Performance of Trickle-Bed Air Biofilter: A Comparative Study of a Hydrophilic and a Hydrophobic Voc

Two lab-scale trickle-bed air biofilters were operated for investigating the difference in performance between a hydrophilic and a hydrophobic volatile organic compound (VOC). Methyl isobutyl ketone (MIBK) and styrene were selected as a model hydrophilic and hydrophobic VOCs, respectively. Effects of loading rates, biofilter re-acclimation, removal profile along biofilter depth, nitrogen consumption, and CO₂ production were compared under three operating conditions, namely, backwashing and two non-use periods (starvation and stagnant). Consistent over 99% removal efficiency up to loading rates of 3.26 kg COD/m³-day was obtained for the MIBK biofilter at 0.76 min empty bed retention time (EBRT) and 1.5 L/d nutrient flow. A similar performance for the styrene biofilter was obtained for loading rates up to 1.9kg COD/m³-day at 2.02 min EBRT and 2.4 L/d nutrient flow. The MIBK biofilter required only an initial acclimation period of 16 days while styrene biofilter required 46 days. Non-use periods can be used as another means of biomass control for both biofilters when the employed loading rate did not exceed 1.27 and 2.17 kg COD/m³-day for styrene and MIBK biofilters, respectively. The re-acclimation of both biofilter was delayed with increase of loading rate. MIBK biofilter re-acclimated in 90 min, while styrene biofilter re-acclimated in more than 600 min. Under similar loading rates, MIBK biofilter utilized less biofilter depth than styrene biofilter. Nitrogen consumption behaviors were apparently different between the two biofilters. Styrene biofilter had higher CO₂ production than MIBK biofilter and its CO₂ production was closely related to the theoretical complete chemical oxidation.     

Treatment of taste and odor causing compounds 2-methyl isoborneol and geosmin in drinking water: A critical review

Problems due to the taste and odor in drinking water are common in treatment facilities around the world. Taste and odor are perceived by the public as the primary indicators of the safely and acceptability of drinking water and are mainly caused by the presence of two semi-volatile compounds – 2-methyl isoborneol (MIB) and geosmin. A review of these two taste and odor causing compounds in drinking water is presented. The sources for the formation of these compounds in water are discussed alongwith the health and regulatory implications. The recent developments in the analysis of MIB/geosmin in water which have allowed for rapid measurements in the nanogram per liter concentrations are also discussed. This review focuses on the relevant treatment alternatives, that are described in detail with emphasis on their respective advantages and problems associated with their implementation in a fullscale facility. Conventional treatment processes in water treatment plants, such as coagulation, sedimentation and chlorination have been found to be ine ective for removal of MIB/geosmin. Studies have shown powdered activated carbon, ozonation and biofiltration to be e ective in treatment of these two compounds. Although some of these technologies are more e ective and show more promise than the others, much work remains to be done to optimize these technologies so that they can be retrofitted or installed with minimal impact on the overall operation and e ectiveness of the treatment system.     

Evaluation of trickle-bed air biofilter performance under periodic stressed operating conditions as a function of styrene loading

Trickle-bed air biofilters (TBABs) are suitable for treating volatile organic compounds (VOCs) at a significantly high practical loading because of their controlled environmental conditions. The application of TBAB for treating styrene-contaminated air under periodic backwashing and cyclical nonuse periods at a styrene loading of 0.64-3.17 kg chemical oxygen demand (COD)/m3 x day was the main focus of this study. Consistent long-term efficient performance of TBAB strongly depended on biomass control. A periodic in situ upflow with nutrient solution under media fluidization, that is, backwashing, was approached in this study. Two different nonuse periods were employed to simulate a shutdown for equipment repair or during weekends and holidays. The first is a starvation period without styrene loading, and the second is a stagnant period, which reflects no flow passing through the biofilter. For styrene loadings up to 1.9 kg COD/m3 x day, removal efficiencies consistently above 99% were achieved by conducting a coordinated biomass control strategy, that is, backwashing for 1 hr once per week. Under cyclical nonuse periods for styrene loadings up to 1.27 kg COD/m3 x day, stable long-term performance of the biofilter was maintained at more than 99% removal without employing backwashing. No substantial impact of nonuse periods on the biofilter performance was revealed. However, a coordinated biomass control by backwashing subsequently was unavoidable for attaining consistently high removal efficiency at a styrene loading of 3.17 kg COD/m3 x day. As styrene loading was increased, reacclimation of the biofilter to reach the 99% removal efficiency following backwashing or the nonuse periods was delayed. After the non-use periods, the response of the biofilter was a strong function of the biomass in the bed. No significant difference between the effects of the two different nonuse periods on TBAB performance was observed during the study period.     

n-Hexane Biodegradation in Trickle Bed Air Biofilters

While hydrophilic compounds are degraded easily in Trickling bed air biofilters (TBABs), hydrophobic compounds are retarded until biological cultures produce a sufficient RNA or enzyme/protein to utilize this compound. Hydrophobic compounds are not readily bio-available which makes them reluctant to biodegradation as mass transfer between the gas and liquid phases is a rate limiting step. To enhance the destruction of hydrophobic compounds in TBABs, the utilization of surfactant was introduced to increase the solubility which helps overcoming the rate limiting step. The surfactant was used as well to limit the growth of excess biomass ensuring smooth flow through the biofilter bed and preventing short circuits. Two different non-ionic non-toxic surfactants were used in this study: Triton X-100 and Tomadol® 25-7. Two lab-scale controlled TBABs were operated for investigating the performance difference for n-Hexane as an example of hydrophobic volatile organic compound (VOC) with and without the addition of surfactant. Operating conditions in both TBABs were as follows: nutrient feed rate (2L/day), air flowrate (1.4L/min), bed depth (60cm), empty bed retention time (120s), bed material (diatomaceous earth pellets) and room-temperature. The inlet concentration was changed from 50 to 100ppmv. Acclimation period, removal profile along biofilter depth, nitrogen consumption, and CO₂ production were compared under continuous loading operation condition. The optimum concentration of surfactant in the nutrient feed was determined by a batch experiment. The effect of different surfactant concentrations on VOC water solubility with time was studied by considering different VOC concentration sets within the TBAB loading rate range.     

Biodegradation kinetics and toxicity of vegetable oil triacylglycerols under aerobic conditions

The aerobic biodegradation of five triacylglycerols (TAGs), three liquids [triolein (OOO), trilinolein (LLL), and trilinolenin (LnLnLn)] and two solids [tripalmitin (PPP) and tristearin (SSS)] was studied in water. Respirometry tests were designed and conducted to determine the biochemical oxygen demand (BOD) parameters of the compounds. In the case of the solid lipids, the degradation process was limited by their extremely non-polar nature. When added to water, PPP and SSS formed irregular clumps or gumballs, not a fine and uniform suspension required for the lipase activity. After 30 days, appreciable mineralization was not achieved; therefore, first-order biodegradation coefficients could not be determined. The bioavailability of the liquid TAGs was restricted due to the presence of double bonds in the fatty acids (FAs). An autoxidation process occurred in the allylic chains, resulting in the production of hydroperoxides. These compounds polymerized and became non-biodegradable. Nevertheless, the non-oxidized fractions were readily mineralized, and BOD rate constants were estimated by non-linear regression: LLL (k = 0.0061 h⁻¹) and LnLnLn (k = 0.0071 h⁻¹) were degraded more rapidly than OOO (k = 0.0025 h⁻¹). Lipids strongly partitioned to the biomass and, therefore, Microtox^® toxicity was not observed in the water column. However, EC₅₀ values (<15% sample volume) were measured in the solid phase.     

Fate of sex hormones in two pilot-scale municipal wastewater treatment plants: conventional treatment

The fate of seven sex hormones (estrone (E1), estradiol (E2), estriol (E3), ethinylestradiol (EE2), testosterone, androstenedione, and progesterone) was determined in two pilot-scale wastewater treatment plants operated under conventional loading conditions. The levels of hormones in both the liquid and the solid matrixes of the plants were determined. Each of the two 20-l/h pilot-scale plants consisted of a primary clarifier followed by a three-stage aeration tank and a final clarifier. The primary sludge and the waste activated sludge (WAS) were digested anaerobically in one pilot plant and aerobically in the other. The pilot plants were fed a complex synthetic wastewater spiked with the hormones. Levels of testosterone, androstenedione and progesterone were close to method detection limit (MDL) concentrations in the final and digester effluents (both liquid and solid phases) and were considered as completely removed. Average mass flux removals from the liquid streams (plant influent minus secondary clarifier effluent) for the natural estrogens were 82% for E1, 99% for E2, and 89% for (E1+E2). An average overall removal of only 42% was achieved for EE2. These values reflect removals averaged for the two pilot plants.     

Role of biological activity and biomass distribution in air biofilter performance

The effects of temporal and spatial changes in biological activity and biomass amount on biofilter performance were investigated in a lab-scale trickle-bed air biofilter at a toluene loading of 46.9gm(-3)h(-1) under two different experimental strategies, namely, periodic backwashing at a rate of 1h once a week and 2d starvation. Analysis of the overall reaction for toluene metabolism revealed that cell synthesis was relatively favored over toluene oxidation in the inlet section of the biofilter, but over time its oxidation became favored throughout the biofilter bed. Periodic in situ backwashing with media fluidization effectively made even spatial distribution of biomass along the bed media, by which consistent high removal performance in the biofilter has been attained. After 2d starvation, the ratio of the biofilm EPS to the total biomass increased along the media bed depth, while the total biomass in the media bed subsequently decreased. The presence of sufficient biomass and microbial activity favorably influenced biofilter reacclimation after restart-up following starvation.     

A comparative study in treating two VOC mixtures in trickle bed air biofilters

Two independent parallel trickling bed air biofilters (TBABs) ("A" and "B") with two different typical VOC mixtures were investigated. Toluene, styrene, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) were the target VOCs in the mixtures. Biofilter "A" was fed equal molar ratio of the VOCs and biofilter "B" was fed a mixture based on EPA 2003 emission report. Backwashing and substrate starvation operation were conducted as biomass control. Biofilter "A" and "B" maintained 99% overall removal efficiency for influent concentration up to 500 and 300 ppmv under backwashing operating condition, respectively. The starvation study indicated that it can be an effective biomass control for influent concentrations up to 250 ppmv for biofilter "A" and 300 ppmv for "B". Re-acclimation of biofilter performance was delayed with increase of influent concentration for both biofilters. Starvation operation helped the biofilter to recover at low concentrations and delayed re-acclimation at high concentrations. Furthermore, re-acclamation for biofilter "B" was delayed due to its high toluene content as compared to biofilter "A". The pseudo first-order removal rate constant decreased with increase of volumetric loading rate for both biofilters. MEK and MIBK were completely removed in the upper 3/8 media depth. While biofilter depth utilization for the removal of styrene and toluene increased with increase of influent concentrations for both biofilters. However, toluene removal utilized more biofilter depth for biofilter "B" as compared to biofilter "A".     

添加玉米秸秆对绿花菜尾菜堆肥植物毒性的影响

为揭示不同比例作物秸秆和蔬菜尾菜堆肥过程中种子毒性变化及其影响机理,开展了为期55 d的以玉米（Zea mays L.）秸秆为辅料,绿花菜（Brassica oleracea L.var.botrytis L.）尾菜为主料的工厂化条垛堆肥,分别设置加入高（湿重比4∶12）和低（湿重比1∶12）比例秸秆与尾菜的堆肥处理.测定了不同时期堆肥p H、电导率（EC）、可溶性有机碳（DOC）、硝氮（NO₃^--N）、氨氮（NH₄⁺-N）、碳氮比（C/N）、大白菜种子（Brassica rapa L.）的发芽指数（Germination Index,GI）、相对生长指数（Relative Growth Index,RGI）和α-淀粉酶、蛋白酶、脂肪酶的变化.结果表明,高比例秸秆堆肥处理的高温（>55℃）持续期显著高于低比例处理.堆肥结束时两个处理的堆肥均呈碱性,且EC、DOC、NH₄⁺-N和NO₃^--N含量均降低,C/N...     

Evaluation of co-metabolic removal of trichloroethylene in a biotrickling filter under acidic conditions

This study investigated the removal of hydrophobic trichloroethylene (TCE) in the presence of methanol (co-metabolite) in a biotrickling filter, which was seeded with fungi at pH 4. Starvation was chosen as the biomass control strategy. Two systems, Biofilter I (methanol:TCE 70:30) and Biofilter II (methanol:TCE 80:20) were run in parallel, each with varying composition ratios. The TCE loading rates for both biofilters ranged from 3.22 to 12.88 g/m³/hr. Depending on the ratio, methanol concentrations varied from 4.08 to 27.95 g/m³/hr. The performance of the systems was evaluated and compared by calculating removal kinetics, carbon mass balance, efficiencies and elimination capacities. Methanol was observed to enhance TCE removal during the initial loading rate. However, methanol later inhibited TCE degradation above 6.44 g TCE/m³/hr (Biofilter I) and 3.22 g TCE/m³/hr (Biofilter II). Conversely, TCE did not impede methanol removal because over 95% methanol elimination was consistently achieved. Overall, Biofilter I was able to outperform Biofilter II due to its greater resistance towards methanol competition.