Biotrickling filtration of isopropanol under intermittent loading conditions

This paper investigates the removal of isopropanol by gas-phase biotrickling filtration. Two plastic packing materials, one structured and one random, have been evaluated in terms of oxygen mass transfer and isopropanol removal efficiency. Oxygen mass transfer experiments were performed at gas velocities of 104 and 312 m h^?1 and liquid velocities between 3 and 33 m h^?1. Both materials showed similar mass transfer coefficients up to liquid velocities of 15 m h^?1. At greater liquid velocities, the structured packing exhibited greater oxygen mass transfer coefficients. Biotrickling filtration experiments were carried out at inlet loads (IL) from 20 to 65 g C m^?3 h^?1 and empty bed residence times (EBRT) from 14 to 160 s. To simulate typical industrial emissions, intermittent isopropanol loading (16 h/day, 5 day/week) and intermittent spraying frequency (15 min/1.5 h) were applied. Maximum elimination capacity of 51 g C m^?3 h^?1 has been obtained for the random packing (IL of 65 g C m^?3 h^?1, EBRT of 50 s). The decrease in irrigation frequency to 15 min every 3 h caused a decrease in the outlet emissions from 86 to 59 mg C Nm^?3 (inlet of 500 mg C Nm^?3). The expansion of spraying to night and weekend periods promoted the degradation of the isopropanol accumulated in the water tank during the day, reaching effluent concentrations as low as 44 mg C Nm^?3. After a 7-week starvation period, the performance was recovered in less than 10 days, proving the robustness of the process.     

Inorganic nitrogen transformations at high loading rates in an oligohaline estuary

A well-defined nitrogen retention and turnover budget was estimated for a shallow oligohaline lake (Lake Pontchartrain, Louisiana, USA). In 1997 a month-long diversion of the Mississippi River filled the Lake with highly concentrated river water (80µM nitrate) and lowered the salinity to 0psu within 2 weeks. After the spillway was closed the Lake mixed with estuarine tidal waters and came to equilibrium over 4 months with the riverine, atmospheric and offshore water nitrogen sources. A flushing rate of 1.78% d^–1 was estimated by analyzing a plot of ln salinity versus time for the first 120 days after the diversion ceased. This flushing rate was similar to the loss rate for total nitrogen (1.75% d^–1), implying no significant net nitrogen losses or gains were occurring inside the Lake. The percent loss of dissolved inorganic nitrogen was higher than that for TN (4.11% d^–1), whereas the loss of organic nitrogen was lower (0.94% d^–1), which suggests a net transfer from inorganic to organic nitrogen. These changes occurred steadily as chlorophyll a concentration ranged from 5 to 200µg l^–1. The results demonstrate the potential significance of the organic nitrogen and interconversion of nitrogen forms when calculating estuarine nitrogen retention budgets and the necessity of measuring all nitrogen forms when performing mass balance estimates. The significance of denitrification in nitrogen removal is minimal at the high loading rates observed during this study. An implication to estuarine water quality management is that the relationships between nitrogen loading and retention are not linear and are controlled by factors other than water residence time.     

Biodiversity in aerobic granule membrane bioreactor at high organic loading rates

Antibacterial peptide CM4 (ABP-CM4) is a small cationic peptide with broad-spectrum activities against bacteria, fungi, and tumor cells, which may possibly be used as an antimicrobial agent. We report here the application of small ubiquitin-related modifier (SUMO) fusion technology to the expression and purification of cationic antibacterial peptide ABP-CM4. The fusion protein expressed in a soluble form was purified to a purity of 90% by Ni-IDA chromatography and 112 mg protein of interest was obtained per liter of fermentation culture. After the SUMO–CM4 fusion protein was cleaved by the SUMO protease at 30 °C for 1 h, the cleaved sample was re-applied to a Ni-IDA. Finally, about 24 mg recombinant CM4 was obtained from 1 l fermentation culture with no less than 96% purity and the recombinant CM4 had similar antimicrobial properties to the synthetic CM4. Thus, the SUMO-mediated peptide expression and purification system potentially could be employed for the production of recombinant cytotoxic peptides.     

Potential cause of aerobic granular sludge breakdown at high organic loading rates

Aerobic sludge granules are compact, strong microbial aggregates that have excellent settling ability and capability to efficiently treat high-strength and toxic wastewaters. Aerobic granules disintegrate under high organic loading rates (OLR). This study cultivated aerobic granules using acetate as the sole carbon and energy source in three identical sequencing batch reactors operated under OLR of 9–21.3 kg chemical oxygen demand (COD) m⁻³ day⁻¹. The cultivated granules removed 94–96% of fed COD at OLR up to 9–19.5 kg COD m⁻³ day⁻¹, and disintegrated at OLR of 21.3 kg COD m⁻³ day⁻¹. Most tested isolates did not grow in the medium at >3,000 mg COD l⁻¹; additionally, these strains lost capability for auto-aggregation and protein or polysaccharide productivity. This critical COD regime correlates strongly with the OLR range in which granules started disintegrating. Reduced protein quantity secreted by isolates was associated with the noted poor granule integrity under high OLR. This work identified a potential cause of biological nature for aerobic granules breakdown.     

Treatment of urban wastewater in a membrane bioreactor at high organic loading rates.

Membrane bioreactors can replace the activated sludge process and the final clarification step in municipal wastewater treatment. The combination of bioreactor and crossflow microfiltration allows for a high chemical oxygen demand (COD) reduction of synthetic wastewater. From biomass, grown at high production rates in the aerobic bioreactor, energy rich biogas can be obtained in a subsequent anaerobic bioreactor. In this paper, experimental data from a laboratory scale membrane bioreactor are presented. The degradation of synthetic wastewater at short hydraulic retention times down to 1.5 h has been studied. The organic loading rate (OLR) has been varied in the range of 6-13 kg m(-3) per day. At steady state a high quality filtrate could be obtained at different operating conditions. At biomass concentrations of 10-22 g l(-1), COD reduction was above 95%.     

Dry anaerobic digestion of high solids content dairy manure at high organic loading rates in psychrophilic sequence batch reactor

Cow manure with bedding is renewable organic biomass available around the year on dairy farms. Developing efficient and cost-effective psychrophilic dry anaerobic digestion (PDAD) processes could contribute to solving farm-related environmental, energy, and manure management problems in cold-climate regions. This study was to increase the organic loading rate (OLR), fed to a novel psychrophilic (20 °C) dry anaerobic digestion of 27 % total solid dairy manure (cow feces and wheat straw) in sequence batch reactor (PDAD-SBR), by 133 to 160 %. The PDAD-SBR process operated at treatment cycle length of 21 days and OLR of 7.0 and 8.0 g total chemical oxygen demand (TCOD)?kg^?1 inoculum day^?1 (5.2?±?0.1 and 5.8?±?0.0 g volatile solids (VS)?kg^?1 inoculum day^?1) for four successive cycles (84 days) produced average specific methane yields (SMYs) of 147.1?±?17.2 and 143.2?±?11.7 normalized liters (NL)?CH₄?kg^?1 VS fed, respectively. PDAD of cow feces and wheat straw is possible with VS-based inoculum-to-substrate ratio of 1.45 at OLR of 8.0 g TCOD kg^?1 inoculum day^?1. Hydrolysis was the limiting step reaction. The VS removal averaged around 57.4?±?0.5 and 60.5?±?5.7 % at OLR 7.0 and 8.0 g TCOD kg^?1 inoculum day^?1, respectively.     

Functional consortium from aerobic granules under high organic loading rates

Functional bacterial consortiums that effectively tolerate high organic loading rates (OLR) were isolated using an organic shock-loading-to-extinction approach. The aerobic sludge granules were cultivated at low OLR and microbial community was challenged with stepwise increase in organic loadings to isolate functional consortiums. Strain Zoogloea resiniphila and at least two uncultured strains, Acinetobacter sp. clone JT2 and bacterium clone P1D1-516, formed the functional consortium of the aerobic granules present under a high OLR. The loss of these uncultured strains caused protein leakage from granules, thereby destabilizing the granules. The proposed organic shock-loading-to-extinction approach is effective in isolating the functional consortium from aerobic granules under high OLR.     

A continuum theory of blood cells filtration at low flow rates

Blood cells filtration with decreasing pressure under gravity was studied for evaluation of the cell fluidity or deformability at a low shear state. A continuum approach was made to the flow and pressure in the filter at the low flow state to relate macro- and micro-scopic quantities. The mass conservation law of each species provided a set of differential equations with respect to the pore fraction and filter resistance. The numerical calculation was made for various values of hematocrit and leukocrit. It was shown that the filter resistance might be increased with decreasing pressure, resulting from both red and white cells. The leukocrit, more than 0.05% white cells, may influence the filtration, depending upon the cell deformation. Even in the absence of the white cell, a decrease in pressure increased the filter resistance markedly. The present result indicates that single red cell shows a nonlinear behavior of flow in pores at the low pressure level.     

Characterization of aerobic granular sludge at various organic loading rates

Aerobic granular sludge was cultivated from activated sludge with two types of supports, namely bivalve shell carrier (BSC) and anaerobic granules (ANG). Granules were characterized at different organic loading rates (OLRs) ranging from 2.5 to 15 kg COD/m³ d and these granules were observed to withstand high OLRs. The physico-chemical characteristics of the aerobic granules were better than those of seed sludge. The granule formation with ANG support was found to be similar to that of non-support cultivation, i.e. formation from activated sludge only. By contrast, BSC support showed better performance in terms of faster settleability, compactness and especially resistance against organic shock loading. It also enabled self-cleaning effect by removing biofilm attached on the reactor wall during the start-up phase resulting rapid granulation process.     

Strain-rate sensitivity of the rabbit MCL diminishes at traumatic loading rates

This study was performed to determine whether the viscoelastic behavior of ligaments persists at high rates of loading, such as those associated with sports-related trauma or motor vehicle accidents. Medial collateral ligaments (MCLs) from 22 skeletally mature New Zealand White rabbits were tensile tested quasi-statically and via two impact conditions at displacement rates of 0.17 mm/s (n=22), 640+/-160 mm/s (n=10) and 2500+/-270 mm/s (n=12) (corresponding to strain rates of approximately 1.0%/s, 3660%/s and 14,000%/s, respectively). Despite dramatic increases in displacement rate, only a modest strain-rate effect was observed when the specimens tested quasi-statically were compared to those tested via impact (24% and 37% increases in stiffness and failure load, respectively). There were no differences in the structural (e.g. 145+/-30 and 136+/-29 N/mm stiffness values, respectively) or failure properties (e.g. 434+/-91 and 443+/-154 N failure load values, respectively) of the two impact-tested groups. Our findings suggest that the rabbit MCL is not viscoelastic at loading rates approximating those associated with high-energy trauma.     

Characterization of aerobic granules by microbial density at different COD loading rates

Aerobic granules were cultivated under temporal alternating aerobic and anoxic conditions without the presence of a carrier material in a sequencing batch reactor (SBR) with a high column height/column diameter ratio. The reactor was operated for 6h per cycle (aerobic: 4.75 h, anoxic: 1.25 h). To determine a new parameter for the definition of aerobic granules, a protocol of 4,6-diamidino-2-phenylindole hydrochloride staining and fluorescence image processing was developed. The d(tm) analysis showed that the increase in the chemical oxygen demand (COD) loading rate promoted no more growth of the aerobic granules. It was inconsistent with the results of the analysis of the sludge volume index (SVI) value but matched well with the results of the COD and nitrogen removal of the SBR and the particle size distribution by LS-PSA. The optimum COD loading rate for aerobic granulation in the SBR was 2.52 kg/m(3)d. When d(tm) was correlated with the biomass concentration and the SVI value during the period of granule formation, d(tm) could be used as a more sensitive and accurate parameter for classifying aerobic granules and optimizing the operational conditions for aerobic granulation processes.     

Interactions between evolutionary processes at high mutation rates

Evolution at high mutation rates is minimally affected by six processes: mutation-selection balance, error catastrophes, Muller's Ratchet, robustness and compensatory evolution, and clonal interference. Including all of these processes in a tractable, analytical model is difficult, but they can be captured in simulations that utilize realistic genotype-phenotype-fitness maps, as done here by modeling RNA folding. Subjecting finite, asexual populations to a range of mutation rates revealed simple criteria that predict when particular evolutionary processes are important. Populations were initiated with a genotype encoding the most fit phenotype. When purifying selection was strong relative to mutation, the initial genotype was replaced by one more mutationally robust, and the maximally fit phenotype was maintained in a mutation-selection balance where the deleterious mutation rate determined mean fitness. With weaker purifying selection, the most fit genotypes were lost. Although loss of the best genotype was ongoing and might have led to a progressive fitness decline, continual compensatory evolution led to an approximate fitness equilibration. Per total genomic mutation rate, mean fitness was similar for strong and weak purifying selection. These results represent a first step at separating interactions between evolutionary processes at high mutation rate, but additional theory is needed to interpret some outcomes.     

Toluene degradation in a polyurethane biofilter at high loading

In the present study, toluene elimination in the polyurethane (PU) biofilter during long-term (145 day) operation was characterized, and assessed the effects of changing the inlet loading and space velocity (SV). A very high elimination capacity of 3.7 kg·m⁻³·h⁻¹ was obtained at an inlet loading of 4.0 kg·m^–3·h⁻¹ (inlet toluene concentration of 900 ppmv at a SV of 1,040 h⁻¹). Backwashing with irrigation and compressed air allowed maintenance of a pressure drop of < 80 mm H₂O·m⁻¹-filter at an SV of 830 h⁻¹ and an elimination efficiency of > 90% during the 145 day of operation. In conclusion, the PU biofilter can overcome the problems of clogging caused by excess biomass growth and of low treatment capacities of conventional biofilters.     

Partial nitritation at elevated loading rates: design curves and biofilm characteristics

There is a need to develop low operational intensity, cost-effective, and small-footprint systems to treat wastewater. Partial nitritation has been studied using a variety of control strategies, however, a gap in passive operation is evident. This research investigates the use of elevated loading rates as a strategy for achieving low operational intensity partial nitritation in a moving bed biofilm reactor (MBBR) system. The effects of loading rates on nitrification kinetics and biofilm characteristics were determined at elevated, steady dissolved oxygen concentrations between 5.5 and 7.0 mg O₂/L and ambient temperatures between 19 and 21 °C. Four elevated loading rates (3, 4, 5 and 6.5 g NH₄⁺-N/m² days) were tested with a distinct shift in kinetics being observed towards nitritation at elevated loadings. Complete partial nitritation (100% nitrite production) was achieved at 6.5 g NH₄⁺-N/m² days, likely due to thick biofilm (572 µm) and elevated NH₄⁺-N load, which resulted in suppression of nitrite oxidation.

     

Effects of air movement on swine at high temperature

Sixty pigs were used to study the effects of air movement (0.05, 0.5, and 1.0 m/s) at constant air temperatures of either 5.6 or 11.1°C above optimum, and at 3 different weight ranges (36–50kg, 54–68 kg, and 73–86 kg) during the growing-finishing stages. An air velocity of 0.5 m/s produced significantly greater weight gain and feed conversion than did 0.05 m/s. An air velocity of 1.0 m/s produced intermediate results.     

Mutation at high rates reduces spatial structure within populations

The question of whether or not the high rates (mu) of mutation that occur for some hypervariable markers can affect commonly used empirical measures of spatial structure of genetic variation within populations is addressed. The results show that values of these measures are approximately halved when mu is 10(-2). Finest spatial-scale correlations, measured by either Moran's I-statistics or conditional kinship, are reduced by 30%-50%. When the mutation rate is 10 times lower, much smaller reductions result, e.g. averaging 7% for the finest scale correlations. Still smaller orders of magnitude of mu cause negligible changes in spatial structure, where any effects normally would not be detectable. The reductions are caused by forward mutations, and when the reductions are measured as percentages, they are nearly independent of the amount of structure produced sans mutation, except when dispersal is nearly minimal. The percent reductions are also nearly independent of the number of alleles and of back mutations, hence of the nature of the mutation process (e.g. stepwise or not). The results demonstrate that some hypervariable loci should have reduced spatial structuring, and that marker choice may affect the values observed in experimental surveys. Moreover, if fine-scale correlations are used to indirectly estimate dispersal distances, then mutation at high rates could inflate estimates, easily up to two- to three-fold.