Anoxic Process Research Articles

Cognitive impairment and pain management: Review of issues and challenges

The assessment and treatment of pain in persons with cognitive impairments pose unique challenges. Disorders affecting cognition include neurodegenerative, vascular, toxic, anoxic, and infectious processes. Persons with memory, language, and speech deficits and consciousness alterations are often unable to communicate clearly about their pain and discomfort. Past research has documented that persons with cognitive impairments, particularly dementia, are less likely to ask for and receive analgesics. This article provides an overview of the assessment, treatment, and management of pain in adults with cognitive impairments. We review types of cognitive impairment; recent work specific to best practices for pain management in patients with dementia, including assessment-tool development and pharmacological treatment; challenges in patients with delirium and in medical intensive care and palliative care settings; and directions for future research.

Structural/Functional Changes in Activated Sludge in PCP- and ONP-Biodegradation Technologies

ABSTRACTDifferent detoxication technologies (aerobic, anaerobic, two stage, hybrid) using oNP, PCP, DCP, TCP like model xenobiotics, have been accomplished in the last 8 years. The results about the details of the technologies have been described previously. In this paper the comparison between the efficiency of the different technologies and structural/functional changes of AS (activated sludge) has been made. The paper is illustrated by means of microscopic and transmission microscopic photographs. The results showed well expressed connection between the efficiency of xenobiotic elimination, type of technology, initial concentration of the particular xenobiotic and adaptive structure of AS. At aerobic shorter adaptation genus Pseudomonas played more important role in the detoxication. At time of the longer anaerobic and anoxic processes genus Acinetobacter assumed the govern role in the structure of xenobiotic-degrading bacterial complex. The deep knowledge of the adaptive structure of the different detoxication technologies presents the valuable information for quick and intelligent management of the detoxication bioremediation technologies.

Fundamentals of biohydrochemistry of anoxic basins

The formation of hydrogen sulfide waters in three anoxic basins—the Black Sea, the Cariaco trench, and the Framvaren fjord—is considered. The accumulation of H2S caused by the oxidation of organic matter (OM) with seawater sulfates is characterized by the relationship between the increase in the total (denoted by the T subscript) carbonate carbon (ΔCT) and the total hydrogen sulfide (ΔST), which is close to the stoichiometric ratio ΔCT/ST = 2. The values of ΔCT, ST, and the pH are inversely related. About 99% of the increase in the total alkalinity (ΔAT) is provided by the growth in the sum of the carbonate and sulfide alkalinities (ΔAC and ΔAS, respectively). The calculated values of ΔAT/ΔCT and ΔAT/ΔST correlate well with the experimental data obtained for the three basins. The concentrations of dissolved ammonium, phosphate, and silica increase proportionally to the growth in CT and ST in anoxic waters. The isotope composition of H2S sulfur (δ34S from −40 to −11‰) and the factor of isotope fractionation (Δ34S from 60 to 40‰) show that the intensity of the sulfate reduction in the waters of the basins differ by 3–4 orders of magnitude: from the maximum value in Framvaren fjord to the minimum value in the Black Sea. The isotope composition of the carbon in dissolved carbonates formed by OM mineralization is distinct from the composition of plankton and organic detritus, being enriched in 13C by 4–7‰. The hydrochemical character of an anoxic basin is determined by two factors: by the intensity of sulfate reduction related directly to the flux of detrital organic matter to the bottom and by the intensity of the anoxic process dependent not only on the sulfate reduction intensity but also on the exchange time for deep and surface waters in the basin (the lifetime of the anoxic zone).

Biological treatment of low-salinity shrimp aquaculture wastewater using sequencing batch reactor

Abstract In order to improve the water quality in shrimp aquaculture operated under low-salinity conditions, a sequencing batch reactor (SBR) was tested for treatment of the wastewater. This water from the backwash of a single-bead filter from the Waddell Mariculture Center, South Carolina, contained high concentrations of carbon and nitrogen and was successfully treated using the SBR. By operating the reactor sequentially in aerobic, anoxic and aerobic modes, nitrification and denitrification were achieved, as well as removal of carbon. Specifically, the initial chemical oxygen demand (COD) concentration of 1201 mg l −1 was reduced to 32 mg l −1 within 8 days of reactor operation. Ammonia in the sludge was nitrified within 3 days. The denitrification of nitrate was achieved by the anoxic process and total removal of nitrate was observed.

Combining anoxic denitrifying ability with aerobic–anoxic phosphorus-removal examinations to screen denitrifying phosphorus-removing bacteria

Anaerobic–aerobic (or anaerobic–anoxic) enhanced biological phosphorus- removal (EBPR) processes were generally considered for P removal. However, some isolated polyphosphate-accumulating organisms (PAOs) or denitrifying P-removal bacteria (DPB) may have varied P-removal characteristics under different conditions. This study investigated proper screening procedures for isolating DPB from piggery sludge, enriched sludge, and winery sludge. We combined anoxic denitrifying ability with aerobic–anoxic P-removal examinations to screen the DPBs as compared with conventional anaerobic–aerobic and anaerobic–anoxic P-removal examinations. It was concluded that denitrification ability detection was recommended as the first step of screening. Subsequently, denitrifiers were cultured under an aerobic–anoxic single-stage process using oxygen and nitrate simultaneously as e− acceptors to examine P-removal abilities. We chose single-stage aerobic–anoxic P-uptake denitrifiers (Types I and II) according to the purpose of P removal, whereas well-grown denitrifiers without obvious P removal might be induced by considerable PHB formation. Moreover, under anaerobic–anoxic P-removal examinations, most of the isolated DPBs had no obvious anaerobic P release, but did have significant anoxic P uptake. Pure isolated DPB cultures behaved like enriched sludge, which showed no anaerobic P release but achieved respective N- and P-removal efficiencies of 96% and 86%.

Geochemical Assessment of Iron and Vanadium Relationships in Oxic Soil Environments

Geochemical assessment has become a cost-effective and highly accurate tool for estimating metal contamination, especially in those cases where the level of contamination is not considered severe. Difficulties frequently arise in attempting to discriminate between pristine metal concentrations and low-level environmental impacts. As an example, Vanadium contamination is frequently associated with coal and petroleum bi-products; however, air and water contamination pathways are also possible. The purpose of this investigation was to characterize the V and Fe concentration relationship among a wide variety of soil types and to formulate an estimate of the pristine V concentrations in these soils. If a linear relationship may be established between Fe and V, then geochemical analysis of impacted soils may discriminate between V as a natural background component and anthropogenic V. Forty-six moderately well-drained to well-drained soil profiles having cambic, argillic or calcic soil horizons were characterized for Fe and V using an aqua-regia digestion to determine if these soils exhibited a one-to-one correspondence between V and Fe. Such a correspondence was authenticated for the majority of these soils and may be used to discriminate between natural and anthropogenic V. The presence of argillic, calcic or fragipan horizons did not reduce the one-to-one correspondence between V and Fe, suggesting that these soil processes did not selectively partition either V or Fe. The method needs to be further evaluated for soils having anoxic soil conditions, lithologic discontinuities and other specific pedogenic processes.

Model concept for nitrate and nitrite utilization during anoxic transformation in the bulk water phase of municipal wastewater under sewer conditions

A two-stage anoxic transformation process, involving growth of biomass utilizing two types of different electron acceptors, namely nitrate and nitrite, has been observed. The present water quality modules established for sewer processes cannot account for the two-stage process. This paper outlines the development of a model concept that enables the two-stage anoxic transformation process to be simulated. The proposed model is formulated in a matrix form that is similar to the Activated Sludge Models and Sewer Process Model matrices. The model was successfully applied to simulate changes in nitrate and nitrite concentrations during anoxic transformations in the bulkwater phase of municipal wastewater.

Uranium secondary phase formation during anoxic hydrothermal leaching processes of UO2 nuclear fuel

Abstract Mobilisation of uranium in geologic environments from UO2 solid phases usually takes place by oxidative dissolution involving a change of U oxidation state from +IV to +VI; however, anoxic or reducing geochemical conditions are expected in many of the planned European disposal sites. This work investigates potential alteration mechanisms of UO2 in contact with groundwater ions (Ca2+, CO 3 2 - , and silicate) under anoxic conditions, at ambient (25 °C) and hydrothermal (180 °C) temperature conditions. SEM–EDX analysis detected (in the case of treatment at 180 °C in high silicate content solutions) a compound with U:Si ratio of 1:1 on the UO2 surfaces after leaching. Minor quantities of phases containing U, Ti, Fe, Si, and Ca were formed, these could not be characterized completely. A further experiment, performed in the presence of dissolving CaO/TiO2/SiO2/Fe(0)–Fe2O3, formed a compound with U:Si:Ca of 1:2:8, a ratio not matching any known uranyl compound. The two phases, possibly identical with coffinite, USiO4, and U-bearing ekanite, UCa2Si8O20, were found to form at different [Ca]/[Si] conditions. The implications upon the final geologic storage of actual, heterogeneous spent fuel are discussed.

Biodegradation and detoxification of -nitrophenol by Rhodococcus wratislaviensis

An indigenous bacterial strain capable of utilizing p-nitrophenol (PNP) as the sole carbon, nitrogen and energy source was isolated from a river sediment in Buenos Aires (Argentina). The 16S rDNA sequence showed a close relationship to Rhodococcus wratislaviensis. This indigenous bacterial strain degrades 0.36 and 0.72 mM PNP in 34 and 56 h, respectively, and releases the nitro group from the compound as nitrite. Aerobic biodegradation assays were performed using a 2-L microfermentor at 28∘C with agitation (200 rpm). Biodegradation was evaluated by spectrophotometry, gas chromatography and microbial growth. As the nitrite released during PNP degradation is also an environmental toxic agent it was removed by adding a denitrification step in an anoxic process. Detoxification was evaluated by using a Daphnia magna toxicity test. Toxicity was not detected after the combination of both, an aerobic biodegradation test and denitrification in an anoxic process.

Long-term optimal aeration strategies for small-size alternating activated sludge treatment plants

This paper discusses the influence of time horizon on dynamic optimization of small-size wastewater treatment plants alternating aerobic and anoxic processes. The optimization problem consists in determining the aeration policy (air-on and air-off periods) that minimizes the energy dissipated by the aeration system subject to both effluent and operating constraints. Optimization over short time horizons is first considered and reductions of the energy consumption up to 30% are obtained with respect to the usual operating mode of the process. But the application of such aeration strategies eventually results in a biomass wash-out when applied over long time periods. Here, it is shown that long time horizon optimized policies guarantee a durable functioning of the treatment plant. The resulting energy consumption savings are however lower (up to 15%), but are still important.

Anoxic control of odour and corrosion from sewer networks

Anoxic processes can effectively control odour and corrosion in sewer networks. However, the absence of fundamental knowledge on the kinetics of anoxic transformation of sewage prevents the engineering applications of anoxic control in sewers. This paper focuss on a basic understanding of the anoxic transformations needed for a conceptual simulation of the water phase processes. Experiments conducted in batch reactors have shown that nitrite builds up in wastewater during denitrification. Part of the nitrate-reducing biomass is capable of utilizing nitrite after nitrate is depleted. Compared with aerobic transformation, anoxic processes have low values of maximum growth rate of the biomass and also a low endogenous respiration rate. Heterotrophic yield determined under anoxic conditions, at level of 0.25 mmol e-eq (mmol e-eq)(-1), accounted for less than 40% of the corresponding aerobic values.

Anoxic dissolution processes of biotite: implications for Fe behavior during Archean weathering

Iron-rich biotite (Fe/Mg=5) dissolution experiments were carried out in a batch system under O2-deficient conditions (PO2<3×10−5 atm; referred to as ‘anoxic’ conditions) at 1 atm of PCO2, pH 4.6, and 100 °C for 7–120 days for a better understanding of ‘anoxic’ weathering processes and Fe behavior during weathering before 2.2 Ga. For comparison, oxic Fe-rich biotite dissolution experiments were conducted under present atmospheric conditions at pH 4.7 and 100 °C for 7–80 days (referred to as oxic conditions) by using the same starting biotite as that for the ‘anoxic’ experiments. The concentrations of Fe in solution after the dissolution experiments were larger by one to more than two orders of magnitude under ‘anoxic’ conditions than under oxic conditions. High-resolution scanning and transmission electron microscopy revealed that Fe(II)-rich vermiculite or smectite was precipitated as a secondary mineral at the edge of biotite under ‘anoxic’ conditions, in contrast to the formation of Fe(III)- and Al-(hydr)oxides under oxic conditions. The results suggest that part of Fe(II) is released to water as ‘anoxic’ weathering proceeds, explaining the decrease of Fe content in pre-2.2 Ga paleosols relative to their parent rocks. The Fe/Mg molar ratio of the secondary vermiculite or smectite was more than 7 while the starting Fe-rich biotite had a value of about 5. The Fe/Mg molar ratio was less than 2.5 in solution. The results of the ‘anoxic’ experiments suggest that Fe(II)-rich vermiculite or smectite could be the precursor of the chlorite preserved in pre-2.2 Ga paleosols. This is further corroborated by the increase in Fe/Mg molar ratios in chlorite with decreasing depth in some Precambrian paleosols.

Effect of platinum deposits on TiO2 on the anoxic photocatalytic degradation pathways of alkylamines in water: dealkylation and N-alkyation.

Most photocatalytic degradation (PCD) reactions of aquatic pollutants require the presence of dissolved oxygen and hence do not occur in anoxic suspensions. We investigated the PCD reactions of alkylamines in anoxic water using TiO2 deposited with Pt nanoparticles. Unlike typical PCD reactions, the absence of dissolved oxygen increases the PCD rates of alkylamines on Pt/TiO2 and generates products that are different from those formed on pure TiO2. In particular, N-alkylated amines (e.g., (CH3)3N produced from (CH3)2NH) as well as dealkylated amines are generated in a deaerated Pt/TiO2 suspension. This anoxic N-alkylation pathway is enabled only in the presence of Pt deposits on TiO2 and is applicable only to neutral alkylamines and not to alkylammonium cations. The Pt surface appears to interactwith the lone-pair electron on the N atom and catalyze the anoxic degradation of alkylamines mainly through a radical mechanism. Methyl radicals generated on Pt participate in the N-methylation reaction. The presence of intermediate methyl radicals on the Pt surface was verified by the detection of CH4 and CH3CH3 gases evolved during the PCD of (CH3)3N in an anoxic Pt/TiO2 suspension, whereas no such products were observed in a pure TiO2 suspension. The anoxic PCD of N-methylethylamine on Pt/TiO2 also produces both N-ethylated and N-methylated amines as byproducts, which indicates that both methyl and ethyl radicals are generated during the anoxic degradation process. From a practical point of view, the present finding that undesirable alkylated amines can be produced on Pt/TiO2 in anoxic conditions indicates that caution is necessary when applying Pt/TiO2 photocatalyst to the treatment of water that contains amines.

Simultaneous Carbon and Nitrogen Removal in Anoxic-Aerobic Circulating Fluidized Bed Biological Reactor (CFBBR)

Biological nutrient removal (BNR) in municipal wastewater treatment to remove carbonaceous substrates and nutrients, has recently become increasingly popular worldwide due to increasingly stringent regulations. Biological fluidized bed (BFB) technology, which could be potentially used for BNR, can provide some advantages such as high efficiency and a compact structure. This work shows the results of simultaneous elimination of organic carbon and nitrogen using a circulating fluidized bed biological reactor (CFBBR), which has been developed recently for chemical engineering processes. The CFBBR has two fluidized beds, running as anoxic and aerobic processes to accomplish simultaneous nitrification and denitrification, with continuous liquid recirculation through the anoxic bed and the aerobic bed. Soluble COD concentrations in the effluent ranging from 4 to 20 mg l-1 were obtained at varying COD loading rates; ammonia nitrogen removal efficiencies averaged in excess of 99% at a minimum total hydraulic retention time (HRT) of 2.0 hours over a temperature range of 25 °C to 28 °C. Effluent nitrate nitrogen concentration of less than 5 mg l-1 was achieved by increasing effluent recycle rate. No nitrite accumulation was observed either in the anoxic bed or in the aerobic bed. The system was able to treat grit chamber effluent wastewater at a HRT of 2.0 hours while achieving average effluent BOD, COD, NH3-N, TKN, nitrates, total phosphate, TSS and VSS concentrations of 10 mg l-1, 18 mg l-1, 1.3 mg l-1, 1.5 mg l-1, 7 mg l-1, 2.0 mg l-1, 10 mg l-1 and 8 mg l-1 respectively. The CFBBR appears to be not only an excellent alternative for conventional activated sludge type BNR technologies but also capable of processing much higher loadings that are suitable for industrial applications.

생물학적 축산폐수 처리공정의 자동제어 방법 및 제어 인자의 안정성

SBR 처리공정의 자동제어 인자로서의 ORP, pH, DO의 안정성과 유용성을 비교 평가하였다. 시스템 운전동안 ORP와 pH(mV)-time profile 상에서 요염물질의 특이적인 변화시점을 나타내는 NBP와 NKP가 잘 나타났으며 이 시점은 MSC(moving slope change)를 이용하여 쉽게 인식될 수 있는 것으로 밝혀졌다. 그러나 부하량과 포기량 혹은 시스템 OUR이 불균형일 때는 DO나 ORP-time profile 상에서 NBP로 잘못 인식될 수 있는 가짜 제어시점이 여러 번 발생하거나 혹은 제어시점으로 인식할만한 변화가 전혀 발생하지 않음을 알 수 있었다. 그러나 pH(mV)-time profile에서는 어떤 운전조건과 상태에서도 항상 뚜렷한 NBP가 발생하고 MSC를 이용한 제어시점 인식이 가능함을 알 수 있었다. 따라서 호기적 처리과정 중의 시스템 진단과 자동제어 인자로 ORP나 DO 보다 pH(mV)가 안정적임을 알 수 있었다. 반면 무산소 상태의 모니터나 제어에 있어서는 pH(mV)-time profile에서 NKP를 안정적으로 인식하는 데에는 한계가 있었으나 ORP에서는 매우 안정적인 것으로 나타나 무산소 처리과정의 진단/제어인자로는 ORP가 다른 인자들 보다 유용함을 알 수 있었다. 이러한 결과로 미뤄 SBR 공정의 안정적인 자동제어를 위해서는 ORP 혹은 pH(mV)를 단독으로 이용하는 것 보다는 병용하는 것이 바람직하며, 이러한 자동제어기술은 유입수내 오염물질의 농도 변이와 운전여건에 상관없이 항상 오염물질의 완전제거를 가능케 함은 물론 처리시간 및 처리용량의 최적화를 위한 실용적 기술이 될 것으로 판단된다. The feasibility and stability of ORP, pH(mV) and DO as a real-time control parameter for SBR process were evaluated in this study. During operation, NBP(nitrogen break point) and NKP(nitrate knee point), which reveal the biological and chemical changes of pollutants, were clearly observed on ORP and pH(mV)-time profiles, and those control points were easily detected by tracking the moving slope changes(MSC). However, when balance of aeration rate to loading rate, or to OUR(oxygen uptake rate), was not optimally maintained, either false NBP was occurred on ORP and DO curves before the appearance of real NBP or specific NBP feature was disappeared on ORP curve. Under that condition, however, very distinct NBP was found on pH(mV)-time profile, and stable detection of that point was feasible by tracking MSC. These results might mean that pH(mV) is superior real-time control parameter for aerobic process than ORP and DO. Meanwhile, as a real-time control parameter for anoxic process, ORP was very stable and more useful parameter than others. Based on these results, a stable real-time control of process can be achieved by using the ORP and pH(mv) parameters in combination rather than using separately. A complete removal of pollutants could be always ensured with this real-time control technology, despite the variations of wastewater and operation condition, as well as an optimization of treatment time and capacity could be feasible.

Performance of wuxi WWTP in china

In Wuxi Wastewater Treatment Plant, the Anaerobic, anoxic and oxic (A2/O) process was employed to remove the nitrogen and phosphorus, which exhibited the positive results of the high removal efficiency for phosphorus with a range of 67.7% to 89.9% and an average value of 78.0. The effluent of phosphorus met the national discharge standard. The removal of TN was effected by both BOD variation of influent and wastewater temperature. TN removal was in the range of 28.5% to 55.8% with an average value of 39.4%. The energy cost was 0.15 kWh (m3d)−1 or 1.35 kWh (kgBOD·d)−1. The annual average sludge production was 46.3 m3d−1, the annual average dosage for dewatering was 40 kg d−1.

An Automatically Controlled Alternate Oxic−Anoxic Process for Small Municipal Wastewater Treatment Plants

A patented automatic control device was applied to management of an alternate oxic−anoxic process in a small wastewater treatment plant (700 PE). The control system enabled the optimal time−length of the aerobic and anoxic phases to be determined by analyzing the dissolved oxygen and the oxidation−reduction potential data. Moreover, also a time set point was introduced to establish the maximum length for the two phases. Results showed high performances in biological nitrogen removal (0.7−5.2 mg of NO3−N L-1 in the effluent) and a reliable control of the treatment process also during wet weather events. In comparison with extended aeration plants of similar size, lower energetic consumption was observed, generally <200 Wh PE-1 day-1. The automatic control device was a reliable system that gave a good performance in a small wastewater treatment plant with low investment and managing costs.

The composition of sedimentary organic matter in relation to the dynamic features of a mangrove-fringed coast in French Guiana

The sedimentary organic matter content of a series of 2-m-deep cores was examined in relation to the evolution of mangrove forest, on the basis of geochemical analyses and optical observations. Avicennia-dominated forest deposits, developing along the highly dynamic coastline of French Guiana, were collected in five stations based on stage of forest evolution. The sedimentary organic matter in the upper sediment of the youngest mangrove swamp is mainly derived from algal mats with low carbon:nitrogen ratios (C:N ratio, from 6 to 8) and typical greyish amorphous organic flakes as observed in optical studies. Indeed, rare young Avicennia trees are present, and effectively, geochemical parameters do not give evidence of a litter made up of higher plant debris, these rare debris being probably exported by the tides. A slight increase with depth in the first decimetres of both total organic carbon (TOC) content and C:N ratio results from the development of the radial cable root-system of the pioneer Avicennia germinans. Early diagenetic conditions of this young forest are rather controlled by dominant suboxic processes, as suggested by high Eh values (range, 200–400 mV) and local anoxic processes (occurrence of pyrite) in micro-environments: this is mainly due to the oxygen available by roots and crab bioturbation. The organic content of the senescent mangrove sediment is mainly derived from higher plant debris in the uppermost 30 cm, as indicated by relatively high C:N ratios and the predominance of ligno-cellulosic debris. The strong decrease in hydrogen index values results from the degradation of the higher plant debris, losing hydrogen bounds through decay processes. Moderately acidic pH values, low Ehs and the presence of pyrite framboids point towards the reducing decay processes in surficial layers of the senescent mangrove mediated by sulphate-reducing bacteria. Whatever the stage of evolution of the forest, the geochemical characteristics of the sediment below 30 cm are those of the shoreface one, with opaque refractory debris derived from the Amazon river detritus discharge. The sediment collected from dead mangrove forests, subsequently recolonized by pioneer mangroves, contains organic markers, which predate recolonization, recording previous phases of erosion and accretion.

Characterization of the microbial community and nitrogen transformation processes associated with moving bed bioreactors in a closed recirculated mariculture system

The microbial consortium of a moving bed bioreactor (MBB) connected to a marine recirculating aquaculture system was examined by denaturing gradient gel electrophoresis (DGGE) of amplified 16S rRNA gene fragments. Both ammonia and nitrite oxidizers, Nitrosomonas cryotolerans and Nitrospira marina, respectively, were found associated with the marine system as well as a number of heterotrophic bacteria, including Pseudomonas sp. and Sphingomonas sp. In addition, two Planctomycetes sp. were detected in the system suggesting the capability for anaerobic ammonia oxidation (anammox). The potential for carrying out different nitrogen transformation processes—nitrification, denitrification and anammox—by the bead consortium in both low and high organic load MBBs was measured by short-term batch incubation. Beads with a high organic load exhibited a lower nitrification rate (25 mg NH 3–N/m 2/h) than low organic load beads (31.5 mg NH 3–N/m 2/h) as well as the ability to carry out denitrification and anammox processes. The potential of using MBBs to induce different nitrogen transformation processes was evaluated, and it was found that this type of bioreactor has the capability to serve as a platform for mediating desired anoxic processes such as denitrification and anammox.

ENHANCED NUTRIENT REMOVALS USING CONVENTIONAL ANOXIC BIOMECHANIC AEROBIC SYSTEM FOR ON-SITE WASTEWATER TREATMENT

ABSTRACT A bench-scale absorbent biofilter system combined with a conventional anoxic process was investigated in regard to its feasibility for removing organic as well as nutrient materials from small community wastewater in Korea. A polyurethane biofilter medium with high porosity and a large surface area were used for the aerobic system. Part of treated wastewater was recirculated into the anoxic process to promote removal rate of nutrients. At three different ratios of recirculation, the BOD and SS of treated wastewater satisfied standard regulations for a small wastewater treatment facility (10 mg/l) during the overall experimental period. The system reduced the concentration of BOD from approximately 130 mg/l to 6.1 (removal rate of 95.2%) and 1.7 mg/l (removal rate of 98.7%). These results correspond to recirculation ratios of 1 and 2, respectively. A further increase of the recirculation ratio did not significantly improve the removal rate or further reduce effluent BOD concentration. Nutrients such as nitrogen and phosphorus also were removed effectively, with maximum removal rates of 65.3 and 84.1% for nitrogen and phosphorus, respectively. The recirculation ratio for optimum nitrogen removal was 2, while the removal of phosphorus continued to increase across the entire range of recirculation ratios tested. With a recirculation ratio of 2, the total phosphorous removal rate increased dramatically as initial ammonium concentration increased, while nitrogen removal was not affected in this manner. During the experimental period of 2 years, the system was quite stable, requiring the minimum amount of maintenance and a relatively low cost compared to other utility expenses. Based on the experimental data, the proposed anoxic-biofilter aerobic recirculation system might be used as a new alternative technology for wastewater treatment in small communities in Korea.