Traditional Activated Sludge Process Research Articles

A low energy gravity-driven membrane bioreactor system for grey water treatment: Permeability and removal performance of organics

Synthetic grey water was treated with a low-pressure gravity-driven membrane bioreactor (GDMBR) system. The system was operated without any direct shear at the membrane surface and without any cleaning or flushing. In order to reduce energy consumption, one reactor was operated without aeration and the results were compared with an aerated reactor. Although the dissolved oxygen content was low (0.4–0.6mg/L) in the non-aerated system, a stable permeability was observed at a level of around 20L/m2hbar (flux of 1L/m2h). The fouling resistance was dominated by the bio-fouling layer, which could be removed hydraulically. In comparison to the aerated system, the bio-fouling layer grown without aeration exhibited a lower biological activity, was thicker and had a lower surface roughness. Furthermore, the stable permeability of the aerated system was higher (40L/m2hbar), which could be explained by a lower content and load of extracellular polymeric substances (including extracellular polysaccharides and proteins). In comparison to filtration through a non-fouled membrane, the rejection of biopolymers and humic substances was strongly enhanced, which shows that the bio-fouling layer acts as a secondary membrane. The energy consumption was 0.02–0.04kWh/m3, which is substantially less than for normal MBRs, and even less than for the traditional activated sludge process. These results show that grey water can be treated in a membrane reactor without any cleaning and flushing and even without any aeration, which makes the process suitable for decentralized wastewater treatment and considerably reduces the energy consumption.

Assessment of the Fate of Escherichia coli in Different Stages of Wastewater Treatment Plants

Seven full-scale wastewater treatment plants were investigated to highlight the effectiveness of each treatment stage on removing Escherichia coli. The primary sedimentation achieved an average E. coli removal efficiency of 30.5% which was much lower than the suspended solids (58%), thus, revealing the absence of a linear relationship between the two parameters. Biological processes proved to be very important in the removal of E. coli through adsorption inside the sludge flocs and complex decay (mortality). In biological processes with a long retention time, such as activated sludge denitrification-nitrification, the decay was very important, whereas in the more traditional activated sludge process, without nitrification, the contribution of adsorption and mortality was quite balanced. Overall, the mechanical-biological treatment achieved a removal efficiency of 91.8–96.5% depending on the process. Additional removal can be achieved by disinfection. The effectiveness of E. coli removal with sodium hypochlorite was strictly depended on the product of residual chlorine (C R) with the contact time (t). The experimental curve fitted the Collins model well, with a standard deviation of less than 7%.

Membrane Bioreactors for Municipal Wastewater Treatment

Recent technical innovations and significant cost reductions have sharply increased the potential for using Membrane Bioreactor (MBR) technology in municipal wastewater treatment. MBR technology displays several advantages compared to the traditional activated sludge processes, such as high effluent quality, limited space requirement and with the possibility of a flexible and phased extension of existing waste water treatment plants.Membrane Bioreactors for Municipal Wastewater Treatment describes the results of a comparative research programme involving four leading membrane suppliers: Kubota (Japan), Mitsubishi (Japan), X-Flow (Netherlands) and Zenon (Canada). Each supplier provided a pilot to represent a suitable scale - right up to full scale. These pilots were operated and optimised in the course of the research programme to achieve the best operating window under different operating regimes. The research focussed on the functionality of the membrane, the biological treatment, membrane fouling, achieved effluent quality, and system operability as well as other factors. In a number of side studies the required pre-treatment, membrane fouling/cleaning, energy usage, effluent quality and sludge processing were also addressed.The comparative pilot research was carried out by DHV Water on location at the wastewater treatment plant at Beverwijk in the Netherlands.This title belongs to Water and Wastewater Practitioner SeriesISBN: 9781843390114 (Print)ISBN: 9781780402925 (eBook)

Enhancing total nitrogen removal from wastewater of a science and industrial park using entrapped biomass

This study employed entrapped biomass technology to augment the conventional activated sludge process with anoxic–oxic (AO)/anaerobic–anoxic–oxic (A2O) functions for the removal of total nitrogen (TN) from wastewater of a science and industrial park in Taiwan. The entrapped biomass unit was fabricated in the format of carrier plates on which microbial cells were entrapped. Due to mass transport limitations, anoxic and anaerobic conditions were created within the bioplates that enabled denitrification to occur. The treatment basin incorporated an equivalent amount of 1300–2400 mg MLSS/L of activated sludge on the bioplates at packing ratios of 10–30% (volume ratio of bioplates to basin) operating with the addition of sodium carbonate for alkalinity and methanol for the electron donor. The results showed nearly 90% of ammonia nitrogen being converted to nitrate and 63% of TN removal, in comparison with typically 10% of TN removal in traditional activated sludge process of domestic wastewater plants.

Organics removal and protein recovery from wastewater discharged during the production of chondroitin sulfate

Bentonite, chitosan and polyaluminum chloride (PAC) were applied to treat wastewater discharged during the production of chondroitin sulfate and recover protein dissolved in the wastewater. The results showed that the combination of pH 9.00, 3-4 mL chitosan solution, 2 g of bentonite and 5 mL of 8% PAC solution per 100 mL of wastewater with a 4.0 h flocculation time were the optimal conditions for the recovery of protein and removal of total organic carbon (TOC) from wastewater. A pilot-scale test also was conducted, and 130 kg (dry weight) of sediment was obtained from 1.1 m(3) of discharged wastewater. This sediment contained abundant amino acids (proteins comprised 61% of the total sediment), after the recovery of protein, the dissolved TOC concentration in wastewater was decreased by approximately 80% and the residual wastewater could be readily disposed using a traditional activated sludge process.

Influence of Strong Diurnal Variations in Sewage Quality on the Performance of Biological Denitrification in Small Community Wastewater Treatment Plants (WWTPs)

The great diurnal variation in the quality of wastewater of small communities is an obstacle to the efficient removal of high nitrogen with traditional activated sludge processes provided by pre-denitrification. To verify this problem, the authors developed a pilot plant, in which the domestic wastewater of community of 15,000 inhabitants was treated. The results demonstrate that average and peak nitrogen removal efficiencies of over 60% and 70%, respectively, are difficult to obtain because of the strong variations in the BOD5/NO3-N ratios and the unexpected abnormal accumulation of dissolved oxygen during denitrification when the BOD5 load is low. These phenomena cause inhibitory effects and BOD5 deficiency in the denitrification process. The results demonstrate the need for a more complex approach to designing and managing small wastewater treatment plants (WWTPs) provided with denitrification than those usually adopted for medium- and large-size plants.

Modeling organics biodegradation and ammonia nitrification by entrapped mixed microbial cell carriers

Entrapped mixed microbial cell (EMMC) process offers good capability to remove organics and nitrogen compounds from wastewater in a single aerobic chamber. This research modeled quantitatively the hydraulic characteristics and biochemical process of immobilized activated sludge process (ASP) for the removal of COD and NH4+-N, providing insights to mass and oxygen transfer limitation in EMMC spherical carriers. Based on the conceptual kinetic model and previous experimental results, hydraulic and reaction rate constants were determined for both COD degradation and NH4+-N nitrification with the EMMC carrier. The dissolved oxygen (DO) distribution profile along the radius of EMMC carriers was also simulated. The depletion of DO in the EMMC carrier was very rapid resulting from COD removal and ammonia nitrification given the mass transport condition of DO. The anoxic/anaerobic zone developed in the EMMC carrier within 1 cm from its external surface in contact with the bulk water phase. Beyond this anoxic/anaerobic boundary, denitrification of nitrate occurred utilizing the residual COD. The efficiency of organics biodegradation and nitrification was not influenced by the thickness or diameter of the EMMC carriers. EMMC carriers of 1 cm in thickness supported removal of organics by biodegradation and nitrogen compounds via nitrification and denitrification processes. The EMMC carrier enabled combined nitrification and denitrification in the aerobic chamber, which signified the enhancement of a traditional ASP to an anoxic/oxic (AO) or anaerobic/anoxic/oxic reactor system via the EMMC carrier in an aeration tank.

Role of carbon substrates in facilitating energy reduction and resource recovery in a traditional activated sludge process: Investigation from a biokinetics modeling perspective

Three activated sludge processes (ASPs) were modeled and driven by dissolved complex organics (F-ASP), propionic acid (P-ASP), and acetic acid (A-ASP), and various parameters were subsequently estimated. The energy depletion for carbon removal was 0.146, 0.120, and 0.119 kWh/m(3) of treated wastewater for F-ASP, P-ASP, and A-ASP, respectively, suggesting that acetic acid can forward energy conservation. The ratio of substrate storage to oxidation in F-ASP, P-ASP, and A-ASP was 0, 0.25, and 0.52, respectively, further demonstrating that substrate eliminations from P-ASP and A-ASP were both dominated by substrate storage for polymer production, not by total oxidation; thus, they exhibited lower energy-consuming levels than F-ASP. Quantification of bioenergy production and nutrient acquisition from the excess sludge of the three ASPs were conducted subsequently, and A-ASP was found to facilitate phosphorus capture.

Improving the Energy Balance of an Integrated Microalgal Wastewater Treatment Process

The inclusion of a microalgal system in a wastewater treatment flowsheet for residual nutrient uptake can be justified by processing the waste biomass for energy recovery. Low energy harvesting technologies and pre-treatment of the algal biomass are required to improve the overall energy balance of this integrated system. Scenedesmus obliquus and Chlorella sp., achieving nitrogen and phosphorus removal rates higher than 90 %, were used to compare cells recovery efficiency and energy requirements of two energy efficient harvesting systems: dissolved air flotation (DAF) and ballasted dissolved air flotation (BDAF). In addition, thermal hydrolysis was used as a pre-treatment to improve biogas production during anaerobic digestion. The energy required for both systems was then considered to estimate the daily energy demand and efficiency of two microalgae wastewater treatment plants with a capacity of 25,000 and 230,000 p.e., respectively. Overall, a high algal cells recovery efficiency (99 %) was achieved using low energy demand (0.04 kWh m−3 for BDAF) and a coagulant dose reduction between 42 and 50 % depending on the algal strain. Anaerobic digestion of pre-treated S. obliquus showed a threefold increase in methane yield. Compared to a traditional activated sludge process, the additional tertiary microalgal treatment generates an integrated process potentially able to achieve up to 76 % energy efficiency.

ESTIMATING AND MODELLING THE SLUDGE EXCESS DISCHARGE IN WASTEWATER TREATMENT PLANTS IN CHINA

A rapid increase of wastewater treatment plants (WWTPs) has made the disposal of excess sludge from WWTPs a serious problem. In order to enhance the management of sludge, both development of sludge reduction technologies and sludge evaluation system are of great importance. Based on the survey data from 696 plants in China in 2009, an empirical model was developed to simulate the production and discharge of excess sludge, which considered influent, temperature, Chemical Oxygen Demand (COD), Suspended Solids (SS), and Total Nitrogen (TN). Four basic wastewater treatment processes including A2O, Oxidation Ditch, SBR and Traditional Activated Sludge Process were selected for the model verification and related parameters and indicators in the model were calculated. The model was applied in a typical plant with process of Oxidation Ditch in South China. Results indicated that it was available for the simulation of the discharge of excess sludge in actual plant, with exception of data in August and September, mainly due to the relatively lower BOD in these two months. Generally, the empirical model established could be applied in the management of excess sludge disposal in WWTPs.

The Application of Fluidized Carrier in Reconstruction Project of Sewage Plant

The traditional activated sludge process was transformed into A2O process with fluidized carriers. This technology was applied in reconstruction project of sewage plant. There was no need of altering civil construction. The effluent COD removal reached 95%. NH4+-N removal reached 92.2%. TN of effluent was less than 15 mg/L and TP was less than 1 mg/L. The process run stable and the effluent quality after secondary treatment could reach design standard.

The Application of Contact Oxidation in Papermaking Wastewater Treatment

Contact oxidation is used to deal with the paper effluent from an enterprise of Tieling in this paper. The practical operation indicates that this technology overcomes the shortcomings of the traditional activated sludge process and has the characteristics of high anti-impact ability, high load, ran stably, the water quality of effluent is high and so on. At the same time, its one-time investment and occupation area are small, and its operation management is convenient. The wastewater quality of Contact oxidation can achieve that: CODcr≤80mg/L; SS≤20mg/L; BOD5≤30mg/L. Every index of the effluent can accord with the pulp and paper industry standards.

Fecal coliform removal in a sulfate reduction, autotrophic denitrification and nitrification integrated (SANI) process for saline sewage treatment

The Sulfate Reduction, Autotrophic Denitrification, Nitrification Integrated (SANI) process has been specially designed to treat saline wastewater. In the process no biological excess sludge is produced. SANI process also has the added advantages of cost and footprint reduction when compared to traditional activated sludge processes. In the SANI pilot plant, the fecal coliform removal efficiency in the sulfate reducing up-flow sludge bed (SRUSB) was found to be 1.4 log, whereas that in the subsequent anoxic and aerobic reactors it was 0.6 and 0.2 log, respectively, leading to a relatively high overall coliform removal of 2.2 log. Sulfide was confirmed to be toxic to fecal coliform and the contact time between the sulfide produced and coliform in the SRUSB played an important role in the removal.

Experimental study on pressurized activated sludge process for high concentration pesticide wastewater

Abstract Pressurized biochemical process derived from traditional activated sludge processes is an innovative technology for wastewater treatment. The main advantage of the pressurized process is that the oxygen transfer barrier can be overcome by increasing the dissolved oxygen level. In this study, high concentration pesticide wastewater was treated by pressurized activated sludge process. It was found that the removal of chemical oxygen demand (COD) increased steadily with the increase of operating pressure, aeration time, and sludge concentration. When the operation pressure was 0.30 MPa and the aeration time was 6 hr, 85.0%-92.5% COD, corresponding to an effluent COD of 230-370 mg/L, was removed from an influent COD of 2500-5000 mg/L. The obtained outlet COD concentration was lower than 350-450 mg/L for the identical process operated under the atmospheric pressure. In addition, pressurized biochemical process could produce a higher COD volumetric loading rate at 5.8-7.6 kg COD/(m 3·day), compared with 2.0-2.8 kg COD/(m 3·day) using the same equipment at the atmospheric pressure. The COD concentration followed a modified Monod model with V max 2.31 day −1 and K S 487 mg/L.

Continuous village sewage treatment by vermifiltration and activated sludge process

Rural sewage treatment is now paid more and more attention in China. Vermifiltration technology could be one of the practical options under the review of previous studies. It showed good removal rates of contaminants on small to pilot scales for short-term tests. However, the impacts of season, temperature or other unknown factors are usually not taken into account. In this study, a larger vermifilter was designed to treat the sewage on village scale for long-term operation. Filter material composition was optimized by a half year experimentation. The treatment effects of vermifiltration were also compared with traditional activated sludge process for the same influent sewage. The results showed that the designed vermifiltration system could continuously treat the sewage produced by more than 100 inhabitants per day. COD, BOD5 and SS concentration in outflow were rather stable despite the fluctuation of hydraulic loading rate and organic input during one year test. It can also remove N and P to some extent. A suspending design of vermifilter bed cause adequate oxygen content in outflow of vermifilter. The comparative test showed that the treatment efficacy of vermifiltration was similar as activated sludge process. Generally, this vermifiltration system has practical application value for village sewage treatment.

Filamentous bacteria in a foaming membrane bioreactor

The foam-forming filamentous bacteria can result in serious membrane fouling problems, not only in traditional activated sludge processes, but also in membrane bioreactors (MBR). In this study, we examine the influence of the hydrophobicity of the membrane on membrane fouling in a submerged MBR using two sets of polytetrafluoroethylene membranes with different surface hydrophobicity. We also identify and compare the foam-forming filamentous bacteria via the Eikelboom method, the combination of a polymerase chain reaction with DNA sequencing, and the fluorescent in situ hybridization (FISH) approach based on non-cultured and cultured methods. The experimental results showed that during foaming period, the transmembrane pressure of the high hydrophobicity membrane increased as the flux decreased; but no significant influence was observed for the low hydrophobicity membrane. Of the foam-forming bacteria identified by non-cultured method, only Actinomycetes and Nosotcoida limicola III were observed using Eikelboom identification keys I and II, while high G + C content Gram-positive (HGC) bacteria was the predominant filamentous bacteria identified via the FISH approach. On the other hand, the Microthrix parvicella, Eikelboom type 1851, Eikelboom type 0092, and Flexibacter were identified as the predominant type of filamentous bacteria using the culture method with Eikelboom identification key I. The HGC bacteria made up 77.1% of the total isolates. Finally, the results of 16S rRNA sequences screened by the Eikelboom method showed that the genera Gordonia and Cytophaga, which contributed 75.7% and 20.1%, respectively, were the predominant filamentous bacteria.

Biodegradation of phenol by aerobic granulation technology

High organic load and fluctuation in organic load in terms of total phenols is fed into a SBR of higher height and diameter ratio (H/D 20) and operated at 4 h cycle basis with a volumetric exchange ratio of 50% resulting in a constant HRT of 8 h. Successful cultivation of aerobic granules was achieved. Aerobic granulation technology system withstands the inhibitory effect as well as fluctuation of organic load and a better efficiency as compared to traditional activated sludge process. Maximum phenol concentration of 650 mg l(-1) is treated efficiently in 4 h which is equal to an organic load of 3.9 kg m(-3) d(-1). After granulation the effluent phenol and COD concentrations were 3 mg l(-1) and 41 mg l(-1) respectively. Phenol removal efficiency and COD removal efficiency of 94% and 95% were achieved. Effluent O.D.(600) stabilizes at 0.15 which corresponds to minimum loss of biomass, which is the main advantage of SBR.

Sludge concentration dynamic distribution and its impact on the performance of UNITANK

UNITANK is a biological wastewater treatment process that combines the advantages of traditional activated sludge process and sequencing batch reactor, which is divided into Tank A, B and C. In this study, the sludge distribution and its impact on performance of UNITANK were carried out in Liede Wastewater Plant (WWTP) of Guangzhou, China. Results showed that there was a strong affiliation between Tank A and B of the system in sludge concentration distribution. The initial sludge concentration in Tank A could present the sludge distribution of the whole system. The sludge distribution was mainly influenced by hydraulic condition. Unsteady sludge distribution had an impact on variations of substrates in reactors, especially in decisive reactor, and this could lead to failure of system. Settler could partially remove substrates such as COD and NO 3-N, but there was adventure of sludge deterioration. The rational initial sludge concentration in Tank A should be 4000–6000 mg/L MLSS.

A pilot study for nitrifying treatment of wastewater from fertilizer production using a gas–liquid–solid three‐phase flow airlift loop bioreactor

AbstractAn 80 m3 pilot‐scale gas–liquid–solid three‐phase flow airlift loop bioreactor (ALR) with a low ratio of height to diameter, in which a biological membrane replaced the activated sludge, was used in the nitrifying treatment of a real effluent from a fertilizer plant. The influences of pH value, air influx (Qg) and hydraulic residence time (HRT) on the reductions in chemical oxygen demand (COD) and ammonia nitrogen (NH4‐N) were investigated and are discussed herein. The optimum operating conditions were obtained at a pH value of 7.0–8.0, air influx of 500 m3 h−1 and an HRT of 10 h. Under these optimum conditions, the effluent COD and NH4‐N were less than 50 mg L−1 and 10 mg L−1 for a 40‐day run, which were far below the primary discharge standard for the chemical fertilizer industry in the People's Republic of China (COD ≤ 100 mg L−1 and NH4‐N ≤ 40 mg L−1). Furthermore, this pilot‐scale airlift loop bioreactor generated only one‐quarter of the sludge waste compared with the traditional activated sludge process. Copyright © 2006 Society of Chemical Industry

Calibrating a side-stream membrane bioreactor using Activated Sludge Model No. 1

Membrane bioreactors (MBRs) are attracting global interest but the mathematical modeling of the biological performance of MBRs remains very limited. This study focuses on the modeling of a side-stream MBR system using the Activated Sludge Model No. 1 (ASM1), and compares the results with the modeling of traditional activated sludge processes. ASM1 parameters relevant for the long-term biological behaviour in MBR systems were calibrated (i.e. Y(H) = 0.72 gCOD/gCOD, Y(A) = 0.25 gCOD/gN, b(H) = 0.25 d(-1), b(A) = 0.080 d(-1) and f(p) = 0.06), and generally agreed with the parameters in traditional activated sludge processes, with the exception that a higher autotrophic biomass decay rate was observed in the MBR. Influent wastewater characterization was proven to be a critical step in model calibration, and special care should be taken in characterizing the inert particulate COD (X(I)) concentration in the MBR influent. It appeared that the chemical-biological method was superior to the physical-chemical method. A sensitivity analysis for steady-state operation and DO dynamics suggested that the biological performance of the MBR system (the sludge concentration, effluent quality and the DO dynamics) are very sensitive to the parameters (i.e. Y(H), Y(A), b(H), b(A) micro(maxH) and micro(maxA), and influent wastewater components (X(I), S(s), X(s) and S(NH)).