New insights into membrane fouling in a submerged anaerobic membrane bioreactor based on characterization of cake sludge and bulk sludge

A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping whitewater was operated for over 7 months to investigate and compare the characteristics of cake sludge and bulk sludge during stable state operation period. Serial analysis showed that cake sludge had a smaller particle size distribution (PSD), much higher specific filtration resistance (1.34 × 10¹⁴ m/kg), 1.5 times higher bound EPS and significantly different microbial community as compared with bulk sludge. Further analysis indicated that small flocs, bound EPS and inorganic materials play important role in cake formation process. The formed cake layer was found to have a heterogeneous structure. The results obtained in this study indicated that cake formation process started from attachment of small flocs and/or specific bacterial clusters which colonize the surface of the membrane and provide enhanced conditions that allow for cake formation to progress.     

Evaluation of Slurry Wall Construction Using Paper Clay for Containment of Contaminated Groundwater

Slurry walls have been used widely as passive vertical barriers to control the horizontal flow of groundwater and contaminants and therefore limit the migration of contaminants through the subsurface. The material used as slurry to reduce contaminant transport is expected to form a filter cake with low permeability along the sides of the trench wall/excavation face. In this article, paper mill sludge (hereafter referred to as paper clay) is investigated as a possible slurry. Previous research by Moo Young et al. (2000) has shown that paper clay has several properties that make its use in vertical barriers very promising. It can be compacted to low permeability values (10^?7?cm/s to 10^?9?cm/s) and has a high organic content that may act as a potential carbon source for microbial growth and sorption sites for heavy metal attenuation. To determine the feasibility of paper clay in a slurry, column testing to determine the dispersion coefficient for transport modeling, slump testing, and filter cake formation tests were performed. It is shown that the coefficient of hydrodynamic dispersion within paper clay is in the order of 10^?7?cm²/ s. It is also shown that paper clay can achieve the required slump of between 5.08 and 15.24?cm (2 and 6 in) similar to that of a workable soil-bentonite backfill. Furthermore, it is shown that the filter cakes that are formed have permeability values similar to those of soil-bentonite filter cakes.     

Nitrogen and Phosphorus Removal from Combined Sewage Components by Microbial Activity

When primary domestic sewage sludge was combined with settled sewage or secondary-treatment plant effluent, synergism resulted. The activity (measured by oxygen uptake, and the removal of Kjeldahl nitrogen and orthophosphate from solution) which resulted from incubating sludge together with settled sewage exceeded the sum of the activities when these components were incubated separately. A similar synergistic effect occurred with sludge and effluent. The sewage sludges were deficient in readily available nitrogen, but no shortage of phosphorus was demonstrated. The addition of ammonium and orthophosphate salts to sludge, in concentrations equivalent to those found in settled sewage and effluent, stimulated sludge oxygen uptake at least 80% as much as settled sewage or effluent. It is suggested that the synergism reflects increased microbial activity resulting from widened carbon-nitrogen and carbon-phosphorus ratios achieved by combining sludge with nutrient-rich settled sewage or effluent.     

Effective diffusivity of oxygen in microbial pellets

In a typical submerged aerobic fermentation with microbial pellets, the effective diffusivity of oxygen in the pellets is probably the most important, yet most difficult transport property to characterize experimentally. Its values directly indicate the efficiency or deficiency of oxygen to individual cells, and thus the biological activity of the microorganisms. In the past, it was not possible to assess reliably the effective diffusivity of oxygen in pellets due to several reasons. Firstly, most oxygen electrodes available were coarse, and hence not suitable for in situ measurements. Secondly, there was a lack of methods rigorous enough to characterize the structure of the microbial pellets. A state-of-the-art review of the literature relating to the feature subject is presented. Emphasis is laid upon development and evolution of the means for quantitative characterization of the effective diffusivity of oxygen in microbial pellets.     

A RESEARCH NOTE: USE OF A SIGNAL DETECTION RANKING ANALYSIS TO MEASURE PREFERENCE FOR COMMERCIAL AND 'HEALTH MODIFIED' CAKES

Consumer preference for a common 'yellow cake' prepared from a commercially available cake mix and for three 'health modified'cakes was measured using signal detection ranking procedures. Consumers found the ranking protocol simple to use, making it a viable alternative to hedonic scaling. Measures of likelihood to choose to eat, after provision of nutritional information about the cakes, showed the same trend as measures of preference taken before. Yet, the dominance of preference for yellow cake over the 'health modified' cakes was reduced.     

Characterization of dewatering process of activated sludge assisted by cationic surfactants

In this work, the dewatering of activated sludge assisted by cationic surfactants was investigated. Dose of dodecyl trimethyl ammonium bromide (DTAB) and cetyl trimethyl ammonium bromide (CTAB) resulted in the release of extracellular polymeric substances (EPS) from sludge and decrease in sludge negative charge. The surfactants significantly promoted sludge dewaterability, as reflected by decreased specific resistance of filtration (SRF) and water content in sludge cakes. The treated sludge were analyzed by combined use of differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) analysis. CTAB was found more effective in releasing bound water from sludge than DTAB, due to its superior surface activity and strong adsorption/bridge capacities with sludge. The specific surface area and pore size of sludge cakes declined after surfactant treatment, indicating an enhanced compressibility. With these results, the surfactant-assisted dewatering mechanism could be attributed to the integrated effects of electrostatic neutralization, enhanced compaction and release of EPS and bound water. Our study clearly characterizes the accelerated dewatering process assisted by cationic surfactants, and demonstrates that cationic surfactants could be used as a potential agent for sludge dewatering.     

Influence of polyaluminum chloride on microbial characteristics in anaerobic membrane bioreactors for sludge digestion

In this study, two parallel lab-scale anaerobic membrane bioreactors (AnMBRs), one of which was dosed with polyaluminum chloride (PAC) for membrane fouling control, were operated for treating excess activated sludge collected from a wastewater treatment plant (WWTP). The AnMBRs were inoculated with anaerobic digested sludge collected from an anaerobic digester of another WWTP. The microbial community of digested sludge and cake layer in AnMBRs, as well as that of excess sludge, was analyzed through polymerase chain reaction coupled with denaturing gradient gel electrophoresis (PCR-DGGE) and Illumina MiSeq. The dynamic variation of archaeal community in AnMBRs was not as obvious as that of bacterial community based on the PCR-DGGE results. Under the circumstance of stable operation, Cloacimonetes, Chloroflexi, Bacteroidetes, Proteobacteria, Firmicutes, and Ignavibacteriae were observed as the predominant phyla in digested sludge based on the Illumina results. In addition to that, the cake layer possessed similar predominant phyla with the digested sludge but owned a higher diversity. Furthermore, overlapping bacterial communities were discovered between the excess sludge and digested sludge. However, the abundance of aerobic bacteria was substantially reduced, while the abundance of anaerobic microorganisms like phylum Cloacimonetes and Smithella was enriched in digested sludge over time. Additional PAC dosing, on the one hand, affected the bioavailable substrate, thus further changing the microbial community structure; on the other hand, aluminum itself also affected specific microbial communities. Besides, PAC dosing indirectly influenced the bacterial diversity in AnMBR as well.

     

Determination of Apparent Ileal Amino Acid Digestibility in Rapeseed Meal and Cake Processed at Different Temperatures Using the Direct and Difference Method with Growing Pigs

Studies were conducted with ten barrows, average initial body weight 34.5 ± 2.1kg, fitted with a T-cannula at the distal ileum, to study the accuracy of determination of the apparent ileal digestibility (AID) values of crude protein (CP) and amino acids (AA) in rapeseed meal and cake and the effects of processing, using the difference method. Five corn starch-based diets in the studies were formulated to contain 17.7% CP and based on soybean meal, prepress-extraction rapeseed meal, prepress-extraction rapeseed meal plus soybean meal, high-temperature press rapeseed cake plus soybean meal, or low-temperature press rapeseed cake plus soybean meal as the sole source of dietary protein. The design was an incomplete Latin Square involving two three-week periods and five-treatments. It was found that the AID values of CP and most AA determined with the difference or direct method were significantly lower in rapeseed meal or cakes than soybean meal. The AID values of CP and most AA in prepress-extraction rapeseed meal, high-temperature press or low-temperature cakes determined with the difference method were no difference from those in prepress-extraction rapeseed meal determined with the direct method. The AID values of CP and AA in rapeseed meal and cake determined with the difference method were accurate, when the contribution of CP and AA from rapeseed was more than 50%. The AID values of CP and AA (especially lysine) were lower in the high-temperature press rapeseed cake than in the low-temperature press cake or the prepress-extraction meal.     

Feeding value of sunflower and groundnut cakes for broilers

Proximate analysis of kernels of 30, and amino acid composition of two, varieties of sunflower seed are reported. Replacement of groundnut cake in the diet of growing chickens by sunflower cake improved growth rate and efficiency of utilization of energy and protein. Diets based on sunflower cake needed only 4% fish meal supplementation as against 8% needed with groundnut cake for equal weight gains (1700 g) in broilers to 70 days of age. A mixture of sunflower and groundnut cakes gave almost similar weight gains with only 2% fish meal. Sunflower hull did not appear to contain any harmful constituent and its presence in the diet did not cause any harm, but it decreased the energy content of the diets. At the 18% dietary protein level, a mixture of sunflower and groundnut cakes gave decidedly higher weight gain than either of the two cakes alone. At 18–26% dietary protein, groundnut cake proved inferior to sunflower cake for growth and feed efficiency. With both cakes, broilers performed better at higher levels of dietary protein. Level of incorporation in the diets did not affect the metabolizable energy of sunflower cake. Decorticated and undecorticated sunflower cakes gave metabolizable energy values of 2.95 and 2.65 Mcal/kg, respectively.     

Oxygen diffusion through zoogloeal flocs

The mechanism of oxygen transfer through a pure culture floc of Zoogloea ramigera I-16M has been described quantitatively. Oxygen uptake rates for both blended and nonblended floc particles indicated that, at a certain dissolved oxygen concentration, diffusion of oxygen through the floc matrix was the mechanism controlling the rate of oxygen utilization by the floc. This mechanism was quantitatively described by determining the oxygen diffusivity values for the floc. The diffusional distances of the floc particles along with the oxygen utilization rates of the floc were measured on floc grown under various conditions. Anoxic core equations were then used to calculate the oxygen diffusivity values for each experiment. These diffusivity values were then used to estimate the oxygen concentrations necessary in activated sludge plants.     

Integrated approach for the management of Meloidogyne javanica on eggplant using oil cakes and biocontrol agents

Investigations were carried out to evaluate the efficacy of biocontrol agents (Paecilomyces lilacinus and Cladosporium oxysporum) and/or oil cakes of castor, linseed, groundnut, mahua and neem in the management of root knot nematode, Meloidogyne javanica infecting eggplant under glasshouse conditions. All the treatments effectively suppressed the nematode population and kept the infection at significantly low level. Individual treatment of P. lilacinus was more effective than C. oxysporum in controlling M. javanica, whereas among oil cakes individual treatment of neem was more effective in the management of M. javanica followed by linseed cake, castor cake, groundnut cake and mahua cake. However, the efficacy of biocontrol agents increased in the presence of oil cakes. The highest improvement in plant growth and best protection against M. javanica was obtained by the integration of P. lilacinus with groundnut cake followed by neem cake, linseed cake, castor cake and mahua cake. On the other hand the integration of C. oxysporum with neem cake followed by groundnut cake, linseed cake, castor cake and mahua cake gave the best results in managing M. javanica on eggplant.     

Fate of Cryptosporidium oocysts, Giardia cysts, and microbial indicators during wastewater treatment and anaerobic sludge digestion.

The extent of reduction in selected microorganisms was tested during both aerobic wastewater treatment and anaerobic digestion of sludge at the wastewater treatment plant in Ottawa to compare the removal of two encysted pathogenic protozoa with that of microbial indicators. Samples collected included the raw wastewater, the primary effluent, the treated wastewater, the mixed sludge, the decanted liquor, and the cake. All of the raw sewage samples were positive for Cryptosporidium oocysts and Giardia cysts, as well as for the other microorganisms tested. During aerobic wastewater treatment (excluding the anaerobic sludge digestion), Cryptosporidium and Giardia were reduced by 2.96 log10 and 1.40 log10, respectively. Clostridium perfringens spores, Clostridium perfringens total counts, somatic coliphages, and heterotrophic bacteria were reduced by approximately 0.89 log10, 0.96 log10, 1.58 log10, and 2.02 log10, respectively. All of the other microorganisms were reduced by at least 3.53 log10. Sludge samples from the plant were found to contain variable densities of microorganisms. Variability in microbial concentrations was sometimes great between samples, stressing the importance of collecting a large number of samples over a long period of time. In all cases, the bacterial concentrations in the cake (dewatered biosolids) samples were high even if reductions in numbers were observed with some bacteria. During anaerobic sludge digestion, no statistically significant reduction was observed for Clostridium perfringens, Enterococcus sp., Cryptosporidium oocysts, and Giardia cysts. A 1-2 log10 reduction was observed with fecal coliforms and heterotrophic bacteria. However, the method utilized to detect the protozoan parasites does not differentiate between viable and nonviable organisms. On the other hand, total coliforms and somatic coliphages were reduced by 0.35 log10 and 0.09 log10, respectively. These results demonstrate the relative persistence of the protozoa in sewage sludge during wastewater treatment.     

Using acoustic cavitation to improve the bio-activity of activated sludge

This paper studied a new method to improve the microbial activity of the activated sludge for wastewater treatment. Concentrated sludge was sonicated in an extra chamber for short period and then returned to the activated sludge system. The results showed that the bio-activity of the activated sludge, expressed as oxygen utilization rate (OUR), could be enhanced by ultrasonic irradiation. Powerful ultrasound (in the magnitude of W/ml) was much more effective than weak ultrasound (in the magnitude of W/L) in stimulating the activated sludge, but too strong sonication (power density higher than 0.5 W/ml) disintegrated the sludge and thus decreased the sludge activity. Low frequency (25 kHz) was more effective than higher ones (80 kHz and 150 kHz), indicating that mechanical effects, instead of free radicals, were responsible for the bio-activity enhancement. The optimal sonication conditions were sound frequency of 25 kHz, power density of 0.2 W/ml and duration of 30s; under which the sludge OUR increased by 28%, the bio-mass growth rate increased by 12.5%, and the wastewater chemical oxygen demand (COD) and total nitrogen removal efficiency increased by 5-6%.     

Effect of oilseed cakes on alpha-amylase production by Bacillus licheniformis CUMC305.

The effects of oilseed cakes on extracellular thermostable alpha-amylase production by Bacillus licheniformis CUMC305 was investigated. Each oilseed cake was made of groundnut, mustard, sesame, linseed, coconut copra, madhuca, or cotton. alpha-Amylase production was considerably improved in all instances and varied with the oilseed cake concentration in basal medium containing peptone and beef extract. Maximum increases were effected by a low concentration (0.5 to 1.0%) of groundnut or coconut, a high concentration (3%) of linseed or mustard, and an Rintermediate concentration (2%) of cotton, madhuca, or sesame. The oilseed cakes made of groundnut or mustard could completely replace the conventional peptone-beef extract medium as the fermentation base for the production of alpha-amylase by B. licheniformis. The addition of corn steep liquor to cotton, linseed, sesame, or madhuca cake in the medium improved alpha-amylase production.     

Membrane fouling in a membrane bioreactor (MBR): sludge cake formation and fouling characteristics

A submerged membrane bioreactor (MBR) with a working volume of 1.4 L and a hollow fiber microfiltration membrane was used to treat a contaminated raw water supply at a short hydraulic retention time (HRT) of approximately 1 h. Filtration flux tests were conducted regularly on the membrane to determine various fouling resistances, and confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were employed to characterize the biofouling development and sludge cake formation on the membrane. The experimental results demonstrate that the MBR is highly effective in drinking water treatment for the removal of organic pollutants, ammonia, and UV absorbance. During the MBR operation, the fouling materials were not uniformly distributed on the entire surface of all of the membrane fibers. The membrane was covered partially by a static sludge cake that could not be removed by the shear force of aeration, and partially by a thin sludge film that was frequently washed away by aeration turbulence. The filtration resistance coefficients were 308.4 x 10(11) m(-1) on average for the sludge cake, 32.5 x 10(11) m(-1) on average for the dynamic sludge film, and increased from 10.5 x 10(11) to 59.7 x 10(11) m(-1) for the membrane pore fouling after 10 weeks of MBR operation at a filtration flux of 0.5 m3/m2 x d. Polysaccharides and other biopolymers were found to accumulate on the membrane, and hence decreased membrane permeability. More important, the adsorption of biopolymers on the membrane modified its surface property and led to easier biomass attachment and tighter sludge cake deposition, which resulted in a progressive sludge cake growth and serious membrane fouling. The sludge cake coverage on the membrane can be minimized by the separation, with adequate space, of the membrane filters, to which sufficient aeration turbulence can then be applied.     

Biodegradation of Total Petroleum Hydrocarbons from Oily Sludge

The present study concerns the biotreatment of oily sludge of petroleum refineries. Experiments were performed to assess the degradation potential of the microbial species present in the oily sludge through augmentation, and using the augmented microbial inoculums to treat oily sludge in a slurry form containing mineral medium and water. The optimum pH of the slurry was found to be 8 for the biodegradation of oily sludge. The effect of oily sludge concentration, stirring rate, and treatment time on degradation of total petroleum hydrocarbons (TPH) was studied. It was found that the degradation process consists of two consecutive stages and that each stage follows a first-order kinetics. The first stage lasted 4 days followed by a second stage up to 7 days. The faster first stage had a rate constant of 0.1 day^?1, whereas the slower second stage had a rate constant of 0.056 day^?1. The kinetics was found to be time-dependent. The study showed that the mineral medium provided essential nutrients to the microbial species and that the degradation efficiency of the whole microbial species present in the oily sludge was quite high (～90%).     

Effect of oilseed cakes on alpha-amylase production by Bacillus licheniformis CUMC305

The effects of oilseed cakes on extracellular thermostable alpha-amylase production by Bacillus licheniformis CUMC305 was investigated. Each oilseed cake was made of groundnut, mustard, sesame, linseed, coconut copra, madhuca, or cotton. alpha-Amylase production was considerably improved in all instances and varied with the oilseed cake concentration in basal medium containing peptone and beef extract. Maximum increases were effected by a low concentration (0.5 to 1.0%) of groundnut or coconut, a high concentration (3%) of linseed or mustard, and an Rintermediate concentration (2%) of cotton, madhuca, or sesame. The oilseed cakes made of groundnut or mustard could completely replace the conventional peptone-beef extract medium as the fermentation base for the production of alpha-amylase by B. licheniformis. The addition of corn steep liquor to cotton, linseed, sesame, or madhuca cake in the medium improved alpha-amylase production.     

Hydrolytic enzyme activities of extracted humic substances during the vermicomposting of a lignocellulosic olive waste

Humic substances and three hydrolytic enzymes (beta-glucosidase, phosphatase and urease) were extracted by neutral sodium pyrophosphate from an olive waste (dry olive cake), alone or mixed with municipal biosolids, during a nine month vermicomposting process. Easily degradable compounds decreased during the vermicomposting process because of microbial consumption. When municipal biosolids were added to dry olive cake, microbial activity increased and the amounts of compounds extracted by pyrophosphate were three times lower than olive cake alone. In both instances, beta-glucosidase, phosphatase and urease activities of the organic extracts either increased or remained the same after a nine month period of vermicomposting, thus suggesting that the humus enzyme complexes resisted microbial and earthworm attack. It is known that humus immobilised enzymes also remain active in soil environments, reactivating the nutrient cycles in soil. The use as amendments of vermicomposted olive cake, alone or when mixed with biosolids, could be a good alternative to reactivate the C, P and N-cycles in degraded soils for regeneration purposes.     

Membrane fouling control and sludge solubilization using high voltage impulse (HVI) electric fields

The effectiveness of a high voltage impulse (HVI) technique in mitigating the membrane fouling occurring in membrane bioreactors was examined. After the activated sludge was membrane filtered, the cake layer was removed by either water-washing cleaning (experimental control) or HVI cleaning. The flux recoveries after HVI induction were always higher than those of the control. The effect of HVI induction on the sludge properties was also examined. The mixed liquor suspended solids (MLSS) concentration decreased with increasing HVI contact time, while the concentrations of soluble-chemical oxygen demand (SCOD), -total nitrogen (TN), -total phosphorus (TP), -polysaccharide, and -protein in the bulk solution increased, indicating that the flocs and cells were damaged by the HVI induction. These results suggest that the HVI induction led to sludge solubilization, which loosened the tightly deposited cake layer on the membrane surface, hence allowing it to be easily dislodged from the membrane surface.     

Food mixing by generalist grasshoppers: Plant secondary compounds structure the pattern of feeding

Plant secondary compounds can prevent feeding by phytophagous insects or, if ingested, can be poisonous to them. Less attention has been paid to the additional effects they have on feeding behavior when they are only weakly deterrent or not deterrent at all. Experiments were carried out on the generalist grass-hopperSchistocerca americana. Individuals were presented either with two cakes of high-quality artificial food with a single deterrent compound added or with two cakes, each with a different added deterrent compound. The deterrents consisted of single plant secondary compounds that were either marginally or strongly deterrent. There were profound differences in feeding behavior between those individuals given identical and those given different cake types, including longer feeding bouts on single cakes when a choice of different cake types was available. The behavioral effects demonstrate that the presence of secondary compounds in one food can influence the patterns of feeding on other available foods and suggest that such chemicals could impact foraging activities in a complex manner.