Sludge Particle Size Research Articles

Performance and microbial community analysis of anaerobic sludge digestion enhanced by in-situ microaeration

The effectiveness of in-situ microaeration was investigated with varied air dosages [0–25 mL/(L·d)] to enhance mesophilic anaerobic digestion (AD) of sludge in semi-continuous systems in terms of specific biogas production and volatile solids (VS) removal rate, focusing on performance evaluation, microbial community analysis, and underlying mechanisms. The optimal dosage of 12.5 mL/(L·d) increased specific biogas production by 15.8 ± 7.3% and enhanced VS removal by 18.3 ± 1.6%. In-situ microaeration stimulated activity of hydrolytic enzymes, enlarged sludge particle size, and improved sludge dewaterability. MiSeq sequencing analysis showed that dominant bacterial and archaeal communities were remarkably different between in-situ microaeration and obligate AD process. The presence of oxygen enriched relative abundances of Deltaproteobacteria, Anaerolineae, Clostridia, Synergistia and Caldilineae, enabling the acid-producing process to metabolize more types of substrates. Due to the selective enrichment, in-situ microaeration significantly enriched aceticlastic methanogens rather than hydrogenotrophic methanogens in the AD reactor. Analysis of coupling microaeration pretreatment and in-situ microaeration for anaerobic digestion indicated that excessive microaeration decreased VS removal rate and methane yield owing to substrates consumption by facultative bacteria. In-situ microaeration-based AD could be a promising process for sludge treatment and bioenergy recovery.

Operational mode affects the role of organic matter in granular anammox process

In the presence of organic matter, the granular anammox system under sequencing batch mode showed more robust anammox performance than that under completely mixed mode, which was attributed to the better biomass retention with high settling ability and stability of granular sludge. Based on the specific anammox activity test, stratified and mixed distribution of heterotrophic bacteria was found under completely mixed and sequencing batch mode, respectively. The stratified microbial distribution resulted in low enzyme activity of anammox bacteria and sludge disintegration by hindering substrate transfer with a large accumulation of EPS on the granular surface. Whereas the heterotrophic bacteria mixed in granules (mixed microbial distribution) act as a “skeleton”, which increased the particle size, density, and stability of granular sludge. Compared with biokinetic-based selection, diffusion-based selection with high substrate penetration depth more likely resulted in the mixed granular structure and strong resistance to organic inhibition under sequencing batch mode.

Transformation of typical components in anaerobically digested sludge during its conditioning process by KMnO4

Many efforts have been made to improve the dewaterability during anaerobically digested sludge (ADS) conditioning. However, the conversion of substances in ADS conditioning, as an important process of sludge treatment and application, has received little attention. This study investigated the transformation process of typical components in sludge such as extracellular polymeric substances (EPS), sulfide, Fe and Mn species. The effects of KMnO4 dosage and pH change on the ADS conditioning were investigated in detail. The results showed that the sludge particle size and capillary suction time decreased with the increase of KMnO4 dosage. The water content of sludge cake by vacuum filtration gradually dropped from 84.5% to 78.8% after conditioning with 0–5.0 g KMnO4/L sludge. Based on fluorescence excitation-emission matrix, EPS and dissolved organic carbon measurements, the improvement of sludge dewaterability was due to the disruption of EPS and the release of intracellular substances. Interestingly, 11.5% sulphides (S2−) in ADS were oxidized into SO42− at KMnO4 dosage of 3.0 g/L, which can effectively inhibit the release of hazardous H2S even the sludge pH changed to 2 in conditioning process. Moreover, about 30 mg/L of PO43− in centrifugate can be completely immobilized by the generated iron, manganese and their binary oxides as a result of the interaction between Fe2+ and KMnO4. These findings provided a new insight to explore the sludge conditioning process and the transformation of typical components.

Treatment of high‐strength synthetic textile wastewater through anaerobic osmotic membrane bioreactor and effect of sludge characteristics on flux

AbstractThe anaerobic osmotic membrane bioreactor (AnOMBR) system was evaluated for the treatment of high‐strength synthetic textile wastewater. The chemical oxygen demand (COD) concentration was above 3,000 mg/L and color above 1,300 Pt‐Co in the synthetic textile wastewater. The study was divided into six cycles of roughly nine days each. Mono ammonium phosphate with 1 M concentration was used as draw solution. Average COD and color removal efficiencies from anaerobic bioreactor were 57% ± 5% and 43.7% ± 6%, respectively; however, in OMBR permeate, these parameters were improved to 91% ± 4% and 91% ± 2%, respectively. After each cycle, membrane cleaning was performed using osmotic backwashing for 3 hours, which produced flux recovery values between 88% and 61% from cycle 2 to cycle 6, respectively. High mixing speed of the stirrer bar (600 rpm) in the bioreactor produced a greater shear force, causing a reduction in average sludge particle size from 10 to 3.5 μm. It increased the release of soluble microbial products and extra polymeric substances to cause an initial flux decline from 3.3 to 2.2 LMH from cycle 1 to cycle 6. The study proved AnOMBR as a promising technology for high‐strength synthetic textile wastewater treatment.

Dispersion Behavior of Blast Furnace Sludge for Valuable Metal Recovery

Blast furnace sludge, which comes from the iron making process, contains many valuable materials including iron, carbon, and zinc, etc. Because a cohesive agent is added during filtration, fine sludge particles are agglomerated together. Therefore, This makes it necessary to disperse the sludge in solution before separating or recovering valuable materials. In this study, the effects of solid/liquid (g/L) ratio, ultrasonic dispersion conditions, the pH of solvent, and the concentration of dispersant on the dispersion of sludge were investigated by measuring the interfacial properties (zeta potential and hydrodynamic size) of sludge particles. High absolute value of zeta potential and small hydrodynamic size suggests that the sludge particles in the solution presents good dispersion. The absolute value of zeta potential increased gradually at high solid/liquid ratio and ultrasonic dispersion intensity. But when the sludge in solution was dispersed for more than 30 minutes, the absolute value of the zeta potential decreased due to increasing contact and interaction between the particles. Optimal dispersion operations were conducted and when the pH of the solution was adjusted to 11, the zeta potential value was measured to be -44.8 mV. This means that the sludge formed the most stable dispersed phase. The lowest zeta potential was measured to be -46.4 mV with the addition of sodium hexametaphosphate (NaPO3)6 in the solution. It is thought that the sodium hexametaphosphate reduced ionic strength by removing alkali metal ions from the solution of sludge.

Compact wastewater treatment process based on abiotic nitrogen management achieved high-rate and facile pollutants removal

Chemically enhanced primary treatment (CEPT), ammonium ion exchange and regeneration (AIR) and membrane bioreactor (MBR) were coupled as CAIRM to treat domestic wastewater compactly and efficiently. CAIRM achieved efficient removal of chemical oxygen demand, ammonia nitrogen, total nitrogen (TN) and total phosphorus with total hydraulic retention time of 4.6 h, and obtained 2.3 ± 0.9 mg/L TN in the effluent. CEPT removed phosphate and impurities and prevented AIR from pollution. AIR maintained excellent nitrogen removal with a slight decrease in the exchange capacity of ion exchangers. MBR polished the effluent from AIR, and the larger particle size and better dewaterability of sludge mitigated the membrane fouling. Many heterotrophic genera, such as Rhodobacter and Defluviimonas, were enriched in the oligotrophic MBR. This study demonstrates the viability and stability of CAIRM in efficient wastewater treatment, which will address critical challenges in insufficient nitrogen removal and high land occupancy of current processes.

Biological power generation and earthworm assisted sludge treatment wetland to remove organic matter in sludge and synchronous power generation

In order to eliminate the weak degradation ability of organic matter in sludge treatment wetland (STW). In current work, a combined biological power generation and earthworm assisted sludge treatment wetland (BE-STW) system is proposed for the first time to accelerate degradation and dehydration process of organics in STW, thusly, recovering biomass energy in sludge. Experimental results show that S4 system (earthworm and bioelectricity combined) yields a voltage of 0.832 V and maximum power density of 94.98 W/m2 in the 5th day. The combination of earthworm, microorganism and plants in STW system can reduce the ratio of volatile solids to total solids (VS/TS) to 15% while the removal rate of total chemical oxygen demand (TCOD) reaches 92.1%. The BE-STW system increases sludge particle size while reduces absolute value of Zeta and extracellular polymeric substances (EPS) content, so that the moisture content of effluent sludge retains to 66.8%. Meanwhile, the richness of bacterial communities in S4 proves that bioelectrochemistry and earthworm can effectively improve the sludge treatment effect.

Structural regulation of electroplating sludge by a metal–organic framework synthesis method for an enhanced denitrification activity

Electroplating sludge contained multi-metals and organics. In previous reports, electroplating sludges were usually recycled by direct calcination and pyrolysis for structural regulations. For the first time, a metal–organic framework synthesis method was utilized to regulate the structure of an electroplating sludge. In brief, the sludge was hydrothermally treated in solution of 1,3,5-trimesic acid, ethanol, and N,N-dimethylformamide. After this strategy, the sludge particle size was decreased; metals and organics formed coordination bond, and transformed oxygen-centered radicals to carbon-centered radicals; amorphous phases were re-crystalized to form well-dispersed crystals. As a result, the regulated sludge showed an enhanced denitrification activity. It removed 61.6% of nitric oxide (990 ppm) at a temperature as low as 150 °C. The activity was even close to 99.9% at 350 °C. What is more, the regulated sludge was characterized by plenty of free carboxylic groups and multi-metal catalytic centers, which make it a better catalyst than the pure-reagent-synthesized catalyst. Therefore, this paper put forward a novel strategy for the high value-added utilization of electroplating sludge.

Treatment of Fracturing Wastewater by Anaerobic Granular Sludge: The Effect of Salinity and its Mechanism

The effects of salinity on the anaerobic treatment of fracturing wastewater regarding COD removal performance, sludge characteristics and microbial community were investigated. Results showed COD removal efficiency decreased from 76.0% to 69.1%, 65.6%, 33.7% and 21.9% with increasing salinity from control group (2.5 g/L) to 10, 15, 25 and 45 g/L, respectively. The cumulative biogas production decreased by 13.8%–81.1% when the salinity increased to 15–85 g/L. The increase of salinity led to the decline in the particle size of granular sludge, and the activity of granular sludge, including SMA, coenzyme F420 and dehydrogenase, was inhibited significantly. The results from flow cytometry indicated the percentage of damaged cells in granular sludge gradually increased with increase of salinity. Sequence analysis illustrated the microbial community structure in anaerobic digestion reactor was affected by the salinity, high salinity reduced the diversity of microbial community and decreased the abundance of methanogens, especially Methanosaeta.

Evaluation of Siltation Degree of Permeable Asphalt Pavement and Detection of Noise Reduction Degree

This study mainly uses PFC (particle follow code) to simulate the void characteristics of permeable asphalt mixture, and uses these to simulate the silting process. Then, a tire drop test was used to evaluate the noise reduction performance of permeable asphalt concrete. Finally, a self-made ring rutting test machine was used to simulate the silting process. Through experiments, the following conclusions were obtained: 1. The critical size of the sludge particle size is 0.3 mm–0.6 mm. 2. The quality of the water-permeable asphalt concrete specimens increased by 13% before and after silting, and the porosity of the specimens finally decreased from about 20% to about 8%. The water-permeable function only retained less than 20% of the original, and the water-permeable function was basically lost. 3. By measuring the road noise detection, it was found that the road noise is directly proportional to the degree of blockage of the permeable road. Compared with the original road with a perfect permeable function, the road noise of the completely blocked road increased by about 4 decibels. This study reveals the silting process of permeable asphalt mixture and the key particle size of the silt, which is of great significance for the detection, cleaning and maintenance of permeable asphalt pavements.

Decomposition process of cefotaxime sodium from antibiotic wastewater by Up-flow Blanket Filter (UBF) reactor: Reactor performance, sludge characteristics and microbial community structure analysis

In this study, a novel Up-flow Blanket Filter (UBF) reactor was applied to the degradation of antibiotic wastewater. The experiments showed that when the hydraulic retention time (HRT) was 24 h and the ratio of volatile fatty acids (VFA) to alkalinity (ALK) was 0.3, the best removal efficiency was achieved in the combined packing UBF reactor, and the COD removal efficiency reached 80.1%–84.6%, exhibiting a significant difference in reaction performance from the other two reactors (P < 0.05) and a good efficiency of cefotaxime sodium removal. Moreover, the microstructure and surface characteristics of the reactor fillers were studied through scanning electron microscope (SEM) analysis, which showed that three fillers all had biofilm adhesion, but the combined packing gave best performance. Energy dispersive spectrometer (EDS) tests indicated abundant element components in the combined packing. The particle size distribution of sludge was also considered in the experiment, and the result showed the particle size of sludge increased with the operation of the reactor. In addition, microbial community structures of sludge and biofilm with the combined packing were analyzed. High-throughput sequencing confirmed the existence of Pseudomonas, which had good adaptability to antibiotic wastewater and became the dominant bacteria. Decomposition process of cefotaxime sodium after hydrolysis and anaerobic treatment was analyzed through Fourier transform infrared spectroscopy (FTIR). The reactor, which is economical, exhibited favorable performance in degrading the pollutions in the antibiotic wastewater.

Effect of Ca(OH)2 on the Release Characteristics of HCl during Sludge Combustion.

With the addition of Ca(OH)2, the effects of combustion temperature, moisture, sludge particle size, and chlorine-containing additives on the removal of HCl during sludge combustion were studied. The experimental results showed that combustion temperature and moisture content promoted the formation of HCl and Ca(OH)2 played a key role in the formation of HCl during sludge combustion. Under the best conditions of a sludge particle size of 380–250 μm, moisture content of 5%, temperature of 850 °C, and Ca(OH)2/sludge weight ratio of 3/10, the HCl capture efficiency was 79.81%. In addition, the effect of PVC on the production of HCl was greater than that of NaCl, probably because the lattice energy of NaCl was much higher, indicating that inorganic chlorine was not the main source of HCl. Ca(OH)2 can effectively inhibit the formation of HCl, which had practical guiding significance for the formation of HCl during the sludge combustion, especially the sludge containing chlorine.

Anaerobic offsite Fe2+ releasing for electrocoagulation in ABMBR: Membrane fouling mitigation, nutrients removal and anodes protection

To solve the problems of pollutants removal and membrane fouling in membrane bioreactor (MBR) and plate passivation in the process of electrocoagulation (EC), anaerobic baffled membrane bioreactor (ABMBR, 4 cells for anaerobic process and 1 cell for membrane separation) was proposed for anaerobic offsite release of Fe2+ in the process of EC. The iron plates were placed in the anaerobic unit and the membrane module was placed outside the electric field. The results showed that the operation time could be extended from 5 to 8 days to 63 days when 3 V intermittent voltage (5 min on and 5 min off) was adapted. As the result of EC, protein and polysaccharide contents of soluble microbial products (SMP) and extracellular polymeric substances (EPS) from sludge and filter cake layer were decreased obviously. The sludge particle size was increased from 400 nm to 80 μm and zeta potential was decreased from −11 mV to −20 mV. The water quality results showed that almost 100 % of ammonia nitrogen (NH4+-N) and 87 % of total phosphorus (TP) were removed under the action of EC without excess sludge discharge. By placing the iron plate in the anaerobic unit, plate passivation was very slow during 195 days of operation, which solved the problem of plate passivation in EC.

Impacts of sulfadiazine on the performance and membrane fouling of a hybrid moving bed biofilm reactor-membrane bioreactor system at different C/N ratios

The performance and membrane fouling of a hybrid moving bed biofilm reactor-membrane bioreactor (MBBR-MBR) system was evaluated when exposed to 0.5 mg/L of antibiotic sulfadiazine (SDZ). Results indicated that although SDZ reduced the removal efficiency of NH4+-N and TN (up to 12%) and TOC (up to 6%) at low C/N (2.5 and 4), it had no significant effect at high C/N (6 and 9). It was found that SDZ was removed 75% and 58% at high C/N of 9 and low C/N of 2.5, respectively. SDZ decreased the ratio of volatile biomass/total biomass and sludge particle size and increased the concentrations of extracellular polymeric substance (EPS) and soluble microbial product (SMP) in MBR. Consequently, this accelerated the membrane fouling rates, with an average increase of 6.85 kPa/d at low C/N (2.5) and 0.513–0.701 kPa/d at medium and high C/N (4, 6 and 9).

Long-Term Investigation into the Membrane Fouling Behavior in Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment Operated at Two Different Temperatures.

In this study, the characteristics of activated sludge flocs were investigated and their effects on the evolution of membrane fouling were considered in the anaerobic membrane bioreactors (AnMBR), which were operated at 25 and 35 °C for municipal wastewater treatment. It was found that the membrane fouling rate of the AnMBR at 25 °C was more severe than that at 35 °C. The membrane fouling trends were not consistent with the change in the concentration of soluble microbial product (SMP). The larger amount of SMP in the AnMBR at 35 °C did not induce more severe membrane fouling than that in the AnMBR at 25 °C. However, the polysaccharide and protein concentration of extracellular polymeric substance (EPS) was higher in the AnMBR at 25 °C in comparison with that in the AnMBR at 35 °C, and the protein/polysaccharide ratio of the EPS in the AnMBR at 25 °C was higher in contrast to that in the AnMBR at 35 °C. Meanwhile, the fouling tendencies measured for the AnMBRs could be related to the characteristics of loosely bound EPS and tightly bound EPS. The analysis of the activated sludge flocs characteristics indicated that a smaller sludge particle size and more fine flocs were observed at the AnMBR with 25 °C. Therefore, the membrane fouling potential in the AnMBR could be explained by the characteristics of activated sludge flocs.

New insight into volatile sulfur compounds conversion in anaerobic digestion of excess sludge: Influence of free ammonia nitrogen and thermal hydrolysis pretreatment

Volatile sulfur compounds (VSCs) are the main toxic components generated simultaneously with biogas in anaerobic digestion (AD) of sludge. The differences of chemical and biological processes involved in the VSCs conversion between conventional AD and thermal hydrolysis pretreated high solid AD (THP-HSAD), widely applied in recent years, have yet to be fully elucidated. This study evaluated the effect of solid content, initial pH, and thermal hydrolysis on the VSCs conversion in AD. This study had evidenced that neither the solids content nor the pH adjustment affects the VSCs conversion. It was found that free ammonia nitrogen concentration, which increased (>500 mg/L) in HSAD, directly inhibited the enzymatic activity of cysteine lyase (R2 = 0.87, P < 0.01) and methionine lyase (R2 = 0.89, P < 0.01), thereby affecting the VSCs conversion. Thermal hydrolysis pretreatment (THP) had no consequential impact on the key enzymes involved in the VSCs conversion. Instead, the particle size of excess sludge reduced by 66.05 ± 6.66%. It was postulated that THP may reduce the sludge particle size, increasing the contact of sulfur compounds with invertase, thus favoring VSCs conversion. These findings contribute to a better understanding of the mechanisms and control measures of the VSCs conversion during the AD of sludge.

Feast/famine ratio determined continuous flow aerobic granulation

Plug flow reactors (PFRs) made of multiple completely stirred tank reactors (CSTRs) in series were used to cultivate aerobic granules in real domestic wastewater. Theoretically, changing the number of CSTR chambers in series will change the nature of plug flow, and thus alter the pattern of the feast/famine condition and impact the aerobic granulation progress. Therefore, PFRs were operated in 4-, 6-, and 8-chamber mode under the same gravity selection pressure (a critical settling velocity of 9.75 m h−1) and hydraulic retention time (6.5 h) until steady states were reached to evaluate the effect of the feast/famine condition on continuous flow aerobic granulation. The sludge particle size, circularity, settleability, specific gravity, zone settling velocity, and extracellular polymeric substance contents were analyzed to evaluate the role that a feast/famine regime plays in aerobic granulation. It was found that aerobic granulation failed whenever the feast/famine ratio was greater than 0.5. The results support a conclusion that the feast/famine condition is likely a prerequisite for continuous flow aerobic granulation.

Pilot-scale textile dyeing wasted sludge reduction via microbial agent and aeration: Parameter optimization and mechanisms exploration

Abstract New methods to treat textile dyeing wasted sludge (TDWS) should be developed. In this study the sludge reduction induced by microbial agent addition and aeration in pilot-scale was studied. The one-off addition mode was employed in which better sludge reduction (i.e., 58.4%) and lower moisture content (i.e., 71.6%) were achieved. 25 L/min of aeration rate was best for sludge reduction and 52.8% of sludge reduction was achieved and aeration did play an important role in the sludge reduction. 15000 mg/L was determined as the suitable initial sludge concentration. The mechanisms of TDWS reduction were explored subsequently. As the results, the sludge particle size decreased with microbial agent addition while no such reduction was observed without microbial agent. The sludge would react with hydrolase to release organic substance and produce chemical oxygen demand (SCOD) in the liquid, which could be consumed by microorganisms. Finally, the change of microbial community was explored so as to further explain the mechanism of sludge reduction. The phylum Bacteroidetes increased from 33.30% to 45.37% with microbial agent addition which indicated the important role in sludge reduction. The genus Sphingopyxis, Thermomonas and Fluviicola would be the most relevant microorganisms with sludge reduction while the moisture content was most related with Dok59.

Study on the influencing factors of removal of NOX from cement kiln flue gas by sewage sludge as a denitration agent

Experimental study on the influencing factors of using sewage sludge as a denitration agent for cement industry was carried out on a self-made laboratory-scale fluid-bed reactor. Results indicate that sludge combustion at 900°C shows an ideal NOX (the sum of NO and NO2) removal activity under simulated working conditions of cement precalciner. The optimal removal efficiency of NOX can reach 70.36 ± 3.59% in the presence of cement raw meal (CRM) at a sludge particle size range of 0.18-0.25mm and the sludge dosage of 0.75g/min. Besides, the NOX removal efficiency increases to 76.94 ± 5.02% in the absence of CRM, indicating that cement raw meal inhibits the NOX removal. This phenomenon may be attributed to the fact that CRM has promotion effect on NH3 produced and obvious inhibitory effect on CO produced; while NH3 and CO play a leading role in NOX reduction, the combined effect leads to the decrease of NOX removal. Moreover, the relationship between the composition of CRM on the inhibition of NOX removal is MgO < CaCO3 < CRM < Al2O3 <Fe2O3. Meanwhile, the effect of additive variety on the sludge denitration activity indicates that urea significantly promotes the NOX removal, which is attributed to the decomposition of urea to form NH3. The stability experiment shows that sludge denitration efficiency remains stable above 70% in the presence of CRM and can reach over 80% when adding appropriate urea. This method can realize the removal of NOX in the cement kiln flue gas and the resource utilization of sludge. It is a promising method for sludge disposal.

Fast Start-Up ANAMMOX Operation Strategy and Flora Characteristics of a Biofilter

To achieve the rapid start-up of anaerobic ammonia oxidation (ANAMMOX) reaction at room temperature and sludge granulation, a small amount of ANAMMOX sludge was inoculated by an upflow biological filter reactor, and ANAMMOX was started by stage variable load and shortening hydraulic residence time (HRT) operation strategy. The reaction was evaluated, and the nitrogen removal characteristics of the biofilter were evaluated. The results showed that the biofilter started the ANAMMOX reaction in a medium-temperature (25-29℃) environment for 22 days. After 97 days of culture, the total nitrogen volume removal rate (NRR) reached 5.64 kg·(m3·d)-1, the total nitrogen (TN) removal rate was close to 80%, and the average particle size of the granular sludge was 4.5 mm. High-throughput sequencing analysis showed that the biofilter formed a layered structure of nitrifying bacteria-heterotrophic bacteria, anaerobic ammonium oxidation bacteria (AAOB), and AAOB-heterotrophic bacteria from bottom to top. The various microflora synergistically denitrified, creating a low dissolved oxygen (DO) stable environment for AAOB, and the dominant population Candidatus Kuenenia (AF375995.1) was enriched. In addition, the removal process of pollutants along the path and the characteristics of sludge along the process were analyzed, and it was verified that the sludge in the reaction zone had good ANAMMOX activity. An ANAMMOX-biofilter reactor achieves rapid start-up of the ANAMMOX reaction, sludge granulation, and efficient operation by effectively maintaining the amount of bacteria and stabilizing the reaction conditions.