Biological Activated Carbon Filtration Research Articles

Water quality factors affecting bromate reduction in biologically active carbon filters

Biological removal of the ozonation by-product, bromate, was demonstrated in biologically active carbon (BAC) filters. For example, with a 20-min EBCT, pH 7.5, and influent dissolved oxygen (DO) and nitrate concentrations 2.1 and 5.1 mg/l, respectively, 40% bromate removal was obtained with a 20 μg/l influent bromate concentration. In this study, DO, nitrate and sulfate concentrations, pH, and type of source water were evaluated for their effect on bromate removal in a BAC filter. Bromate removal decreased as the influent concentrations of DO and nitrate increased, but bromate removal was observed in the presence of measurable effluent concentrations of DO and nitrate. In contrast, bromate removal was not sensitive to the influent sulfate concentration, with only a slight reduction in bromate removal as the influent sulfate concentration was increased from 11.1 to 102.7 mg/l. Bromate reduction was better at lower pH values (6.8 and 7.2) than at higher pH values (7.5 and 8.2), suggesting that it may be possible to reduce bromate formation during ozonation and increase biological bromate reduction through pH control. Biological bromate removal in Lake Michigan water was very poor as compared to that in tapwater from a groundwater source. Bromate removal improved when sufficient organic electron donor was added to remove the nitrate and DO present in the Lake Michigan water, indicating that the poor biodegradability of the natural organic matter may have been limiting bromate removal in that water. Biological bromate removal was demonstrated to be a sustainable process under a variety of water quality conditions, and bromate removal can be improved by controlling key water quality parameters.

Retention of herbicides and pesticides in relation to aging of RO membranes

Amsterdam Water Supply (AWS) intends to increase the capacity of the Leiduin production plant. In the existing plant (capacity 70×10 6 m 3/y) pretreated Rhine River water was infiltrated in the dune area west of Amsterdam for artificial recharge and after a residence time of approximately 100 days extracted and posttreated to achieve drinking water quality. In the extension (capacity 13×10 6 m 3/y) the pretreated (coagulation, sedimentation, filtration) Rhine River water was not infiltrated in the dunes, but was treated directly without soil passage. First, an additional pretreatment (ozonation, biological activated carbon filtration and slow sand filtration) was carried out, and finally reverse osmosis (RO) was used for desalination, hardness removal, disinfection and removal of pesticides and others micro-pollutants. Former research on removal of pesticides has already showed a removal of >99.5% with the ozonation/BACF preceding RO. To prove high retention of RO membranes as a second barrier and to examine the influence of aging of the membranes, several dosing experiments were carried out by AWS and Kiwa. During the period before March 1997, Toray SU 710L membranes were used. From then on Fluid Systems 4821 ULP membranes have been used in the RO pilot plant. The RO feed flow is 9 m 3/h and the recovery is 85%. To compare the removal of pesticides and herbicides with the two different applied RO membranes, six dosing experiments were carried out: two with the Toray membranes and four with the Fluid Systems membranes. A cocktail of pesticides was dosed with a feed concentration of approximately 5 μg/l. The results of the test showed an equal retention for bentazon, DNOC and pirimicarb for both types of membranes. The removal of metamitron and metribuzin was substantially higher with the Fluid Systems membranes. As a result, it was concluded that RO is a second barrier for pesticides in this treatment concept as biological activated carbon filtration in the first barrier. Retention of the Fluid Systems membranes is higher than the retention of the Toray membranes. After 3 years of operation with the Fluid Systems membranes, no pesticide retention decline was observed.

Modified Fouling Index ultrafiltration to compare pretreatment processes of reverse osmosis feedwater

Existing fouling indices to measure the particulate fouling potential of reverse osmosis (RO) feedwater, the SDI and MFI 0.45 do not include smaller colloidal particles. Therefore, the MFI using ultrafiltration (UF) membranes was developed (1000–100,000 Da pore size) to incorporate and measure smaller particles. A 13,000 Da membrane was selected as the most promising reference membrane for application in the MFI-UF test. This research investigates its application to (1) measure the particulate fouling potential of RO feedwater and (2) evaluate the efficiency of pretreatment processes on particle removal at two RO pilot plants. Where possible a comparison was made with the SDI, MFI 0.45, and particle counts. Both RO plants use conventional pretreated surface water. Subsequently, the Rhine River plant uses ozonation, biological activated carbon filtration, and slow sand filtration while the Ijssel Lake plant uses ultrafiltration (150–200,000 Da). The MFI-UF of the influent feedwater was about 400–1400 higher than the corresponding MFI 0.45 and SDI, due to the retention of smaller particles. A reduction in the particulate fouling potential, > -80%, was found by MFI-UF with pretreatment at both plants. For the larger particles the MFI 0.45 gave a 90–≈100% reduction at the Rhine River plant, while the SDI gave more variable results: 70 > 90%.

Benefits of ozone-activated carbon filtration in integrated treatment processes, including membrane systems

Amsterdam Water Supply introduced ozone-activated carbon filtration (biological activated carbon filtration) in the production plant Leiduin in 1995. This full-scale plant (capacity 70 million m 3 yr −1 ) can be characterized as an integrated treatment process. Experience since 1995 has revealed that biological activated carbon filtration has several benefits in integrated treatment processes. It is a very effective barrier for organics in general and for pesticides and organic micropollutants in particular. Due to the preceding ozonation both adsorption and biodegradation take place, resulting in a very long lifetime of the carbon filters (2 years). The ozonation significantly increases the disinfection capacity of the plant. Together with the other process steps, the disinfection capacity is at such a high level that, in combination with the biological stability of the finished water and good engineering practice in the distribution system, no chlorination has to be applied to guarantee hygienic quality. The process stability of the final treatment step, slow sand filtration, is, importantly, increased by the introduction of ozone-activated carbon filtration. Running times of the slow sand filters are longer than 2–3 years, while before the introduction of ozone-activated carbon filtration they never exceeded 1 year. In integrated membrane processes—which may be used in the treatment plant Leiduin in the future and therefore are being tested on pilot plant scale—ozone-activated carbon filtration also offers many advantages. In a reverse osmosis pretreatment scheme, comprising ozone-activated carbon filtration and slow sand filtration, the reverse osmosis system was shown to have a running time of 1 year without any membrane cleaning, due to the excellent reverse osmosis feed water quality. The application of ozone-activated carbon filtration also enables the use of electrodialysis as an alternative for reverse osmosis in an integrated membrane system. It is concluded that ozone-activated carbon filtration is a versatile process, offering many benefits in integrated treatment systems.

Biological Filtration for Ozone and Chlorine DBP Removal

This paper presents results from a water treatment pilot testing program in Winnipeg, Canada (pop. 650,000) which evaluated a DAF/ozone/deep bed filtration process. As part of the testing program, biological filtration using GAC and anthracite media was assessed for the removal of ozone DBPs and background chlorine DBPs (due to upstream chlorination of the source water). The results were used to evaluate the effectiveness of biological filtration for DBP removal. High filtration rates were tested in this study. The 2.1m deep filters were run at a hydraulic loading rate (HLR) of 35 m/h with an empty bed contact time (EBCT) of only 3.6 minutes. The important findings of this work are ▪The high-rate biologically active carbon (BAC) filters met the objective of controlling ozone DBPs. These results confirm that high rate, low EBCT filters can provide significant biodegradation. Anthracite biofilters provided significantly less removal of ozone DBPs. ▪The high rate BAC filters showed significant reduction of background HAAs. BAC reduced the background HAAs to below the long-term target of 30 μg/L. Anthracite biofilters did not exhibit HAA removal. ▪Biological filtration with either media was ineffective for background THM removal. The long-term target of 40 μg/L could not be achieved without GAC adsorption.

Treatment of Trace Organic Compounds by Ozone–Biological Activated Carbon for Wastewater Reuse: The Lake Arrowhead Pilot Plant

Organic and trace organic performance data for preozonation and biological activated carbon (BAC) filtration of the Lake Arrowhead, California, water reclamation pilot plant secondary effluent were analyzed to determine treatment efficiency of these processes in a potable water reuse project. Five types of organic analysis were performed: dissolved organic carbon (DOC), UV at 254 nm (UV‐254), ultimate soluble biochemical oxygen demand (SBODU), baseneutral analysis (BNA), and specific aldehyde analyses. Preozonation favored the breakdown of high‐molecular‐weight organic matter (> 1000 daltons [Da]), measured as DOC, to biodegradable organic compounds, measured as an increase in SBODU. Also, a shift in mass concentration of BNAs from the higher scan index fraction (< 1000 Da) to the lower scan index fraction was shown by gas chromatography–mass spectrometry profile analysis. After preozonation, organic compounds were sorbed and biodegraded through the BAC filter. Steady state was reached for DOC and UV‐254 absorbance after 50 to 100 days. Trace organic compounds started breaking through the column 200 days after BAC startup. Breakthrough was not uniform for BNAs. Apparent differences between the lower and higher molecular weight fractions of BNAs were shown, indicating a greater breakthrough rate for the higher scan index fractions. Finally, lists of tentatively identified BNA compounds were created, highlighting the change in chemical composition of the base‐neutral fraction before and after each process.

The use of Biological Activated Carbon Filtration for the Removal of Natural Organic Matter and Organic Micropollutants from Water

Amsterdam Water Supply (AWS) uses Biological Activated Carbon Filtration (BACF) for the removal of natural organic matter in general and the removal of organic micropollutants in particular. In order to minimize costs and environmental burden, it is important to know whether successive reactivations of carbon reduces its effectivity, and whether pesticides are effectively removed after prolonged running times of the carbon filters. The first aspect avoids the necessity of carbon replacement (i.e. costs), while the second aspect reduces the reactivation frequency (i.e. environmental burden). In a future extension scheme, AWS considers the use of an Integrated Mebrane System (IMS), and it is important to know whether the application of BACF is beneficial in the IMS. Six years of operation of BACF in the River-Lake Waterworks (31 million m3/year) have shown that successive reactivations do not affect the DOC removal capacity of the carbon. Three years of operation of BACF in the River-Dune Waterworks (70 million m3/year) have shown that the carbon retains its pesticide removal capacity. The use of BACF in an IMS shows important perspectives in minimizing the fouling of reverse osmosis membranes and in minimizing the organic carbon content in the membrane concentrate.

Dissolved Organic Carbon Removal from a Prairie Water Supply Using Ozonation and Biological Activated Carbon

Abstract Large quantities of dissolved organic carbon in prairie surface water reservoirs make sustainable treatment quite challenging. Organic material is a precursor for the formation of disinfection by-products. Here, ozonation and biological activated carbon filtration were used as methods for removing dissolved organic carbon from the water of a small prairie reservoir used as a drinking water source. Biofiltration alone yielded significant reductions in dissolved organic carbon, colour, total trihalomethanes and chlorine demand. When ozonation preceded biofiltration, the increased proportion of biodegradable dissolved organic carbon allowed for significantly greater (p<0.05

Reduction of bromate in a BAC filter

Water treatment plants already using ozone and GAC filters can readily implement this method of removing bromate.Bromate removal was observed during biologically active carbon (BAC) filtration. Microorganisms in the BAC reduced bromate to bromide, although the formation of other intermediate species is possible. The effects of dissolved oxygen (DO) concentration, nitrate concentration, and empty bed contact time (EBCT) on microbial bromate reduction were examined. Oxygen and nitrate, common microbial electron acceptors, hindered bromate reduction. For example, at an influent DO concentration of 2 mg/L in a BAC filter with a 25‐min EBCT, bromate was reduced by 86 percent at an influent nitrate concentration of 0.2 mg/L, whereas it was reduced by 76 percent at an influent nitrate concentration of 5.1 mg/L. In general, lengthening the EBCT increased bromate removal. Biological bromate removal in a conventional ozone–granular activated carbon plant was deemed possible if the DO concentration in the BAC filter is controlled.

Influence de facteurs contrôlant l'enlèvement de la demande en chlore et de précurseurs de sous-produits de chloration dans des filtres biologiques

Resume The addition of an ozonation step followed by a second stage biological activated carbon (BAC) filtration to a conventional treatment (coagulation–flocculation, settling and sand–anthracite filtration) has been identified as a good mean for controlling chlorination by-product precursors. Lately, the addition of an ozonation step before filtration and the replacement of sand–anthracite filtration by sand-BAC filtration has been proposed as an economical solution when retrofitting treatment plants. The accumulation of flocs and particulate matter in first stage sand-BAC filters may cause nevertheless some problems of substrate or oxygen diffusion to the biomass fixed on the BAC. The main objectives of this study were to verify the impact of flocs/particle accumulation in first stage sand-BAC filters by: (1) studying the effects of filter backwash on the removal of chlorination by-product precursors; (2) comparing the efficiency of sand-BAC filtration with that of first stage sand–anthracite filtration and second stage BAC filtration. Figure Fig. 1 shows the flow chart of the pilot facilities used for this study. The raw water, from the Mille-iles River, was settled in the St. Rose filtration plant (nominal capacity of 110,000 m 3 /d). This settled water was then pumped to the pilot plant (nominal capacity of 48 m 3 /d) where it was ozonated in two sequential ozone reactors. The ozonated water stream was then split by open weirs to three filtration trains. Four pilot filters were used: two replicate first stage sand-BAC filters (filtres sable–CAB #1 and sable–CAB #2), one first stage sand–anthracite filter (filtre SA) followed by one second stage BAC filter (filtre CAB). Table Table 1 shows the design and the operational parameters of the filters. Properties of filter media are described in Table Table 2 . Table Table 3 shows additional sampling information. Analytical monitoring included chlorine demand, dissolved organic carbon (DOC), ammonia, hexane extractable disinfection by-product precursors (HEDBPp) and haloacetic acid precursors (HAAp). Table Table 5 indicates the HEDBPp and the HAAp measured. All these parameters were measured on water samples taken at different filter depths according to empty bed contact time (EBCT). Results showed that floc and particle accumulation in first stage sand-BAC filters impaired the removal of some chlorination by-product precursors, such as HAAp which are considered to be easily biodegradable. Fortunately, filter backwash restored these removals. Chloropicrin precursors were also identified as being easily removed in biological filters when compared to the biodegradation kinetics of dissolved organic carbon. Chloroform and trichloropropanone precursors were found to be removed as the global pool of dissolved organic carbon. The replacement of first stage sand–anthracite filter by sand-BAC filter and the addition of an interozonation step could improve the quality of the water produced by the treatment plant. In fact, this study showed that sand–anthracite filtration was not suitable for the removal of chlorine demand, chloroform precursors, chloropicrin precursors and trichloropropanone precursors. Furthermore, the water quality of the effluent of first stage sand-BAC filtration and of BAC filtration was shown to be very similar. However, the coagulation–floculation step must be enhanced in a manner to prevent the accumulation of flocs and particulate matter in first stage sand-BAC filters. Results also suggested that the potential of removal of biodegradable precursors of chlorination by-products is limited and should be part of a global strategy including the optimisation of natural organic matter removal by other treatment processes (coagulation, settling, membranes).

Biodegradable organic matter removal in biological filters: evaluation of the CHABROL model

The implementation of biological filtration on granular activated carbon under various operating conditions has revealed that biodegradable organic matter (BOM) removal performance is not easily predicted. In this context, the statistical analysis of the differences between experimental data and data calculated by a deterministic model may provide insight into the source of prediction errors. The CHABROL model, developed by Billen et al., (1992), relates BOM consumption to biomass densities in order to predict BOM removal profiles in biological activated carbon filters (BAC) and rapid sand filters. This work presents the results of testing the CHABROL model using a large database from pilot and full-scale filters located in two Canadian cities: Laval and Montreal. This database includes data from two different water sources and three biological filtration configurations (direct filtration, first-stage dual-medium sand-BAC filters and second-stage mono-medium BAC filters). Since nearly half of all experimental data were obtained at very low temperatures (≤1°C), the impact of prolonged acclimation to very cold temperatures was investigated to ensure accurate prediction by the CHABROL model. Experimental results have shown that modifications in the CHABROL model have to be made to account for the acclimation to very cold temperature and to prevent under estimations of the BDOC removals. The results of the model testing show overall satisfactory results in the ability to predict BDOC removals in various types of filters, except for the sampling campaigns completed just prior to backwash. This comparison shows the interest of using a predictive model to predict performance in dynamically operated filters which may be used for design and operation.

The use of biological activated carbon filtration for the removal of natural organic matter and organic micropollutants from water

Amsterdam Water Supply (AWS) uses Biological Activated Carbon Filtration (BACF) for the removal of natural organic matter in general and the removal of organic micropollutants in particular. In order to minimize costs and environmental burden, it is important to know whether successive reactivations of carbon reduces its effectivity, and whether pesticides are effectively removed after prolonged running times of the carbon filters. The first aspect avoids the necessity of carbon replacement (i.e. costs), while the second aspect reduces the reactivation frequency (i.e. environmental burden). In a future extension scheme, AWS considers the use of an Integrated Mebrane System (IMS), and it is important to know whether the application of BACF is beneficial in the IMS. Six years of operation of BACF in the River-Lake Waterworks (31 million m3/year) have shown that successive reactivations do not affect the DOC removal capacity of the carbon. Three years of operation of BACF in the River-Dune Waterworks (70 million m3/year) have shown that the carbon retains its pesticide removal capacity. The use of BACF in an IMS shows important perspectives in minimizing the fouling of reverse osmosis membranes and in minimizing the organic carbon content in the membrane concentrate.

Integrated multi-objective membrane systems application of reverse osmosis at the Amsterdam Water Supply

Within the scope of a project funded by AWWARF and USEPA three very promising IMS's were identified for surface water treatment. This paper will cover some highlights of the research carried out by Amsterdam Water Supply (AWS) and Kiwa on the combination of biological activated carbon filtration, slow sand filtration and (ultra low pressure) reverse osmosis. Primary objectives of this IMS study are restriction of (bio)fouling, productivity control, disinfection and removal of DBP-precursors. To prevent fouling two pretreatment schemes were tested. The reference scheme consisting of coagulation, sedimentation, rapid sand filtration and slow sand filtration lowered the MFI to 2 s/l 2. The alternative scheme consisting of the reference scheme extended with ozonation and biological activated carbon filtration before slow sand filtration lowered the MFI to 1 s/l 2. Biofouling was characterized by AOC and biofilm formation rate. Average AOC values were low (<10 μg/l) and the biofilm formation rates were lower than the standard for biologically stable drinking water. After 9 months of operation no significant membrane fouling was observed. For both pretreatments only a slight flux decline was observed during a period of nine months of operation. No significant increase in pressure drop was observed. After an initial flux decline during the first two months for both pretreatments only little flux decline occurred. The flux of the RO pretreated with only slow sand filtration (reference scheme) still showed a (small) decline after the nine months test period. After the initial flux decline, the RO with extended pretreatment consisting of an additional ozonation and biological activated carbon filtration (alternative scheme) operated at a nearly constant MTC. Disinfection and integrity were tested by MS2 phage spiking resulting in a removal capacity of 3.4 log units. Because of their larger size the removal of other micro-organisms should be at least equal. However, with direct cell counts and heterotrophic plate counts a lower efficiency was found. This might be due to regrowth in the RO installation on the permeate side. The DBP-precursor content after both pretreatments was low. The Cl 2 demand for the reference scheme was twice as high as the Cl 2 demand for the alternative scheme. The DBP-precursor content in the permeate of both treatments was below the detection limit. It is concluded that the IMS at Leiduin is reliable. Fouling is manageable and productivity is nearly constant. The dosing of MS2 phages shows an acceptable removal. DBP-precursors are removed to below the detection limits by the ultra low pressure membranes.

PH and Mg/Ca control for biological treatment of an offensive flavour (2-MIB)

From a series of experimental observations, it was found that removal rates of the offensive flavor 2-methyl-isoborneol(2-MIB) and ammonia by a biological treatment for water supply were rather unstable and that the removal rates of them often became reverse such as low removal in 2-MIB and high removal of ammonia. One reason for the reverse phenomenon was found that the affinities of sludge around bacteria with 2-MIB and ammonia often became reversed. The affinities of sludge with 2-MIB and ammonia were found to be changeable depending upon pH along with magnesium (Mg) and calcium (Ca) concentrations in sludge. From these findings, control of pH and magnesium calcium ratio (Mg/Ca) of raw water was recommended for simultaneous and stable removal of 2-MIB and ammonia. From plant scale experiments equipped with automatic pH controller, the effects of pH and Mg/Ca control for biological treatment of 2-MIB and ammonia were observed in a biological activated filtration. Here, a biological activated carbon filtration means a longer filtration than 40 to 50 days from the beginning. The obtained results were almost as expected, showing high removal rates of both 2-MIB and ammonia.

Control of bio-regenerated granular activated carbon by spreadsheet modelling

The optimisation of water purification with biological activated carbon (BAC) is described. Procedures are suggested to control biofilm growth and to use bio-indicators to predict TOC (total organic carbon) and COD (chemical oxygen demand) removal efficiencies. Empty bed contact time (EBCT) was a major physical control parameter. Dissolved oxygen (DO), pH and nutrients of the influent were controlled according to the abundance of bacteria, protozoa and rotifers. Numbers of micro-organisms in BAC beds were determined. Certain genera of ciliated protozoa, representing healthy environmental conditions, were employed as biological indicators for system performance during biological regeneration of exhausted granular activated carbon (GAC). There was a strong positive correlation between the abundance of some protozoa in the liquid phase of the BAC bed and COD concentration in the effluent. Mathematical spreadsheet models were constructed to estimate COD removal efficiency of BAC filters with different loading rates, DO, pH, nutrient requirements and populations of micro-organisms.

Control of bio‐regenerated granular activated carbon by spreadsheet modelling

The optimisation of water purification with biological activated carbon (BAC) is described. Procedures are suggested to control biofilm growth and to use bio-indicators to predict TOC (total organic carbon) and COD (chemical oxygen demand) removal efficiencies. Empty bed contact time (EBCT) was a major physical control parameter. Dissolved oxygen (DO), pH and nutrients of the influent were controlled according to the abundance of bacteria, protozoa and rotifers. Numbers of micro-organisms in BAC beds were determined. Certain genera of ciliated protozoa, representing healthy environmental conditions, were employed as biological indicators for system performance during biological regeneration of exhausted granular activated carbon (GAC). There was a strong positive correlation between the abundance of some protozoa in the liquid phase of the BAC bed and COD concentration in the effluent. Mathematical spreadsheet models were constructed to estimate COD removal efficiency of BAC filters with different loading rates, DO, pH, nutrient requirements and populations of micro-organisms. © 1998 SCI

高度浄水処理における生物活性炭と生物ろ過の処理特性

In drinking water treatment process including ozonation and biological activated carbon (BAC) filtration, the treatment capability of BAC filter was compared with that of biological filter with a carrier having no adsorption capacity, to clarify the effect of adsorption and biodegradation activity on the mechanism in BAC filtration. Trihalomethane formation potential (THMFP) and E260 were highly removed by the combination of ozonation and BAC filtration. On the other hand, the biological filter had generally lower removal potentiality compared with BAC filter. However it appeared that higher removal potentiality close to that of BAC filter was achieved by the combination of ozonation and biological filter at high water temperature. Number of bacteria on BAC was little different from that on the medium for biological filter.The removal potentiality of THMFP and E260 in the combination of ozonation and BAC filtration was little different from that in BAC filtration without ozonation. However the adsorption load for BAC was decreased by oxidation and improvement of biodegradability at preozonation.

Backwashing first‐stage sand–BAC filters

Does it increase removal of biodegradable organic matter and ammonia?The effect of filter backwash on the efficiency of first‐stage sand–biological activated carbon (BAC) filters was evaluated by comparing, in first‐stage sand–BAC filters, concentrations of ammonia, biodegradable dissolved organic carbon, aldehydes, and oxalate. These concentrations were measured before and after filter backwash. Filter position (first‐stage sand–BAC filters versus second‐stage BAC filters) was also studied to understand how flocs and particle accumulation influenced the efficiency of the first‐stage sand–BAC filter. A first‐stage sand–anthracite filter operated under similar hydraulic conditions and effluent turbidity acted as a reference. Filter backwash improved the efficiency of sand–BAC filters, especially in cold water sources. However, both filters produced similar water quality. First‐stage sand–anthracite filters did not adequately remove biodegradable organic matter and ammonia.

PH and Mg/Ca control for biological treatment of an offensive flavour (2-MIB)

From a series of experimental observations, it was found that removal rates of the offensive flavor 2-methyl-isoborneol(2-MIB) and ammonia by a biological treatment for water supply were rather unstable and that the removal rates of them often became reverse such as low removal in 2-MIB and high removal of ammonia. One reason for the reverse phenomenon was found that the affinities of sludge around bacteria with 2-MIB and ammonia often became reversed. The affinities of sludge with 2-MIB and ammonia were found to be changeable depending upon pH along with magnesium (Mg) and calcium (Ca) concentrations in sludge. From these findings, control of pH and magnesium calcium ratio (Mg/Ca) of raw water was recommended for simultaneous and stable removal of 2-MIB and ammonia. From plant scale experiments equipped with automatic pH controller, the effects of pH and Mg/Ca control for biological treatment of 2-MIB and ammonia were observed in a biological activated filtration. Here, a biological activated carbon filtration means a longer filtration than 40 to 50 days from the beginning. The obtained results were almost as expected, showing high removal rates of both 2-MIB and ammonia.

Micropollutant removal with saturated biological activated carbon (BAC) in ozonation–BAC process

The objective of this study is to evaluate the adsorption capacity of BAC saturated with natural organic matter (NOM) for micropollutant removal which intermittently enter into water sources and to compare this to sand filtration that has no adsorbability but has biodegradability. The removal of intermittently applied micropollutants was examined with two BAC and sand filters. Two BAC filters which have been operated for 6 and 20 months and a sand filter being used for 6 months for the treatment of reservoir water were used in this experiment. EBCT of these BAC and sand filter were 15 minutes. Bromophenol (highly adsorbable but refractory) and phenol (adsorbable and biodegradable) were used instead of targeted micropollutants. Bromophenol and phenol of about 200 μg·l−1 were applied for 24 hours. The BAC 1, which was used for 20 months had already lost its adsorbability because it was saturated with NOM. BAC 2 filter which was used for 6 months had small adsorption capacity for NOM. As a result, either BAC 2 or BAC 1 removed bromophenol (160 μg·l−1) completely for 24 hours spike, but sand filter did not removed at all. Bromophenol can be removed only by adsorption, therefore bromophenol might be removed through adsorption by BAC. On the other hand, phenol (220 μg·l−1) whose adsorbability is lower than bromophenol, was removed completely by both BAC 1 and BAC 2. These results indicate that micropollutants with similar adsorbability as that of phenol and bromophenol can be removed by BAC even after a long period of operation and saturation with NOM.