Sludge Loss Research Articles

Realizing stable operation of anaerobic ammonia oxidation at low temperatures treating low strength synthetic wastewater

The low activity of Anammox bacteria at low temperatures and competition from nitrite oxidation bacteria (NOB) when treating low strength wastewater have been major bottlenecks in implementing Anammox in mainstream wastewater treatment. By intermittent high strength feeding (IHSF) and stepwise temperature reduction, stable operation of a granular Anammox reactor was realized at low temperatures (down to 15°C) for 28days when treating low strength synthetic wastewater. The nitrogen loading rate reached 1.23–1.34kgN/m3/day, and the total nitrogen removal rate reached 0.71–0.98kgN/m3/day. The IHSF enriched the Anammox sludge in high strength cycles and compensated for sludge loss in low strength cycles, and the high concentration of ammonium in high strength cycles inhibited NOB. The 16SrRNA gene sequencing results revealed that Candidatus Kuenenia was predominant in the reactor at low temperatures.

Optimization of Anaerobic Granular Sludge by Removing Biogas

The loss of granular sludge and acidification of sludge are common problems in highly efficient anaerobic reactors in operation at present, which results in that the reactors cannot reach the design COD removal rates. The problems must be solved for the widespread use of the highly efficient anaerobic reactors. There are many different studies on the formation and loss of granular sludge in an anaerobic reactor, however, the researchers ignore the effects of the gas-producing and biogas-off process of granular sludge on the formation mechanism of granular sludge. The sedimentation and buoyancy phenomena of the granular sludge cultured by self-made transparent reactor were observed in the lab and their relative velocities were measured by photos. Granular sludge and their biogas are coexistent, that is, any size particles of granular sludge can form high floating speed when granular sludge particles contain a lot of bubbles and the granular sludge particles can precipitate well when the air bubbles of granular sludge particles are released in time. So the water test on the sedimentation rate of granular sludge is insufficient. Unified consideration of granular sludge and biogas is beneficial to solve the loss of granular sludge and acidation of sludge in anaerobic reactors and to ensure the normal operation of anaerobic reactors. The biogas-off of biogas produced by anaerobic sludge has essential effects on the granulation of granular sludge. It is conducive to highly efficient anaerobic reactors and three phase separator to reconstruct.

Oxidation stability of lubricating base oils

ABSTRACTThe oxidative stability of three base lubricating oils of different grades light, medium and heavy oils (B1, B2 and B3, respectively) was studied at oxidative times 50, 100 and 150 hours. The quality of base oils under investigation were evaluated on the basis of total acid number, vaporization loss, kinematic viscosity and quantity of sludge formed. Also, the chemical composition of the studied lubricating oils was achieved via capillary gas chromatography. The comparative study of the oxidative performance of the base oils showed that the higher degrees of heavy oil than light one. The increase in the oxidation time led to increases of the evaporation loss and lubricant viscosity. Analysis of a lubricant's oxidation stability therefore contributes to a better understanding of its effectiveness under normal operating conditions and its suitability for formulating automotive lubricants. The aim of this work is the study the Potential life of lubricant oils inside engine motor at different oxidative times in view of their oxidation stability.

Methane Cycle Anaerobic Membrane Bioreactor with Desulfurization for Treating High Sulfate Organic Wastewater at Normal Temperature

The operational performance of a methane cycle anaerobic membrane bioreactor (MCAnMBR) with desulfurization for the treatment of high sulfate organic wastewater was investigated. Within 63 days, the MCAnMBR with desulfurization was started successfully at a normal temperature of 26-34℃. The two main problems at the beginning of debugging, sludge loss and increased pH, were effectively solved by adjusting the gas path system and adding methanol to the inflow for acclimation. The results show that the inflow concentration of SO42- from 650 mg·L-1to 5800 mg·L-1can be treated well with the conditions of hydraulic retention time (HRT)=120 h, a volume loading of 3.61-4.36 kg·(m3·d)-1, pH of 7.18-7.61, and temperature of 23.3-25.4℃. The effluent chemical oxygen demand (COD) concentration could be lowered to 23 mg·L-1. The total removal rate of COD could remain stable at 96.23%-99.77%, and the SO42- conversion rate was about 83.83%-95.51%. These results indicated that the MCAnMBR reactor with desulfurization could effectively solve the problem of secondary sulfide inhibition. A gradient experiment revealed that the high Na2SO4 inflow could be treated when the influent COD ranged from 18000 mg·L-1to 21000 mg·L-1, the concentration of SO42- ranged between 9082 mg·L-1 and 9600 mg·L-1, and the COD/SO42-=2.

Phosphorus Removal Capacity of Domestic Wastewater Treated by a Modified CAST Process Under Different Operating Modes

A modified cyclic activated sludge technology (CAST) treating domestic wastewater was employed to investigate the effects of different operating modes, such as C/P ratio, reflux ratio, and temperature on phosphorus removal. The results illustrated that at room temperature the phosphorus removal of the system improved significantly when the influent C/P ratio increased from 50 to 100, with the removal efficiency increasing rapidly from 15% to 95.6%. Decreasing the C/P ratio to 75, the phosphorus removal performance declined due to influent carbon source deficiency, and the mean phosphorous removal efficiency decreased to 51.4%. At the same time, the long-term addition of an easily degradable carbon source resulted in sludge bulking and a large amount of sludge loss. With a low C/P ratio, the phosphorus removal performance increased by 2.3 times when the sludge reflux ratio decreased from 25% to 12.5%. However, the phosphorus removal performance declined when reducing it to 0. The temperature experiment results showed that the phosphorous removal efficiency of the system remained stable, above 90%, in the low temperature system (14℃±1℃). However, the phosphorous removal efficiency of a shortcut nitrification system at high temperature (27℃±1℃) was only 14.1%, suggesting that a low temperature was beneficial for removing phosphorous. It was observed from the batch tests that the sludge at room temperature could utilize dissolved oxygen, nitrate, and nitrite as electron acceptors to take up phosphate. The sludge in the low temperature system could use both dissolved oxygen and nitrate as the electron acceptors. However, the sludge in the high temperature system could only use dissolved oxygen as the electron acceptors to take up phosphate. In addition, it was also found that sludge under starvation conditions resulting from short-term idling of the system favored phosphorus removal.

CFD optimization of the baffle angle of an expanded granular sludge bed reactor

In present study, the internal flow field of expanded granular sludge bed (EGSB) reactors was investigated using CFD simulation. A two-dimensional Eulerian three phases (wastewater, biogas and sludge) fluid model was applied to investigate the impact of baffle angle (θ) on the separation efficiency and the hydraulic characteristics in three-phase separation zone. The results showed that when θ was 40°, the sludge loss rate was the smallest and the reflux condition of sludge was the best. To verify the practical applicability of the fluid model, a tracer experiment was conducted. A good relationship between simulation and experiment was discovered, which further confirmed that the baffle angle has significant impact on the separation efficiency of the three-phase separator.

Energy saving control strategies for Haliscomenobacter hydrossis filamentous sludge bulking in the A/O process treating real low carbon/nitrogen domestic wastewater

ABSTRACTThe control strategies of energy saving for filamentous sludge bulking were investigated in the A/O process under low dissolved oxygen (DO) with low carbon/nitrogen (C/N) ratio, and the dominant filamentous bacteria were identified by using fluorescent in situ hybridization. Initially, the sludge volume index reached nearly 500 mL/g and serious bulking occurred when the DO value was 0.5 mg/L, with Haliscomenobacter hydrossis as the major filamentous bacteria in the bulking sludge. Later on, the compartment number increased in the aerobic zone, increasing by this way DO, to control serious bulking. Increasing DO to 1 mg/L based on the increase of compartment number in the aerobic zone was the favorable controlling method, which solved the sludge loss, improved the effluent quality to the national discharge standard and allowed for energy costs saving. As a result, the effective control method for H. hydrossis filamentous sludge bulking provided the economical, convenient and longstanding method for most municipal wastewater treatment plants treating real low C/N domestic wastewater.

An anoxic-aerobic system for simultaneous biodegradation of phenol and ammonia in a sequencing batch reactor.

A laboratory-scale sequencing batch reactor (SBR) was investigated to treat artificial pretreated coal gasification wastewater that was mainly contained of ammonia and phenol. The efficiency of SBR fed with increasing phenol concentrations (from 150 to 300mgl-1) and the relationship among phenol, nitrogen removal, and the microbial community structure were evaluated. When the phenol feeding concentration was increased to about 300mgl-1, the removal efficiency was above 99.0%, demonstrating the robustness of phenol removal capacity. The study showed that most phenol was degraded in anoxic stage. The average removal efficiencies of ammonia and total nitrogen were 98.4 and 81.9%, respectively, with average NH4+-N concentration of 107.5mgl-1 and COD/N 7.5. Low temperature caused sludge loss that led to the decreased performance. Increasing the temperature could not recover the performance effectively. The data from bacterial analysis revealed that Delftia, Hydrogenophaga, and unclassified Xanthomonadaceae played a significant role in phenol degradation before the temperature increase, while uncultured Syntrophococcus sp. and unclassified Rhodocyclaceae were responsible for phenol degradation after the temperature increase. These results imply that the SBR holds potential for the simultaneous removal of phenolic compounds and nitrogen through aerobic ammonia oxidation and anoxic denitrification with phenol as the co-organic carbon source.

Preliminary investigation of the microwave pyrolysis mechanism of sludge based on high frequency structure simulator simulation of the electromagnetic field distribution

Under microwave irradiation, raw sludge was pyrolyzed mainly by evaporation of water, with a weight loss ratio of 84.8% and a maximum temperature not exceeding 200°C. High-temperature pyrolysis of SiC sludge could be realized, with a weight loss ratio of 93.4% and a final pyrolysis temperature of 1131.7°C. Variations between the electric field intensity distribution are the main reason for the differences of pyrolysis efficiencies. HFSS simulation showed that the electric field intensity of the raw sludge gradually decreased from 2.94×104V/m to 0.88×104V/m when pyrolysis ends, while that of SiC sludge decreased from 3.73×104V/m at the beginning to 1.28×104V/m, then increased to 4.03×104V/m. The electromagnetic effect is the main factor (r≥0.91) influencing the temperature increase and weight loss of raw sludge. Both the electromagnetic effect and heat conduction effect influenced temperature rise and weight loss of SiC sludge, but the former’s influence was comparatively larger.

Prediction of Ignition Loss and Heating Value of Sewage Sludge by Thermo Gravimetry and Differential Thermal Analysis (TG-DTA)

Prediction of Ignition Loss and Heating Value of Sewage Sludge by Thermo Gravimetry and Differential Thermal Analysis (TG-DTA)

Biological nitrogen removal in a modified anoxic/oxic process for piggery wastewater treatment

Piggery wastewater is characterized by its high ammonium concentration and low COD/nitrogen ratio. The indiscriminate discharge of untreated piggery wastewater from scattered household pig farms has posed a potential risk of surface water pollution in rural areas of southern China. In this study, an anoxic/oxic (A/O) process with elastic fillers tightly packed in each tank was investigated for piggery wastewater treatment. Two anoxic tanks and two aerobic tanks were used in series and the hydraulic retention time of each was 24 h. Dissolved oxygen concentration in the aerobic tanks was intentionally controlled at below 2 mg L–1 for the implementation of nitritation. After sludge acclimation, three recycle ratios from 100 to 300% were tested. More than 90% of organic matter was removed from raw piggery wastewater despite recycle ratio values. However, the NH4+-N concentrations in the effluent slightly increased from 30 to 65 mg L–1 as the recycle ratio increased. Higher recycle ratio benefited the removal of total nitrogen (TN) and dramatically increased the nitrite accumulation rate in the aerobic tanks. The tightly packed elastic fillers successfully prevented the loss of sludge and increased the biomass in reactors. Moreover, the formation of biofilms on the surface of the elastic fillers developed simultaneous nitritation and denitrification in the aerobic tanks, which counted for approximately 30% of the total removed nitrogen in the proposed system. The employment of elastic fillers in A/O process effectively improved TN removal at a relatively smaller recycle ratio, and consequently reduced the running cost of recirculation for nitrogen removal.

Electrochemical treatment of sugar industry wastewater: COD and color removal

The removal of chemical oxygen demand (COD) and color of the Sugar industry wastewater (SIWW) was investigated using electrochemical (EC) process iron as electrode material. The process yielded maximum 84% COD and 86% color reduction at current density 178A/m2, initial pH 6 and electrode gap 20mm in 120min of treatment. Effect of various parameters in range initial pH (2–10), current density (39–195A/m2), electrode gap (10–25mm) and treatment time (0–120min) were evaluated on COD and color reduction of SIWW. Energy consumption, electrode loss, filtration and settling of sludge were found to pH dependent. Significant amount of COD and color reduction of wastewater by the process indicates that it may be better alternative to the convention biological treatment. Thermo gravimetric analysis of residue indicates its inorganic nature.

Filamentous sludge bulking control by nano zero-valent iron in activated sludge treatment systems.

Sludge bulking causes loss of biomass in the effluent and deterioration of effluent water quality. This study explored the use of nano zero-valent iron (NZVI with an average particle size of 55 ± 11 nm) for sludge bulking control. In two Modified Ludzack-Ettinger (MLE) activated sludge treatment systems, a single dose of NZVI at the final concentration of 100 mg Fe per L in the mixed liquor reduced the number of filamentous bacteria Type 021N by 2-3 log units (a reduction of 99.9 and 96.7% in MLE tank #1 and #2, respectively). The side effect of the use of NZVI depended on sludge bulking conditions and biomass concentration. In the system with sludge bulking and significant sludge loss (average biomass concentration of 1022 ± 159 COD mg per L or at the ratio of 0.098 g Fe per g biomass COD), the use of NZVI increased effluent COD, NH4(+)-N and NO2(-)-N concentrations, as also evident with the loss of nitrifying populations and nitrifying activities resulting in more than 40 days to have the full recovery of the activated sludge system. In contrast, in the system with the early stages of bulking and the biomass concentration of 1799 ± 113 COD mg per L (at the ratio of 0.056 g Fe per g biomass COD), the effluent water quality and overall bioreactor performance were only slightly affected for a few days.

Effects of Metal Oxides during Pyrolysis Sludge by Kinetic Analysis

On the basis of proximate analysis, element analysis and calorific value that carried out on the sewage sludge, thermogravimetric analyzer (TGA) was conducted on the research of sewage sludge pyrolysis. The loss of sludge under different heating rates was comparative analyzed. And we calculated the activation energy by using Ozawa method, Satava method was also used to infer the most probable mechanism function and kinetic parameters. the result shows that sludge pyrolysis process can be divided into three parts as 200-450°C,450-600°C and above 600°C, the Reaction mechanism functions for the pre main two parts were G(α)=(1-α)-1 and G(α)=[-ln(1-α)]2/3respectively. Its proved that Al2O3,MgO probably inhibited the decomposition while Fe2O3,CaO,ZnO promoted the degradation of organic matters under 200-450°C. CaO and Fe2O3 showed advantage while MgO, Al2O3, ZnO turned to be disadvantagble when temperature arised to 450-600°C. At the end of pyrolysis, the advantage effects order on pyrolysis : Al2O3> Fe2O3>MgO >ZnO>CaO.

Treatment of Munitions Decomposing Wastewater Using Membrane Biological Reactor

Wastewater from the munitions decomposing process typically contains the widely used explosive-trinitrotoluene (TNT), which is also toxic and mutagenic. Commonly used technologies for degradation of TNT,such as activated carbon adsorption and chemical oxidation, are proved to be feasible but not cost-effective. In this study, the effectiveness of biodegradation of TNT by co-metabolism was evaluated in a hybrid hydrolysis acidification and aerobic membrane bioreactor. After six weeks acclimatization, over 90% TNT was removed with influent TNT concentration ranging between 70-85mg/L. Simultaneously remarkable MLSS concentration increase from 1.4 g/l to 6.9 g/l was observed, which indicated that the acclimatization and incubation of biomass was successful. The membrane effectively prevented loss of sludge and kept large biomass in the reactor, which made the system maintained in a high volume loading rate and low sludge loading rate. The experiment results showed that addition of carbon source was an essential factor in biodegradation of TNT wastewater.

A new oxic-settling-anaerobic (NOSA®) activated sludge process for minimizing excess sludge in secondary biological treatment plants: a pilot-scale evaluation of the absorption–biodegradation process

This study compared the sludge reduction performance of a new oxic-settling-anaerobic (NOSA) process with that of a conventional adsorption-biodegradation process. A 50 m(3)/d pilot trial system with two different process configurations was operated for 6 months. The NOSA process functioned effectively in removing both chemical oxygen demand and nitrogen with the efficiencies of 86 and 92.5%, respectively, which reduced approximately 40% of the excess sludge. In this research, 0.77 kg volatile suspended solids/d sludge vanished in the anaerobic tank, which accounted for 58.9% of the total sludge loss in the NOSA process. Economic calculation suggests that the new process can dramatically upgrade the sludge reduction in wastewater treatment plants without a digestion device, and the investment for fundamental upgrading can be recovered in 5-6 years by cutting the costs of excess sludge dewatering and disposal treatment.

Treatment of low-strength wastewater in an anaerobic down-flow hanging sponge (AnDHS) reactor at low temperature

The process performance of a novel anaerobic down-flow hanging sponge (AnDHS) reactor for the treatment of low strength wastewater was investigated. A lab-scale experiment was conducted in which 300–400 mgCOD L−1 of artificial wastewater was fed in over 600 days. The reactor exhibited sufficient performance: 70–90% of total COD removal, and 60–90% of methane recovery were maintained at 20°C, with a hydraulic retention time (HRT) of 2 h. It was possible to maintain COD removal by extending the HRT to 4 h at 15°C and 10 h at 10°C. With regard to the wastewater feed, one-pass mode (without effluent recirculation) gave better performance in COD removal as compared with recirculation mode. The results of batch feeding experiments using single substrates (such as acetate, propionate or sucrose) indicated that acetate degradation was more strongly affected by decreasing operational temperature. In addition, the AnDHS reactor system had no significant problems related to sludge retention such as massive loss of sludge throughout the experiment. Microbial structure analysis of the retained sludge with respect to the domain Archaeal 16S rRNA gene showed the proliferation of relatives of both the acetate-utilizing genus Methanosaeta and the hydrogen-utilizing genus Methanolinea.

Effects of increase modes of shear force on granule disruption in upflow anaerobic reactors

Sludge washout is listed among the top practical problems of the high rate upflow anaerobic reactors. This study investigated quantitatively two sludge washout processes operated under different hydrodynamic shear increase modes with the intervals of 1 and 10 days respectively. The results reveal that the sludge washout accompanying with large-scale granule disruption could lead to performance failure with heavy sludge loss ratio of about 46.1% at sludge loss rate about 0.35 gVSS L−1 d−1 during the process with shear increase interval of 1 day, while the highest sludge loss rate was only 0.12 gVSS L−1 d−1 during the process with 10-day interval. The intensified shear conditions could weaken the granules through inhibiting the extracellular polymers production and bioactivity. As consequences, an outbreak of large-scale granule disruption would raise and then significantly accelerate the sludge washout. Since long interval could provide the granules the opportunity to recover from these negative effects to some extent, the shear increase strategy of long interval over 10 days is favorably recommended to operate full-scale reactors during the start-up and shock load periods. The pioneer use of the micro particle image velocimetry in this study offers the possibility to discover the real hydrodynamic conditions around granules at microscale for the first time and reveals that the shear force exerts directly on the granular surface as a mechanical disruption force and big granules undergo high disruption force. The granule disruption is a result of the competition between the granule and the ambient hydrodynamic shear conditions rather than a process with shear force as a sole dominant factor. These could facilitate the understanding of the complicated interactions between the hydrodynamics and reactor performance and favor then a better control of the full-scale reactors.

Composition of intake sugars and emission of gases from paper sludges by Coptotermes formosanus Shiraki

Paper sludge is a by-product of the pulping process and is landfilled or incinerated for disposal. In this study, we evaluated ingestion and digestibility of carbohydrates, by the termite Coptotermes formosanus, in two kinds of sludges: sludge C from the chemical pulp mill and sludge M from the mechanical pulp mill. The no-choice tests using the termite for three weeks showed that the mass loss of sludge C was significantly higher than that of the control samples: a bleached pulp and red pine wood. It is considered that the higher inorganic content of sludge C resulted in the higher mass loss when the same amount of carbohydrates was taken by the pulp- or wood-fed termite. Although the inorganic content of sludge M was almost the same as that of sludge C, the higher lignin content in sludge M is thought to have resulted in the lower mass loss. Analysis of sugar composition in the faecal materials of the termite showed that about 73% of glucose and 81% of xylose in sludge C were digested. It was concluded that the digestibility of these sugars in sludge C was the same as that of the control samples despite containing high amounts of inorganic compounds. However, the hydrogen conversion rate by the termites that were fed sludge was lower than that of the termites that were fed pulp in the no-choice test for three days: one mole of glucose from the sludge and pulp was converted to 0.51 and 0.80 moles of hydrogen, respectively.

Limited filamentous bulking in order to enhance integrated nutrient removal and effluent quality

Limited filamentous bulking has been proposed as a means to enhance floc size and make conditions more favorable for simultaneous nitrification/Denitrification (SND). Moreover a slightly heightened SVI is supposed to increase the removal of small particulates in the clarifier. Integrated nitrogen, phosphorus and COD removal performance under limited filamentous bulking was investigated using a bench-scale plug-flow enhanced biological phosphorus removal (EBPR) reactor fed with raw domestic wastewater. Limited filamentous bulking in this study was mainly induced by low DO levels, while other influencing factors associated with filamentous bulking (F/M, nutrients, and wastewater characteristics) were not selective for filamentous bacteria. The optimum scenario for integrated nitrogen, phosphorus and COD removal was achieved under limited filamentous bulking with an SVI level of 170–200 (associated with a DO of 1.0–1.5 mg/L). The removal efficiencies of COD, TP and NH 4 +–N were 90%, 97% and 92%, respectively. Under these conditions, the solid–liquid separation was practically not affected and sludge loss was never observed. A well-clarified effluent with marginal suspended solids was obtained. The results of this study indicated the feasibility of limited filamentous bulking under low DO as a stimulation of simultaneous nitrification/denitrification for enhancing nutrient removal and effluent quality in an EBPR process.