Turning Waste Water Treatment Works into CO2 Sinks: A Simple Chemistry Idea
By Rami Elias Kremesti * M.Sc. CSci, CEnv, CWEM
Kremesti Environmental Consulting Ltd.
2 Westfield Walk, High Wycombe HP123JN
Transmutare Substantiarum Basium In Aurum TM
First Published March 22, 2025
© 2025 Kremesti Environmental Consulting – All Rights Reserved
Introduction
The problem of Green House Gas emissions is a global, urgent one as it results in climate change and global warming. One of the most recalcitrant GHG’s is CO2, a linear, acidic, non-polar molecule that is slightly soluble in water and forms carbonic acid, one of the acids that makes our carbonate beverages so tangy.
As we pump billions of tons of CO2 into the earth’s atmosphere, more and more CO2 is dissolving in the oceans which is resulting in a decreasing trend in pH in sea water.
Figure 1: Average ocean pH over time from 1985 to 2022 – Source Statista. Note that Ocean pH pre-Industrial Revolution is Estimated to have Been around 8.2
CO2 Capture From The Ocean
One of the ideas that is floating in the idea-sphere to counter this alarming trend in pH, which has an impact on crustaceans’ ability to form tougher and thicker protective shells, is to remove CO2 from the ocean. A form of sea water CO2 capture, the water equivalent of DAC = Direct CO2 Air Capture.
The university of Exeter is working on such a pilot called SeaCURE:
https://sites.exeter.ac.uk/seacure/
The idea is a noble one but it suffers from one obvious drawback: the massive dilution factor. Billions of tons of sea water would have to be filtered to remove a tiny fraction of CO2 which has already been diluted in the atmospheric air from the source. In order for CO2 capture to be effective, it needs to be done at the source where the concentration of CO2 is high.
Ocean Alkalinity Enhancement (OAE) and Marine Carbon Dioxide Removal (mCDR) are novel ideas about countering the decreasing trend in Ocean pH. OAE is a carbon removal strategy that aims to increase the ocean’s capacity to absorb atmospheric carbon dioxide (CO2) by adding alkaline substances to seawater, accelerating the natural process of carbon sequestration. Several institutes are looking into this:
https://climate.mit.edu/explainers/ocean-alkalinity-enhancement
The Context of Our Idea
A recent online publication caught my attention.
It is about pilot tests on using Magnesium Oxide MgO to increase the pH in the ocean and capture CO2 in the process.
Figure 2: In this photo provided by the Ocean Alk-Align project, pink dye is released into Tufts Cove along Halifax Harbour in Nova Scotia, Canada, as part of a project by the company Planetary Technologies to test whether adding alkaline minerals to the ocean can help slow climate change, Thursday, Aug. 10, 2023. (Ocean Alk-Align project via AP).
There is even a patent titled “Methods and products utilizing magnesium oxide for carbon dioxide sequestration”:
https://patents.google.com/patent/US20120291675A1/en
Here is a very interesting article about this in Nature:
https://www.nature.com/articles/s43247-024-01506-4
Our Idea
Our idea is to dose the MgO upstream in the Municipal waste water treatment process, before the aeration step where BOD removal and Nitrification take place: the benefits will be two fold or even three fold.
First Magnesium will help with removal of ammonia as it reacts with Ammonia and phosphate to form struvite and secondly, the resulting alkalinity from dissolution of MgO in water will fix CO2 produced by the BOD oxidation process in the form of Magnesium Carbonate. Thirdly, it is possible that as less dissolved oxygen will be needed to nitrify Ammonia, energy consumption to maintain the optical DO in the aeration basin will probably decrease.
A pilot test that we conducted on a sewage treatment plant in County Donegal in Ireland in 2024 showed that the dosing of small amounts of Magnesium Chloride into the raw sewage results in perceptible sustainable decreases in ammonia in the effluent. The mechanism could be two fold: Magnesium is an essential nutrient for nitrifying bacteria and it reacts with ammonia and phosphate in the sewage to form Struvite.
Annnual Emissions of GHG’s from WWTW’s Facilities
According to recent estimates, the yearly emissions of greenhouse gases from wastewater treatment facilities worldwide amount to around 1.43 billion metric tonnes, with a corresponding social cost of $264.5 billion (He et al., 2023, He et al., 2023).
The cost of 1 ton of MgO on Alibaba is = High Purity Magnesium Oxide/Magnesium Oxide Price. $ 145-180/ton. Min. order: 1 metric ton.
MgO + CO2 -> MgCO3
Molecular weight of MgO = 40.3044 g/mol
Molecular weight of MgCO3 = 84.3139 g/mol
Molecular Weight of CO2 = 44.009 g/mol
Therefore, the ratio of MgO to CO2 removed is 40 grams to 44 grams or roughly 1 to 1 ton removed.
A simple comparison to the social cost of CO2 emissions above shows that the economics is feasible and cost effective. MgO is a diprotic base which means one molecule of MgO can capture 1 molecule of CO2 as opposed to NaOH of which we need two molecules to capture one of CO2.
Life Cycle Assessment
Returning CO2 back to the ocean in the form of Carbonates would correct the decreasing trend in pH and return CO2 to where it came from: fossil fuels.
Conclusion
We strongly believe that the CO2 GHG emission global problem can be solved using simple chemistry and this will happen in the next 10-20 years as historical lessons from solving global environmental problems teach us. Historically, global environmental pollution problems appear in cycles of 10-20 years and are also solved in roughly the same time frame. Case in point: acid rain, the ozone layer, PCB’s, Sulphur Dioxide and NOx emissions from power stations, Lead in Leaded Petrol etc. Currently GHG emissions, microplastics and PFAS are the most recalcitrant global environmental problems to solve.
Kremesti Environmental Consulting is a small consultancy based out of High Wycombe with a passion for Chemistry and 20 years of experience in water treatment and power station chemistry. We strongly believe that the solution for Climate Change is a chemical one based on simple chemistry. The flip side or the root cause of course is rampant consumerism and population growth.
The founder and managing director, Rami Elias Kremesti, is a published author and keen nature lover. He regularly hikes the Chilterns AONB and is fascinated by how plants convert inorganic chemistry to organic chemistry. The slogan and mission statement of the consultancy Transmutare Substantiarum Basium In Aurum was inspired by the great alchemists who believed in transforming base substances into gold.
Rami Elias Kremesti Portrait
© 2025 Kremesti Environmental Consulting – All Rights Reserved