CarbonPlan recently published a blog post on Isometric’s Wastewater Alkalinity Enhancement (WAE) Protocol. This kind of open dialogue is important for ensuring continual improvement of the carbon dioxide removal (CDR) ecosystem. The authors contributed valuable comments during the protocol’s consultation period and we are grateful for their feedback and look forward to further discussions with them on this topic.
CarbonPlan’s main critique of Isometric’s WAE Protocol is that they believe it could lead to credits for emissions reductions in certain scenarios rather than strictly for carbon removal. As CarbonPlan noted in this excellent piece, this is a nuanced issue that needs careful case-by-case consideration.
Isometric defines a broad system boundary when quantifying carbon removal, which includes upstream, in-plant, and downstream carbon fluxes. The guiding principle is that to be defined as carbon removal, a process must be net-negative—meaning a process that removes more carbon dioxide from the atmosphere than it emits. Wastewater alkalinity enhancement is unique in that the counterfactual scenarios can include both significant carbon emissions and carbon drawdown, meaning there are factors in both directions that determine whether a project has net negative emissions. Let’s look at an example.
Some materials commonly used as a pH amendment wastewater treatment—such as NaOH—release more carbon from their production process than they draw down from the atmosphere. This means the use of NaOH in the existing wastewater treatment is a net-emitting process. Therefore, we do not consider this to be a pre-existing carbon removal pathway. In order for a WAE project developer to achieve carbon removal, they must make the entire process net-negative, which necessitates using a less carbon intensive feedstock.
This is the example illustrated in Figure 1 of CarbonPlan’s article.
In this scenario, the authors claim that there is no carbon removal because the gross removals did not change, and only the feedstock emissions decreased. They would instead view this as an emissions reduction project.
We disagree on this point. The actual impact on the atmosphere is determined by net removals of carbon dioxide, not gross removals. Therefore comparing the gross removals as the authors do provides a limited representation of a project’s impact. Looking at the net impacts to the atmosphere shown in the arrows, the WAE project turned a net-emitting process into a net-removing process. Given that the ultimate purpose of CDR is to remove legacy emissions in a net-zero world, and this scenario achieves that purpose, Isometric considers this to be carbon removal. Replacing a clearly net emitting process is preferable from a climate perspective to the alternative of only targeting wastewater treatment plants using no prior pH amendments.
We also disagree with the authors’ interpretation that the protocol allows for the crediting of emissions reduction. If this was a project designed for crediting emissions reductions, the calculation would be centred on the total difference between the counterfactual emissions and project emissions, which would result in 15 reduction credits. In fact, if a project was previously net-emitting, we conservatively assume 0 counterfactual emissions, and only issue credits for the net removals achieved in the project itself. This results in 5 removal credits in the example.
It’s worth noting that wastewater treatment plants present many different counterfactual scenarios depending on baseline operations, and each case must be treated individually. In the case where the counterfactual scenario is marginally net-negative, then the full gross removal from the counterfactual would need to be considered. More details on calculating WAE project counterfactuals can be found in Section 8.3 and Appendix 3 of the protocol.
There are other important points that the authors raised that we agree with. For example, it is important to protect against gaming so that project developers don’t artificially inflate counterfactual emissions to make the pre-existing process appear net-emitting. We are always interested in feedback and ideas that can strengthen existing safeguards in future protocol updates. Examples of additional safeguards that will be clarified in the next update include a requirement that counterfactual feedstock emissions exceed the drawdown potential by a margin that exceeds the uncertainty, and a requirement for multiple years of records showing the history of the feedstock used in a wastewater treatment plant prior to a WAE project intervention.
CDR projects are full of nuance, as set out in this previous CarbonPlan article. Isometric’s approach is aligned with the four key questions CarbonPlan posed in that piece when evaluating whether a project can be considered CDR.
- “Is the activity part of a system that will exist at scale in a net-zero world?
- Can the system as a whole become net-negative?
- Can the full effects of an activity be accurately quantified, and are elements of the system that lie beyond the activity’s boundary effectively governed?
- Does the activity drive innovation and learning?”
For WAE projects, the answer is “yes” to all of these questions.
Acknowledgements: We thank Zeke Hausfather for his contributions to this blog post.
