test starting condition.

Applicability of two-stage anoxic/oxic shortcut nitrogen removal via partial nitrification and partial denitrification for municipal wastewater by adding sludge fermentation products continuously

Partial nitrification and partial denitrification combined with anammox is a promising process for sewage treatment. In this study, real municipal wastewater was treated in a continuous two-stage anoxic/oxic (A/O) reactor. External mixed sludge fermentation products were added in the anoxic zone, simultaneously achieving partial nitrification and partial denitrification and achieving a high and relatively stable accumulation of nitrite. The maximum accumulation rates of NO2−-N in A1.2 and A2.1-A2.4 zones of the reactor reached 70% and 61%–37%, respectively, which improved denitrification efficiency and created conditions that supported the coupling of subsequent anammox. The influent nitrogen load of the system was 0.078 kg/(m3•d), and the mean influent and effluent total nitrogen were 51 and 12 mg/L, respectively. The mean total nitrogen removal rate reached 76%. Further analysis revealed that Hyphomicrobium (incomplete denitrifiers) and Nitrosomonas (ammonia oxidizing bacteria) were enriched, which may have facilitated the high nitrite accumulation. Moreover, the batch test showed that adding sludge fermentation during denitrification significantly suppressed nitrite reduction, resulting in the nitrite accumulation.

Survival strategy of comammox bacteria in a wastewater nutrient removal system with sludge fermentation liquid as additional carbon source

Complete ammonia oxidizing (comammox) bacteria are frequently detected in wastewater biological nutrient removal (BNR) systems. This study identified “Candidatus Nitrospira nitrosa”-like comammox bacteria as the predominant ammonia oxidizers (97.5–99.4%) in a lab-scale BNR system with acetate and sludge fermentation liquid as external carbon sources. The total nitrogen and phosphorus removals of the system were 75.9% and 86.9% with minimal N2O emission (0.27%). Low ammonia concentration, mixotrophic growth potentials and metabolic interactions with diverse heterotrophs collectively contributed to the survival of comammox bacteria in the system. The recovered draft genomes of comammox bacteria indicated their potentials in using acetate and propionate but not butyrate. Acetate and propionate indeed stimulated the transcription of comammox amoA genes (up-regulated by 4.1 folds compared with no organic addition), which was positively correlated with the ammonia oxidation rate of the community (r = 0.75, p < 0.05). Comammox bacteria could provide vitamins/cofactors (e.g., cobalamin and biotin) to heterotrophs (e.g., Burkholderiaceae), and in return receive amino acids (e.g., phenylalanine and tyrosine) from heterotrophs, which they cannot synthesize. Compared with comammox bacteria, ammonia oxidizing bacteria (AOB) exhibited lower metabolic versatility, and lacked more pathways for the synthesis of amino acids and vitamin/cofactors, leading to their washout in the studied system. BNRs with comammox bacteria as the major nitrifiers hold great potentials in achieving superior performance at low aeration cost and low N2O emission and at full-scale plants.