CeBER Research Day 2014: Wastewater Biorefineries
Today I want to give you an overview of wastewater biorefineries. This is a new project funded by the Water Research Commission (WRC) which started in April of this year.
This is the project team I represent.
(Sue Harrison, Bernelle Verster, Madelyn Johnstone-Robertson, Shilpa Rumjeet, Lefa Nkadimeng, Mark Kerr, Robbie Pott, Sharon Rademeyer, Tayana Raper)
This project can be seen as driven by the need for better wastewater treatment, caused by things like growing human populations, increased industrial water use driven by increased affluence, and the need for a more sustainable society. This is however not the full story.
There are technological solutions to intensify the process which reduces land area requirements, but these still involve large upfront investment costs, and additional energy demands. I consider these small investments into a process that makes the system as a whole work better, but this view is often not shared by political and social interests. The bottom line is that this is not a tech problem.
Like most of you (the CeBER research group postgraduate cohort) I chose to study bioprocess engineering because of the many, to me obvious, opportunities that the biobased economy represents, hence I will not explore these opportunities here today. In some ways, I feel that this has been a bit of a scam, but I will come back to that in a moment. What this movement does represent is a lot of hype and political interest.
So with this project I wanted to explore if we can use these opportunities and this political drive to make waste (and here I wanted to use my favourite word but the team objected) more socially attractive.
The next few slides are a bit word heavy, but I wanted to include the whole definition because it takes a bit of time to get your head around it, and the text may help. What I want you to focus on is the integrated, multifunctional nature of this definition. It is not a single raw material to single product idea, like the biofuels movement was - that I definitely think was a scam. Also notice the emphasis on using the raw materials as far as possible. The objective is to leave as little waste as possible.
A biorefinery is characterised as an explicitly integrative, multifunctional overall concept that uses biomass as a diverse source of raw materials for the sustainable generation of a spectrum of different intermediates and products (chemicals, materials and bioenergy/fuels) whilst including the fullest possible use of all raw material components.
Co-products can also be food or feed. These objectives necessitate the integration of a range of different methods and technologies. The biorefinery process chain consists essentially of the pre-treatment and preparation of biomass, as well as the separation of biomass components (primary refining) and subsequent conversion and processing steps (secondary conversion). (German biorefinery report, Timoteo de la Fuente)
An encouraging development is this increasing global trend to move away from this single product outlook to a more diversified stream. To paraphrase a group at Wageningen University, it will be more sustainable to produce high value-added products from this biomass and its associated side-streams and use residual fractions for conversion to biogas or other energy-carriers.
So I am not saying biofuels should not be produced, but it should not be the first or sole objective of the process.
A wastewater biorefinery has the added subtle nuance that the water carrying the biomass is also a product. This has implications in the reactor and process design. Coming back to the social and political imperatives, we are trying to achieve closer links between the people producing the wastewater and those who need to clean it, which hopefully would create increased interest and care in how the water is produced and what makes its way into the water in the first place. This contributes to this concept of a circular economy, and, by the way, a very fashionable phrase in politics at the moment is 'both and' solutions rather than 'either or' solutions - so try that out at your next networking event!
A wastewater biorefinery needs to generate products of sufficient value to make it economically viable, as well as having unit processes (producing products of variable value) to produce clean water as a product.
This concept contributes to seeing wastewater treatment as an integrated system rather than a unit process, and potentially provide a link between the users of water and those responsible for its management where resources are recovered in closed loop cycles, and thus contributing to progressing towards the concept of a circular economy.
As an example of what such a wastewater biorefinery could look like, I include my process flow diagram. This is particularly to do with municipal wastewater, my passion. I won't focus on the details today, but I want you to see the range of products exiting the system - not just one product (for example the bacterial product, or bioplastic that I started my PhD on). In this case we see only one raw material - albeit a complex one - entering the system, but it is also likely that we will complement this stream with supplementing nutrients, extra carbon sources like agricultural wastes or other organic solid wastes.
This may all be well and good then, but I mentioned earlier that I thought this biobased economy may be a bit of a scam. Yes, it offers many opportunities, but in many cases the products end up being more expensive, and the whole process may not be more environmentally sustainable. Three factors in particular influences the outcome - raw material costs, energy and sterilisation costs and downstream processing costs.
Most of us in CeBER by now also know that while using waste materials reduces the raw material cost, the suboptimal nature of the waste may often make the total cost more expensive. In addition the transporting and logisitics of waste materials also represent a cost, so that these wastes are seldom really 'free'. In the case of wastewater, the infrastructure often does exist, so this can be considered as free, but the other two costs becomes even more exorbitant using conventional methods!!
A challenge to the biobased economy is that commodity bioproducts from renewable resources are often not economically competitive, and the challenge is threefold:
- The costs of the raw material, which could account for up to 80% of the total cost. Much current research is about using wastes as 'free' raw materials, but because of the suboptimal nature of the waste, often this method may make the total cost more expensive.
- Work by Harding (2009) and Richardson (2011) show that energy and sterilization contribute not only to the operating costs but also carry significant environmental impact.
- Downstream processing (DSP) is often difficult and expensive; purification may accounts for up to 80% of the total processing cost. (Doran, 1995)
Looking at ways to combat this was the focus of my work last year, and it comes down to reactor design. Again, I don't want to go into details here today, but the reactors need to focus on four areas: The often large volumes of these wastewaters, the complex, variable nature of the water, which I will come back to in a minute, that the water is released into the environment (which limits what additives you can add to the process) and the downstream processing (DSP).
Surprisingly we saw that DSP is already very well developed, but that reactor design is often not optimised to make best use of the DSP following it.
The bottom line is that we are trying to prevent working with the bulk of the volume, so you are trying to get what is important to you into a much smaller space. This means that you want to separate, or concentrate the growing biomass - the stuff that is producing your product, which in engineering terms means decoupling the solid and hydraulic retention times, and separate the product as well. What this means, in effect, is that we will be working a lot more with solids, so we have included that into the project by being more inclusive, more towards 'waste biorefineries'. Which is a bit sad for someone with a tattoo of water on her wrist and goes by the nickname of water maverick. But anyways.
In terms of the complexity of the stream, Barry Coetzee, at the City of Cape Town, sums it up well. “The reality of treatment works is that they are receptors; this is not a controlled environment. The technology in use needs to cope in the face of e.g. backyard industries that don’t classify their waste and just flush it down the drain, shut down of metal finishing works over holidays etc.” [edit: the grammar in the image is my mistake, will fix it when I'm on the image-savvy computer)
We are not only working with wastes that are complex to start off with, but we know roughly what's in them. We are also working with things that are undefined, where nobody knows what's in them. Then, we have to deal with streams that are known most of the time, and then things like power cuts or floods, or holiday shutdowns happen. We have to be able to deal with all of that.
Very early on in the project we realised that there are different groupings of wastewater, which presumably would be more suitable for different things. So rather than a one size fits all solution, we need to be able to make some decisions about what to use different types of wastewaters for, and which products would be more suitable for which types. This would enable us to advise industry players on the best options and partnerships to best utilise their wastewater.
Wastewaters can be grouped according to volume, concentration and complexity. The first two groups are easy, as once you know the volume and concentration, you can design for that, it's pretty straightforward. The complexity is tricky, as you can have changing compositions, changing concentrations, combinations of many different compounds present... and the reactor and biological populations need to cope in the face of this and still produce products. Addressing this is a big focus of the project.
One of the first questions I get asked is 'which products can we get from this approach?' People would like to hear simple answers like, biogas, this type of bioplastic, this chemical compound (TM), but because of the dirty nature of the wastewater, it is likely that we most of the time would get more dirty products, as cleaning them to become chemically pure would make the overall process financially unviable. A better approach is to focus on the product characteristics, and work on function-based products - for example bioflocculants, biosurfactants etc. It also makes sense to produce products that can add value to the industries producing the wastewaters, and here the types of wastewaters again plays a role in the selection. This is a big, challenging, exciting chunk of this project which I haven't really wrapped my head around yet.
What we have learnt from this project so far, in addition to the focus on solids, the need to define the differences in groups of wastewaters and the characteristics of potential products again is not technological, but more social. Quoting Barry again: “This is a young industry and no-one really knows where it’s going yet. Very few are willing to stick their neck out. We’re integrating systems that were not integrated previously. This represents a huge risk.”
A large part of this project is to translate the knowledge we gain into useful bits that make people more comfortable with this risk.
Something that I guess shouldn't have surprised us, but is disappointing nonetheless is the patchy, inconsistent reporting on wastewater by the players producing it. It's the out of sight out of mind mentality perhaps, the flush-and-forget, and also the fear of litigation in the case of non-compliance, and perhaps the risk of being able to reverse-engineer trade secret processes if you can figure out what is present in the wastewater. This is a mindset we will need to gently nudge into different directions.
My acknowledgement slide is a bit sparsely populated, not because there are not many to thank; there are too many to mention. Let's all have a moment of the warm and fuzzies here. It's more because I wanted to emphasize the support and funding of the WRC, and specifically Valerie Naidoo.
And to close, this was not as pretty and visually interesting presentation as I usually have, so I end with a pretty slide on what wastewater biorefineries could look like. If you are interested, I direct you to a talk I gave about this in Amsterdam, which has more pretty pictures and links.