Survival of selected bacterial species in sterilized activated carbon filters and biological activated carbon filters

The survival of selected hygienically relevant bacterial species in activated carbon (AC) filters on a bench scale was investigated. The results revealed that after inoculation of the test strains the previously sterilized AC absorbed all bacteria (10(6) to 10(7)). After a period of 6 to 13 days without countable bacteria in the effluent, the numbers of Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas putida increased up to 10(4) to 10(5) CFU/ml of effluent and 10(6) to 10(7) CFU/g of AC. When Klebsiella pneumoniae and Streptococcus faecalis were used, no growth in filters could be observed. The numbers of E. coli, P. aeruginosa, and P. putida, however, decreased immediately and showed no regrowth in nonsterile AC from a filter which had been continuously connected to running tap water for 2 months. Under these conditions an autochthonous microflora developed on the carbon surface which could be demonstrated by scanning electron microscopy and culturing methods (heterotrophic plate count). These bacteria reduced E. coli, P. aeruginosa, and P. putida densities in the effluent by a factor of more than 10(5) within 1 to 5 days. The hypothesis that antagonistic substances of the autochthonous microflora were responsible for the elimination of the artificial contamination could not be confirmed because less than 1% of the isolates of the autochthonous microflora were able to produce such substances as indicated by in vitro tests. Competition for limiting nutrients was thought to be the reason for the observed effects.     

Survival of selected bacterial species in sterilized activated carbon filters and biological activated carbon filters.

The survival of selected hygienically relevant bacterial species in activated carbon (AC) filters on a bench scale was investigated. The results revealed that after inoculation of the test strains the previously sterilized AC absorbed all bacteria (10(6) to 10(7)). After a period of 6 to 13 days without countable bacteria in the effluent, the numbers of Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas putida increased up to 10(4) to 10(5) CFU/ml of effluent and 10(6) to 10(7) CFU/g of AC. When Klebsiella pneumoniae and Streptococcus faecalis were used, no growth in filters could be observed. The numbers of E. coli, P. aeruginosa, and P. putida, however, decreased immediately and showed no regrowth in nonsterile AC from a filter which had been continuously connected to running tap water for 2 months. Under these conditions an autochthonous microflora developed on the carbon surface which could be demonstrated by scanning electron microscopy and culturing methods (heterotrophic plate count). These bacteria reduced E. coli, P. aeruginosa, and P. putida densities in the effluent by a factor of more than 10(5) within 1 to 5 days. The hypothesis that antagonistic substances of the autochthonous microflora were responsible for the elimination of the artificial contamination could not be confirmed because less than 1% of the isolates of the autochthonous microflora were able to produce such substances as indicated by in vitro tests. Competition for limiting nutrients was thought to be the reason for the observed effects.     

Growth and persistence of pathogens on granular activated carbon filters.

Three enteric pathogens Yersinia enterocolitica O:8, Salmonella typhimurium, and enterotoxigenic Escherichia coli, were examined for their ability to colonize granular activated carbon (GAC) in pure cultures and in the presence of autochthonous river water organisms. All three organisms readily colonized sterile GAC and maintained populations of ca. 10(5) to 10(7) CFU g-1 for 14 days when suspended in sterile river water. Exposure of pathogen biofilms on GAC to unsterile river water resulted in a gradual decline in pathogens on the carbon (0.08 to 0.14 log day-1). When pathogens were introduced to sterile GAC in the presence of heterotrophic plate count organisms, they attached at levels similar to those in the pure cultures and then decreased (0.10 to 0.22 log day-1). When added with heterotrophic plate count bacteria to GAC supporting a mature biofilm of native river water bacteria, they attached at a lower level (1.0 X 10(4) to 4.6 X 10(4) CFU g-1) and decreased at a more rapid rate (0.11 to 0.70 log day-1).     

Bioregeneration of granular activated carbon in simultaneous adsorption and biodegradation of chlorophenols

The objectives of this study are to obtain the time courses of the amount of chlorophenol adsorbed onto granular activated carbon (GAC) in the simultaneous adsorption and biodegradation processes involving 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP), respectively, and to quantify the bioregeneration efficiency of GAC loaded with 4-CP and 2,4-DCP by direct measurement of the amount of chlorophenol adsorbed onto GAC. Under abiotic and biotic conditions, the time courses of the amount of chlorophenol adsorbed onto GAC at various GAC dosages for the initial 4-CP and 2,4-DCP concentrations below and above the biomass acclimated concentrations of 300 and 150 mg/L, respectively, were determined. The results show that the highest bioregeneration efficiency was achieved provided that the initial adsorbate concentration was lower than the acclimated concentration. When the initial adsorbate concentration was higher than the acclimated concentration, the highest bioregeneration efficiency was achieved if excess adsorbent was used.     

Adsorption and bioadsorption of granular activated carbon (GAC) for dissolved organic carbon (DOC) removal in wastewater

In this study, the performances of GAC adsorption and GAC bioadsorption in terms of dissolved organic carbon (DOC) removal were investigated with synthetic biologically treated sewage effluent (BTSE), synthetic primary treated sewage effluent (PTSE), real BTSE and real PTSE. The main aims of this study are to verify and compare the efficiency of DOC removal by GAC (adsorption) and acclimatized GAC (bioadsorption). The results indicated that the performance of bioadsorption was significantly better than that of adsorption in all cases, showing the practical use of biological granular activated carbon (BGAC) in filtration process. The most significance was observed at a real PTSE with a GAC dose of 5g/L, having 54% and 96% of DOC removal by adsorption and bioadsorption, respectively. In addition, it was found that GAC adsorption equilibrium was successfully predicted by a hybrid Langmuir-Freundlich model whilst integrated linear driving force approximation (LDFA)+hybrid isotherm model could describe well the adsorption kinetics. Both adsorption isotherm and kinetic coefficients determined by these models will be useful to model the adsorption/bioadsorption process in DOC removal of BGAC filtration system.     

Effects of carbon substrate enrichment and DOC concentration on biodegradation of PAHs in soil

AIMS: Two common reasons to explain slow environmental biodegradation of polycyclic aromatic hydrocarbons (PAHs), namely lack of appropriate carbon sources for microbial growth and limited bioavailability of PAHs, were tested in a laboratory bioassay using a creosote-contaminated soil. METHODS AND RESULTS: The soil, containing a total of 8 mg g-1 of 16 PAHs, was sieved and incubated in bottles for 45 days. The first explanation was tested by enrichment with the analogue anthracene and the non-analogue myristic acid, and both failed to stimulate degradation of all PAHs except anthracene. The second explanation was tested by addition of different concentrations of dissolved organic carbon (DOC), with effects depending on the DOC concentration and the molecular size of the PAH. The degradation was enhanced from 10 to 35% for 12 PAHs when the soil was saturated. The degraded amounts of individual PAHs were proportional to their concentration in the soil. CONCLUSIONS: The slow in situ degradation of PAHs was enhanced by more than three times by adding water as a solvent. Addition of DOC facilitated the degradation of four- to six-ring PAHs. SIGNIFICANCE AND IMPACT OF STUDY: Bioremediation of PAH-contaminated sites may be facilitated by creating water-saturated conditions but retarded by addition of other carbon substrates, such as analogue compounds.     

Changes of biomass and bacterial communities in biological activated carbon filters for drinking water treatment

Biological activated carbon (BAC) filtration can usually perform well in removal of biodegradable organic compounds in drinking waters. In this study, a pilot-scale down-flow BAC filtration system was constructed for treatment of ozonated waters. The changes of biomass concentration and bacterial community in the BAC filters with contact time and service time were characterized using phospholipid fatty acid (PLFA) analysis and 16S rRNA gene clone library analysis, respectively. The operational results indicated the BAC filtration system could effectively remove dissolved organic carbon (DOC) and assimilable organic carbon (AOC). Biomass concentration decreased with contact time, but showed only a slight change with service time. Contact time and service time could affect the microbial community structure. Alphaproteobacteria was the largest bacterial group and might have important links with the DOC and AOC removal. This work might provide some new insights into microbial community and biological process in the drinking water biofilters.     

Polaromonas and Hydrogenophaga species are the predominant bacteria cultured from granular activated carbon filters in water treatment

Aim:  Identification of the predominating cultivable bacteria in granular activated carbon (GAC) filters used in a variety of water treatment plants for selecting representative strains to study the role of bacteria in the removal of dissolved organic matter.
Methods and Results:  Bacterial isolates were collected from 21 GAC filters in nine water treatment plants treating either ground water or surface water with or without oxidative pretreatment. Enrichment of samples in dilute liquid medium improved culturability of the bacteria by approximately log unit, to 9% up to 70% of the total cell counts. Genomic fingerprinting and 16S rDNA sequence analysis revealed that most (68%) of the isolates belonged to the Betaproteobacteria and 25% were identified as Alphaproteobacteria . The number of different genera within the Betaproteobacteria was higher in the GAC filters treating ozonated water than in the filters treating nonozonated water. Polaromonas was observed in nearly all of the GAC filters (86%), and the genera Hydrogenophaga , Sphingomonas and Afipia were observed in 43%, 33% and 29% of the filter beds, respectively. AFLP analysis revealed that the predominating genus Polaromonas included a total of 23 different genotypes.
Conclusions:  This study is the first to demonstrate that Polaromonas , which has mainly been observed in ultraoligotrophic freshwater environments, is a common component of the microbial community in GAC filters used in water treatment.
Significance and Impact of the Study:  The predominance of ultraoligotrophic bacteria in the GAC filters indicates that very low concentrations of substrates are available for microbial growth. Polaromonas species are suited for further studies on the nutritional versatility and growth kinetics enabling the modelling of biodegradation processes in GAC filters.     

Effect of activated carbon on the biological treatment of oil-water emulsions

Waste water, derived from the reprocessing of used emulsions or suspensions, contains high concentrations of emulsified mineral oil and stabilizers, as well as different additives that are needed during the treatment process. Two stirred-tank reactors and two fixed-bed reactors were used to study the biodegradation of these waste-water compounds during two-stage biological treatment. The waste water was first proceesed in an activated sludge reactor to remove easily biodegradable substances. The effluent from the first stage was treated in three parallel operating reactors: an activated sludge tank containing different amounts of powdered activated carbon (PAC, between 0 and 2%), an upflow anaerobic fixed-bed reactor and an aerobic fixed-bed reactor (trickling filter). The results from the continuous treatment were compared with laboratory batch experiments. About 60% of the influent TOC was reduced by the first activated sludge treatment. The removal efficiency increased to about 70% by using a second activated sludge stage. This degradation was comparable to the maximum degree of degradation measured in laboratory batch experiments. PAC addition to the second activated sludge tank resulted in increased degradation rates. The removal efficiency increased to about 76% when 0.1% PAC was added and to 96% with 1% PAC. The removal efficiency decreased to 84% when the proportion of PAC was further increased to 2%. Variations in the amount of PAC addition per unit influent volume in the range of 50 and 200 mg/l had no significant effect on the TOC removal. Degradation models based on the MONOD-type equation were found to be in close correlation with the results obtained from batch experiments. However, the biological removal rates measured in batch experiments did not reflect the removal capacity determined in continuous operating treatment systems.     

Electrochemical sterilization of bacteria adsorbed on granular activated carbon

Subcellular distribution of chitin synthetase has been studied in germ tubes of Candida albicans. Two fractions with synthetase activity were separated from cell homogenates: (i) a mixed membrane fraction where the enzyme, partly in an active form, is associated with the plasma membrane (isopycnic centrifugation of mixed membrane fraction on linear sucrose gradients resolved a unique peak of activity matching with [3H]ConA-labelled membranes at a buoyant density of 1.195 g/ml); and (ii) a cytoplasmic fraction containing fully zymogenic enzyme associated with particles whose buoyant density (determined by isopycnic centrifugation on linear sucrose gradients) depended on the cell breakage conditions. The actual cytoplasmic fraction-enzyme may correspond to particles with buoyant density 1.135 g/ml (chitosomes), whereas the enzyme particles with other densities (1.085 and 1.165 g/ml) probably originated during cell disruption, as has been reported previously to occur during the preparation of yeast cell homogenates.     

Increased removal capacity for 1,2-dichloroethane by biological modification of the granular activated carbon process

The removal of 5 mg 1^–1 1,2-dichloroethane [(CH₂Cl)₂] was studied in two granular activated carbon (GAC) reactors run with hydraulic retention times of below 1 h. One reactor was operated abiotically. The other one was inoculated with microorganisms able to degrade (CH₂Cl)₂. While the (CH₂Cl)₂-adsorption capacity of the non-inoculated GAC reactor was exhausted after 20 days, it apparently did not exhaust for at least 170 experimental days in the biologically activated system because (CH₂Cl)₂ was removed to over 95% as a result of the microbial degradation. The biodegradation was quantified: during the passage through the biologically activated GAC reactor, (CH₂Cl)₂ (5± mg l^–1) disappeared, chloride ions (3.3±0.2 mg l^–1) were produced, and oxygen (4 to 6 mg l^–1) was consumed. Removal of 30% of GAC at the entrance of the reactor, which visibly carried most of the biomass, and its replacement by virgin GAC at the end of the column did not change the apparent (CH₂Cl)₂removal capacity of the GAC column, indicating that still enough biomass was available to degrade most of the chemical fed. After the addition of the virgin carbon, the effluent concentration fell for a short period of time from about 200 g l^–1 to below 100 g l^–1, indicating partial adsorption of the non-degraded (CH₂Cl)₂ at the end of the reactor by the virgin carbon. Thus, the modification of the adsorption process by inoculation and maintenance of bacteria with special degradation capabilities resulted in a lower consumption of GAC and thus led to an extended service life of the GAC columns.     

Enhanced biodegradation ofo-cresol by activated sludge in the presence of powdered activated carbon

Summary Addition of powdered activated carbon to a continuous-flow activated-sludge culture in a gas-lift bioreactor growing on o-cresol in a mineral-salts medium resulted in a reduction of the effluent o-cresol concentration during steady-state conditions as well as during shock-load conditions. During the latter conditions the activated carbon acted as a buffer. Bioregeneration of loaded activated carbon did occur, resulting in enhanced biodegradation of o-cresol. Adsorption of o-cresol by activated carbon was not sufficient to explain the total difference in effluent o-cresol concentration between the system with activated carbon and the system without activated carbon. Offprint requests to: R. J. de Jonge     

Retention of titanium dioxide nanoparticles in biological activated carbon filters for drinking water and the impact on ammonia reduction

Given the increasing discoveries related to the eco-toxicity of titanium dioxide (TiO₂) nanoparticles (NPs) in different ecosystems and with respect to public health, it is important to understand their potential effects in drinking water treatment (DWT). The effects of TiO₂ NPs on ammonia reduction, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in biological activated carbon (BAC) filters for drinking water were investigated in static and dynamic states. In the static state, both the nitrification potential and AOB were significantly inhibited by 100 μg L^?1 TiO₂ NPs after 12 h (p < 0.05), and the threshold decreased to 10 μg L^?1 with prolonged exposure (36 h, p < 0.05). However, AOA were not considerably affected in any of the tested conditions (p > 0.05). In the dynamic state, different amounts of TiO₂ NP pulses were injected into three pilot-scale BAC filters. The decay of TiO₂ NPs in the BAC filters was very slow. Both titanium quantification and scanning electron microscope analysis confirmed the retention of TiO₂ NPs in the BAC filters after 134 days of operation. Furthermore, the TiO₂ NP pulses considerably reduced the performance of ammonia reduction. This study identified the retention of TiO₂ NPs in BAC filters and the negative effect on the ammonia reduction, suggesting a potential threat to DWT by TiO₂ NPs.     

Microbial ecosystems in compost and granular activated carbon biofilters

Compost and granular activated carbon biofilters operated at a wastewater treatment plant simultaneously removed low concentrations of hydrogen sulfide and volatile organic compounds. Through the use of phospholipid fatty acid analyses, the effects of declining pH caused by sulfide oxidation were established for microbial growth, microorganism stress, and microbial community structure. Microorganisms on both media demonstrated increases in microbial densities, varying degrees of environmental stress, and domination by gram-negative bacteria. However, the declining pH had little effect on compound removal, which was greater than 99% for the hydrogen sulfide and greater than 70% for the oxygenated and aromatic hydrocarbons. The microbial communities adjusted to difficult environmental conditions through acclimation of the species present or by growth of low-pH-tolerant species. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 296-303, 1997.     

Disinfection of bacteria attached to granular activated carbon.

Heterotrophic plate count bacteria, coliform organisms, and pathogenic microorganisms attached to granular activated carbon particles were examined for their susceptibility to chlorine disinfection. When these bacteria were grown on carbon particles and then disinfected with 2.0 mg of chlorine per liter (1.4 to 1.6 mg of free chlorine residual per liter after 1 h) for 1 h, no significant decrease in viable counts was observed. Washed cells attached to the surface of granular activated carbon particles showed similar resistance to chlorine, but a progressive increase in sublethal injury was found. Observations made by scanning electron microscope indicated that granular activated carbon was colonized by bacteria which grow in cracks and crevices and are coated by an extracellular slime layer. These data suggest a possible mechanism by which treatment and disinfection barriers can be penetrated and pathogenic bacteria may enter drinking water supplies.     

Effect of point-of-use, activated carbon filters on the bacteriological quality of rural groundwater supplies.

The water quality of 24 rural, domestic groundwater supplies treated with point-of-use, powdered activated carbon (PAC) filters was monitored to determine how such treatment might impact the bacteriological quality of private, residential drinking water supplies. Heterotrophic-plate-count (HPC) and total coliform analyses were performed on raw, PAC-treated, and overnight or stagnant (first-draw) PAC-treated water samples. Densities of HPC bacteria were elevated by 0.86 and 0.20 orders of magnitude for spring and well water systems, respectively, in PAC-treated effluents following overnight stagnation compared with levels in untreated treated effluents. Densities of HPC bacteria in PAC-treated effluents were significantly reduced (P < 0.01) below influent levels, however, after the point-of-use device was flushed for 2 min. While PAC significantly reduced the number of coliforms in product waters (P < 0.01), these indicator organisms were still detected in some effluents. Seasonal variations were evident in microbial counts from spring but not well water systems. It appears that aside from periods following stagnant-water use, such as overnight, PAC treatment does not compromise the bacteriological quality of drinking water obtained from underground sources.     

Bacteria associated with granular activated carbon particles in drinking water

A sampling protocol was developed to examine particles released from granular activated carbon filter beds. A gauze filter/Swinnex procedure was used to collect carbon fines from 201 granular activated carbon-treated drinking water samples over 12 months. Application of a homogenization procedure (developed previously) indicated that 41.4% of the water samples had heterotrophic plate count bacteria attached to carbon particles. With the enumeration procedures described, heterotrophic plate count bacteria were recovered at an average rate of 8.6 times higher than by conventional analyses. Over 17% of the samples contained carbon particles colonized with coliform bacteria as enumerated with modified most-probable-number and membrane filter techniques. In some instances coliform recoveries were 122 to 1,194 times higher than by standard procedures. Nearly 28% of the coliforms attached to these particles in drinking water exhibited the fecal biotype. Scanning electron micrographs of carbon fines from treated drinking water showed microcolonies of bacteria on particle surfaces. These data indicate that bacteria attached to carbon fines may be an important mechanism by which microorganisms penetrate treatment barriers and enter potable water supplies.     

Predominant bacterial genera in granular activated carbon water treatment systems

Granular activated carbon (GAC) beds may be used for removal of dissolved organic matter during the treatment of drinking water. However, they might also change the microbiological quality of the water entering the distribution system either by changing the predominant bacteria or the bacterial density of the treated water. A 3-year pilot plant study of water treatment using GAC beds was conducted at the Baxter Water Treatment Plant in Philadelphia. During the study, bacteria were isolated from the raw water and from the effluents of the GAC treatment units. At the end of the study, bacteria were also isolated from the GAC units and from sand beds operated in parallel with the GAC units. Bacterial genera in the GAC effluents and in the GAC units themselves were similar to those found in the raw water and in the sand beds. Prechlorination and (or) preozonation of the water before GAC treatment had no noticeable effect on the bacterial genera found as compared with GAC unit having no predisinfection. The bacterial genera found in this study were similar to those found in seven other studies of GAC water treatment that used a variety of treatment schemes and a variety of heterotrophic plate count techniques to evaluate bacterial populations. From these several studies it appears that GAC treatment does not change the nature of the bacterial populations associated with drinking water.     

Aerobic biodegradation of tert-butyl alcohol (TBA) by psychro- and thermo-tolerant cultures derived from granular activated carbon (GAC)

Tert-butyl alcohol (TBA) is a metabolite of methyl tert-butyl ether and is itself possibly a fuel oxygenate. The goals of this study were to enrich and characterize TBA-degrading micro-organism(s) from a granular activated carbon (GAC) unit currently treating TBA. The results reported herein describe the first aerobic, TBA-degrading cultures derived from GAC. Strains KR1 and YZ1 were enriched from a GAC sample in a bicarbonate-buffered freshwater medium. TBA was degraded to 10% of the initial concentration (2–5 mM) within 5 days after initial inoculation and was continuously degraded within 1 day of each re-amendment. Resting cell suspensions mineralized 70 and 60% of the TBA within 24 h for KR1 and YZ1, respectively. Performance optimization with resting cells was conducted to investigate kinetics and the extent of TBA degradation as influenced by oxygen, pH and temperature. The most favorable temperature was 37°C; however, TBA was degraded from 4 to 60°C, indicating that the culture will sufficiently treat groundwater without heating. This is also the first report of psychrotolerant or thermotolerant TBA biodegradation. The pH range for TBA degradation ran from 5.0 to 9.0. Phylogenetic data using a partial 16S rRNA gene sequence (570 bases) suggest that the primary members of KR1 and YZ1 include uncharacterized organisms within the genera Hydrogenophaga, Caulobacter, and Pannonibacter.     

Effect of chloroethene concentrations and granular activated carbon on reductive dechlorination rates and growth of Dehalococcoides spp

This study focused on the investigation of (i) the tetrachloroethene (PCE) toxicity threshold of a reductively dechlorinating mixed culture containing Dehalococcoides spp., (ii) the adsorption of PCE on different types of granular activated carbon (GAC), and (iii) the bioavailability and reductive dechlorination in the presence of GAC. The abundance of Dehalococcoides spp. detected by quantitative real-time polymerase chain reaction (qPCR) was found to increase by 2-4 orders of magnitude during degradation of PCE. No degradation occurred at dissolved concentrations beyond 420 μM (70 mg/L). Different adsorption isotherms were determined for thermally and chemically activated carbons. The addition of GAC to biological assays reduced the dissolved PCE concentration below the toxicity threshold. The combination of microbial reductive dechlorination with GAC adsorption proved to be a promising method for remediation of groundwater contaminated by high concentrations of chloroethenes.