Operational mode and powdered activated carbon promoting syntrophic propionate oxidation during anaerobic digestion of complex organic substances.

Operational mode and powdered activated carbon (PAC) are key factors facilitating microbial syntrophy and interspecies electron transfer during anaerobic digestion, consequently benefiting process stability and efficient methanogenesis. In this study, continuous-flow reactor (CFR) and sequencing batch reactor (SBR), with and without the addition of PAC, respectively, were operated to examine their effects on system performance and methanogenic activity. Based on the cycle-test result, the PAC-amended CFR (CFRPAC) recorded both the highest methane yield (690.1 mL/L) and the maximum CH4 production rate (28.8 mL/(L·h)), while SBRs exhibited slow methanogenic rates. However, activity assays indicated that SBRs were beneficial for organics removal in batch experiments fed with peptone. Taxonomic and functional analysis confirmed that CFRs were optimal for proliferating oligotrophs (e.g., Geobacter) and SBRs were more suitable for copiotrophs (e.g., Desulfobulbus). Metagenomic analysis revealed that CFRs had efficient acetate metabolic pathways from propionate and ethanol, whereas SBRs did not, resulting in the buildup of propionate. Furthermore, Methanobacterium and Methanothrix were acclimated to the different operational conditions, while acetoclastic Methanosarcina and hydrogenotrophic Methanolinea were acclimated in SBRs (5.1-13.4%) and CFRs (0.3-1.7%), respectively. This study confirmed the enhancement of microbial syntrophy by the addition of PAC as well as the acclimation of electroactive bacteria (e.g., Geobacter) with complex organic substances.

Electron Transfer of Activated Carbon to Anode Excites and Regulates Desalination in Flow Electrode Capacitive Deionization.

The desalination performance of flow electrode capacitive deionization (FCDI) is determined by the ion adsorption on the powdered activated carbon (PAC) and the electron transfer between the current collector and PAC. However, a comprehensive understanding of rate-limiting steps is lacking, let alone to enhance FCDI desalination by regulating the PAC characteristics. This study showed that the electron transfer between PAC and the current collector on the anode side was the rate-limiting step of FCDI desalination. Compared with W900, the desalination performance of FCDI decreased by 95% when W1200 with weak electron transfer ability was used as a flow electrode. The PAC selected in this study transferred electrons directly through the conductive carbon matrix in FCDI and was mainly affected by graphitization. The desalination performance of FCDI was improved by 20 times when the graphitization degree of PAC increased from 0.69 to 1.03. The minimum energy required for electrons to escape from the PAC surface was reduced by the high degree of graphitization, from 4.27 to 3.52 eV, thus improving the electron transfer capacity of PAC on the anode side. This study provides a direction for the optimization of flow electrodes and further promotes the development of FCDI.

The adsorption of biogenetic odorants onto activated carbon: Adsorption characteristics and impacts of algal organic matter.

Powdered activated carbon (PAC) adsorption is regarded as an efficient method for removing odorants from drinking water. However, in eutrophic aquatic environments, the presence of algal organic matter (AOM) produced by cyanobacteria considerably impedes the adsorption of odorous compounds by activated carbon. This study focused on investigating the adsorption characteristics of three representative odorants: 2-methylisoborneol (2-MIB), ß-cyclocitral (ß-cyclo), and butyl sulfide (BS) by PAC and the effects of AOM on the PAC adsorption of odorants. The removal of the three odorants reached 83.5-97.5% at a PAC dosage of 10 mg/L after 12 h of exposure in a competition-free scenario. The adsorption kinetics demonstrated higher conformity (R2 > 0.9) with the pseudo-second-order model, whereas the adsorption capacity exhibited stronger conformity (R2 > 0.9) with the Freundlich model. The presence of AOM resulted in varying levels of competition for PAC for the adsorption of the three odorants. As the concentration of AOM increased from 0 to 5 mg C/L, the removal of 2-MIB was the most affected (from 83.5% to 10.0%), followed by ß-cyclo (from 86.6% to 55.0%), and BS (from 97.5% to 92.0%). The competitive adsorption of AOM at the molecular level was studied using density functional theory (DFT). The DFT results suggested that odorants with higher and more uniformly distributed electrostatic potentials exhibited a heightened affinity for PAC adsorption and a diminished susceptibility to disruption caused by AOM. This study provides valuable insights into the mitigation of odorous compounds during drinking water purification.

Study of the Influence of the Wastewater Matrix in the Adsorption of Three Pharmaceuticals by Powdered Activated Carbon.

The use of powdered activated carbon (PAC) as an absorbent has become a promising option to upgrade wastewater treatment plants (WWTPs) that were not designed to remove pharmaceuticals. However, PAC adsorption mechanisms are not yet fully understood, especially with regard to the nature of the wastewater. In this study, we tested the adsorption of three pharmaceuticals, namely diclofenac, sulfamethoxazole and trimethoprim, onto PAC under four different water matrices: ultra-pure water, humic acid solution, effluent and mixed liquor from a real WWTP. The adsorption affinity was defined primarily by the pharmaceutical physicochemical properties (charge and hydrophobicity), with better results obtained for trimethoprim, followed by diclofenac and sulfamethoxazole. In ultra-pure water, the results show that all pharmaceuticals followed pseudo-second order kinetics, and they were limited by a boundary layer effect on the surface of the adsorbent. Depending on the water matrix and compound, the PAC capacity and the adsorption process varied accordingly. The higher adsorption capacity was observed for diclofenac and sulfamethoxazole in humic acid solution (Langmuir isotherm, R2 > 0.98), whereas better results were obtained for trimethoprim in the WWTP effluent. Adsorption in mixed liquor (Freundlich isotherm, R2 > 0.94) was limited, presumably due to its complex nature and the presence of suspended solids.

The impact of powdered activated carbon types on membrane anti-fouling mechanism in membrane bioreactors.

Dosing powdered activated carbon (PAC) has been proven to be an economical and effective method to mitigate membrane fouling. However, the effects of pretreated PAC with different redox properties on membrane fouling still need to be further investigated. Here, the impact of commercial PAC, oxidized-PAC, and reduced-PAC on membrane fouling was investigated in membrane bioreactors (MBRs). Surprisingly, the filtration cycles were extended from 12-36 h to 132-156 h only by dosing reduced-PAC and commercial PAC with a finial dosage of 3 g/L, which were provided with reductive properties. However, few improvements of filtration cycle (less than 50 h) were achieved by dosing oxidized-PAC in the same dosage, which had the same adsorption performance as reduced-PAC and commercial PAC. The biomass and foulant concentration suggested that the enhanced anti-fouling performances by PAC with reductive properties were mainly attributed to the reduction of extracellular polymer substances (EPS) and soluble microbial products (SMP) content in the bulk solutions after 14 days of continuous operation. The model foulant degradation tests and the confocal laser scanning microscope (CLSM) images of activated sludge further demonstrated that PAC with reductive properties directly affected the microbial activities by controlling the EPS and SMP concentrations in the bulk solution, thereby suppressing membrane fouling. Such a finding provides new insights into anti-fouling mechanisms that the redox properties of PAC played a decisive role in membrane fouling mitigation, and also provides a strategy to prolong the anti-fouling effects by restoring the reductive properties of PAC. KEY POINTS: • The anti-fouling mechanisms of PAC with reductive property were investigated. • Reductive property was the main reason for fouling control instead of adsorption. • PAC with reductive property hindered the sludge activity to produce fewer foulants.

Hybrid powdered activated carbon-activated sludge biofilm formation to mitigate biofouling in dynamic membrane bioreactor for wastewater treatment.

Membrane costs and biofouling limit applications of membrane bioreactors (MBRs) for wastewater treatment. Here, powdered activated carbon (PAC) utilization in the formation and performance of a self-forming dynamic membrane consisting of activated sludge and PAC during hybrid wastewater treatment process was studied. Short-term agitation helped (non)biological particles to quickly uniformly settle on mesh filter, forming more uniform PAC-containing dynamic membranes (PAC-DMs). PAC adsorbed adhesive materials, resulting in an increase in average floc size and DM permeability while decreasing biofouling. The most efficient PAC concentration was 4 g L-1 considering techno-economics, i.e. the highest effluent quality (turbidity of 19.89 NTU) and the lowest biofouling (transmembrane pressure rise of 2.89 mbar). Short-term performance of hybrid PAC-DM bioreactor (PAC-DMBR) showed stability in effluent quality improvement including 92%, 95%, 83%, 84% and 98% reductions in turbidity, chemical oxygen demand, total dissolved solids, total nitrogen, and total phosphorous, respectively. Accordingly, adopting hybrid PAC-DMBR has potential to alleviate biofouling and capital cost.

Removal of micropollutants from municipal wastewater using different types of activated carbons.

The water reservoirs are getting polluted due to increasing amounts of micropollutants such as pharmaceuticals, organic polymers and suspended solids. Powdered activated carbon (PAC) has been proved to be a promising solution for the purification of water without having harmful impacts on the environment. Parameters such as PAC dosing, wastewater hardness, the effect of coagulant and flocculant were evaluated in a batch scale study. These parameters were further applied on a pilot plant scale for the performance evaluation of PAC based removal of micropollutants concerning the contact time and PAC dosing with main focus on recirculation of PAC sludge. The obtained optimum dose was 10-20 mg/L providing 84.40-91.30% removal efficiency of suspended solid micropollutants (MPs) and this efficiency increased to 88.90-93.00% along with coagulant which further raised by the addition of polymer and recirculation process at batch scale. On pilot plant scale, the concentration in contact reactor and PAC removal effectiveness of dissolved air flotation, lamella separator and sedimentation tank were compared. Constant optimisation resulted in a concentration ranging from 2.70 to 3.40 g/L at dosing of PAC 10 mg/L, coagulant 2.00 mg/L and polymer 0.50 mg/L. PAC doses of 10-20 mg/L with 15-30 min contact time proved best for above 70-80% elimination. The recirculation system has also proved an efficient technique because the PAC's adsorption capacity was practically completely used. Small PAC dosages yielded high micropollutants elimination.

Adsorptive performance of activated carbon reused from household drinking water filter for hexavalent chromium-contaminated water.

Powdered activated carbon blocks (PACBs) are waste products obtained from household drinking water purification systems. In this study, we demonstrate that they can be used as adsorbents for the cost-effective and environmentally benign removal of hexavalent chromium (Cr(VI)) from contaminated-water and rinse electroplating wastewater. To evaluate Cr(VI) sorption onto the PACB, studies on equilibrium, kinetics, and thermodynamics were performed using batch mode experiments. The experimental results indicated that Cr(VI) ions were efficiently adsorbed under acidic conditions (i.e., at initial pH below 3) and low initial Cr(VI) concentrations. The adsorptive behaviors of the PACB for Cr(VI) were well explained by the Langmuir isotherm, as well as pseudo-second-order kinetic models, suggesting that a Cr(VI) monolayer was adsorbed onto the PACB surface via chemisorption. The maximum adsorption capacity of Cr(VI) onto the PACB was determined to be 6.207 mg/g. The results of thermodynamic studies revealed that the adsorption process of Cr(VI) onto PACB was endothermic and non-spontaneous. Additionally, analysis of the PACB after Cr(VI) adsorption at an initial pH of 2 using scanning electron microscopy, energy dispersive spectrometry, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) revealed that the interaction between the surface oxygenic functional groups on the PACB and Cr(VI) was primarily responsible for Cr(VI) sorption via surface complexation and electrostatic interactions. Based on the result of XPS analysis, the presence of trivalent chromium on the PACB surfaces indicated that some synergistic redox reactions involving Cr(VI) could have occurred during the sorption process. Although a commercially available powdered activated carbon outperformed the PACB adsorbent with respect to Cr(VI) removal from wastewater, complete Cr(VI) adsorption could be achieved using relatively large quantities of the PACB. These findings indicate that the PACB adsorbent could be used as a cheap and efficient material for the removal of Cr(VI) from wastewater.

Optimized photocatalytic regeneration of adsorption-photocatalysis bifunctional composite saturated with Methyl Orange.

Photo-responsive adsorption-photocatalysis nanocomposites are generally used in water and wastewater decontamination; however, the prolonged adsorption capacity of composites and the role of adsorption in concomitant photocatalysis are typically neglected. These composites can be regenerated under light irradiation as their adsorption capacity decreases. Herein, a novel adsorption-photocatalysis bifunctional nanocomposite, Bi-doped TiO2 supported on powdered activated carbon (Bi2O3/TiO2/PAC), was prepared using the sol-impregnation-hydrothermal procedure. Bi2O3/TiO2/PAC with a secondary calcination temperature of 700°C under a nitrogen atmosphere was selected for maximum adsorption capacity on Methyl Orange (MO). The composite displayed an excellent adsorption capacity and was easily separated and recycled. The results demonstrate that 71.2% photocatalytic regeneration efficiency could be attained under visible light irradiation for 1 hr at an intensity of 750 W/m2 and pH 7. Characterization of the as-prepared Bi2O3/TiO2/PAC nanocomposite (700°C) indicates that it possesses a highly specific surface area and great optical properties, showing bifunctional adsorption-photocatalysis characteristics. The p-n heterojunction of the composite played a dominant role in the photocatalytic regeneration process, and effective degradation of MO could be achieved along with composite regeneration.

Pharmaceutical emerging pollutants removal from water using powdered activated carbon: Study of kinetics and adsorption equilibrium.

Pharmaceutical products and their byproducts which are present in wastewater and superficial water are becoming an environmental problem. A large effort has been made to introduce new and more efficient treatment processes for removing these emerging pollutants. Among them, activated carbon is currently being studied to be implemented in wastewater treatment plants. In the present study the equilibrium and kinetics of the adsorption of carbamazepine (Cbz) and sildenafil citrate (Sil) onto powdered activated carbon are presented. Batch experiments were performed to assess the potential of this kind of activated carbon for removing these recalcitrant pharmaceuticals from aqueous systems. In addition, its adsorption efficiency was compared with the granular activated carbon. The isotherms of Langmuir, Freundlich, Langmuir-Freundlich and Redlich-Peterson were applied. Pseudo-first and pseudo-second order models, as well as a combined model and an intraparticle diffusion model were assayed on the results obtained. Linear and non-linear analyses were carried out to compare the best fitting isotherms and kinetics. The Langmuir isotherm was a good fit for the adsorption of Sil, whereas the Redlich-Peterson isotherm described the adsorption of Cbz. The experimental results for both pharmaceuticals follow a kinetic of pseudo first order. Comparative studies preparing the solutions with distilled water, dechlorinated water and wastewater were performed. No significant differences were observed in these studies. When initial concentrations similar to those found in surface waters for both pharmaceuticals were evaluated, removal efficiencies greater than 85% were obtained. Therefore, the use of this kind of activated carbon seems to be an efficient tool for the removal of recalcitrant emerging pollutants, such as Sil and Cbz.

Natural organic matter removal from algal-rich water and disinfection by-products formation potential reduction by powdered activated carbon adsorption.

Algal blooms intensified operational problems in water treatment due to the increases of taste- and odor-causing compounds and natural organic matter (NOM). Effects of powdered activated carbon (PAC) addition during algal blooms on NOM removal was investigated in this study using an algal-rich water. Water quality analyses including dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254) and specific UV absorbance (SUVA) were performed to elucidate characteristics of NOM removal by PAC adsorption. Variations of MW distributions and emission/excitation matrix (EEM) spectra with increasing PAC dosages were also measured. In addition, formation potential (FP) of trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs) was evaluated with increasing PAC dosage. The correlations between disinfection by-products formation potential (DBPFP) and water qualities such as DOC, UV254, SUVA, and EEM spectra were also investigated to identify factors associated with DBPFP. The PAC addition was effective to remove NOM, especially low molecular weights NOM and proteinaceous substances with weak aromatics. The PAC addition showed the consistent reduction of THMFPs, HAAFPs, and HANFPs with increasing PAC dosage while the greater reduction of HAN precursors was eminent compared to the other two FPs. The close correlations between UV254 and the three DBPFPs were obtained. The low molecular weight (i.e., 1-700 Da) NOM and three fluorescence spectra peaks, i.e., T1, A and C peaks, also showed high correlation factors with the three DBPFPs. Those analyses with high correlations with DBPFPs would provide useful information to reduce DBPs during algal blooms.

Dynamic membrane bioreactor performance enhancement by powdered activated carbon addition: Evaluation of sludge morphological, aggregative and microbial properties.

The effects of powdered activated carbon (PAC) addition on sludge morphological, aggregative and microbial properties in a dynamic membrane bioreactor (DMBR) were investigated to explore the enhancement mechanism of pollutants removal and filtration performance. Sludge properties were analyzed through various analytical measurements. The results showed that the improved sludge aggregation ability and the evolution of microbial communities affected sludge morphology in PAC-DMBR, as evidenced by the formation of large, regularly shaped and strengthened sludge flocs. The modifications of sludge characteristics promoted the formation process and filtration flux of the dynamic membrane (DM) layer. Additionally, PAC addition did not exert very significant influence on the propagation of eukaryotes (protists and metazoans) and microbial metabolic activity. High-throughput pyrosequencing results indicated that adding PAC improved the bacterial diversity in activated sludge, as PAC addition brought about additional microenvironment in the form of biological PAC (BPAC), which promoted the enrichment of Acinetobacter (13.9%), Comamonas (2.9%), Flavobacterium (0.31%) and Pseudomonas (0.62%), all contributing to sludge flocs formation and several (such as Acinetobacter) capable of biodegrading relatively complex organics. Therefore, PAC addition could favorably modify sludge properties from various aspects and thus enhance the DMBR performance.

Simultaneous removal of ammonia and N-nitrosamine precursors from high ammonia water by zeolite and powdered activated carbon.

When adding sufficient chlorine to achieve breakpoint chlorination to source water containing high concentration of ammonia during drinking water treatment, high concentrations of disinfection by-products (DBPs) may form. If N-nitrosamine precursors are present, highly toxic N-nitrosamines, primarily N-nitrosodimethylamine (NDMA), may also form. Removing their precursors before disinfection should be a more effective way to minimize these DBPs formation. In this study, zeolites and activated carbon were examined for ammonia and N-nitrosamine precursor removal when incorporated into drinking water treatment processes. The test results indicate that Mordenite zeolite can remove ammonia and five of seven N-nitrosamine precursors efficiently by single step adsorption test. The practical applicability was evaluated by simulation of typical drinking water treatment processes using six-gang stirring system. The Mordenite zeolite was applied at the steps of lime softening, alum coagulation, and alum coagulation with powdered activated carbon (PAC) sorption. While the lime softening process resulted in poor zeolite performance, alum coagulation did not impact ammonia and N-nitrosamine precursor removal. During alum coagulation, more than 67% ammonia and 70%-100% N-nitrosamine precursors were removed by Mordenite zeolite (except 3-(dimethylaminomethyl)indole (DMAI) and 4-dimethylaminoantipyrine (DMAP)). PAC effectively removed DMAI and DMAP when added during alum coagulation. A combination of the zeolite and PAC selected efficiently removed ammonia and all tested seven N-nitrosamine precursors (dimethylamine (DMA), ethylmethylamine (EMA), diethylamine (DEA), dipropylamine (DPA), trimethylamine (TMA), DMAP, and DMAI) during the alum coagulation process.

Activated carbon adsorption of quinolone antibiotics in water: Performance, mechanism, and modeling.

The extensive use of antibiotics has led to their presence in the aquatic environment, and introduces potential impacts on human and ecological health. The capability of powdered activated carbon (PAC) to remove six frequently used quinolone (QN) antibiotics during water treatment was evaluated to improve drinking water safety. The kinetics of QN adsorption by PAC was best described by a pseudo second-order equation, and the adsorption capacity was well described by the Freundlich isotherm equation. Isotherms measured at different pH showed that hydrophobic interaction, electrostatic interaction, and π-π dispersion force were the main mechanisms for adsorption of QNs by PAC. A pH-dependent isotherm model based on the Freundlich equation was developed to predict the adsorption capacity of QNs by PAC at different pH values. This model had excellent prediction capabilities under different laboratory scenarios. Small relative standard derivations (RSDs), i.e., 0.59%-0.92% for ciprofloxacin and 0.09%-3.89% for enrofloxacin, were observed for equilibrium concentrations above the 0.3mg/L level. The RSDs increased to 11.9% for ciprofloxacin and 32.1% for enrofloxacin at µg/L equilibrium levels, which is still acceptable. This model could be applied to predict the adsorption of other chemicals having different ionized forms.

Improving the performance of an aerobic membrane bioreactor (MBR) treating pharmaceutical wastewater with powdered activated carbon (PAC) addition.

In this study, the effects of organic loading rate (OLR) and the addition of powdered activated carbon (PAC) on the performance and membrane fouling of MBR were conducted to treat real pharmaceutical process wastewater. Over 145 days of operation, the MBR system was operated at OLRs ranging from 1 to 2 kg COD m(-3) day(-1) without sludge wasting. The addition of PAC provided an improvement in the flux, despite an increase in the OLR:PAC ratio. The results demonstrated that the hybrid PAC-MBR system maintained a reduced amount of membrane fouling and steadily increased the removal performance of etodolac. PAC addition reduced the deposition of extracellular polymeric substance and organic matter on the membrane surface and resulted an increase in COD removal even at higher OLRs with low PAC addition. Membrane fouling mechanisms were investigated using combined adsorption fouling models. Modified fouling index values and normalized mass transfer coefficient values indicated that predominant fouling mechanism was cake adsorption.

Performance evaluation of powdered activated carbon for removing 28 types of antibiotics from water.

Currently, the occurrence and fate of antibiotics in the aquatic environment has become a very serious problem in that they can potentially and irreversibly damage the ecosystem and human health. For this reason, interest has increased in developing strategies to remove antibiotics from water. This study evaluated the performance of powdered activated carbon (PAC) in removing from water 6 representative groups of 28 antibiotics, namely Tetracyclines (TCs), Macrolides (MCs), Chloramphenicols (CPs), Penicillins (PNs), Sulfonamides (SAs) and Quinolones (QNs). Results indicate that PAC demonstrated superior adsorption capacity for all selected antibiotics. The removal efficiency was up to 99.9% in deionized water and 99.6% in surface water at the optimum conditions with PAC dosage of 20 mg/L and contact time of 120 min. According to the Freundlich model's adsorption isotherm, the values of n varied among these antibiotics and most were less than 1, suggesting that the adsorption of antibiotics onto PAC was nonlinear. Adsorption of antibiotics followed well the pseudo-second-order kinetic model (R(2) = 0.99). Analysis using the Weber-Morris model revealed that the intra-particle diffusion was not the only rate-controlling step. Overall, the findings in this study confirm that PAC is a feasible and viable option for removing antibiotics from water in terms of water quality improvement and urgent antibiotics pollution control. Further research is essential on the following subjects: (i) removing more types of antibiotics by PAC; (ii) the adsorption process; and (iii) the mechanism of the competitive adsorption existing between natural organic matters (NOMs) and antibiotics.

Integrating powdered activated carbon into wastewater tertiary filter for micro-pollutant removal.

Integrating powdered activated carbon (PAC) into wastewater tertiary treatment is a promising technology to reduce organic micro-pollutant (OMP) discharge into the receiving waters. To take advantage of the existing tertiary filter, PAC was pre-embedded inside the filter bed acting as a fixed-bed adsorber. The pre-embedding (i.e. immobilization) of PAC was realized by direct dosing a PAC solution on the filter top, which was then promoted to penetrate into the filter media by a down-flow of tap water. In order to examine the effectiveness of this PAC pre-embedded filter towards OMP removal, batch adsorption tests, representing PAC contact reactor (with the same PAC mass-to-treated water volume ratio as in the PAC pre-embedded filter) were performed as references. Moreover, as a conventional dosing option, PAC was dosed continuously with the filter influent (i.e. the wastewater secondary effluent with the investigated OMPs). Comparative results confirmed a higher OMP removal efficiency associated with the PAC pre-embedded filter, as compared to the batch system with a practical PAC residence time. Furthermore, over a filtration period of 10 h (approximating a realistic filtration cycle for tertiary filters), the continuous dosing approach resulted in less OMP removal. Therefore, it was concluded that the pre-embedding approach can be preferentially considered when integrating PAC into the wastewater tertiary treatment for OMP elimination.

Estimating biokinetic coefficients in the PACT™ system.

When powdered activated carbon (PAC) is continuously added to the aeration tank of an activated sludge reactor, the modification is called a PACT™ process (for powdered activated carbon treatment). The PAC provides many benefits, but complicates the determination of biological phenomena. Determination of bio-oxidation kinetics in a PACT system is a key to fully understanding enhanced biological mechanisms resulting from PAC addition. A model is developed to account for the main mechanisms involved in the PACT system -- adsorption, air stripping and bio-oxidation. The model enables the investigation of biokinetic information, including possible synergistic effects. Six parallel reactors were used to treat a synthetic waste; three activated sludge and three PACT. The PACT reactors provided significantly reduced effluent TOC (total organic carbon). Biokinetic coefficients were obtained from steady-state data using averaged reactor data and by using all data (22 points for each reactor). As expected, the PACT reactors resulted in a substantial reduction in the effluent concentration of non-biodegradable total organic carbon. The Monod equation's half-saturation coefficient (Ks) was reduced significantly in the PACT reactors, resulting in higher growth rates at lower concentrations. The maximum specific substrate utilization (qm) rate was also reduced about 25% using the averaged data and remained unchanged using all the data. The substrate utilization values are affected by errors in biomass determination and more research is needed to accurately determine biomass.

Mathematical modeling of COD removal via the combined treatment of domestic wastewater and landfill leachate based on the PACT process.

The experiments performed in this study consisted of 16 batch reactors fed different mixtures of landfill leachate combined with synthetic wastewater treated using the Powdered Activated Carbon Treatment (PACT) process. The objective was to measure the COD mass removal per liter each day for each reactor using two models: the first model combined the variables PAC concentration (0 g·L(-1), 2 g·L(-1), 4 g·L(-1), and 6 g·L(-1)) and leachate rate in the wastewater (0%, 2%, 5%, and 10%), and the second model combined the PAC concentration and the influent COD. The Response Surface Methodology with Central Composite Design was used to describe the response surface of both models considered in this study. Domestic wastewater was produced under controlled conditions in the laboratory where the experiments were performed. The results indicated that the PAC effect was null when the influent did not contain leachate; however, as the concentration of leachate applied to the mixture was increased, the addition of a higher PAC concentration resulted in a better COD mass removal in the reactors. The adjusted R(2) values of the two models were greater than 0.95, and the predicted R(2) values were greater than 0.93. The models may be useful for wastewater treatment companies to calculate PAC requirements in order to meet COD mass removal objectives in combined treatment.

Pretreatment with alum or powdered activated carbon reduces bacterial predation-associated irreversible fouling of membranes.

This study evaluated the co-application of bacterial predation by Bdellovibrio bacteriovorus and either alum coagulation or powdered activated carbon adsorption to reduce fouling caused by Escherichia coli rich feed solutions in dead-end microfiltration tests. The flux increased when the samples were predated upon or treated with 100 ppm alum or PAC, but co-treatment with alum and predation gave the best flux results. The total membrane resistance caused by the predated sample was reduced six-fold when treated with 100 ppm PAC, from 11.8 to 1.98 × 10(11) m(-1), while irreversible fouling (Rp) was 2.7-fold lower. Treatment with 100 ppm alum reduced the total resistance 14.9-fold (11.8 to 0.79 × 10(11) m(-1)) while the Rp decreased 4.25-fold. SEM imaging confirmed this, with less obvious fouling of the membrane after the combined process. This study illustrates that the combination of bacterial predation and the subsequent removal of debris using coagulation or adsorption mitigates membrane biofouling and improves membrane performance.