Team:UCL/Implementation
Overview
Despite problem-oriented and end-user-centered strategy for our Human Practices work, for Proposed Implementation, we have adopted a relatively conservative strategy to maximize the probability of bringing fruitful results to our target markets. Thus, we have proposed Southern California as our test market before launching our project to the target market of coastal regions in Ghana and Nigeria as it suffers from the similar issues and has already had plants with experiences of sea water desalination such as Carlsbad Desal Facility. We have also created a flowchart which we sought for suggestions from engineers working in various areas including plastic recycling, water infrastructure, water treatment and distribution, wastewater management, desalination, etc. for rolling out our project in the real world.
Part 1: Proposed end users
As we have stated in the Human Practices page, our proposed end-users are identified as local people, especially farmers, living in the coastal regions in Ghana and Nigeria such as Accra (the capital city of Ghana) and Lagos who are suffering from both issues of oceanic plastic pollution and water scarcity. On the other hand, people/farmers living in Southern California are our proposed intermediate-users as we also proposed to launch our project there not only because Southern California is facing the same issues, but more importantly, with more talents and technological support, the real design and implementation of our project can be facilitated. When the technologies are getting mature, they can then be effectively tailored to meet more specific conditions of our target markets, and therefore, reducing the inequality between developing and developed regions as what Sustainable Development Goal (SDG) 10 stands for.
Based on this initial idea, and to ensure our implementation strategy is on the right track, we have conducted interviews with experts standing at the ‘frontline’ of plastic treatment and water desalination in Southern California – Anika from Algalita and Tyler and Christy from University of California San Diego (UCSD). Algalita is an NGO focusing on educating and inspiring the next generation of plastic pollution prevention. On the other hand, as Tyler and Christy have much experience working on microbial desalination cells, they have also provided us with solid suggestions on feasibility of and alternatives to our implementation strategy.
Both Anika and Christy have suggested that we expand our implementation strategy to not only be restricted to seawater desalination but to also touch the domain of city wastewater or brine treatment/desalination because actually issues of wastewater in California can be more severe. Thus, this could further enlarge the pool of our proposed end-users as our project might be implemented in cities where all people would be our beneficiaries.
Part 2: Proposed implementation strategy
Once launched, our project would be considered to be a novel infrastructure carrying out the work of plastic degradation and seawater desalination in the real world. For our implementation strategy, we have made our implementation flowcharts and improved by 3 versions according to the suggestions we got from industrial experts.
Infrastructure location selection
Based on the location selection of Carlsbad Desalination Plant, we proposed to construct our desalination plant near the sea to avoid long-distance pipeline system and mitigate the energy and labor requirement of the pumping system and plastic collection and transfer.
Sources of operation
It was quite apparent that sea water and PET would be the sources for the operation of our plant. However, to avoid potential blockage of the MDC, we considered to mimic the pretreatment strategy of Carlsbad which uses 3 layers: anthracite, sand and gravel for carrying out pretreatment.
First meeting with UCSD - MDC Engine room (Aerobic or Anaerobic?)
The follow-up MDC would be the core of implementation. It is where PET would be degraded, and bioelectricity would be generated for seawater desalination. However, it is also the trickiest part of the design as we initially proposed to co-culture the 3 bacteria, E. coli, P. putida and Shewanella. oneidensis in an anode chamber. Nevertheless, E. coli and P. putida have to be cultured under aerobic conditions to produce lactate while Shewanella, though being facultative anaerobe, has to be under anaerobic conditions to effectively utilize lactate and produce electricity. Different oxygen requirement indicates our co-culture strategy might collapse. Fortunately, after our first meeting with UCSD, we were told that actually E. coli and Pseudomonas can survive under anaerobic conditions and that was what they had confirmed with experiments. Thus, at this stage, we chose our MDC to be operated under anaerobic conditions.
Product - desalinated water
Although Carlsbad Desalination Plant was the benchmark, since we would use GMOs to degrade plastic and desalinate which is different from the reverse osmosis (RO) membrane that Carlsbad uses for desalination, to ensure safety, we proposed our product to be used in agriculture only such as irrigation.
Reflection on modelling - MDC Engine room (Aerobic or Anaerobic?)
In this version, the biggest change we have made was in the oxygen condition of our MDC Engine room. Instead of co-culturing the bacteria under totally anaerobic conditions shown in version 1.0, we modified it to be microaerobic which means we proposed to supply minimum amount of oxygen because according to our FBA modelling results, P. putida and E. coli could not work together to produce lactate without oxygen. However, this microaerobic condition was based on our assumption that Shewanella cells would form biofilms attached to the surface of the anode, thus, although the cells on the surface of the biofilm would be exposed to oxygen, the inner cells on the surface of the anode would be protected and under anaerobic conditions.
Addition of RO membrane filtration
During one of our weekly journal clubs, we investigated different configurations of MDCs and we found that in order to meet the irrigation water quality standards, we have to achieve the level of 90% salt removal which indicates our MDC configuration design might not be sufficiently effective on salt removal. Thus, we followed what Carlsbad had done, putting an additional unit operation of RO membrane filtration. Although that might drive up the cost and energy consumption, compared with the ‘raw seawater’ which Carlsbad applies directly to the RO membrane, the pressure required in this step would be much lower.
Visit to VEOLIA Water Treatment Plant - Addition of disinfection step
Built upon version 1.0, we found that most of our implementation design strategies had been based on literature and suggestions from professionals. However, sole successful lab bench scale trials might not be enough to predict the success at the manufacturing scale. Far more details and procedures have to be included before real implementation. Thus, one of our team members, Li, has gone a visit to Shanghai Linjiang Water Treatment Plant to explore what water treatment and supply in the real world is like.
One point that drew much of our attention was that disinfection is carried out three times in the procedure, one being pre-ozonation, another being UV disinfection and the last being disinfection in the chloramination tank. This reminded us that in fact, disinfection would be even more significant for our implementation as GMOs would be involved in our procedure. Thus, based on the information from Director Zhu who said that ‘Only 2 secs are needed for using UV light to disinfect water passing through the pipes, and that can already eliminate 99% of the microorganisms in the water’, we chose to adopt UV disinfection after MDC desalination and before being distributed. After the visit, we deeply realized that desalinated water was definitely not equal to water ready for use.
Meeting with ARUP - Seawater and plastic pre-treatment, brine treatment
As stated before, because of working experiences and looking at problems from different angles, industrial experts could always provide us with new thoughts on implementation. Besides VEOLIA, Arup was another company that we consulted regarding actual implementation. After we had described our project idea to Vincent via email, he posed 10 thoughtful questions to us. We also arrange a follow-up interview with him.
Due to the lack of lab access and the pandemic restrictions, our project productivity was totally based on modelling results and we were not allowed do many outreaching activities, which rendered it even harder to answer these 10 questions. However, along with our project going, we tried to identify some of the answers.
Brine Treatment
One of the Arup’s features is its experiences in wastewater management. Thus, during the interview, we have mainly discussed issues of how the brine left after desalination could be treated. From his perspective, physical methods - evaporation and crystallization, dominate the ways of treating brine. For our implementation, he suggested that we should try to recover the salts left in the brine to see if they would probably possess any commercial value to complement the enormous cost of building up solar evaporation and crystallization facilities and intensive energy consumption.
Fortunately, Vincent mentioned that ‘In hot countries, you can pump the brine in a lake and wait for evaporation and recover the salt.’ As our target markets are two tropical African countries – Ghana and Nigeria, temperature there can be relatively high throughout the year. Thus, that might be a solution of brine treatment for the future implementation. Moreover, we have also come across a paper from MIT, which illustrated that NaOH and HCl could be extracted from the brine left after desalination. These two chemicals can be recycled to clear the MDC and adjust pH in seawater pretreatment [1]. However, that point was doubt by Vincent as he argued that ‘the manufacturing costs of HCl and NaOH are already relatively low and you can even buy them from the market directly. Although your project might reduce energy consumption with the involvement of biological energy, if you try to recover the salt, the energy consumption might be even higher than traditional desalination.’ Thus, from the aspect of commercial and technical brine treatment, he suggested us conduct lab trials for investigating the purity of the salts recovered, especially the bulk of NaCl, and consider their industrial usage.
On the other hand, we have discussed the potential solutions to dispose the cells so as to minimize the impact on environment. Basically, Vincent has provided us with two possible reasons why the cells would have to be disposed. One was because they would be inactive while the other was the population of the cells would be too large which would exceed our capacity of PET supply. For the first case, that indicates we have to replace the cells for a certain period, and we could either incinerate the inactive cells to regenerate energy for the operation of our plant or through some specific process, we can turn them into other nutrients such as vitamin. For the second case, too large cell population does not mean the cells are inactive. Thus, we could try to recycle the cells on the basis of maintaining a steady ratio between cell population and PET supply. Furthermore, Vincent informed us that usually anaerobic cells grow much slower than aerobic cells. That indicates we can probably sell extra anaerobic cells on the existing biological treatment market, again, to complement the cost.
Seawater and plastic pre-treatment
Finally, Vincent confirmed our consideration that both seawater and plastics would have to be pre-treated. For seawater pre-treatment, he said the process had already been well-proven. The most important aspect of seawater pre-treatment is pH adjustment to avoid membrane fouling issues such as crystallization, precipitation and calcification when some salts achieve the saturation levels that might exist in further steps. In terms of plastic pre-treatment, he strongly suggested us carry out experimentation for investigating necessary steps that should be involved in plastic pre-treatment. The legislation of plastic manufacturing might be changed and perhaps raw materials for making plastics would be more biodegradable.
Second meeting with UCSE - MDC Engine room (Aerobic or Anaerobic?)
Until the second meeting with UCSD, the problem of whether we would co-culture the 3 bacteria under aerobic or anaerobic conditions were still not decided. However, after that meeting, we got constructive design ideas.
Since it seemed almost impossible to co-culture all 3 bacteria together given their different oxygen requirements, we had to compromise on separating them into 2 chambers, one would be supplied with oxygen while the other would be under anaerobic conditions. To transfer the lactate produced in the aerobic chamber, we would apply unit operations of centrifugation and depth filtration. Centrifugation would be used to separate the lactate dissolved in the media with the cells while depth filtration would be used to recover the cells and put back to the aerobic chamber if they are still active. Finally, the lactate contained solution would be pumped to the anaerobic chamber for Shewanella.
Meeting with ARUP x Carlsbad, California – Final polish
Since we used Carlsbad Desalination Plant as the benchmark of our implementation strategy, finally we invited and conducted an interview with Sheba from Arup, who had been involved in the design and construction of Carlsbad in San Diego.
We have uploaded the recording of the interview with Sheba on our YouTube channel.
For project introduction to Sheba, please check here.
For the following A&A session with Sheba, please check: here.
Carlsbad’s brine treatment strategy
Instead of recovering salts from brine as what Vincent had suggested, Sheba informed us that Carlsbad has taken the advantage of the nearby power generation plant. It has been using the cooling tower water coming from the adjacent power plant for massive dilution before pumping the diluted brine back to the ocean. This cooperation strategy has been proven to be more cost-effective.
Systematic post-treatment
Sheba agreed on our decision to include the UV disinfection step for the post-treatment. In addition, she also suggested us bring the pH of the desalinated water back to neutral to avoid corroding the distribution system pipeline linings, and metal ions should be rebalanced as well. Thus, besides UV disinfection, a more well-established post-treatment system would be needed.
Flowchart version 3.0 was the final version we had proposed to implement our project. However, without access to the lab, we were not able to conduct lab trials to test the feasibility of some steps mentioned above. Lab trials can be done by future teams and the results of which can be used to create further versions of flowcharts.
Part 3: Challenges and critiques from industrial and NGO experts
Implementation strategy is never perfect. Besides suggestions from experts, they also informed us of potential challenges we would face in the future implementation. Challenges mentioned by experts during interview included costs, regulations, PET sources and cell replacement and culture maintenance which are discussed below. However, it is believed that far more challenges would arise in the actual implementation.
From all industrial experts’ point of view, cost is the biggest challenge that we would come across. As what Sheba has said ‘benefits have to be recovered within a realistic time limit, if it is really costly to implement but takes decades to produce a return, it will not be favored by industry.’ Thus, to do an initial trial of cost analysis, we have created a lab bench scale cost analysis table with items listed for consideration and calculation:
Despite that Vincent has suggested us potential ways to complement the huge cost of construction and operation of our proposed plant such as recovering salts and anaerobic biomass from the brine for direct sale or turning them into nutrients or generating energy by incineration, that might only be able to cover a tiny proportion of the total cost, let along the further cost needed to carry out lab trials for setting up the recovery process and the cost of construction of salt recovery facilities.
Moreover, costs of implementing our project could come from far more aspects. For example, the initial construction of hardware such as the pipe and pump system, whether it should be buried or opened would be worth considering. Raw seawater quality could affect the cost of seawater pre-treatment while overhead costs such as electric power and also labor costs would highly depend on the locations for implementation.
Regulations would be another quite obvious challenge and are correlated with the challenge of costs. As we proposed our project to tackle global issues, perhaps we would implement it in far more different countries besides Ghana, Nigeria and the US. Regulations on quality of irrigation water and plastic manufacturing can vary a lot in different countries which indicates we might not be able to develop a universal implementation strategy for all.
One of the challenges mentioned by Anika (from Algalita) was that by implementing our project, we might will have created a direct competition on plastic sources with existing plastic recycling plants. She argued that since using physical methods to recycle PET had already been well defined, degrading PET that had just been used once might force plastic manufacturer to produce more plastic. If we would truly want to degrade PET, she reckoned our project would be more welcomed by wastewater plants in California because our idea can be incorporated into waste management systems to degrade microfibers in sedimented sludge (which is mostly PET) and also to generate freshwater for non-potable use.
Another option would be that we could start to degrade PET after two rounds of recycling so that we can end the life cycle of PET, but when we raised this point to Vincent, he noted that the characteristics of PET might be changed after being recycled twice.
Finally, if in the future, we find that source of PET is not viable, Anika suggested us perhaps search for other plastic composing materials such as polypropylene whose recycling methods had not been well characterized for degrading.
How to maintain and replace the cells in the MDC was Vincent’s top concerns. He reckoned that the MDC would be the engine room of our whole process, and therefore, replacing the cells indicates the whole process would be temporarily shut down. Moreover, there would actually be a tiny ecosystem in the MDC containing different microorganisms, being either natural or GMOs. Thus, it might also be challenging for ensuring the GMOs can survive in the potentially competitive environment.
Part 4: Safety aspects to consider
Safety issues of implementation can be first considered from 2 stages – Pre-implementation and Construction and Operation stages. Furthermore, since our final product would be desalinated freshwater used for irrigation, product safety must be considered, and final consumers of the crops would have to be informed of the involvement of the desalinated water.
Before the actual launch of the project, we would have to do more deeper market research to identify the actual most suitable locations to launch our project. This would be highly related to the safety and security of our market research participants’ personal data. Besides on-site market research, we would have to consult experts from various industries and academia as well as government in different regions to ensure the smooth launch process. We might come across lots of businesses and governmental secretes which we would have to ensure their safety and confidentiality.
From another perspective, to ensure our implementation would be successful, we would have to do lots of lab trials in which our proposed GMOs would be involved. Thus, there would be possibility that the GMOs might be released into the environment despite that chances of their survival in nature would be quite low as E. coli and P. putida would be designed to be auxotrophs.
Being a novel plant infrastructure, our project would have to be constructed on the seaside by skillful construction workers whose safety would have to be ensured during construction. Furthermore, once the plant enters into its operation stage, people working in the plant might have direct exposure to GMOs during cell replacement and culture condition preparation.
After all, the product from the desalination plant would be freshwater used for irrigation. Despite that the desalinated water would have gone through a whole set of post-treatment and disinfection, we would have to have the monitoring system ready all the time for testing the level of bacteria (CFU) in the desalinated water as well as in the pipeline system. It would also be necessary for us to inform our end-users – farmers that how the water they use for irrigation comes, and the crops irrigated by the desalinated water should also be specially labelled to inform the consumers.