Harnessing immobilised algae for high rate wastewater treatment

Algal systems can be used to decrease the concentration of nitrogen (N) and phosphorus (P) in wastewater to low levels, and hence reduce the harm of wastewater discharge and facilitate water reuse. Immobilisation of algae by entrapment in alginate beads can overcome the shortcomings of suspended algal systems of long treatment times, difficulty in harvesting and control of the algal species being cultivated. The aim of this lab-scale study was to investigate and improve nutrient removal from municipal wastewater by alginate-immobilised algae and to explore pathways for its implementation in wastewater treatment plants. Comparison of intensified nutrient removal systems of biofilm, alginate-entrapped, suspended microalgae (Chlorella vulgaris) and macroalgae (Oedogonium cardiacum) demonstrated that the rate of nutrient removal depended more on the respective ability of each system to accumulate algal biomass in the reactor rather than the type of system affecting the rate of nutrient transfer into each unit of biomass. Macroalgae retained with a mesh is a promising option for both nutrient removal and biomass generation that would be simple to operate. The macroalgae produced 102 ± 4 mg/L/d dry weight of biomass and reached levels of 1.3 ± 0.6 mg/L total phosphorus (TP) and 8.5 ± 1.5 mg/L total dissolved nitrogen (TDN) from a feed of 7 and 24 mg/L respectively, and operated for 30 days at a 12 h hydraulic retention time (HRT). Alginate-immobilised algal cells were retained in the reactor more effectively than the other microalgal systems as this system lost only 0.03 times the biomass increase in the reactor compared with 2.6 times for the biofilm and 1.7 times for the suspended systems. However, the alginate-immobilised algal system treated the wastewater for less than 6 days before bead deterioration, meaning frequent bead generation would be needed to initiate new treatment cycles. This would add to the operating costs of the system and therefore was subsequently addressed by alginate product and species selection. To reduce the cost of alginate supply, a non-laboratory product was shown to be a suitable option for immobilisation of C. vulgaris for wastewater treatment and did not negatively impact N and P removal or bead durability. The non-laboratory alginate led to the production of 36 mg/L/d dry weight of algae compared with 47 mg/L/d for the best performing laboratory product, however this was outweighed by raw material cost savings. The sugars of the alginate polymer chain were found to be an important characteristic that governed bead durability, with a high G:M (L-guluronate:D-mannuronate) ratio found to reduce swelling and loss of structural strength when the beads were exposed to wastewater. Investigation of where immobilised C. vulgaris can be implemented within the wastewater treatment train showed that the cells could adjust their internal nutrient content (N of 4.6-7.8%, P of 1.2-3.2%) to a range of nutrient concentrations (TDN of 6.5-54.3 mg/L, TP of 6.2-14.8 mg/L) in several different wastewater sources (two lagoon effluents, secondary effluent samples taken on different dates, and a primary effluent). A strong relationship between the wastewater NH4+ concentration and algal N content (p-value = 0.00004) that was independent of wastewater source demonstrated that the algal cells could adapt well to wastewater with a high NH4+ content and remove more N per cell. Hence, wastewater with a high NH4+ concentration would be a suitable target for algal treatment and would provide extra benefit in N removal. By quantifying abiotic and biotic nutrient removal pathways separately it was determined that wastewater with a high NO3- content led to increased indirect N and P removal and poorer adaptation of algal assimilation to the wastewater N concentration. It was also shown that immobilisation of C. vulgaris did not impact how the algal cells adapted to the wastewater. Comparison of four algal species showed that Scenedesmus abundans could treat the wastewater for longer (42 d) than Chlorella vulgaris (22 d), Coelastrum microporum (8 d) and Selenastrum capricornutum (8 d). The beads of S. abundans were more durable in the wastewater because the algal cells adapted better to growth in the alginate beads and removed nutrients that can damage the Ca-alginate matrix more efficiently. This meant eachbead of S. abundans removed more N (101 ± 8 µg TN/bead) and P (45.9 ± 1.9 µg TP/bead)before needing to be replaced with new beads than did C. vulgaris (41.1 ± 3.8 µg TN/bead, 17.2 ± 0.8 µg TP/bead), Coel. microporum (13.8 ± 3.1 µg TN/bead, 3.7 ± 0.6 µg TP/bead) andSel. capricornutum (14.7 ± 2.3 µg TN/bead, 4.3 ± 0.3 µg TP/bead), enabling more efficient utilisation of alginate.. Differences in the N and P concentration and ratio of the medium used to culture the algae before immobilisation and wastewater inoculation did not impact treatment performance for any of these algal species. Concentrations of ≤ 1 mg TP/L and ≤ 10 mg TN/L were achieved with a fluidised-bed reactor of alginate-immobilised S. abundans treating wastewater with 8.9 mg TP/L and 18.3 mg TN/L at a HRT of 12 h (6 h active bed) for 30 days, and produced 3.3 ± 0.6 x 106 cells/mL/d. Co-digestion of S. abundans biomass without pre-treatment with anaerobic digestor sludge (based on the scenario of separation and reuse of alginate rather than also digesting it) led to biomethane production of 248 ± 10 mL CH4/g VS. Use of alginate-immobilised algae was thus demonstrated to remove the need for alternative P removal systems, to partly offset the amount of N removal needed from other processes, and to produce biomass for energy recovery. This work has contributed to the improvement of alginate-immobilised algae systems for wastewater treatment and demonstrated its technical feasibility for nutrient removal from different wastewaters. The findings can be used to guide how to best implement and integrate alginate-immobilised algae into new and existing wastewater treatment plants and can form the basis for viability assessment of its commercial application

Experiments and Simulations on Day-to-Day Route Choice-Behaviour

The paper reports laboratory experiments on a day-to-day route choice game with two routes. Subjects had to choose between a main road M and a side road S. The capacity was greater for the main road. 18 subjects participated in each session. In equilibrium the number of subjects is 12 on M and 6 on S. Two treatments with 6 sessions each were run at the Laboratory of Experimental Economics at Bonn University using RatImage. Feedback was given in treatment I only about own travel time and in treatment II on travel time for M and S. Money payoffs increase with decreasing time. The main results are as follows. 1. Mean numbers on M and S are very near to the equilibrium. 2. Fluctuations persist until the end of the sessions in both treatments. 3. Fluctuations are smaller under treatment II .The effect is small but significant. 4. The total number of changes is significantly greater in treatment I. 5. Subjects’ road changes and payoffs are negatively correlated in all sessions. 6. A direct response mode reacts with more changes for bad payoffs whereas a contrary response mode shows opposite reactions. Both response modes can be observed. 7. The simulation of an extended payoff sum learning model closely fits the main results of the statistical evaluation of the data.travel behaviour research, information in intelligent transportation systems, day-to-day route choice, laboratory experiments, payoff sum model

Vector chiral order in frustrated spin chains

By means of a numerical analysis using a non-Abelian symmetry realization of the density matrix renormalization group, we study the behavior of vector chirality correlations in isotropic frustrated chains of spin S=1 and S=1/2, subject to a strong external magnetic field. It is shown that the field induces a phase with spontaneously broken chiral symmetry, in line with earlier theoretical predictions. We present results on the field dependence of the order parameter and the critical exponents.Comment: 8 pages, 9 figure

Monte Carlo sampling of Wigner functions and surface hopping quantum dynamics

The article addresses the achievable accuracy for a Monte Carlo sampling of Wigner functions in combination with a surface hopping algorithm for non-adiabatic quantum dynamics. The approximation of Wigner functions is realized by an adaption of the Metropolis algorithm for real-valued functions with disconnected support. The integration, which is necessary for computing values of the Wigner function, uses importance sampling with a Gaussian weight function. The numerical experiments agree with theoretical considerations and show an error of 2–3%

Stress-dependent ultrasonic scattering in polycrystalline materials

Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of the differential scattering cross-section, which defines how strongly an incident wave is scattered into various directions. Nine stress-dependent differential scattering cross-sections or scattering coefficients are defined to include all possibilities of incident and scattered waves, which can be either longitudinal or (two) transverse wave types. The evaluation of the scattering coefficients considers polycrystalline aluminum that is uniaxially stressed. An analysis of the influence of incident wave propagation direction, scattering direction, frequency, and grain size on the stress-dependency of the scattering coefficients follows. Scattering coefficients for aluminum indicate that ultrasonic scattering is much more sensitive to a uniaxial stress than ultrasonic phase velocities. By developing the stress-dependent scattering properties of polycrystals, the influence of acoustoelasticity on the amplitudes of waves propagating in stressed polycrystalline materials can be better understood. This work supports the ongoing development of a technique for monitoring and measuring stresses in metallic materials

Analyses of the vrl gene cluster in Desulfococcus multivorans: Homologous to the virulence-associated locus of the ovine footrot pathogen Dichelobacter nodosus strain A198

Major parts of the virulence-associated vrl locus known from the gammaproteobacterium Dichelobacter nodosus, the causative agent of ovine footrot, were analyzed in the genome of the sulfate-reducing deltaproteobacterium Desulfococcus multivorans. In the genome of D. multivorans 13 of the 19 vrl genes described for D. nodosus are present and highly conserved with respect to gene sequence and order. The vrl locus and its flanking regions suggest a bacteriophage-mediated transfer into the genome of D. multivorans. Comparative analysis of the deduced Vrl proteins reveals a wide distribution of parts of the virulence-associated vrl locus in distantly related bacteria. Horizontal transfer is suggested as driving mechanism for the circulation of the vrl genes in bacteria. Except for the vrlBMN genes D. multivorans and Desulfovibrio desulfuricans G20 together contain all vrl genes displaying a high degree of similarity. For D. multivorans it could be shown that guanine plus cytosine (GC) content, GC skew, di-, tri- or tetranucleotide distribution did not differ between the vrl locus and its flanking sequences. This could be a hint that the vrl locus originated from a related organism or at least a genome with similar characteristics. The conspicuous high degree of conservation of the analyzed vrl genes may result from a recent transfer event or reflect a function of the vrl genes, which is still unknown and not necessarily disease associated. The latter is supported by the evidence for expression of the vrl genes in D. multivorans, which has not been described as pathogen or to be associated to any disease pattern before

Finite Amplitude Wave Propagation in Anisotropic Materials

Often, ultrasound used in nondestructive evaluation is applied to materials that are elastically anisotropic. A few example materials include composites, welds, and rolled metal plates. The influence of elastic anisotropy on the propagation of ultrasound in materials that are linearly elastic is well understood. For example, elastic constants of a composite can be determined reasonably well by measuring phase velocities for propagation in certain directions. However, the influence of elastic anisotropy on nonlinear ultrasonic techniques has received much less attention. In this work, finite amplitude bulk wave propagation is considered for materials with general elastic anisotropy of the second-, third-, and fourth-order elastic constants (anisotropy associated with triclinic symmetry). Three displacement solutions are obtained for arbitrary propagation directions of the three possible bulk wave modes (one quasi-longitudinal and two quasi-transverse). The solution corresponding to each wave mode is a harmonic series having contributions from the fundamental, second-, and third-harmonic waves. The second-harmonic wave amplitude is a function of the quadratic (β) nonlinearity parameter while the thirdharmonic amplitude is a function of both the quadratic and cubic () nonlinearity parameters. β is given in terms of displacement and propagation directions along with elastic tensors that define the second- and third-order elastic constants of the material. An additional contribution from the elastic tensor defining the fourth-order elastic constants is needed to define . Closed-form evaluation of β and for the three different wave modes has been conducted for a variety of materials having different crystallographic point group symmetries. Surfaces will be presented for selected materials, which illustrate the three-dimensional spatial distribution of β and for any propagation direction of the fundamental wave. The vanishing of β for shear waves propagating within material planes of symmetry causes the surface to display the symmetry of the material elegantly. Lastly, straightforward expressions for β and are given for some pure mode directions