Scum Formation Research Articles

SOx対応技術のエンジン潤滑への影響

The International Maritime Organization (IMO) has decided to strengthen regulations on sulphur oxide (SOx) emissions from ships by 2025. This paper consists of two parts. The first part shows the various types of fuels and their combinations which may be used by marine vessels in the next ten years, and presents the influence these fuels may have on engine lubrication. The second part deals with heavy fuel oil (HFO) with scrubbing, and presents the generation of black scum in scrubbers installed on 2-stroke engines. The author proposes a mechanism for scum formation and suggests two countermeasures to prevent its formation. One countermeasure is the use of specifically formulated cylinder lubricants, and the other is the improvement of lubricant demulsibility.

Performance of a Novel Downward Plug-Flow Anaerobic Digester for Methane Production from Chopped Straw

In China, there is an urgent need for an efficient anaerobic digester to sustainably treat rice straw. In this study, a downward plug-flow anaerobic digester (DPAD) was designed in which the total working core is separated into three sections: an upper liquid zone, a lower liquid zone, and a solid-state bed (SSB) in the middle. A solid/liquid separation mechanism was designed to recirculate liquor and the discharged solid residue after complete digestion. The 70-L DPAD was run indoors for 100 d, time in which chopped rice straw (30 to 50 mm in length) was fed every 20 d. The digestion performance and biogas production were analysed to assess the feasibility for practice application. The results showed that the DPAD can control scum formation and offers a methane yield of 162.60 L/kg volatile solids, 21.1% higher than that of the control test. It was also found that straw was continuously and efficiently digested by the DPAD in 3 experimental stages. Methane production rates increased by 76.30%, 57.37%, and 13.33% on the second day compared to the first day, respectively, and then, all decreased as the substrate was gradually exhausted. Based on the results, it is clear that the DPAD is a promising solution for chopped straw digestion.

Leaching characteristics of poultry litter in first phase of multistage anaerobic digestion

Poultry litter is highly biodegradable in nature. Therefore, it could be subjected to biomethanation to produce valuable biogas and bio-manure as byproducts. Some studies have been conducted along these lines in India by utilizing the poultry litter as a substrate in batch type dung digesters of KVIC and DENABANDHU models. However, these reactors have the drawbacks of high residence time (30 – 35 days), scum formation problems etc. Moreover, these batch type plants are not suitable for the treatment of large quantities of solid waste. Multistage anaerobic digestion has the potential to overcome some of the aforesaid issues. Anaerobic leaching experiments were conducted at different total solids concentration and pH using poultry litter in order to evaluate the leachate quality for a period of 7 days. The increase in Total solids (TS) % from 15 to 20% show inverse effect on VFA and Alkalinity. The change in pH from 8.5 to 5.5 didn’t show much impact on VFA but there is a small impact on alkalinity. It was also observed that the leaching of the organic matter in the solid to the liquid phase is very fast and it is taking place approximately in three to four days and subsequently leachate getting saturated. Therefore, reactor set up was made in the last phase to regularly remove the water from the reactor so that higher driving force is available for leaching. The study resulted in leaching of maximum organic content in the solid to liquid within three days. DOI: http://dx.doi.org/10.3126/ije.v3i2.10516 International Journal of the Environment Vol.3(2) 2014: 76-82

Cause of scum formation on the water surface of flocculation basin in water treatment plant

Scum is often found on the water surface of flocculation and sedimentation basin in water treatment plants, although water treatment facilities should always be in clean condition. A series of analytical experiments were conducted on the raw water and scum to investigate the cause and characteristics of scum formation in the Seokseong water treatment plant, which has been experiencing scum treatment problems. The measurements results in the field indicated that the raw water in the receiving well was oversaturated with dissolved oxygen by the pressure of the intake pumping and conveyance. The oversaturated oxygen triggered micro-bubbles because of the sudden decrease in surface tension that is caused by the coagulant dose. Observations of the experimental facilities revealed that bubbles are generated originally on the surface of a floc, and the flocs are acting as a nucleation of the bubble formation. The chemical composition of scum consists of various hydrophobic compounds, similar to the sludge in the sedimentation basin. These findings led us to conclude that with an exception of the nucleation of bubble formation, the mechanism of scum formation is similar to the particle separation of the flotation process in the water treatment plant. Therefore, scum formation may be prevented or reduced if excessive increase in pipeline pressure is avoided when mixing with air during processes of intake pumping and conveyance.

UVB Radiation as a Potential Selective Factor Favoring Microcystin Producing Bloom Forming Cyanobacteria

Due to the stratospheric ozone depletion, several organisms will become exposed to increased biologically active UVB (280–320 nm) radiation, not only at polar but also at temperate and tropical latitudes. Bloom forming cyanobacteria are exposed to UVB radiation on a mass scale, particularly during the surface bloom and scum formation that can persist for long periods of time. All buoyant species of cyanobacteria are at least periodically exposed to higher irradiation during their vertical migration to the surface that usually occurs several times a day. The aim of this study is to assess the influence on cyanobacteria of UVB radiation at realistic environmental intensities. The effects of two UVB intensities of 0.5 and 0.99 W/m2 in up to 0.5 cm water depth were studied in vitro on Microcystis aeruginosa strains, two microcystin producing and one non-producing. After UVB exposure their ability to proliferate was estimated by cell counting, while cell fitness and integrity were evaluated using light microscopy, autofluorescence and immunofluorescence. Gene damage was assessed by TUNEL assay and SYBR Green staining of the nucleoide area. We conclude that UVB exposure causes damage to the genetic material, cytoskeletal elements, higher sedimentation rates and consequent cell death. In contrast to microcystin producers (PCC7806 and FACHB905), the microcystin non-producing strain PCC7005 is more susceptible to the deleterious effects of radiation, with weak recovery ability. The ecological relevance of the results is discussed using data from eleven years’ continuous UVB radiation measurements within the area of Ljubljana city (Slovenia, Central Europe). Our results suggest that increased solar radiation in temperate latitudes can have its strongest effect during cyanobacterial bloom formation in spring and early summer. UVB radiation in this period may significantly influence strain composition of cyanobacterial blooms in favor of microcystin producers.

Coupling hydrodynamics and buoyancy regulation in Microcystis aeruginosa for its vertical distribution in lakes

In this research we introduce a coupled column model to simulate the vertical migration of Microcystis aeruginosa in natural lakes. M. aeruginosa is a unicellular cyanobacteria that form colonies. They produce toxins and therefore become a potential threat to water quality and human health. Understanding the distribution of this species in space and time is important for improving water management strategies. The model we propose includes both hydrodynamics and physiological responses including explicitly buoyancy regulation in Microcystis cells. Our model applies the Langevin–Fokker–Planck approach to simulate the total colony number concentration along the water column. This approach allows the description of sinking and rising velocities of colonies of different sizes and compositions subjected to turbulent mixing. The model is first applied to the 30m deep Lake Vlietland in the Netherlands for the summer of 2009. During this summer, the lake showed high blooms of Microcystis which eventually led to scum formation along the shore. The simulations show the preferential distribution of M. aeruginosa through the water column and their strong dependency on colony size. On a daily cycle, small colonies (50–200μm) do not remain near the surface but are highly concentrated in the middle of the epilimnion, whereas large colonies (≥800μm) are able to migrate to greater depths and concentrate only temporarily near the surface. For comparing our computer model with available measurements of Microcystis concentration distributions we applied it to Lakes IJsselmeer and Vinkeveen. The results show a good agreement with the observations of diurnal changes in buoyancy status.

Membrane bioreactor (MBR) sludge inoculation in a hybrid process scheme concept to assist overloaded conventional activated sludge (CAS) process operations

This study analyzes the effect of inoculating membrane bioreactor (MBR) sludge in a parallel-operated overloaded conventional activated sludge (CAS) system. Modelling studies that showed the beneficial effect of this inoculation were confirmed though full scale tests. Total nitrogen (TN) removal in the CAS increased and higher nitrate formation rates were achieved. During MBR sludge inoculation, the TN removal in the CAS was proven to be dependent on MBR sludge loading. Special attention was given to the effect of inoculation on sludge quality. The MBR flocs, grown without selection pressure, were clearly distinct from the more compact flocs in the CAS system and also contained more filamentous bacteria. After inoculation the MBR flocs did not evolve into good-settling compact flocs, resulting in a decreasing sludge quality. During high flow conditions the effluent CAS contained more suspended solids. Sludge volume index, however, did not increase. Laboratory tests were held to determine the threshold volume of MBR sludge to be seeded into the CAS reactor. Above 16-30%, supernatant turbidity and scum formation increased markedly.

Structural analysis of N[sbnd]H⋯O in viscoelastic scum formation during solvent extraction of sulfuric acid with trioctylamine

In the paper, Fourier transform infrared spectroscopy combined with Gaussian function linear fitting is used to analyze the structure of the viscoelastic scum formed during solvent extraction of sulfuric acid with trioctylamine (TOA). The results show that when the molar ratio of sulfuric acid to TOA is low in the system, it would form N⋯HO through TOA coupling with sulfuric acid or TOA coupling with water. The N⋯H stretching vibration is around 3400cm−1. With the increase of molar ratio of sulfuric acid to TOA, three peaks, near 2660cm−1, 2610cm−1, and 2535cm−1, appear in the infrared spectrum and they are assigned to NH+ combining with water, NH+ combining with OS, NH+ combining with water and OS in the extraction system. The wave-number of CN stretching vibration increases with the increase of molar ratio of sulfuric acid to TOA.

음식물 탈리액 처리를 위한 막결합형 고온 2상 혐기성 소화 공정의 평가

This study evaluated the performance of a thermophilic two-phase anaerobic digestion (TTPAD) coupled with membrane process treating garbage leachate. The pilot-scale treatment system is consisted of thermophilic acidogenic reactor (TAR) and thermophilic methanogenic reactor (TMR) coupled with an ultrafiltration (UF) membrane unit. The hydraulic retention time of TAR and TMR were 4 and 20 days, respectively. Effluent TCOD and SCOD of the TTPAD were g/L, respectively, and the corresponding TCOD and SCOD removal efficiencies were 77% and 81%, respectively. Propionate was major acids as 75% in the effluent. Scum formation was not observed in TTPAD, which might be resulted from complete lipid degradation. However, TTPAD was appeared to be sensitive to free ammonia toxicity. The UF membrane was operated with constant pressure filtration at average TMP 1.3 atm. Permeate flux had a range of 15-30 . With UF membrane, TCOD removal increased from 77% to 93%, and this SS free effluent would be beneficial to subsequent processes such as ammonia stripping.

Handbook of Biological Wastewater Treatment: Design and Optimisation of Activated Sludge Systems

The scope of this comprehensive new edition of Handbook of Biological Wastewater Treatment ranges from the design of the activated sludge system, final settlers, auxiliary units (sludge thickeners and digesters) to pre-treatment units such as primary settlers and UASB reactors.The core of the book deals with the optimized design of biological and chemical nutrient removal. The book presents the state-of-the-art theory concerning the various aspects of the activated sludge system and develops procedures for optimized cost-based design and operation. It offers a truly integrated cost-based design method that can be easily implemented in spreadsheets and adapted to the particular needs of the user.Handbook of Biological Wastewater Treatment: Second Edition incorporates valuable new material that improves the instructive qualities of the first edition. The book has a new structure that makes the material more readily understandable and the numerous additional examples clarify the text.On the website www.wastewaterhandbook.com three free excel design spreadsheets for different configurations (secondary treatment with and without primary settling and nitrogen removal) can be downloaded to get the reader started with their own design projects.New sections have been added throughout:• to explain the difference between true and apparent yield while the section on the F/M ratio, and especially the reasons not to use it, has been expanded;• to demonstrate the effect of the oxygen recycle to the anoxic zones on both the denitrification capacity and the concept of available nitrate is explained in more detail.• the latest developments on the causes and solution to sludge bulking and scum formation• to show the rapid developments of innovative nitrogen removal and sludge separation problems• the anaerobic pre-treatment section is completely rewritten based on the experiences obtained from an extensive review of large full-scale UASB based sewage treatment plants• a new section on industrial anaerobic wastewater treatment• three new appendices have been added. These deal with the calibration of the denitrification model, empirical design guidelines for final settler design (STORA/STOWA and ATV) and with the potential for development of denitrification in the final settler.• A new chapter on moving bed biofilm reactorsHandbook of Biological Wastewater Treatment: Second Edition is written for post graduate students and engineers in consulting firms and environmental protection agencies. It is an invaluable resource for everybody working in the field of wastewater treatment.ISBN: 9781780400006 (Print)ISBN: 9781780400808 (eBook)

Effect of hydroxyl on formation of viscoelastic scum during solvent extraction of sulfuric acid with trioctylamine

In the paper, Fourier transform infrared spectroscopy (FTIR) is employed to investigate the formation of viscoelastic scum during solvent extraction of sulfuric acid with trioctylamine (TOA) as extractant. The spectra are deconvolved and peak-fitted to study the change of wave-number and the peak area of O–H stretching vibration. Results suggest that the water plays an important role in viscoelastic scum formation. The water, sulfuric acid and TOA can combined as SO…HOH…N or HOH…OS or NH…OS. With the increase of the molar ratio of sulfuric acid to TOA, the combination of the water, sulfuric acid and TOA would transform to SO…HOH…OS or N+…HOH, which may be form macro-molecules in the extraction system.

Lipase production by strains of Aspergillus species isolated from contaminated body creams

Aspergillus species isolated from contaminated body creams were screened for their ability to produce extracellular lipase. Of the 6 strains tested two, identified as Aspergillus niger AC-5 and AC-7 and one strain ofAspergillus fumigatus. AF-3 were capable of producing extracellular lipase in appreciable amounts. A. nigerAC-5 was the highest lipase producer, followed by A. fumigatus AF-3, while Aspergillus flavus showed the least potential for lipase production. The maximal lipase production (14.4 µ/ml) was produced by strain AC-5 in 6 days culture supplied with 3% (v/v) olive oil as the carbon source. The optimum pH and temperature for the crude lipase activity were 6.5 and 40°C respectively, for strains tested. The enzyme was stable over a wide range of pH and temperature. The enzymes retained certain levels of their original activities when assayed at 60°C for 1 h. Body creams contaminated with these lipolytic moulds produced off-odours in addition to other physico-chemical changes such as discolouration, formation of tints and scum, emulsion breakage and changes in pH. This is a source of concern and calls for urgent amendment in the existing formulation protocols and strict adoption of good manufacturing practice to ensure microbiologically stable product. Key words: Lipase, body cream, lipolytic molds, physico-chemical changes.

Performance of anaerobic bioreactor treating fish-processing plant wastewater pre-hydrolyzed with a solid enzyme pool

The effect of a lipase-rich enzyme preparation produced by the fungus Penicillium simplicissimum on solid-state fermentation was evaluated in a 4.9 L up-flow anaerobic sludge blanket bioreactor (UASB) treating fish-processing plant wastewater containing 1500 mg oil and grease (O&G)/L. The oil and grease hydrolysis step was carried out with 0.5% or 0.2% (w/v) of the solid enzyme preparation (SEP) at 30 °C for 8 h. The bioreactor operated at 30 °C with a hydraulic retention time of 10 h for a period of over 100 days, showed high total COD removal efficiencies (85.3% for 0.5% SEP and 90.9% for 0.2% SEP), when fed with pre-hydrolyzed wastewater, compared to a Control bioreactor fed with raw wastewater (79.9%). The Control bioreactor also showed high oil and grease accumulation in the biomass throughout the operational period (the O&G content reached 1.7 times that found in the inoculum of the UASB bioreactor), intensive scum formation, and several episodes of cessation of treatment to clean the three-phase separator. Thus it can be concluded that the enzyme pre-hydrolysis step together with anaerobic treatment of the fish-processing plant wastewater improved the quality of the treated effluent and reduced operational problems.

Multi stage high rate biomethanation of poultry litter with self mixed anaerobic digester

A multi stage high rate biomethanation process with novel self mixed anaerobic digester (SMAD) was developed in the present study to reduce the hydraulic residence time (HRT), increase the volatile solids (VS) loading rate, improve the VS destruction efficiency and enhance the methane yield. Specific design features of SMAD were useful in mixing the digester contents without consuming power and de-alienated the problem of scum formation. In the first phase, poultry litter having 10% total solids (TS) was subjected to high rate biomethanation in multi stage configuration (SMAD-I and II in series with UASB reactor). It was observed that gross VS reduction of 58%, gross methane yield of 0.16 m3 kg(-1) (VS reduced) and VS loading rate of 3.5 kg VS m(-3) day(-1) at HRT of 13 days was obtained. In the second phase SMAD-II was bypassed from the process scheme keeping the other parameters same as in the first phase. The results obtained were not as encouraging as in the first phase. The study showed that multi stage configuration with SMAD design improved the anaerobic digestion process efficiency of poultry litter.

Effects of buoyancy, transparency and zooplankton feeding on surface maxima and deep maxima: Comprehensive mathematical model for vertical distribution in cyanobacterial biomass

Inhomogeneous vertical distributions of the cyanobacterial biomass are widely observed during the summer season in stratified lake ecosystems. Among these are surface maxima characterized by surface scum formation and deep or subsurface maxima also known as deep chlorophyll maxima (DCM). The former occurs at the epilimnion in eutrophic lakes, and are usually caused by colonial cyanobacteria such as Microcystis. On the other hand, the latter occurs at the metalimnion and the upper part of the hypolimnion near the thermocline in oligotrophic lakes, and are referred to filamentous cyanobacteria such as Oscillatoria. The aim of this paper is to present a simple mathematical model that can simultaneously describe these phenomena including the annual and diurnal variations, emphasizing the roles of buoyancy regulation, transparency of the lake and zooplankton feeding on cyanobacteria. According to our computer analyses, the increased buoyancy, the low clarity of the lake and the low rate of zooplankton feeding take significant roles in formation of surface maxima, while the reversal of these factors makes deep maxima predominant. Our two-component model with nutrients and cyanobacteria can distinguish between two phenomena by changing the parameters for these factors, without altering the model itself.

Degasification of mixed liquor improves settling and biological nutrient removal

Degasification of mixed liquor by subjecting it to vacuum is a physical process used in biological nutrient removal (BNR) to improve settleability and allow for achieving higher mixed liquor suspended solids (MLSS). Vacuum degassing installation is located between the last cell of the bioreactor and secondary clarifiers. In this process two operations are performed: gas bubbles contained in mixed liquor leaving the bioreactor are removed and concentration of gasses (mainly nitrogen gas) dissolved in the liquid is reduced. Lack of gas bubbles and concentration of dissolved nitrogen gas below saturation in mixed liquor significantly improved sludge settling in secondary clarifiers and eliminated floating scum formation. Presented settleability tests of degasified MLSS and return activated sludge (RAS) from various BNR facilities showed continued settling and/or thickening for over 3 h at room temperature, without exhibiting any solids separation. Settleability tests of biomass that was not degasified typically led to flotation of portion of the sludge after about 1.5 h. Plants equipped with vacuum degasification consistently operate at larger than typically recommended final clarifier sludge surface loading rates. Rates as high as 180-220 kg TSS/m2d and deep sludge blankets have been employed. Such plants were shown to maintain operational levels of MLSS at 4500 to 6000 mg/L and higher.

Anaerobic lipid degradation through acidification and methanization

In biological wastewater treatment high lipid concentration is known to inhibit microorganisms and cause active biomass flotation. To reduce lipid inhibition, a two-phase anaerobic system, consisting of an anaerobic sequencing batch reactor (ASBR) and an upflow anaerobic sludge blanket (UASB) reactor, was applied to synthetic dairy wastewater. During 153 days of operation, the two-phase system showed stable performance in lipid degradation. In the ASBR, a 13% lipid removal efficiency and 10% double bond removal efficiency were maintained. In the UASB, the chemical oxygen demand (COD), lipid and volatile fatty acid (VFA) removal efficiencies were more than 80%, 70% and 95%, respectively, up to organic loading rate 6.5 g COD/L/day. There were no operational problems such as serious scum formation or sludge washout. Protein degradation occurred prior to degradation during acidogenesis.

Potential of low-temperature anaerobic digestion to address current environmental concerns on swine production1

Environmental issues associated with swine production are becoming a major concern among the general public and are thus an important challenge for the swine industry. There is now a renewed interest in environmental biotechnologies that can minimize the impact of swine production and add value to livestock by-products. An anaerobic biotechnology called psychrophilic anaerobic digestion (PAD) in sequencing batch reactors (SBR) has been developed at Agriculture and Agri-Food Canada. This very stable biotechnology recovers usable energy, stabilizes and deodorizes manure, and increases the availability of plant nutrients. Experimental results indicated that PAD of swine manure slurry at 15 to 25 degrees C in intermittently fed SBR reduces the pollution potential of manure by removing up to 90% of the soluble chemical oxygen demand. The process performs well under intermittent feeding, once to 3 times a week, and without external mixing. Bioreactor feeding activities can thus be easily integrated into the routine manure removal procedures in the barn, with minimal interference with other farm operations and use of existing manure-handling equipment. Process stability was not affected by the presence of antibiotics in manure. The PAD process was efficient in eliminating populations of zoonotic pathogens and parasites present in raw livestock manure slurries. Psychrophilic anaerobic digestion in SBR could also be used for swine mortality disposal. The addition of swine carcasses, at loading rates representing up to 8 times the normal mortality rates on commercial farms, did not affect the stability of SBR. No operational problems were related to the formation of foam and scum. The biotechnology was successfully operated at semi-industrial and full commercial scales. Biogas production rate exceeded 0.20 L of methane per gram of total chemical oxygen demand fed to the SBR. The biogas was of excellent quality, with a methane concentration ranging from 70 to 80%. The recovery of green energy, the production of a value-added odorless fertilizer, the elimination of manure pathogens, and the proper disposal of swine mortalities will substantially reduce the carbon and environmental footprints on products of swine origin.

Effect of Different Larval Rearing Temperatures on the Productivity (Ro) and Morphology of the Malaria VectorAnopheles superpictusGrassi (Diptera: Culicidae) Using Geometric Morphometrics

Effect of Different Larval Rearing Temperatures on the Productivity (R_o) and Morphology of the Malaria Vector<i>Anopheles superpictus</i>Grassi (Diptera: Culicidae) Using Geometric Morphometrics

Control of scum accumulation in a double stage biogas collection (DSBC) UASB reactor treating domestic wastewater

This paper presents an innovative reactor concept which is based on a double-stage biogas collection (DSBC) device aimed at controlling scum formation and accumulation in UASB reactors treating municipal wastewater. Scum production inside a control reactor and a DSBC-UASB reactor was compared and much lower scum yield coefficients were observed for the DSBC-UASB reactor. However, the mass balance indicated that the dominant control mechanism was scum disaggregation and exit to settler zone rather than scum degradation.