VFAs bioproduction from waste activated sludge by coupling pretreatments with Agaricus bisporus substrates conditioning

Recovery of organic matters by activated sludge from municipal wastewater: Performance and characterization

Municipal wastewater treatment processes consume a significant amount of energy and generate substantial carbon emissions. However, organic matters existing in municipal wastewater hold the potential as a valuable carbon source. Activated sludge has the potential to capture and recover the organic matters, thereby enriching carbon sources and facilitating subsequent sludge anaerobic digestion as well as in line with the concept of sustainable development. Based on above, this study investigated the enrichment and recovery characteristics and mechanisms of activated sludge adsorption on carbon sources in municipal wastewater, while optimizing the recovery conditions. The results indicated that insoluble organic matters, as well as a fraction of dissolved organic matters, can be effective recovered within approximately 40 min. Specifically, 74.1% of insoluble organic matters and 25.8% of soluble organic matters were successfully captured by the activated sludge, resulting in a 5.0% increase in sludge organic matter content. Moreover, activated sludge demonstrated remarkable recovery of particulate organic matters across various particle sizes, particularly larger particles (>5 μm) with high protein content. Notably, the dissolved biodegradable organics such as tryptophan and tyrosine protein-like substances according to 3D-EEM and lipids, proteins/amino sugars, and carbohydrates according to FT-ICR MS can be effectively recovered. Finally, the study revealed that the recovery of organic matters from the wastewater by activated sludge followed the pseudo-second-order kinetics model, with surface binding, hydrogen bonding and interparticle diffusion in sludge flocs as the primary adsorption mechanisms. This approach had abroad application prospects for improving the profitability of wastewater treatment plants.

Carbon source recovery from waste sludge reduces greenhouse gas emissions in a pilot-scale industrial wastewater treatment plant

Carbon cycle regulation and greenhouse gas (GHG) emission abatement within wastewater treatment plants (WWTPs) can theoretically improve sustainability. Currently, however, large amounts of external carbon sources used for deep nitrogen removal and waste sludge disposal aggravate the carbon footprint of most WWTPs. In this pilot-scale study, considerable carbon was preliminarily recovered from primary sludge (PS) through short-term (five days) acidogenic fermentation and subsequently utilized on-site for denitrification in a wool processing industrial WWTP. The recovered sludge-derived carbon sources were excellent electron donors that could be used as additional carbon supplements for commercial glucose to enhance denitrification. Additionally, improvements in carbon and nitrogen flow further contributed to GHG emission abatement. Overall, a 9.1% reduction in sludge volatile solids was achieved from carbon recovery, which offset 57.4% of external carbon sources, and the indirect GHG emissions of the target industrial WWTP were reduced by 8.05%. This study demonstrates that optimizing the allocation of carbon mass flow within a WWTP has numerous benefits.

Study on the preparation and feasibility of a novel adding-type biological slow-release carbon source

The development of slow-release carbon sources is an effective biological treatment to remove nutrients from wastewater with low carbon-to-nitrogen ratio (C/N). Most filling-type slow-release carbon could not fulfil the needs of current wastewater treatment plants (WWTPs) process. And most adding-type slow-release carbon sources were prepared using some expensive chemical materials. In this study, combining the advantages of the aforementioned types, a novel adding-type wastepaper-flora (AT-WF) slow-release carbon source was proposed, aiming to realise wastepaper recycling in WWTPs. The screening and identification of the mixed flora, AT-WF carbon source release behaviour, and denitrification performance were investigated. The results showed that through the proposed screening method, a considerable proportion of cellulose-degradation-related genera was enriched, and the cellulose degradation ability and ratio of readily available carbon sources of flora T4, S4 and S5 were effectively strengthened. AT-WF had significant carbon release ability and stability, with an average total organic carbon (TOC) release of 8.82 ± 2.36 mg/g. Kinetic analysis showed that the entire carbon release process was more consistent with the first-order equation. Piecewise fitting with the Ritger-Peppas equation exhibited that the rapid-release (RR) stage was skeleton dissolution and the slow-release (SR) stage was Fick diffusion. Denitrification efficiency can achieve a high average removal efficiency of 94.17%, which could theoretically contribute 11.2% more to the total inorganic nitrogen (TIN) removal. Thus, this study indicated that AT-WF could be utilised as an alternative carbon source in WWTPs.

Effects of three surfactants on co-conversion of endogenous carbon and nitrogen of dairy wastewater in mesophilic hydrolytic acidification coupled microalgae culture system

To determine the feasibility of enhancing co-conversion of endogenous C and N in dairy wastewater by surfactants, the effects of varying dosages of sodium lignosulfonate (LS), sodium dodecyl sulfate (SDS), and Tween-80 on mesophilic hydrolytic acidification coupled microalgae culture system were investigated. Tween-80 had a positive effect on hydrolytic acidification, while LS had no clear effect and SDS had a negative effect. Tween-80 significantly increased the C/N ratio in hydrolytic acidification liquor (HAL) (maximum HAc/NH₄⁺-N rate reached 7.90 in 2.9% Tween-80 test). Pyrosequencing analysis demonstrated that community richness and diversity decreased and the proportion of acidobacteria increased with increasing Tween-80 dosage. Furthermore, the effect of Tween-80-enhanced HAL on microalgae (Chlorella pyrenoidosa) growth and nitrogen removal and the assimilation of C and N on the microalgae culture system were investigated. The biomass concentration and a C and N assimilation yield of 4.8% Tween-80 test (1.75 g/L, 825.01 mg/L, 126.68 mg/L) were significantly higher than those of both the low-concentration Tween-80 tests and control. The yield of protein and carbohydrates and higher heating value in the microalgae culture system were also promoted by Tween-80.

Waste activated sludge lysate treatment: Resource recovery and refractory organics degradation

Sludge lysate is an unavoidable and refractory liquid produced from the waste activated sludge hydrothermal pyrolysis, which contains plenty of hazardous refractory organic compounds and value-added organic resources. Here, the proof of concept for an integrated strategy that couples technically compatible pretreatment to microbial electrolysis assisted AD (ME-AD) system is investigated for sludge lysate treatment and resource recovery. The pretreatment process shows a positive effectiveness on the ME-AD by reducing the organic load and inhibitory matters, which promote the residual refractory organic compounds (Maillard reaction products and humic acid-like substances) and carbon sources further biodegradation and bio-transformation. Combining membrane separation with ME-AD increased not only both the yield and purity of methane to 268.76 mL CH₄/g COD and 98%, respectively, but also the recovery of 70.0~82.4% crude proteins (9.1 ± 0.5 g/L) from sludge lysate. Alternatively, the alkaline precipitation combined with ME-AD enhanced the recovery efficiency of short-chain fatty acids (SCFAs). The visible decreasing in the unpleasant color of the effluents was observed, implying that the degradation of harmful refractory organic was almost eliminated in sludge lysate. This strategy is worthy to be developed in WWTP for sludge lysate treatment with considerable bio-resources recovery and refractory organics removal.

Cation exchange resin-induced hydrolysis for improving biodegradability of waste activated sludge: Characterization of dissolved organic matters and microbial community

This study reported an efficient and green approach towards facilitating hydrolysis of waste activated sludge (WAS) using cation exchange resin (CER) as a recyclable additive. Through CER-mediated removal of multivalent cations, WAS flocs were disintegrated into small particles with extracellular polymeric substance (EPS) solubilization. At CER dosage of 1.75 g/g SS, SCOD increased to 2579 mg/L (SCOD/TCOD = 15.9%) after 8-h hydrolysis. Afterwards, CER displayed further sludge hydrolysis performance lasting 2 days, i.e. SCOD/TCOD = 34.2%. Meanwhile, proteins, carbohydrates and other organics in dissolved organic matters (DOMs) were major contributors for volatile fatty acids (VFAs) accumulation, with composition percentage: VFAs (58.9%) > proteins (21.8%) > other organics (8.8%) > humic acids (5.9%) > carbohydrates (4.4%). The biodegradable tryptophan-like and tyrosine-like proteins were major proteins, while other organics included amino acids, aliphatic and metabolic intermediates. More than 85.2% of DOMs were easily biodegradable. Moreover, CER-induced hydrolysis modified microbial community structure through inhibiting VFAs-utilizing microbes, while hydrolytic-acidogenic bacteria were enriched, responsible for DOMs biodegradation.

Improving methane productivity of waste activated sludge by ultrasound and alkali pretreatment in microbial electrolysis cell and anaerobic digestion coupled system

In order to enhance the productivity of methane from the waste activated sludge (WAS), a coupled system of microbial electrolysis cell (MEC) and anaerobic digestion (AD) was proposed. In this study, alkali, ultrasound-alkali, high-temperature coupled microaeration (TM) were applied as pretreatment methods to disintegrate the WAS flocs and break bacterial cell. After ultrasound-alkali pretreatment, the maximum accumulated concentration of VFAs and SCOD increased by 6.4 and 13.8 times compared with the initial concentration, which were 2.8 and 2.6 times of alkali pretreatment, and 2.1 and 2.1 times of TM pretreatment. Then, the pretreated sludge was transferred into MEC-AD coupled reactors and control group of AD reactors. The results showed that, methane production rate was enhanced to 0.15 m³ CH₄/m³ reactor/d in the coupled reactors, which was improved by 3 times compared with control AD (0.05 m³ CH₄/m³ reactor/d). The methane yield of MEC-AD coupled reactors achieved 808 ± 8 mL, which were increased by 97.0% ± 1.85% compared to control AD (410 mL). Using MEC can promote the rate of organics degradation and methane yield. The MEC-AD coupled system realized a good performance on the treatment of WAS and improved the efficiency of methane production.

Insights into redox mediator supplementation on enhanced volatile fatty acids production from waste activated sludge

Anaerobic fermentation of waste activated sludge (WAS) for recycling valuable volatile fatty acids (VFAs) is economically valuable. However, the fermentation of protein is the rate-limiting step of VFA production with WAS as a substrate. In this study, the effect of redox mediators (RMs, i.e., riboflavin and lawsone) on the enhanced production of VFAs from WAS was investigated. The results indicate that both RMs can promote protein-dependent fermentation, increasing maximum VFA accumulation by 43.9% and 42.5% respectively. In cultures supplemented with riboflavin and lawsone, VFA production was highly correlated with protease activities, but not with α-glucosidase activities. This implies that RMs affected the redox reaction of amino acids degradation, resulting in an increased release of ammonia. Sequencing results showed that RMs significantly increased the abundance of bacteria related to VFA fermentation and protein/amino acid degradation at the levels of phylum, class, order, family, and even genus.

A review on the conversion of volatile fatty acids to polyhydroxyalkanoates using dark fermentative effluents from hydrogen production

The production of bio/microbial-based polymers, polyhydroxyalkanoates (PHAs) from volatile fatty acids (VFAs) of dark fermentative effluents in the bio-H₂ reactor is being paid attention, owing to their commercial demand, applications and as carbon as well as energy storage source. Since, they are the cheap precursors for such valuable renewable biopolymers which all possess the properties; those are analogous to the petro-derived plastics. Several studies were stated, related to the consumption of both individual and mixed VFAs for the potential PHAs production. Their biodegradability nature makes them extremely desirable alternative to fossil-derived synthetic polymers. In this regard, this review summarizes the use of bio-based PHAs production via both microbial and biochemical pathways using dark fermentative bio-H₂ production from waste streams as feedstock. Furthermore, this review deals the characteristics, synthesis and production of the bio-based PHAs along with their co-polymers and applications to give an outlook on future research.

Proof-of-Concept of Spent Mushrooms Compost Torrefaction—Studying the Process Kinetics and the Influence of Temperature and Duration on the Calorific Value of the Produced Biocoal

Poland, being the 3rd largest and growing producer of mushrooms in the world, generates almost 25% of the total European production. The generation rate of waste mushroom spent compost (MSC) amounts to 5 kg per 1 kg of mushrooms produced. We proposed the MSC treatment via torrefaction for the production of solid fuel—biocoal. In this research, we examined the MSC torrefaction kinetics using thermogravimetric analyses (TGA) and we tested the influence of torrefaction temperature within the range from 200 to 300 °C and treatment time lasting from 20 to 60 min on the resulting biocoal’s (fuel) properties. The estimated value of the torrefaction activation energy of MSC was 22.3 kJ mol−1. The highest calorific value = 17.9 MJ kg−1 d.m. was found for 280 °C (60 min torrefaction time). A significant (p < 0.05) influence of torrefaction temperature on HHV increase within the same group of torrefaction duration, i.e., 20, 40, or 60 min, was observed. The torrefaction duration significantly (p < 0.05) increased the HHV for 220 °C and decreased HHV for 300 °C. The highest mass yield (98.5%) was found for 220 °C (60 min), while the highest energy yield was found for 280 °C (60 min). In addition, estimations of the biocoal recirculation rate to maintain the heat self-sufficiency of MSC torrefaction were made. The net quantity of biocoal (torrefied MSC; 65.3% moisture content) and the 280 °C (60 min) torrefaction variant was used. The initial mass and energy balance showed that MSC torrefaction might be feasible and self-sufficient for heat when ~43.6% of produced biocoal is recirculated to supply the heat for torrefaction. Thus, we have shown a concept for an alternative utilization of abundant biowaste (MSC). This research provides a basis for alternative use of an abundant biowaste and can help charting improved, sustainable mushroom production.

Upgrading volatile fatty acids production through anaerobic co-fermentation of mushroom residue and sewage sludge: Performance evaluation and kinetic analysis

Due to complex inherent structure of lignocellulosic biomass, inefficient hydrolysis and acidification limits fermentative volatile fatty acids (VFA) production of mushroom residues. Meanwhile, the mushroom residues present insufficient nutrient with a high C/N ratio. To solve this issue, anaerobic co-fermentation of cellulose-rich Oyster champost and sewage sludge was tested to enhance the VFA production, and the effect of proportion of mixed substrate was investigated in this study. The results indicated that the sewage sludge yielded higher VFAs than the Oyster champost in single-substrate fermentative system. The maximal VFA yield of 595 mgCOD/gVS_added was achieved when the proportion of sewage sludge increased to 50% in the mixed substrate. In the co-fermentation system, the optimal C/N ratio and features of mixed substrate contributed to the enhancement in hydrolysis and acidification in terms of organic solubilization and VFA production, respectively. But the co-fermentation could not increase VFA/SCOD ratio, probably due to the existence of refractory products such as humic-like and protein-like materials. Besides, this co-fermentation system had strong buffer capacity and it was not necessary to dose chemicals to control the system pH for stable VFA production. Acetate was the dominant VFA product in co-fermentation systems. A modified-Logistic model fitted co-fermentation of sludge and Oyster champost well, and presented a faster rate and higher efficiency of VFA production.

Continuous acidogenic fermentation: Narrowing the gap between laboratory testing and industrial application

This study explored the potential of acidogenic fermentation of sewage sludge (SS) in an 80 L automatized pilot scale platform. A high-rate VFA production was obtained at HRT 5 d and pH 9, with a volatile fatty acid (VFA) yield of 336 mg VFA g^-1 VS and a VFA productivity of 2.15 kg VFA m^-3 d^-1. During co-fermentation of SS with OFMSW, a reversible pH shift from pH 9 to pH 6, evidenced a higher acidogenic activity which promoted the butyrate metabolic pathway, with 13.97 g COD L^-1 of butyric acid and a VFA peak 23.2 g COD L^-1. The results show the degree of flexibility of mixed culture fermentation systems, where other pH control methods other than steady control could be used to enhance the fermentation process. Ultrafiltration was a feasible technology to obtain a VFA rich permeate where 12.3-26.6 g COD L^-1 could be recovered.

Dissolved organic matter in urban forestland soil and its interactions with typical heavy metals: a case of Daxing District, Beijing

As an active substance, dissolved organic matter (DOM) acts a pivotal part in heavy metals (HMs) transportation from urban forestland soil to aquatic ecosystem. In this study, the soil samples from 35 individual subareas were scientifically collected with the aid of geographical information system (GIS) technology. UV-visible (UV-vis) and excitation-emission matrix (EEM)-related parameters suggested that the DOM in urban forestland soil mainly originated from terrestrial and microbial sources. Fluorescence quenching titration associated with parallel factor (PARAFAC) modeling was applied to quantify the complexation ability of four HMs (Cu, Cd, Pb, and Ni) and DOM in urban forestland soil. One fulvic-like (C1), two humic-like (C2 and C3), and one protein-like fluorophores (C4) were identified by EEM-PARAFAC modeling. Considerable differences in fluorescence quenching curves were observed between individual organic constituents and target HMs. Among the four HMs, addition of Cu(II) ions resulted in EEM spectra quenching of each PARAFAC-decomposed organic constituent. However, relatively strong fluorescence quenching phenomena were only detected in humic-like constituents (C2 and C3) with the titration of Pb(II) and Ni(II), which revealed that these types of organic constituent were predominantly responsible for Pb(II) and Ni(II) binding in urban forestland soil-derived DOM. Furthermore, considering the resistant nature of C2 and C3 constituents along with their significant quenching effects for the four target HMs, the concentrations of humic-like constituents in urban forestland soil may be a useful parameter to evaluate the potential risk of HMs immobilization and transformation.

Full-scale production of VFAs from sewage sludge by anaerobic alkaline fermentation to improve biological nutrients removal in domestic wastewater

A full-scale project of thermal-alkaline pretreatment and alkaline fermentation of sewage sludge was built to produce volatile fatty acids (VFAs) which was then used as external carbon source for improving biological nitrogen and phosphorus removals (BNPR) in wastewater plant. Results showed this project had efficient and stable performances in VFA production, sludge reduce and BNPR. Hydrolysis rate in pretreatment, VFAs yield in fermentation and total VS reduction reached 68.7%, 261.32 mg COD/g VSS and 54.19%, respectively. Moreover, fermentation liquid with VFA presented similar efficiency as acetic acid in enhancing BNPR, obtaining removal efficiencies of nitrogen and phosphorus up to 72.39% and 89.65%, respectively. Finally, the project also presented greater economic advantage than traditional processes, and the net profits for VFAs and biogas productions are 9.12 and 3.71 USD/m³ sludge, respectively. Long-term operation indicated that anaerobic alkaline fermentation for VFAs production is technically and economically feasible for sludge carbon recovery.

Enhanced carboxylic acids production by decreasing hydrogen partial pressure during acidogenic fermentation of glucose

In this study, the effect of reduced hydrogen partial pressure (P_H2) on the generation of carboxylic acids from acidogenic fermentation of glucose was investigated. Three strategies were applied to reduce P_H2: headspace removal (T1), CO₂ sparging (T2) and H₂:CO₂ (80:20) sparging (T3). Results showed that the production of carboxylic acids in T1-T3 were 10.21, 11.64 and 12.71g/L, respectively, which were 1.04, 1.19 and 1.30-fold of that in the control (T4). The composition of carboxylic acids changed significantly in T3 with enhancement of homoacetogenesis, as more acetate and butyrate were produced comparing to the control. In addition, decreasing P_H2 led to more carbon flow to carboxylic acids. Species of Clostridium became dominant in treatment T3, resulting in the shift of metabolic pathways. This study demonstrated that decreasing P_H2 could increase the production of carboxylic acids, especially under the strategy of enhancing homoacetogenesis.

Computational and experimental analysis of organic degradation positively regulated by bioelectrochemistry in an anaerobic bioreactor system

Methane production was tested in membrane-less microbial electrolysis cells (MECs) under closed-circuit (R_CC) and open-circuit (R_OC) conditions, using glucose as a substrate, to understand the regulatory effects of bioelectrochemistry in anaerobic digestion systems. A dynamic model was built to simulate methane productions and microbial dynamics of functional populations, which were colonized in groups R_CC and R_OC during the start-up stage. The experiment results showed significantly greater methane production in R_CC than R_OC, the average methane production of R_CC was 0.131 m³/m³/d, which was 1.4 times higher than that of R_OC (0.055 m³/m³/d). The simulation results revealed that bioelectrochemistry had a significant influence on the abundance of microorganisms involved in acidogenesis and methanogenesis. The abundance of glucose-uptaking microorganisms was 87% of the total biomass in R_OC without applied voltage, which was 20% higher than that in R_CC (67%) when external voltages were applied between the anode and cathode. The abundance of hydrogenotrophic methanogens in R_CC was 6% higher than that in R_OC. The simulation results were verified through 16S rDNA high-throughput sequencing analysis. An electron balance analysis revealed that alteration of the acidogenesis type led to more acetate and hydrogen production from glucose fermentation, compared with the situation without bioelectrochemistry. An additional pathway from acetate to hydrogen was introduced by bioelectrolysis. These two factors resulted in significant enhancement of methane production in R_CC. Bioelectrolysis process directly contributed to 26% of the total methane production after the start-up stage. When the applied voltages were cut down or decreased, R_CC could maintain considerable methane productions, because the microbial communities and electron transfer pathways were already formed. Starting-up with high voltage, but operating under low voltage, could be an energy-favorable strategy for accelerating biogas production in bioelectro-anaerobic bioreactors.

Characterization of biocarbon-source recovery and microbial community shifts from waste activated sludge by conditioning with cornstover: Assessment of cellulosic compositions

Most studies on the production of volatile fatty acids (VFAs) from waste activated sludge (WAS) digestion have focused on operating conditions, pretreatments and characteristic adjustments. Conditioning by extra carbon sources (ECS), normally added in a solid form, has been reported to be an efficient approach. However, this has caused considerable waste of monomeric sugars in the hydrolysate. In this study, the effects of two added forms (pretreated straw (S) and hydrolyzed liquid (L)) of cornstover (CS) on WAS acidification were investigated. To obtain different cellulosic compositions of CS, low-thermal or autoclaved assisted alkaline (TA or AA) pretreatments were conducted. The results showed that AA-L test achieved the highest VFAs value (653 mg COD/g VSS), followed by AA-S (613 mg COD/g VSS). These values were 12% and 28% higher, respectively, than that obtained in the TA-L and TA-S tests. Meanwhile, higher percentages of acetic acid were observed after AA pretreatment (~62% versus ~53% in TA). The added forms of CS played an important role in structuring the innate microbial community in the WAS, as shown by high-throughput sequencing and canonical correspondence analysis. The findings obtained in this work may provide a scientific basis for the potential implementation of co-digesting WAS with ECS simultaneously obtaining energy and high value-added products.

What could the entire cornstover contribute to the enhancement of waste activated sludge acidification? Performance assessment and microbial community analysis

BACKGROUND

Volatile fatty acids (VFAs) production from waste activated sludge (WAS) digestion is constrained by unbalanced nutrient composition (low carbon-to-nitrogen ratio). Characteristics conditioning by extra carbon sources, normally in the mixture of raw solid, has been reported to be an efficient approach to enhance WAS acidification. However, little attention has been paid to the contributions of other adjustment forms. Moreover, the corresponding ecological estimation has not been investigated yet.

RESULTS

In this study, the feasibility of corn stover (CS) conditioning with three adjustment forms [pretreated straw (S), hydrolysate (H) and hydrolysate + straw (HS)] in improving VFAs production from WAS was demonstrated. It was observed that the highest VFAs yield was achieved in H co-digesting test (574 mg COD/g VSS), while it was only 392 mg COD/g VSS for WAS digesting alone. VFAs composition was strongly adjustment form-dependent, as more acetic (HAc) and propionic (HPr) acids were generated in CS_HS and S, respectively. High-throughput sequencing analysis illustrated that acid (especially HAc)-producing characteristic genera (Bacteroides, Proteiniclasticum and Fluviicola) and HPr-producing characteristic genera (Mangroviflexus and Paludibacter) were detected by CS_HS and S conditioning, respectively.

CONCLUSIONS

Corn stover conditioning greatly upgraded the WAS acidification performance, especially for the CS_H adjustment form, and the VFAs yield gained was considerably larger than that previously reported. CS adjustment forms played an important role in structuring the innate microbial community in WAS. Canonical correlation analysis illustrated that characteristic genera, with better hydrolysis and acidification abilities, could be enriched by the feedstocks with certain content of cellulose, hemicellulose or their saccharification hydrolysates. Moreover, ecological estimation revealed that, as far as the entire CS (including S and H) per acre was concerned, the capacity of WAS treatment would reach that produced in a one million mts capacity wastewater treatment plants (WWTPs) per day. These findings may have crucial implications for the operation of WWTPs.

Volatile fatty acids produced by co-fermentation of waste activated sludge and henna plant biomass

Anaerobic co-fermentation of waste activated sludge (WAS) and henna plant biomass (HPB) for the enhanced production of volatile fatty acids (VFAs) was investigated. The results indicated that VFAs was the main constituents of the released organics; the accumulation of VFAs was much higher than that of soluble carbohydrates and proteins. HPB was an advantageous substrate compared to WAS for VFAs production; and the maximum VFAs concentration in an HPB mono-fermentation system was about 2.6-fold that in a WAS mono-fermentation system. In co-fermentation systems, VFAs accumulation was positively related to the proportion of HPB in the mixed substrate, and the accumulated VFAs concentrations doubled when HPB was increased from 25% to 75%. HPB not only adjust the C/N ratio; the associated and/or released lawsone might also have a positive electron-shuttling effect on VFAs production.

Microbial network for waste activated sludge cascade utilization in an integrated system of microbial electrolysis and anaerobic fermentation

BACKGROUND

Bioelectrochemical systems have been considered a promising novel technology that shows an enhanced energy recovery, as well as generation of value-added products. A number of recent studies suggested that an enhancement of carbon conversion and biogas production can be achieved in an integrated system of microbial electrolysis cell (MEC) and anaerobic digestion (AD) for waste activated sludge (WAS). Microbial communities in integrated system would build a thorough energetic and metabolic interaction network regarding fermentation communities and electrode respiring communities. The characterization of integrated community structure and community shifts is not well understood, however, it starts to attract interest of scientists and engineers.

RESULTS

In the present work, energy recovery and WAS conversion are comprehensively affected by typical pretreated biosolid characteristics. We investigated the interaction of fermentation communities and electrode respiring communities in an integrated system of WAS fermentation and MEC for hydrogen recovery. A high energy recovery was achieved in the MECs feeding WAS fermentation liquid through alkaline pretreatment. Some anaerobes belonging to Firmicutes (Acetoanaerobium, Acetobacterium, and Fusibacter) showed synergistic relationship with exoelectrogens in the degradation of complex organic matter or recycling of MEC products (H2). High protein and polysaccharide but low fatty acid content led to the dominance of Proteiniclasticum and Parabacteroides, which showed a delayed contribution to the extracellular electron transport leading to a slow cascade utilization of WAS.

CONCLUSIONS

Efficient pretreatment could supply more short-chain fatty acids and higher conductivities in the fermentative liquid, which facilitated mass transfer in anodic biofilm. The overall performance of WAS cascade utilization was substantially related to the microbial community structures, which in turn depended on the initial pretreatment to enhance WAS fermentation. It is worth noting that species in AD and MEC communities are able to build complex networks of interaction, which have not been sufficiently studied so far. It is therefore important to understand how choosing operational parameters can influence reactor performances. The current study highlights the interaction of fermentative bacteria and exoelectrogens in the integrated system.

Microbial network for waste activated sludge cascade utilization in an integrated system of microbial electrolysis and anaerobic fermentation

BACKGROUND

Bioelectrochemical systems have been considered a promising novel technology that shows an enhanced energy recovery, as well as generation of value-added products. A number of recent studies suggested that an enhancement of carbon conversion and biogas production can be achieved in an integrated system of microbial electrolysis cell (MEC) and anaerobic digestion (AD) for waste activated sludge (WAS). Microbial communities in integrated system would build a thorough energetic and metabolic interaction network regarding fermentation communities and electrode respiring communities. The characterization of integrated community structure and community shifts is not well understood, however, it starts to attract interest of scientists and engineers.

RESULTS

In the present work, energy recovery and WAS conversion are comprehensively affected by typical pretreated biosolid characteristics. We investigated the interaction of fermentation communities and electrode respiring communities in an integrated system of WAS fermentation and MEC for hydrogen recovery. A high energy recovery was achieved in the MECs feeding WAS fermentation liquid through alkaline pretreatment. Some anaerobes belonging to Firmicutes (Acetoanaerobium, Acetobacterium, and Fusibacter) showed synergistic relationship with exoelectrogens in the degradation of complex organic matter or recycling of MEC products (H2). High protein and polysaccharide but low fatty acid content led to the dominance of Proteiniclasticum and Parabacteroides, which showed a delayed contribution to the extracellular electron transport leading to a slow cascade utilization of WAS.

CONCLUSIONS

Efficient pretreatment could supply more short-chain fatty acids and higher conductivities in the fermentative liquid, which facilitated mass transfer in anodic biofilm. The overall performance of WAS cascade utilization was substantially related to the microbial community structures, which in turn depended on the initial pretreatment to enhance WAS fermentation. It is worth noting that species in AD and MEC communities are able to build complex networks of interaction, which have not been sufficiently studied so far. It is therefore important to understand how choosing operational parameters can influence reactor performances. The current study highlights the interaction of fermentative bacteria and exoelectrogens in the integrated system.

Selective simplification and reinforcement of microbial community in autothermal thermophilic aerobic digestion to enhancing stabilization process of sewage sludge by conditioning with ferric nitrate

The effect of ferric nitrate on microbial community and enhancement of stabilization process for sewage sludge was investigated in autothermal thermophilic aerobic digestion. The disinhibition of volatile fatty acids (VFA) was obtained with alteration of individual VFA concentration order. Bacterial taxonomic identification by 454 high-throughput pyrosequencing found the dominant phylum Proteobacteria in non-dosing group was converted to phylum Firmicutes in dosing group after ferric nitrate added and simplification of bacteria phylotypes was achieved. The preponderant Tepidiphilus sp. vanished, and Symbiobacterium sp. and Tepidimicrobium sp. were the most advantageous phylotypes with conditioning of ferric nitrate. Consequently, biodegradable substances in dissolved organic matters increased, which contributed to the favorable environment for microbial metabolism and resulted in acceleration of sludge stabilization. Ultimately, higher stabilization level was achieved as ratio of soluble chemical oxygen demand to total chemical oxygen demand (TCOD) decreased while TCOD reduced as well in dosing group comparing to non-dosing group.

EPS solubilization and waste activated sludge acidification enhanced by alkaline-assisted bi-frequency ultrasonic pretreatment revealed by 3D-EEM fluorescence

The effect of alkaline-assisted bi-frequency (28 + 40 kHz) ultrasonic pretreatment on extracellular polymeric substances (EPS) solubilization and waste activated sludge (WAS) acidification was investigated.

Comparison of Different Strategies for Selection/Adaptation of Mixed Microbial Cultures Able to Ferment Crude Glycerol Derived from Second-Generation Biodiesel

Objective of this study was the selection and adaptation of mixed microbial cultures (MMCs), able to ferment crude glycerol generated from animal fat-based biodiesel and produce building-blocks and green chemicals. Various adaptation strategies have been investigated for the enrichment of suitable and stable MMC, trying to overcome inhibition problems and enhance substrate degradation efficiency, as well as generation of soluble fermentation products. Repeated transfers in small batches and fed-batch conditions have been applied, comparing the use of different inoculum, growth media, and Kinetic Control. The adaptation of activated sludge inoculum was performed successfully and continued unhindered for several months. The best results showed a substrate degradation efficiency of almost 100% (about 10 g/L glycerol in 21 h) and different dominant metabolic products were obtained, depending on the selection strategy (mainly 1,3-propanediol, ethanol, or butyrate). On the other hand, anaerobic sludge exhibited inactivation after a few transfers. To circumvent this problem, fed-batch mode was used as an alternative adaptation strategy, which led to effective substrate degradation and high 1,3-propanediol and butyrate production. Changes in microbial composition were monitored by means of Next Generation Sequencing, revealing a dominance of glycerol consuming species, such as Clostridium, Klebsiella, and Escherichia.

Occurrence and behaviors of fluorescence EEM-PARAFAC components in drinking water and wastewater treatment systems and their applications: a review

Fluorescence excitation emission matrices-parallel factor analysis (EEM-PARAFAC) is a powerful tool for characterizing dissolved organic matter (DOM), and it is applied in a rapidly growing number of studies on drinking water and wastewater treatments. This paper presents an overview of recent findings about the occurrence and behavior of PARAFAC components in drinking water and wastewater treatments, as well as their feasibility for assessing the treatment performance and water quality including disinfection by-product formation potentials (DBPs FPs). A variety of humic-like, protein-like, and unique (e.g., pyrene-like) fluorescent components have been identified, providing valuable insights into the chemical composition of DOM and the effects of various treatment processes in engineered systems. Coagulation/flocculation-clarification preferentially removes humic-like components, and additional treatments such as biological activated carbon filtration, anion exchange, and UV irradiation can further remove DOM from drinking water. In contrast, biological treatments are more effective for protein-like components in wastewater treatments. PARAFAC components have been proven to be valuable as surrogates for conventional water quality parameter, to track the changes of organic matter quantity and quality in drinking water and wastewater treatments. They are also feasible for assessing formations of trihalomethanes and other DBPs and evaluating treatment system performance. Further studies of EEM-PARAFAC for assessing the effects of the raw water quality and variable treatment conditions on the removal of DOM, and the formation potentials of various emerging DBPs, are essential for optimizing the treatment processes to ensure treated water quality.

Toward bioenergy recovery from waste activated sludge: improving bio-hydrogen production and sludge reduction by pretreatment coupled with anaerobic digestion–microbial electrolysis cells

A novel and attractive technology for renewable bioenergy recovery from WAS and sludge reduction has been investigated.

Freezing/thawing pretreatment coupled with biological process of thermophilic Geobacillus sp. G1: Acceleration on waste activated sludge hydrolysis and acidification

A novel pretreatment method combining freezing/thawing with Geobacillus sp. G1 was employed to pretreat waste activated sludge (WAS) for enhancing the WAS hydrolysis and subsequent short-chain fatty acids (SCFAs) production. Results showed that freezing/thawing combined with Geobacillus sp. G1 pretreatment achieved the maximal concentrations of soluble protein from 40±6mg COD/L (non-pretreated) to 1226±24mg COD/L (pretreated), and accumulated SCFAs concentration increased from 248±81mg COD/L to 3032±53mg COD/L. Excitation emission matrix (EEM) fluorescence spectroscopy revealed the highest fluorescence intensity (FI) of protein-like substances, which was the dominant fluorescent organic matters, indicating the synergistic effect of freezing/thawing and Geobacillus sp. G1 pretreatment on organics hydrolysis. High-throughput pyrosequencing analysis investigated that the abundance of bacteria responsible for WAS hydrolysis (such as Clostridium and Caloramator) and SCFAs production (such as Parabacteroides and Bacterodies) was greatly enhanced due to the novel pretreatment method used.

Enhanced short chain fatty acids production from waste activated sludge conditioning with typical agricultural residues: carbon source composition regulates community functions

BACKGROUND

A wide range of value-added by-products can be potentially produced from waste activated sludge (WAS) through anaerobic fermentation, among which short-chain fatty acids (SCFAs) are versatile green chemicals, but the conversion yield of SCFAs is usually constrained by the low carbon-to-nitrogen ratio of the original WAS. Conditioning of the WAS with cellulose-containing agricultural residues (ARs) has been reported to be an efficient and economical solution for balancing its nutrient components. However, contributions of different ARs to SCFAs production are still not well understood.

RESULTS

To optimize SCFAs production through carbon conditioning of WAS, we investigated the effects of two typical ARs [straws and spent mushroom substrates (SMSs)] on WAS hydrolysis and acidification in semi-continuous anaerobic fermentation. Straw-conditioning group showed a threefold increase in short-chain fatty acids yield over blank test (without conditioning), which was 1.2-fold higher than that yielded by SMS-conditioning. The maximum SCFAs yield in straw-conditioning groups reached 486.6 mgCOD/gVSS (Sludge retention time of 8 d) and the highest volumetric SCFAs productivity was 1.83 kgCOD/([Formula: see text]) (Sludge retention time of 5 d). In batch WAS fermentation tests, higher initial SCFAs production rates were achieved in straw-conditioning groups [49.5 and 52.2 mgCOD/(L·h)] than SMS-conditioning groups [41.5 and 35.2 mgCOD/(L·h)]. High-throughput sequencing analysis revealed that the microbial communities were significantly shifted in two conditioning systems. Carbohydrate-fermentation-related genera (such as Clostridium IV, Xylanibacter, and Parabacteroides) and protein-fermentation-related genus Lysinibacillus were enriched by straw-conditioning, while totally different fermentation genera (Levilinea, Proteiniphilum, and Petrimonas) were enriched by SMS-conditioning. Canonical correlation analysis illustrated that the enrichment of characteristic genera in straw-conditioning group showed positive correlation with the content of cellulose and hemicellulose, but showed negative correlation with the content of lignin and humus.

CONCLUSIONS

Compared with SMSs, straw-conditioning remarkably accelerated WAS hydrolysis and conversion, resulting in higher SCFAs yield. Distinct microbial communities were induced by different types of ARs. And the communities induced by straw-conditioning were verified with better acid production ability than SMS-conditioning. High cellulose accessibility of carbohydrate substrates played a crucial role in enriching bacteria with better hydrolysis and acidification abilities.

Combination of ultrasound and Fenton treatment for improving the hydrolysis and acidification of waste activated sludge

US/Fenton had a synergetic effect on improving the hydrolysis and subsequent acidification of WAS.