SCIENCE OF THE TOTAL ENVIRONMENT

SCIENCE OF THE TOTAL ENVIRONMENT

ABSTRACT

In different regions around the globe water scarcity is becoming worse due to the increased water demand and the decreasing level of water supply. Typically, it is to our expectation that the unconventional water resources like the desalinated water bridge the gap between the demand and supply of water. However, the approaches which directly depend on rainfall and river runoff in regions with limited water, cannot reach the level of demand by humans. The data containing the synthesis of desalinization indicates that the operational plants for desalination are about 15,906, which yield desalinated water for human consumption amounting to approximately 95 million m3 per day.

A crucial limitation hindering desalination process is the formation of brine which is a hypersaline concentrate which needs to be disposed of. Disposal of this product is a bit expensive and causes environmental pollution. On approximation, 142 million m3of brine is produced each day.

The adverse effects of brine on the environment requires that advanced strategic management aspects of controlling the environmental impacts of brine and the disposal cost, be implemented. This will enhance development in the process 0f desalination thereby maintaining a constant supply of water for present and the coming generation.

INTRODUCTION

            According to Djuma et al. (2016) “The increasing demand for water-related to population growth, high rate of water consumption per capita and economic growth, followed by ceasing water supplies due to climatic fluctuations and contamination are exacerbating water scarcity in most regions around the globe” (pp.2298). The current approximations indicate that about 40% of the global population experience intensified scarcity of water, the rate is forecasted to rise to 60% coming the year 2025.

Research by Mekonnen and Hoekstra (2016) suggest that 66% of the total population around the globe stays in a state of intensified water scarcity of about one month per year. From the above statistical analysis, it is evident that the conventional water sources like rainfall, snowmelt and river runoff which are collected in lakes, rivers, and aquifers are currently insufficient to continuously supply water in the areas with a high scarcity of water. This is a factor which is in contrary to the Sustainable Development Goal (SDG) 6, which is focused on maintaining the availability of clean water for consumption.

 

2          Methodology

2.1The global status of desalination: research and practice

2.1.1 Desalination in research

            For evaluation of the vital research trends in the area of desalination, a technique known as the bibliometric analysis was implemented. Here desalination publication is categorized by major research themes which are; technology, environment, economic and energy, and social interest. Under the technology category, we have the Reverse osmosis, Multi-Effect Distillation’, ‘Multi-Stage Flash,’ ‘Electrodialysis,’ ‘Emerging’ and ‘Other.’

  2.1.2 Desalination in practice.

 

The database which contains information on plant status was obtained from the Global Water Intelligence (GWI). The report included the plant status, operational year, plant capacity geographic location, customer type, and feed water type of each desalination plant. The geographic area was plotted on an ArcGIS using latitude and longitude data. The data entered in excel using the pivot tables to facilitate statistics of multiple desalination plants in each region and nationally. The analysis for each category was as follows;

Plants status were classified as either; Online, Presumed Online, Construction, Presumed offline, and Offline.  Also, eight geographic regions were analyzed; East Asia & Pacific, Eastern Europe & Central Asia,  Latin  America & Caribbean, Middle East & North America, Southern Asia, Sub-Saharan Africa, Western Europe.   Each desalination plant to were was assigned four economic levels using the data from each country, this was done based on the 2018 World Bank Income groups in which the GNI per capita $ is approximated by the World Bank Atlas method. The following economic classification; High income, (>$12,055 GNI per capita), Upper middle Income ($ 3896 to $12,055), Lower middle income ($966 to $ 3895), and the low income (<$995).

The customer type for each desalination plant was divided into six categories Municipal Including tourist drinking water facilities, Industry, power station, Irrigation, Military, and uses of demonstration and water injection.

Feed water type is divided into six distinction in Desadelta (2018) illustrated in ppm Total Dissolved Solids (TDS): Seawater (SW) [20,000-50,000 ppm TDS], Brackish Water (BW) [3000-20,000 ppm TDS], River Water (RW) [500-3000 ppm TDS], pure water (PW)  [<500 ppm TDS], Brine (BR) [>50,000 ppm TDS] and Wastewater(WW). RW is applied in drinking water and irrigation to minimize the salinity in water. PW as a feed water source is basically used for the industrial appliance which needs very high-quality water such as the pharmaceutical and industries of food production

Desalination technology was divided into seven categories; Reverse Osmosis, (RO), Multi-Stage Flash (MSF), Mult-Effect Distillation (MED), Nanofiltration (NF), Electrodialysis Reversal (ED), Electrodeionization (EDI), and others such as the Forward Osmosis (FO), Hybrid (HYB), Membrane distillation (MD), Vapour compression (VP), and Unknown.

2.2 Brine production

The volume of brine which was obtained was evaluated per individual desalination plant by use of three determinants found inDesalData 2018 which are feedwater type, desalination technology and capacity of treatment in an m3per day. Typically we adopt the recovery ration to calculate the brine production and plant capacity using the following Eq:

Qb= Qd/RR*(1-RR)

Qb = Volume of brine produced (m3/day)

Qd= Desalination plant treatment capacity (m3/day)

RR= recovery ratio

A total of 41 different feed water type and desalination technology combination are today in operation. The recovery ratio was found using two techniques which are; literature study and influent and effluent salinity data from single desalination plants which operate using membrane technologies was applied to make estimation recovery ratios through the following Eqs.

Sb= Sf/1-RR

RR=1-(Sf/Sb)

Sb=brine salinity

Sf=feed water salinity expressed in the same units, i.e. mS/cm for EC, mg/1 for TDS.

Fourteen additional units of recovery ratios were obtained through this method, which was put together with the ratios obtained from the literature method to give 119 records.  From this average, the recovery ratio could be provided by 18 of the 41 technology feed water. To obtain recovery ratio for the remaining feed water-technology combinations, several assumptionswere derived as shown in the following table

 

The distance of each desalination plant from the nearestcoastline was determined through the latitudes and longitudes, this was archived through the spatial analyst tool in ArcGIS.

  1. Results

3.1 Research trends in desalination.

The following figure provides trends in the research history of desalination.

Research in the desalination has tremendously grown, as the number of publications doubles in every five years. A good exampleis that in 2010 it was ¬5000 coming 2015 it rose to ¬11000. However the many majorities of publications focuses on technological aspects of desalination, in 2015 it was about 75%. The overall trend in desalination research has been amplified by desalination literature majoring on the technological aspects.

Apparently, putting economic trends into consideration publication number has drastically increased from <400 (2000) to >5000 (2018). Before the year 2000, there wassevere negligence’s on matters concerning the environmental effects of desalination the free number during this time was around 118.  Currently  a constant increase in the number of literature published in this category, but on the other hand, the number of publications focusing on the political aspects of desalination is at lower level. According to March et al, (2014) ‘’Desalination is not typically associated with social opposition and conflict associated with other water supply scheme like river regulation and water transfers’’ (pp.2648). It is globally expected that the number of all publications in all the categories will spontaneously arise.

 

Figure 1Number of desalination publications by categorisation (total, technical, social, environment, energy & economic).

 

As we can see from figure one, it is evident that the publications addressing the technological aspects have embodied the research history of desalination. This trend is further explored in figure 2, through distinguishing each technical publication of specific technology. The technology aspect which IS mostly researched throughout the entire time period is the RO, it is identified to have its number of publication doubling after every five years.

Figure 2Number of publications by type of desalination technology (Reverse Osmosis [RO], Multi-Effect Distillation [MED], Multi-Stage Flash [MSF], Electrodialysis [ED]), emerging technologies (Nanofiltration [NF], Forward Osmosis [FO] and Membrane Distillation [MD]) and other (Humidification-Dehumidification [HDH], Solar Stills [SS] and Vapour Compression [VC]).

 

 

 

3.2 Global State of desalination

            Currently, about 15,906 operational desalination plants are having a total of 95.37 million m3 / day desalination capacity.  This constitutes about 81% of the total number and 93% capacity of desalination plants ever constructed. This illustrated in figure 3a.  Early desalination like in the year the 1980s 84% of the all the desalinate water around the globe was being produced by two thermal technologies which were MSF & MED. Coming to 2000 the capacity of desalinated water was amounting 11.6 million m3 / day dominated by MSF technology and 11.4 million m3/day dominated by the RO technology, this summed a total of 93% of the resulting amount of the desalinated amount of water produced. This is illustrated in figure 3b.

Ever since the year 2000 the number and volume of the RO produce have drastically increased at a greater height, whereas thermal technology has undergone a marginal increase. See figure 3b.

The produce from reverse osmosis is still at 65.5 million m3 per day this represents about 69% of the total volume of the output.

 

Figure 3. Trends in global desalination by (a) number and capacity of total and operational desalination facilities and (b) functional capacity by desalination technology.

 

Figure 4 illustrates the spatial distribution, size and customer type of the desalination facilities (>1000 m3 per day). Globally the desalination plants are much concentrated along the coastline. But the plants producing municipal water are located almost everywhere around the globe. But East and North Africa are the major dominants.

The figure indicates that the United States, China and Australia and some regions around Europe and the Middle Eastpossess a more significant number of desalination facilities, while South America and Africa, have a small number of desalination facilities. The facilities are majorly assigned to give water to the industrial sector. About half of the global desalination capacity is found in the MiddleEast and North Africa region. The volume and number of desalination plants as represented by geographic region, country income level and sectoral appliance of desalinated water is illustrated in Table 2;

 

 

 

 

 

 

 

Regions

 

Number of Plants

 

Desalination Capacity

 

 

(million m3/day) (%)
           Geographic

 

The Middle East and North Africa
East Asia and Pacific
North America

 

Western Europe

Latin America and the Caribbean
Southern Asia
Eastern Europe and Central Asia
Sub-Saharan Africa

Income level

High
Upper middle
Lower middle
Low

Sector use

Municipal
Industry
Power
Irrigation
Military
Other
         1590

 

4826
3505
2341

 

2337

1373
655
566
303
 

10,684

3075
2056
53
 

6055

7757
1096
395
412
191
        953

 

45.32
17.52
11.34

 

8.75

5.46
2.94
2.26
1.78
 

67.24

19.16
8.88
0.04
 

59.39

28.80
4.56
1.69
0.59
0.90
100

 

47.5
18.4
11.9

 

9.2

5.7
3.1
2.4
1.9
 

70.5

20.1
9.3
0.0
 

62.3

30.2
4.8
1.8
0.6
0.4
 

Table 2

Number, capacity and global share of operational desalination plants by region, country income level and sector use.

 

 

3        Brine production

According to (Xu et al., 2013) When quantifying brine production the type of desalination technology and the quality of feedwater used must be put into consideration. The following tabulation represents the water recovery ratios associated with the significant feed water-technology combinations in operation.

   

 

R

 

 

MS

 

 

MF

 

 

N

 

 

F

 

 

ED

 

 

ED

 

 

Other

Seawater(SW) 0.42 0.22 0.25 0.69 0.86 0.90   0.40
Brackish(BW) 0.65 0.33 0.34 0.83 0.90 0.97 0.90 0.60
River (RW) 0.81   0.35 0.86 0.90 0.97 0.96 0.60
Pure (PW) 0.86 0.35   0.89 0.90 0.97 0096 0.60
Brine (BR) 0.19 0.09 0.12   0.85     0.40
Wastewater (WW) 0.65 0.33 0.34 0.83 0.90 0.97   0.40

Table 3

Recovery ratio of different feedwater-technology combinations producing desalinated water

Table 4 The current global brine production is at 141.5 million m3/day this is a total of 51.7 billion m3/year. This value is estimated as being 50% more than the total capacity of desalinated water produced around the world. The value is also estimated as being double the volume of desalinated water being produced. This illustrates that the desalination plants in these regions operate at a meager water recovery ratio of 0.25. High level of brine production is around the areas of the Middle East and North Africa.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Brine Production    
(million m3/day) (%)  

 

Global

Geographic region

 

 

141.5   100
The Middle East & North Africa  

 

99.4   70.3
East Asia & Pacific   14.9   10.5
North America   5.6   3.9
Western Europe   8.4   5.9
Latin America & Caribbean  

 

5.6   3.9
Southern Asia   3.7   2.6
Eastern Europe & Central Asia  

 

2.5   1.8
Sub-Saharan Africa

Income level

 

 

1.5   1.0
High   110.2   77.9
Upper middle   20.7   14.6
Lower middle   10.5   7.4
Low

Sector use

 

 

0.03   0.0
Municipal   106.5   75.2
Industry   27.4   19.3
Power stations   5.8   4.1
Irrigation   1.1   0.8
Military   0.5   0.3
Other   0.3   0.2
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4        Discussion

The above study majorly focused on statistical analysis of the scientific literature demonstrating an array of desalination topics from the year 1980, emphasizing on the diverse range of social an technical aspects, putting into consideration the publication date, revealing patterns in publishing trends. The findings imply that research in desalination has shown a severe increase for the last 40 years. According to (Arnal et al., 2005) ‘’The research has typically emphasized on the technological aspects of desalination, having a vast number of publications pointing to the RO and Novel methodologies that can produce desalinated water at a relatively economical cost and with less negative environmental implications.”

Publications emphasizing on economic, environmental and socio-political aspects of desalination are increasing as the desalination process expands globally.Our findings also indicate that the volume of brine produced far exceeds the capacity of desalinated water produced (by ~50%), and hence that the current quantifications of the amount of brine produced are gross underestimations

 

 

5        Conclusions & outlook

Today, desalinated water is becoming a more viable option to bridge the gap between water demand-supply. Majorly in focusing on domestic and municipal needs. Typically desalinated water can significantly increase the volume of high-quality water supplies available for human consumption. However, due to its high economic cost, the process is concentrated in developed countries only. Due to this, there is a need to make desalination technology more affordable,to expand on its concentration globally.

 

Reference

Djuma, H., Bruggeman, A., Eliades, M., Lange, M.A., 2016. Non-conventional water resources

research in semi-arid countries of the Middle East. Desalin. Water Treat. 57

(5), 2290–2303.

Xu, P., Cath, T.Y., Robertson, A.P., Reinhard, M., Leckie, J.O., Drewes, J.E., 2013. A critical review of desalination concentrate management, treatment, and beneficial use. Environ. Eng. Sci. 30 (8), 502514.

 

Arnal, J.M., Sancho, M., Iborra, I., Gozálvez, J.M., Santafé, A., Lora, J., 2005. Concentration of brines from RO desalination plants by natural evaporation. Desalination 182 (13), 435439.

 

March, H., Saurí, D., Rico-Amorós, A.M., 2014. The end of scarcity? Water desalination as the new cornucopia for Mediterranean Spain. J. Hydrol. 519, 26422651

 

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