Study on activated carbon derived from sewage sludge for adsorption of gaseous formaldehyde

The aim of this work is to evaluate the adsorption performances of activated carbon derived from sewage sludge (ACSS) for gaseous formaldehyde removal compared with three commercial activated carbons (CACs) using self-designing adsorption and distillation system. Formaldehyde desorption of the activated carbons for regeneration was also studied using thermogravimetric (TG) analysis. The porous structure and surface characteristics were studied using N₂ adsorption and desorption isotherms, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results show that ACSS has excellent adsorption performance, which is overall superior to the CACs. Adsorption theory indicates that the ACSS outperforms the CACs due to its appropriate porous structure and surface chemistry characteristics for formaldehyde adsorption. The TG analysis of desorption shows that the optimum temperature to regenerate ACSS is 75 °C, which is affordable and economical for recycling.     

Powdered activated carbon added biological treatment of pre-treated landfill leachate in a fed-batch reactor

Biological treatment of landfill leachate usually results in low treatment efficiencies because of high chemical oxygen demand (COD), high ammonium-N content and also presence of toxic compounds such as heavy metals. A landfill leachate with high COD content was pre-treated by coagulation-flocculation followed by air stripping of ammonia at pH = 12. Pre-treated leachate was biologically treated in an aeration tank operated in fed-batch mode with and without addition of powdered activated carbon (PAC). PAC at 2 g l^–1 improved COD and ammonium-N removals resulting in nearly 86% COD and 26% NH₄-N removal.     

添加厨余垃圾对剩余污泥厌氧消化产沼气过程的影响

为提高剩余污泥厌氧消化的沼气产量和甲烷含量,研究了厨余垃圾的不同添加量对剩余污泥厌氧消化性能的影响。结果表明,在35℃下,随着剩余污泥中厨余垃圾添加量的增加,厌氧消化系统中碳氮质量比（C／N）、胞外多聚物（EPS）等生理生化指标均有不同程度的改善。其中当剩余污泥与厨余垃圾质量比为2：1时,混合有机废弃物中沼气产量和甲烷含量均达到最大值,每克挥发性固体（VS）产生了156．56mL沼气,甲烷体积分数为67．52％,分别比剩余污泥单独厌氧消化时的产气量提高了5倍和1．5倍。     

Bioregeneration by mixed microorganisms of granular activated carbon loaded with a mixture of phenols

The role of mixed microorganisms on the bioregeneration of granular activated carbon (GAC) loaded with a mixture of phenol and 2,4-dichlorophenol was investigated. In a biological activated-carbon, sequencing batch reactor (BAC-SBR), bioregeneration efficiency for phenol was enhanced from 39 to 48% and for 2,4-dichlorophenol from 38 to 43% by increasing solid retention time from 3 to 8 days. Prolonging the sludge retention time induced both progressive desorption of adsorbates due to biodegradation in the bulk solution and direct assimilation of adsorbates on GAC by attached microorganisms.     

Robust control of the activated sludge process

In this work, a robust control strategy is proposed for maintaining the oxygen concentration in the aerobic tank and the pollutant, i.e., ammonium, nitrate, nitrite, concentrations at acceptable levels in the effluent water at the outlet of the activated sludge process. To this end, the Activated Sludge Model no. 1 (ASM1) is first reduced using biological arguments and a singular perturbation method, and a simplified model of the secondary settler is included. In contrast with previous studies that make use of piecewise linear models, an average operating point is evaluated using available data (here data from the COST Action 624) and the reduced‐order model is linearized around it using standard techniques. Finally, a H₂ robust control strategy acting on the oxygen injection and the recirculated flow rate is designed and tested in simulation. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Impacts of single‐walled carbon nanotubes on microbial community structure in activated sludge

Aims: Single‐walled carbon nanotubes (SWNTs) are likely to become increasingly widespread and yet their environmental impact is not well understood. The purpose of the current study was to evaluate the impact of SWNTs on microbial communities in a ‘sentinel’ environmental system, activated sludge batch‐scale reactors. Methods and Results: Triplicate batch reactors were exposed to SWNTs and compared to control reactors exposed to impurities associated with SWNTs. Automated ribosomal intergenic spacer analysis (ARISA) was used to assess bacterial community structure in each reactor. SWNT exposure was found to impact microbial community structure, while SWNT‐associated impurities had no effect, compared to controls. 16S rRNA gene sequence analysis indicated that dominant phylotypes detected by ARISA included members of the families Sphingomonadaceae and Cytophagacaceae and the genus Zoogloea. ARISA results indicated an adverse impact of SWNTs on the sphingomonad relative to other community members. Changes in community structure also occurred in both SWNT‐exposed and control reactors over the experimental time period and with the date on which activated sludge was obtained from a wastewater treatment facility. Conclusions: These results indicate that SWNTs differentially impact members of the activated sludge reactor bacterial community. Significance and Impact of the Study: The finding that community structure was affected by SWNTs indicates that this emerging contaminant differentially impacted members of the activated sludge bacterial community and raises the concern that SWNTs may also affect the services it provides.     

Growth inhibition of activated sludge by humus

Humus at 0.5 to 1 mg l–1 inhibited growth of activated sludge by about 55% in batch and long-term repeated batch cultures without decreasing sugar utilization. The growth inhibition was considerable when concentrations of substrates in the medium supplied per unit weight of activated sludge were low.     

Multiple approaches to assess filamentous bacterial growth in activated sludge under different carbon source conditions

Aims:  To compare molecular and microscopic approaches in determining which filamentous bacteria grow in activated sludge reactors when different carbon sources and different activated sludge mixed liquor inocula are used.
Methods and Results:  Microscopic and molecular (Denaturing Gradient Gel Electrophoresis and Fluorescent In Situ Hybridization) techniques were used to determine which filamentous bacteria became dominant in lab scale reactors treating wastewater composed of different carbon sources. Molecular analysis indicated the presence of Sphaerotilus natans and Thiothrix -related organisms . Microscopy indicated the presence of Nostocoida limicola in some reactors. Sludge volume index increased as filament abundance increased. The detection level of DGGE analysis increased when the abundance levels of the filaments were high.
Conclusions:  Simultaneous application of traditional and molecular methods was effective, and highlighted the advantages and limitations of each method. Readily biodegradable substances favoured the growth of specific filaments in a mixed liquor environment. The origin of inoculum influenced which specific filamentous bacteria grew.
Significance and Impact of the Study:  The study shows the potential problems when using particular techniques, and highlights the need for multiple approaches when studying filaments. The study also provides more information on which filaments will grow under different carbon source conditions for a given inoculum.     

Modeling of activated sludge transient behavior induced by regulation of carbon and nitrogen metabolism

An experimental protocol to evaluate the structured biomass model proposed by Lavallée (Lavallée, Lessard, and Vanrolleghem, J Environ Eng Sci 2005;4:517-532) is presented. The protocol was devised to induce transient behavior and characterize the evolution of several internal biomass components. The proposed model is based on biochemical principles, and was fitted to the collected data. In these experiments, it was observed that filling the storage capacity of cells leads to special transient behavior, including a temporarily reduced metabolic activity. The model-based interpretation of the results showed that the observed transient behavior can be explained by cross-regulation of carbon and nitrogen metabolism. Hence, according to an extensive literature review, the cross-regulation of carbon and nitrogen can be used to model some observed transient behaviors and regulation of the storage process in activated sludge.     

Reducing effect of aerobic selector on the toxicity of synthetic organic compounds in activated sludge process

The effects of phenol, 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and 1,2,4-trichlorobenzene (1,2,4-TCB) on the biodegradation kinetics of the conventional activated sludge system (CASS) and the selector activated sludge system (SASS) were investigated. Experiments were carried out using a respirometric method on unacclimated biomass from two lab-scale systems that were operated with the sludge age of 8 days. Toxicity of the test compounds for both reactors were arranged according to EC₅₀ (effective concentration) values in order as: 1,2,4-TCB > 2,4-DCP > 2-CP > phenol. All selected test compounds induced higher inhibition effect in the CASS. The SASS appeared to reduce inhibition effect in comparison to the CASS, by 21.36%, 66.95%, 64.37% and 33.33% for phenol, 2-CP, 2,4-DCP and 1,2,4-TCB, respectively. Consequently, the SASS may be recommended as a promising configuration alternative for the waste streams containing toxic compounds.     

Examination into the gamma irradiation of activated sludge

This study has shown that the treatment of activated sludge by gamma irradiation resulted in a deterioration in the filterability, a decrease in the size of the floc particles and an increase in the organic matter present in the sludge supernatant. A significant difference was found between the results obtained for filamentous and non-filamentous sludges in relation to the amount of soluble polysaccharide produced.     

Glutamic acid removal and PHB storage in the activated sludge process under dynamic conditions

Glutamic acid removal in the activated sludge process is studied herein, primarily the formation of storage polymers under dynamic conditions. The activated sludge process was operated by using a sequencing batch reactor (sludge age of 6 d) fed with a synthetic mixture of readily available carbon sources, including glutamic acid. Removal of glutamic acid as the only carbon sources was studied in batch tests, along with oxygen consumption, ammonia uptake-release, and formation of storage polymers. It was found that poly-3-hydroxybutyrate (PHB) was stored and that the storage also occurred simultaneously to biomass growth. PHB storage accounted for 16% of the overall solids that were formed from glutamic acid, as the average value of nine batch tests. Neither other Polyhydroxyalkanoates nor polyglutamic acid were detected. Nuclear magnetic resonance analysis, performed on biomass extracts, allowed us to clarify the main metabolic pathways involved in glutamic acid removal and, in particular, the pathways involved in PHB storage. It was found that glutamic acid enters the Krebs cycle as alpha-ketoglutaric acid and exits to form pyruvic acid and then acetyl-CoA, which is the starting point of PHB production pathway.     

Improving the biotreatment of hydrocarbons-contaminated soils by addition of activated sludge taken from the wastewater treatment facilities of an oil refinery

Addition of activated sludge taken from the wastewater treatment facilities ofan oil refinery to a soil contaminated with oily sludge stimulated hydrocarbonbiodegradation in microcosms, bioreactors and biopile. Microcosms containing50 g of soil to which 0.07 % (w/w) of activated sludge was added presented ahigher degradation of alkanes (80 % vs 24 %) and polycyclic aromatic hydrocarbons(PAHs) (77 % vs 49 %) as compared to the one receiving only water, after 30days of incubation at room temperature. Addition of ammonium nitrate or sterilesludge filtrate instead of activated sludge resulted in a similar removal of PAHsbut not of alkanes suggesting that the nitrogen contained in the activated sludgeplays a major role in the degradation of PAHs while microorganisms of thesludge are active against alkanes. Addition of sludge also stimulated hydrocarbonbiodegradation in 10-kg bioreactors operated during 60 days and in a 50-m³ biopile operated during 126 days. This biopile treatment allowed the use of the soil for industrial purpose based on provincial regulation (``C' criteria). In contrast, the soil of the control biopile that received only water still exceeded C criteria for C₁₀–C₅₀ hydrocarbons, total PAHs, chrysene and benzo[a]anthracene.The stimulation effect of sludge was stronger on the 4-rings than on 2-rings PAHs.The soil of the biopile that received sludge was 4–5 times less toxic than the control. These results suggest that this particular type of activated sludge could be used to increase the efficiency of the treatment of hydrocarbon-contaminated soils in a biopile.     

Prediction of adsorption from multicomponent solutions by activated carbon using single-solute parameters. Part II--Proposed equation

Prediction of multicomponent adsorption is still one of the most challenging problems in the adsorption field. Many models have been proposed and employed to obtain multicomponent isotherms from single-component equilibrium data. However, most of these models were based on either unrealistic assumptions or on empirical equations with no apparent definition. The purpose of this investigation was to develop a multicomponent adsorption model based on a thermodynamically consistent equation, and to validate that model using experimental data. Three barbiturates--phenobarbital, mephobarbital, and primidone--were combined to form a ternary system. The adsorption of these barbiturates from simulated intestinal fluid (without pancreatin) by activated carbon was studied using the rotating bottle method. The concentrations, both before and after the attainment of equilibrium, were determined with a high-performance liquid chromatography system employing a reversed-phase column. The proposed equation and the competitive Langmuir-like equation were both fit to the data. A very good correlation was obtained between the experimental data and the calculated data using the proposed equation. The results obtained from the original competitive Langmuir-like model were less satisfactory. These results suggest that the proposed equation can successfully predict the trisolute isotherms of the barbituric acid derivatives employed in this study.     

Anaerobic phosphate release from activated sludge with enhanced biological phosphorus removal. A possible mechanism of intracellular pH control

The biochemical mechanisms of the wastewater treatment process known as enhanced biological phosphorus removal (EBPR) are presently described in a metabolic model. We investigated details of the EBPR model to determine the nature of the anaerobic phosphate release and how this may be metabolically associated with polyhydroxyalkanoate (PHA) formation. Iodoacetate, an inhibitor of glycolysis, was found to inhibit the anaerobic formation of PHA and phosphate release, supporting the pathways proposed in the EBPR metabolic model. In the metabolic model, it is proposed that polyphosphate degradation provides energy for the microorganisms in anaerobic regions of these treatment systems. Other investigations have shown that anaerobic phosphate release depends on the extracellular pH. We observed that when the intracellular pH of EBPR sludge was raised, substantial anaerobic phosphate release was caused without volatile fatty acid (VFA) uptake. Acidification of the sludge inhibited anaerobic phosphate release even in the presence of VFA. From these observations, we postulate that an additional possible role of anaerobic polyphosphate degradation in EBPR is for intracellular pH control. Intracellular pH control may be a metabolic feature of EBPR, not previously considered, that could have some use in the control and optimisation of EBPR. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 507–515, 1999.     

Reduced modeling and state observation of an activated sludge process

This article first proposes a reduction strategy of the activated sludge process model with alternated aeration. Initiated with the standard activated sludge model (ASM1), the reduction is based on some biochemical considerations followed by linear approximations of nonlinear terms. Two submodels are then obtained, one for the aerobic phase and one for the anoxic phase, using four state variables related to the organic substrate concentration, the ammonium and nitrate‐nitrite nitrogen, and the oxygen concentration. Then, a two‐step robust estimation strategy is used to estimate both the unmeasured state variables and the unknown inflow ammonium nitrogen concentration. Parameter uncertainty is considered in the dynamics and input matrices of the system. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Extraction of activated sludge bacteria exopolymers by ultrasonication

Ultrasonication for the extraction of activated sludge exopolymers was evaluated by total cell count, exopolymer extraction and transmission electron microscopy (TEM). A high deflocculation was achieved after 30 s of sonication in PBS (phosphate-buffered saline). TEM showed that cell lysis was minimal only when sludges were sonicated for 30 s. For sludges sonicated for 30, 90 and 420 s and stained with Ruthenium Red, exopolymers were not extracted on a large scale without considerable cell lysis. Sludges sonicated for 30 s in EDTA gave a larger fraction of damaged cells and also showed copious amounts of attached exopolymers.     

Effects of combining biological treatment and activated carbon on hexavalent chromium reduction

The objectives of the present work were: (a) to analyze the Cr(VI) removal by combining activated sludge (AS) with powdered activated carbon (PAC), (b) to analyze the effect of PAC and Cr(VI) on the growth kinetics of activated sludge, and (c) to determine if the combined method (AS-PAC) for Cr(VI) removal can be considered additive or synergistic with respect to the individual processes. Chromate removal was improved by increasing PAC concentrations in both PAC and AS-PAC systems. Cr(VI) removal using the AS-PAC system was higher than using AS or PAC. The increase of Cr(VI) caused longer lag phase and lower observed specific growth rate (μ_obs), biomass yield (Y_X/S), and specific growth substrate consumption rate (q_S) of activated sludge; additionally, PAC did not enhance the growth kinetic parameters (μ_obs, Y_X/S, q_S). Cr(VI) reduction in AS-PAC system was the result of the additive effect of each individual Cr(VI) removal process.