Simultaneous removal of organic substances and nitrogen using amembrane bioreactor seeded with anaerobic granular sludge under oxygen-limited conditions

An innovative process, the oxygen-limited membrane bioreactor seeded with anaerobic granular sludge, wasproposed and its performance investigated for concurrent removal of organic substances and nitrogen from synthetic domestic wastewaters. An air diffuser was installed just above the granular sludge bed to supply air to the reactor at an intermittent mode. The internal recycle from the upper part of the reactor to the bottom was introduced to provide the granular sludge bed under the oxygen-limited conditions. The oxygen addition rates were controlled at 3-4 g O₂ 1⁻¹d⁻¹. The total COD removal efficiency of more than 94% was achieved throughout the whole operation period. N was removed through the simultaneous nitrification and denitrification process that took place in the granular sludge bed. TN levels decreased with the decrease of ammonium levels, indicating that nitrification was the rate-limiting step. The TN removal efficiency reached 80-91% at an hydraulic retention time of 15 h. Nitrate was scarcely detected and nitrite was the main NO_x-N species in the effluent, indicating that nitrite oxidizers were inhibited in the system.     

黄贮玉米秸秆在全混流、竖向推流、折流板竖向推流反应器中的厌氧发酵特性

为提高厌氧发酵的效率和秸秆利用率,将玉米干秸秆经过物理生物联合预处理形成黄贮玉米秸秆。本研究通过实验考察了黄贮玉米秸秆在竖向推流反应器（vertical plug flow,VPF）、全混流反应器（continuous stirred tank reactor,CSTR）和由本文作者课题组首创的折流板竖向推流反应器（baffled vertical plug flow,BVPF）中的厌氧发酵产气性能。结果表明,VPF反应器在有机负荷率（organic loading rate,OLR）为0.5gVS/(L·d)时运行良好,但提高OLR会出现出料困难的问题。CSTR有搅拌装置,所以反应器能够快速达到产气平衡。在OLR为1gVS/(L·d)时,BVPF达到稳定所需时间比CSTR多7天,但最终趋于稳定时CSTR和BVPF反应器的单位挥发性固体（volatile solid,VS）的日产气量分别为390.9mL和382.4mL。在OLR为2gVS/(L·d)时,BVPF达到稳定所需时间仅比CSTR多2天,稳定时CSTR和BVPF反应器的单位VS日产气量分别为291.3mL和294.9mL。此外,3种反应器在运行阶段,pH和VFA/TIC值都能维持稳定。在提高OLR后,BVPF和CSTR能够达到新的平衡状态。本实验结果表明VPF反应器只能用于低OLR的情况;CSTR达到稳定状态所需的时间较短,但CSTR和BVPF在稳定运行时的产气效率基本持平。由于BVPF的耗能量、耗水量低,因此该类反应器有良好的商业应用前景。     

Characteristics of simultaneous nitrogen and phosphorus removal in a pilot-scale sequencing anoxic/anaerobic membrane bioreactor at various conditions

This study was conducted to evaluate the performance of pilot-scale sequencing anoxic/anaerobic membrane bioreactor (SAM) process under various real situations. During the pilot experiment, the effect of three important operational parameters, such as hydraulic retention time (HRT), solids retention time (SRT) and internal recycling time mode were estimated and the long-term membrane fouling behaviour was also investigated. During the operation period, the COD removal efficiency was higher than 95% regardless of change of operational conditions because the membrane significantly contributed to remove COD by the complete retention of all particulate COD and macromolecular COD components. The change of Ax/An ratio representing internal recycling time mode significantly affected on nitrogen and phosphorus removal. As increasing Ax/An ratio, nitrogen removal efficiency increased but phosphorus removal efficiency decreased. As HRT decreased, phosphorus removal efficiency increased and nitrogen removal efficiency also increased until a certain limit of HRT (6.5 h in this study). However, when HRT decreased over the limit, nitrogen removal efficiency decreased because of insufficient nitrification. Relation between phosphorus removal efficiency and SRT was a little bit complex because SRT determined both the phosphorus content in the sludge and the sludge wasting rate. However, in this study, the shorter SRT resulted in the higher phosphorus removal efficiency. The effect of changes in all operational conditions was sensitive on phosphorus rather than on nitrogen removal efficiency. The increasing in influent flowrate resulted in the increase of flux and caused a rapid membrane fouling. Thus, the flux of 7.7 L/m²/h was more desirable compared to the 10.7 or 15.4 L/m²/h in this study.     

Continuous methanogenesis of black liquor of pulp and paper mills in an anaerobic baffled reactor using an immobilized cell system

An anaerobic baffled reactor together with an immobilized cell system has been proposed for methanogenesis of the black liquor from pulp and paper mills in a continuous system. A maximum chemical oxygen demand reduction of 50%, and biogas generation of 10 L d^?1, having methane content of 66% (v/v) at an organic loading rate (OLR) of 7 kg m^?3 d^?1 with hydraulic retention time of 2 days, were recorded. OLR values higher than 7 kg m^?3 d^?1 were toxic to methanogenesis and destabilized the reactor system. Copyright © 2006 Society of Chemical Industry     

Plant response to the management of fluid and solid N fertilizers applied to furrow-irrigated corn

The use of fluid fertilizers has increased in recent years. Plant response to field management practices of fluid and solid N fertilizers in furrow-irrigated field studies has not been well-documented. This research studied the response of corn (Zea mays L.) to several field management practices of fluid and solid N fertilizers applied at several rates. Corn grown with sidedressed applications of the fluid fertilizers, urea ammonium nitrate (UAN) and 18-0-0+7Ca, generally had higher grain yields, higher yield efficiencies, higher ear populations, larger seed size, more kernels per ear, and a higher ear leaf N concentration than corn grown with preplant broadcast treatments of urea, ammonium nitrate (AN), and UAN. In 1988, corn grown with 280 kg N ha^–1 of AN applied preplant broadcast had a lower grain yield, yield efficiency, kernels per ear, and ear leaf N concentration, while ear population and kernel size were unchanged, in comparison to split applications of UAN at 224 kg N ha^–1. In 1989, corn grown with three split applications of UAN at 280 kg N ha^–1 had a higher grain yield and produced more kernels per ear without affecting yield efficiency, ear population, kernel size, or ear leaf N concentration compared with treatments at the 224 kg N ha^–1 rate. Use of split, side-dressed N management practices in furrow-irrigated corn should eliminate the need to use excessive N rates while maintaining grain yields and other plant responses, resulting in more efficient N use than traditionally achieved.     

Modeling and optimization of the electric flocculation of wastewater containing Cr6+ using response surface methodology

Wastewater containing Cr⁶⁺ with large water quantity and high levels of toxicity damages human health through the food chain. Electric flocculation was one of the commonly used methods for heavy metals wastewater treatment, which was applied to remove Cr⁶⁺ from wastewater. In this study, response surface methodology (RSM) was used to investigate the effects of different operating conditions on the removal efficiency of Cr⁶⁺ by the electric flocculation with iron electrodes. Box–Behnken design (BBD) was used for the optimization of the electric flocculation process to evaluate the effects and interactions of process variables such as initial pH, the electrode distance, the current density, and reaction time on the removal efficiency of Cr⁶⁺. The optimum values were found to be 5.48, 2.51 cm, 87.55 A/m², and 25.6 min, respectively. Under this condition, the removal efficiency of Cr⁶⁺ reached 99.34%.     

Performance of an industrial biofilter from a composting plant in the removal of ammonia and VOCs after material replacement

BACKGROUND: Biofiltration is a suitable odor reduction technique for the treatment of gaseous emissions from composting processes, but little is known about the start‐up of full‐scale biofilters after material replacement and their performance after several years of operation. RESULTS: Biofilter material (wood chips used previously as bulking agent in a composting process) can effectively remove ammonia and most of the volatile organic compounds (VOCs) content, achieving removal efficiencies greater than 70% for VOCs and near 90% for ammonia immediately after material replacement. These removal efficiencies were maintained for several months after material replacement. In the studied full‐scale biofilter no lag phase was observed in the removal of ammonia whereas in the case of VOCs different patterns were detected during biofilter start‐up. For the old biofilter material, after 4 years of operation, a statistically significant decrease of removal efficiency for ammonia in comparison with the new material was detected. No statistically significant differences were found in the case of VOCs. CONCLUSIONS: Data on the emissions of several pollutants from biofilters treating composting exhaust gases have been systematically obtained. The tested filtering media presented adequate properties for biofiltration of gases emitted during the composting process. Copyright © 2009 Society of Chemical Industry     

Photoanodic response of iron oxide electrode in aqueous solution and its application to Pb removal under visible light irradiation

The iron oxide electrode was prepared from thermal oxidation of iron at 600 °C for 3 h in air atmosphere. This electrode with the structure of Fe₃O₄ and α-Fe₂O₃ showed the response of photoanodic current to the light with wavelength shorter than 600 nm. The band gap energy of this electrode was 1.99 eV. The onset potential of distinct steady photocurrent and also the flatband potential were 0.80 and 0.09 V vs. Ag/AgCl, respectively, in 0.1 M HNO₃ aqueous solution. The cell consisting of the iron oxide photoanode in HNO₃-Pb(NO₃)₂ and the graphite cathode in H₂SO₄-Ce(SO₄)₂ caused the PbO₂ deposit on the surface of the former electrode due to visible light irradiation without application of voltage. By holding the potential of this electrode at more positive value than 0.90 V, the photoanodic removal rate of Pb²⁺ in HNO₃-Pb(NO₃)₂ solution was higher than that observed when Ce⁴⁺ was used as electron acceptor.     

Performance response and recovery of temporal and spatial phase separated process for nutrients removal in short-term shock loadings

This study was conducted to evaluate the stability and performance response under short-term hydraulic and organic shock load conditions in temporal and spatial phase separated process. The overall removals of BOD, TN, and TP declined slightly despite the hydraulic shock loading, and rapid recovery could be observed again after four cycles of 16 h. It seems that rapid recovery may be achieved by the unique characteristics of the system operated in a fed-batch manner. The effect of shock load on nitrogen removal due to increment of flow rate was higher than that of phosphorus, because of the insufficient reaction time for the nitrification and denitrification. After the organic shock, however, recovery time for phosphorus removal was needed rather than that of organics and nitrogen, because the overload to micro organisms related to the phosphorus release is attained by short-term organic shock loading.     

Attempts to reduce water and chemical usage in the removal of reactive dyes: Part 1 bis(aminochlorotriazine) dyes

Dyeings on cotton obtained using three commercial reactive dyes were subjected to three wash-off processes namely, a standard, five-stage method which used a proprietary wash-off agent, a five-stage process in which Na₂CO₃ was used in place of the commercial wash-off agent and a three-stage, chemical-free method. Dyeings that were generally of the same hue and colour strength and which also displayed similar levels of fastness to repeated washing, were obtained using each of the three wash-off processes. The replacement of the commercial wash-off agent in the five-stage, standard wash-off process with Na₂CO₃ reduced, considerably, both the COD and BOD₅ loads of the residual wastewater; the corresponding COD/BOD₅ ratios showed an improvement in the biodegradability of the residual wastewater. Although reducing the number of wash-off stages from five to three and replacing Na₂CO₃ with 98 °C water rinses increased both COD and BOD₅ loads, the ensuing biodegradability of the residual wastewater was improved. Thus, by using a three-bath, water-only wash-off process, not only was the amount of water used for reactive dye wash-off reduced but also the wastewater generated was of higher biodegradability.     

Addition of activated carbon to batch activated sludge reactors in the treatment of landfill leachate and domestic wastewater

Leachate from a municipal landfill was combined with domestic wastewater and was treated in batch activated sludge systems. The effectiveness and applicability of the addition of Powdered Activated Carbon (PAC) to activated sludge reactors was investigated. Isotherm tests were carried out with PAC in order to estimate the extent of adsorption of organic matter onto PAC. Then, in activated sludge reactors COD (Chemical Oxygen Demand) removal and nitrification were studied both in the absence and presence of PAC for comparison purposes. In both cases, Oxygen Uptake Rates (OUR) were measured with respect to time in order to investigate substrate removal and change in microbial activity. Addition of PAC to activated sludge increased COD removal by removing mainly the non‐biodegradable fraction in leachate. The COD decreases in batch reactors were best expressed by a first‐order kinetic model that incorporated this non‐biodegradable leachate fraction. With added PAC, nitrification was also enhanced. But in all of the batch runs a significant accumulation of NO₂ ‐N took place, indicating that the second step of nitrification was still inhibited. © 2001 Society of Chemical Industry     

Application of response surface methodology to optimize the operation process for regeneration of acid and base using bipolar membrane electrodialysis

BACKGROUND: Bipolar membrane electrodialysis (BMED) has been widely used for desalination, concentration, separation, and purification in many fields. The purpose of this study is to optimize the operation conditions using response surface methodology (RSM) for the regeneration of sulfuric acid and ammonia from ammonium sulfate solution by BMED coupled with ammonia in situ stripping. RESULTS: A three‐factor central composite design of RSM was used to analyze the effect of operation conditions (current density, flow rate, initial acid concentration) on average current efficiency (ACE) and establish the optimal operation conditions. The ACE was 76.7 ± 2.2% under optimal operation conditions (current density 23.8 mA cm^?2, flow rate 27.3 L h^?1, initial acid concentration 0.09 mol L^?1). CONCLUSION: A suitable regression model for predicting ACE within the ranges of variables used was developed based on experimental results. The operation conditions were optimized by RSM and the ACE obtained under the optimal operation conditions was in good agreement with the value predicted by the regression model (78%), which proved the validity of the model. Copyright © 2007 Society of Chemical Industry     

Comparative response of bread and durum wheat cultivars to nitrogen fertilizer in a rainfed Mediterranean environment: soil nitrate and N uptake and efficiency

A 3-year multi-site study was carried out on rainfed Vertisols under Mediterranean conditions in southern Europe to determine the influence of the N fertilizer rate on soil nitrates, N uptake and N use efficiency in bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. Durum Desf.) in rotation with sunflower (Heliathus annuus L.). Nitrogen fertilizer rates were 0, 100, 150 and 200 kg N ha⁻¹ applied in equal proportions at sowing, tillering and stem elongation. The experiment was designed as a randomized complete block with a split plot arrangement and four replications. Nitrogen harvest index (NHI), N uptake/grain yield (NUp/GY), N use efficiency (NUE), N utilization efficiency (NUtE), N uptake efficiency (NUpE) and N apparent recovery fraction (NRF) were calculated. Differences were observed in N use efficiency between the two modern bread wheat and durum wheat cultivars studied. In comparison to durum, bread wheat displayed greater N accumulation capacity and a more efficient use of N for grain production. While under N-limiting conditions, the behavior was similar for both wheat types. No difference was noted between wheat types with regard to changes in soil residual levels over the study period at the various sites. The 100-kg ha⁻¹ N fertilizer rate kept soil nitrates stable at a moderate level in plots where both wheat types were sown.     

高炉水淬渣对电镀废水中重金属和COD吸附的响应面优化

为了考察高炉水淬渣处理实际电镀废水中重金属离子和COD的可行性,分别研究了吸附剂投加量、pH、吸附时间以及温度等单因素对Cu²⁺、Zn²⁺或COD去除率的影响。在单因素实验的基础上,应用 Box-Behnken中心组合方法进行三因素三水平试验,建立二次多项数学模型,并验证该模型的有效性。采用响应曲面法探讨吸附剂投加量、pH、吸附时间3个因子的交互作用及其最佳水平。结果表明：在吸附剂投加量为1.4g、pH为8、吸附时间为120min的最优化条件下,电镀废水中Cu²⁺、Zn²⁺和COD去除率达到最大,分别为99.35%、98.46%和53.63%。经对最优条件进行验证,预测值与验证实验平均值接近。吸附后废水中的Cu²⁺和Zn²⁺低于GB 21900-2008电镀废水新建企业污染物排放限值要求,而COD没有满足排放要求,所以仅应用高炉水淬渣吸附技术还不足以去除电镀废水中所有有害物质,因此可利用此技术作为辅助工艺,联合其他技术共同去除电镀废水中的重金属离子和有机物,使出水水质达到国家排放标准。     

Performance studies of various cracking catalysts in the conversion of canola oil to fuels and chemicals in a fluidized-bed reactor

Studies were conducted at atmospheric pressure at temperatures in the range of 400–500°C and fluidizing gas velocities in the range of 0.37–0.58 m/min (at standard temperature and pressure) to evaluate the performance of various cracking catalysts for canola oil conversion in a fluidized-bed reactor. Results show that canola oil conversions were high (in the range of 78–98 wt%) and increased with an increase in both temperature and catalyst acid site density and with a decrease in fluidizing gas velocity. The product distribution mostly consisted of hydrocarbon gases in the C₁–C₅ range, a mixture of aromatic and aliphatic hydrocarbons in the organic liquid product (OLP) and coke. The yields of C₄ hydrocarbons, aromatic hydrocarbons and C₂–C₄ olefins increased with both temperature and catalyst acid site density but decreased with an increase in fluidizing gas velocity. In contrast, the yields of aliphatic and C₅ hydrocarbons followed trends completely opposite to those of C₂–C₄ olefins and aromatic hydrocarbons. A comparison of performance of the catalysts in a fluidized-bed reactor with earlier work in a fixed-bed reactor showed that selectivities for formation of both C₅ and iso-C₄ hydrocarbons in a fluidized-bed reactor were extremely high (maximum of 68.7 and 18 wt% of the gas product) as compared to maximum selectivities of 18 and 16 wt% of the gas product, respectively, in the fixed-bed reactor. Also, selectivity for formation of gas products was higher for runs with the fluidized-bed reactor than for those with the fixed-bed reactor, whereas the selectivity for OLP was higher with the fixed-bed reactor. Furthermore, both temperature and catalyst determined whether the fractions of aromatic hydrocarbons in the OLP were higher in the fluidized-bed or fixed-bed reactor.     

Effect of defoliation and phosphorus concentration in the sown seed on the response of swards of annual pasture legumes to superphosphate applications

The relationship between dry matter (DM) herbage yield and the level of superphosphate applied to the soil (soil P) was measured for swards of annual pasture legumes in four glasshouse and two field experiments. A single cultivar of one species was used in each experiment. The swards were either uncut, or cut at weekly intervals to a height of 1.5 to 3 cm from the soil surface from about one month after sowing. The sown seeds of each species were of the same size but contained different P concentrations (seed P).For the glasshouse experiments, defoliation reduced DM herbage yields of the species (Trifolium subterraneum, T. balansae, Medicago polymorpha andOrnithopus compressus) by between 20 to 50% two months after sowing, and by 50 to 75% three months after sowing. Higher seed P increased DM herbage yields two months after sowing by about 25% for the lowest soil P level and by 15% for the highest soil P level. Three months after sowing the values were 12 and 8%.In one field experiment, compared with uncut swards, the DM herbage yields for the weekly cut swards ofT. subterraneum were reduced by up to about 5% for the lowest soil P, compared with up to 25% for the highest soil P. Corresponding reductions forM. polymorpha swards in the other field experiment were about 15 and 20%. For the weekly cut swards, high seed P produced large increases in the cumulative DM yields of the weekly cut herbage. Increases for low soil P were about 300% at 2.5 months after sowing and 30% at 4.5 months after sowing. Corresponding values for high soil P were 100 and 20%. However, higher seed P produced only small (zero to 15%) increases in total DM yield of uncut and weekly cut swards (for the weekly cut swards, total DM yield was the cumulative yields of the weekly cut herbage plus the DM yield of the plant residues that were below the cutting height of the mower). Compared with uncut swards, seed production, measured forM. polymorpha only, was reduced by 40% when the swards were regularly cut. Higher seed P increased seed production of uncut swards by 40% for the lowest soil P level and by 25% for the highest soil P level. Corresponding values for the weekly cut swards were 30 and 20%.