Mobilising chemical engineering resources to mitigate drought
IN 1959, Chemical Engineering Science1 published an article by Andreas Acrivos and colleagues on the challenges of ensuring pre-defined fluid flow distribution through a pipe manifold with multiple junctions or orifices. That paper talked to the nascent use of “computing machines” to predict the underlying pressure variations and frictional losses within a given pipe network. It alluded to dynamic behaviour, but was constrained in its ability to engage with this by its necessarily restrictive assumption set. Yet its insights have informed much of process engineering pipe flow analysis since. It was an excellent example of what could be achieved within a prevailing technical paradigm if the problem is framed suitably.
But real life is seldom ‘steady state’ and one-dimensional. Edwin Abbott made that clear in his social satire Flatland2 from 1884. Life is much richer in prospect. Technology is a vehicle, not a destination. Understanding human behaviour and judgement is critical. Preconceived notions of character are often found wanting and self-limiting. Perspective is often ephemeral.
In 2010, Roland Clift delivered the Danckwerts Memorial Lecture3 on the topic of Chemical Engineering Outside the Pipe: Industrial Ecology and Sustainability. His main argument was to challenge chemical engineers to deploy their systems thinking skills to address the broader socio-environmental, technical-economic challenges which beset 21st century living. The notions of being able to engage with complexity, and unpacking values-laden decision making were deeply embedded in his premise. It put people front and centre in the conversation.
Whilst published more than 100 years apart, I would like to suggest that these three publications provide essential perspective to engage with the following narrative.
IChemE has more than 40,000 members in multiple countries. That’s a significant resource base. One of the Institution’s key challenges is to ensure its continued relevance to that large base, in part by mobilising its collected resources to engage with critical problems and opportunities across the globe. Case studies are helpful in this regard. I offer one here from South Africa.
As I write this, some parts of South Africa are in the midst of a 1/200 year drought. It is well known that South Africa is a dry country. It is also a country where there is significant migration of its people from rural to urban areas (as is the general trend in Africa), which places additional stress on public infrastructure. Its water and sanitation system is teetering (only 1/3 of engineering positions in the National Department of Water and Sanitation are currently occupied). The country suffers from massive unemployment, an education system in crisis, and an economy whose historical base of mining and agriculture is under threat – the first because of failure to keep abreast of market needs, impeded by a constrained labour market, and to keep pace with technology and innovation; the second compounded by climate change impacts. Maybe some of these alarm bells are unique, but I reckon some are symptomatic of the situation in many developing economies.
It is well known that South Africa is a dry country...Its water and sanitation system is teetering (only 1/3 of engineering positions in the National Department of Water and Sanitation are currently occupied)
The Western Cape, and Cape Town specifically, is feeling the effect of the drought most acutely. All of Cape Town’s bulk potable water supply comes from surface reservoirs, via a single riverine system close to 300 km in length, embracing a catchment area close to 8,000 km2, which is supported by dam collections and some inter-basin transfers. The City draws about 65% of the water available in this catchment, with agriculture making up the bulk of the difference. Smaller towns along the river fight for what’s left. It’s a winter rainfall area, and agricultural water consumption peaks in the hot, dry summer months, mainly via open-channel irrigation systems. Think of this as a pipe with multiple off-takers, but where the volumetric flow is a huge variable, and many demand points are either simply variable, or completely unknown. Most flows are metered, but not all (evaporation loss from agriculture is unquantified). Catchment management modelling is sophisticated, but water resource planning lags growth in demand, and has failed to understand the implications of sustained drought. Different layers of government exercise control over water supply and distribution, which often leads to conflict. Industry growth is constrained by water and energy availability. Nowhere has there been rigorous systems modelling to explore all the interdependencies and optimise the system as a whole. Life cycle thinking and industrial-ecology arguments are missing.
All credible climate change predictive models suggest that the south west of the country will get drier. Various water resource models predict “zero water availability” from local catchments within 3–4 months of 2018 unless it rains (no one is banking on that). As of 1 January 2018, householders will be fined, or subjected to other penalties (including forced supply restrictions), if monthly household consumption exceeds 10.5 kL. That figure is a rather arbitrary number, trying to restrict personal consumption to less than 90 L/d, based on a four-person household. To put that number into perspective, that equates to a personal daily water allocation of a 2-min shower (no bathing), four toilet flushes, one wash load per week, decent allowances for drinking and cooking, and a modest allocation to house cleaning. But all external uses of potable water are forbidden. Right now, only about 30% of Cape Town households are able to meet this target. From 1 February 2018, that household allocation is being reduced to 6 kL/month (based on 50 L/person/d), accompanied by a punitive tariff structure for those who exceed it. In parallel, the City is doing its utmost to ensure the poor and elderly are not adversely impacted by these restrictions. There can be few examples anywhere of such a complicated juggling act to try and ensure an equitable allocation of this precious resource.
That said, the City’s daily consumption (between 500–600 ML/d) is considerably less than half of what it was before water restrictions were introduced 12 months ago. Other demand management measures include mains pressure reduction, which poses its own set of problems (like ensuring the continued effectiveness of emergency fire-fighting equipment). Contingency plans are in place to have personal allocations reduced to 20 L/d; and even distributing potable water from community points under armed guard! The science-fiction of “water wars” could be a reality in future.
But demand management alone will not suffice. Punishing consumers is cheap and effective, but blaming consumers for the situation is merely a political ploy to cover up government inadequacies, and the failure of adequate planning and investment. There are perverse outcomes too. Municipalities derive revenue from water sales on a sliding tariff. Reducing demand means less money to support the significant investment in new bulk water supply infrastructure which is now essential. Putting aside the lack of planning and political will which has allowed this situation to develop, there is now considerable focus on new bulk supply provision. Cape Town alone is proposing investment in up to 500 ML/d new bulk water supply in 12–18 months. This would be a world-scale project, comprising a mix of groundwater abstraction (never attempted at scale in SA), advanced wastewater treatment (right now, treatment plants manage only BOD reduction, nutrient removal and disinfection), and large-scale desalination. The situation in other provinces of the country, whilst not immediately commensurate, is not far behind. At least coastal areas have access to desalination should they choose to develop this resource. Individual projects will likely be public-private partnerships (a contracting model with which South Africa has had limited experience to date). But there is no doubt that lessons learned here will have regional significance, especially as the impacts of climate change start to bite.
None of the proposed new supply options is risk-free. We know from experience that direct re-use doesn’t meet with immediate societal acceptance – Toowoomba in Australia being a case in point. Lessons learned there are being put into place in cities like San Diego in California, which will use reservoir storage as an environmental buffer before adding recycled water to its potable supply. We know too that groundwater abstraction from aquifers carries significant uncertainty, including the risk of salt water ingress. The Western Cape aquifers are well documented, and carry more than three times the amount of water in surface catchments when these are full. But no significant abstraction has been attempted before within these fragile eco-systems, and little is known about aquifer re-charge. Large-scale desalination also carries risks. Plants on the East Coast of Australia serve as good examples of investments which, whilst attractive in terms of security of supply, have failed to deliver commercial returns because of their low usage.
In such times of crisis, life cycle arguments are often missing – in particular, optimising the energy costs of new supply, and exposing the socio-economic impacts of specific interventions (or lack thereof). This is particularly meaningful in the South African context, given the precariousness of its energy/power network, and the need to better understand the food-water-energy nexus. Agriculture in the Western Cape may be a relatively small contributor to GDP, but it is a significant employer. The drought has already led to 1/3 of the labour force being retrenched, causing significant social disruption, and placing additional stress on urban infrastructure. The economic impact of sudden changes in water allocation to agriculture and agri-processing are only now being quantified. This is the obvious trade-off. Constrain water for agriculture to secure more for urban consumers. But at what cost, and with what benefit? This is where demand management as a sole strategy can only but fail. Looking at the energy dimension, to what extent could an expanded commitment to utility-scale renewables assist these new water supply interventions? Will people be more accepting of massive investment in water infrastructure if it helps drive the renewable energy agenda? Will financiers share that view? At a technical level, could the prospect of natural gas imports to power new electricity plants unlock opportunities for thermal desalination using waste heat, as an alternative to reverse-osmosis membrane processes? Could large scale desalination be used to help grid balancing through load shifting? And, from an industrial ecology perspective, could desalination brines provide feedstock for a new chlor-alkali industry, which is needed to support some of the proposed minerals beneficiation projects planned for the region.
This article is a call to arms to IChemE members. South Africa’s water crisis talks to many issues which are (or should be) at the forefront of our chemical engineering philosophy and practice. Whilst some of the challenges facing Cape Town are technical, most are not. They are political, institutional, regulatory, commercial and financial. That said, their resolution requires clear technical input, guided by systems thinking. How can you build resilient infrastructure to meet sustainable development objectives and priorities if you don’t understand the interconnectedness of all the component parts, and fail to commit to broad-based stakeholder engagement? We need to think differently about such complex infrastructure systems. We need to expose opportunities for technical and system innovation. And we need to ensure chemical engineers continue to provide meaningful contributions to investment decisions in these areas. Lessons learned here will have value in many other developing country contexts. And that should be exciting for IChemE and its members.
1. Acrivos, A, Babcock, B and Pigford, R (1959), Chem Eng Sci (10), 110–124.
2. Abbott, EA, (1884), Flatland: A Romance in Many Dimensions, New York: Dover Thrift Edition (1992 unabridged).
3. Clift, R, Chemical Engineering Outside the Pipe: Industrial Ecology and Sustainability, AICHE meeting, Salt Lake City, Nov 2010.