Relationships among trihalomethane formation potential, organic carbon and lake enrichment

Trihalomethanes (THMs) are potential carcinogens formed from the reaction of the disinfectant chlorine with organic matter in the source water. This study of Kansas drinking water supply lakes evaluates the relationship among THM formation potential (THMFP), organic carbon and lake trophic state (LTS). THMFP was positively correlated to organic carbon. Total THMFP and total organic carbon were positively correlated to LTS, an estimator of lake enrichment, when very turbid lakes were omitted. These very turbid lakes (due to high suspended solids concentrations) had higher than expected THMFP, based on LTS, and higher organic carbon concentrations. THM data measured in the treated drinking water were positively correlated to THMFP, total organic carbon and LTS. The levels of organic carbon that contribute to THMs are a result of lake and watershed factors related to increasing levels of enrichment and suspended sediments. These factors are controllable by appropriate management practices.     

Kinetics of peat soil dissolved organic carbon release from bed sediment to water. Part 1. Laboratory simulation

Temporary water reservoirs built upon peat soil may exhibit water quality impairment from elevated dissolved organic carbon (DOC). Microbiological decay of the organic carbon in the bed with subsequent release produces "tea" colored water which may require treatment prior to use. This paper describes laboratory experiments designed to obtain data on the release process of DOC from soils containing 0.65%, 10% and 19% carbon. Parallel experiments with and without sodium azide treatment clearly distinguished the initial release of a porewater residual fraction and the microbial produced fraction. A one to two day quick-release DOC fraction, which ranges from 28% to 50%, first emerged from the bed, Step-1. This was followed by a constant rate of DOC production over four weeks, Step-2. The Step-2 average production rates were 3.4, 12, and 31 mg DOC/kg(dry)/day for the respective soils and increased as soil carbon content increased. The inorganic carbon (IC) behaved oppositely; its rate of production decreased with increasing soil carbon. A consistent and simple rate equation described the Step-2 DOC production process. This and other evidence obtained provided the basis for developing a mathematical model that couples both steps of the bed-to-water DOC release chemodynamics. The model is presented in a companion paper (Part-2).     

Kinetics of peat soil dissolved organic carbon release to surface water. Part 2. A chemodynamic process model

Temporary water reservoirs built upon peat soil may exhibit water quality impairment from elevated dissolved organic carbon (DOC). Microbiological decay of the organic carbon in the bed with subsequent release produces "tea" colored water which may require treatment prior to use. This paper contains a process-based mathematical model that quantifies the DOC release from the bed and its build-up in the water column. The model elements are based on microbial DOC production rates and bed sediment transport kinetics describing its' release from the organic soil systems. It relies on laboratory data obtained from an experimental study, Part 1, designed to simulate the DOC chemodynamics of aquatic reservoirs built upon peat soils. A two-step DOC release process was structured based on the experimental findings. The model mechanism assumes a quick release fraction that characterizes the upper soil surface layers as a "tea bag" type release process. This is followed by a fraction that is continuously produced and then released at a constant rate overtime by on-going microbial processes within the upper soil layers. The depth of the active layer, selected as h* = 0.3 cm, is the single adjustable parameter in the model. Concentration predictions of the are consistent with the laboratory simulations and field observations. Measured vs. model-calculated DOC concentrations for both in the microcosm bed and water column are used to test critical features of the proposed model. As conceived and structured it appears to be a realistic first step in quantifying the DOC release consequences for the water column of a reservoir sited upon a peat-soil bed. The development ends with an application to a hypothetical reservoir in order to illustrate model strengths and uncertainties.     

Characteristics of biotic and abiotic removals of dissolved organic carbon in wastewater effluents using soil batch reactors.

Biodegradable dissolved organic carbon (BDOC) analyses and abiotic adsorption of dissolved organic carbon (DOC) from different wastewater effluent were conducted to evaluate biotic and abiotic removal mechanisms as a function of the initial DOC concentration and source of DOC using soil batch reactors. To obtain high DOC concentrations, a laboratory-scale reverse osmosis unit was used. It was found that BDOC fraction was independent of the initial DOC concentration and was dependent on the source of wastewater and/or the types of wastewater treatment. The BDOC fractions varied from 9 to 73%. Trickling filter effluent (Tucson, Arizona) showed the highest BDOC, ranging from 65 to 73% biodegradable, while wastewater treated by the soil aquifer treatment (SAT) (NW-4) was found to be most refractory, with DOC removals of 9 to 14%. For nitrified/denitrified tertiary effluent (Mesa, Arizona) and secondary effluent (Scottsdale, Arizona), 36 to 42% removal of DOC was observed during the BDOC test. The amount of BDOC in the wastewater depended not on the concentration of DOC, but on the effectiveness of pretreatment. Abiotic adsorption capacity of wastewater effluent varied from 6 to 18%. Molecular weight distribution analyses showed that more than 50% of DOC in the Scottsdale concentrate had a molecular weight of less than 1000 Da, and no significant change in distribution profiles occurred after approximately 12% abiotic adsorption with both soils with acclimated microorganisms (SAT soil) and soils without acclimated microorganisms (non-SAT soils). Hence, preferential adsorption was not observed and the presence of acclimated microbes did not influence adsorption.     

Effects of dissolved organic carbon on sorption of 3,4-dichloroaniline and 4-bromoaniline in a calcareous soil

To evaluate the effects of dissolved organic carbon on sorption of 3,4-dichloroaniline (3,4-DCA) and 4-bromoaniline (4-BA) on soils, batch sorption experiments were carried out. The soil used was a typical calcareous soil from south-eastern Spain. Two different types of dissolved organic carbon were used, that is, dissolved organic carbon extracts from a commercial peat (DOC-PE) and high-purity tannic acid (DOC-TA). The experiments were carried out in a 0.01 M CaCl2 aqueous medium at 25 degrees C. The results obtained from the sorption experiments show that the presence of both DOC-PE and DOC-TA, over a concentration range of 15-100 mg l-1, produced in all cases, an increase in the amount of 3,4-DCA and 4-BA adsorbed on the soil studied.     

The influence of organic acids in relation to acid deposition in controlling the acidity of soil and stream waters on a seasonal basis

Much uncertainty still exists regarding the relative importance of organic acids in relation to acid deposition in controlling the acidity of soil and surface waters. This paper contributes to this debate by presenting analysis of seasonal variations in atmospheric deposition, soil solution and stream water chemistry for two UK headwater catchments with contrasting soils. Acid neutralising capacity (ANC), dissolved organic carbon (DOC) concentrations and the Na:Cl ratio of soil and stream waters displayed strong seasonal patterns with little seasonal variation observed in soil water pH. These patterns, plus the strong relationships between ANC, Cl and DOC, suggest that cation exchange and seasonal changes in the production of DOC and seasalt deposition are driving a shift in the proportion of acidity attributable to strong acid anions, from atmospheric deposition, during winter to predominantly organic acids in summer.     

Dissolved organic carbon from sewage sludge and manure can affect estrogen sorption and mineralization in soils

In this study, effects of sewage sludge and manure borne dissolved organic carbon (DOC) on 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) sorption and mineralization processes were investigated in three agricultural soils. Batch equilibrium techniques and equilibrium dialysis methods were used to determine sorption mechanisms between DOC, estrogens and the soil solid phase. It was found that that the presence of organic waste borne DOC decreased estrogen sorption in soils which seems to be controlled by DOC/estrogen complexes in solution and by exchange processes between organic waste derived and soil borne DOC. Incubation studies performed with ¹⁴C-estrogens showed that DOC addition decreased estrogen mineralization, probably due to reduced bioavailability of estrogens associated with DOC. This increased persistence combined with higher mobility could increase the risk of estrogen transport to ground and surface waters.     

Changes in soil organic matter chemical properties after organic amendments

Organic inputs are used to improve soil physical and chemical properties, but the corresponding changes in soil organic matter (SOM) chemical properties are not well known. In this study, we compared some characteristics of the SOM of a soil receiving either no organic inputs, or two different amendments during 15 years (straw or conifer compost). Quantities of organic carbon and C/N values were determined on particle size fractions after physical soil fractionation to localize changes due to amendments. Contents in reactive functional groups, acid-base properties and copper binding affinities were determined by titration experiments for the soluble fraction of SOM: the fulvic acid fraction (FA). Data of FA extracted from the bulk soil were compared to data of FA extracted from the <20 microm size fraction with the help of either a discrete or a continuous model (fit of data with FITEQL or NICA, respectively). Copper binding characteristics of FA extracted from the <20 microm size fraction did not change significantly after organic inputs, while those of FA extracted from the bulk organic-amended soils were found different from the ones with no amendment. Minor effects observed in the finer soil fractions were ascribed to their low turn-over of organic carbon and/or to a greater homogeneity in the nature of the organic carbon entering these fractions. Our results show major chemical changes in coarser soil organic fractions after organic amendments.     

Influence of soil conditions on dissolved organic matter leached from forest and wetland soils: a controlled growth chamber study

This study investigated the effects of various soil conditions, including drying-rewetting, nitrogen deposition, and temperature rise, on the quantities and the composition of dissolved organic matter leached from forest and wetland soils. A set of forest and wetland soils with and without the nitrogen deposition were incubated in the growth chambers under three different temperatures. The moisture contents were kept constant, except for two-week drying intervals. Comparisons between the original and the treated samples revealed that drying-rewetting was a crucial environmental factor driving changes in the amount of dissolved organic carbon (DOC). The DOC was also notably increased by the nitrogen deposition to the dry forest soil and was affected by the temperature of the dry wetland soil. A parallel factor (PARAFAC) analysis identified three sub-fractions of the fluorescent dissolved organic matter (FDOM) from the fluorescence excitation–emission matrices (EEMs), and their compositions depended on drying-rewetting. The data as a whole, including the DOC and PARAFAC components and other optical indices, were possibly explained by the two main variables, which were closely related with the PARAFAC components and DOC based on principal component analysis (PCA). Our results suggested that the DOC and PARAFAC component information could provide a comprehensive interpretation of the changes in the soil-leached DOM in response to the different environmental conditions.     

Aging and temperature effects on DOC and elemental release from a metal contaminated soil

The combined effect of time and temperature on elemental release and speciation from a metal contaminated soil (Master Old Site, MOS) was investigated. The soil was equilibrated at 10, 28, 45, 70 and 90 degrees C for 2 days, 2 weeks, and 2 months in the laboratory. Dissolved organic carbon (DOC), total soluble elements (by ICP), and labile metals (by DPASV) were determined in the filtered (0.22 microm) supernatants. For the samples equilibrated at 90 degrees C, DOC fractions were size fractionated by filtration and centrifugation; a subsample was only centrifuged while another was also filtered through a 0.45 microm filter. Analyses of the supernatants (ICP, DPASV, DOC) were performed on all size fraction subsamples. Dissolved organic carbon (DOC) increased both with temperature and incubation time; however, metal behavior was not as uniform. In general, total soluble metal release (ICP) paralleled the behavior of DOC, increasing with both time and temperature, and confirming the importance of soil organic matter (SOM) in metal retention. Voltammetric analysis (dpasv) of Cu and Zn showed that very little of these metals remains labile in solution due, presumably, to complexation with dissolved organic matter. Labile concentrations of Cd, on the other hand, constituted a significant portion (50%) of total soluble Cd. Copper and Al increased in solution with time (up to 2 months) and temperature up to 70 degrees C; however, at 90 degrees C the soluble concentration declined sharply. The same behavior was observed after equilibration for longer periods of time (550 days) at lower temperatures (23 and 70 degrees C). While concentrations of labile Cu and total soluble Cu and Al increased in the unfiltered samples, the trend remained the same. DPASV analysis showing shifts in labile Cu complexes with temperature and time, together with the results from the unfiltered samples, lead to the hypothesis that Cu was complexing with large polymers that could form at the elevated temperature, and thus be removed from the analyzed solution. It is possible that Cu and Al released by SOM oxidation has re-sorbed or complexed to more recalcitrant organic matter or to mineral phases. Variations in the relative molecular size fractions present within the DOC pool produced by increased time and temperature may influence the element-DOC complexes present in solution and their behavior in soil environments.     

The size distribution of organic carbon in headwater streams in the Amazon basin

Despite the strong representativeness of streams in the Amazon basin, their role in the accumulation of coarse particulate organic carbon (CPOC), fine particulate organic carbon (FPOC), and dissolved organic carbon (DOC) in transport, an important energy source in these environments, is poorly known. It is known that the arboreal vegetation in the Amazon basin is influenced by soil fertility and rainfall gradients, but would these gradients promote local differences in organic matter in headwater streams? To answer this question, 14 low-order streams were selected within these gradients along the Amazon basin, with extensions that varied between 4 and 8 km. The efficiency of the transformation of particulate into dissolved carbon fractions was assessed for each stream. The mean monthly benthic organic matter storage ranged between 1.58 and 9.40 t ha^?1 month^?1. In all locations, CPOC was the most abundant fraction in biomass, followed by FPOC and DOC. Rainfall and soil fertility influenced the distribution of the C fraction (p?=?0.01), showing differentiated particulate organic carbon (POC) storage and DOC transportation along the basin. Furthermore, the results revealed that carbon quantification at the basin level could be underestimated, ultimately influencing the global carbon calculations for the region. This is especially due to the fact that the majority of studies consider only fine particulate organic matter and dissolved organic matter, which represent less than 50 % of the stored and transported carbon in streambeds.     

Impact of sewage sludge spreading on nickel mobility in a calcareous soil: adsorption–desorption through column experiments

A soil column adsorption–desorption study was performed on an agricultural calcareous soil to determine the impact of sewage sludge spreading on nickel mobility. Ni adsorption experiments were followed by desorption tests involving the following liquid extractants: water, calcium (100 mg/L), oxalic acid (525 mg/L equivalent to 100 mg carbon/L), and sludge extracts (0.5 and 2.5 g/L). Desorption tests were also conducted after sewage sludge spreading at three application rates (30, 75, and 150 t/ha). According to the breakthrough curve, Ni adsorption was irreversible and occurred mainly through interactions with calcite surface sites. Nickel desorption from the soil column was promoted in presence of significant dissolved organic carbon (DOC) concentration as observed with oxalic acid elution and sludge extract at 2.5 g/L. In sludge-amended soil columns, the maximum Ni levels occurred in first pore volumes, and they were positively correlated to the sludge application rate. The presence of DOC in leaching waters was the main factor controlling Ni desorption from the sludge-amended soil columns. This finding implies that DOC generated by sludge applied on calcareous soils might facilitate the leaching of Ni due to the formation of soluble Ni–organic complexes. Thus, sludge application can have potential environmental impacts in calcareous soils, since it promotes nickel transport by decreasing Ni retention by soil components.     

Quantity and spectroscopic properties of soil dissolved organic matter (DOM) as a function of soil sample treatments: air-drying and pre-incubation

The dissolved organic matter (DOM) in soils is essentially defined by the way in which it is obtained. Therefore, we need to understand as to how pre-treatment of a soil will affect the characteristics of DOM, since this fraction may be strongly influenced by a soil's water content. The effect of two different pre-treatments on DOM from the A-horizons of a large variety of ecosystems and regions were compared. In both cases the soils were allowed to air-dry. In one case the air-dried soil was directly extracted (AD), while in the other case it was preincubated for 1 week at 50% of its water holding capacity (INCU). AD is simpler, but INCU brings the soil, and especially its microbial population, back to a standardised state, which is more representative of the usual state in the field. Both methods are used whenever an adjustment of the soil water content is essential to compare different regions or to eliminate short term weather effects. A significant regression indicated that the dissolved organic carbon (DOC) extracted from INCU samples was only 20% of AD DOC. Both the absorptivity (UV absorption divided by DOC) of 86% of the samples, and a fluorescence emission spectrum based Humification Index in all cases increased as a result of preincubation. This would indicate that labile compounds released during drying were metabolised during the incubation. However, the magnitude of this increase varied, and no correlation with soil organic and microbial carbon, pH, or texture could be detected. The results show that DOM extracted from AD and INCU soils is not comparable and that the differences are mainly due to the impact of air-drying on the microbial activity.     

Soil phosphorus fractions in solution: influence of fertiliser and manure, filtration and method of determination.

This study investigated the forms of soil P released to solution, accuracy of their determination, and influence of colloids on P sorption/desorption dynamics. A Hagerstown silt loam, amended with dairy and poultry manure or superphosphate at five rates (0, 25, 50, 100, and 200 kg P ha(-1)), was extracted at two soil:solution ratios (1:5 and 1:100) and filtered at three pore sizes (0.8, 0.45, and 0.22 microm). Results showed that relative to the proportion of dissolved organic P (DOP, determined as the difference between total dissolved P [TDP] and P detected by ion chromatography), DRP increased with amendment rate. Relative to Mehlich-3 extractable P, DRP exhibited a power relationship with a much greater potential for soil P release at concentrations in excess of ca. 50 mg Mehlich-3 P kg(-1). Concentrations of DRP, determined by the acid molybdate method, were on average 12.5% greater than P detected by ion chromatography indicating P was solubilised during colorimetric determination. A linear relationship was found between total Al and DRP, which could indicate acid mediated hydrolysis of A1-humic-P substances, although acid mediated desorption of P from colloids cannot be discounted. No difference in solubilised P was found between solutions filtered at 0.22 and 0.45 microm, but was found between 0.8 microm and smaller filter sizes. Organic P extracted from manured soils was more recalcitrant than that extracted from soils amended with superphosphate, the later attributed to its accumulation in more labile pools. The sorption/desorption of P by colloids in solution were greatly affected by the rate of amendment and the soil:solution extraction ratio. More P was sorbed by superphosphate solutions compared to dairy manure amended soil solutions and was attributed to the saturation of colloidal P sorption sites by organic matter. In order to minimise the effects of colloids on P dynamics and the potential for hydrolysis in solution, filtration to at least 0.45 microm is required. However, soils with a lesser aggregate stability may require additional filtration.     

Changes in pH,dissolved organic matter and Cd species in the rhizosphere soils of Cd phytostabilizer Athyrium wardii (Hook.) Makino involved in Cd tolerance and accumulation

Phytostabilization has great practical significance and flexibility in the ecological restoration of mining tailings and remediation of heavy metals polluted soils. However, potential use of metallophytes in phytostabilization is limited by a lack of knowledge of many basic plant processes. A mining ecotype (ME) Athyrium wardii, Pb/Cd phytostabilizer, and a non-mining ecotype (NME) A. wardii were grown in a pot experiment to investigate the chemical characteristics of the rhizosphere when exposed to the Cd polluted soils. Rhizobags were used to collect rhizosphere and bulk soils, separately. The results indicated that the ME A. wardii was more efficient in Cd accumulation in the root than NME after growing in Cd polluted soils for 50 days in a green house. Soil solution pH and dissolved organic carbon (DOC) concentration in the rhizosphere of ME A. wardii were higher than in the bulk soil and initial values (before planting), whereas the increment in the ME A. wardii were greater than NME. Owing to the increasing of rhizosphere soil pH, exchangeable Cd significantly decreased, whereas the other Cd species were increased with increasing soil DOC values. It is assumed that the ME A. wardii was effective in stabilizing Cd from the mobile fraction to non-mobile fractions. Results from this study suggest that rhizosphere alkalinization and the exudation of high amounts of dissolved organic matter (DOM) to reduce heavy metal mobility might be the two important mechanisms involved in the metal tolerance/accumulation of ME A. wardii.     

Transformation of effluent organic matter during subsurface wetland treatment in the Sonoran Desert

The fate of dissolved organic matter (DOM) during subsurface wetland treatment of wastewater effluent in a hot, semi-arid environment was examined. The study objectives were to (1) discern changes in the character of dissolved organics as consequence of wetland treatment (2) establish the nature of wetland-derived organic matter, and (3) investigate the impact of wetland treatment on the formation potential of trihalomethanes (THMs). Subsurface wetland treatment produced little change in DOM polarity (hydrophobic-hydrophilic) distribution. Biodegradation of labile effluent organic matter (EfOM) and internal loading of wetland-derived natural organic matter (NOM) together produced only minor changes in the distribution of carbon moieties in hydrophobic acid (HPO-A) and transphilic acid (TPI-A) isolates of wetland effluent. Aliphatic carbon decreased as a percentage of total carbon during wetland treatment. The ratio of atomic C:N in wetland-derived NOM suggests that its character is determined by microbial activity. Formation of THMs upon chlorination of HPO-A and TPI-A isolates increased as a consequence of wetland treatment. Wetland-derived NOM was more reactive in forming THMs and less biodegradable than EfOM. For both HPO-A and TPI-A fractions, relationships between biodegradability and THM formation potential were similar among EfOM and NOM isolates; the less biodegradable isolates exhibited greater THM formation potential.     

Partitioning of chloroaromatic compounds between the aqueous phase and dissolved and particulate soil organic matter at chlorophenol contaminated sites

The retention and mobility of hydrophobic organic contaminants (HOCs) in soil is mainly determined by hydrophobic partitioning to dissolved and particulate organic matter (DOM and POM, respectively). The aqueous phase, DOM, and POM fractions were extracted and separated from soils at three sites contaminated with technical chlorophenol formulations. Concentrations of chlorophenols (CP), polychlorinated phenoxyphenols (PCPP), polychlorinated diphenyl ethers (PCDE) and polychlorinated dibenzo-p-dioxins and furans (PCDD/F) were determined. The partitioning to POM, in relation to DOM, increased in all three soils with increasing hydrophobicity in the order CP < PCPP ~ PCDE ~ PCDF < PCDD. Differences in partitioning to DOM (logK(DOC)) and POM (logK(POC)) could not be explained by differences in gross organic C chemistry. Black carbon did not contribute significantly to the sorption of PCDDs, whereas >70% wood fibre in one soil resulted in a decrease of logK(POC) of 0.5 units for CPs and PCDDs. We conclude that logK(OC) for both DOM and POM need to be explicitly determined when the retention and mobility of HOCs is described and modelled in soils.     

Effects of copper concentration on methane emission from rice soils

Outdoor pot experiments with various paddy soils representing five soil types were conducted at Nanjing Agricultural University during the 2000 and 2001 rice-growing seasons. Eighteen soils and ten out of the eighteen soils were involved in the 2000 and the 2001 experiment, respectively. Two treatments were designed as mineral fertilization (MF) and mineral fertilizer + wheat straw incorporation (MF + WS) for the 2001 experiment. Seasonal average rate of CH4 emission from different soils ranged from 1.96 to 11.06 mg m(-2) h(-1) in the 2000 experiment, and from 0.89 to 5.92 mg m(-2) h(-1) for the MF treatment in the 2001 experiment, respectively. Incorporation of wheat straw enhanced considerably CH4 emission with an average increment of 7.09 mg m(-2) h(-1). CH4 emissions from the two-year experiment were negatively correlated to soil available and total copper concentration. A further investigation showed that CH4 emission from the MF treatment was positively related to the dissolved organic carbon (DOC) in the soil (r = 0.904, p < 0.001), and that the DOC was negatively correlated to the concentrations of available copper (r = -0.844, p < 0.01) and total copper (r = -0.833, p < 0.01), respectively. Nevertheless, the incorporation of wheat straw did not enhance the soil DOC, and the relationship between CH4 emission and soil DOC was not statistically significant (r = 0.470, p < 0.20). It was concluded that higher concentration of copper in the soils resulted in lower soil DOC and thus reduced CH4 emission when there was no additional organic matter input. Incorporation of wheat straw did not affect soil DOC and available copper concentration but enhanced CH4 emission.     

Evaluation of impacts of soil fractions on phenanthrene sorption

Phenanthrene sorption to soils and soil fractions was investigated using two contrasting soils with different clay mineral and organic carbon (OC) contents in an attempt to evaluate the contribution of each soil fraction to phenanthrene sorption and the applicability of the carbon-normalized distribution constant (K(OC)) in soils. Sorbents were characterized using surface analysis, solid-state (13)C NMR analysis, and glass transition temperature (T(g)) analysis to gain a insight into the chemical nature of OC in soils. Dissolved organic carbon (DOC) in the soil solution impeded the phenanthrene sorption, while humins accounted for the predominant phenanthrene sorption in soils. The contribution of OC to phenanthrene sorption in soil would be overestimated if only a K(OC)-approach was adopted, since clay minerals could account for much of the sorption, especially when OC was low in soils. Nitrogen gas was shown to be inappropriate for probing non-polar sorption capacity. The results obtained highlight the importance of clay minerals in governing the sorption of phenanthrene in soil, and emphasize the inapplicability of the carbon-normalized distribution coefficient K(OC) in soils.     

Improvement of DOC removal by multi-stage AOP-biological treatment

The single and multi-stages advanced oxidation process (AOP)-biological treatments were evaluated to apply for drinking water treatment, especially for the water containing less susceptible dissolved organic carbon (DOC) to ozone, comparing with the ozonation-biological treatment. Minaga reservoir water and the secondary effluent from a Municipal wastewater treatment plant were used as dissolved organic matter (DOM) solutions. DOC removals after 60 min AOP-biological treatment were 62% and 41% in the Minaga reservoir water and the secondary effluent, respectively, whereas those in the ozonation-biological treatment only 40% and 15% of DOC were removed, respectively. The result indicated that the single-stage AOP-biological treatment could improve DOC removal in comparison with the single-stage ozonation-biological treatment. This is because the AOP mineralized both biodegradable dissolved organic carbon (BDOC) produced in the early stage of oxidation and non-biodegradable dissolved organic carbon (NBDOC), whereas only BDOC was mineralized by further ozonation and NBDOC was not oxidized in the ozonation-biological treatment. The multi-stage treatment could not improve DOC removal in comparison with the single-stage treatment in the ozonation-biological treatment for the secondary effluent containing less susceptible DOC to ozone. However, the multi-stage AOP-biological treatment significantly reduced DOC and achieved 71% of DOC removal by 4 times repetition of 15 min oxidation, whereas DOC removal was 41% in the single-stage AOP-biological treatment for the same oxidation time. The improvement of DOC removal by the multi-stage AOP-biological treatment was due to BDOC removal as a radical scavenger by subsequent biological treatment in the early stage of oxidation and direct mineralization in the latter stage of oxidation.