Performance of a fungal biofilter treating gas-phase solvent mixtures during intermittent loading

Biological treatment processes used to remove and degrade volatile organic compounds (VOCs) from contaminated gases emitted by industrial operations or waste treatment processes are almost always subjected to transient loading conditions because of the inherently unsteady-state nature of contaminant generating processes. In the study presented here, a laboratory-scale biofilter populated by a mixed culture of fungi was used to study the transient response to various periods of no contaminant loading in a system treating a model waste gas stream containing a mixture of commonly used solvents. The biofilter, packed with cubed polyurethane foam media and operated with an empty bed residence time of 15s, was supplied with a four-component mixture of n-butyl acetate, methyl ethyl ketone, methyl propyl ketone, and toluene at target influent concentrations of 124, 50.5, 174, and 44.6 mg/m(3), respectively. This corresponds to a total VOC loading rate of 94.3g/(m(3)h). Biofilter performance was evaluated over a 94-day period for three loading conditions intended to simulate processes generating contaminated gases only during daytime operation, daytime operation with weekend shutdown periods, and with long term (9-day) shutdown. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating solvent contaminated off-gases even under discontinuous loading conditions.     

The effect of nitrate on VOC removal in trickle-bed biofilters

In response to the growing concern over volatile organic compounds (VOCs), biofiltration is becoming an established economical air pollution control technology for removing VOCs from waste air streams. Current research efforts are concentrating on improving control over key parameters that affect the performance of gas phase biofilters. This study utilized diethyl ether as a substrate, nitrate as the sole nutrient nitrogen source within two co-currently operated trickle-bed biofilters, for over 200 days. The two pelletized medium biofilters were operated at a low empty bed contact time of 25 s, inlet gas flow rates of 8.64 m³/day, nutrient liquid flow rates of 1 liter/day, and COD loading rates of 1.8 and 3.6 kg/m³ per day, respectively. Operational parameters including contaminant concentration in the gas phase, nutrient nitrate concentration in the aqueous phase, and the frequency of biomass removal were considered. Special attention was given to the effect and the role of nitrate on VOC removal. Throughout the experiment, nitrate persisted in the liquid effluent and the ether removal efficiencies improved with increasing influent nitrate concentration, which suggest that the nitrate diffusion into the biofilms is rate determining. By increasing the concentration of oxygen in the feed to this biofilter from 21% (ambient air) to 50 and 100%, while maintaining an influent ether concentration of 133 ppmv and a feed nitrate concentration of 67 mg-N/liter, the performance of the biofilter was not significantly affected. These results suggest that nitrogen was rate limiting as a growth nutrient rather than as an electron acceptor for the respiration of ether. The results also indicated that removal of excess biomass is necessary to maintain long-term performance. However, the required frequency of biomass removal depends on operating parameters such as loading.     

Treatment of gas-phase methanol in conventional biofilters packed with lava rock

The performance of laboratory scale methanol-degrading biofilters packed with lava rock was checked during almost 1 yr under different conditions. The biomass concentration and biomass adaptation of the inoculum dramatically affected the start-up and the performance of the systems during the first stages of operation. A fast start-up was obtained when using concentrated and adapted inocula, while diluted or non-adapted inocula proved to be much less efficient. The performance of the reactor during long-term operation was significantly affected by the toxic load and moisture content of the gas. Critical loads between 120 and 280 g/m(3)h were reached during different phases of the study. The reactor had a high stability to EBRT changes when working at values between 48.0 and 91.1s, showing little or no negative effect when decreasing the EBRT. Hardly any difference was observed regarding performance when using either a downflow or upflow feed, although slightly better results were obtained when working in a downflow mode.     

Experimental investigation on the performance, gaseous and particulate emissions of a methanol fumigated diesel engine

Experiments were conducted on a 4-cylinder direct-injection diesel engine with fumigation methanol injected into the air intake of each cylinder. The fumigation methanol was injected to top up 10%, 20% and 30% of the power output under different engine operating conditions. The effects of fumigation methanol on engine performance, gaseous emissions and particulate emission were investigated. The experimental results show that there is a decrease in the brake thermal efficiency when fumigation methanol is applied, except at the highest load of 0.67 MPa. At low loads, the brake thermal efficiency decreases with increase in fumigation methanol; but at high loads, it increases with increase in fumigation methanol. The fumigation method results in a significant increase in hydrocarbon (HC), carbon monoxide (CO), and nitrogen dioxide (NO(2)) emissions. The concentration of nitrogen oxides (NOx) is significantly reduced except at close to full load condition. There is also a reduction in the smoke opacity and the particulate matter (PM) mass concentration. For the submicron particles, the total number of particles decreases at low and medium loads but increases at high loads. In all cases, there is a shift of the particles towards smaller geometrical mean diameter, especially at high loads. The increase in nano-sized particles and the increase in NO(2) emission could have serious impact on human health.     

Integrated anaerobic-aerobic fixed-film reactor for slaughterhouse wastewater treatment

An integrated anaerobic-aerobic fixed-film pilot-scale reactor with arranged media was fed during 166 days with slaughterhouse wastewater. Operation temperature was 25 degrees C and the anaerobic-aerobic volume ratio was decreased from 4:1 to 3:2 and finally to 2:3. Overall organic matter removal efficiencies of 93% were achieved for an average organic loading rate of 0.77 kg COD/m3 d, and nitrogen removal efficiencies of 67% were achieved for nitrogen loading rates of 0.084 kg N/m3 d. The high internal recirculation associated to the air-lift effect linked to the aeration of a part of the reactor section caused high mixing between the anaerobic and aerobic zones, so that most organic matter was removed aerobically. The nitrification process achieved an efficiency of 91% for nitrogen loads of 0.15 kg N/m3 d when the anaerobic-aerobic volume ratio was 2:3 and was limited by dissolved oxygen concentration below 3 mg/l. The influence of the heterotrophic biomass growing in the outer biofilm was checked. Denitrification only implied the 12-34% of the total nitrogen removal and was limited by dissolved oxygen concentration in the anaerobic zone above 0.5 mg/l caused by the mixing regime. Most removed nitrogen was employed in synthesis of heterotrophic bacteria.     

Effect of shock and mixed nitrophenolic loadings on the performance of UASB reactors

The effect of nitrophenolic shock loads on the performance of three bench-scale upflow anaerobic sludge blanket (UASB) reactors was studied using synthetic wastewater. Reactors R1, R2 and R3 were fed with 30 mg/L concentration of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP), respectively, along with methanol (COD = 2000 mg/ L), sodium nitrate (NO3(-)-N=200mg/L), and other nutrients. The reactors were in continuous operation for more than 2 years before the shock loading study was performed. Five nitrophenolic shock loadings of 45, 60, 75, 90 and 120mg/L d were administrated by increasing the influent nitrophenolic concentration to 45, 60, 75, 90 and 120mg/L, respectively, while keeping hydraulic retention time as 24h. The shocks were given continuously for a period of 4 days before switching back to normal nitrophenolic loading (30mg/Ld). The reactors were allowed to recover to normal performance level before administrating the next nitrophenolic shock load. The study showed that the nitrophenolic shock load of as high as 120 mg/L d did not affect the reactors performance irreversibly. After resuming the normal nitrophenolic loading, it took almost 3-18 days for the reactors to recover from the shock effect. The study was further extended to assess the maximum possible mixed nitrophenolic loading (2NP:4NP:2,4:DNP = 1:1:1) to which 2,4-DNP acclimated granular sludge containing reactor (R3) can be exposed without hampering the reactor (R3) performance irreversibly. The reactor was able to achieve pseudo-steady-state at a mixed nitrophenolic loading of 180 mg/L d with more than 90% removal of all the three nitrophenols, but failed at a mixed nitrophenolic loading of 225 mg/Ld.     

Development of biomass in a drinking water granular active carbon (GAC) filter

Indigenous bacteria are essential for the performance of drinking water biofilters, yet this biological component remains poorly characterized. In the present study we followed biofilm formation and development in a granular activated carbon (GAC) filter on pilot-scale during the first six months of operation. GAC particles were sampled from four different depths (10, 45, 80 and 115 cm) and attached biomass was measured with adenosine tri-phosphate (ATP) analysis. The attached biomass accumulated rapidly on the GAC particles throughout all levels in the filter during the first 90 days of operation and maintained a steady state afterward. Vertical gradients of biomass density and growth rates were observed during start-up and also in steady state. During steady state, biomass concentrations ranged between 0.8-1.83 x 10⁻⁶ g ATP/g GAC in the filter, and 22% of the influent dissolved organic carbon (DOC) was removed. Concomitant biomass production was about 1.8 × 10¹² cells/m²h, which represents a yield of 1.26 × 10⁶ cells/μg. The bacteria assimilated only about 3% of the removed carbon as biomass. At one point during the operational period, a natural 5-fold increase in the influent phytoplankton concentration occurred. As a result, influent assimilable organic carbon concentrations increased and suspended bacteria in the filter effluent increased 3-fold as the direct consequence of increased growth in the biofilter. This study shows that the combination of different analytical methods allows detailed quantification of the microbiological activity in drinking water biofilters.     

Performance and biofilm activity of nitrifying biofilters removing trihalomethanes

Nitrifying biofilters seeded with three different mixed-culture sources removed trichloromethane (TCM) and dibromochloromethane (DBCM) with removals reaching 18% for TCM and 75% for DBCM. In addition, resuspended biofilm removed TCM, bromodichloromethane (BDCM), DBCM, and tribromomethane (TBM) in backwash batch kinetic tests, demonstrating that the biofilters contained organisms capable of biotransforming the four regulated trihalomethanes (THMs) commonly found in treated drinking water. Upon the initial and subsequent increased TCM addition, total ammonia nitrogen (TOTNH₃) removal decreased and then reestablished, indicating an adjustment by the biofilm bacteria. In addition, changes in DBCM removal indicated a change in activity related to DBCM. The backwash batch kinetic tests provided a useful tool to evaluate the biofilm’s bacteria. Based on these experiments, the biofilters contained bacteria with similar THM removal kinetics to those seen in previous batch kinetic experiments. Overall, performance or selection does not seem based specifically on nutrients, source water, or source cultures and most likely results from THM product toxicity, and the use of GAC media appeared to offer benefits over anthracite for biofilter stability and long-term performance, although the reasons for this advantage are not apparent based on research to date.     

Effect of shock and mixed loading on the performance of SND based sequencing batch reactors (SBR) degrading nitrophenols

The effect of nitrophenolic shock loads on the performance of three lab scale SBRs was studied using a synthetic feed. Nitrophenols were biotransformed by Simultaneous heterotrophic Nitrification and aerobic Denitrification (SND) using a specially designed single sludge biomass containing Thiosphaera pantotropha. Reactors R1, R2 and R3 were fed with 200 mg/L concentration of 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP), and 2,4,6-trinitrophenol (2,4,6-TNP) whereas reactor R was used as a background control. Three nitrophenolic shock loadings of 400, 600 and 800 mg/L d were administrated by increasing the influent nitrophenolic concentration while keeping the hydraulic retention time as 48 h. The shocks were given continuously for a period of 4 days before switching back to normal nitrophenolic loading (200 mg/L d). The reactors were allowed to recover to normal performance level before administrating the next nitrophenolic shock load. The study showed that a nitrophenolic shock load, as high as 600 mg/L d was completely degraded by the 4-NP & 2,4-DNP bioreactors while almost half degraded by the 2,4,6-TNP bioreactor without affecting the reactor’s performance irreversibly. After resuming the normal nitrophenolic loading, it took almost 8-10 days for the reactors to recover from the shock effect. The study was further extended to evaluate the maximum possible mixed nitrophenolic loading (4-NP:2,4-DNP:2,4,6-TNP 1:1:1) to which a reactor (R3) containing 2,4,6-TNP acclimated single sludge biomass can be exposed without hampering the reactor performance irreversibly. The reactor was able to achieve pseudo-steady-state at a mixed nitrophenolic loading of 300 mg/L d with more than 90% removal of all the three nitrophenols, but could remove half of the mixed nitrophenolic loading of 600 mg/L d.     

Response of the anaerobic fluidized bed reactor to transient changes in process parameters

Anaerobic fluidized bed reactors treating a high strength dairy type waste water were subjected to transient decreases in temperature and increases in influent flowrate or COD for 4 and 8 h periods. The quality of the effluent deteriorated during a shock load but returned to normal steady state values 6–22 h after original conditions had been restored, the stability of the reactor during increases in influent COD were found to be influenced by the bicarbonate buffering capacity of the feed.     

Emission reduction from diesel engine using fumigation methanol and diesel oxidation catalyst

This study is aimed to investigate the combined application of fumigation methanol and a diesel oxidation catalyst for reducing emissions of an in-use diesel engine. Experiments were performed on a 4-cylinder naturally-aspirated direct-injection diesel engine operating at a constant speed of 1800 rev/min for five engine loads.The experimental results show that at low engine loads, the brake thermal efficiency decreases with increase in fumigation methanol; but at high loads, it slightly increases with increase in fumigation methanol. The fumigation method results in a significant increase in hydrocarbon (HC), carbon monoxide (CO), and nitrogen dioxide (NO₂) emissions, but decrease in nitrogen oxides (NO_x), smoke opacity and the particulate mass concentration. For the submicron particles, the total number of particles decreases. In all cases, there is little change in geometrical mean diameter of the particles. After catalytic conversion, the HC, CO, NO₂, particulate mass and particulate number concentrations were significantly reduced at medium to high engine loads; while the geometrical mean diameter of the particles becomes larger. Thus, the combined use of fumigation methanol and diesel oxidation catalyst leads to a reduction of HC, CO, NO_x, particulate mass and particulate number concentrations at medium to high engine loads.     

Response of dissolved oxygen to changes in influent organic loading to activated sludge systems

The major objective of this investigation was to examine the response of the activated sludge process to transient organic loadings and to evaluate the applicability of dissolved oxygen (DO) concentration and oxygen uptake rate as process control variables.A modified laboratory-scale activated sludge unit was used to continuously measure the ambient dissolved oxygen level. The change of the dissolved oxygen concentration responded to variations in the influent composition of the wastewater. First, the system was maintained at steady-state and system variables were measured for soluble TOC, MLVSS and oxygen uptake rate. The organic shock loading was induced by increasing or decreasing the baseline feeding of TOC concentration. As soon as a transient loading occurred the DO levels in the system were continuously monitored with the DO analyzer.A simplified material balance equation for dissolved oxygen in the system was developed and the dynamic behavior of oxygen uptake rate was examined. It was demonstrated that under transient conditions the changes in the dissolved oxygen concentration reflected the variations in the exogenous respiration rate of the biomass in the system due to fluctuations in the influent waste characteristics. Based upon the rapid response to the shock loading and the correlation of the change in the DO level to the magnitude of the shock loading, the two variables (DO concentration and oxygen uptake rate) generated from this biological monitor showed potential as a control variable for the activated sludge process.     

倒置A2/O生物脱氮除磷工艺的生产性试验

青岛李村河污水处理厂采用改良A／O工艺，具有脱氮及部分除磷功能。通过调节使其按倒置A^2／O模式运行，并开展了脱氮除磷的生产性试验，考察了溶解氧浓度、污泥回流比、温度等对除污效果的影响。结果表明，倒置A^2／O工艺对有机物、氮、磷的去除效果好，且运行稳定、抗冲击负荷能力强，适合在我国城市污水处理领域推广。     

生物滤塔处理含三甲胺气体的研究

研究了分别填充堆肥和污泥的生物滤塔对含三甲胺气体的处理能力.结果表明,两种生物滤塔均能有效处理含三甲胺的气体,对三甲胺的去除率几乎达到了100%,三甲胺被生物降解并生成氨.堆肥生物滤塔各段填料中的硝态氮含量随时间的延长呈显著提高的趋势,但pH值出现下降,说明其中发生了氨的硝化作用.而在污泥生物滤塔中,随着氨的积累则各填料层的pH值迅速升高,并且没有观察到亚硝态氮以及硝态氮含量的增加,因此其不具备进一步降解氨的能力.     

Treatment of a colored groundwater by ozone-biofiltration: pilot studies and modeling interpretation

Pilot studies investigated the fates of color, dissolved organic carbon (DOC), and biodegradable organic matter (BOM) by the tandem of ozone plus biofiltration for treating a source water having significant color (50 cu) and DOC (3.2 mg/l). Transferred ozone doses were from 1.0 to 1.8 g O3/g C. Rapid biofilters used sand, anthracite, or granular activated carbon as media with empty-bed contact time (EBCT) up to 9 min. The pilot studies demonstrated that ozonation plus biofiltration removed most color and substantial DOC, and increasing the transferred ozone dose enhanced the removals. For the highest ozone dose, removals were as high as 90% for color and 38% for DOC. While most of the color removal took place during ozonation, most DOC removal occurred in the biofilters, particularly when the ozone dose was high. Compared to sand and anthracite biofilters, the GAC biofilter gave the best performance for color and DOC removal, but some of this enhanced performance was caused by adsorption, since the GAC was virgin at the beginning of the pilot studies. Backwashing events had no noticeable impact of the performance of the biofilters. The Transient-State, Multiple-Species Biofilm Model (TSMSBM) was used to interpret the experimental results. Model simulations show that soluble microbial products, which comprised a significant part of the effluent BOM, offset the removal of original BOM, a factor that kept the removal of DOC relatively constant over the range of EBCTs of 3.5-9 min. Although improved biofilm retention, represented by a small detachment rate, allowed more total biofilm accumulation and greater removal of original BOM, it also caused more release of soluble microbial products and the build up of inert biomass in the biofilm. Backwashing had little impact on biofilter performance, because it did not remove more than 25% of the biofilm under any condition simulated.     

负荷变化对ABR运行效果的影响研究

利用厌氧折流板反应器(ABR) 处理屠宰废水,研究了负荷变化对厌氧折流板反应器（ABR）运行效果的影响。研究结果表明：厌氧折流板反应器对负荷变化的适应能力较强,ABR反应器的特殊结构为其提供了良好的抗负荷变化的能力。当维持进水COD浓度在2 500~3 000 mg/L范围之内,改变水力负荷,使HRT由27.5 h下降到15 h,COD去除率下降不超过5％;当维持反应器HRT为20 h时,改变有机负荷,使进水COD浓度由2 500 mg/L提高到4 800 mg/L,在负荷改变后的第二天,COD去除率仅降     

Non-steady state simulation of BOM removal in drinking water biofilters: applications and full-scale validation

A biofilter model called "BIOFILT" was used to simulate the removal of biodegradable organic matter (BOM) in full-scale biofilters subjected to a wide range of operating conditions. Parameters that were varied included BOM composition, water temperature (3.0-22.5 degrees C), and biomass removal during backwashing (0-100%). Results from biofilter simulations suggest a strong dependence of BOM removal on BOM composition. BOM with a greater diffusivity or with faster degradation kinetics was removed to a greater extent and also contributed to shorter biofilter start-up times. In addition, in simulations involving mixtures of BOM (i.e. readily degradable and slowly degradable components), the presence of readily degradable substrate significantly enhanced the removal of slowly degradable material primarily due to the ability to maintain greater biomass levels in the biofilters. Declines in pseudo-steady state BOM removal were observed as temperature was decreased from 22.5 to 3 degrees C and the magnitude of the change was significantly affected by BOM composition. However, significant removals of BOM are possible at low temperatures (3-6 degrees C). Concerning the impact of backwashing on biofilter performance, BOM removal was not affected by backwash resulting in biomass removals of 60% or less. This suggests that periodic backwashing should not significantly impact biofilter performance as observed biomass removals from full-scale biofilters were negligible. In general, the simulation results were in good qualitative and quantitative agreement with experimental results obtained from full-scale biofilters.     

Effects of temperature shock treatments on the stability of anaerobic digesters operated on separated cattle slurry

Using laboratory-scale daily fed digesters operating at steady-state on separated cattle slurry, the temperature was lowered in a similar manner to that which might be expected on a farm due to heating failure; three different recovery methods were then tested. Raising the operating temperature from 3–6°C to 35°C in a single day had only a transient effect on digester stability. Steady-state conditions were re-established within 8 days of the temperature rise when a 25-day retention time was employed and within 6 days at 10-day retention time. However, slowly raising the operating temperature (over several days) had a more deleterious effect on digester stability. When a 25-day retention time was employed 10 days were required from the initial temperature rise before steady-state conditions were re-established, whilst at a 10-day retention time the period was greater than 12 days. It is therefore proposed that the digester temperature should be raised back up to the normal operating temperature as soon as possible after a heating failure. Digesters which were not fed during the recovery period showed a rapid removal of potentially toxic volatile fatty acids, and this procedure is recommended in the period following temperature shock.The main indicator of digester instability was a dramatic but unequal rise in the concentration of the individual volatile fatty acids. An order of sensitivity to the temperature shock treatment was established: i-butyrate i-valerate i-caproate > propionate > n-valerate n-caproate > acetate n-butyrate. Those to the left accumulated most rapidly in the temperature stressed digester, and were removed least quickly during the recovery period. Thus the bacteria responsible for the breakdown of the higher volatile fatty acids (presumably the obligate proton-reducing bacteria) were more sensitive to the shock treatment applied than those catabolising acetate (presumably the acetate-utilizing methanogenic bacteria).The concentration of the branched volatile fatty acids and propionic acid were the most sensitive to the temperature shock treatment, and therefore represent more sensitive monitors of digester stability than acetic acid or the total volatile fatty acid concentration.     

Nitrate removal characteristics of high performance fluidized-bed biofilm reactors

Two laboratory-scale high performance fluidized bed biofilm reactors (FBBR) with sand as the biofilm carrier were used to investigate the denitrification of high-strength nitrate wastewater with specific emphasis on the effect the nitrogen loading rate and the superficial velocity (V(s)). The results demonstrated that the FBBR system is capable of efficiently handling an exceptionally high nitrate nitrogen concentration of 1000 mg N/L. At a loading rate of 6.3 kg-N/m(3)(bed).d almost complete denitrification was achieved with a removal efficiency of 99.8% and an effluent concentration of 2mg N/L at V(s) values of 45, 55 and 65 m/h. The maximum efficient loading rate (R(max)) at which the US drinking water nitrate-nitrogen standard concentration of 10mg N/L would be exceeded was found to be a function of the applied V(s). The R(max) was found to be 12 kg-N/m(3)(bed).d at a V(s) value of 45 m/h. As V(s) was increased to 55 and 65 m/h, the optimum R(max) dropped to 9.5 and 8 kg-N/m(3)(bed).d, respectively. Higher denitrification rates were achieved at relatively lower V(s). However, there is a minimum practical velocity below which agglomeration of biomass would occur. The suspended solids concentration in the effluent was below 30 mg/L throughout the study.     

包埋固定化菌深度处理污水厂出水的研究

采用包埋固定化菌颗粒对苏州市某污水处理厂的出水进行深度处理,考察了其对氨氮和COD的去除效果。结果表明,在DO=3mg/L、pH=6．5～8．0、自然温度条件下,包埋固定化菌对氨氮具有较强的去除能力和良好的耐冲击负荷能力,出水氨氮〈2mg/L,达到了《城镇污水处理厂污染物排放标准》（C-B18918-2002）的一级A标准;对COD有一定的去除效果,大部分出水COD〈50mg／L。