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Recent experimental results have shown that the detection of cues in behavioral attention tasks relies on transient increases of acetylcholine (ACh) release in frontal cortex and cholinergically driven oscillatory activity in the gamma frequency band (Howe et al. Journal of Neuroscience, 2017, 37, 3215). The cue-induced gamma rhythmic activity requires stimulation of M1 muscarinic receptors. Using biophysical computational modeling, we show that a network of excitatory (E) and inhibitory (I) neurons that initially displays asynchronous firing can generate transient gamma oscillatory activity in response to simulated brief pulses of ACh. ACh effects are simulated as transient modulation of the conductance of an M-type K + current which is blocked by activation of muscarinic receptors and has significant effects on neuronal excitability. The ACh-induced effects on the M current conductance, g Ks , change network dynamics to promote the emergence of network gamma rhythmicity through a Pyramidal-Interneuronal Network Gamma mechanism. Depending on connectivity strengths between and among E and I cells, gamma activity decays with the simulated g Ks transient modulation or is sustained in the network after the g Ks transient has completely dissipated. We investigated the sensitivity of the emergent gamma activity to synaptic strengths, external noise and simulated levels of g Ks modulation. To address recent experimental findings that cholinergic signaling is likely spatially focused and dynamic, we show that localized g Ks modulation can induce transient changes of cellular excitability in local subnetworks, subsequently causing population-specific gamma oscillations. These results highlight dynamical mechanisms underlying localization of ACh-driven responses and suggest that spatially localized, cholinergically induced gamma may contribute to selectivity in the processing of competing external stimuli, as occurs in attentional tasks.

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The influence of the key structural features of sludge that are responsible for the low anaerobic conversion efficiency of sludge is poorly understood. In this study, sludge organic substances are reclassified into extracellular organic substances (EOSs) and cell biomass on the basis of sludge structure. The roles of EOSs in the biogas conversion of both sewage sludge (SS) and model sludge (MS) were investigated. It is observed that with increasing EOS content the net cumulative methane production (NCMP) of the sludge decreased by 36.4%, implying the crucial roles of EOSs in anaerobic sludge digestion. The experimental results showed that with increasing EOS content in sludge, the extracted EOS content decreased, indicating that the structural stability of EOSs in sludge was reinforced. Considering that the biodegradation of EOSs typically depends on structural stability, spatial configuration of EOSs has been hypothesized to account for the low anaerobic digestion efficiency. Further analyses of the spatial configuration of EOSs from the MS and SS revealed that the random-coil shape with extended chains in MS is more readily biodegradable than the dense globule shape with cross-linked chains in SS. These findings shed light on the underlying mechanism responsible for the low biogas conversion of sludge.

The easy biodegradable organic matter, non-biodegradable organic matter, metal ions, and micron-sized silica particle and their interactions were the key factors for limiting the biogas production from anaerobic sludge digestion.

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Anaerobic bioconversion of waste activated sludge (WAS) into methane is often limited by the slow hydrolysis rate and/or poor methane potential. In this study, a novel pretreatment strategy based on the isoelectric point of sludge particulate is proposed to enhance methane production from WAS. Pretreatment of WAS for 4 h at room temperature substantially changed the physicochemical properties of sludge particulate, resulting in the disintegration of WAS. The experimental results showed that the apparent activation energy of sludge organic solubilization was decreased by 49.5% and the surface site density of sludge particulate was increased by 71.2%, indicating that by this pretreatment WAS solubilization was enhanced and the surface binding sites for enzymes were decreased. In addition, compared to the conventional pretreatment methods, the main metal contents of WAS were decreased by 41.4% after this pretreatment, suggesting the possibility of simultaneously enhancing methane conversion and removing heavy metals from WAS. The biochemical methane potential assays demonstrated that after pretreatment the hydrolysis and acidification of sludge were significantly improved, with the highest volatile fatty acid concentration (3364 ± 28 mg/L) being more than twice that of the untreated samples. Model-based analysis indicated that pretreatment improved methane potential by approximately 19% (from 197.5 ± 8.3 to 242.8 ± 6.2 mL CH4/g volatile solids (VS)), thereby changing methane production kinetics. Further analysis indicated that after pretreatment the methanogenic bacteria growth, rather than the hydrolysis reaction of sludge, became the rate-limiting step in the anaerobic digestion (AD) process. These findings, however, may provide a new direction for enhancing the AD efficiency of WAS.