Enhancement of anaerobic digestive efficiency by the use of exchange resin to remove cations in sewage sludge

<p>Hydrolysis is considered as the rate-limiting stage of anaerobic digestion which is one of the most applied stabilization processes in the disposition of sludge. It is urgent to accelerate the hydrolysis of the sludge particles and improve its biodegradability. This study utilized cation-exchange resin (CER) to adsorb divalent cations in the supernatant of activated sludge with the purpose of making the sludge floc disintegrated. The results showed that the biopolymers incorporated in the tightly bound extracellular polymeric substances can be released to the bulk using CER to remove cations. However, the lack of essential elements led to a much lower methane yield of treated sludge than that of activated sludge. The treated sludge got a higher methane production rate constants after added Fe²⁺. It is necessary to add Fe²⁺ or regenerated liquid of resin-containing essential elements in order to maintain the activities of microbial life.</p

Effect of Increasing Total Solids Contents on Anaerobic Digestion of Food Waste under Mesophilic Conditions: Performance and Microbial Characteristics Analysis

<div><p>The total solids content of feedstocks affects the performances of anaerobic digestion and the change of total solids content will lead the change of microbial morphology in systems. In order to increase the efficiency of anaerobic digestion, it is necessary to understand the role of the total solids content on the behavior of the microbial communities involved in anaerobic digestion of organic matter from wet to dry technology. The performances of mesophilic anaerobic digestion of food waste with different total solids contents from 5% to 20% were compared and the microbial communities in reactors were investigated using 454 pyrosequencing technology. Three stable anaerobic digestion processes were achieved for food waste biodegradation and methane generation. Better performances mainly including volatile solids reduction and methane yield were obtained in the reactors with higher total solids content. Pyrosequencing results revealed significant shifts in bacterial community with increasing total solids contents. The proportion of phylum <i>Chloroflexi</i> decreased obviously with increasing total solids contents while other functional bacteria showed increasing trend. <i>Methanosarcina</i> absolutely dominated in archaeal communities in three reactors and the relative abundance of this group showed increasing trend with increasing total solids contents. These results revealed the effects of the total solids content on the performance parameters and the behavior of the microbial communities involved in the anaerobic digestion of food waste from wet to dry technologies.</p></div

Taxonomic compositions of bacterial communities at phyla level in each sample retrieved from pyrosequencing.

<p>Taxonomic compositions of bacterial communities at phyla level in each sample retrieved from pyrosequencing.</p

Taxonomic composition of bacterial communities at the genus level for the sequences retrieved from each sample.

<p>Taxonomic composition of bacterial communities at the genus level for the sequences retrieved from each sample.</p

Performance parameters of three reactors with different total solids contents.

a<p>Y_biogas: biogas yield.</p>b<p>Y_methane: methane yield.</p>c<p>VS_r: VS reduction.</p>d<p>SBP: specific biogas production rate based on removed VS.</p>e<p>SMP: specific methane production rate based on removed VS.</p>f<p>BP: volumetric biogas production rate.</p>g<p>MP: volumetric methane production rate.</p

Taxonomic compositions of methanogens at order level in each sample retrieved from pyrosequencing.

<p>Taxonomic compositions of methanogens at order level in each sample retrieved from pyrosequencing.</p

Characteristics of the substrates and inoculums.

<p>–Not determined.</p>a<p>FW: food waste.</p>b<p>TS: total solids.</p>c<p>VS: volatile solids.</p>d<p>TAN: total ammonia nitrogen.</p

Magnetite Triggering Enhanced Direct Interspecies Electron Transfer: A Scavenger for the Blockage of Electron Transfer in Anaerobic Digestion of High-Solids Sewage Sludge

At present, high-solids anaerobic digestion of sewage sludge has drawn great attention due to the superiority of its small land area footprint and low energy consumption. However, a high organic loading rate may cause acids accumulation and ammonia inhibition, thus leading to an inhibited pseudo-steady state in which electron transfer through interspecies hydrogen transfer (IHT) between acetogens and methanogens is blocked. In this study, adding 50 mg/g TS (total solid) magnetite clearly reduced the accumulation of short-chain fatty acids and accelerated methane production by 26.6%. As demonstrated, the individual processes of anaerobic digestion could not be improved by magnetite when methanogenesis was interrupted. Analyzing stable carbon isotopes and investigating the methanogenesis pathways using acetate and H₂/CO₂ as substrates together proved that direct interspecies electron transfer (DIET) was enhanced by magnetite. Metatranscriptomic analysis and determination of key enzymes showed that IHT could be partially substituted by enhanced DIET, and acetate-dependent methanogenesis was improved after the blockage of electron transfer was scavenged. Additionally, the expression of both pili and c-type cytochromes was found to decrease, indicating that magnetite could replace their roles for efficient electron transfer between acetogens and methanogens; thus, a robust chain of electron transfer was established

Spatial Configuration of Extracellular Organic Substances Responsible for the Biogas Conversion of Sewage Sludge

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

<i>In Situ</i> Reforming of the Volatile by Char during Sewage Sludge Pyrolysis

In this study, the volatile from sewage sludge (SS) pyrolysis is passed through the hot char from the same source in a fixed bed reactor. The reforming effect of the sewage sludge char (SSC) on the quality and energy distribution of liquid and gas products is studied. In comparison to dolomite, SSC presents a better tar-eliminating effect from 450 to 650 °C. The production of combustible products, including CH₄, H₂, and CO, is significantly increased by both the catalytic cracking on the SSC surface and the volatile–char reaction. After the reforming effect at the pyrolysis temperature of 650 °C, the gas yield is increased from 17.19 to 34.27 wt % and the fraction of combustible components is increased by 54.28 vol %. The quality of the oil is also upgraded by reforming of SSC, with the escalation of the light components, and nitrogen-containing and oxygenated fractions are greatly reduced. When the pyrolysis temperature is fixed at 650 °C and the reforming temperature is increased from 450 to 650 °C, the liquid yield is decreased from 18.76 to 10.67 wt %. In addition, the combustible fraction in the gaseous product is greatly increased. The calculation of the energy distribution indicates that, via the reforming process, a lot more heating value will concentrate on the gas product and the overall high heat value of the pyrolysis volatile and SSC will be significantly promoted