Effects Of Sludge Properties Research Articles

Effects of sludge properties in a combined process of mesophilic anaerobic-aerobic digestion

The combined medium-temperature anaerobic digestion and medium-temperature aerobic digestion (MAND/MAD) is a strategy that is suitable for the disposal of conventional activated sludge. The MAND/MAD sludge stabilization process was performed at three retention times (17, 24, and 38 days) of anaerobic digestion (AND-time) with further duration up to 22 days of the MAD process. The retention time of the MAND process had an important role in sludge stabilization. Its extension enhanced sludge stability in the aerobic digestion stage. During a MAD process, values of volatile/total solids ratio (VS/TS) presented the lowering course for the three investigated retention AND-times. The relatively long retention time of MAND leads to a higher level of soluble organic compounds (SCOD) and extracellular polymers (EPS) in the supernatant. Due to the shorter capillary uptake time at the end of digestion in the MAND/MAD system, the sludge with an AND-time of 38 days was extremely susceptible to dewatering compared to the sludge with an AND-time of 17 and 24 days.

Effects of sludge properties in a combined process of mesophilic anaerobic digestion and thermophilic aerobic digestion

The combination of mesophilic anaerobic digestion and thermophilic aerobic digestion (MAN-TAD) has been recognized as a suitable technology to deal with conventional activated sludge. The MAN-TAD system can make sludge achieve better stability. The retention time of anaerobic digestion (AD-time) had an important role in the sludge stabilization process. With the extension of anaerobic digestion retention time, MAN-TAD system can make sludge achieve better stability. In comparison, volatile/total solids ratio (VS/TS) at AD-time of 38 d presented the lowest values among the three different AD-time with the value of 0.32. Long retention time of anaerobic digestion resulted in high amounts of soluble organic compounds (SCOD), and extracellular polymers (EPS) in the supernatant. Such high amount of organic compounds caused deterioration in sludge dewaterability. Compared with sludges of AD-time 17 d and 24 d, sludge of AD-time 38 d became extremely difficult to dewater due to its high capillary water absorption time (CST) at the end of digestion.

Thermodynamic prediction and experimental investigation of short-term dynamic membrane formation in dynamic membrane bioreactors: Effects of sludge properties.

In dynamic membrane bioreactors (DMBRs), a dynamic membrane (DM) forms on a support material to act as the separation membrane for solids and liquids. In this study, batch filtration tests were carried out in a DMBR using nylon mesh (25 μm) as support material to filtrate sludge suspensions of variable properties from three different sources to evaluate the effects on the short-term DM formation process (within 240 min). Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was applied to analyze the sludge adhesion and cohesion behaviors on the mesh surface to predict quantitative parameters of the short-term DM formation process (including initial formation and maturation stage). The filtration results showed that the order of the initial DM formation time (permeate turbidity <1 NTU as an indicator) was as follows: sludge with poor settleability and dewaterability < normal sludge < sludge with poor flocculability. Moreover, normal sludge (regarding settleability, dewaterability, flocculability, and extracellular polymeric substance) showed a more acceptable DM formation performance (short DM formation time, low permeate turbidity, and high permeate flux) than sludge with poor settleability, dewaterability and flocculability. The influence of sludge properties on the initial DM formation time corroborates the prediction of sludge adhesion behaviors by XDLVO theory. Additionally, the XDLVO calculation results showed that acid-based interaction, energy barrier, and secondary energy minimum were important determinants of the sludge adhesion and cohesion behaviors. Therefore, short-term DM formation process may be enhanced to achieve stable long-term DMBR operation through positive modification of the sludge properties.

Polycyclic aromatic hydrocarbon formation from gasification of sewage sludge in supercritical water: The concentration distribution and effect of sludge properties

The changes in the polycyclic aromatic hydrocarbon (PAH) concentration and distribution in 10 different types of raw sewage sludge and gasified residues were investigated, and the effects of the sludge properties and the organic matter composition were determined. The results showed that the concentrations of 2-ring and 6-ring PAHs increased significantly during the gasification process. The PAHs in raw sludge were dominated by 3-ring and 4-ring PAHs, and those after gasification were dominated by 2-ring and 3-ring PAHs. The total PAH concentration increased with the increasing volatile matter content and decreased with the increasing pH value. Phenols have been considered to be important precursors for PAH synthesis. The crude fat and carbohydrate content can promote lower-molecular-weight PAH formation, while lignin and humic substance content can promote higher-molecular-weight PAH formation, which indicates that the organic matter composition in raw sludge has a high impact on the PAH distribution.

Influence of sludge properties on the direct gasification of dewatered sewage sludge in supercritical water

In the present study, ten different types of dewatered sewage sludges were treated in supercritical water in a high-pressure autoclave under a given condition (at 400 °C, 60 min and 23 MPa). The feasibility of direct gasification and the effect of sludge properties on the gasification of dewatered sewage sludge with various properties in supercritical water were investigated. The results showed that dewatered sewage sludge with various water contents (73.48–88.51 wt%), organic matter contents (29.25–73.02 wt%, on dry basis) and inorganics can be directly gasified in supercritical water. The total gas and phenol production increased linearly with the increment of organic matter content in dewatered sewage sludge. The difference in hydrogen content in the gaseous product may be related to the content of water and inorganic as well as pH value of the sludge. The char/coke formed in the solid residue increased with decrement of water content, which inhibited the gasification reaction and resulted in the carbonization reaction.

Effect of Modified Diatomite Addition on Sludge Properties for Membrane Fouling Alleviation in Submerged Membrane Bioreactor

To alleviate the membrane fouling in membrane bioreactor, a kind of modified diatomite was used as anti-fouling agent to examine the effect on sludge properties in submerged membrane bioreactor for synthetic domestic wastewater treatment. Three submerged membrane bioreactor setups were operated under fixed membrane flux 21.9m3/m2·h, meanwhile, modified diatomite was added into each membrane bioreactor with dosage of 0mg/L, 1000mg/L and 2000mg/L respectively. Sludge particle size, extracellular polymeric substances and molecular weight distribution were characterized as the activated sludge properties in this study. The experiment results showed that with the increase of modified diatomite dosage, the number of sludge particle size less than 10μm was declined, however, the number between 10–20μm was increased correspondingly. Total extracellular polymeric substances and big molecular weight substances were decreased remarkably with modified diatomite addition dosage of 1000mg/L. The results indicated that addition of modified diatomite could effect of sludge properties in submerged membrane bioreactor. Therefore, membrane filtration performance could be improved by modified diatomite adding which alleviate membrane fouling directly.

Effects of Sludge Properties on the Thickening and Dewatering of Waste Activated Sludge

The thickening and dewatering of waste activated sludge, from a pilot-scale submerged membrane bioreactor and two bench-scale, complete-mix activated sludge reactors (high-shear and low-shear aeration) treating the same municipal primary effluent, were investigated. Solids settling and compaction were measured using the diluted sludge volume index (DSVI) analysis and a batch centrifugation analysis, respectively. Elevated levels of filamentous microorganisms resulted in higher DSVI values and lower centrifuged pellet concentration. Elevated levels of nocardioform bacteria resulted in lower solids float concentrations, and higher colloidal material reduced solids recovery in batch flotation experiments. Sludge filterability, measured as time-to-filter, was shown to be a function of extracelluar polymeric substances and colloidal material, where higher levels of either reduced sludge filterability. Additional research is necessary to confirm these results using full- or demonstration-scale thickening and dewatering units.