Role of Dissolved Organic Matter in Sorption of Perfluorooctanoic Acid to Metal Oxides.

Perfluorooctanoic acid (PFOA) is an important perfluorinated chemical of significant environmental concern. It has been widely found at high concentrations in the environment. We have exposed sediment constituent minerals SiO2, Fe2O3, and Al2O3 to PFOA and humic acid (HA) and studied the adsorption of PFOA by introducing the adsorbates in different orders. The results suggest concurrent sorption of PFOA and HA to the mineral surface or enhanced PFOA sorption when both are introduced to the aqueous phase. However, when PFOA is introduced to the mineral surface that has already been exposed to and extensively coated with HA, little PFOA adsorption occurs, which implies that PFOA released to rivers rich in dissolved organic matter (DOM, i.e. HA) may be immune to sorptive retention by the sediment and be transported downstream unabated. DOM thus can play a significant role in the transport and fate of PFOA in the natural water system.

Deciphering visible light photoreductive conversion of CO2 to formic acid and methanol using waste prepared material.

As gradual increases in atmospheric CO2 and depletion of fossil fuels have raised considerable public concern in recent decades, utilizing the unlimited solar energy to convert CO2 to fuels (e.g., formic acid and methanol) apparently could simultaneously resolve these issues for sustainable development. However, due to the complicated characteristics of CO2 reduction, the mechanism has yet to be disclosed. To clarify the postulated pathway as mentioned in the literature, the technique of electron paramagnetic resonance (ESR) was implemented herein to confirm the mechanism and related pathways of CO2 reduction under visible light using graphene-TiO2 as catalyst. The findings indicated that CO(-•) radicals, as the main intermediates, were first detected herein to react with several hydrogen ions and electrons for the formation of CH3OH. For example, the generation of CO(-•) radicals is possibly the vital rate-controlling step for conversion of CO2 to methanol as hypothesized elsewhere. The kinetics behind the proposed mechanism was also determined in this study. The mechanism and kinetics could provide the in-depth understanding to the pathway of CO2 reduction and disclose system optimization of maximal conversion for further application.

Photocatalytic reduction of carbon dioxide to methanol and formic acid by graphene-TiO2.

UNLABELLED: Graphene-TiO2 was obtained by reduction of graphite oxide by the hydrothermal method. Using photocatalytic activity to reduce carbon dioxide to methanol and formic acid was investigated in this study. The results show that the graphene loading affects the absorption of light in the visible light region. A larger surface area can also improve the catalytic activity. The largest yield of methanol and formic acid, under light of 365 nm, can reach 160 and 150 micromol g(-1), respectively with 8.5% graphene loading. An increase in graphene loading can enhance photocatalytic performance, but too much will also decrease the reduction efficiency by shielding the light from reaching the catalytic surface. The effect of pH was also investigated. The mechanism of the reaction was also discussed in this study. IMPLICATIONS: Graphene-TiO2 hybrids were prepared by the hydrothermal method. Surface area and visible light adsorption increased with the graphene loading. Increased graphene loading improved the methanol and formic acid production. Too much graphene loading will decrease the reduction efficiency. The effect of pH shows that the HCO3- species prefers the formation of formic acid. The mechanism of the reaction was also discussed in this study.

Improving total nitrogen removal in aeration basin retrofitted with entrapped biomass.

This study presented a method to upgrade existing aeration tanks to remove total nitrogen (TN). Bioplates carrying entrapped biomass were installed in an aeration basin to create anoxic/anaerobic zones where denitrification can proceed. In a reactor that coupled bioplates containing entrapped biomass (equivalent to as high as 7,500 mg/L of biomass) and an activated sludge suspension (at mixed liquor suspended solids of 1,300-2,400 mg/L), nitrification efficiency exceeded 95% for an influent wastewater containing 21-54 mg/L of NH3-N. In all cases amended with alkalinity and with or without added methanol as an electron source, TN removal was between 60 and 70%. The results demonstrated anoxic/oxic or anaerobic/anoxic/oxic processes could be incorporated in a conventional aeration basin, requiring no substantial modifications of the vessel and operation, and thus providing improved treatment in terms of nitrogen removal in the conventional suspended-growth process.

Enhancing total nitrogen removal from wastewater of a science and industrial park using entrapped biomass.

This study employed entrapped biomass technology to augment the conventional activated sludge process with anoxic-oxic (AO)/anaerobic-anoxic-oxic (A20) functions for the removal of total nitrogen (TN) from wastewater of a science and industrial park in Taiwan. The entrapped biomass unit was fabricated in the format of carrier plates on which microbial cells were entrapped. Due to mass transport limitations, anoxic and anaerobic conditions were created within the bioplates that enabled denitrification to occur. The treatment basin incorporated an equivalent amount of 1300-2400mg MLSS/L of activated sludge on the bioplates at packing ratios of 10-30% (volume ratio ofbioplates to basin) operating with the addition of sodium carbonate for alkalinity and methanol for the electron donor. The results showed nearly 90% of ammonia nitrogen being converted to nitrate and 63% of TN removal, in comparison with typically 10% of TN removal in traditional activated sludge process of domestic wastewater plants.

A novel sensor platform matching the improved version of IPMVP option C for measuring energy savings.

It is easy to measure energy consumption with a power meter. However, energy savings cannot be directly computed by the powers measured using existing power meter technologies, since the power consumption only reflects parts of the real energy flows. The International Performance Measurement and Verification Protocol (IPMVP) was proposed by the Efficiency Valuation Organization (EVO) to quantify energy savings using four different methodologies of A, B, C and D. Although energy savings can be estimated following the IPMVP, there are limitations on its practical implementation. Moreover, the data processing methods of the four IPMVP alternatives use multiple sensors (thermometer, hygrometer, Occupant information) and power meter readings to simulate all facilities, in order to determine an energy usage benchmark and the energy savings. This study proposes a simple sensor platform to measure energy savings. Using usually the Electronic Product Code (EPC) global standard, an architecture framework for an information system is constructed that integrates sensors data, power meter readings and occupancy conditions. The proposed sensor platform is used to monitor a building with a newly built vertical garden system (VGS). A VGS shields solar radiation and saves on energy that would be expended on air-conditioning. With this platform, the amount of energy saved in the whole facility is measured and reported in real-time. The data are compared with those obtained from detailed measurement and verification (M&V) processes. The discrepancy is less than 1.565%. Using measurements from the proposed sensor platform, the energy savings for the entire facility are quantified, with a resolution of ±1.2%. The VGS gives an 8.483% daily electricity saving for the building. Thus, the results show that the simple sensor platform proposed by this study is more widely applicable than the four complicated IPMVP alternatives and the VGS is an effective tool in reducing the carbon footprint of a building.

Spatially variable deoxygenation in the Danshui River: improvement in model calibration.

A modeling study of the Danshui River, Taiwan, reveals that in-stream BOD deoxygenation rates vary significantly along the river as a result of the highly variable strength of wastewater discharges, which directly reflect the effluent characteristics. A comprehensive field data gathering and lab analysis effort for the study site is presented. Results of the data analyses yielded spatially variable CBOD deoxygenation and nitrification rates, which were incorporated in a model of the river. The model results indicate significant improvement of model calibration, thus enhancing the predictive capability of the model for its use in water quality management. To maximize the benefits of pollution control for the Danshui River system and to achieve the water quality management goal, concurrent reductions of CBOD and ammonia loads, instead of phased reduction of CBOD followed by ammonia reduction, are strongly recommended by the model results.

Photocatalytic degradation of malathion by TiO2 and Pt-TiO2 nanotube photocatalyst and kinetic study.

Photocatalytic degradation of malathion, is investigated using Titanium Nanotubes (TNT) and Pt modified TNT (Pt-TNT) photocatalyst in an aqueous solution under 365 nm UV lamp irradiation. The TNT photocatalyst is prepared on pretreated strong alkaline solution via the hydrothermal method. The Pt-TNT was prepared by light deposition. The variations in morphology, formation mechanism, phase structure, and pore structure of TNT and Pt-TNT are characterized using UV-Vis, transmission electron microscopy (TEM), and N2 adsorption/desorption isotherm analyzer, respectively. The effect of the initial malathion concentration, reaction temperature, catalyst loading, solution pH value, irradiation time and Pt loading are studied and the optimized values are obtained. Moreover, the photodegradation performance and kinetics of malathion onto TNT and Pt-TNT are also examined with the aid of model analysis by kinetic data. The results show that under acid conditions, the performance of photocatalysts for treating malathion is high. The time of complete degradation increases with an increase in the initial malathion concentration. The degradation rate decreases with increasing initial malathion concentration. The degradation efficiency can reach 100% under acid conditions for any initial malathion concentration when the reaction time is 70 min. In addition, experimental decoloration kinetics data follow the pseudo-first-order reaction model.

Estimation of phosphorus flux in rivers during flooding.

Reservoirs in Taiwan are inundated with nutrients that result in algal growth, and thus also reservoir eutrophication. Controlling the phosphorus load has always been the most crucial issue for maintaining reservoir water quality. Numerous agricultural activities, especially the production of tea in riparian areas, are conducted in watersheds in Taiwan. Nutrients from such activities, including phosphorus, are typically flushed into rivers during flooding, when over 90% of the yearly total amount of phosphorous enters reservoirs. Excessive or enhanced soil erosion from rainstorms can dramatically increase the river sediment load and the amount of particulate phosphorus flushed into rivers. When flow rates are high, particulate phosphorus is the dominant form of phosphorus, but sediment and discharge measurements are difficult during flooding, which makes estimating phosphorus flux in rivers difficult. This study determines total amounts of phosphorus transport by measuring flood discharge and phosphorous levels during flooding. Changes in particulate phosphorus, dissolved phosphorus, and their adsorption behavior during a 24-h period are analyzed owing to the fact that the time for particulate phosphorus adsorption and desorption approaching equilibrium is about 16 h. Erosion of the reservoir watershed was caused by adsorption and desorption of suspended solids in the river, a process which can be summarily described using the Lagmuir isotherm. A method for estimating the phosphorus flux in the Daiyujay Creek during Typhoon Bilis in 2006 is presented in this study. Both sediment and phosphorus are affected by the drastic discharge during flooding. Water quality data were collected during two flood events, flood in June 9, 2006 and Typhoon Bilis, to show the concentrations of suspended solids and total phosphorus during floods are much higher than normal stages. Therefore, the drastic changes of total phosphorus, particulate phosphorus, and dissolved phosphorus in rivers during flooding should be monitored to evaluate the loading of phosphorus more precisely. The results show that monitoring and controlling phosphorus transport during flooding can help prevent the eutrophication of a reservoir.

C, N, and P stoichiometry for leaf litter of 62 woody species in a subtropical evergreen broadleaved forest.

To understand leaf litter stoichiometry in a subtropical evergreen broadleaved forest, we measured the contents of carbon (C), nitrogen (N) and phosphorus (P) in leaf litters of 62 main woody species in a natural forest of C. kawakamii Nature Reserve in Sanming, Fujian Province. Differences in leaf litter stoichiometry were analyzed across leaf forms (evergreen, deciduous), life forms (tree, semi-tree or shrub), and main families. Additionally, the phylogenetic signal was measured by Blomberg's K to explore the correlation between family level differentiation time and litter stoichiometry. Our results showed that the contents of C, N and P in the litter of 62 woody species were 405.97-512.16, 4.45-27.11, and 0.21-2.53 g·kg-1, respectively. C/N, C/P and N/P were 18.6-106.2, 195.9-2146.8, and 3.5-68.9, respectively. Leaf litter P content of evergreen tree species was significantly lower than that of deciduous tree species, and C/P and N/P of evergreen tree species were significantly higher than those of deciduous tree species. There was no significant difference in C, N content and C/N between the two leaf forms. There was no significant difference in litter stoichiometry among trees, semi-trees and shrubs. Effects of phylogeny on C, N content and C/N in leaf litter was significant, but not on P content, C/P and N/P. Family differentiation time was negatively correlated with leaf litter N content, and positively correlated with C/N. Leaf litter of Fagaceae had high C and N contents, C/P and N/P, and low P content and C/N, with an opposite trend for Sapidaceae. Our findings indicated that litter in subtropical forest had high C, N content and N/P, but low P content, C/N, and C/P, compared with the global scale average value. Litter of tree species in older sequence of evolutionary development had lower N content but higher C/N. There was no difference of leaf litter stoichiometry among life forms. There were significant differences in P content, C/P, and N/P between different leaf forms, with a characteristic of convergence.

[Effects of forest conversion on litterfall nutrient return and nutrient use efficiency in Mid-subtropical China.] / ä¸­äºšçƒ­å¸¦æ£®æž—è½¬æ¢å¯¹å‡‹è½ç‰©å »åˆ†å½’è¿˜åŠå »åˆ†åˆ©ç”¨æ•ˆçŽ‡çš„å½±å“.

To understand the impacts of mid-subtropical forest conversion on carbon and nutrient cycling, we conducted a 4-year investigation to examine litterfall, nutrient return and nutrient use efficiency of Castanopsis carlesii natural forest, C. carlesii secondary forest and Cunninghamia lanceolata plantation which were transformed from C. carlesii natural forest. The results showed that after C. carlesii natural forest was transformed into C. carlesii secon-dary forest and C. lanceolata plantation, the annual litter production decreased by 29.0% and 45.7%, nitrogen return of litter decreased by 34.0% and 72.7%, and phosphorus return decreased by 38.1% and 56.4%, respectively. The amount of carbon returned from litterfall in C. carlesii natural forest was 25.6% and 44.3% higher than that in C. carlesii secondary forest and C. lanceolata plantation, respectively. For C. lanceolata plantation, C. carlesii secondary forest and C. carlesii natural forest, nitrogen use efficiency of litterfall was 175.4, 94.8 and 92.0 kg·kg-1, respectively, and phosphorus use efficiency of litterfall was 3031.0, 2791.6 and 2537.2 kg·kg-1, respectively. It was concluded that C. lanceolata plantation was more limited by nitrogen compared with C. carlesii natural forest and secondary forest, and the effects of phosphorus limitation had similar effects on the three forests.

[Effects of warming on physicochemical property of Cunninghamia lanceolata branch and leaf litter in subtropical plantation]. / 增温对亚热带杉木枝和叶凋落物理化性质的影响.

At the regional scale, substrate properties are the key factors driving litter decomposition rate. In this study, soil temperature was increased by buried heating cables to explore the impacts of climate warming on the physical and chemical properties in branch and leaf of Cunninghamia lanceolata litter. The results showed that after 5 years of soil warming (4 ℃), the contents of nitrogen (N), phosphorus (P) and water-soluble substance in branch litter increased by 35.2%, 40.8% and 7.6%, while that in leaf litter increased by 41.2%, 45.9% and 5.9%, respectively. The contents of carbon (C), cellulose and C/N in branch litter decreased by 5.1%, 11.6% and 28.8%, and in leaf litter decreased by 5.3%, 11.3% and 33.3%, respectively. Soil warming led to 29.8% increase in specific leaf area (SLA) and 40.7% decrease in tensile strength (LTS) of leaf litter. However, warming did not affect lignin content and pH value in both branch and leaf litter. 13C NMR and infrared spectrum analysis showed that the contents of amino acids, polysaccharides, polyphenols and aliphatic compounds in litter changed significantly after warming. Warming effect differed between litter organs, in that polysaccharides increased significantly only in leaf litter and the increase of amino acids in branch litter was greater than that in leaf litter. Overall, soil warming significantly changed the physical and chemical properties in C. lanceolata branch and leaf litter, which might accelerate the decomposition rate at the initial stage due to the increase of N, P contents and the decrease of LTS, but might decelerate the decomposition rate at the later stage due to an increase of complex polymers content in the litter.

Capture of metallic copper by high gradient magnetic separation system.

Valence copper was recovered from wastewater by chemical reduction and use of a high gradient magnetic separation (HGMS) system. Ammonia (NH3) and sodium dithionate (Na2S2O4) at a molar ratio of [Cu]:[NH3]:[Na2S2O4] = 1:4:3 at pH = 9.5 were used first to chemically reduce copper ion to metallic copper; the resultant metal solids were captured in an upflowing reactor space equipped with a permalloy matrix net under a high gradient magnetic field. The captured solids were predominantly 6-20 microm in diameter, with Cu2O and CuO present among the solids. Four treatment configurations with and without the use of magnetic field and metal alloy as the matrix net were tested and their effects evaluated: (1) no magnetic field or matrix, (2) no magnetic field but with matrix, (3) with magnetic field but no matrix, (4) with both magnetic field and matrix. At flow rates of 40, 60, 80 and 100 cm3/min, capture efficiencies for metallic copper in the absence of magnetic field were 87%, 86%, 63%, and 39%, respectively, and in the presence of magnetic field were 99%, 98%, 95%, and 93%, respectively. The HGMS was critical for a high capture efficiency, whereas a matrix net only marginally enhanced it. Additional tests with a larger reactor confirmed similarly high efficiencies of > 85%. The use of an alloy matrix appeared to be important when high flow rates are most likely to be employed in practical applications.

Recovery of metallic copper by integrated chemical reduction and high gradient magnetic separation.

The recovery of metals from waste effluents is necessary for pollution prevention and sustainable practice. High gradient magnetic separation (HGMS) is seen as a viable method. We investigated the capture of valence copper from aqueous copper ion by HGMS in combination with a chemical reduction process. When a copper solution (3.9 or 15.6 mM) was exposed to excess of dithionite (mole ratio of 1:3) in the presence of ammonia (mole ratio of 4) and amended with MnCl2 (2.5 g/L) and the mixture passed through a flow reactor under a strong magnetic field (10000 Gauss), valence copper was obtained and captured in the reactor with well over 95% yields. The chemical reduction reactions were unaffected by the presence of MnCl2 while the amount of MnCl2 (0, 20 and 32 mM) has significantly varied the copper recovery efficiency, especially in the case of high initial copper ion concentration (15.6 mM). Formation of MnO2 flocs was found to have a detrimental effect on copper removal efficiency. The HGMS method offers a tool of resource recovery for copper from waste effluents.

Effects of mass retention of dissolved organic matter and membrane pore size on membrane fouling and flux decline.

Ultrafiltration (UF) fouling has been attributed to concentration polarization, gel layer formation as well as outer and inner membrane pore clogging. It is believed that mass of humic materials either retained on membrane surface or associated with membrane inner pore surface is the primary cause for permeate flux decline and filtration resistance build-up in water supply industries. While biofilm/biofouling and inorganic matter could also be contributing factors for permeability decline in wastewater treatment practices. The present study relates UF fouling to mass of dissolved organic matter (DOM) retained on membrane and quantifies the effect of retained DOM mass on filtration flux decline. The results demonstrate that larger pore membranes exhibit significant flux decline in comparison with the smaller ones. During a 24-h period, dissolved organic carbon mass retained in 10 kDa membranes was about 1.0 gm(-2) and that in 100 kDa membranes was more than 3 times higher (3.6 gm(-2)). The accumulation of retained DOM mass significantly affects permeate flux. It is highly likely that some DOMs bind or aggregate together to form surface gel layer in the smaller 10 kDa UF system; those DOMs largely present in inner pore and serving as pore blockage on a loose membrane (100 kDa) are responsible for severe flux decline.

Using the entrapped bioprocess as the pretreatment method for the drinking water treatment receiving eutrophic source water.

Control of organic matter, nutrients and disinfection byproduct formation is a major challenge for the drinking water treatment plants on Matsu Islands, Taiwan, receiving source water from the eutrophic reservoirs. A pilot entrapped biomass reactor (EBR) system was installed as the pretreatment process to reduce organic and nitrogen contents into the drinking water treatment plant. The effects of hydraulic retention time (HRT) and combination of preceding physical treatment (ultraviolet and ultrasound) on the treatment performance were further evaluated. The results showed that the EBR system achieved higher than 81%, 35%, 12% and 46% of reduction in chlorophyll a (Chl a), total COD (TCOD), dissolved organic carbon (DOC) and total nitrogen (TN), respectively under varied influent concentrations. The treatment performance was not significantly influenced by HRT and presence/absence of physical pretreatment and the effluent water quality was stable; however, removal efficiencies and removal rates of Chl a, TCOD and DOC showed strong correlation with their influent concentrations. Excitation-emission matrix (EEM) fluorescence spectroscopy identified fulvic-like and humic-like substances as the two major components of dissolved organic matter (DOM) in the reservoir, and decreased intensity of the major peaks in effluent EEM fluorescence spectra suggested the effective removal of DOM without production of additional amount of soluble microbial products in the EBR. Through the treatment by EBR, about 10% of reduction of total trihalomethane formation potential for the effluent could also be achieved. Therefore, the overall results of this study demonstrate that EBR can be a potential pretreatment process for drinking water treatment plants receiving eutrophic source water.

Removal of natural organic matter by ultrafiltration with TiO2-coated membrane under UV irradiation.

This study investigates the performance of ultrafiltration (UF) by membranes coated with titanium dioxide (TiO2) photocatalyst under ultraviolet (UV) illumination in removing natural organic matter (NOM) and possibly in reducing membrane fouling. Experiments were carried out using heat-resistant ceramic disc UF membranes and humic acids as model substances representing naturally occurring organic matter. Membrane sizes of 1, 15, and 50 kDa were used to examine the effects of coating under ultraviolet irradiation. A commercial humic solution was subjected to UF fractionation (batch process); gel filtration chromatography was applied to study the effects of molecular weight distribution of NOM on UF membrane fouling. When compared to naked membranes, UV254 (ultraviolet light of lambda=254 nm) illumination of TiO2-coated membranes exhibits more flux decline with similar effluent quality. Although the UF membrane is able to remove a significant amount of humic materials, the incorporated photocatalysis results in poor performance in terms of permeate flux. The TiO2-coated membrane under UV254 irradiation alters the molecular weight (MW) distribution of humic materials, reducing them to <1 kDa, which is smaller than the smallest (1-kDa) membrane in this study. Thus, TiO2-coated membranes under UV254 irradiation do not perform any better in removing natural organic matter and reducing membrane fouling.

Greenhouse gases emissions from waste management practices using Life Cycle Inventory model.

When exploring the correlation between municipal solid waste management and green house gas emission, the volume and physical composition of the waste matter must be taken into account. Due to differences in local environments and lifestyles the quantity and composition of waste often vary. This leads to differences in waste treatment methods and causes different volumes of greenhouse gases (GHGs), highlighting the need for local research. In this study the Life Cycle Inventory method was used with global warming indicator GHGs as the variables. By quantifying the data and adopting a region-based approach, this created a model of household MSWM in Taipei City, a metropolitan region in Taiwan. To allow analysis and comparison a compensatory system was then added to expand the system boundary. The results of the analysis indicated that out of all the solid waste management sub-models for a function unit, recycling was the most effective method for reducing GHG emissions while using kitchen food waste as swine feeding resulted in the most GHG emissions. As for the impact of waste collection vehicles on emissions, if the efficiency of transportation could be improved and energy consumption reduced, this will help solid waste management to achieve its goal of reducing GHG emissions.

Degradation of 4-chlorophenol in TiO2, WO3, SnO2, TiO2/WO3 and TiO2/SnO2 systems.

The present study was undertaken to evaluate the degradation performance of 4-chlorophenol (4-CP) using TiO2/WO3 and TiO2/SnO2 systems. A BET surface area analyzer, UV-vis spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron spectroscopy for chemical analysis (ESCA) were employed to characterize the photocatalyst. The band edge wavelength increased to 475 nm and gap energy decreased to 2.61 eV in the TiO2/WO3 system as compare to the single TiO2. Although the specific surfaces area of TiO2/WO3 decreases due to its larger size as compared to either TiO2 or WO3, the 4-CP degradation efficiency significantly increased as compared to single TiO2 or WO3 system at 435 nm wavelength. The TiO2/WO3 degradation of 4-CP at 369 nm was in fact inhibited. For TiO2/SnO2, the degradation efficiency also suffered at 369 nm, and only slightly increased compared to otherwise hardly 4-CP degraded in single TiO2 or SnO2 system. Since there is a significant accumulation of byproducts, the buildup of these intermediates on the catalyst surface may be responsible for their poor performance.

Entrapped biomass for removal of organics and total nitrogen from anaerobic reactor effluents.

Anaerobic processes have been applied to treat low-strength domestic wastewaters with significant energy saving. However, anaerobic process effluents must be further removed of residual organics and total nitrogen before discharge. Reported here are an aerobic entrapped bio-technology (EBT) system and an EBT coupled with activated sludge (EBT + AS) system being tested as a post-anaerobic treatment. Both systems have been operated under aerobic condition to provide organics and total nitrogen removal, achieving COD removal by 74-88% and TN removal by 58-65% at hydraulic retention times of 8-24 h. ΔCOD/ΔNO3 ratios that represent the carbon usage efficiency as electron donors for denitrification were 1.82-1.93 in the EBT and 2.01-2.02 in the EBT + AS systems, with both ratios being lower (i.e. more efficient) than 6 typically required in traditional activated sludge bioreactors. Both systems demonstrate promise for polishing removal of COD and TN.