Electron transfer performance and mechanism in twin microbial fuel cell powered electro-Fenton system with waste activated sludge as substrate.

Recent advances and perspectives in roles of humic acid in anaerobic digestion of waste activated sludge

The overall objective of this thesis was to investigate ways to improve the extent and rate of waste activated sludge (WAS) hydrolysis by researching the WAS degrading activities and mechanisms of the aquatic worm Tubifex tubifex (T. tubifex) as a starting point. The WAS degrading aquatic worms were taken as a model “biochemical reactor” of which its conversion processes still need to be unravelled. Because the worms are known for their excellent performance in WAS-solids reduction, i.e., up to 45% volatile solids (VS) reduction in 4 – 5 days, the focus was on worm-based enzymatic processes for improving WAS hydrolysis. Generally, T. tubifex predation shows significantly higher WAS conversion rates compared to anaerobic and aerobic digestion processes. However, information on the effect of WAS predation on the overall WAS biodegradability was lacking. Hereto, experiments were conducted to assess the ultimate WAS biodegradability potential, after which results were used as a reference to compare the biodegradability potential of different combinations of worm predation and anaerobic digestion. Interestingly, worm predation combinations showed superior solids removal rates and superior overall conversion rates, compared to solely conventional anaerobic digestion. However, the overall WAS biodegradability potential was similar in both experimental set-ups, reaching 58% and 49% removal for chemical oxygen demand (COD) and VS respectively. The improved WAS conversion rates during worm predation were related to the efficient removal of protein-like and, to a smaller extent, polysaccharide-like substances from the sludge matrix. Additionally, alginate-like exopolysaccharides (ALE), were partly consumed during worm treatment of WAS. The removal of protein, polysaccharide and ALE-like substances resulted in the disintegration of sludge flocs and the release of fulvic and humic substances as well as the cations Mg2+, Al3+ and Fe3+ from the sludge matrix. The cations and the humic and fulvic substances have a known structural function in the extracellular polymeric substances (EPS) of sludge flocs and are therefore, most likely tightly associated with the removed protein-like fraction. Corroborating with the removal of a protein-like fraction, an increased protease activity was observed in the predated WAS. The improved protease activity was likely related to T. tubifex based enzymes and/or the excretion of intestinal proteolytic bacteria. More specifically, a maximum of 73% of the proteolytic activity, related to the conversion of the model substrate casein, was due to the activity of the worms, while the remaining activity could be linked to the intestinal proteolytic bacteria. The synergy between bacteria and worms was further investigated using microbial community analysis. We showed that the worm faeces produced through WAS predation shared more similarities in microbial structure with predated protein rich substrates as compared to the WAS itself. The microbial change towards a microbiome, which was apparently related to protein degradation, was probably due to favourable conditions in the worm gut that facilitated a protein-degrading microbial community. It was further found that the genera Burkholderiales, Chryseobacterium and Flavobacterium were associated with predation by T. tubifex and are likely related to protein degradation. Overall, the research demonstrated that the key aspects of efficient WAS hydrolysis are related to the removal and conversion of protein- and alginate-like substances as well as elevated protease activity. The type of proteases and possibly other mechanisms such as the lytic capabilities of the aquatic worms are yet to be investigated.

Insight into the improvement of dewatering performance of waste activated sludge and the corresponding mechanism by biochar-activated persulfate oxidation

Correlating black soldier fly larvae growths with soluble nutrients derived from thermally pre-treated waste activated sludge

Aged landfill leachate enhances anaerobic digestion of waste activated sludge

The effect of ultrasonic specific energy on waste activated sludge (WAS) solubilization and enzyme activity was investigated in this study. Experimental results showed that the increase of ultrasonic specific energy in the range of 0 - 90000 kJ/kg dried sludge (DS) benefited WAS particle size reduction and the solubilization of organic matter in WAS. The changes of ultrasonic specific energy also gave impact on the activities of hydrolytic enzymes (protease, α-glucosidase, acid and alkaline phosphatase) which were related to the hydrolysis of protein and carbohydrate in WAS. Further investigation revealed that the activities of four hydrolytic enzymes reached the highest at the specific energy of 30000 kJ/kg DS with the disintegration degree of 38.2%. Also, the releases of soluble ammonia and phosphorus was studied during the ultrasonic treatment of WAS.   Key words: Waste activated sludge (WAS), ultrasonic, solubilization, disintegration degree, enzyme activity.

Synergistic effects between solid potato waste and waste activated sludge for waste-to-power conversion in microbial fuel cells

Thermophilic alkaline fermentation followed by mesophilic anaerobic digestion (TM) for hydrogen and methane production from waste-activated sludge (WAS) was investigated. The TM process was also compared to a process with mesophilic alkaline fermentation followed by a mesophilic anaerobic digestion (MM) and one-stage mesophilic anaerobic digestion (M) process. The results showed that both hydrogen yield (74.5 ml H2/g volatile solids [VS]) and methane yield (150.7 ml CH4/g VS) in the TM process were higher than those (6.7 ml H2/g VS and 127.8 ml CH4/g VS, respectively) in the MM process. The lowest methane yield (101.2 ml CH4/g VS) was obtained with the M process. Taxonomic results obtained from metagenomic analysis showed that different microbial community compositions were established in the hydrogen reactors of the TM and MM processes, which also significantly changed the microbial community compositions in the following methane reactors compared to that with the M process. The dynamics of bacterial pathogens were also evaluated. For the TM process, the reduced diversity and total abundance of bacterial pathogens in WAS were observed in the hydrogen reactor and were further reduced in the methane reactor, as revealed by metagenomic analysis. The results also showed not all bacterial pathogens were reduced in the reactors. For example, Collinsella aerofaciens was enriched in the hydrogen reactor, which was also confirmed by quantitative PCR (qPCR) analysis. The study further showed that qPCR was more sensitive for detecting bacterial pathogens than metagenomic analysis. Although there were some differences in the relative abundances of bacterial pathogens calculated by metagenomic and qPCR approaches, both approaches demonstrated that the TM process was more efficient for the removal of bacterial pathogens than the MM and M processes.IMPORTANCE This study developed an efficient process for bioenergy (H2 and CH4) production from WAS and elucidates the dynamics of bacterial pathogens in the process, which is important for the utilization and safe application of WAS. The study also made an attempt to combine metagenomic and qPCR analyses to reveal the dynamics of bacterial pathogens in anaerobic processes, which could overcome the limitations of each method and provide new insights regarding bacterial pathogens in environmental samples.

Volatile fatty acids produced by waste activated sludge with low-dose nano-zero-valent iron synchronized with low-intensity ultrasonication pretreatment.

Phosphorus recovery from waste activated sludge (WAS) is a sustainable solution to the ever-increasing global phosphorus challenge. Thermochemical technologies, including pyrolysis, incineration, and gasification, reduce sludge volume and retain phosphorus in the solid phase, but their performance is strongly dependent on WAS characteristics and upstream treatment processes. Existing reviews often overlook the effects of WAS's physical and chemical characteristics on recovery efficiency, pre-treatment requirements, and technology selection. This review analyses correlations between upstream factors, sludge characteristics, and thermochemical pathways, and maps phosphorus transformation from raw WAS to final products. Sludge with high organic phosphorus (OP) and polyphosphate (poly-P) (from biological phosphorus removal), and low moisture, favours pyrolysis with minimal post-treatment, whereas high-moisture sludge rich in inorganic phosphorus requires incineration or gasification with more intensive processing. The feasibility of thermochemical pathways is affected by energy recovery, product marketability, feedstock variability, and social and regulatory constraints. To facilitate scalable, sustainable, and financially feasible phosphorus recovery and advance circular nutrient management in wastewater treatment, it is imperative to incorporate customised technology selection, high-value products, energy and resource recovery, and supportive regulations. • Waste activated sludge (WAS) is a promising source for phosphorus recovery. • Thermochemical technologies recover phosphorus and reduce sludge from WAS. • Characteristics of WAS and phosphorus speciation are key for efficient recovery. • Scale up faces feedstock, regulatory, economic, and social challenges.

Influences of released humic acids during thermal hydrolysis on sludge anaerobic digestion: New insights from the molecular weight of humic acids

Electricity production and nutrient recovery from waste activated sludge via microbial fuel cell and subsequent struvite crystallization: Effect of low temperature thermo-alkaline pretreatment

Identification and degradation of structural extracellular polymeric substances in waste activated sludge via a polygalacturonate-degrading consortium

Current advances and challenges for direct interspecies electron transfer in anaerobic digestion of waste activated sludge

Fe(II) catalyzing sodium percarbonate facilitates the dewaterability of waste activated sludge: Performance, mechanism, and implication