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Biofiltration of ozonated humic water in expanded clay aggregate filters
Abstract
Treatment of hurruc water was studied in a pilot-scale ozonation/biofiltration treatment plant. The raw water had TOC and CODMn concentrations of 3.2–5.0 and 4.1–6.6 mgO l−1, respectively, and colour (410 nm) of 30–50 mgPt l−1. The effect of biofilter loading rate on removal of organic matter and ozonation by-products was investigated in two upflow biofilters containing expanded clay aggregate (Filtralite) media. The empty bed contact times ranged from 11 to 54 min. The TOC removals varied from 18 to 37% and the CODMn removals from 30 to 48% with ozone dosages from 1.0 to 1.7 mgO3 mgTOC−1. The ozone dosage seemed to have larger effect on removal efficiency than the loading rate. Concentrations of aldehydes (sum of formaldehyde, acetaldehyde, glyoxal and methyl glyoxal) were 41–47 μg l−1 in ozonated water. Formaldehyde and glyoxal were the only aldehydes detected from the biofilter effluents at concentrations higher than 1 μg l−1, but their mean concentrations were below 2.1 μg l−1. The ketoacid concentrations (sum of glyoxylic, pyruvic and ketomalonic acids) ranged from 272 to 441 μg l−1. Average biofilter effluent concentrations varied from 5.3 (glyoxylic acid) up to 67 μg l−1 (ketomalonic acid) with steady-state reductions generally over 80%. The aldehydes and ketoacids accounted on average for 16% of the biodegraded TOC. The results show that expanded clay aggregate media is a good alternative as biofilter material.
... Higher P-sorption was observed for LECA+CaCO 3 more than LECA (Melin & Odegaard, 1999) ECA TOC, COD, colour and ozonated humid water ...
... The phosphate % removal efficiency values for GI-2, GI-5, GI-7 and GI-8 were 46.47%, 33.35%, 41.33% and 40% respectively. Higher removal efficiency values attributed to lower pH, high surface area and high pore volume were recorded as against those reported by (Johansson, 1997;LinkManagerBM_REF_g8QsYbG5Łopata et al.), 79-90% were reported by (Alzeyadi et al., 2019) using Biomass Bottom Ash (BBA), however 57%-75% removal efficiencies were reported for the biofiltration of ozonated humid water (Melin & Odegaard, 1999). ...
Elevated levels of contaminants in surface and ground water pose serious and adverse health challenges in the twenty-first century. It is imperative that the quality of life of people without safe drinking water is improved by providing safe, clean and affordable water using appropriate purification technology. Natural clay and rice husk-Na2CO3 modified clay were used to produce expanded clay aggregates adsorbents. Characterizations were done using SEM, XRD, XPS and BET to reveal their salient features. Filtration studies were carried out to ascertain the disinfection assay of E. Coli and removal efficiencies of nitrate and phosphate. Batch adsorption experiments were employed to determine the effect of pH, contact time and adsorbent dosage for effective removal of Arsenic (III) and lead (II) including isotherm models. Aluminosilicates and associated minerals with high surface areas between 456.143–566.998 m²/g and significant adsorption sites were revealed. Log four bacteria disinfection assay was achieved. Reduction efficiencies for phosphate and nitrate for all adsorbents varied from 27.33% to 76% and 10.67% to 46% respectively. High correlation coefficients made Langmuir isotherm model more favourable than Freundlich model. The adsorption capacities for both lead and arsenic were high and reaction was fast, making the adsorbents suitable for water remediation applications.
... Humic substances represent the major fraction of NOM present in virtually all surface waters [8]. This group of compounds is not readily biodegradable, and the little biodegradation of them that does occur is generally slow and site-specific [9], although it can be enhanced by water pre-treatment and oxidative disinfection processes10111213. Humic substances are highly heterogeneous in both their structure and composition and consequently difficulties in their analysis and identification make them a poorly characterised group of compounds. ...
... Humic substances represent the major fraction of NOM present in virtually all surface waters [8]. This group of compounds is not readily biodegradable, and the little biodegradation of them that does occur is generally slow and site-specific [9], although it can be enhanced by water pre-treatment and oxidative disinfection processes [10][11][12][13]. Humic substances are highly heterogeneous in both their structure and composition and consequently difficulties in their analysis and identification make them a poorly characterised group of compounds. ...
The artificial recharge of sand aquifers with raw source waters is a means both explored and utilised by many water utilities to meet the future potable water demands for increasing urban populations. The microbial ecology within these systems is however, poorly understood, as is the role that microbial biofilms play in the quality of finished water. Knowledge of the ability of biofilm bacteria to metabolise natural organic matter (NOM) is limited, particularly in respect to the degradation of normally recalcitrant hydrophilic and hydrophobic humic acid fractions by sessile and planktonic microbial consortia within sand aquifer systems. To simulate the artificial recharge of sand aquifers that were proposed for the Greater Stockholm Area, four separate 4 m deep sand columns were fed raw lake water and examined over a 45-week study period. The simulated aquifer system (hydraulic retention time 9-16 h) demonstrated the removal of total organic carbon (TOC) (10+/-5%), direct total counts (DTC) of bacteria (74+/-11%), heterotrophic plate count (HPC) bacteria (87+/-5%) and assimilable organic carbon (AOC) (87+/-5%), thereby fulfilling an important barrier function, except for the removal of TOC. Hydrophilic humic acid fractions were more readily metabolised by microbiota (HPC and EUB338-positive cells) harvested from the raw source water (SSM-W), whilst hydrophobic humic acid fractions promoted higher activity by microbiota harvested from the sand matrix (SSM-S). The apparent low activity demonstrated by biofilm microbiota (approximately 40% and 25% of DTC were positive to EUB338 probing for sand matrix and slide biofilms, respectively) could be attributed to the highly recalcitrant nature of the organic loads, whilst at the same time explain the poor removal of TOC. Following nutrient activation (by the PAC assay) nonetheless, a 3-fold increase in the percentage of EUB-positive bacteria was observed on glass slides. Furthermore, the incubation of SSM-S with R2A increased probe-active cells from 57+/-8% to 75+/-7% of DTC and at the same time increased SSM-W from 38+/-8% to 50+/-10%. Whilst these results may imply a good potential for the biological treatment of water by shallow sand aquifers, further work should address the poor removal of TOC observed in this study.
... These findings are in agreement with observations published by Saltnes et al. (2002), where no significant difference in total organic carbon (TOC) removal was observed between ceramic and anthracite filters receiving in-line coagulated tap water. However other studies that examined expanded clay material (as biofiltration media) have reported TOC reductions of 13e28% (C 0 ¼ 2e5 mg/L) across biofilters receiving pre-ozonated water spiked with a humic concentrate (Melin and Ødegaard, 1999). ...
Media type is a critical design consideration when implementing biofiltration for drinking water treatment. Granular activated carbon (GAC) has been shown to provide superior performance when compared to a wide range of media types, largely due to its higher surface area. Engineered ceramic media is an attractive alternative to GAC as it has a similar surface area but at a lower cost. This pilot-scale biofiltration study compared the performance of GAC, anthracite and two different effective sizes of ceramic (CER) media (1.0 mm and 1.2 mm), in terms of dissolved organic carbon (DOC), head loss, turbidity, and disinfection by-product formation potential (DBPFP). Biological acclimation was monitored using adenosine tri-phosphate (ATP) measurements; biomass was further examined using laccase and esterase enzyme activity assays. When compared to other media types examined, biological GAC had higher (p > 0.05) removals of DOC (9.8 ± 3.8%), trihalomethane formation potential (THMFP, 26.3 ± 10.2%), and haloacetic acid formation potential (HAAFP, 27.2 ± 14.0%). CER media required 6-7 months to biologically acclimate, while filters containing GAC and anthracite were biologically active (>100 ng of ATP/g media) following 30-45 days of operation. Once acclimated, ATP values of 243 and 208 ng/g attained for CER 1.0 and 1.2, respectively, were statistically comparable to GAC (244 ng/g) and higher than anthracite (110 ng/g), however this did not translate into greater organics removal. Esterase and laccase enzyme kinetics were highest for GAC, while CER was shown to have greater biodegradation potential than anthracite. The four media types attained similar turbidity reduction (p > 0.05), however ceramic media filters were observed to have run times which were 1.5-2.3 times longer when compared to anthracite, which could represent potential cost savings in terms of energy for pumping and backwash requirements. Overall, ceramic media was shown to be a potential alternative to anthracite when considering biofiltration, especially during cold water conditions (T < 10 °C).
... Average influent and effluent TOC corresponded to 9.1 and 4.9 mg/L, respectively, yielding an average TOC removal of around 46 %. Similar TOC removal efficiency was obtained by Melin and Odegaard (1999), who also employed an upflow biofilter filled with expanded clay media. These authors reported a TOC removal of 18-37 % in the treatment of humic water previously subjected to ozonation to enhance its biodegradability. ...
The combination of biological and chemical oxidation processes is an interesting approach to remove ready, poor, and non-biodegradable compounds from complex industrial wastewaters. In this study, biofiltration followed by H2O2/UV oxidation (or microfiltration) and final reverse osmosis (RO) step was employed for tertiary treatment of an oil refinery wastewater. Biofiltration alone allowed obtaining total organic carbon (TOC), chemical oxygen demand (COD), UV absorbance at 254 nm (UV254), ammonium, and turbidity removal of around 46, 46, 23, 50, and 61 %, respectively. After the combined biological-chemical oxidation treatment, TOC and UV254 removal amounted to 88 and 79 %, respectively. Whereas, the treatment performance achieved with different UV lamp powers (55 and 95 W) and therefore distinct irradiance levels (26.8 and 46.3 mW/cm(2), respectively) were very similar and TOC and UV254 removal rates were highly affected by the applied C/H2O2 ratio. Silt density index (SDI) was effectively reduced by H2O2/UV oxidation, favoring further RO application. C/H2O2 ratio of 1:4, 55 W UV lamp, and 20-min oxidation reaction corresponded to the experimental condition which provided the best cost/benefit ratio for TOC, UV254, and SDI reduction from the biofilter effluent. The array of treatment processes proposed in this study has shown to be adequate for tertiary treatment of the oil refinery wastewater, ensuring the mitigation of membrane fouling problems and producing a final effluent which is suitable for reuse applications.
... Most of the ozone-biofiltration systems reported in literature deal with the removal and fate of primary organic substrates defined as NOM, UVA 254 , DOC, humic substances, AOC, BDOC, ozonation and chlorination by-products (Carlson and Amy 2001, Graham 1999, Griffini et al. 1999, Hozalski et al. 1999, Huck 1999, Melin and Odegaard 1999, Moll and Summers 1999, Odegaard et al. 1 999, Rittmann et al. 2002a, Sumitomo 1992, Urfer and Huck 2000, Nishijima et al. 2003. These reports have concluded that ozone helps with the biodegradation filters by hydrolyzing large molecules and making them easier to degrade by the bacteria in biofilm. ...
... This is especially important if water has low pH or low buffer capacity. Filtralite media is manufactured by Norsk Leca for biofilters treating wastewater and potable water (Melin and Ødegaard, 1999). ...
Four parallel biofilters were tested for treatment of ozonated humic water. Two of them contained Kaldnes plastic cylinders (KMT media), one marble and one expanded clay aggregates (Filtralite NC) as biofilm media. Dual-media filter was used for removal of bacteria from biofilter effluents. After four months of operation, average TOC removal was 37-38% and COD(Mn) removal was 43-45% in the ozonation/biofiltration process. Ozonation removed 83% of colour from the raw water. Over 83% removal of ozonation by-products (aldehydes and ketoacids) was also achieved. Biofiltration increased the levels of heterotrophic bacteria in the water but they were reduced by 88% in the dual-media filter. The biofilter media did not have significant effect on treatment efficiency at the empty bed contact time of 30-40 min.
... To produce an aesthetically pleasing drinking water, the discoloration of the river water is removed prior to filtration by using ozone, a powerful oxidant. The high molecular weight, poorly biodegradable humic and fulvic substances present are oxidised into biodegradable, low molecular weight compounds (Melin and Odegaard, 1999). Therefore, ozonation increases the biodegradable organic carbon content of the raw water, encouraging the growth of heterotrophic micro-organisms within the schmutzdecke. ...
The unique feature of slow sand filters is the schmutzdecke, a biofilm formed at the sand - water interface. Scanning electron microscopy was used to observe the surface of sand obtained from the schmutzdecke of a newly seeded and a mature slow sand filter. The complex nature of the biofilm formed on the sand was observed. A distinct difference was seen between the freshly seeded schmutzdecke compared to the schmutzdecke from a mature filter. It was found that a larger amount of extracellular matrix was present within the schmutzdecke removed from a mature filter. The images obtained show that sand, at the sand-water interface of slow sand filters, offers an attractive environment for the colonisation of a variety of micro-organisms including diatoms, algae, bacteria and their extracellular products.
... Humic substances give yellow-brown color to water (Bennett and Darikas, 1993), form complexes with pesticides and heavy metals (Hiraide, 1992;Pacheco et al., 2003), cause plugging and fouling problems on membranes (Kulovaara et al., 1999), increase the bacteria regrowth potential in distribution system resulting in pipe corrosion (Camper, 2004) and most importantly they react with chlorine and cause hazardous disinfection by-products in water (Rook, 1974). Thus many different treatment technologies such as enhanced coagulation, advanced oxidations (Kitis and Kaplan, 2007), adsorption (Peng et al., 2006), biofiltration (Melin and Odegaard, 1999;Sobecka et al., 2006), membrane processes (Petala and Zouboulis, 2006), and photocatalysis (Bekbolet et al., 1998;Selcuk et al., 2003;Murray and Parsons, 2004) were applied in order to remove humic acid (HA) from water. UV/TiO 2 is a promising alternative purification and disinfection method (Dunlop et al., 2002;Malato et al., 2003;Lhomme et al., 2008). ...
In this study, photocatalytic (PC) and photoelectrocatalytic (PEC) treatment methods were comparatively investigated as a possible means of removing humic acid (HA) following absorbance at 254 nm (UV(254)) and total organic carbon (TOC) analysis. The enhanced HA degradation rates were obtained in the PEC system over the conventional PC process under acidic, neutral and alkaline conditions. Preliminary and binary experiments were performed to determine the selectivity of the photoanode in terms of HA and chloride oxidation. TOC, chlorine and photocurrent parameters proved that HA was selectively removed before chlorine generation. The inhibitory effect of carbonate ions on the performance of photoanode was also studied under different pH values.
Solar radiation experiments showed a shift in the composition of natural organic matter (NOM). Due to irradiation, the concentration of high molecular weight (HMW) molecules decreased, and that of the low molecular weight (LMW) fraction increased. Microbiological analyses showed that biodegradation was neglectable. To assess the consequences for water treatment processes, coagulation jar tests were performed by comparing the removal effectivity for NOM fractions from irradiated and unirradiated raw water. The degree of dissolved organic carbon (DOC) removal by coagulation was lower for irradiated waters. As primarily HMW organic compounds are removed by coagulation, the decrease in coagulation performance is attributed to the increase in the LMW concentration due to photochemical reactions induced by solar radiation. Flocs were about 15% larger for irradiated water. Possibilities to adapt water treatment to respond to changes in DOC composition and concentration are outlined. Ozonation-biofiltration is judged as the most promising treatment process to cope with climate change related challenges in drinking water treatment.
The relative critical overview of indicators, which set norms to the drinking water and are used as background for regulatory instruments of the USA, the EU, the WHO, Ukraine and Russia, has been revealed. The analytical review of current problems in drinking water preparation technology at centralized drinking water treatment plants has been delivered. The role of natural organic compounds of natural origin in drinking water quality has been revealed. The application of different technological measures to prepare high quality drinking water has been analysed and explained. The influence of condition of water distribution system on the drinking water quality has been evaluated. It has been cited the examples of modern technological systems of drinking water treatment. A new concept of supply the population with a quality drinking water has been introduced. It is based on representation the need to consume adequate water by a person, which is genetically safe, comprises no man induced alloys, and is characterized by occurrence of such natural substances and microelements that are easiest to digest for a body from water.
A small full-scale ozonation/biofiltration plant was operated for 1.5 years in mid-Norway. A three-media biofilter was used to remove biodegradable organic matter from ozonated water. The biofilter contained granular activated carbon (GAC), phonolith and CaCO3 and was operated at 26-30 min. empty bed contact time. The water temperature varied between 2 and 14°C but the biofilter was operated most of the time at temperatures below 10°C. Total phosphorus concentration in the raw water was also very low (1.1-2.0 μg L-1). Batch tests showed that low phosphorus concentration and low temperature are potential limitations for microbial growth and organic carbon removal. Initially, the GAC adsorbed organic carbon while the microbial activity was building up. Most of the adsorption capacity was used after 1.5 months of operation. After this period, 14-33% of the TOC was removed (average 23%). Although the overall TOC removal in the process was modest, average BDOC removal of 55% was observed even at 3°C. Ozonation was effective in reducing colour with average removal of 80%. The results show that significant biological activity can be achieved and maintained in biofilter treating ozonated water even at low temperatures and phosphorus limited conditions.
Biological pre-filtration technique for the removal of natural organic and inorganic compounds from surface water was described. Biological pretreatment was shown as a viable process to remove dissolved manganese from difficult to treat humic surface waters. It was observed that the biofilters reduced a fraction of hydrophobic NOM that otherwise passed the subsequent chemical treatment to a large extent. It was also found that the rapid filtration pre-treatment of surface water caused a rapid pressure drop in nanofilter (NF) membranes operated at a comparably low flux.
The effects of UV-C (254 nm) radiation on the biodegradability and chlorine demand of natural organic matter (NOM) were investigated. Biodegradability was assessed using the biological regrowth potential and biodegradable dissolved organic carbon (BDOC) methods and remained unchanged for doses of 40 to 1,000 mJ cm -2, but increased when the water was exposed to higher doses. The DOC concentration and UV absorbance values were reduced in UV-treated waters, but the chlorine demand remained the same as for raw water. Exposure of the UV-treated water to microbial treatment (via the BDOC test) gave a reduced DOC concentration and chlorine demand, indicating that the chlorine-consuming compounds resulting from irradiation were biodegradable. High performance size exclusion chromatography showed that both biodegradability assessment methods preferentially removed smaller molecules. Formaldehyde, acetaldehyde, glyoxal and glyoxylic acid were detected in UV-treated waters and were removed by the BDOC test. Chlorine demand correlated well with the concentration of low molecular weight (LMW) carbonyl compounds, which can be considered to be a surrogate for a large number of unidentified organics contributing to the chlorine demand and biodegradability.
Hydroponics culture greenhouses usually work in closed and semi-closed irrigation systems for nutrients and water-saving purposes. Photo-Fenton reaction has been revealed as an efficient way to depollute that kind of recycled effluents containing pesticides, even for high salinity concentrations. However, the inefficacy of organic matter chemical depletion imposes the use of a subsequent treatment. This work proposes the suitability of an integration of that named Advanced Oxidation Process with a subsequent bioreactor to treat greenhouse lixiviates effluents at high or extremely high conductivity (salts concentration up to 42 g·L(-1)). As a first step of the study, the performance of a series of sequencing batch reactors was monitored in order to check biocompatibility of photo-Fenton pretreated effluents depending on their salinity content. On the second step, those same pretreated effluents were loaded to a biofiltration column filled with expanded clay. Finally, bacterial 16S rRNA gene sequencing was applied to analyze microbial diversity of the biomass developed in the column. Results stated that the chemical-biological coupled system is effective for the treatment of water effluents containing pesticide. The integrated system is able to deplete more than 80% of the organic load, even for extremely high salinity.
In this work heterogeneous photocatalysis has been used in order to eliminate Cr(VI) as well as humic acid in a laboratory reactor and in a pilot reactor. The reactors have been constructed with proportional geometric properties and similar nominal powers. In the laboratory reactor a kinetic study of the reduction of Cr(VI) to Cr(III) has been done for different concentrations of the catalyst at pH 4 and 7. The influence in the increase of the reduction of chromium(VI) that is obtained by the presence of humic acid has been determined. It has been verified that all the reactions possess pseudo-first-order kinetics, and the values of the apparent kinetic constants obtained for all systems studied have been compared. These values have allowed selection of the values of the variables to be used in the pilot reactor as it is desired to eliminate Cr(VI) by reduction and precipitation and humic acid by oxidation. A comparative evaluation of the efficiencies of the reactors was based on kinetic determinations.
Highlights
► Variations in AOC and microbial diversities in an advanced water treatment plant were evaluated. ► Effects of hydrological factors on AOC concentrations in raw water samples were studied. ► Higher AOC was observed in wet seasons due to the resuspension of organic-contained sediments. ► Biofiltration system was able to remove AOC effectively. ► Higher hydraulic retention time caused higher microbial colonies and diversity in the biofilter.
The enhancement of TOC, CODMn, and UV254 reduction in the conventional drinking water treatment process by pre-ozonation was investigated in South China on treating dam source water with a pilot plant consisting of pre-ozonation, coagulation-sedimentation, and filtration units. Pre-ozonation enhanced the reduction of NOM in the conventional coagulation-sedimentation and filtration process, and the total removals of UV254, CODMn and TOC were improved for 34.6%, 18.1% and 15.3%, respectively by the adoption of pre-ozonation under an ozone dose (in ozone consumption base) of 0.85 mg/L. The enhancement of UV254 and CODMn removals was mainly achieved through direct ozonation on humic substances, and that for TOC removal was achieved through biodegradation in sand filtration. In comparison with the TOC removal of 38%, a removal of 49% was acquired for SDS-THM under a pre-ozonation dose of 0.80 mg/L, indicating the selective removal of THMFP. The reduction of SDS-THM paralleled the reduction of CODMn to a significant degree, suggesting that the CODMn might be an effective surrogate parameter for SDS-THM if the raw water does not contain the reductive inorganic matters. Although the source water contains 13.2–27.0μg/L bromide, the formation of bromate was negligible when the ozone dose was below 1.0 mg/L.
This study addresses the removal of humic acid (HA) dissolved in an aqueous medium by a photoelectrocatalytic process. UV254 removal and the degradation of color (Vis400) followed pseudo-first order kinetics. Rate constants were 1.1 × 10−1 min−1, 8.3 × 10−2 min−1 and 2.49 × 10−2 min−1 (R2 > 0.97) for UV254 degradation and 1.7 × 10−1 min−1, 6.5 × 10−2 min−1 and 2.0 × 10−2 min−1 for color removal from 5 mg dm−3, 10 mg dm−3 and 25 mg dm−3 HA respectively. Following a 2 h irradiation time, 96% of the color, 98% of the humic acid and 85% of the total organic carbon (TOC) was removed from an initial 25 mg dm−3 HA solution in the photoanode cell. Photocatalytic removal on the same photoanode was also studied in order to compare the two methods of degradation. Results showed that the photoelectrocatalytic method was much more effective than the photocatalytic method especially at high pH values and with respect to UV254 removal. The effect of other important reaction variables, eg pH, external potential and electrolyte concentration, on the photoelectrocatalytic HA degradation was also studied. Copyright © 2003 Society of Chemical Industry
The effect of biofilter loading rate on the removal of organic ozonation by-products (OBPs) was studied in three biofilters used for the pretreatment of drinking water. One of the biofilters contained plastic biofilm media (KMT) and the two others contained expanded clay aggregates (Filtralite). Tests were carried out with ozonated humic water at several OBP concentration levels using empty bed contact times (EBCTs) from 6.2 to 48 min. The sum of aldehyde (formaldehyde, acetaldehyde, glyoxal and methyl glyoxal) and acetone concentrations ranged from 21 to 77 μg l−1 in the ozonated water. The total ketoacid (glyoxylic, pyruvic, and ketomalonic acids) concentrations varied from 92 to 521 μg l−1. The results were modelled using a first-order model including parameter for minimum substrate concentration (Smin). The OBPs showed different sensitivities to decreasing EBCT. Formaldehyde and pyruvic acid had the highest specific removal rates and their removal was little affected by increased loading rate. Ketomalonic acid had the lowest specific removal rate and its removal efficiency was reduced most with decreasing EBCT. The other studied OBPs had specific removal rates close to each other. The ketoacids had higher Smin concentrations than aldehydes and the Smin concentrations were influenced by the influent OBP concentrations. The biofilter media did not have a significant effect on OBP removal efficiency. Generally, over 80% removal efficiency was obtained for OBPs at EBCTs over 20 min. The significance of OBP concentrations close to Smin for the biological stability of drinking water needs to be determined.
Humic substances can be removed from water by a number of different treatment processes because the humic substances are high molecular weight organic molecules carrying a negative charge, like colloids. The conventional treatment method is by coagulation/floc separation, but also sorption processes like ion exchange and adsorption on activated carbon as well as membrane filtration processes and oxidatiort/biofiltration processes can be used. In this paper an overview of design and operational experiences with all these treatment processes is given based on the experiences that have been gathered in Norway during the last 25 years.
This study addresses the application of a photoelectrocatalytic (PEC) system with separated hole and electron reactions to treat humic acid (HA) from river water. A TiO2 electrode, coated by the sol-gel method, is used for that purpose. The degradation of humic acid in the river water was followed with respect to time using parameters of UV254, color and total organic carbon (TOC). For comparison purposes the photocatalytic (PC) removal of HA was also studied on the same photoanode. The obtained results showed that the PEC system was much more effective than the PC method. The effect of other important reaction variables, such as external potential, oxygen and UV intensity on HA degradation were also investigated. For all the external applied potential conditions and UV intensity range over 90% removal of UV254 and color were obtained with the PEC system while TOC removal was between 58-80%.
Biofouling control is considered as a major challenge in operating membrane systems. A lab-scale RO system was setup at a local water reclamation plant to study the feasibility of using biofiltration as a pretreatment process to control the biofouling. The biological activity in the RO system (feed, product, reject streams) was tested using the standard serial dilution plating technique. Operational parameters such as differential pressure (DP) and permeate flowrate of the system were also monitored. Effects of biofilter on AOC and DOC removals were investigated. Biofiltration was found to be a viable way of assimilable organic carbon (AOC) and dissolved organic carbon (DOC) removals, with removal efficiencies of 40-49% and 35-45% at an empty bed contact time (EBCT) of 30 min. It was also found that using the biofiltration as a pretreatment reduced the rate of biofouling. It took only about 72 h for biofouling to have a significant impact on the performance of the RO membrane, when the system was operated without using biofiltration as pretreatment. There was, however, a five times increase in operational length to more than 300 h when biofiltration was used. This study presented the suitability of the biofilter as an economical and simple way of biofouling control for RO membrane.
Pilot-scale studies were conducted to determine the effects of preozonation and water column biofilm support media on slow sand filtration. The performance of the enhanced slow sand filters was compared with that of the full-scale treatment facility at Andover, Mass., which uses preozonation and granular activated carbon to enhance its conventional processes. Preozonation and biofilm support were observed to have a positive influence on filter performance, transformation of natural organic matter, microbiology, and removal of biodegradable dissolved organic carbon (BDOC). The pilot filter with the media of a larger effective size, an ozone dose of 2 mg per mg of nonpurgeable dissolved organic carbon (NPDOC), and biofilm support produced removals of turbidity, NPDOC, UV absorbance, and trihalomethane formation potential comparable to the full-scale facility. And the enhanced pilot filter produced a lower finished-water BDOC value than the full-scale plant. Thus, enhanced slow sand filters hold promise for utilities that must comply with the Surface Water Treatment Rule and future disinfection by-product rules.
A direct ion chromatography method was applied to the determination of short-chain carboxylic acids (acetic, formic, and oxalic) in drinking water treated with ozone. These organic acids were separated on an anion exchange column (Ionpac AS11; Dionex Corp., Sunnyvale, CA), using a 50-μL sample loop. Samples were collected from the ozone pilot plant of the Metropolitan Water District of Southern California to study the formation of carboxylic acids and their removal by two different types of biologically active filters. Preliminary results indicate that the carboxylic acid concentrations out of the ozone contactor were the greatest for oxalic acid (∼380 μg/L), followed by formic (∼130 μg/L) and acetic (∼60 μg/L) acid, and that the sum of the three acids on a carbon basis was ∼160 μg/L. Approximately 80 percent of these carboxylic acids were removed during biofiltration. Aldehydes and assimilable organic carbon (AOC) were also measured from the same batch of samples, and the removal percentages were similar to those obtained in the carboxylic acid analyses. The percent fractions of AOC at the ozone effluent for combined carboxylic acids and combined aldehydes were 36.9 and 3.7 percent, respectively.
This article presents data on the formation and removal of carboxylic acids in a full-scale treatment plant employing ozonation and biological filtration. Carboxylic acid concentrations increased after ozonation and decreased through subsequent filtration. Simple linear relationships between major water quality parameters (e.g., temperature, pH) and acid formation did not exist. Yields of carboxylic acids on ozonation were an order of magnitude greater than for the corresponding aldehyde. An empirical linear model could describe the removal of carboxylic acids through biological filtration from a practical point of view. However, the data suggest the removal mechanism may be complex. Although contact times in the filters were quite long (on the order of 30 min), removal of several carboxylic acids was incomplete (e.g., average effluent concentration of formate was 44 μg/L).
Although the biofiltration process may not control the design of a filter bed, results described here can help the engineer better understand the tradeoffs.
Pilot‐scale biofiltration experiments were conducted to determine how empty bed contact time (EBCT) and hydraulic loading rate (HLR) affected the removal of biodegradable organic matter (BOM). The removal of BOM formed during ozonation was measured as the reduction (resulting from biodegradation) of dissolved organic carbon in the filter; it was referred to as biodegradable dissolved organic carbon–filter (BDOC filter ). Ten ozone by‐products were measured to understand the composition of BDOC filter and to assess whether these by‐products might be used as a surrogate for BOM; none sufficed. BOM formed during ozonation limited the removal of BDOC during biofiltration with two exceptions: nonsteady‐state BOM loading conditions and inadequate EBCT. Both of these conditions were limited by biomass formation. HLR had no effect on BDOC filter even though markedly different biomass profiles were observed.
A steady-state biofilm is defined as one that has neither net growth nor decay over time. The model, developed for steady-state-biofilm kinetics with a single substrate, couples the flux of substrate into a biofilm to the mass (or thickness) of biofilm that would exist at steady-state for a given bulk substrate concentration. Based on kinetic and energetic constraints, this model predicts for a single substrate that a steady-state bulk concentration, Smin, exists below which a steady-state biofilm cannot exist. Thus, in the absence of adsorption of bacteria from the bulk water and for substrate concentration below Smin, substrate flux and biofilm thickness are zero. Equations are provided for calculating the steady-state substrate flux and biofilm thickness for S greater than Smin. An example is provided to demonstrate the use of the steadystate model.
Carboxylic acids were formed upon ozonation but were not completely removed by biological filtration, which could have implications for bacterial regrowth in distribution systems.
This article presents data on the formation and removal of carboxylic acids in a full‐scale treatment plant employing ozonation and biological filtration. Carboxylic acid concentrations increased after ozonation and decreased through subsequent filtration. Simple linear relationships between major water quality parameters (e.g., temperature, pH) and acid formation did not exist. Yields of carboxylic acids on ozonation were an order of magnitude greater than for the corresponding aldehyde. An empirical linear model could describe the removal of carboxylic acids through biological filtration from a practical point of view. However, the data suggest the removal mechanism may be complex. Although contact times in the filters were quite long (on the order of 30 min), removal of several carboxylic acids was incomplete (e.g., average effluent concentration of formate was 44 μg/L).
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.
Many factors could account for the good performance of coal‐based GAC biofilters, including the quantity of biomass attached to the media.
A phospholipid analytical technique was used to measure the amount of biomass attached to the surfaces of drinking water filter media. The method was reproducible and able to detect significant differences in biomass concentrations in different filters and at various depths within filters. The amount of attached biomass decreased as filter depth increased, suggesting that most removal of natural organic matter occurred at the top of the biofilters. The results show that granular activated carbon media were able to hold more biomass than were anthracite and sand media and that concentrations of biomass in anthracite‐sand filters were lower with chlorine in the backwash water.
Batch experiments with two Texas surface waters were employed to study the removal of the precursors of trihalomethanes (THMs) and haloacetic acids (HAAs) by ozonation alone and with subsequent biodegradation. Ozone doses of 0.5 to 5 mg/mg total organic carbon (TOC) were tested. Little biodégradation of THM precursors occurred in the absence of preozonation, whereas 25-30 percent of HAA precursors were biodegraded without ozonation. Ozonation and biodegradation combined removed up to 50 percent of THM precursors and up to 70 percent of HAA precursors. In some cases, ozone dosages larger than that now used in practice (1 mg/mg TOC) enhanced removal by the two processes combined. HAA precursors appeared to be more biodegradable than THM precursors, and ozonation enhanced HAA precursor biodegradation more than precursor biodegradation. Se emplearon experimentos en tandas en las aguas superficiales de dos sitios en Texas con el fin de estudiar la remoción de los precursores de trihalometanos (THMs) y los ácidos haloacéticos (HAAs) por medio de la ozonización pura y subsecuente biodegradación. Se probaron dosis de ozono de 0.5 a 5 mg/mg del carbón orgánico total (TOC). Ocurrió poca biodegradación de los precursores del THM cuando la preozonización estaba ausente, mientras que de un 25 a un 30 porciento de los precursores de HAA se biodegradaron sin ozonización. La ozonización y la biodegradación combinada removieron hasta el 50 porciento de los precursores de THM y hasta el 70 porciento de los precursores de HAA. En algunos casos, dosis más grandes que las que normalmente se usan hoy (1 mg/mg TOC) incrementaron la remoción con los dos procesos combinados. Se descubrió que la presencia de una concentración significativa de bromo en una fuente de agua complicó el tratamiento del agua y la interpretación de los datos del comportamiento del proceso.
Recently developed analytical techniques allow for the quantification of C₁-C₁₀ straight-chain aliphatic aldehydes, benzaldehyde, and the dialdehydes glyoxal and methylglyoxal down to 1 μg/L. These compounds are formed as the partial oxidation products of the reaction between disinfectants (particularly ozone) and naturally occurring organic matter. Various full-scale and pilot treatment plants in North America that employ ozonation were surveyed using these techniques, which showed a trend toward both monoaldehyde and dialdehyde formation. Once formed, aldehydes can persist in the water and their concentrations may even increase following postdisinfection. An effective means of aldehyde removal appears to be the use of biologically active granular activated carbon filters, whose filtration mode determines the actual degree of removal. Dialdehydes require a slower filtration rate for their removal than formaldehyde and acetaldehyde. Técnicas analíticas creadas recientemente permiten la cuantificación de las cadenas lineales de aldehidos alifáticos CiCio, el benzaldehído, y los dialdehídos glyoxiales y metilglioxiales hasta de 1 μg/L. Estos compuestos se forman como productos de oxidación parcial provenientes de la reacción que se produce entre los desinfectantes (en especial el ozono) y la materia orgánica natural. Usando estas técnicas, se investigaron varias plantas de escala normal y escala de planta piloto en norteamérica que emplean la ozonización. Las plantas demostraron una tendencia hacia la formación de monoaldehídos y dialdehídos. Una vez formados, los aldehidos pueden permanecer en el agua, y sus concentraciones pueden aumentar después de la post-desinfección. Los filtros de carbón granular activado que son biológicamente activos parecen ser métodos efectivos para remover los aldehidos, y su medio de filtración determina el grado actual de remoción. Los dialdehídos requieren menores velocidades de filtración que los formaldehídos y los acetaldehídos.
The purpose of the survey described in this article was to take stock of where and how ozone technology is being used for water treatment in North America. Specific objectives were to provide a data base on existing plants, to project future conditions, and to learn from previous experience. El propósito de la investigación descrita en este artículo fué el de hacer un inventario de dónde y como se usa la tecnología del ozono para el tratamiento de aguas en Norte America. Objetivos especificos fueron los de proveer una base de datos de las plantas existentes para proyectar problemas futuros y aprender de las experiencias anteriores.
Ozonation by-products were analyzed for two surface water sources in Southern California-Los Angeles Aqueduct Water (LAAW) and State Project Water (SPW). Included are data obtained when LAAW was being treated at the Los Angeles Aqueduct Filtration Plant and similar data obtained during a two-day experiment in which the plant was treating SPW. Some batch-scale ozonation studies are also reported. Ozonation by-products were monitored using three methods: closed-loop stripping analysis, nonionic resin accumulation, and a direct aqueous derivatization method for low-molecular-weight aldehydes, each followed by gas chromatography-mass spectrometry analysis of the extracts. The major neutral by-products appear to be aliphatic aldehydes, but the levels are unexpectedly low in SPW compared with LAAW treated under similar conditions. Low levels of several other compounds were found in ozonated water, including bromoform and some compounds tentatively identified as ketones.
Impacts of ozonation followed by biological filtration on the formation of disinfection byproducts and the production of biologically stable water were studied on pilot plant and full-scale at two U.S. locations (Oakland, CA and Tampa, FL). Also evaluated is a method to estimate bacterial regrowth potential by comparing it to assimilable organic carbon (AOC) measurements. At both locations, settled plant water is diverted to the pilot plant where it is split into two parallel trains. One train is ozonated, then Filtered through anthracite/sand dual media followed by GAC or through a GAC/sand dual media filter. The other train (control) is identical except that the water is not ozonated. The full scale plants have sedimentation, ozonation, then GAC/sand filtration.
An extensive review of the technical literature was conducted in order to determine the advantages and disadvantages of the various media used for biological filtration of ozonated drinking water. Granular activated carbon (GAC) filters were found to be significantly more efficient than conventional filters such as sand and anthracite coal. The type of activated carbon also impacted the performance of biofilters; due to their greater adsorption capacity, microporous GACs were found to be better suited than macroporus GACs.
Biodegradable organic matter formed during the ozonation of natural waters was fractionated into rapidly and slowly degradable components based on measurements of biodegradable organic carbon (BDOC). The rapidly degradable fraction (BDOCrapid) was defined using the specific BDOC reactor incubation time that resulted in biodegradation similar to that in a pilot scale biofilter. Ozone dose was found to increase the formation of BDOCrapid up to a transferred dose of 1.0 to 1.5 mg O3/mg DOC. This fraction was insensitive to DOC quantity or character. The formation of BDOCslow was not sensitive to ozone dose but was sensitive to DOC quantity.
Optimizing the coagulant dosage offers the most effective means of maximizing TOC removal; biofiltration may be used to augment removals.
Laboratory‐scale biologically active sand filters were used to evaluate the effect of natural organic matter (NOM) source and empty bed contact time (EBCT) on the removal of total organic carbon (TOC) from coagulated and ozonated NOM solutions. Ozonation at dosages in the range of 2.0 to 4.0 mg ozone/mg TOC were used to enhance biodegradation of the organic matter. TOC removal in the biofilters ranged from 16 to 33 percent of the biofilter influent concentration. TOC removal was significantly affected by the source of the organic carbon but was independent of EBCT in the range of 4 to 20 min. In the context of an entire water treatment plan, including coagulation and biofiltration, the contribution of biofiltration to TOC removal was relatively small compared with total removals across the entire treatment train. In one biofiltration experiment, however, removal of the biodegradable fraction of TOC was 100 percent, suggesting that biofilters may be effective in reducing subsequent regrowth in distribution systems.
Batch experiments proved to be effective for obtaining a preliminary estimate of the biodegradation potential of NOM.
Batch degradation experiments were conducted to evaluate the extent of biodegradation of natural organic matter (NOM) as a function of ozone dosage. Four NOM sources that might be encountered in drinking water treatment were characterized and tested. The biodegradability of all sources was enhanced as the ozone dose was increased from 0 to 7.3 mg ozone/mg total organic carbon (TOC). Increased ozonation resulted in cnsistently improved TOC removals for NOM souces having a large fraction of high‐molecular‐weight organics. Greater biodegradation was observed for the unozonated sources with lower UV‐absorpotion ‐to‐TOC rations and larger fraction of low‐molecular‐weight organics.
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.
The effect of biofilter loading rate on the removal of organic ozonation by-products (OBPs) was studied in three biofilters used for the pretreatment of drinking water. One of the biofilters contained plastic biofilm media (KMT) and the two others contained expanded clay aggregates (Filtralite). Tests were carried out with ozonated humic water at several OBP concentration levels using empty bed contact times (EBCTs) from 6.2 to 48 min. The sum of aldehyde (formaldehyde, acetaldehyde, glyoxal and methyl glyoxal) and acetone concentrations ranged from 21 to 77 μg l−1 in the ozonated water. The total ketoacid (glyoxylic, pyruvic, and ketomalonic acids) concentrations varied from 92 to 521 μg l−1. The results were modelled using a first-order model including parameter for minimum substrate concentration (Smin). The OBPs showed different sensitivities to decreasing EBCT. Formaldehyde and pyruvic acid had the highest specific removal rates and their removal was little affected by increased loading rate. Ketomalonic acid had the lowest specific removal rate and its removal efficiency was reduced most with decreasing EBCT. The other studied OBPs had specific removal rates close to each other. The ketoacids had higher Smin concentrations than aldehydes and the Smin concentrations were influenced by the influent OBP concentrations. The biofilter media did not have a significant effect on OBP removal efficiency. Generally, over 80% removal efficiency was obtained for OBPs at EBCTs over 20 min. The significance of OBP concentrations close to Smin for the biological stability of drinking water needs to be determined.
This paper summarizes the main applications of ozonation and associated oxidation processes in the treatment of natural waters (surface and ground waters) for drinking water production. In fact, oxidants may be added at several points throughout the treatment: pre-oxidation, intermediate oxidation or final disinfection. So, the numerous effects of chemical oxidation are discussed along the water treatment: removal of inorganic species, aid to the coagulation-floculation process, degradation of organic matter and disinfection. Of prime importance in potable water production is the removal of organic matter (natural humic substances, as well as micropollutants, especially pesticides) to avoid degradation of the distributed water (mainly bad odors and tastes; formation of disinfection by-products such as trihalomethanes; microbial regrowth in the distribution system). Consequently, this point has been particularly detailed in this paper. As a matter of fact, complete mineralization hardly occurs during the process; as a consequence, further treatment (i.e. sand or granular activated carbon filtration) is required to improve the distributed water quality, and to meet the drinking water regulations.
The Development of an OzonationlBiofiltration Process for the Removal of Humic Substances. In: Advances in Slow Sand and Alternative Biological Filtration
- H Odegaard
Odegaard, H. (1996). The Development of an OzonationlBiofiltration Process for the Removal of Humic Substances. In: Advances in Slow Sand and Alternative Biological Filtration, N. Graham and R. Collins (eds.), John Wiley & Sons, pp. 39-49.
Treatment of Humic Water by Ozonatton
- O Kolstad
Kolstad, O. (1997). Treatment of Humic Water by Ozonatton/Biofiltration, M.Sc. thesis, Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology (in Norwegian).
Formation and Removal of Aldehydes in Plants that Use Ozone Idennflcation and Quantification ofOzonation By-products: Keto-acids in Drinking Water
- H S Weinberg
- W H Glaze
- S W Krasner
- M J Sclimenti
Weinberg, H. S., Glaze, W. H., Krasner, S. W. and Sclimenti, M. J. (1993). Formation and Removal of Aldehydes in Plants that Use Ozone. J. Am. Wat. Works Assoc, 85(5), 72-85, Xie, Y. and Reckhow, D. A. (1992). Idennflcation and Quantification ofOzonation By-products: Keto-acids in Drinking Water. Paper #5 In The Proceedings ofthe IDA Pan American Committee, Pasadena Conference: Ozonationfor Drmking Water treatment, March 10-13, 1992.
Removal ofOzonation By-products in Biologically Active Filters: Development of a Mechanistic Modeling Approach. In: Advances in Slow Sand and Alternative Biological Filtration
- S D J Booth
- P M Huck
- R M Slawson
- B J Butler
Booth, S. D. J., Huck, P. M., Slawson, R. M. and Butler, B. J. (1996). Removal ofOzonation By-products in Biologically Active Filters: Development of a Mechanistic Modeling Approach. In: Advances in Slow Sand and Alternative Biological Filtration, N. Graham and R. Collins (eds.), John Wiley & Sons, pp. 71·77.
Ion-Chromatographic Determination of Three Short-Chain Carboxylic ACids In Ozonated Dnnkmg Water The Performance and Microbiology of Ozone-Enhanced Biological Filtranon
- Kuo
- H.-C Wang
- S W Krasner
- M K Davis
- J P Malley Jr
- T T Eighmy
- M R Collins
- J A Royce
- D F Morgan
Kuo, c-v., Wang, H.-C., Krasner, S. W. & Davis, M. K. (1996). Ion-Chromatographic Determination of Three Short-Chain Carboxylic ACids In Ozonated Dnnkmg Water. In Water Disinfection and Natural Organic Matter, R. A. Minear and G. L. Amy (eds.), ACS Symposium Senes 649, Amencan Chenucal SOCiety, Washington DC, pp. 350-365. Malley Jr., J. P., Eighmy, T. T., Collins, M. R., Royce, J. A. and Morgan, D. F. (1993). The Performance and Microbiology of Ozone-Enhanced Biological Filtranon. J. Am Wat Works Assoc, 85(12),47-57.