Development of laboratory-scale photobioreactor for water purification by use of a biofilter composed of the aerial microalga Trentepohlia aurea (Chlorophyta)

Biofilms formed by the green alga Trentepohlia aurea could be a useful tool in the removal of nitrate and phosphate from water. When a prepared biofilter was dampened with medium and incubated under low light intensity (10 μmol photons m⁻² s⁻¹) between 5 and 50 μmol photons m⁻² s⁻¹, the efficiency of removal of inorganic compounds from water was higher without the decomposition of chlorophylls in the cells. Algal cells immobilized on a glass fiber filter could be kept for 12 weeks under dark conditions at 4°C in the refrigerator. We tried to construct a laboratory-scale photobioreactor for the removal of inorganic nitrogen and phosphate from water by the biofilm. In this study, the synthetic wastewater was prepared by diluting 18-fold Bold’s basal medium with deionized water. The photobioreactor could efficiently remove nitrate and phosphate from the synthetic wastewater under continuous illumination. The removal ability of nitrate and phosphate per sheet of the biofilter in the photobioreactor exhibited about an 8- and 16-fold increase, respectively, in 3 days, compared with the bath experimental results. This study showed that the cycling of wastewater in the reactor by the pump led to a significant improvement in the efficiency of the inorganic ion uptake from water.     

Anammox-zeolite system acting as buffer to achieve stable effluent nitrogen values

For a successful nitrogen removal, Anammox process needs to be established in line with a stable partial nitritation pretreatment unit since wastewater influent is mostly unsuitable for direct treatment by Anammox. Partial nitritation is, however, a critical bottleneck for the nitrogen removal since it is often difficult to maintain the right proportions of NO₂-N and NH₄-N during long periods of time for Anammox process. This study investigated the potential of Anammox-zeolite biofilter to buffer inequalities in nitrite and ammonium nitrogen in the influent feed. Anammox-zeolite biofilter combines the ion-exchange property of zeolite with the biological removal by Anammox process. Continuous-flow biofilter was operated for 570 days to test the response of Anammox-zeolite system for irregular ammonium and nitrite nitrogen entries. The reactor demonstrated stable and high nitrogen removal efficiencies (approximately 95 %) even when the influent NO₂-N to NH₄-N ratios were far from the stoichiometric ratio for Anammox reaction (i.e. NO₂-N to NH₄-N ranging from 0 to infinity). This is achieved by the sorption of surplus NH₄-N by zeolite particles in case ammonium rich influent came in excess with respect to Anammox stoichiometry. Similarly, when ammonium-poor influent is fed to the reactor, ammonium desorption took place due to shifts in ion-exchange equilibrium and deficient amount were supplied by previously sorbed NH₄-N. Here, zeolite acted as a preserving reservoir of ammonium where both sorption and desorption took place when needed and this caused the Anammox-zeolite system to act as a buffer system to generate a stable effluent.     

Photosynthetic based algal-bacterial combined treatment of mixtures of organic pollutants and CO2 mitigation in a continuous photobioreactor

An algal-bacterial microcosm was synthetically constructed of Chlorella vulgaris MMl and Pseudomonas MTl. This microcosm was able to treat simulated wastewater supplemented with mixtures of phenol and pyridine up to 4.6 and 4.4 mM, respectively, in a continuous stirred tank bioreactor (CSTR) using photosynthetic oxygenation. Complete pollutant removal and detoxification and 82 % removal of introduced chemical oxygen demand (COD) were achieved at a hydraulic retention time (HRT) of 2.7 days. Increasing the influent load to 5.3 and 6.3 mM reduced the removal of phenol, pyridine and COD to 78, 21 and 59 %, respectively. Fertilization of the photobioreactor with 24 mM NaHCO₃ restored the treatment and detoxification efficiencies. The system was able to additionally mitigate up to 72 mM NaHCO₃ at the same HRT. Although the fertilization increased the system treatment efficiency, the settleability of the algal-bacterial microcosm was significantly reduced. When the photobioreactor was operated at HRT of 2.7 days in a 12/12 h of dark/light cycle, complete removal of 4.7 mM phenol was recorded but only 11 % of 5.7 mM pyridine was removed. The COD removal efficiency and CO₂ mitigation were also reduced to 65 and 86 %, respectively, and the effluent retained significant toxicity where 73 % inhibition was recorded. Elongation of the illumination time to 48 h (HRT of 4 days at 12/12 h dark/light cycle) restored the treatment and detoxification efficiencies.     

Impact of nitrogen and drought on phycobiliprotein content in terrestrial cyanobacterial strains

Cyanobacteria are highly adaptable microorganisms, characterized by an ability to survive in different environments with unfavorable conditions. In order to determine the content and composition of phycobiliproteins in cyanobacterial strains, depending on environmental factors, such as drought, darkness, and lack of nutrients in the substrate, the quantity of these pigments was investigated in 21 cyanobacterial strains. The study was conducted with terrestrial, filamentous, N₂-fixing cyanobacterial strains, which belong to Nostoc and Anabaena genera, isolated from different soil types in the Vojvodina region (Serbia). All strains were cultivated in nitrogen-free medium, medium with nitrate concentration of 2 g?L^?1 in the presence of light, and in drought conditions (water activity less than 0.5 %), on inorganic substrate, in the dark. Statistically significant differences of phycocyanin and allophycocyanin contents were found in the case of strains cultivated in nitrogen-free medium compared to strains grown in the medium containing nitrogen. There were no statistically significant differences in phycoerythrin and total phycobilin contents between strains grown in media with and without nitrogen. The results suggest that nitrogen availability affects composition of phycobiliproteins in the tested strains without affecting the total phycobiliprotein content, which implies maintenance of balanced pigment abundance as cyanobacterial response to nitrogen source. Significantly lower concentrations of the studied pigments, which varied from 0.8 to 16.9 μg mg^?1 dry weight, were detected in strains exposed to dry and dark conditions. These data indicate the presence of preserved phycobiliproteins after a period of 10 years of cyanobacterial exposure to drought and darkness, which can be of great importance for the study on their stability under unfavorable environmental conditions.     

Effects of nitrogen and phosphorus availabilities on growth, pigment, and protein contents in Hypnea cervicornis J. Agardh (Gigartinales, Rhodophyta)

The selection of seaweed species for their use as biofilters should be based on the knowledge of their nutrient requirements and tolerance to wide variations of nutrient concentrations. Therefore, tolerance and the physiological capabilities of Hypnea cervicornis J. Agardh (Gigartinales, Rhodophyta) to growth under nitrate, ammonium, and phosphate variations and to assimilate them into soluble proteins and photosynthetic pigments were evaluated in laboratory conditions. Treatments were composed of sterilized seawater enriched with 25 % von Stosch solution (without nitrogen and phosphorus), and nitrate or ammonium and phosphate were added in combination of 100:1 and 10:1 nitrogen/phosphorus (N/P). Nitrate concentrations varied from 0 to 500 μM, and ammonium concentrations varied from 0 to 50 μM. Growth rates of H. cervicornis increased linearly with addition of ammonium, but with nitrate addition, growth varied following a saturation kinetic, and the highest growth rate (14.45 % d^?1) was observed in 200 μM of N/P ratio of 10:1. An excess of nutrients was accumulated as proteins and phycobiliproteins (mainly as allophycocyanin and phycoerythrin) at higher phosphate availability (N/P ratio of 10:1), and H. cervicornis tolerated the highest ammonium and nitrate concentrations (50 and 500 μM, respectively). These physiological responses suggest that this species could be used as biofilter for nutrient removal in eutrophicated seawater and could be cultivated in integrated multitrophic aquaculture systems.     

Cost-effective IMTA: a comparison of the production efficiencies of mussels and seaweed

This paper compares the biofilter capacity and cost-effectiveness of blue mussels (Mytilus edulis) and seaweed for use in integrated multi-trophic aquaculture (IMTA) based on experiences in Ireland and Denmark. This comparison shows that weight for weight, mussels are a better biofilter than seaweed with regard to the amount of nitrogen assimilated. Furthermore, in optimized systems, areal requirement for mussels is similar to the cultivation of the same tonnage (1,000 t) of seaweed (approximately 8 ha). The cost-effectiveness of a mussel biofilter is €11–30 kg^?1 nitrogen (N) removed based on various examples compared to production costs of €209–672 removed and €1,013 kg^?1 N removed, respectively, for Laminaria digitata and Alaria esculenta from extrapolated laboratory and field trials. However, commercial seaweed (Saccharina latissima) producers claim that production costs are less than €10–38 kg^?1 N removed. These up-scaled and commercial figures make the seaweed cost competitive to mussels for removal of nitrogen. Disadvantages such as predators (e.g. eider ducks) and biofouling should also be taken into account before choice of biofilter is made. These drawbacks can reduce overall biofilter capacity and biomass value as a consequence of biomass spoilage or loss. However, disadvantages may be mitigated by seasonal choice of cultivation and harvest times. Cultivation technologies and harvesting methods may be improved together with breeding to improve the cost-efficiency of the biofilter, especially in the newer European seaweed cultivation. Furthermore, upscaling of IMTA to commercial proportions, other than the Danish example, would allow more real data on production costs and revenues.     

Physiological responses and biofilter potential of <Emphasis Type="Italic">Hypnea aspera</Emphasis> (Rhodophyta,Gigartinales) cultivated in different availabilities of nitrate,ammonium, and phosphate

Along with the search for new species of seaweeds with biofilter capacity, it is also necessary to understand the physiological and biochemical responses of these seaweeds cultivated in different availabilities of nitrate, ammonium, and phosphate. To accomplish this, a laboratory study was performed to evaluate the ability of Hypnea aspera Kützing (Gigartinales, Rhodophyta), to growth under different nitrate, ammonium, and phosphate availabilities and to uptake, assimilate, and remove these nutrients from seawater. Treatments were composed of sterilized seawater enriched with quarter-strength von Stosch’s nutrient solution modified (without any nitrogen and phosphorus compounds). Nitrate or ammonium, together with phosphate, was added in combined N/P ratios of 100:1 and 10:1. Nitrate concentrations varied from 0 to 150 μM, and ammonium concentrations varied from 0 to 70 μM. Growth rates of H. aspera increased with nitrate addition, and the highest value was 4.68 ± 0.76 % day^?1 in 150 μM, but the addition of high ammonium concentration (70 μM) in N/P ratio of 10:1 inhibited the growth rates (?3.89 ± 1.03 % day^?1). Nitrogen was accumulated as proteins and phycobiliproteins, mainly phycoerythrin, at higher phosphate availability (N/P ratio of 10:1) for nitrate addition (150 μM for proteins and 50, 100, and 150 μM for phycoerythrin), and lower phosphate availability (N/P ratio of 100:1) for ammonium addition (50 and 70 μM for proteins and 50 μM for phycoerythrin). Nitrogen and phosphate were assimilated into thallus in all treatments with nutrient addition. Hypnea aspera showed high removal efficiency (higher than 90 %) of nitrate, nitrite, ammonium, and phosphate present in the seawater. These results suggest that H. aspera could be cultivated in integrated multitrophic aquaculture systems to reduce nutrient loading in eutrophic seawater.     

Linking performance to microbiology in biofilters treating dimethyl sulphide in the presence and absence of methanol

The performance and microbiology of two inorganic biofilters treating dimethyl sulphide (DMS) in the presence and absence of methanol was investigated. Addition of methanol was shown to result in an increase in DMS removal for methanol loadings below 90 g MeOH per cubic metre per hour with the optimal methanol loading around 10–15 g MeOH per cubic metre per hour for a DMS loading of 3.4 g DMS per cubic metre per hour, a fivefold increase in the DMS removal rate compared to the biofilter treating DMS alone. Microbial community analysis revealed that the addition of methanol led to a significant increase of up to an order of magnitude in the abundance of Hyphomicrobium spp. in the biofilter co-treating DMS and methanol compared to the biofilter treating DMS alone, whilst there was no significant difference in the abundance of Thiobacillus spp. between the two biofilters. Given the behaviour of the biofilter co-treating DMS and methanol, the magnitude of the increase in Hyphomicrobium spp. in the biofilter co-treating DMS and methanol and the ability of Hyphomicrobium spp. to use both methanol and DMS as growth substrates, it was concluded that Hyphomicrobium spp. were the microorganisms responsible for the bulk of the DMS degradation in the biofilter co-treating DMS and methanol.     

Autotrophic denitrification by nitrate-dependent Fe(II) oxidation in a continuous up-flow biofilter

A continuous-upflow biofilter packed with sponge iron was constructed for nitrate removal under an anaerobic atmosphere. Microbacterium sp. W5, a nitrate reducing and Fe(II) oxidizing strain, was added to the biofilter as an inoculum. The best results were achieved when NO₃ ^?-N concentration was 30 mg/L and Fe²⁺ was 800 mg/L. Nitrite in influent would inhibit nitrate removal and aqueous Fe²⁺ resulted in encrustation. Fe(II)EDTA would prevent cells from encrustation and the maximum nitrogen removal efficiency was about 90 % with Fe(II)EDTA level of 1100 mg/L. Nitrate reduction followed first-order reaction kinetics. Characteristics of biofilms were analyzed by X-ray fluorescence spectroscopy.     

Bioremediation potential of Palmaria palmata and Chondrus crispus (Basin Head): effect of nitrate and ammonium ratio as nitrogen source on nutrient removal

Palmaria palmata and Chondrus crispus were grown for 4 weeks in 1-L flasks at 10 °C to evaluate nutrient uptake and their potential application as nutrient biofilters in effluent from finfish culture. For greatest bioremediation benefit within an integrated system, we conclude that a seaweed biofilter using these species should be placed prior to bacterial biofiltration for exposure to greater proportions of ammonium than nitrate, though it is apparent that the productivity of both species is not influenced by the nitrogen source. Five combinations of ammonium– and nitrate–nitrogen were compared, each with a total N concentration of 300 μM (300:0, 270:30, 150:150, 30:270, 0:300). Molar nitrogen/phosphorus ratio was 10:1. The maximum growth rates were 8.9 and 6.0 % per day for P. palmata and C. crispus, respectively. For both species, the total nitrogen uptake was highest at 300 μM ammonium, 4.46 mgN gDW^?1 day^?1 for P. palmata and 3.40 mg?N? g?DW^?1?day^?1 for C. crispus. Over a 24-h period, 23–37 % of the available nitrate and 91–100 % of the available ammonium were taken up by P. palmata. In the same period, C. crispus took up 55–87 % of available nitrate and 89–100 % of ammonium. Tissue N in P. palmata was highest (4.1 %) at 270 and 300 μM ammonium, while the nitrogen source did not have a significant effect on the tissue N of C. crispus (mean of 4.6 %).     

An applicable nitrogen supply strategy for attached cultivation of Aucutodesmus obliquus

The “attached cultivation” method of microalgae in which the wet paste of algal biomass is attached onto supporting materials to form an immobilized biofilm layer, and the culture medium is supplied to this layer to provide nutrients and moisture for growth was highly efficient in biomass production and represents a promising technology to improve the biofuel industry. To optimize the nitrogen supply strategy for this attached cultivation method, the growth and total lipids accumulation properties for the green alga Aucutodesmus obliquus with this method were studied under different quantities of nitrogen source and different volumes of aqueous medium that continuously circulated inside the photobioreactor. Results showed that, compared with medium volume, the nitrogen quantity was a stronger factor affecting the growth and total lipid accumulation. An optimized nitrogen supply strategy for the attached cultivation of A. obliquus is proposed as circulating ca. 60 L of BG-11 medium containing 1/10 of nitrate concentration for 1 m² of cultivation surface. With this strategy, the attached A. obliquus accumulated biomass and total lipids simultaneously and obtained a high triacylglyceride productivity of 2.53 g m^?2 day^?1 in 7 days under subsaturated illumination of 100 μmol photons m^?2 s^?1. The water usage of 60 L m^?2 was potentially decreased to <2 L m^?2 if the nutrient supply was further improved. Dissolving the nitrogen source in small volume was the best way to efficiently utilize the nitrogen source with minimum of waste.     

Ammonium removal using algae–bacteria consortia: the effect of ammonium concentration,algae biomass,and light

In this study, the effects of ammonium nitrogen concentration, algae biomass concentration, and light conditions (wavelength and intensity) on the ammonium removal efficiency of algae-bacteria consortia from wastewater were investigated. The results indicated that ammonium concentration and light intensity had a significant impact on nitrification. It was found that the highest ammonia concentration (430 mg N/L) in the influent resulted in the highest ammonia removal rate of 108 ± 3.6 mg N/L/days, which was two times higher than the influent with low ammonia concentration (40 mg N/L). At the lowest light intensity of 1000 Lux, algae biomass concentration, light wavelength, and light cycle did not show a significant effect on the performance of algal–bacterial consortium. Furthermore, the ammonia removal rate was approximately 83 ± 1.0 mg N/L/days, which was up to 40% faster than at the light intensity of 2500 Lux. It was concluded that the algae-bacteria consortia can effectively remove nitrogen from wastewater and the removal performance can be stabilized and enhanced using the low light intensity of 1000 Lux that is also a cost-effective strategy.     

Simultaneous nitrification and denitrification with different mixed nitrogen loads by a hypothermia aerobic bacterium

Microorganism with simultaneous nitrification and denitrification ability plays a significant role in nitrogen removal process, especially in the eutrophic waters with excessive nitrogen loads. The nitrogen removal capacity of microorganism may suffer from low temperature or nitrite nitrogen source. In this study, a hypothermia aerobic nitrite-denitrifying bacterium, Pseudomonas tolaasii strain Y-11, was selected to determine the simultaneous nitrification and denitrification ability with mixed nitrogen source at 15 °C. The sole nitrogen removal efficiencies of strain Y-11 in simulated wastewater were obtained. After 24 h of incubation at 15 °C, the ammonium nitrogen fell below the detection limit from an initial value of 10.99 mg/L. Approximately 88.0 ± 0.33% of nitrate nitrogen was removed with the initial concentration of 11.78 mg/L and the nitrite nitrogen was not detected with the initial concentration of 10.75 mg/L after 48 h of incubation at 15 °C. Additionally, the simultaneous nitrification and denitrification nitrogen removal ability of P. tolaasii strain Y-11 was evaluated using low concentration of mixed NH₄⁺-N and NO₃^?–N/NO₂^?–N (about 5 mg/L-N each) and high concentration of mixed NH₄⁺–N and NO₃^?–N/NO₂^?–N (about 100 mg/L-N each). There was no nitrite nitrogen accumulation at the time of evaluation. The results demonstrated that P. tolaasii strain Y-11 had higher simultaneous nitrification and denitrification capacity with low concentration of mixed inorganic nitrogen sources and may be applied in low temperature wastewater treatment.     

On the nitrogen and phosphorus removal in algal photobioreactors

This study shows results of nitrogen and phosphorus removal by microalgae (tertiary treatment) in a prototype of tubular photobioreactor tested under controlled and uncontrolled conditions. The wastewater was the supernatant coming from a secondary settler of a municipal wastewater activated sludge treatment plant without nitrification and denitrification units. The algal biomass was directly selected from the supernatant and it was principally composed of genus Scenedesmus (autochthonous algae). All the experiments evaluated both nitrogen and phosphorus removal and biomass and lipid production. A satisfactory nutrients removal - about 99.9% for the nitrogen and phosphorus - and a specific biomass productivity of 0.25 g/l d have been obtained in the indoor photobioreactor; less satisfactory results have been reached in the outdoor photobioreactor because of ambient condition instability and limiting nutrients concentration.     

Nitrogen removal and microbial communities in a three-stage system simulating a riparian environment

The riparian zone is an active interface for nitrogen removal, in which nitrogen transformations by microorganisms have not been valued. In this study, a three-stage system was constructed to simulate the riparian zone environments, and nitrogen removal as well as the microbial community was investigated in this ‘engineered riparian system’. The results demonstrated that stage 1 of this system accounted for 41–51 % of total nitrogen removal. Initial ammonium loading and redox potential significantly impacted the nitrogen removal performances. Stages 1 and 2 were both composed of an anoxic/oxic (A/O) zone and an anaerobic column. The A/O zone removed most of the ammonium load (6.8 g/m²/day), while the anaerobic column showed a significant nitrate removal rate (11.1 g/m²/day). Molecular biological analysis demonstrated that bacterial diversity was high in the A/O zones, where ammonium-oxidizing bacteria and nitrite-oxidizing bacteria accounted for 8.42 and 3.32 % of the bacterial population, respectively. The denitrifying bacteria Acidovorax sp. and the nitrifying bacteria Nitrosospira/Nitrosomonas were the predominant microorganisms in this engineered riparian system. This three-stage system was established to achieve favorable nitrogen removal and the microbial community in the system was also retained. This investigation should deepen our understanding of biological nitrogen removal in engineered riparian zones.     

Temperature-induced changes in treatment efficiency and microbial structure of aerobic granules treating landfill leachate

This paper investigates the effect of temperature on nitrogen and carbon removal by aerobic granules from landfill leachate with a high ammonium concentration and low concentration of biodegradable organics. The study was conducted in three stages; firstly the operating temperature of the batch reactor with aerobic granules was maintained at 29 °C, then at 25 °C, and finally at 20 °C. It was found that a gradual decrease in operational temperature allowed the nitrogen-converting community in the granules to acclimate, ensuring efficient nitrification even at ambient temperature (20 °C). Ammonium was fully removed from leachate regardless of the temperature, but higher operational temperatures resulted in higher ammonium removal rates [up to 44.2 mg/(L h) at 29 °C]. Lowering the operational temperature from 29 to 20 °C decreased nitrite accumulation in the GSBR cycle. The highest efficiency of total nitrogen removal was achieved at 25 °C (36.8 ± 10.9 %). The COD removal efficiency did not exceed 50 %. Granules constituted 77, 80 and 83 % of the biomass at 29, 25 and 20 °C, respectively. Ammonium was oxidized by both aerobic and anaerobic ammonium-oxidizing bacteria. Accumulibacter sp., Thauera sp., cultured Tetrasphaera PAO and Azoarcus–Thauera cluster occurred in granules independent of the temperature. Lower temperatures favored the occurrence of denitrifiers of Zooglea lineage (not Z. resiniphila), bacteria related to Comamonadaceae, Curvibacter sp., Azoarcus cluster, Rhodobacter sp., Roseobacter sp. and Acidovorax spp. At lower temperatures, the increased abundance of denitrifiers compensated for the lowered enzymatic activity of the biomass and ensured that nitrogen removal at 20 °C was similar to that at 25 °C and significantly higher than removal at 29 °C.     

Is an organic nitrogen source needed for cellulase production by Trichoderma reesei Rut-C30?

The effect of organic and inorganic nitrogen sources on Trichoderma reesei Rut-C30 cellulase production was investigated in submerged cultivations. Stirred tank bioreactors and shake flasks, with and without pH control, respectively, were employed. The experimental design involved the addition of individual organic nitrogen sources (soy peptone, glutamate, glycine and alanine) within a basal medium containing Avicel (i.e. micro crystalline cellulose) and ammonium sulphate. It was found that in the shake flask experiments, the highest cellulase activities (~0.1 ± 0.02 FPU ml^?1) were obtained with media containing soy peptone (3–6 g l^?1) and glutamate (3.6 g l^?1). However, these improvements in the cellulase titers in the presence of the organic nitrogen sources appeared to be related to smaller changes in the pH of the medium. This was confirmed using stirred tank bioreactors with pH control. No significant differences were observed in the highest cellulase titers and the protein pattern (according to the SDS-PAGE) of supernatants from pH controlled stirred tank bioreactor cultivations, when different nitrogen sources were used in the medium. Here the cellulase activities (~1.0 ± 0.2 FPU ml^?1) were also much greater (8–150 times) than in shake flask cultivation. Consequently, the addition of ammonium sulphate as sole nitrogen source to Avicel basal medium is recommended when performing cultivations in stirred tank bioreactors with strict pH controlled conditions.     

Role of Thiobacillus thioparus in the biodegradation of carbon disulfide in a biofilter packed with a recycled organic pelletized material

This study reports the biodegradation of carbon disulfide (CS₂) in air biofilters packed with a pelletized mixture of composted manure and sawdust. Experiments were carried out in two lab-scale (1.2 L) biofiltration units. Biofilter B was seeded with activated sludge enriched previously on CS₂-degrading biomass under batch conditions, while biofilter A was left as a negative inoculation control. This inoculum was characterized by an acidic pH and sulfate accumulation, and contained Achromobacter xylosoxidans as the main putative CS₂ biodegrading bacterium. Biofilter operation start-up was unsuccessfully attempted under xerophilic conditions and significant CS₂ elimination was only achieved in biofilter A upon the implementation of an intermittent irrigation regime. Sustained removal efficiencies of 90–100 % at an inlet load of up to 12 g CS₂ m^?3 h^?1 were reached. The CS₂ removal in this biofilter was linked to the presence of the chemolithoautotrophic bacterium Thiobacillus thioparus, known among the relatively small number of species with a reported capacity of growing on CS₂ as the sole energy source. DGGE molecular profiles confirmed that this microbe had become dominant in biofilter A while it was not detected in samples from biofilter B. Conventional biofilters packed with inexpensive organic materials are suited for the treatment of low-strength CS₂ polluted gases (IL <12 g CS₂ m^?3 h^?1), provided that the development of the adequate microorganisms is favored, either upon enrichment or by inoculation. The importance of applying culture-independent techniques for microbial community analysis as a diagnostic tool in the biofiltration of recalcitrant compounds has been highlighted.     

Coupling microbial fuel cells with a membrane photobioreactor for wastewater treatment and bioenergy production

Microbial fuel cells (MFCs) and membrane photobioreactors are two emerging technologies for simultaneous wastewater treatment and bioenergy production. In this study, those two technologies were coupled to form an integrated treatment system, whose performance was examined under different operating conditions. The coupled system could achieve 92–97 % removal of soluble chemical oxygen demand (SCOD) and nearly 100 % removal of ammonia. Extending the hydraulic retention time (HRT) of the membrane photobioreactor to 3.0 days improved the production of algal biomass from 44.4 ± 23.8 to 133.7 ± 12.9 mg L^?1 (based on the volume of the treated water). When the MFCs were operated in a loop mode, their effluent (which was the influent to the algal reactor) contained nitrate and had a high pH, leading to the decreased algal production in the membrane photobioreactor. Energy analysis showed that the energy consumption was mainly due to the recirculation of the anolyte and the catholyte in the MFCs and that decreasing the recirculation rates could significantly reduce energy consumption. The energy production was dominated by indirect electricity generation from algal biomass. The highest energy production of 0.205 kWh m^?3 was obtained with the highest algal biomass production, resulting in a theoretically positive energy balance of 0.033 kWh m^?3. Those results have demonstrated that the coupled system could be an alternative approach for energy-efficient wastewater treatment and using wastewater effluent for algal production.     

Removal of the sesquiterpene β-caryophyllene from air via biofiltration: performance assessment and microbial community structure

Experiments were conducted in a laboratory-scale biofilter to assess the ability of a fixed-film biological process to treat an air stream containing β-caryophyllene, a sesquiterpene emitted by a variety of conifer trees as well as industrial wood processing operations. Treatment performance was evaluated under a variety of pollutant loading conditions and nutrient supply rates over an operational period lasting more than 240 days. At empty bed contact times (EBCTs) as low as 10 s and daily average pollutant loading rate as high as 24.2 g C/(m³ h) (grams pollutant measured as carbon per cubic meter packed bed volume per hour), removal efficiencies in excess of 95 % were observed when sufficient nutrients were supplied. Results demonstrate that, as with biofilters treating other compounds, biofilters treating β-caryophyllene can experience local nutrient limitations that result in diminished performance. The biofilter successfully recovered high removal efficiency within a few days after resumption of pollutant loading following a 14-day interval of no contaminant loading. Construction of a 16S rRNA gene library via pyrosequencing revealed the presence of a high proportion of bacteria clustering within the genera Gordonia (39.7 % of the library) and Rhodanobacter (37.6 %). Other phylotypes detected at lower relative abundances included Pandoraea (6.2 %), unclassified Acetobacteraceae (5.5 %), Dyella (3.3 %), unclassified Xanthomonadaceae (2.6 %), Mycobacterium (1.8 %), and Nocardia (0.6 %). Collectively, results demonstrate that β-caryophyllene can be effectively removed from contaminated gas streams using biofilters.