The samples of the detection node are known. If the distribution is normal, get the value range of the significance level according to 13 , choose an any significance level in the range, calculate the test statistic as 9 , and go to Step 3.
When the test statistic satisfies the test criterion 10 , the node detects the pollution; otherwise, the node fails to detect the pollution. Calculate which is the sum of ranks of Samples 3 in Table 2. When the sum satisfies the test criterion 7 , the node detects the pollution; otherwise, the node fails to detect the pollution.
Experiment 1. A simulation is carried out to test the proposed detection algorithms. The distribution of monitoring noises is normal. Starting from time h, the solution with pollutant is injected into the water. The mass of the pollutant is kg. The nodes in the network sample the concentration uniformly with interval h.
The diffusion can be depicted by the model: where is the current time. The locations of the monitoring nodes are 2. The monitoring values in the experiment are the simulation values of 14 adding the noise with a normal distribution. The given parameters are and , and there are 10 nodes,.
A The Pollution Detection of the Network. According to constraint 13 and the sample size table of test in [ 18 ], it is can be deduced that under the given parameters , , and in Table 3. For different values and significance levels, detect the pollution at the initial observation time 0. B The Pollution Detection of the Node. Detect whether the node has detected the pollution source based on the observed data of the node 1. The monitoring data is as shown in Table 4. Compare with the simple detection method in which the criterion of whether the pollution source has been detected is that the monitoring value is larger than a given threshold, and the results are shown in Table 5.
Comparing the results in the table, it can be seen that the detection method using hypothesis testing is more stable if an appropriate significance level is chosen, and in the simple detection, to detect the pollution source timely the threshold should be as small as possible. But apparently, if the noise in the practical applications is considered, small thresholds may bring about large false alarm rates. Experiment 2. A practical experiment is carried out to test the proposed detection algorithms.
There is a continuous source at the boundary. Starting from s, the solution of MgSO4 is discharged to the water continually. The nodes deployment is depicted by Figure 2. The monitoring values of different sensor nodes in the experiment are shown in Table 6. Distribution Verification. So, the detection methods based on the Wilcoxon rank sum tests are used. The significance level is , and the time when nodes 0, 1, 2, 3, 4, 5, 6, and 7 find the pollution is shown in Table 7.
The detection method is as The results show that the pollution can be detected by the nodes only when there are some increasing concentration samples. From the results of the experiments above, it can been seen that, in the simple detection method, an appropriate decision threshold is hard to be given, so the pollution source detection by using hypothesis testing is more preferable. Whether the distribution of the sample noise is normal or not, the corresponding detection algorithms are available.
Water pollution detection is important in the water environment monitoring. The pollution source detection problems of the network and of the node are discussed based on hypothesis testing. The sample size requirements in different detection problems are also analyzed. In implementation examples, the proposed pollution detection algorithms are tested.
The effectiveness of the detection algorithms is proved. This work mainly focuses on theoretical detection approaches based on hypothesis testing. In the future work, more problems in the practical applications will be studied when the proposed detection algorithms are adopted, such as the optimized detection methods of the node related to large or small concentration variations, and the influences of the concentration variations on the statistical distribution in the distribution test step.
The founding sponsors had no role in the design of the study; the collection, analyses, or interpretation of data; the writing of the manuscript; and the decision to publish the results. The authors declare that there is no conflict of interests regarding the publication of this article. The authors would like to thank Dr. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Journal overview. Special Issues. Academic Editor: Andrea Cusano. Received 17 Oct Revised 10 Dec Accepted 15 Dec Published 16 Jan Abstract Water pollution detection is of great importance in water conservation. Problem Statement 2. Network Deployment The self-organizing sensor network is used in the water pollution monitoring.
Figure 1. Sample 1 Sample 2. Table 1. The two groups of independent samples in the detection of the network. Table 2. The two groups of independent samples in the detection of the node. Significance levels Detection results 0. Table 3. Table 4. The monitoring values of node 1. Table 5. The detection results comparing with the simple detection method. Table 6. The monitoring values in Experiment 2. Figure 2. The nodes deployment in Experiment 2.
Table 7. The new method also measures the amount and proportion of nitrate stable isotopes in water. Nitrogen has two stable isotopes with different weights, according to Environmental Protection Online. The weight difference is not the same in human waste or fertilizers. For example, isotopes can be used to identify the source. The new technique allows scientists to run more samples and much more cheaply for large-scale studies. I think it is a game changer," Wassenaar said to Environmental Protection Online.
Do you know a rising star or industry icon? Cr VI is considered as lethal for human being at a dose higher than 3 g same as an example of Cr, other metals Cu, Cd, and Pb also cause high degree of pollution based on their toxicity and their ability to generate different compounds in water. Thus, it can be noted from this discussion that heavy metal pollution of soil and water can be treated using plant species.
The drastic permanent solution can be obtained if we choose the right plant species to be used after knowing the actual causes of water and soil pollution. Government personnel, scientists, and the public are concerned about the ever growing ecological threats that include global warming, the diminishing natural resources that promoted intensive research for the development of new techniques for removing heavy metals from the polluted sites, such as using plant species, improving existing and new decontamination procedures [ 13 , 68 , 69 ].
The problem is also amplified in advanced as well as developing countries, as a result of the ever increasing industrialization and auricular development releasing high amount of toxic materials if their drainage water into the existing natural ecosystems [ 56 , 68 , 70 , 71 ].
All these consequences have promoted the use of phytoremediation for the removal of toxic pollutants, because aquatic plants grow and flourish naturally in drainage canals [ 2 ]. Phytoremediation, using aquatic plants such as Reed plants, provides a chance for its use as a feasible non-destructive technology to eliminate pollutants from soils or water ecosystems. This was assured by the work of many scientists who analyzed aquatic plant tissues for their mineral contents [ 55 , 72 , 73 ].
Reed Phragmites australis PA plant is a perennial aquatic plant species that has given wide attentiveness for treating heavy metal polluted soils and water sites due to the fact that it can tolerate the adverse effects of high levels of toxic metals, without affecting its growth and high yield rates, PA can naturally grow well in natural or artificial sites polluted with Zn, Ni, Pb, As, and Cd [ 3 , 74 ]. It is recorded growing naturally in low-level coastal plains or river-flooded areas in North America, Europe, Middle East, Africa, and Australia.
The reed plants can grow to a stem length of more than cm and is characterized by its efficiency to move O 2 from its shoot zone to its root system. The root system can develop and extend even in water-logged environments [ 65 , 66 ]. Kilkuth in Germany used Reed beds for drainage water treatment in s and in England in [ 75 ].
In recent years, different procedures were developed to eliminate metal pollutants from drainage and drinking water [ 12 ]. These procedures are discussed as follows.
It is considered as one of the widespread procedures for the removal of metal ions from water solutions [ 76 ]. The methodology involves the production of metallic hydroxides, e.
The main hindrances of this procedure are the high amounts of chemicals used, and excessive wastes that are produced which need to be eventually treated. In addition, cumbersome metal deposition, fiddling sediment of hydroxides, assemblage of metal depositions, and long-term effects of the disposal of wastewater also need to be taken care of [ 77 , 78 ].
Coagulation and flocculation happen in successive operations in order to upset the stability of the unsettled particles, to permit particle impact and to regulate the growth of aggregates. Both operations must be achieved to accomplish the elimination of pollutants [ 79 ]. Coagulation, fore mostly, takes place to upset the stability of the particles leading to their precipitation.
Flocculation increases the size of the particles through the aggregation of unsettled particles. This is mainly accomplished by pH modification and addition of ferric or aluminum compounds to control the dissonance within the colloidal particles. The use of lime, as coagulating agent, improves the settlement of the sludge, reduces watering, and makes it capable for controlling bacterial activities. The main drawback of the use of lime is the high costs [ 78 ]. This methodology is effective for liquids as it uses bleb connection to split up solids.
There are five kinds of flotation, i. The most widely used one for metal removal from drainage water is dissolved-air flotation [ 79 ]. Aeration is needed when the water has oxygen shortage condition due to municipal, agricultural, and industrial drainage water discharge. Aeration is conducted by introducing air at the bottom of the water reservoir or by surface stirring generating a basal device that allow air and water mixing which would help in releasing and removing of harmful gasses, e.
It can be utilized to handle both drainage and drinking waters. It can be classified into surface, sub-surface, and natural aeration [ 79 ]. This technique is beneficial because no chemicals were used, and has a comparatively minimal energy use and it can easy be conducted in gradual stages. This process can be used to remove dissolved pollutants, e. There are different sorts of filtration mechanisms that can be used, based on the targeted particle size that is required to be removed. Ultrafiltration uses permeable membranes with pores ranging between 5 and 20 nm depending on the material to be extracted.
Nanofiltration technique depends on the steric effect as well as the electrical effect. In reverse osmosis, the exerted pressure forces keep the trace elements and clean water can be collected from the second direction of the membrane. The exchange of ions of the same charge between an insoluble solid and a solution in contact with it used in water-softening and other purification and separation processes.
Thus, metals can be extracted from solution with the help of suitable reagents [ 13 ]. This procedure is effective when pH of the solution polluted water source ranges from 2 to 6 and demands the removal of the suspended solids by other methods prior to the implementation of the ion exchange method [ 79 ]. This procedure performs metal extraction using the combination of membrane and ion exchange mechanisms.
The main methodology is accomplished by passing polluted water through an ion exchange membrane. This membrane consists of thin plastic materials that have either cationic or anionic electric charge. This methodology is efficient, although it is expensive as far as chemicals, sludge handling costs, and its high-energy use [ 13 ]. The utilization of non-living microbial tissues for retaining heavy metals, which is not a metabolic activity, is defined as biosorption [ 80 ].
The microbial cells are good biosorbents because they have a high surface area, and thus have high number of biosorption sites. Industrial activities, such as electroplating and mining, produce high amounts of biomass that could be used in the removal of heavy metal pollutants [ 25 ]. Biomass can be also been grown using fermentation techniques and inexpensive growth media.
Dead cell biomass can be more beneficial as compared to live cell biomass, as systems utilizing living cells can be affected by metal ion concentrations, temperature, pH, and constant requirement of nutrient supply for living cells [ 13 , 81 ].
The industrial waste when fermented can be processed into biomass. Microbial cells in the biomass can be removed by many methods such as heat treatment, autoclaving, and vacuum drying, using acids, alkalis, detergents, organic compounds, and mechanical disruption. The effective amount of absorbing material to be used can be estimated by comparing its strength to remove the sorbent material from polluted water with other substances reported in other studies.
The amount is defined in terms of the amount of heavy metal extracted milligrams per amount of sorbent used gram. The biosorption methodology is affected by pH, temperature as well as the ion concentration in the solution [ 80 ]. Phytoremediation is a technique that uses plant species and associated-soil micro-organisms to extract metals present in the ecosystem, i. Phytoremediation is now utilized for treating pollutants, e.
All other traditional methods for the removal of heavy metal pollutants from the natural ecosystems are costly and use large quantities of chemicals and create waste treatment problems, even if these procedures are advantageous for their rapid extraction of pollutants in small sites [ 17 ].
Phytoremediation surpassed the traditional procedures because it helped in maintenance of biological activity, site restoration, and partial decontamination as well as it is unobtrusive, has a possibility of bio-recovery of metals and not costly [ 47 , 84 ]. Phytoremediation has been classified into five divisions: Phytoextraction: plants uptake metals and accumulate them in the usable tissues [ 85 ];. Phytodegradation: plant species and associated micro-organisms break down organic pollutants [ 86 , 87 ];.
Phytostabilisation: plant species reduce pollutants bioavailability in the natural ecosystems by fixation or by prohibition of their migration [ 88 ] and,. Phytovolatilization: volatilization of pollutants into the atmosphere through plants [ 86 , 89 ].
The next section explains a detailed review of this emerging green technology. Phytovolatilization: the evaporation of pollutants into the air via plants [ 86 , 89 ]. The advances in the fields of research and technology have promoted the growth of different industries resulting in matchless unrests in the ecological cycles [ 78 ]. The recent admission of toxic chemicals and resettlement of natural substances into different ecosystems soils, water, and air have given rise to major demands of self-purifying capacity of the natural ecosystems [ 90 , 91 ].
The present off-site procedures for treating polluted water resources include extracting and treating of pollutants using adsorption capacity of activated carbon, micro-organism or air denudation; while on-site procedures for treating polluted water resources include stimulation of aquifers aerobic and anaerobic micro-organisms activities.
All predominant procedures are expensive and require high technical human resources to execute. Thus, stakeholders are looking forward for the development of cheaper and speedy techniques for treating highly contaminated water resources, wetlands, and soils [ 13 ]. This indicates that the removal of water pollutants can be performed using the cheap phytoremediation technology [ 92 ].
Many experimental studies have been conducted on the use of plant technologies in treating contaminated natural resources [ 93 — 96 ]. When the water pollutants, i. The main phytoremediation procedures can be classified as on-site, in a living organism and off-site types. On-site phytoremediation is the modest and cheaper of all three classes and the plants are growing in direct contact with pollutants. There are numerous technicalities by which plant species can rectify water and soil pollution.
During phytoremediation, the merits of the technique can be influenced by physical and chemical pollutants traits molecular weight, vapor pressure as well as their solubility in water , environmental traits organic matter in the water solution, pH as well as temperature , and plant traits root system characteristics and enzymes [ 90 ].
Many plant species have capabilities to uptake and accumulate high levels of metallic organic compounds without any toxic impacts, such as reed plants Phragmites australis , Indian mustard Brassica juncea L. These plant species have attained heavy metal tolerance characteristics that modified them to survive in highly heavy metal polluted ecosystems [ 13 , 99 ], and they show high strength to accumulate heavily metallic ions, such as nickel, zinc, copper, chromium, and even radionuclides.
The threshold for hyper-accumulation of heavy metals is known as the accumulation in plant tissues of concentrations greater than 0. Many types of plant species could be utilized in phytoremediation [ 61 ]. These plant species have specific characteristics that assist in their normal growth in polluted sites and at the same time uptake and accumulate heavy metals in their roots and shoots [ , ].
Reed PA plants are plant species that are widely dispersed and are found in wide range of habitats worldwide [ ]. PA plants are aquatic perennial grass [ ].
A number of studies have been conducted on PA plants growth and development [ ], mineral content [ ], response to heavy metals [ 49 , , — ], response to salt stress, [ , ] as well as the different reed plant subspecies phenotypic, genotypic, evasive characteristics [ 49 , 96 , ].
The results on the available research studies indicated that reed plant species significantly differ in their response to salt stress [ , , ], this could be due to genotypic differences [ , ]. This is expedited by limited intake and conveyance to the shoots of sodium, sulfur, and to some extent Chlorine, the capability of maintaining a comparatively high photosynthetic rate, the capability of promoting water use efficiency, and proline production of osmotic adjustment.
NaCl and Na 2 SO 4 influence the water and gas operations during photosynthesis. NaCl is more poisonous to plants than Na 2 SO 4 [ ].
The reed plants can tolerate high-environmental stresses due to their ecological, physiological as well as morphological characteristics and will develop normally in heavy metal Zn, Cd, and Pb polluted ecosystems [ ].
These plants possess high phytoremediation as well as detoxification traits and have been excessively utilized in the construction of artificial wetlands for the treatment of heavy metal pollution of industrial drainage water [ ]. With the recent improvements in the application of scientific knowledge of phytoremediation for practical purposes, especially in pollution eradication and the search for greener alternatives for pollution enucleation, the interest has been directed toward reed plants reactions to heavy metal environmental stresses [ , ].
0コメント