Empty Bed Research Articles

Trace and bulk organics removal during ozone-biofiltration treatment for potable reuse applications.

This study investigated impact of ozone/biological activated carbon (BAC) filtration design and operational parameters on contaminants of emerging concern (CEC) and bulk organics removal over 450days of operation. Two parallel BAC filters with identical media and influent were maintained, each at a different empty bed contact time of 10 and 20min. This study captured the CEC removal performance of a BAC filter over an extended operational period after treating 65,000 bed volumes. Ozone system was operated at ozone dose to TOC ratio range of 0.9-2. Biofilter with lower EBCT (10min) and exhausted media resulted in poor removals of Tris(2-chloroethyl) phosphate (TCEP), perfluorooctanoic acid (PFOA), sucralose, meprobamate, N,N-diethyl-m-toluamide (DEET), and cotinine. Biofilter with higher EBCT (20min) and remaining adsorptive effects resulted in significant (84% or more) removal of all CECs that were detected in the ozonated effluent. Increasing both ozone dose and BAC EBCT resulted in increased removal of UV absorbance (UVA254 ). The evaluation of impact of ozone:TOC ratio and BAC EBCT on CEC removal, bulk organics (TOC), and UVA254 performed in this study confirmed the importance of these two parameters on overall success of nonreverse osmosis (RO) potable reuse projects. PRACTITIONER POINTS: Ozone-BAC biofiltration is feasible strategy for indirect potable reuse water reclamation. Ozone-BAC empty bed contact time is a critical design parameter. Adsorption and biodegradation are both important mechanisms for trace organic contaminant removalin BAC.

Column adsorption of Cr (VI) from dilute aqueous solution on tailored micro-mesoporous low-cost activated carbon: performance indicators and breakthrough modeling

The adsorption technology based on low-cost adsorbents is of great interest for alternative sustainable abatement of toxic heavy metals from dilute industrial wastewaters. In this study, the performance of tailored low-cost activated carbon (AC) in column adsorption of Cr (VI) from dilute aqueous solution is evaluated using the rapid small scale column tests procedure. At solutions pH 2, the response of column performance indicators such as number of bed volumes, carbon usage rate, breakthrough capacity and column utilization for achieving effluent discharge limit of 0.5 mg L−1 Cr (VI) to changes in flow rate and bed height are studied. At breakpoints, the low-cost AC showed number of bed volumes (38–259) and column utilization (10–72%) for empty bed contact time (0.8–6.13 min). The bed regeneration efficiency was low at 48%. Also, the low-cost AC exhibited total dynamic selectivity for Cr (VI) from simulated electroplating wastewater. The breakthrough data were correlated using a mass transfer model of Michael’s constant-pattern behavior. The results of this study demonstrate the possible application of the tailored low-cost AC for efficient column adsorption of Cr (VI) from dilute wastewaters.

Adsorption of phosphate on magnetite-enriched particles (MEP) separated from the mill scale

Phosphate is a major pollutant in water, causing serious environmental and health consequences. In present study, the phosphate adsorption on novel magnetite-enriched particles (MEP) was comprehensively investigated. A new method and device were introduced for the separation of MEP from the mill scale at low magnetic intensity. Particles were characterized with different techniques such as XRD, XRF, SEM and EDS. The XRD and XRF analysis of MEP identified the dominant existence of crystalline magnetite. Furthermore, the morphological analysis of MEP confirmed the agglomerate porous morphology of magnetite. Oxygen and iron, the main constituents of magnetite were acknowledged during the elemental analysis using EDS. The phosphate adsorption on MEP is well explained using various isotherm and kinetic models, exhibiting the monolayer adsorption of phosphate on the surface of MEP. The maximum adsorption capacity was determined 6.41 mg/g. Based on particle size (45-75 and 75-150 μm) and empty bed contact time (1 and 2 h), four columns were operated for 54 days. MEP were appeared successful to remove all phosphate concentration from the column influent having 2 mg/L concentration. The operated column reactors were successfully regenerated with alkaline solution. The results indicated potential for practical application of the MEP for phosphate removal.

PERBAIKAN KUALITAS AIR BAKU OLEH ISOLAT BAKTERI NITRIFKASI INDIGENOUS MENGGUNAKAN MOVING BED BIOFILTER REACTOR (MBBR)

Bio-filtration technology is considered as one of prevention solutions for declining raw water quality. The research purpose was to identify biofilm growth formation as viability cell in acclimatization period that can be used for ammonia elimination by using various indigenous chemo-heterotroph bacteria isolated from bio-filter media specimen and moving bed bio-filter reactor performance. Reactor was configured within aerobic system comparing two biofilm–attached support–medium filters (i.e. drinking-water-bottle-PET-chips and PVC). Bacteria potency on ammonia removal in kinetics modeling was advance investigated. Kinetics determination was based on empirical approach in first order by using formula of Cout = Cin exp(-k.EBRT), where Cout is ammonia concentration in outlet, Cin is ammonia concentration in inlet, k is first-order reaction rate constant and Empty Bed Retention Time (EBRT) can be formulated about setting comparison the discharge ammonia load (Q) and volume reactor (V). Total thirteen potential biofilm bacterias were successfully isolated in 24–hours–incubation at 37oC and by using Bergey’s method successfully identified prime biofilm isolates of Bacillus sp and Pseudomonas sp, then re-selected to determine one with the best ammonia removal ability. The ammonia removal kinetics constant of each reactor was obtained as followed: (1) kPET =0.421h-1(ɳ = 62.47%-NH3) and (2) kPVC = 0.412 h-1(ɳ = 58.80%-NH3).Keywords:ammonia removal, biofilm viability, bio-filtration, raw water, polyethylene terephthalate chips

Simultaneous removal of hydrogen sulfide and volatile organic sulfur compounds in off-gas mixture from a wastewater treatment plant using a two-stage bio-trickling filter system

Simultaneous removal of hydrogen sulfide (H2S) and volatile organic sulfur compounds (VOSCs) in off-gas mixture from a wastewater treatment plant (WWTP) is difficult due to the occasional inhibitory effects of H2S on VOSC degradation. In this study, a two-stage bio-trickling filter (BTF) system was developed to treat off-gas mixture from a real WWTP facility. At an empty bed retention time of 40 s, removal efficiencies of H2S, methanethiol, dimethyl sulfide, and dimethyl disulfide were 90.1, 88.4, 85.8, and 61.8%, respectively. Furthermore, the effect of lifting load shock on system performance was investigated and results indicated that removal ofboth H2S and VOSCs was slightly affected. Illumina Miseq sequencing revealed that the microbial community of first-stage BTF contained high abundance of H2S-affinity genera including Acidithiobacillus (51.43%), Metallibacterium (25.35%), and Thionomas (8.08%). Analysis of mechanism demonstrated that first stage of BTF removed 86.1% of H2S, mitigating the suppression on VOSC degradation in second stage of BTF. Overall, the two-stage BTF system, an innovative bioprocess, can simultaneously remove H2S and VOSC.

Microbial community in a pilot-scale biotrickling filter with cell-immobilized biochar beads and its performance in treating toluene-contaminated waste gases

Cell-immobilized bamboo-biochar beads (cell-biochar beads) that were made of an environmentally friendly material were used as packing material in biotrickling filters (BTFs). Cell-biochar beads play the double role of an adsorber of pollutants and a carrier for the growth of attached bacteria, increasing the efficiency of pollutant removal by BTFs. A toluene removal rate of over 99% was achieved. The best organic loading rate (OLR) of BTF on toluene was 46.2 g m−3 h−1 and its elimination capacity (EC) was 34.9 g m−3 h−1 at an exhaust gas flow rate of 0.015 m3 min−1 and an empty bed residence time (EBRT) of 99 s. According to a microbial community analysis, when the cell-biochar beads were immobilized with a targeted pollutant-degrader under various operating conditions, they were dominated by microbes, revealing that the beads had mitigated the inhibition effect of substrate on biodegradation. Therefore, when cell-biochar beads are used as a packing material in a BTF, the exhaust gas can be effectively treated; the impact of the organic load can be effectively buffered and the EC can be improved by scaling up.

Treatment and hybrid modeling of domestic reverse osmosis concentrate using biological activated carbon

The simulation and removal of organics from municipal reverse osmosis concentrate (ROC) using biological activated carbon (BAC) was investigated. BAC treatment of ROC achieved a TOC removal of 25.5% and 28.1% for empty bed contact time (EBCT) of 40 min and 60 min, respectively. Batch studies revealed that the TOC removal followed a first order reaction with a rate constant of 2.735 at R2 > 0.98. Most of the organics were removed within 80 min of treatment, with an average non-biodegradable fraction of 0.6453. The results obtained from the batch studies were then used for simulation of the continuous lab-scale BAC reactors, yielding average relative deviations of 7%–8% and normalized root mean square errors (RMSE) of 0.09–0.1. Results from a third reactor with EBCT of 80 min were used to train and verify a machine learning model. The model was then used for calculating the non-biodegradable organics fraction of ROC, which will be fed into the first order reaction model. The resulting serial hybrid modeling further reduced the average relative deviations to 5%–6% and a normalized RMSE of 0.08.

The styrene purification performance of biotrickling filter with toluene-styrene acclimatization under acidic conditions

ABSTRACT The obvious disadvantages of biotrickling filters (BTFs) are the long start-up time and low removal efficiency (RE) when treating refractory hydrophobic volatile organic compounds (VOCs), which limits its industrial application. It is worthwhile to investigate how to reduce the start-up period of the BTF for treating hydrophobic VOCs. Here, we present the first study to evaluate the strategy of toluene induction combined with toluene-styrene synchronous acclimatization during start-up in a laboratory-scale BTF inoculated with activated sludge for styrene removal, as well as the effects of styrene inlet concentration (0.279 to 2.659 g·m−3), empty bed residence time (EBRT) (i.e., 136, 90, 68, 45, 34 sec), humidity (7.7% to 88.9%), and pH (i.e., 4, 3, 2.5, 2) on the performance of the BTF system. The experiments were carried out under acidic conditions (pH 4.5) to make fungi dominant in the BTF. The start-up period for styrene in the BTF was shortened to about 28 days. A maximum elimination capacity (ECmax) of 126 g·m−3·hr−1 with an RE of 80% was attained when styrene inlet loading rate (ILR) was below 180 g·m−3·hr−1. The highest styrene RE(s) [of BTF] that could be achieved were 95% and 93.4%, respectively, for humidity of 7.7% and at pH 2. A single dominant fungal strain was isolated and identified as Candida palmioleophila strain MA-M11 based on the 26S ribosomal RNA gene. Overall, the styrene induction with the toluene-styrene synchronous acclimatization could markedly reduce the start-up period and enhance the RE of styrene. The BTF dominated by fungi exhibited good performance under low pH and humidity and great potential in treating styrene with higher inlet concentrations. Implications: The application of the toluene induction combined with toluene-styrene synchronous acclimatization demonstrated to be a promising approach for the highly efficient removal of styrene. The toluene induction can accelerate biofilm formation, and the adaptability of microorganisms to styrene can be improved rapidly by the toluene-styrene synchronous acclimatization. The integrated application of two technologies can shorten the start-up period of biotrickling filters markedly and promote its industrial application.

Wavelet denoising and nonlinear analysis of solids concentration signal in circulating fluidized bed riser

Particles, particle aggregates, and reactor walls complicate the dynamic microstructures of circulating fluidized beds (CFBs). Using local solids concentration data from a 10-m-high and 76.2-mm-inner-diameter riser with FCC (Fluid Catalytic Cracking) particles (dp=67μm, ρp=1500kg/m3), this paper presents an improved denoising process for use before nonlinear chaos analysis. Using the soft-threshold denoising method in the wavelet domain with experimental empty bed signals as base data to estimate the denoising threshold, an efficient denoising algorithm was proposed and used for the dynamic signals in CFBs. Analysis shows that for the local solids concentration time series, high-frequency fluctuations may be one of the system properties, while noise interference can also make a low-frequency contribution. An exact denoising method is needed in such cases. The correlation dimension and Kolmogorov entropy were calculated using denoised data and the results showed that the particle behavior in the CFB is highly complex. Generally, two correlation dimensions coexist in a low-flux CFB. The first correlation dimension is low and corresponds to small-scale fluctuations that reveal a high-frequency pseudo-periodic movement, but the second correlation dimension is high and corresponds to large-scale fluctuations that indicate multi-frequency movements, including particle aggregation and breakage. At the same axial level, the first correlation dimensions change slightly with radial position, and the main tendency is high at the center but slightly lower near the wall. However, the second correlation dimensions show large changes along the radial direction, are again high in the core region, and after r/R≥0.6 (r as radial position, R as radius of the riser), the dimensions clearly drop down. This indicates that the particle behavior is more complex and has higher degrees of freedom at the center, but clusters near the wall are restrained to some degree because of wall effects.

Water disinfection using fixed bed reactors packed with silver nanoparticle immobilized glass capillary tubes

The present study focused on development of a robust point-of-use (POU) water disinfection device employing immobilized silver nanoparticles (AgNPs) for water disinfection in continuous flow through mode. Glass capillary tubes functionalized with positively charged amino groups using silane as the cross-linking agent facilitated the immobilization of citrate stabilized AgNPs. A fixed bed reactor (FBR) packed with these AgNP immobilized glass substrate was used for conducting POU water disinfection. The effect of various parameters such as, flow rate, initial concentration of bacteria and bed volume on disinfection performance of the device was evaluated. The total volume of water treated at breakpoint was found to improve with increase in flow rate and 2596–5172 bed volumes of water could be disinfected under the various conditions tested, i.e., empty bed contact time (EBCT) 0.29 to 5.8 min. Silver leaching studied under various operating conditions revealed minimal release of silver (<100 μg/l) in treated water over time throughout the duration of the studies. Plug flow reactor with dispersion (PFDR) model with open boundary condition showed good fit to the E-curve generated by pulse input of chloride tracer and revealed significant dispersion in the FBR. Antibacterial material exhaustion rate (AER) was significantly affected by the EBCT, empty bed volume of the FBR, and load of bacteria in the influent.

A comparative study on dynamic Hg(II) and MeHg(II) removal by functionalized agrowaste adsorbent: breakthrough analysis and adsorber design

The adsorption dynamics of inorganic mercury, Hg(II) and organic methylmercury, MeHg(II) removal by low-cost reactive agrowaste adsorbents namely CP-Pure, CP-MPTES and CP-RR was investigated in a fixed-bed adsorber. The results show that the breakthrough and saturation times were delayed with decreasing flow rate (F) and initial concentration (Co), and increasing bed height (Z). The Hg(II) possessed better adsorption performance than MeHg(II). The isotherm and kinetic model analyses of adsorption data followed the Temkin isotherm and the pseudosecond order kinetic models, respectively. The breakthrough curve was simulated well by the Thomas and Yoon-Nelson models, and then was further used for scale-up studies. The empty bed contact time (EBCT) concept was successfully demonstrated for the adsorber design and scale-up studies. The regeneration studies showed that the regenerated CP-Pure and CP-MPTES have a high regeneration efficiency up to third adsorption cycle.

Detection and Treatment Methods for Perfluorinated Compounds in Wastewater Treatment Plants

We surveyed the variation in perfluorinated compound (PFC) concentrations entering urban wastewater treatment plants and then designed an optimal PFCs treatment method based on a pilot test. The PFCs influent concentration was found to be affected by the types of industries and operating rate. The concentration of PFCs in the wastewater treatment effluent was slightly lower than that of the influent. Thus, PFCs had not been adequately removed by the existing biological treatments. The pilot test results showed that about 10% of PFCs was removed by coagulation and precipitation, and the ozone and chlorine test showed that few, if any, PFCs were removed regardless of the oxidant dose. The activated carbon adsorption test showed that the removal significantly increased with empty bed contact time, with about a 60% removal in five minutes and over 90% removal in over 15 minutes. Therefore, a more stable and higher PFCs removal would result from continuous oxidation processes, such as ozone and adsorption processes involving activated carbon, rather than a single biological treatment.

Performance assessment of gas-phase toluene removal in one- and two-liquid phase biotrickling filters using artificial neural networks

The main aim of this work is to study gas-phase toluene removal in one- and two-liquid phase biotrickling filters (O/TLP-BTF) and model the BTF performance using artificial neural networks (ANNs). The TLP-BTF was operated for 60 d in the presence of silicone oil at empty bed residence times (EBRTs) of 120, 60, and 45 s, respectively, and toluene concentrations in the range of 0.9–3.1 g m−3. A t-test analysis indicated that increasing the silicone oil volume ratio from 5 to 10% v/v, did not significantly improve the TLP-BTF performance (p-value = 0.65 > 0.05). The results from ANN modeling showed that toluene removal was more negatively affected by the inlet concentration (casual index, CI = −5.63) due to the kinetic limitation. The CI values for inlet concentration (+4.01) and liquid trickling rate (−2.45) indicated that the diffusion-limited regime controlled the removal process in the OLP-BTF.

Evaluation of a pilot-scale bio-trickling filter as a VOCs control technology for the chemical fibre wastewater treatment plant.

The performance of lab- and pilot-scale bio-trickling filters (BTFs) for the treatment of emissions from a chemical fibre wastewater treatment plant was investigated. These systems were installed mainly to demonstrate the effectiveness of bio-trickling technologies in purifying exhaust gases containing different kinds of volatile organic compounds (VOCs). Results showed that 12 days more were necessary for the pilot-scale BTF to start up successfully than the lab-scale one. Both the lab- and pilot-scale BTFs exhibited contaminant removal efficiency higher than 90% at an empty bed residence time of 59 s, corresponding to gas flow of 0.2 m3 h-1 and 550 m3 h-1, respectively. The reduction of the microelement in the nutrient solution had little effect on the performance of the pilot-scale BTF. The abundance and diversity of the microorganism analysis showed that the diversity of the contaminants had a significant influence on the microorganism distribution in the BTF. Economic feasibility study showed that BTF might be an efficient solution for VOCs control with a lower cost than adsorption technology and regenerative catalytic oxidation.

Biofiltration performance and kinetic study of hydrogen sulfide removal from a real source.

Biofiltration is one of the most accepted technologies in odor control in wastewater facilities. A biofilter system consists of a bed of organic material providing both as the carrier for the active microorganisms and as nutrient supply. This study was aimed to evaluate and model a biofilter performance operated under real conditions of odor emission from a wastewater pump station located in Khorramabad, Iran. The media was a mixture of compost and wood chips with a weight ratio of 5:1. The treatment performance of the biofilter was assessed during a 90-day operation period and the gathered data were utilized to develop and determine the best fit kinetic model based on Michaelis-Menten and Ottengraf models. The best fit model was used in the analysis of scenarios defined based on inlet H2S loading fluctuations. Also, the effectiveness of the main parameters in biofilter performance was evaluated using a dimensionless sensitivity coefficient. The best fit model was found the Ottengraf zero-order type limited by diffusion based on the values of R-square (0.98) and mean square error (MSE) (0.002). The results demonstrated a high H2S removal efficiency of about 98% in an EBRT (empty bed residence time) of 60s. despite high fluctuations of inlet concentration under real conditions. The system was able to meet the effluent standard limit of 10ppm even if the inlet H2S loading increases up to two times the base level. According to the results of the defined sensitivity coefficient, the system performance was more sensitive to the inlet concentration than EBRT with a ratio of 1.4. In addition to the acceptable efficiencies of biofilter in odor removal, the results proved the worth of using a kinetic model in forecasting the system performance which is a useful tool in the design and operation of such systems.

Photocatalytic degradation of azithromycin using GO@Fe3O4/ ZnO/ SnO2 nanocomposites

Sewage output contains a wide range of organic materials, such as pharmaceutical compounds. These compounds have harmful effects on the environment, such as generation of antibiotic-resistant bacteria; therefore, their degradation has been considered as one of the environmental challenges. The purpose of this research is to synthesize graphene reinforced with nanocomposites of iron oxide/zinc oxide/tin oxide and evaluate its ability to photocatalytic degradation of azithromycin in the aqueous environment. GO@Fe3O4/ZnO/SnO2 nanocomposite was characterized by various techniques including XRD, FT-IR, TEM and VSM. In the batch system, the effect of pH, contact time, catalyst content and initial concentration of azithromycin was investigated; in this system, under optimal conditions of pH = 3, 120 min with 1 g/L of GO@Fe3O4/ZnO/SnO2, 90.06% of 30 mg/L azithromycin were degraded under UV-C irradiation. In the continuous system, the variables of bed height, flow rate and initial concentration of azithromycin have been investigated. The times to reach the column breakthrough point (Cb = 0.02C0) at heights of 6, 8 and 10 cm are 5, 8 and 14 min, respectively. By increasing the height of the bed from 6 to 10 cm, the azithromycin degradation rate increases; the reason for this increase can be due to the increase in contact time. The results indicate that the degradation of azithromycin in a constant bed column strongly depends on these parameters; actually, the time to reach the breaking point decreased with increase of flow rate and initial concentration of azithromycin while increasing with increase of bed height. Estimating the empty bed residence time showed that this model is in good agreement with laboratory data. Therefore, considering the high ability of GO@Fe3O4/ZnO/SnO2 to eliminate azithromycin, this compound can be used as an effective catalyst for the degradation of antibiotics in aquatic environments.

Role of reduced empty bed contact times and pre-treatment by coagulation with Fe(III) salts on the removal of trace organic compounds during sequential biofiltration

Sequential biofiltration (SBF) has been demonstrated to be a promising approach to achieve enhanced biological removal of various trace organic compounds (TOrCs) from wastewater treatment plant (WWTP) effluents by establishing oxic and carbon-limited conditions. This study investigated options to further advance the feasibility of SBF systems by reducing empty bed contact times (EBCTs). Additional experiments were conducted to investigate the pre-treatment of WWTP effluent by coagulation as an option to further decrease the organic carbon availability during SBF. Results indicated that an EBCT reduction in the first filter stage from 90 to 45 and 30 min adversely affected process performance regarding the removal of organic bulk parameters and several TOrCs over short-term. However, after an extended adaptation period of ten weeks comparable performance was observed in two SBF systems with first stage filters operated at EBCTs of 90 and 45 min. The pre-treatment of secondary effluent by coagulation, flocculation and sedimentation was not found to enhance the performance of an SBF system despite substantial removal of organic bulk parameters during the pre-treatment. However, despite the vast removal of total phosphorous during coagulation, nutrient limitation was not found to adversely affect the biological performance of the subsequent SBF system.

Influence of trickling liquid velocity, low molar ratio of nitrogen/sulfur and gas-liquid flow pattern in anoxic biotrickling filters for biogas desulfurization

Hydrogen sulfide has been successfully removed from biogas using anoxic biotrickling filters but an in-depth study of the main operational variables has not yet been carried out. The effect of (i) the empty bed residence time (32–164 s) at a hydrogen sulfide concentration of 2,000 ppmv, (ii) the inlet hydrogen sulfide concentration (2,000–10,000 ppmv), (iii) the trickling liquid velocity (4.8–20.9 m h−1) and (iv) the feed of low nitrogen/sulfur molar ratio (0.334–0.409 mol N-NO3– mol−1 S-H2S) on the hydrogen sulfide removal efficiency have been studied. The BTF (total packed volume of 2.8 L, height/diameter ratio of 9.8) was filled with polypropylene Pall rings (5/8″) and fed continuously with nitrate and a biogas mimic operating in counter-current and co-current flow modes.The maximum elimination capacity was 282.0 gS-H2S m–3 h–1 (RE 97 ± 0.5%) for counter-current flow and 287.5 gS-H2S m–3 h–1 (RE 99 ± 0.4%) for co-current flow mode for an EBRT of 164 s. In addition, in terms of the nitrogen/sulfur molar ratio a higher elemental sulfur production was found in counter-current flow (97.6 ± 2.0%) when compared to co-current flow (87.6±2.8%) since a better depletion of nitrate occurred in co-current flow mode.Finally, three different nitrogen/sulfur molar ratios (0.4, 1.0 and 1.6 mol N-NO3– mol–1 S-H2S) were compared economically. The low and high ratios would involve a nitrate cost of 0.54 and 2.15 € per kg of treated of S-H2S and an elemental sulfur production of 21.5 metric tons and zero production, respectively.

Bio-attenuation of arsenic and iron coupled with nitrate remediation in multi-oxyanionic system: Batch and column studies.

Co-occurrence of arsenic and iron along with nitrate in groundwater makes the trio an onerous combination both in terms of potability and treatment. To meet drinking water guidelines, batch and column laboratory trials were conducted on simulated and bore-well water for attenuation of arsenic (1000 μg/L), iron (5 mg/L) and nitrate (150 mg/L). Increment in sulphate showed a direct individual impact on iron removal, meeting WHO guidelines. The bio-kinetic parameters were in the range of: μmax = 0.079-0.551/d, Ks = 116.18-645.19 mg/L, Kd = 0.0009-0.0077/d and Y = 0.034-0.094 mg MLVSS/mg COD. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed orpiment precipitation and/or co-precipitation with mackinawite are the key mechanisms for arsenic and iron attenuation. Column experiments were conducted by charging simulated groundwater containing arsenic (500 μg/L), nitrate (50 mg/L), sulphate (25 mg/L) and iron (3 mg/L) in an acetate (105 mg/L as COD) fed flow-through bioreactor at constant empty bed contact time of 60 min. Profile sampling illustrated segregation of different terminal electron accepting zones following thermodynamic yield for sequential removal of different oxyanions. This study showed the importance of considering microbially mediated terminal electron-accepting processes (TEAP) for multi-oxyanion removal in engineered systems.

Nutrient removal from urban stormwater runoff by an up-flow and mixed-flow bioretention system.

Bioretention is one of the most popular technical practices for urban runoff pollution control. However, the efficiency of nutrient removal from urban stormwater runoff by bioretention systems varies significantly. To improve the nutrient removal performance, innovative up-flow and mixed-flow bioretention systems were proposed in this study, and a laboratory study was conducted to investigate the runoff retention and nutrient removal performance. During the leaching experiment using tap water as the inflow, turbidity, chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) leaching phenomenon was obvious. COD and TN leaching controls were obviously improved when the up-flow and mixed-flow bioretention systems were adopted comparing with the conventional bioretention. During the semi-synthetic runoff experiments, after the leaching experiments' performance (accumulated 2.78 times of empty bed volume), there were no significant differences in COD mass removal efficiencies of conventional and up-flow bioretention processes (p > 0.05); however, the COD mass removal efficiencies of the mixed-flow bioretention processes increased by 10% when compared with conventional bioretention. The TN mass removal efficiencies of the up-flow and mixed-flow bioretention increased obviously from 17% ± 13% (conventional) to 41% ± 23% (up-flow) and 31% ± 16% (mixed-flow). However, there were no significant differences in TP mass removal or runoff reduction among the three bioretention columns (p > 0.05). Both up-flow and mixed-flow bioretention can effectively improve TN mass removal, and the mixed-flow bioretention did not show a better TN removal performance than the up-flow bioretention because these two bioretention had almost the same volume of the saturated zone. Overall, the results indicate the mixed-flow bioretention proposed in this study can effectively improve TN mass removal and slightly improve COD mass removal relative to conventional methods via increases in hydraulic retention time and in-flow paths, respectively.