• Journal of Korean Society of Water and Wastewater
• /
• v.20 no.4
• /
• pp.617-626
• /
• 2006

Compared with the sludge from gravity sedimentation, it is difficult for operations to settle the sludge occurred from dissolved-air-flotation (DAF). Even though there are some problems in treating DAF sludge with conventional gravity thickeners, those has been used until now. In this study, Solid Flux theory for gravity thickening was applied to the Solid Flux of DAF sludge through flotation in order to develop new methodology for treatment of DAF sludge. Also, characteristics of DAF sludge were investigated. From the experiment results, it was revealed that the higher the polymer dosage, at fixed the solid concentration, the greater the rising velocity becomes. When we applied solid flux theory, the relationship, which is similar to that of gravity thickening, has been achieved. Also, we could find the proper polymer dosage from the rising velocity is about 50 mg/L. Consequently, the limiting solid flux can be derived from the relationship between the total solid flux and the withdrawal velocity of DAF sludge. Furthermore, the factors, such as solid concentrations, bubble volume, pH, zeta potential, and temperature, have effects on the flotation and sedimentation for DAF sludge treatment.

• Journal of Korean Society on Water Environment
• /
• v.22 no.1
• /
• pp.97-103
• /
• 2006

Excess sludge treatment and disposal currently represent a rising challenge for domestic or wastewater treatment plants due to economic, environmental and regulation factors. Conventional gravity sedimentation process has been widely used in sludge thickening. The operation method of the process is very simple, but the process requires long detention time for sludge thickening, uses polymers, and shows low sludge thickening efficiency. To solve the problems, we studied on DAF (Dissolved Air Flotation) system. We use bulking sludge of a paper manufacturing plant. The effects of parameters such as SVI (Sludge Volume Index), storage time, initial concentration and wet density of excess sludge were examined. The results showed that the more SVI was low, the more sludge was thickened. As storage time goes by, SVI was increased and thickening performance was deteriorated. In order to improve flotation performance at high concentration, high recycling ratio and pressure did not increase the concentration due to thickening limitation. The addition of 0.8 g/L of loess was increased flotation efficiency of 1.41 times.

• Journal of the Korea Organic Resources Recycling Association
• /
• v.3 no.2
• /
• pp.37-45
• /
• 1995

The performance and the operational problems of UASB(Upflow Anaerobic Sludge Blanket) reactor for treatment of dairy wastewaters were investigated. Synthetic milk wastewater was successfully treated up to the loading rate of 3.9kg $COD/m^3.day$, with a specific gas production rate of 1. 23 I/I. day and a COD removal efficiency of over 90%. However, the sludge rising was observed at the loading rate of 2.1kg $COD/m^3.day$, due probably to the formation of scum layer at the surface of settling compartment. The BMP(biochemical methane potential) of raw milk wastewater and ice cream wastewater, measured by using SBT(serum bottle test), were 0.135 and 0.66ml $CH_4/mg\;COD_{added}$, respectively. The sludge activity increased more than 8 times from 0.159g $COD-CH_4/g$ VSS. d during 90 days of operation.

• Membrane and Water Treatment
• /
• v.9 no.4
• /
• pp.245-253
• /
• 2018

The aim of this study is to investigate the membrane fouling in a thermophilic membrane bioreactor (TMBR) operated different sludge retention times (SRTs). For this purpose, TMBR was operated at four different SRTs (10, 30, 60 and 100 days). Specific cake resistance (${\alpha}$), cake resistance, gel resistance, total resistance, MFI (modified fouling index) and FDR (flux decrease ratio) were calculated for all SRTs. It was observed that flux in the membrane increases with rising SRT although the sludge concentrations in the TMBR increased. The steady state flux was found to be 31.78; 34.70; 39.60 and 43.70 LMH ($Liter/m^2/h$) for the SRTs of 10, 30, 60 and 100 days respectively. The concentrations of extracellular polymeric substance (EPS) and soluble microbial product (SMP) decreased with increasing SRT. The membrane fouling rate was higher at shorter SRT and the highest fouling rate appeared at an SRT of 10 d. Both the sludge cake layer and gel layer had contribution to the fouling resistance, but the gel layer resistance value was dominant in all SRTs.

• Journal of Korean Society on Water Environment
• /
• v.16 no.4
• /
• pp.513-521
• /
• 2000

Intermittently aerated activated sludge process was applied as a water reuse process of $70m^3/day$ for the upgrade of organic, nitrogen and phosphorus removal efficiency and clarifier performance. After application of the intermittently aeration, removal efficiency of BOD, SS, T-N and T-P were achieved 95%, 90%, 80% and 60%, respectively. Removal efficiencies in intermittently aerated process were considerably increased. comparing to those of continuously aerated activated sludge process. Also sludge rising problem in clarifier was improved. Average concentration of supplied reusing water were BOD 5 mg/L, turbidity 4 NTU and after chlorination, residual chlorine 0.4 mg/L, coliform 0 MPN/100mL. Intermittently aerated activated sludge process could be one of the best alternative process for the retrofit of conventional activated sludge process for the removal of nutrient in water reuse system.

• Membrane and Water Treatment
• /
• v.4 no.3
• /
• pp.175-189
• /
• 2013

A membrane bioreactor (MBR) with sludge retention time (SRT) of 300 days was maintained for over 2 years. Polypropylene microfiltration (MF) membrane with pore size of 0.2 ${\mu}m$ was used in the MBR system. The fouling behaviors of various sludge fractions from the MBR were studied and sub-divided resistances were analyzed. It was observed that $R_{cp}$ was a dominant resistance during the filtration of activated sludge, contributing 63.0% and 59.6% to the total resistance for MBR and sequential batch reactor (SBR) respectively. On the other hand, $R_c$ played the significant role during the filtration of supernatant and solutes, varying between 54.54% and 67.18%. Compared with $R_{cp}$ and $R_c$, $R_{if}$ was negligible, and $R_m$ values remained constant at $0.20{\times}10^{12}m^{-1}$. Furthermore, resistances of all sludge fractions increased linearly with rising mixed liquor suspended solids (MLSS) concentration and growing trans-membrane pressure (TMP), while the relationship was inversed between fraction resistances and cross flow velocity (CFV). Among all fractions of activated sludge, suspended solid was the main contributor to the total resistance. A compact cake layer was clearly observed according to the field emission scanning electro microscopy (FE-SEM) images.

• Journal of Korean Society of Environmental Engineers
• /
• v.36 no.8
• /
• pp.549-553
• /
• 2014

Variation of sewage sludge interface height and flow rate by rainfall were applied to the actual public sewage treatment plant, and the efficiency of sewage treatment was evaluated by measuring $BOD_5$, $COD_{Mn}$, SS, T-N, and T-P. When both flow and interfacial height are increased, the treatment efficiencies in terms of the five water pollutants are decreased. Among them SS is the most critical pollutant in rainfall. When 0.5 Q inflow was applied, the efficiencies were 74.2% at the sludge interface height of 0.5 m, 76.4% at 1.0 m, 70.2% at 1.5 m, and 60.7% at 2.0 m. When 1.0 Q inflow was applied, the efficiencies were 71.7% at the sludge interface height of 0.5 m, 71.9% at 1.0 m, 46.4% at 1.5 m, and -38.0% at 2.0 m. Operation at 2.0 Q~2.0 m and 3.0 Q~1.0 m above the sludge rising phenomenon occurred causing adverse effects on the public bodies. If the flow rate increases, the processing efficiency is reduced from 74.2% to 17.3%, even though the sludge interface height was maintained at 0.5 m, so that the inflow adjustment was most important during rainfall, and the interface height of 1.0 m should be maintained to minimize the adverse effect on public water system.

• Journal of Energy Engineering
• /
• v.20 no.2
• /
• pp.84-89
• /
• 2011

In this study, individual(alkaline, ultrasonic) and combined(alkaline+ultrasonic) pretreatment effect on sewage sludge solubilization was investigated. COD solubilization rates increased with the dose of NaOH added: solubilization reached 27.6%. Additional alkaline agents did not increase solubilization further. Ultrasonic pretreatment achieved 33~39% solubilization when 140 W/L amplitude. In(alkaline(pre-treatment)+ultrasonic (after-treatment)) treatment, solubilization increased as the combined intensity in creased($70.4{\pm}9.4%$). SCOD rising rate(0.076) was achieved.

• Journal of Korean Society of Environmental Engineers
• /
• v.27 no.7
• /
• pp.739-745
• /
• 2005

Simultaneous denitrification and methanogenesis at various influent COD/Nitrate-N(below C/N) ratio was investigated with two different anaerobic sludges of which one was inoculated with glucose only and the other was inoculated with glucose and nitrate. Three different C/N ratios of 30, 20, and 10 were applied with each anaerobic sludge in serum bottles agitated in a rotary shaker to monitor the time related changes of amount of gas production and gas composition. Glucose was used as a single carbon source, which was adjusted to 1,000 mg/L as COD and potassium nitrate was used as a nitrogen source to adjust the each C/N ratio. COD removal by methanogenesis was dominant at higher C/N ratios, while COD removal by denitrification was dominant at lower C/N ratios. With the sludges cultured at C/N ratios below 10, SMA and SDNR rising different carbon substrates were investigated. The most efficient carbon substrate was acetate and the highest SMA and SDNR were 0.76 g COD/g VSS day with pure anaerobic sludge and 1.38 g ${NO_3}^--N/g$ VSS day with sludge cultured at C/N ratio of 5, respectively.

• Journal of Korean Society of Environmental Engineers
• /
• v.29 no.9
• /
• pp.1044-1050
• /
• 2007

In this study, Bio-hydrogen is produced from organic waste mixtures containing food waste and waste activated sludge (WAS). The effects of different operational factor on hydrogen production, including various solubilization methods for pretreatments of WAS, pH and different ratios of food waste and WAS, were investigated. The highest hydrogen production values are obtained as 4.3 mL $H_2/g$ $VS_{consumed}$ in the case of applying the mixed pre-treatments of alkali and ultrasonic. The pH value in bio-reactor increased from 4 to 8 after the ultrasonic treatment with alkali and the hydrogen yield touched its highest value in the pH range of 5.0 to 5.5. Similarly, the hydrogen production reached the level of 13.8 mL $H_2/g$ $VS_{consumed}$ using the same pre-treatment method from the mixture of food waste and WAS. The ratio of 2 : 1 produced a maximum amount of hydrogen of 5.0 L $H_2/L/d$. The amount of volatile fatty acids(VFAs) including acetate, propionate and butyrate, were also varied considerably. Propionate decreased consistently with rising of hydrogen while butyrate comparing to acetate relatively increased in the effluent.