161 research outputs found
A New Approach in the Design of Air Stripping Columns for the Treatment of Groundwater Contaminated With Volatile Organic Compounds
Volatile organic compounds are a common source of groundwater contamination that can be easily removed by air stripping in columns with random packing and using a counter-current flow between the phases. This work proposes a new methodology for column design for any type of packing and contaminant which avoids the necessity of an arbitrary chosen diameter. It also avoids the employment of the usual graphical Eckert correlations for pressure drop. The hydraulic features are previously chosen as a project criterion. The design procedure was translated into a convenient algorithm in C++ language.
A column was built in order to test the design, the theoretical steady-state and dynamic behaviour. The experiments were conducted using a solution of chloroform in distilled water. The results allowed for a correction in the theoretical global mass transfer coefficient previously estimated by the Onda correlations, which depend on several parameters that are not easy to control in experiments.
For best describe the column behaviour in stationary and dynamic conditions, an original mathematical model was developed. It consists in a system of two partial non linear differential equations (distributed parameters). Nevertheless, when flows are steady, the system became linear, although there is not an evident solution in analytical terms. In steady state the resulting ODE can be solved by analytical methods, and in dynamic state the discretization of the PDE by finite differences allows for the overcoming of this difficulty.
To estimate the contaminant concentrations in both phases in the column, a numerical algorithm was used. The high number of resulting algebraic equations and the impossibility of generating a recursive procedure did not allow the construction of a generalized programme. But an iterative procedure developed in an electronic worksheet allowed for the simulation. The solution is stable only for similar discretizations values. If different values for time/space discretization parameters are used, the solution easily becomes unstable.
The system dynamic behaviour was simulated for the common liquid phase perturbations: step, impulse, rectangular pulse and sinusoidal.
The final results do not configure strange or non-predictable behaviours
Some reflections on acquisition, processing and analysis of statistical data in forest soils
Beyond the classical statistical approaches (determination of basic statistics, regression
analysis, ANOVA, etc.) a new set of applications of different statistical techniques has
increasingly gained relevance in the analysis, processing and interpretation of data
concerning the characteristics of forest soils. This is possible to be seen in some of the
recent publications in the context of Multivariate Statistics. These new methods require
additional care that is not always included or refered in some approaches. In the particular
case of geostatistical data applications it is necessary, besides to geo-reference all the data
acquisition, to collect the samples in regular grids and in sufficient quantity so that the
variograms can reflect the spatial distribution of soil properties in a representative
manner. In the case of the great majority of Multivariate Statistics techniques (Principal
Component Analysis, Correspondence Analysis, Cluster Analysis, etc.) despite the fact
they do not require in most cases the assumption of normal distribution, they however
need a proper and rigorous strategy for its utilization. In this work, some reflections about
these methodologies and, in particular, about the main constraints that often occur during
the information collecting process and about the various linking possibilities of these
different techniques will be presented. At the end, illustrations of some particular cases of
the applications of these statistical methods will also be presented
Nanoparticles based Permeable Reactive Barriers as an Eco-efficient Technology for nitrate remediation in soil and groundwater
The need to increase agricultural yield led, among others, to an increase in the consumption of nitrogen based fertilizers. As a consequence, there are excessive concentrations of nitrates, the most abundant of the reactive nitrogen (Nr) species, in several areas of the world.
The demographic changes and projected population growth for the next decades, and the economic shifts which are already shaping the near future are powerful drivers for a further intensification in the use of fertilizers, with a predicted increase of the nitrogen loads in soils. Nitrate easily diffuses in the subsurface environments, portraying high mobility in soils. Moreover, the presence of high nitrate loads in water has the potential to cause an array of health dysfunctions, such as methemoglobinemia and several cancers. Permeable Reactive Barriers (PRB) placed strategically relatively to the nitrate source constitute an effective technology to tackle nitrate pollution. Ergo, PRB avoid various adverse impacts resulting from the displacement of reactive nitrogen downstream along water bodies. A four stages literature review was carried out in 34 databases. Initially, a set of pertinent key words were identified to perform the initial databases searches. Then, the synonyms of those initial key words were used to carry out a second set of databases searches. The third stage comprised the identification of other additional relevant terms from the research papers identified in the previous two stages. Again, databases searches were performed with this third set of key words. The final step consisted of the identification of relevant papers from the bibliography of the relevant papers identified in the previous three stages of the literature review process. The set of papers identified as relevant for in-depth analysis were assessed considering a set of relevant characterization variables
Permeable Reactive Barriers using nanoparticles to remediate nitrate pollution
Nitrat e (NO3
-
) i s per vasi ve i n t he bi ospher e[ 1, 2]. Cont emporar y agri cult ural pr acti ces are
a mong t he maj or ant hr opogeni c sources of r eacti ve nitrogen speci es, wher e nitrat ei s t he most abundant of
t hese [ 2]. Excessi ve a mount s of r eacti ve nitrogen i n soil s and gr oundwat er ar e creati ng si gnifi cant t hr eat s t o
hu man healt h and saf et y [ 3] as well as a host of undesirabl e environment al i mpact s [ 2]; it i s curr ently
consi der ed t he second most r el evant environment al i ssue, aft er car bon di oxide e mi ssi ons. Nowadays,
a mong t he most r el evant and pr omi si ng appr oaches t o r educe nitrat e concentrati on i n wat er, na mel y
gr oundwat er, ar e denitrifi cati on- based pr ocesses [ 4]. Per meabl e r eacti ve barri ers ( PRB) have been pr oven
eff ecti ve i n r educi ng vari ous cont ami nant s i n copi ous a mount s, parti cul arl y i n shall ow gr oundwat er [ 5].
However t he possi bl e added eff ecti veness of usi ng nanoparti cl es i n t hese structur es t o obt ai n nitrogen gas
from nitrat es requires f urt her i nvesti gati on
Spectral solution for the air stripping pollutants removal dynamic model with non linear steady state conditions
This work deals with the numerical simulation of air stripping process
for the pre-treatment of groundwater used in human consumption. The model established
in steady state presents an exponential solution that is used, together with
the Tau Method, to get a spectral approach of the solution of the system of partial
differential equations associated to the model in transient state
Nanoparticles for the remediation of agrogenic contaminated soil and groundwater – a review
The wide spread use and strong reliance on both
fertilizers and pesticides made of agrigenic pollution one
of the major contemporary threats to environment and
human health. Impacts on the environment vary from
local effects, such as eutrophycation1, 2, loss of
biodiversity and diminished ecosystem health3, to global
effects, such as the aggravation of global warming2, 4 and
ozone layer depletion5. The novelty of nanoremediation
and its early successes, reported for various contexts,
present the prospect for the development of relevant
applications for agrigenic contaminants
Occupational risk in a glass manufacturing industry unit
Risk assessment is one of the main pillars of the framework directive
and other directives in respect of health and safety. It is also the basis
of an effective management of safety and health as it is essential to
reduce work-related accidents and occupational diseases. To survey
the hazards eventually present in the workplaces the usual
procedures are i) gathering information about tasks/activities,
employees, equipment, legislation and standards; ii) observation of
the tasks and; iii) quantification of respective risks through the most
adequate risk assessment among the methodologies available. From
this preliminary evaluation of a welding plant and, from the different
measurable parameters, noise was considered the most critical.
This paper focus not only the usual way of risk assessment for noise
but also another approach that may allow us to identify the technique
with which a weld is being performed
Avaliação do impacto do fogo controlado na vulnerabilidade dos solos florestais – uma contribuição
A floresta portuguesa constitui
um dos pilares do desenvolvimento
económico e social
do PaÃs e enfrenta dificuldades
de gestão face à incerteza associada
à sanidade florestal, Ã
economia do futuro e ao clima.
A sustentabilidade dos recursos
florestais requer, entre outras
acções, medidas de preservação
dos georecursos e de garantia
da diversidade biológica e da
fruição estética das florestas. Na
floresta, o fogo é um fenómeno
ecológico natural. Contudo, a
maioria dos incêndios florestais
que ocorrem anualmente em
Portugal possuem uma natureza
antropogénica inequÃvoca, não
só pela origem das ignições mas
também pela natureza do coberto
vegetal, fortemente determinado
pela intervenção humana.
As consequências ambientais
que se verificam após a ocorrência
de um incêndio são indesejáveis
reflectem-se em prejuÃzos
nos solos até então protegidos
pelo coberto florestal
Space-time monitoring of prescribed burnt soils performance – an effective tool for forest management
Among the most important measures to prevent wild forest fires is the use of prescribed and controlled
burning actions in order to reduce the availability of fuel mass. However, the impact of these activities on
soil physical and chemical properties varies according to the type of both soil and vegetation and is not fully
understood. Therefore, soil monitoring campaigns are often used to measure these impacts. In this paper we
have successfully used three statistical data treatments - the Kolmogorov-Smirnov test followed by the
ANOVA and the Kruskall-Wallis tests – to investigate the variability among the soil pH, soil moisture, soil
organic matter and soil iron variables for different monitoring times and sampling procedures
MIARforest Reproducibility and Reliability for Assessing Occupational Risks in the Rainforest
The Method for the Integrated Assessment of Risks for rainforest (MIARforest) is a specific
methodology for assessing the risk of occupational accidents associated with working in native tropical
forests. MIARforest was validated for the results’ reproducibility and the reliability of calculated
risk levels through the Delphi approach. Two rounds of questionnaires illustrating ten scenarios
of activities associated with the logging process in the Eastern Amazon’s native rainforest (Brazil)
were presented to forestry and occupational health and safety (OHS) experts. In the first round, the
questionnaire was answered anonymously by 55 experts, and in the second, by 46. A percentage of
agreement of at least 80% in each question was considered to close the process. Questions that did not
meet the criterion in the first round were reassessed in the second round. The obtained results lead to
the conclusion that MIARforest, an occupational accident risk assessment tool, has been effectively
validated, demonstrating inter-rater reproducibility and reliability in determining risk values. These
results highlight the objectivity and reliability of MIARforest.info:eu-repo/semantics/publishedVersio
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