Choon Aun Ng

Operation of Membrane Bioreactor with Powdered Activated Carbon Addition

Abstract The effect of powdered activated carbon (PAC) addition to the activated sludge (AS) in a membrane bioreactor (MBR) has been investigated. The long term nature of the tests allowed the PAC to gradually incorporate into the biofloc forming biologically activated carbon (BAC). One series of tests involved 4 bench scale (2 L) MBRs operated at sludge retention times (SRTs) of 30 days with PAC inventories of 0, 1, 3 and 5 g/L and steady state biomass concentrations of 12.0±1.0 g/L. The characteristics of the mixed liquors (MLSS) from the 4 reactors were compared. Short term filtration tests, including measurement of specific cake resistance (SCR), flux decline profile, and irreversible fouling resistance in an unstirred cell and “sustainable” flux (by monitoring transmembrane pressure (TMP) rise) in a crossflow cell all showed better filtration performance for the MLSS with BAC compared with the AS alone. In terms of SCR and flux decline profile the 1 g/L PAC addition performed best, but in terms of minimizing irreversible membrane fouling and maximizing “sustainable” flux the 5 g/L PAC was best. All 4 systems showed lower total organic carbon (TOC) in the permeate compared to the bioreactors, but the lowest permeate TOC (and the best removal) was for the highest PAC loading. The benefit of PAC addition was confirmed in a second series of tests with two 20 L MBRs with submerged hollow fibers, one operated without PAC, the MBR(AS), and the other with 5 g/L PAC, the MBR(BAC). For an SRT of 30 days (which involved 3.3% sludge wastage per day and 3.3% new PAC addition per day) and a fixed flux of 21 L/m2hr the MBR(AS) showed a TMP rise of about 2.4 kPa/day whereas the MBR(BAC) showed a rise of only 0.8 kPa/day. However when the MBRs were operated without wastage the performance of the MBR(BAC) was worse than the MBR(AS). Thus the improved performance of the MBR(BAC) requires regular replenishment of aged BAC with fresh PAC.

Optimization of membrane bioreactors by the addition of powdered activated carbon.

It was found that with replenishment, powdered activated carbon (PAC) in the membrane bioreactor (MBR) would develop biologically activated carbon (BAC) which could enhance filtration performance of a conventional MBR. This paper addresses two issues (i) effect of PAC size on MBR (BAC) performance; and (ii) effect of sludge retention time (SRT) on the MBR performance with and without PAC. To interpret the trends, particle/floc size, concentration of mixed liquor suspended solid (MLSS), total organic carbon (TOC), short-term filtration properties and transmembrane pressure (TMP) versus time are measured. The results showed improved fouling control with fine, rather than coarse, PAC provided the flux did not exceed the deposition flux for the fine PAC. Without PAC, the longer SRT operation gave lower fouling at modest fluxes. With PAC addition, the shorter SRT gave better fouling control, possibly due to greater replenishment of the fresh PAC.

The competency of various applied strategies in treating tropical municipal landfill leachate

AbstractLeachate is a major pollution source associated with municipal solid waste landfill. This study was carried out to evaluate the effectiveness of various techniques in treating mature landfill leachate generated from landfill in Malaysia, a tropical country. Treatment processes such as biological, ion exchange, coagulation–flocculation, adsorption, advanced oxidation processes (AOPs), and flotation were analyzed. The efficiency of each process was analyzed based on chemical oxygen demand (COD), color, and NH3-N percentage removals. Ion exchange treatment via cationic/anionic sequence achieved the best removal of color (96.8%), COD (87.9%), and NH3-N (93.8%) from leachate as compared with other treatment methods. Coagulation–flocculation and AOPs were successful for COD and color removals from leachate. However, both could not treat NH3-N effectively. Biological treatment could remove NH3-N (71%) effectively, but it was poor in terms of COD (29%) and color (22%) removals. Adsorption via a new carbon...

Mechanisms of Fouling Control in Membrane Bioreactors by the Addition of Powdered Activated Carbon

This paper describes the experiments and observations that examine the mechanisms by which the addition of powdered activated carbon (PAC), in the form of biologically activated carbon (BAC), improves the filtration performance of a submerged membrane bioreactor (MBR). The membrane performance was observed to increase significantly with steady state PAC concentration. It is necessary to steadily replenish the PAC, to match that which is lost in sludge wastage. The enhancement mechanisms identified are, first, the role of PAC as an adsorbent of organics and planktonic bacteria, second, the effect of PAC as a scouring agent that limits foulant deposition, and third, the effect of the combined adsorption and biodegradation of BAC on the foulant components. The effectiveness of each mechanism in decreasing the fouling rate has been carefully evaluated. All three mechanisms play a role and the most significant appears to be the combined adsorption and biodegradation effect. The properties and filtration characteristics of activated sludge, with and without BAC have been measured and compared in both short-term tests and long-term continuous operation runs. The results of the short-term (cross flow mode) tests are in qualitative agreement with long-term performance.

Digital Image Processing and Analysis for Activated Sludge Wastewater Treatment

Activated sludge system is generally used in wastewater treatment plants for processing domestic influent. Conventionally the activated sludge wastewater treatment is monitored by measuring physico-chemical parameters like total suspended solids (TSSol), sludge volume index (SVI) and chemical oxygen demand (COD) etc. For the measurement, tests are conducted in the laboratory, which take many hours to give the final measurement. Digital image processing and analysis offers a better alternative not only to monitor and characterize the current state of activated sludge but also to predict the future state. The characterization by image processing and analysis is done by correlating the time evolution of parameters extracted by image analysis of floc and filaments with the physico-chemical parameters. This chapter briefly reviews the activated sludge wastewater treatment; and, procedures of image acquisition, preprocessing, segmentation and analysis in the specific context of activated sludge wastewater treatment. In the latter part additional procedures like z-stacking, image stitching are introduced for wastewater image preprocessing, which are not previously used in the context of activated sludge. Different preprocessing and segmentation techniques are proposed, along with the survey of imaging procedures reported in the literature. Finally the image analysis based morphological parameters and correlation of the parameters with regard to monitoring and prediction of activated sludge are discussed. Hence it is observed that image analysis can play a very useful role in the monitoring of activated sludge wastewater treatment plants.

Anaerobic stabilized landfill leachate treatment using chemically activated sugarcane bagasse activated carbon: kinetic and equilibrium study

AbstractAdsorption via activated carbon (AC) is one of the best methods to treat stabilized landfill leachate. However, this technique has been justified due to expensive and limited resource of AC precursor. Thus, in this study, sugarcane bagasse, a cheap and abundant biomass from agricultural waste, was used to prepare AC. The prepared sugarcane bagasse activated carbon (SCAC) was tested for color, chemical oxygen demand (COD), and ammoniacal nitrogen (NH3-N) removals from anaerobic stabilized landfill leachate. SCAC was prepared using physical and chemical activation. SCAC was characterized for its surface area, surface morphology, and functional groups. The performance of the adsorbent was examined in a batch mode study by varying the shaking speed, contact time, adsorbent dosage, and pH. The experimental results indicated that SCAC could adsorb and remove the pollutants from anaerobic municipal stabilized landfill. Removal of color, COD, and NH3-N were favorably described by Langmuir isotherm model, ...

Morphological analysis of activated sludge flocs and filaments

Purification of waste water is commonly done using the activated sludge process. The ratio of the activated sludge flocs and filamentous bacteria play a key role in the purification process of waste water. The sludge bulking or filamentous bulking is a common problem in activated sludge plants that prevents flocs to settle down. Digital imaging techniques can play an important role in monitoring activated sludge flocs and filaments in waste water treatment plants (WWTPs). In this paper, an algorithm to segment the flocs and the filaments of the microscopic sludge images captured at 4 times magnification in brightfield microscopy has been proposed. Morphological parameters, like, compactness, roundness, convexity, equivalent diameter are analyzed. Comparison with laser particle size analysis method has been done for the interpretation of the imaging results.

Local adaptive approach toward segmentation of microscopic images of activated sludge flocs

Abstract. Activated sludge process is a widely used method to treat domestic and industrial effluents. The conditions of activated sludge wastewater treatment plant (AS-WWTP) are related to the morphological properties of flocs (microbial aggregates) and filaments, and are required to be monitored for normal operation of the plant. Image processing and analysis is a potential time-efficient monitoring tool for AS-WWTPs. Local adaptive segmentation algorithms are proposed for bright-field microscopic images of activated sludge flocs. Two basic modules are suggested for Otsu thresholding-based local adaptive algorithms with irregular illumination compensation. The performance of the algorithms has been compared with state-of-the-art local adaptive algorithms of Sauvola, Bradley, Feng, and c-mean. The comparisons are done using a number of region- and nonregion-based metrics at different microscopic magnifications and quantification of flocs. The performance metrics show that the proposed algorithms performed better and, in some cases, were comparable to the state-of the-art algorithms. The performance metrics were also assessed subjectively for their suitability for segmentations of activated sludge images. The region-based metrics such as false negative ratio, sensitivity, and negative predictive value gave inconsistent results as compared to other segmentation assessment metrics.

Segmentation assessment of activated sludge flocs at different magnifications for wastewater treatment

Activated sludge process form an important part of wastewater treatment plant with domestic effluent. The variations in the state of the process are appeared as those in the size and structure of flocs and filaments found in the wastewater samples from aeration tank of secondary treatment. The normal operation requires proper settling of flocs in the secondary clarifier, which is affected by problem of bulking and pin point flocs. Conventional physico-chemical methods take a lot of time to detect the abnormal operation, consequently leaving insufficient time for precautionary measures. Image processing and analysis of microscopic images can offer a time-efficient alternative to monitor the operation of activated sludge process. Segmentation is a necessary part of image processing and analysis for identification of regions of interest in the image, and its acceptable accuracy is pre-requisite of the morphological analysis. In this paper, three segmentation techniques, fuzzy cmeans, k-means and Otsu thresholding, were used to segment flocs in microscopic images of samples taken from aeration tank of activated sludge process. The performance of the segmentation algorithms was evaluated for images taken at four different objective magnifications of microscope, using metrics of global consistency error (GCE), random index (RI) and variation of information (VI). The performance metrics were evaluated by comparing the segmented images with the approximation of ground truth images. Finally, the effect of magnification was investigated on the image segmentation and analysis procedure and observed that the size of floc, perceptible to the image segmentation and analysis procedure is greater and more precise at higher magnification.

Illumination Compensated Segmentation of Microscopic Images of Activated Sludge Flocs

Image processing and analysis is a useful tool for monitoring of activated sludge wastewater treatment plant. However its effectiveness is dependent on performance of the segmentation algorithms. The activated sludge plant is monitored by image processing and analysis of images acquired through trinocular microscope. The sample observed under microscope is collected from aeration tank of the plant. In this paper, a segmentation technique with integrated illumination compensation is proposed for the microscopic images of the activated sludge samples. The illumination noise was modeled and estimated as Gaussian distribution symmetric about a threshold value determined by global Otsu thresholding algorithm. The performance of the algorithm was evaluated using time required for segmentation, Rand index, accuracy and quantification of flocs. In order to compare with the state-of-the-art algorithms, gold approximations of ground truth images were manually prepared. The performance was assessed by combining the evaluation metrics in an integrated perspective. The proposed algorithm exhibits better performance in terms of both integrated and non-integrated perspectives.