A Review of the Problem of Brine Disposal Connected With Desalination.

[NNadir]

Last edited Sun Jan 27, 2019, 04:53 PM - Edit history (1)

The scientific paper I will discuss in this post is this one: The state of desalination and brine production: A global outlook (Jones et al, Science of the Total Environment, 657 (2019) 1343–1356). It is a review article, with over 100 references to the primary scientific literature.

It is very clear to me that all efforts to address climate change have failed miserably. This failure, and indeed worldwide political and social outcomes that are actually accelerating the problem, not limited to the likes of Trump and Bolsanaro, but also including those who think that so called "renewable energy" is "green" energy and that it is a serious way to address climate change. It isn't. When one looks at the data one can see that the attempt to displace dangerous fossil fuels with so called "renewable energy" is rather the equivalent of announcing that the best way to deal with the floods associated with hurricane Katrina would have been to form a line of Louisianans stretching to New Mexico passing water filled Dixie cups to one another. The metaphor is entirely appropriate.

It's that bad.

Coupled with denial, our insistence of having faith in technologies that will not work and have experimentally demonstrated as much leaves the task of cleaning up our garbage to future generations, generations we have already robbed by the consumption (and dilution) of irreplaceable resources, thus impoverishing them.

As over my long lifetime I've grown increasingly appalled at this now inevitable environmental train wreck, and the father of two young men well along on establishing their careers, I've begun to focus my attention on the scientific investigation of technologies that may allow for the reversal of entropy associated with the accumulation of carbon dioxide in the atmosphere. With due (and great) respect to the marvelous science of people like Christopher W. Jones, (I hope to discuss the linked paper in a future post on this site), I personally believe that the key to removing carbon dioxide from the atmosphere will rely on using the oceans as an extraction device.

This technology will only be economically viable where the ocean water is also processed for other purposes, the most obvious being desalination, since an immediate effect of climate change - already being observed around the world - will be to destabilize fresh water supplies.

One should not, however, regard this technology as a "green" panacea, as people still - in spite of its obvious failure - regard so called "renewable energy" technologies like wind and solar.

The problem with desalination, as the paper referenced at the outset makes clear, is the disposal of brine.

According to the paper, there are 15,906 desalination plants operating around the world, a large fraction of them being located in the Middle East. The paper gives a nice overview of the types of technology that are employed to desalinate water, and the common abbreviations (which I will also use hereafter in this post) used to denote them:

Desalination technology was separated into seven categories: 1) Reverse Osmosis (RO); 2) Multi-Stage Flash (MSF); 3) Multi-Effect Distillation (MED); 4) Nanofiltration (NF); 5) Electrodialysis/Electrodialysis Reversal (ED); (6) Electrodeionization (EDI); and 7) Other. ‘Other’ included a variety of technologies such as 1) ForwardOsmosis (FO); 2)Hybrid (HYB); 3) Membrane distillation (MD); 4) Vapour compression (VP); and 5) Unknown. As the technologies grouped together under the ‘Other’ category contribute a total of b1% of the total desalinated water produced, these technologies were not considered individually.

All of these technologies require energy to operate.

For perspective, according to the paper these 15,906 plants produce roughly 95 million cubic meters of fresh water per day, which works out to 34.7 billion cubic meters per year. According to a public policy website in California, the State of California in a "wet" year, uses about 104 million "acre-feet" of water:



This translates to 128 billion cubic meters, meaning that all of the world's existing desalination plants produce - in the "percent talk" so loved by pixilated "renewable energy" advocates - about 27% of the water consumed in California in a flush year.


My own opinion is that from a purely environmental standpoint - albeit with several very important materials science issues being in need of consideration - those technologies that derive energy from heat, as listed above, MSF and MED, are superior, particularly if coupled with two technologies considered in the "other" category, VP and - for addressing issues with brine that the review paper discusses - FO.

It is worth noting that it seems to me at least that certain electrodialysis processes can actually recover some of the energy utilized for desalination, since an electrical current can be generated using certain kinds of membranes separating two solutions having a saline gradient, a factor that might prove worthwhile at say, oceanic outfall pipes for municipal waste water, simultaneously cleaning the water and recovering energy. I encounter papers along these lines from time to time in the journals I read, and sometimes briefly scan them; but will not discuss them further since I clearly have no serious expertise in this area.

My opinion on what might be environmentally sustainable technologies for desalination are informed by my also frequently stated opinion that nuclear energy, whether fission or in some far off future fusion, are the only sustainable technologies to address climate change, and that high temperature nuclear reactors are the best approach to the utilization of nuclear energy. High temperature reactors offer the capability of thermal desalination as a side product of isolating carbon based materials from air or seawater, a viable form of sequestration, as well as manufacturing chemical fuels where needed, thus closing the carbon cycle.

Still the paper makes clear there is a problem with brine produced by desalination, not all of which is the desalination of seawater.

The paper provides a map of desalination plants around the world, and one should immediately note that many are far from the ocean:



The caption:

Fig. 4. Global distribution of operational desalination facilities and capacities (N1000 m^3/day) by sector user of produced water.

This obviously implies that there are great differences in the types of water subject to "desalination" or in some cases, re-purification.

The authors provide a list, along with some useful brief comments, similar to that of the technologies in use for these feed water types:

Feedwater type is separated into six categories in DesalData (2018) expressed in ppm Total Dissolved Solids (TDS): 1) Seawater (SW) [20,000–50,000 ppm TDS]; 2) Brackish water (BW) [3000–20,000 ppm TDS]; 3) River water (RW) [500–3000 ppm TDS]; 4) Pure water (PW) [b500 ppm TDS]; 5) Brine (BR) [N50,000 ppm TDS]; and 6) Wastewater (WW). Despite having a typically high base quality (low salinity), desalination of RW is practiced for a range of different sectoral uses (e.g. drinking water, irrigation) to reduce water salinity below specific sectoral thresholds. PW as a feedwater source is typically used for industrial applications which require very high quality (low salinity) water, such as the pharmaceutical and food production industries.

The authors also discuss the level of scientific attention being paid to desalination technologies, some of which are clearly not mainstream but very worthy of deeper consideration. They do this by listing the number of scientific papers devoted to each type of technology.



The caption:

Fig. 2. Number 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]).

While it may seem that in the case of MED and MSF, the technologies in which I personally have much hope, that not much is left to be said that serious issues remain to be addressed, in particular scaling (fouling) which can have effects on both heat transfer and corrosion. These are materials science questions, and I personally support deeper research into them.

The focus of scientific papers discussing desalination is also graphed:




The caption:

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

Is anyone surprised at the relative position of "environmental" is in this graphic, although it must be said that the combined category of energy and economic has definite implications for environmental factors?

The number and type of desalination plants around the world are also graphed:



The caption:

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

An alternative graphic, including information on feedwater type is also provided.




The caption:

Fig. 5. Number and capacity of operational desalination facilities by (a) technology and (b) feedwater type.

Nevertheless, irrespective of the technology and feed water type, a concentrated "waste" flow is produced, what the authors refer to in this paper as "brine," although the removed impurities may not be strictly limited to salts.

The authors offer a geographical graphic on the magnitude of this brine issue:



The caption:

Fig. 7. Volume of brine produced per country at a distance of a) b10 km and b) N50 km from the coastline.

I will plainly confess that I have not read the full paper, much less accessed the many interesting references therein, but it's certainly worth spending some time on this important issue.

My personal environmental philosophy is that there should be no such thing as "waste" of any type, or at least, to the extent possible, it should be minimized. The authors briefly suggest some approaches to utilizing "brine:"

Other potential economic opportunities associated with brine production have also sparked a wave in innovation in brine management that seeks to turn an environmental probleminto an economic opportunity (Sánchez et al., 2015). For example, Blackwell et al. (2005) identified sequential biological concentration (SBC) of saline drainage streams creating a number of financial opportunities,whilst concentrating thewaste streaminto a manageable volume. Qadir et al. (2015) suggested that integrating agriculture and aquaculture systems based on the SBC system using saline drainage water sequentially has the potential for commercial, social and environmental gains. Reject brine has been used for aquaculture, with increases in fish biomass of 300% achieved (ICBA, 2018). Reject brine has also been successfully used for Spirulina cultivation and the irrigation of halophytic forage shrubs and crops although this method was unable to prevent progressive land salinisation (Sánchez et al., 2015).

Good stuff, probably not all that significant given the scale of the problem, but good stuff all the same.

Seawater contains a lot of valuable resources, obviously NaCl itself, but also considerable amounts of other minerals, notably magnesium, which can be a key reagent for the control of carbon dioxide and carbonates, as well as an important material for many other applications. I often note that I favor the utilization of seawater's ability to extract uranium from rock and magma, which makes nuclear fuel inexhaustible. And, most importantly, seawater contains the bulk of the free carbon dioxide on earth, both as solvated gas and in the form of carbonate and bicarbonate ions and salts.

None of this is a panacea, of course, and any such utilization needs to be conducted with careful attention to environmental issues, which are profound. Nevertheless, as said, it's a worthy consideration.

I wish you a pleasant Sunday afternoon.