Article

Biofiltration of ozonated humic water in expanded clay aggregate filters

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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.

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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.
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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).
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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
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Removal ofOzonation By-products in Biologically Active Filters: Development of a Mechanistic Modeling Approach. In: Advances in Slow Sand and Alternative Biological Filtration
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Ion-Chromatographic Determination of Three Short-Chain Carboxylic ACids In Ozonated Dnnkmg Water The Performance and Microbiology of Ozone-Enhanced Biological Filtranon
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