Eichhornia crassipes capability to remove naphthalene from wastewater in the absence of bacteria.

The aim of the current study was to investigate the potential of an aquatic plant, the water hyacinth (Eichhornia crassipes) devoid rhizospheric bacteria, to reduce naphthalene (a polyaromatic hydrocarbon) present in wastewater and wetlands. The capability of sterile water hyacinth plants to remove naphthalene from water and wastewater was studied in batch systems. Water hyacinths enhance the removal of pollutants through their consumption as nutrients and also through microbial activity of their rhizospheric bacteria. Experimental kinetics of naphthalene removal by water hyacinth coupled with natural rhizospheric bacteria was 100% after 9 d. Plants, decoupled of rhizospheric bacteria, reduced naphthalene concentration up to 45% during 7 d. Additionally, naphthalene uptake by water hyacinth revealed a biphasic behavior: a rapid first phase completed after 2.5 h, and a second, considerably slower rate, phase (2.5-225 h). In conclusion, water hyacinth devoid rhizospheric bacteria reduced significantly naphthalene concentration in water, revealing a considerable plant contribution in the biodegradation process of this pollutant.

Removal of phenol in a constructed wetland system and the relative contribution of plant roots, microbial activity and porous bed.

Analysis of a low organic load constructed wetland (CW) system was performed in order to understand the relative role of its various components contribution in phenol removal (100 mg/L) under controlled plant biomass/gravel/water experimental ratios (50 g/450 g/100 mL). The results [expressed as phenol50/time (hours) required to remove 50% of the initial phenol concentration] showed that the highest phenol removal occurred by combined biofilms from roots and gravel attached (phenol50=19), followed by gravel biofilm (phenol50=105) and planktonic (suspended in water) bacteria (phenol50=>200). An in depth analysis revealed that plants contribution alone (antibiotics sterilized) was minor (phenol50=>89) while roots supported biofilm resulted in a significant phenol removal (phenol50=15). Therefore in this type of CW, the main phenol removal active fraction could be attributed to plant roots' biofilm bacteria.

Removal of microbial biofilm on Water Hyacinth plants roots by ultrasonic treatment.

The capacity of floating aquatic plants to purify sewage effluents drops rapidly as a result of biofouling processes that occur on the plant roots. This is due to the high concentration of microorganisms (MO) present in the wastewater. The possibility to apply low frequency (20 kHz) in sonification was examined under laboratory conditions. The ability of US to remove MO from the roots was studied using commercially available sonicators at intensity levels ranging from 2.7 W/cm(2) to 81.4 W/cm(2), (corresponding power levels ranging from 75 W to 500 W) while varying application periods between 5 and 60 min. The results show that MO can be removed effectively (up to 98%) by exposing the Eichhornia crassipes roots to US for 5 min at the intensity level of 64.5 W/cm(2). The efficiency of the wastewater treatment increased with exposure time and power input. The study proved that the US treatment is effective in removing MO that otherwise adhere to the roots, by more then two orders of magnitude.

Removal of high organic loads from winery wastewater by aquatic plants.

Laboratory- and field-scale purification tests of raw and diluted winery wastewater (WWW) were carried out using aquatic plants at high organic loads. The laboratory tests were performed using artificial light at 1800 to 1900 lux. The objective of the current study was to define the potential of floating and emergent aquatic macrophytes and the microorganisms attached to their roots, to reduce high organic loads that characterize WWW, thereby providing, for these effluents, an effective treatment and management system. These microorganisms are believed to have a major role in the treatment process. In this context, the potential of floating and emergent macrophytes to improve the water quality of raw compared with diluted WWW was evaluated. In raw WWW (chemical oxygen demand [COD] 5.6 g/L),growth inhibition of both water hyacinth (Eichhornia crassipes) and water pennywort (Hydrocotyle umbellata) was observed. A 1:1 dilution of WWW with fresh (tap) water facilitated growth of these plants. At this dilution level, growth of pennywort was limited, while that of water hyacinth was robust. In terms of reductions in biochemical oxygen demand, COD, and total suspended solids, both water hyacinth and pennywort performed better in diluted compared with raw WWW. At 1:1 and 1:3 dilution, 95.9 to 97% of the COD was removed after 23 days, in the presence of Hydrocotyle and Eichhornia plants and aeration. The capacity of new emergent plants to remove high organic loads from WWW, at enhanced kinetics, was demonstrated. This unique property was tested and compared with the role of the gravel media that support growth of the high-capacity emergent plants. In the presence of reed and salt marsh plants, 83 to 99% of the COD was removed within a period of 24 to 29 days, at 1.5:1 dilution. The new emergent plants proved to be effective, even at record high levels of COD. At an initial level of 16,460 mg/L, the COD was brought down to 2870 mg/L after 24 days (82.6% removal), while 12 230 mg/L was lowered to 106 mg/L, giving 99.1% removal from the highly contaminated WWW. These results indicate a significant extension of the range of applicability of emergent plants for the treatment of raw and diluted WWW. In this context, daily removal rates as high as 2000 mg/L in the first treatment days, and an average of over 550 mg/L per day in 24 days of treatment, were recorded. The indoor experiments were conducted without proper acclimatization of the plants to high-strength WWW. This might have affected the plants' health in case, with acclimatization, they might have behaved differently.

Effect of evapotranspiration on the salinity of wastewater treated by aquatic plants.

The shortage of good quality water resources is becoming an important issue in arid and semi-arid zones. Irrigation systems must be developed that are capable of delivering low quality wastewater while taking into account environmental and health requirements. For this reason, the availability of water resources of marginal quality, such as desalinated wastewater, can be a significant contribution to the water supply. We investigated changes in salinity, in conjunction with evaporation kinetics of treated wastewater by aquatic plants. These plants enhance the removal of pollutants by consuming them in the form of plant nutrients and through the microbial activity on their roots. In particular, this treatment applies to urban and agricultural sewage, where treatment units of different sizes can be applied at the pollution source while acting as green environments. In these treatment units, increased salinity due to effect of evapotranspiration (ET) must be managed. The rates of evaporation (E) from the free water surface and transpiration (T) from the plants were determined under field and laboratory conditions. To this end, batch experiments were performed with floating and emergent aquatic plants. After 4 days in the presence of floating plants, the biochemical oxygen demand (BOD) decreased from its 100-110 mg L(-1) initial value down to 30-40 mg L(-1) (65% to 70% removal), concurrent with a 2% to 5% increase in the chlorides level, and 5% to 8% in the electroconductivity. The ET rates were found to be a significant factor in the water balance governing the treatment process. The results of this work provide guidelines for recommended wastewater treatment times that safeguard against undesirable rises in salinity, yet with marginal change in parameters such as BOD. The change of salinity is shown to be relatively minor in the first days of treatment where the change in BOD is faster, whereas in the following days the picture is reversed. This result indicates the advantage of applying shorter treatment periods when the rise in salinity is avoided.

Advanced extraction and lower bounds for removal of pollutants from wastewater by water plants.

The capacity to reach lower bounds for extraction of pollutants from wastewater by four floating aquatic macrophytes--water hyacinth (Eichhornia crassipes), water lettuce (Pistia stratiotes), salvinia (Salvinia rotundifolia), and water primroses (Ludvigia palustris)--is investigated. It is shown that the following lower bounds can be established for wastewater purification with water hyacinth: biochemical oxygen demand (BOD), 1.3 mg/L; chemical oxygen demand (COD), 11.3 mg/L; total suspended solids (TSS), 0.5 mg/L; turbidity, 0.7 NTU; ammonia, 0.2 mg/L; and phosphorus, 1.4 mg/L. Also, the following lower bounds can be established for wastewater purification with water lettuce: BOD, 1.8 mg/L; COD, 12.5 mg/L; TSS, 0.5 mg/L; turbidity, 0.9 NTU; ammonia, 0.2 mg/L; and phosphorus, 1.6 mg/L. These lower bounds were reached in 11- to 17-day experiments that were performed on diluted wastewater with reduced initial contents of the tested water quality indicators. As expected, water hyacinth exhibited the highest rates and levels of pollutant removal, thereby producing the best lower bounds of the water quality indicators. Given the initially low levels, BOD was further reduced by 86.3%, COD by 66.6%, ammonia by 97.8%, and phosphorus by 65.0% after 11 days of a batch experiment. The capacity of water plants to purify dilute wastewater streams opens new options for their application in the water treatment industry.

Water vapor and air transport through ponds with floating aquatic plants.

The purpose of this paper is to estimate the evaporation rate in the purification of wastewater by aquatic plants with aeration. Evaporation of surface water is important in dewatering processes. In particular, this is true in arid climates, where evaporation rates are high. Aeration is known to enhance the wastewater purification process, but it increases concurrently the water evaporation rates. Evaporation and evapotranspiration rates were tested under field and laboratory conditions. Batch experiments were performed to study the levels of evaporation and evapotranspiration in free-water-surface, aquatic-plant systems. The experiments verified that, in these systems, the rate of evaporation increased as a result of aeration in the presence and absence of the aquatic plants. The evaporation rates resulting from aeration were found to be significant in the water balance governing the purification process. A preliminary model for description of the effect of rising air bubbles on the transport of water vapors was formulated. It is shown that aeration may account for a significant part of water losses that include surface evaporation.

Application of Eichhornia crassipes and Pistia stratiotes for treatment of urban sewage in Israel.

The effectiveness of sewage purification by aquatic plants, such as water hyacinth (Eichhornia crassipes) and water lettuce (Pistia stratiotes), was tested on laboratory and pilot scales. Cascade and semi-continuous pilot experiments verified that the plants are capable of decreasing all tested indicators of water quality to levels that permit the use of the purified water for irrigation of tree crops. This applies to biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), and turbidity. The laboratory-scale tests confirm the capacity of the plants to reach and hold reasonably low levels of BOD (5-7 mg L(-1)) and COD (40-50 mg L(-1)) and very low levels of TSS (3-5 mg L(-1)) and turbidity (1-2 NTU). In the experimental pilot setup, with circulation, COD decreased from 460 to 100 mg L(-1) after 2.5-4 days of treatment, while 6-7 days were required to this end without circulation. This doubled the active pond area and provided a two-level hydraulic loading (8 and 12 L min(-1)) with circulation that proved to be effective during the summer as well as the winter season. The outflow concentrations were 50-85 mg L(-1) of COD and 4-6 mg L(-1) of BOD. The results show that the use of this free water surface flow system (FWS) and its low maintenance system for treatment of urban and agricultural sewage is a viable option.

Structural evolution of self-expanding arrays of charged particulates.

Self-expansion patterns of unconstrained assemblies of charged particulates are simulated by solution of their individual trajectories. The general behaviour of these systems is considered regarding their expansion shape and structure. As the particulates cannot be described, in general, in terms of massless charged entities, the complete equation of motion, inclusive of the inertial and other size effects, must be applied to each and every member of the assembly. It is shown that irrespective of the initial position of the particulates and the time dependent shape of the assembly, when expanding in free space or else the particulates are identical in size, shape and mass, they self-expand asymptotically into a circular or spherical shape with an inner structure that tends to uniformity. This behaviour persists irrespective of the size and charge level of the particulates, or whether they form a single or multiple separate groups in one, two and three dimensions. In this context, ionic gaseous assemblies that fit into the realm of continua, are included. Two- and three-dimensional examples of simulation outputs for different particulate assemblies, illustrate typical self-expansion patterns. Internal structures that evolve in two-dimensional self-expanding arrays are shown to be different compared to those obtained in three dimensions. These simulations show that models of particle capture by random self-expanding arrays of charged particulates, may lack physical grounds, as they contradict the asymptotic mode of uniform and ordered self-expansion that is expected from the array.

Energy and hydrodynamic approaches to magnetocapillary instability of nonconducting jets.

The field energy and magnetocapillary instability of isothermal incompressible and inviscid nonconducting liquid jets in a uniform magnetic field are considered. The equivalence between static and dynamic approaches at the onset of instability and cutoff wavelength is shown and its implications are discussed. A new dispersion relation for magnetocapillary instability in such jets is derived. This relation differs from that given in the literature. The existence of a critical magnetic field that stabilizes jets with finite susceptibility is established. It is shown that the jet is stabilized by the field irrespective of its being para- or diamagnetic, but the extent of stabilization is different.

Use of naturally growing aquatic plants for wastewater purification.

This paper examines potential uses of naturally growing aquatic plants for wastewater purification. These plants enhance the removal of pollutants by consuming part of them in the form of plant nutrients. This applies to urban and agricultural wastewater, in particular, where treatment units of different sizes can be applied at the pollution source. The effectiveness of wastewater purification by different plants was tested on laboratory and pilot scales. The growth rate of the plants was related to the wastewater content in the water. Batch and semicontinuous experiments verified that the plants are capable of decreasing all tested indicators for water quality to levels that permit the use of the purified water for irrigation. This applies to biochemical oxygen demand (BOD), chemical oxygen demand, total suspended solids. pH, and turbidity. In specific cases, the turbidity reached the level of drinking water. Comparison of BOD concentrations with typical levels in water treatment facilities across the country indicates the effectiveness of water purification with plants. A major effect of treatment with plants was elimination of the disturbing smell from the wastewater. It is shown that mixtures of wastewater and polluted water from the Kishon River are amenable in varying degrees to treatment by the plants. The higher the wastewater content in the mixture, the more effective the treatment by the plants. In this context, a scheme for rehabilitation and restoration of the Kishon River is presented and technical and economical aspects of the purification technology are considered.

Microscale thermoviscosity and evaporation at the three-phase contact zone.

A microscale model of wetting at the three-phase contact zone that incorporates the thermoviscosity effect under nonisothermal and evaporation conditions is presented. The thermoviscosity effect is shown to change the content of both governing equations and boundary conditions. The differential equation of the liquid-vapor interface profile is expressed in terms of previously defined dimensionless groups and the new thermoviscosity change factor D(s). The temperature-dependent viscosity eta(T), and capillary number C(*) are defined as a product of eta and C and of 1-D(s)Theta(I), respectively. Model outputs show that increase of D(s) decreases the wave length and amplitude of the solution profile as well as the film thickness and slope. In the tested cases of water, nitrogen, and helium, increase of D(s) extends the physically feasible range of contact angle and wall temperature versus fluid velocity. Under rewetting conditions, the effect of increased D(s) is to shift the allowable range of wall temperatures toward smaller values, concurrent with increasing the feasible values of corresponding quench velocities. The capacity of the dimensionless groups, C, Ctheta(2)/F, N, and A, to change the liquid-vapor interface profile is diminished by D(s), the capillary number C and the Hamaker constant being most and least sensitive in this respect.

On the mechanism of spray formation from liquid jets.

A fundamental physical mechanism whereby sprays are formed from liquid jets is formulated. It is shown that a combination of axial disturbances cannot produce the necessary conditions for non-axial evolution of drops. These conditions are satisfied by a non-axial sequence of superimposed disturbances, propagating one on top of the other. The resulting model is used to describe the evolution of liquid jets into sprays. It is postulated that every consecutive superimposed disturbance, which is characterized by a self-instability parameter, travels tangent to the surface that supports its propagation. Model outputs show that starting from the first superimposed disturbance, highly complex profiles of the jet surface are generated. Fourier analysis of the derived superimposed disturbance functions is performed in conjunction with the basic building blocks of classic instability theory. This is achieved by assigning to each term a self-instability factor. The sum of these building blocks results in intricate profiles of the jet. In these profiles, multiplicity of radial position of the jet interface as a function of axial distance provides the necessary conditions for evolution of non-axial drops. The model accuracy, which depends on the disturbance rank, is sufficient to disclose the mechanism that turns the jet into a spray. The observed jump in the level of error is commensurate with the sudden increase in flow complexity that follows an increase in the disturbance rank. Finally, model outputs are used to study the effect of instability parameters on the evolution patterns of the jet and the non-axial discharge of drops.

Entropy of electromagnetic polarization.

The entropy of electromagnetic polarization is considered in this paper. It is shown that unless the non-field entropy, and not the total entropy, is used as the independent variable in the expression for the internal energy, the first law is violated and the meaning of heat flow, as given by the second law, is contradicted. The total entropy and its field and non-field components are shown to be state functions. The field entropy comprises contributions from the field generated by the contents of the system and stored within as well as outside its boundaries. The contribution of the field stored outside the system boundaries is derived and demonstrated for the case of a uniformly polarized sphere. Finally, expressions are derived for field entropies and entropy densities, in composite systems, using the concept of interaction entropy. The results are shown to be fundamentally different compared to those used in the current literature.

Determination of the quench velocity and rewetting temperature of hot surfaces: Formulation of a nonisothermal microscale hydrodynamic model.

A nonisothermal microscale model of the three-phase, solid-liquid-gas, contact zone is formulated in the context of rewetting phenomena. The model incorporates hydrodynamics, heat transfer, interfacial phenomena, and intermolecular long range forces, in a two-dimensional proximal region of the order of 1000 A in width and 100 A in thickness. The model comprises scaled mass, momentum, and energy balances, and their corresponding scaled boundary conditions. The small contact angles which are characteristic of rewetting situations facilitate the use of the lubrication approximation, and the dynamics of the liquid and gas phases is decoupled by applying the one-sided simplification. The microscale hydrodynamic model reflects the strong effect of the solid-liquid interactions on the film profile, and the attendant flow and thermal fields. Thinner films having smaller contact angles involve stronger solid-liquid attraction forces, and consequently they exhibit higher rewetting temperatures and lower evaporation and vapor recoil effects. Thermocapillary and evaporation and conduction effects are expressed by appropriate dimensionless numbers. A set of such numbers is defined in the context of the differential equations of the microscale model. This model covers the hydrodynamic aspect of rewetting phenomena, which are also controlled by thermodynamic and macroscale constraints. This calls for interfacing and appropriate combination between the microscale hydrodynamic model, thermodynamics, and other macroscale rewetting models, for the determination of rewetting temperatures and quench velocities of liquids on hot solid surfaces. This is addressed elsewhere, in subsequent papers that follow this work.