Kinds Of Sludge Research Articles

Ultrasonic treatment of waste activated sludge

AbstractActivated sludge processes are key technologies to treat wastewater. These biological processes produce huge amounts of waste activated sludge (WAS), now commonly called biosolids. Mechanical, thermal, and/or chemical WAS conditioning techniques have been proposed to reduce the sludge burden. The ultrasonic treatment of WAS is quite novel.The present paper reports on extensive investigations using an ultrasonic treatment of WAS, to study its potential to meet one or all of four objectives: (1) reduce WAS quantities; (2) achieve a better dewaterability; (3) provoke a release of soluble chemical oxygen demand (COD) from the biosolids, preferably transformed into biodegradable organics; and (4) possibly destroy the filamentous microorganisms responsible for sludge bulking. Although meeting these objectives would help to solve the problems cited, the energy consumption could be a considerable drawback: the paper will thus assess whether all or some objectives are met, and at what operational cost.A literature survey defines the occurring phenomena (cavitation) and the important operation parameters [such as frequency, duration, specific energy input (SE)].The experiments are carried out in a batch reactor of volume up to 2.3 L. The ultrasonic equipment consisted of a generator, a converter, and a sonotrode, supplied by Alpha Ultrasonics under the brand name of Telsonic. Three different kinds of sludge were tested, with different concentrations of dry solids (DS) between approximately 3.5 and 14 g DS/L WAS. Ultrasonic energy was introduced in a continuous manner (against possible pulsed operation). The major operational parameters studied include duration of the ultrasonic treatment and specific energy input. The applied frequency was set at 20 kHz.The release of COD from the WAS phase into the filtrate phase is a function of the specific energy input with yields of nearly 30% achievable at SE values of 30,000 kJ/kg DS. A major fraction of the COD is transformed into biodegradable organics (BOD). The reduction in DS fraction of the sludge is proportional to the COD release rates.Although the DS content is reduced, the dewaterability of the sludge is not improved. This reflects itself in increased filtration times during vacuum filtration and in increased values of the capillary suction time (CST). This more difficult dewaterability is the result of considerably reduced floc sizes, offering an extended surface area: more surface water is bound (CST increases) and the filterability decreases as a result of clogging of the cake. To reach the same dryness as for the untreated cake, the required dosage of polyelectrolyte is nearly doubled when the SE of the ultrasound treatment is increased from 7500 to 20,000 kJ/kg DS.The ultrasonic reduction of filamentous WAS organisms is not conclusive and very little effect is seen at low intensities and short treatment durations. Microscopic analysis of the WAS identified the dominant presence of Actynomyces.The release of soluble COD and BOD certainly merit further research. © 2006 American Institute of Chemical Engineers Environ Prog, 2006

Effect of cadmium on composition and diversity of bacterial communities in activated sludges

Microbial communities of two kinds of activated sludge for removing carbon, nitrogen and phosphate (nutrient removal sludge) were identified and compared by combining cloning–denaturing gradient gel electrophoresis methods. The sludges were sampled in an anaerobic–anoxic–oxic system operating under the same conditions, except for one without the addition of cadmium (Cd0) and the other with addition of 5 mg cadmium l 1 (Cd5). Bacteria in the phylum Proteobacteria were predominant in both Cd0 and Cd5 sludges (39.6% and 35.1% of total bacteria, respectively). However, bacteria in the class Betaproteobacteria were significantly more abundant in Cd0 than in Cd5 sludge (30.7% and 2.1%, respectively). Species related to nutrient removal, such as nitrifying bacteria (Nitrosomonas communis), floc-forming bacteria (Zoogloea ramigera) and phosphate-accumulating organisms (Rubrivivax gelatinosus), were the predominant species in Cd0 sludge, but were not found in Cd5 sludge. Cadmium was significantly toxic to the bacterial community in nutrient removal sludge, especially to the bacteria in the Betaproteobacteria. The comparison of microbial communities between these two kinds of sludge was further discussed in the paper. r 2005 Elsevier Ltd. All rights reserved.

Structure Characterization and Adsorption Properties of Pyrolyzed Sewage Sludge

Sewage sludges produced from wastewater treatment plants continue to set environmental problems in terms of volume and way of reuse. Thermal treatment of sewage sludge is considered as an attractive method in reducing sludge volume, and at the same time, it produces reusable byproducts. This paper deals with porous carbonaceous materials production from sewage sludge by pyrolysis (or carbonization) process with a goal of different industrial applications. Carbonization experiments were carried out on two kinds of sludge, namely viscous liquid sludge and limed sludge by varying carbonization temperature between 400 degrees C to 1000 degrees C. The porous structure and surface chemistry of the materials obtained were characterized using nitrogen adsorption, scanning electron microscopy, elemental analysis, Boehm titration, and pH of zero point of charge determination. The results show that basic character of the carbonized residues increases with increasing carbonization temperature. Then, carbonization allows specific surface area and pore volumes to be developed. Carbonized viscous liquid sludge and carbonized limed sludge are mainly mesoporous in nature, with specific surface areas reaching about 100 m2 g(-1) and 60 m2 g(-1), respectively. Finally, adsorption experiments, in aqueous solution, were carried out and show that carbonized viscous liquid sludges and limed sludge remove effectively the metallic ion Cu2+, acid and basic dyes, and phenol. Pyrolyzed sludges properties seem to be encouraging for the preparation of activated carbon by physical activation process.

Distribution and persistence of fecal bacterial populations in liquid and dewatered sludge from a biological treatment plant

The changes in composition and structure of fecal coliforms (FC) and enterococci (ENT) populations, as well as the elimination of spores of sulphite-reducing bacteria (SRB), were compared between municipal sewage and their derived sludge in a biological treatment plant in order to determine any selective reduction or adsorption to sludge during the treatment process. Additionally, the persistence of antibiotic-resistant enterococcal populations in two kinds of sludge was also considered to evaluate their potential elimination in the treatment process. Microbial indicators, vancomycin-resistant and erythromycin-resistant enterococci were enumerated. The structure and composition of FC and ENT populations were determined by biochemical fingerprinting and clustering analyses. Raw and treated sewage showed a concentration of FC 1 log unit higher than ENT and nearly 2 log units higher than spores of SRB. However, the three studied indicators showed similar concentrations in both types of sludge. Consequently, FC were eliminated in higher proportion than ENT and spores of SRB in sludge. FC and ENT populations showed high diversity and similarity population indexes for all kinds of samples. Antibiotic-resistant enterococci persisted in a similar proportion in respect to total enterococci not only in treated sewage but also in sludge. The persistence of antibiotic-resistant strains in sludge as well as in treated sewage should be considered if they are used for land disposal or for water reutilization, respectively.

Influence of the application of sewage sludge on the degradation of pesticides in the soil

A study was made of the influence of the application of sewage sludge on the degradation of pesticides in the soil. Two kinds of sludge were used, with different characteristics, one from an urban treatment plant and one from a food processing plant. Three organophosphorus insecticides, fenitrothion, diazinon and dimethoate, were studied. The relative importance was determined of the chemical and biological degradation processes, which involved experiments on soil and sterile soil samples. A comparative study was also made of the degradation of pesticide residues and the evolution of the microbial population. The application of sludge seems to have a complex effect on the degradation of pesticides, determined by the bioavailability and biodegradability of their active ingredient. The biodegradation of pesticide residues brings about alterations in the microorganism population of the soil.

Combustibility of dried sewage sludge and its mineral transformation at different oxygen content in drop tube furnace

Combustion of two kinds of sludge was studied in a laboratory-scaled drop tube furnace to understand their combustibility and evolution of mineral matters in the process. Experimental conditions were selected as: reaction temperature was 1200 °C; oxygen content was 10%, 30% and 50%, and the residence time varied from 0.6 to 2.4 s. The experimental results show that increasing the oxygen content significantly improved the combustibility of sludge. Sludge with high volatile matter, e.g., 70.8% in sludge B, could not combust completely even at 50% O 2, which is due to the fact that the formed ash surrounded the combusting char, it acted as a resistance for the diffusion of oxygen to unburnt carbon, about 2–6% unburnt carbon, having particle size of about 1.5 μm, was kept in the ash. In addition, at low oxygen content, the major mineral compounds in sludge, including calcium oxide, phosphorus oxide and aluminosilicate, mainly underwent coalescence within char to form the large molten agglomerates. Increasing oxygen content resulted in the rapid decomposition of sludge, and accordingly, many droplets were formed and condensed into fine particles. Finally, the vaporization model for both sodium and zinc was built considering the internal diffusion of both two elements with char and their reaction with phosphates. The simulation results had a fairly good consistence with experiments. Sodium was mainly released under the controlling of its internal mass-transfer diffusion within ash layer. Conversely, zinc was released under the controlling of both internal mass-transfer diffusion and its reaction with molten phosphate salts. Improving oxygen content mitigated the diffusion resistance in ash layer, and hence, more the sodium and zinc were vaporized.

TG-MS as a technique for a better monitoring of the pyrolysis, gasification and combustion of two kinds of sewage sludge

Sewage sludge disposal is a difficult task owing to increasingly restrictive re-use policies. Its final destination will obviously depend on its nature and composition but the generation of energy is a significant option. The thermochemical conversion requires exhaustive gas emission controls. In this regard, this paper offers the results of the use of mass spectrometry together with a thermogravimetric analysis system used to study the thermal conversion processes of two kinds of sewage sludge under different atmospheres simulating pyrolysis, gasification and combustion. This TG-MS combination indicates that gasification is the best process for one kind of sludge while a co-combustion process is more suitable for the other.

Characterisation of dusts and sludges generated during stainless steel production in Brazilian industries

During the stainless steel production process, wastes are generated at the electric arc furnace (EAF) and at the converters. These wastes are a problem for stainless steel industries, for they must be disposed of in controlled landfills. Finding areas to make more landfills is becoming difficult, and new landfills are being placed far from the industries. This leads to an increase in disposal prices and, furthermore, in production prices. Recycling of these wastes, besides solving the disposal and environmental problems, makes it possible to recover valuable metals such as iron, chromium, and nickel. These three metals are needed in stainless steel manufacture and could be returned to the production procedure, hence bringing profit to the industry. It is important, therefore, to develop a recycling process. Waste characterisation is an essential step in the definition of such a process. Four kinds of dust and two kinds of sludge, generated in stainless steel production, were characterised in the present work. The techniques used to characterise the waste were chemical analysis, size separation, density measurement, X-ray diffraction analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) microanalysis. The largest proportion of the dust and sludge particles was of spherical shape. This kind of particle was composed mainly of iron and chromium in the form of a spinel, or of oxides. Precipitation of a secondary phase was identified in some particles.

Study on Sludge Expansion During Treatment of Salad Oil Manufacturing Wastewater by Yeast

Five yeast strains, namely Rhodotorula rubra, Candida tropicalis, Candida utilis, Candida boidinii, Trichosporon cutaneum, were isolated from soil spots of a salad oil factory, and applied for continuous treatment of salad oil manufacturing wastewater. The oil and COD removal performance of the mixed cultures were comparable to the results other researchers obtained. Sludge expansion, accompanied with sludge morphology change from pseudomycelia to true mycelia, occurred during continuous treatment of wastewater. The true mycelia dominated sludge had a much higher water content and SVI value than that of the yeast pure cultures, although the two kinds of sludge had similar oil removal performance. A mold, Geotrichum candidum, was isolated from the expanded sludge, and was suspected to be a reason for sludge expansion. Addition of 0.3% sodium propionate into batch cultures degraded SVI value from around 100 to 60. In a continuous running, addition of 10 mg l−1 sodium hypochlorite decreased SVI value from over 200 to below 100. The yeast activity, however, was weakened to a large extent at the same time.

Thermal drying of residual sludge

The drying of residual sludge is a current environmental problem not well described in scientific literature. Thus research investigations on this dewatering process are necessary according to the industrial demand. This paper proposes, from laboratory convective drying experiments, a macroscopic approach in terms of kinetics curve and drying potential. This criterion which groups a set of external conditions into an unique parameter ( T, RH, v) allows an easy classification of different operating strategies—then it can be the first step for design investigations. Moreover this study allowed us to compare the behaviour of two very different kinds of sludge. It also described a crust phenomenon in the case of activated sludge and a large permeability of the PVC drying cake according to water transport.

Inference of methanogenic bacteria in wastewater digestor sludges by lipid component analysis

The presence of methanogens of the genera Methanosarcina and Methanosaeta, and the family Methanomicrobiaceae, and the absence of the family Methanobacteriaceae were inferred from the analysis of lipid component parts in three kinds of sludge from two anaerobic digestors by comparison with the distribution of the lipid component parts among 31 species of methanogens previously reported.

高級脂肪酸の嫌気的分解過程における硫酸塩還元菌の生態学的役割

The ecological role of sulface-reducing bacteria (SRB) in anaerobic degradation of a long-chain fatty acid (LFA) was investigated using three anaerobic sludge consorita cultivated at different sulfate loading rates. The three kinds of sludge (referred to as Sludge A, B and C) were cultivated in a fill-and-draw mode for 100 days by feeding with plamitate as a major carbon source (feeding concentration : 1.0g COD·l-1), but with different levels of sulfate, i.e., 600mg-SO42-·l-1 for Sludge A, 300 for Sludge B, 0 for Sludge C.Degradation of palmitate into acetate in the presence of sulfate can be performed by either of the following three trophic groups : 1) symbiosis between palmitate-degrading proton-reducing acetogens (P-PRA) and hydrogen-utilizing SRB (H-SRB), 2) symbiosis between P-PRA and hydrogen-utilizing methanogens (H-MPB), 3) palmitate-oxidizing SRB (P-SRB). Three sludge consortia exhibited different behavior of palmitate degradation, depending on their sulfate loadings. As for Sludge A, the first group, P-PRA+H-SRB had the greatest contribution in palmitate degradation, and the extent of the second, P-PRA+H-MPB and the third, P-SRB were about half of the first, respectively. For Sludge B, P-PRA+H-MPB had the superior contribution over P-PRA+H-SRB and P-SRB. The lowest contributor, P-SRB was only one-tenth of the largest contributor, P-PRA+H-MPB. For Sludge C, palmitate degradation was accounted for only by P-PRA+H-MPB, and the contributions by P-PRA+H-MPB and P-SRB were negligible small.

The behavior of ash components in the sludge melting process

The Coke-bed sludge melting process is used for incinerating sewage sludge and producing slag that is recycled as construction materials. The behavior of ash exiting the melting furnace was examined. Heating tests were carried out with different kinds of sludge. Heating from 600°C to 1200°C, weight reduction of around 30% was measured, but reduction rate was due to the kind of sludge. Weight reduction was big when heating up to 815°C, and reduction at a temperature over 815°C was due to the type of sludge. Main materials causing weight reduction were unburnt carbon (C) and some other elements like sulfur (S), chlorine (Cl), some metals like sodium (Na), potassium (K) and oxygen (O) released from some kinds of oxides. Even though very small quantity, zinc (Zn) and lead (Pb) were also vaporized. Some of these vaporized substances precipitate and produce fine particle dust at the low-temperature section of gas treatment facilities. Washing harmless salts out from the dust then recycling the dewatered dust in the melting furnace was found to be effective in maximizing slag recovery and reducing the precipitator load.

Anaerobic Treatment of Sewage Sludge Treated by Catalytic Wet Oxidation Process in Upflow Anaerobic Sludge Blanket Reactors

To increase the efficiency of methane recovery in anaerobic treatment, sewage sludge was treated by catalytic wet oxidation process(CWOP).The CWOP is designed to treat sewage sludge with the aid of a newly developed catalyst. It is a treatment process, by which concentrated COD components and suspended solids in various kinds of sludge can be simultaneously oxidized and treated with great efficiency in a single step without dilution. After CWOP, this supernatant was treated by upflow anaerobic sludge blanket(UASB) for recovery of methane. This experiment was to evaluate the acclimation of UASB process to the supernatant of sewage sludge treated by CWOP. For the granule growth and accumulation, supernatant was introduced stepwise (25%, 33%, 50%, 100%). The supernatant was 7,200 mg-COD/L which contained 53% carbonic acids. The reactor was operated at a volumetric loading rate from 1.8 (kg·COD/m3·day) to 14.4 (kg·COD/m3·day) and overall HRT of less than 24 hrs throughout the experiment. In the conventional anaerobic biochemical process of methane gas recovery was limited to 50% of COD recovery. As a result of this study, the COD recovery to about 93% was obtained by the coebination of CWOP and UASB process. The following conditions were enough for pretreatment: temperature, 270°C; pressure, 86kg/m2; stoichiometric air ratio, 1.1; reaction time, 24 min. These results indicate that the CWOP-UASB process may be attractive as an alternative sewage sludge treatment.

Freeze–thaw sludge conditioning and double layer compression

Freeze–thaw conditioning of water and wastewater sludges is known to be an effective and economical means of promoting dewatering when natural freezing is employed. When sludge freezes, both the suspended and dissolved solids are rejected by the growing ice front. Particles trapped in ice are known to have a very thin layer of water surrounding them and this water does not freeze at normal temperatures. Dissolved solids are thought to accumulate in this layer, causing an increase in the ionic strength of the water. This may cause compression of the double layer, leading to neutralization of repulsive forces, thus promoting aggregation. In order to test this hypothesis, ionic strength was increased by adding sodium chloride (NaCl) to water and wastewater sludges and measuring dewaterability (filtration) with the capillary suction time (CST) apparatus. Four different kinds of sludge were used: alum sludge (water treatment), waste-activated sludge, simultaneous precipitation, and anaerobically digested mixed sludge. Salinities of 0–20 000 mg/L as NaCl were tested with every sludge. No enhancement in dewaterability with freeze–thawed sludges of raised ionic strength compared to zero salinity was recorded, therefore the hypothesis of double layer compression being a major factor in freeze–thaw conditioning does not seem to be correct. Key words: sludge, freezing, coagulation, dewatering.

The comparison of activated and digested sludge applied to flowering Chinese cabbage, brassica parachinensis bailey

Abstract Seedlings of the Chinese White Cabbage, Brassica parachinensis were grown in garden soil alone, and with two kinds of sludge, namely activated and digested sludge with l:500 and 2:500 (dry weight) application rates, respectively. The results showed a positive effect with the addition of both types of sludge at the 1:500 and a negative effect at the 2:500. This was indicated by the total dry weight after the seedlings had been cultured for a period of 30 days. Foliar analyses of the plants revealed a significantly higher uptake of Cd (P<0.01) in the activated sludge amended‐soil and both Cd and Mn (P<0.01) in the digested sludge amended‐soil at 1:500 application rates when compared with those grown in the garden soil alone. More heavy metals were transferred to the leaf tissues at the 2:500 application rate. However, the crops in all the pots showed no visual metal toxicity symptoms, possibly due to the short growing period and the comparatively lower content of heavy metal in the sludge. Land app...