Settling Characteristics Of Sludge Research Articles

Evaluation of activated sludge settling characteristics from microscopy images with deep convolutional neural networks and transfer learning

Timely assessment and prediction of changes in microbial compositions leading to activated sludge settling problems, such as filamentous bulking (FB), can reduce water resource recovery facilities (WRRFs) upsets, operational challenges, and negative environmental impacts. This study presents a computer vision approach to assess activated sludge-settling characteristics based on Microscopy Images (MIs). We utilize MIs to train deep convolutional neural networks (CNN) using transfer learning to investigate the morphological properties of flocs and filaments. The methodology was tested on the offline MI dataset collected over two years at a full-scale industrial WRRF in Belgium. Various CNN architectures were tested, including Inception v3, ResNet18, ResNet152, ConvNeXt-nano, and ConvNeXt-S. The sludge volume index (SVI) was used as the final prediction variable, but the method can be easily adjusted to predict any other settling metric of choice. The best-performing CNN, ConvNeXt-nano, could predict SVI values with MAE (37.51 ± 4.02), MTD (11.65 ± 1.94), MAPE (0.18 ± 0.02), and R2 (0.75 ± 0.05). The model was tested in real-life FB events, where it identified early indicators of bulking by predictive surges in SVI values. We used an explainable AI technique, Eigen-CAM, to discover key morphological indicators of sludge bulking transitions. The findings highlight the SVI multimodality issue, where SVI readings as a unidimensional metric could not capture delicate shifts from good to poor sludge settling, while the model detected these subtle changes. The key morphological attributes of threshold conditions leading to FB were identified, which can provide actionable insight for preemptive WRRF management.

Seasonal tourism's impact on wastewater composition: Evaluating the potential of alternating activated adsorption in primary treatment

Primary treatment processes have gained attention in recent research and development due to their potential for redirecting carbon towards anaerobic digestion, which can subsequently be used for the production of biomethane. The alternating activated adsorption (AAA) process is implemented on full-scale at several wastewater treatment plants across Europe. However, there is a lack of full-scale studies of advanced carbon capture technology implementations in literature. This study demonstrates the ability of a full-scale AAA process to remove and redirect carbon in a region heavily influenced by tourism. Periods in high and off-season were compared to study the impact of tourism on the composition of the wastewater and the AAA-process. The wastewater characteristics of the high season differed significantly from the low season. During the high season, the PE increased by 37 %, total suspended solids went up by 75 % and chemical oxygen demand increased by 58 %, compared to the low season. Additionally, 80 % of the low volatile lipophilic substances (LVLS) measured were attributed to the impact of tourism. A mass-balance of primary treatment for chemical oxygen demand (COD) and LVLS was conducted for both trial periods. The primary treatment was able to eliminate 56 % of the COD and 62 % of the LVLS in the non-tourist season and 53 % of the COD and 54 % of the LVLS in the tourist season. The increased wastewater load was effectively managed in the AAA-process. Key process parameters like sludge settling characteristics, hydraulic retention time and total suspended solids removal rates remained stable during the high season in winter.

Exposure of the static magnetic fields on the microbial growth rate and the sludge properties in the complete-mix activated sludge process (a Lab-scale study)

BackgroundIn this study, the effect of static magnetic fields (SMFs) on improving the performance of activated sludge process to enhance the higher rate of microbial growth biomass and improve sludge settling characteristics in real operation conditions of wastewater treatment plants has been investigated. The effect of SMFs (15 mT), hydraulic retention time, SRT, aeration time on mixed liquor suspended solids (MLSS) concentrations, mixed liquor volatile suspended solids (MLVSS) concentrations, α-factor, and pH in the complete-mix activated sludge (CMAS) process during 30 days of the operation, were evaluated.ResultsThere were not any differences between the concentration of MLSS in the case (2148.8 ± 235.6 mg/L) and control (2260.1 ± 296.0 mg/L) samples, however, the mean concentration of MLVSS in the case (1463.4 ± 419.2 mg/L) was more than the control samples (1244.1 ± 295.5 mg/L). Changes of the concentration of MLVSS over time, follow the first and second-order reaction with and without exposure of SMFs respectively. Moreover, the slope of the line and, the mean of α-factor in the case samples were 6.255 and, − 0.001 higher than the control samples, respectively. Changes in pH in both groups of the reactors were not observed. The size of the sluge flocs (1.28 µm) and, the spectra of amid I' (1440 cm−1) and II' (1650 cm−1) areas related to hydrogenase bond in the case samples were higher than the control samples.ConclusionsSMFs have a potential to being considered as an alternative method to stimulate the microbial growth rate in the aeration reactors and produce bioflocs with the higher density in the second clarifiers.

Effect of operating parameters on the sludge settling characteristics by treatment of the textile dyeing effluent using electrocoagulation

Abstract This study invested the impact of the operational parameters (pH, Current Density (CD) and Electrode Gap (EG)) on the sludge generated after electrocoagulation treatment of textile dyeing effluent (TDE) by studying sludge settleability and filterability characteristics of EC generated sludge. Electrocoagulation treatment evaluated at laboratory scale with aluminum as electrode material at operating condition of parameters of pH, CD and EG. (pH-5.5, CD-105.12 A/m2 and EG-2.5 cm). Under these operating conditions, maximum COD reduction was achieved 88.45 % and maximum color reduction was about 66.92 %. Settling characteristics of TDE was studied by sludge volume index (SVI) and Centrifugal settleability index (CSI). From disposal point of view, filterability characteristic was also studied by simple gravity filtration method. Specific cake resistance, α (m/kg), filter medium resistance, R m(m−1) was also studied. The specific cake resistance was found in the order of 38.4 × 1013 >34.13 × 1013 >22.25 × 1013 >11.19 × 1013 >7.30 × 1013 (m/kg) at the pH 9.5, 7.5, 1.5, 5.5 and 3.5 respectively. While filter medium resistance was found to be 111.22 × 109, 92.28 × 109, 82.33 × 109, 41.38 × 109 and 13.87 × 109 m−1 at pH 7.5, 9.5, 3.5, 5.5 and 1.5 respectively.

Performance assessment of ultrasonic sludge disintegration in activated sludge wastewater treatment plants under nutrient-deficient conditions

Although biological oxidation is a commonly applied technique for the removal of pollutants in industrial and municipal wastewater, one major drawback is its excess sludge production, having both an environmental and economic impact. The integration of ultrasonic sludge disintegration in a conventional biological wastewater treatment plant was explored experimentally via assessing the long-term effects on excess sludge reduction by conducting on-site pilot tests at a food processing company and a biodiesel production plant. Two sequencing batch reactors, each with a maximum active volume of 700 L, were operated in parallel for the treatment of industrial wastewater with nutrient deficient characteristics (COD/N/P ratio of 100/1.4/0.12) for over 6 months. One of the reactors was equipped with a side-stream recirculation system to enable the ultrasonic treatment of part of the settled sludge, whereas the other was operated in a conventional way as a reference. The experimental results show a reduction of the observed sludge production yield by 15% to 45% for the ultrasonically treated sequencing batch reactor compared to the conventional one, at a relatively low specific energy of less than 6,000 kJ/kg DS when 15 to 30% of the total sludge mass is treated per day. It was proven that the sludge reduction efficiency is directly proportional to the applied sludge retention time, suggesting that the ultrasonic treatment converts part of the hardly biodegradable particulate material in the activated sludge and improves its biodegradability. During the long-term pilot experiment at the biodiesel production plant, the electrical energy needed for decreasing the excess sludge production by 1 ton could be reduced by more than 80% when the sludge retention time was increased from 11 to 44 days. In addition, the sludge settling characteristics at the food processing company were considerably improved by the ultrasonic treatment, enabling to reduce or even avoid the need for external addition of expensive nutrients to prevent sludge bulking. Finally, an improved effluent quality was observed. Improvements of 7 to 17%, 9 to 20% and 17 to 30% for COD, nitrogen and phosphorus removal, respectively, were established.

Assessment of laboratory scale cylindrical sequencing batch reactor for the treatment of abattoir effluent

Meat factory effluent contains fat, protein, diluted blood, and suspended solids. As a result, nutrient and organic concentrations in this effluent are incredibly high, and residues are slightly solubilized, likely to impact environmental pollution on streams, rivers, and other watercourses if discharged untreated. The biodegradation of abattoir waste was studied using a laboratory-scale cylindrical sequencing batch reactor (SBR) in aerobic mode. The aerobic sludge was collected from the aeration compartment of a paper and pulp effluent treatment facility and cultivated in a 2.83-L Perspex-based laboratory SBR. The raw wastewater comprised 6494 ± 2144 mg/l chemical oxygen demand (COD), 1946 ± 607 mg/l biochemical oxygen demand (BOD), 1722 ± 159 mg/l total suspended solids (TSS), 3062 ± 592 mg/l CaCO3 alkalinity, 7.00 ± 0.27 pH. The duration of a complete cycle was 24 h and comprised four phases: fill (5 min), react (23 h 10 min), settle (40 min) and draw (5 min). The whole experiment was divided into four phases and the dilution was done with the help of domestic sewage. In the first stage, the reactor was fed four times diluted slaughterhouse effluent on a 24-h cyclic operation for two weeks. After achieving a significant reduction in COD, the organic content of the input was raised by lowering the dilution factor. In the second and third phases, the reactor was fed three times and twice diluted samples for two weeks each operating at the same cyclic interval. In the final stage, raw effluent was fed to the reactor for two more weeks. The average COD value of diluted wastewater in the first, second, third and fourth phase was 1040 mg/l, 3168 mg/l, 4800 mg/l, and 5200 mg/l, respectively. The COD removal efficiency at the end of the first, second, third and fourth phase was 83%, 93%, 85% and 97%, respectively. The average BOD value of diluted wastewater at the end of the first, second, third and fourth phase was 1120 mg/l, 610 mg/l, 1502 mg/l, and 1350 mg/l, respectively. The BOD removal efficiency at the end of the first, second, third and fourth phase was 84%, 88%, 85% and 98%, respectively. After 8 weeks, at an organic loading rate of 3.06 kg/m3/d, the final phase has achieved BOD and COD removal efficiency of 98% and 97%, respectively. The pH and alkalinity levels were within acceptable ranges. After two months, the sludge's settling characteristics have improved, and the nitrification efficiency of the reactor was roughly 60% at the time of deactivation of the reactor.

Flocs in disguise? High granule abundance found in continuous-flow activated sludge treatment plants

To date, high performance of full-scale aerobic granular sludge (AGS) technology has been demonstrated on a global scale. Its further integration with existing continuous flow activated sludge (CFAS) treatment plants is the next logical step. All granular sludge reactors operated in sequencing batch reactors (SBR) mode with anaerobic feeding conditions select for growth of phosphorus and glycogen accumulating organisms (PAO and GAO, respectively), which are known to enhance sludge settling characteristics. Therefore, we hypothesized that AGS are commonly present at full-scale CFAS processes with enhanced biological phosphorus removal (EBPR) and low sludge volume index (SVI). This hypothesis was confirmed at 13 EBPR plants, where granules were found present (at plants where SVI was lower than 100 ml/g) with a strong correlation between high granule abundance and low SVI. A wide range of granule abundance was found among the plants, ranging from 0.5% to as high as 80%. Evaluations of the EBPR plant process configurations showed that high granule abundances may be related to selector design features such as high anaerobic food to mass (F/M) ratios, unmixed in-line fermentation, and high influent soluble COD fraction. Granules were also observed at a non-EBPR plant with an aerobic selector receiving high F/M feeds. Quantitative PCR and 16S rRNA gene sequencing analyses revealed higher relative gene abundance of Accumulibacter PAO and Competibacter GAO in the granules over flocs, as well as a correlation between granule abundance and some possible EPS producers such as Flavobacterium and Competibacter. Our results indicated that process configurations that select for slow-growing or EPS-producing heterotrophs play an important role for granule formation in full-scale CFAS systems as previously shown in SBR configurations.

Modelling the effects of ferric salt dosing for chemical phosphorus removal on the settleability of activated sludge

There is a growing utilisation of ferric salts (Fe3+) for precipitation of phosphorus from wastewater due to tighter regulatory limits for wastewater effluent discharge. The effect of Fe3+dosing on activated sludge settleability indicators; zone settling velocity (ZSV) and stirred specific volume index (SSVI) were examined in laboratory-based batch settleability tests over a three years period. The experimental data revealed that ZSV increased with increasing dose of ferric salt as SSVI decreased with the highest changes obtained at a dose rate of 50 mgL-1. Fe3+ facilitated the agglomeration of the activated sludge flocs, thereby improving settleability. At >50 (mgL-1) of Fe3+, there was a slight breakdown in sludge settleability due mainly to surface charge reversals. The modelling of the settleability of ferric sludge in recent wastewater engineering practice for design and improvement purposes is presently based on conventional empirical sludge settleability models. This paper proposed a new activated sludge settleability model that describes the effects of Fe3+ dosing on the ZSV and SSVI of activated sludge. The exponential form of the Vesilind equation was optimised and validated to include ferric chemical dosing parameters. The proposed ferric settleability equations were found to effectively describe the settling characteristics of ferric sludge.

Application of electro-Fenton process for treatment of composting plant leachate: kinetics, operational parameters and modeling.

Composting plant leachate is considered as one of the highly polluted wastewaters which is necessary to be treated by simple, economic, fast and environmentally compatible methods. In this study, treatment of fresh composting plant leachate by electro-Fenton (EF) process was investigated. The effect of various input variables like pH (2-7), DC currents (1.5-3 A), H2O2 concentrations (theoretical ratio H2O2/COD: 0.1-0.6), TDS changes (4-6%), feeding mode, and BOD/COD ratio at the optimal point were studied. The settling characteristics of the waste sludge produced by the treatment (sludge volumes after 30-min sedimentation: V30) were also determined. Artificial neural network (ANN) approach was used for modeling the experimental data. Based on the results, the best removal rate of COD was obtained at pH: 3, 3 A constant DC current value, 0.6 theoretical ratio H2O2/COD and the feeding mode at four step injection. BOD/COD ratio at the optimal point was 0.535 and the maximum COD removal was achieved at TDS = 4%. In the optimal conditions, 85% of COD was removed and BOD/COD ratio was increased from 0.270 to 0.535. The data follow the second-order kinetic (R2 > 0.9) and neural network modeling also provided the accurate prediction for testing data. Results showed that EF process can be used efficiently for treatment of composting plant leachate using the proper operating conditions.

Using image processing for determination of settled sludge volume

Determination of the sludge volume index is key to describing the settling characteristics of sludge in the aeration process of wastewater treatment plants (WWTPs). The two core components of this calculation are the settled sludge volume (SSV) and suspended solids. While the measurement procedure for SSV is generally defined by national or international standards, in practice a wide variety of vessel sizes and shapes are used by operators to monitor WWTP performance. Furthermore, differences in how these tests are carried out can lead to poor data, inefficient WWTP operation and a lack of comparable metrics for WWTP operational monitoring. Thus, there is a requirement to improve operational performance of WWTPs to meet the increasingly stringent legislation regarding discharge limits. The aim of this study was to utilise a novel image-processing system (AutoSSV) to (i) determine its efficacy in describing SSV and (ii) measure and compare different methodologies for measurement of SSV. The AutoSSV system was tested using samples from various WWTPs and the results compared to those determined by standard manual measurement. Both standard and modified settlement tests were conducted on 30 mixed liquor samples, with modified settlement tests consistently resulting in lower SSV measurements. Results from the study showed a strong correlation between the SSV measurements provided by the AutoSSV system and results obtained from current manual measurement methods. The proposed technique would help to standardise the measurement in practice and increase the frequency of monitoring, particularly in small-scale rural WWTPs where there may not be permanent operators on site, and thus provide sufficient performance monitoring for efficient and effective operation.

Assessment of Microbial Community Structure and Function in Serially Passaged Wastewater Electro-Bioreactor Sludge: An Approach to Enhance Sludge Settleability

Several studies have been carried out to understand bulking phenomena and the importance of environmental factors on sludge settling characteristics. The main objective of this study was to carry out functional characterization of microbial community structure of wastewater electro-bioreactor sludge as it undergoes serial passaging in the presence or absence of a current density over 15 days. Illumina MiSeq sequencing and QIIME were used to assess sludge microbial community shifts over time. (α) and (β) diversity analysis were conducted to assess the microbial diversity in electro-bioreactors. A phylogeny-based weighted UniFrac distance analysis was used to compare between bacterial communities while BIO-ENV trend and Spearman’s rank correlation analysis were performed to investigate how reactor operational parameters correlated with bacterial community diversity. Results showed that the removal efficiency of soluble chemical oxygen demand (sCOD) ranged from 91–97%, while phosphorous (PO43−-P) removal was approximately 99%. Phylogenetic analysis revealed stark differences in the development of sludge microbial communities in the control and treatment reactor. There was no mention of any studies aimed at characterizing functional microbial communities under electric field and the results communicated here are the first, to our knowledge, that address this gap in the literature.

Marrying Step Feed with Secondary Clarifier Improvements to Significantly Increase Peak Wet Weather Treatment Capacity: An Integrated Methodology.

The need to increase the peak wet weather secondary treatment capacity of the City of Akron, Ohio, Water Reclamation Facility (WRF) provided the opportunity to test an integrated methodology for maximizing the peak wet weather secondary treatment capacity of activated sludge systems. An initial investigation, consisting of process modeling of the secondary treatment system and computational fluid dynamics (CFD) analysis of the existing relatively shallow secondary clarifiers (3.3 and 3.7 m sidewater depth in 30.5 m diameter units), indicated that a significant increase in capacity from 416 000 to 684 000 m3/d or more was possible by adding step feed capabilities to the existing bioreactors and upgrading the existing secondary clarifiers. One of the six treatment units at the WRF was modified, and an extensive 2-year testing program was conducted to determine the total peak wet weather secondary treatment capacity achievable. The results demonstrated that a peak wet weather secondary treatment capacity approaching 974 000 m3/d is possible as long as secondary clarifier solids and hydraulic loadings could be separately controlled using the step feed capability provided. Excellent sludge settling characteristics are routinely experienced at the City of Akron WRF, raising concerns that the identified peak wet weather secondary treatment capacity could not be maintained should sludge settling characteristics deteriorate for some reason. Computational fluid dynamics analysis indicated that the impact of the deterioration of sludge settling characteristics could be mitigated and the identified peak wet weather secondary treatment capacity maintained by further use of the step feed capability provided to further reduce secondary clarifier solids loading rates at the identified high surface overflow rates. The results also demonstrated that effluent limits not only for total suspended solids (TSS) and five-day carbonaceous biochemical oxygen demand (cBOD5) could be maintained, but also for ammonia-nitrogen and total phosphorous (TP). Although hydraulic limitations in other parts of the WRP prevent this full capacity to be realized, the City is proceeding to implement the modifications identified using this integrated methodology.

USE OF A GRIFFITH TUBE TO EVALUATE THE ANAEROBIC SLUDGE SEDIMENTATION IN A UASB REACTOR TREATING AN EFFLUENT WITH LONG-CHAIN FATTY ACIDS

Abstract - This paper proposes to study the sedimentation characteristics of anaerobic sludge, by determining the settling velocity of sludge granules with the Griffith Tube. This is a simple, low-cost method, suitable for use in full-scale treatment plants. The settling characteristics of sludge from two laboratory-scale UASB reactors fed with saccharose and different concentrations of sodium oleate and sodium stereate were evaluated. Addition of fatty acids caused a gradual destabilization of the system, affecting overall performance. The sedimentation profile changed after addition of fatty acids to the synthetic substrate, decreased sedimentation velocity and increased granule diameter. This behaviour was attributed to the adsorption of fatty acids onto the granules, modifying the diameter, shape and density of these bioparticles. Keywords : Anaerobic process; UASB reactor; Long chain fatty acids; Griffith tube; Sludge settleability. INTRODUCTION Anaerobic wastewater treatment biotechnology has been greatly advanced by the development of the upflow sludge bed reactor concept, such as the up-flow anaerobic sludge bed (UASB) (Kim

Effects of Particle Size on the Zone Settling Velocity of Activated Sludge

Abstract Activated sludge samples collected from 20 full-scale wastewater treatment plants were investigated to determine the effects of floc size (D50) on sludge settling characteristics. Results indicated that no simple and apparent relationship was found between D50 and sludge volume indices (SVIs) because of the complicated affecting mechanism of various parameters. Effects of D50 on the Vesilind settling model parameters were evaluated. Results indicated that no apparent relationship was found between D50 and V0. However, in the case of activated sludge with higher V0 (>5 m/h), there was a power function type correlation (V0 = 67.368·D50−0.4298, R2 = 0.5304) between V0 and D50. Furthermore, the parameter k decreased with increasing D50 through the relationship of k = 11.37·D50−0.5273 (R2 = 0.5593), except for samples with D50 < 100 μm and k < 1.0 m3/kg. V0 and k sludge were negatively correlated with sludge concentration because higher sludge concentrations contributed more resistance to settling vel...

Start-up of sequencing batch reactor with Thiosphaera pantotropha for treatment of high-strength nitrogenous wastewater and sludge characterization.

Biological treatment of high-strength nitrogenous wastewater is challenging due to low growth rate of autotrophic nitrifiers. This study reports bioaugmentation of Thiosphaera pantotropha capable of simultaneously performing heterotrophic nitrification and aerobic denitrification (SND) in sequencing batch reactors (SBRs). SBRs fed with 1:1 organic-nitrogen (N) and NH4+-N were started up with activated sludge and T. pantotropha by gradual increase in N concentration. Sludge bulking problems initially observed could be overcome through improved aeration and mixing and change in carbon source. N removal decreased with increase in initial nitrogen concentration, and only 50-60% removal could be achieved at the highest N concentration of 1000mgL-1 at 12-h cycle time. SND accounted for 28% nitrogen loss. Reducing the settling time to 5-10min and addition of divalent metal ions gradually improved the settling characteristics of sludge. Sludge aggregates of 0.05-0.2mm diameter, much smaller than typical aerobic granules, were formed and progressive increase in settling velocity, specific gravity, Ca2+, Mg2+, protein, and polysaccharides was observed over time. Granulation facilitated total nitrogen (TN) removal at a constant rate over the entire 12-h cycle and thus increased TN removal up to 70%. Concentrations of NO2--N and NO3--N were consistently low indicating effective denitrification. Nitrogen removal was possibly limited by urea hydrolysis/nitrification. Presence of T. pantotropha in the SBRs was confirmed through biochemical tests and 16S rDNA analysis.

Catalytic thermal treatment (catalytic thermolysis) of a rice grain-based biodigester effluent of an alcohol distillery plant

The catalytic thermolysis (CT) process is an effective and novel approach to treat rice grain-based biodigester effluent (BDE) of the distillery plant. CT treatment of rice grain-based distillery wastewater was carried out in a 0.5 dm3 thermolytic batch reactor using different catalysts such as CuO, copper sulphate and ferrous sulphate. With the CuO catalyst, a temperature of 95°C, catalyst loading of 4 g/dm3 and pH 5 were found to be optimal, obtaining a maximum chemical oxygen demand (COD) and colour removal of 80.4% and 72%, respectively. The initial pH (pHi) was an important parameter to remove COD and colour from BDE. At higher pHi (pH 9.5), less COD and colour reduction were observed. The settling characteristics of CT-treated sludge were also analysed at different temperatures. It was noted that the treated slurry at a temperature of 80°C gave best settling characteristics. Characteristics of residues are also analysed at different pH.

Powdered activated carbon – membrane bioreactor operated under intermittent aeration and short sludge retention times for micro-polluted surface water treatment

Long sludge retention time (SRT) and continuous aeration are generally adopted in powdered activated carbon – membrane bioreactor (PAC-MBR) process for micro-polluted surface water treatment. However, in this study, the performance of a pilot-scale PAC-MBR under intermittent aeration and short SRTs (2, 4, 6, and 8 d) was investigated. The settling characteristics of sludge and the decay of dissolved oxygen (DO) concentration in the mixed liquor were examined. The results showed that intermittent aeration with proper aeration intervals barely reduced the removal efficiency of pollutants, due to the low DO consumption in the bioreactor and the low settling velocity of the sludge (mostly at the range of 0.04–0.08 m min−1). High concentration ammonia (∼3 mg L−1) could be effectively removed even at a fairly short SRT (6 d). As the SRT increased, the removal efficiencies of organic matter and ammonia increased, but the membrane fouling aggravated correspondingly. The successful adoption of intermittent aeration and short SRTs in the pilot-scale PAC-MBR implied that the results could be extrapolated to full-scale applications to reduce operating costs and alleviate membrane fouling.

Practical experience with full-scale structured sheet media (SSM) integrated fixed-film activated sludge (IFAS) systems for nitrification.

Many wastewater treatment plants in the USA, which were originally designed as secondary treatment systems with no or partial nitrification requirements, are facing increased flows, loads, and more stringent ammonia discharge limits. Plant expansion is often not cost-effective due to either high construction costs or lack of land. Under these circumstances, integrated fixed-film activated sludge (IFAS) systems using both suspended growth and biofilms that grow attached to a fixed plastic structured sheet media are found to be a viable solution for solving the challenges. Multiple plants have been retrofitted with such IFAS systems in the past few years. The system has proven to be efficient and reliable in achieving not only consistent nitrification, but also enhanced bio-chemical oxygen demand removal and sludge settling characteristics. This paper presents long-term practical experiences with the IFAS system design, operation and maintenance, and performance for three full-scale plants with distinct processes; that is, a trickling filter/solids contact process, a conventional plug flow activated sludge process and an extended aeration process.

Investigation of Sewage Sludge Anaerobic Digestion Performance Using Peracetic Acid as a Pretreatment

Sewage sludge is difficult to degrade in anaerobic digestion systems and pretreatments have been shown to speed up the hydrolysis stage. In this paper sludge anaerobic digestion experiments with peracetic acid as a pretreatment were carried out and the effects of acid pretreatment using peracetic acid on subsequent digestion were investigated. It has been proved that this treatment effectively leads to a solubilisation of organic material and thus leads to a increase of soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFA) concentration. Besides, the SV of sludge was reduced and the settling characteristics of sludge were improved. But high dosage of peracetic acid lead to a decrease in biogas production and the proper dosage was 20 g/kg DS. It can be concluded that sludge anaerobic digestion with peracetic acid pretreatment is an effective method for biomass material transformation.

슬러지 농도 최적화에 따른 합리적인 활성슬러지공정 설계방안 연구

활성슬러지 공정의 생물학적 반응조 및 2차 침전지 설계와 관련해서 정상상태 설계식(Ekama et al., 1986; WRC, 1984) 및 1-D flux theory 설계식(Ekama et al., 1997)을 사용하여 슬러지 농도에 따라 두 가지 공정을 일괄적으로 설계하였다. 또한, 슬러지 농도에 따른 생물학적 반응조 및 2차 침전지 크기 변화를 도식화하고, 유입수 성상이나 슬러지 침강성, 환경 및 운전조건 그리고 첨두유량이 각 공정의 크기결정에 미치는 영향을 평가하였다. 먼저유입수의 특성과 관련하여 난분해성 용해성 물질(fs,us)은 반응조 크기 결정에 큰 영향이 없었지만, 난분해성 입자성 물질(fs,up), 무기고형물(fi) 및 유기물 강도(Sti)의 영향은 크게 나타났다. 운전인자인 Sludge Retention Time (SRT)의 경우, 슬러지 생산량과 관련되므로 반응조 크기결정에 역시 큰 영향을 미쳤다. 2차 침전지의 설계요소인 Sludge Volume Index (SVI) 및 첨두유량이 커질수록 2차 침전지에 수리학적 부하가 커지게 되어, 2차 침전지가 크게 설계되어야 했다. 본 설계과정에서는, 온도 변화가 미치는 영향은 작게 나타났다. 대규모 처리장의 경우 반응조 및 2차 침전지 전체 크기 결정과 함께 1개조 크기의 상한선을 설정하여 개수를 산정하였다. 최종적으로 엔지니어는 여러 가지 슬러지 농도에 대하여 반응조 및 2차 침전조의 크기, 개수 및 현장조건을 고려한 건설비용을 반복적으로 계산하게 되면, 최소비용 설계와 함께 최적의 슬러지 농도를 결정하게 된다. The design procedures for a biological reactor and a secondary settling tank (SST) of an activated sludge system are based on the steady state design method (Ekama et al., 1986; WRC, 1984) and the 1-D flux theory design method (Ekama et al., 1997), respectively. This study combined both of the design procedures, to determine the optimum sludge concentration in the reactor and the best design with the lowest cost. The best design of the reactor volume and the SST diameter at the optimum sludge concentration were specified with varying wastewater and sludge characteristics, temperature, sludge retention time (SRT) and peak flow rate. The effects of the influent wastewater characteristics, such as substrate concentration and unbiodegradable particulate fraction, were found to be considerable, but the effect of unbiodegradable soluble fraction was to be negligible. The effects of sludge settling characteristics, were also significant. SRT, as an operating parameter, was found to be an important factor for determining the optimum sludge concentration. However, the effect of temperature was found to be small. Furthermore, for designing a large scale wastewater treatment plant, the number of reactors or SSTs could be estimated, by dividing the total reactor volume or SST area. The new combined design procedure, proposed in this research, will be able to allow engineers to provide the best design of an activated sludge system with the lowest cost.