The role of total organic carbon within wastewater treatment
Thames Water recently received a record £20 million fine for releasing millions of litres of untreated sewage into rivers in Oxfordshire, Buckinghamshire and Berkshire between 2012 and 2014. This caused significant environmental damage, including death to wildlife and disruption to businesses and recreational users of the river. In this piece Peter Morgan, Product Specialist at Elementar UK, a leading supplier of TOC instrumentation, discusses the role of TOC testing within environmental testing and wastewater treatment.
How is the quality of water tested?
One of the most commonly used tests to evaluate water quality is TOC testing. The TOC content of water is a basic indication of the level of organic contamination and water purity. Water can contain both natural and synthetic organic matter, both of which are measured by TOC testing. An example of natural organic matter would be humic acids (typically from soil or peat), amine, urea and in the case of the river Thames, faecal matter. Typical synthetic sources could be detergents, pesticides, fertilizers, herbicides and other industrial chemicals. Both of these sources can affect the growth of microorganisms in the water and the toxicity of the water. TOC has been shown to lead to disease in humans, so must be monitored in drinking water.
Alongside organic carbon there may be a significant amount of inorganic carbon (TIC) present in river water. Sources of inorganic carbon include dissolved carbon dioxide and carbonates from the river bedrock, and weathering of surrounding rocks. To get an accurate measurement of the TOC content of water, the TIC must be removed. Fortunately, this is fairly simple to achieve by adding acid to the sample and purging with inert gas free of CO2. All carbonates will then be converted to carbon dioxide and vented along with any dissolved carbon dioxide. Any bacteria present in the sample will also produce carbon dioxide via respiration. This carbon dioxide may also be present in the sample and lost during acidification. For this reason, this type of TOC analysis is known as Non-Purgeable Organic Carbon (NPOC). As the acidification stage is easily automated, NPOC testing is the most common type of TOC testing for water samples.
There are two main types of TOC instrument available (which lend themselves towards different applications).
The first type are combustion analysers. These instruments measure the TOC content after acidification by combusting the sample at 850 °C in the presence of a catalyst. The sample is fully oxidised and all carbon converted to carbon dioxide and detected either by an Electrochemical Detector (ECD) or, for lower detection limits, a Non-Dispersive Infra-Red detector(NDIR). An example of a combustion analyser would be the vario TOC cube and vario TOC select.
Wet Chemical Analysers
The second type of TOC analysers uses the wet chemical UV oxidation/sodium persulphate method. After acidification, sodium persulphate is added to the sample and the sample is illuminated with UV light. This forms hydroxyl radicals and organic compounds are converted to carbon dioxide. Again, the carbon dioxide is detected by an NDIR detector. An example of a wet chemical analyser would be the Acquray.
Which method is best?
The combustion method can oxidise solid particles in the sample, and so it is advantageous for dirty samples like those found in the River Thames. They can also be easily converted for use on solid samples such as solid waste and sludges, giving them greater versatility for some users. The wet chemical method has a lower overall detection limit as larger samples can be analysed and can also be more reproducible. This makes it better for clean water samples such as testing drinking water and pharmaceutical cleaning validation samples. Also, the simpler hardware required gives a lower instrument cost.
In addition to TOC, the amount of Total Bound Nitrogen or TNb is often analysed for in tandem with TOC. While a certain amount of nitrogen in water is required for plant and animal life, an excessive amount becomes another form of pollutant. Nitrogen can be present in the form of ammonia, nitrates and their related forms. TNb is analysed in the same way as TOC but with Nitrous Oxide (NO) detected for, thus TOC instruments are capable of analysing for both TOC and TNb simultaneously in the same sample run.
When testing samples that potentially contain high levels of TOC, such as river and surface water, a combustion analyser would be the instrument of choice to ensure all solid matter is accounted for. For testing of drinking water post-purification treatment, however, a wet chemical instrument offers lower detection limits and lower cost sampling.
Read the April 2017 edition of Energy Digital magazine
Carbon dioxide removal revenues worth £2bn a year by 2030
Carbon dioxide removal revenues could reach £2bn a year by 2030 in the UK with costs per megatonne totalling up to £400 million, according to the National Infrastructure Commission.
Engineered greenhouse gas removals will become "a major new infrastructure sector" in the coming decades - although costs are uncertain given removal technologies are in their infancy - and revenues could match that of the UK’s water sector by 2050. The Commission’s analysis suggests engineered removals technologies need to have capacity to remove five to ten megatonnes of carbon dioxide no later than 2030, and between 40 and 100 megatonnes by 2050.
The Commission states technologies fit into two categories: extracting carbon dioxide directly out of the air; and bioenergy with carbon capture technology – processing biomass to recapture carbon dioxide absorbed as the fuel grew. In both cases, the captured CO2 is then stored permanently out of the atmosphere, typically under the seabed.
The report sets out how the engineered removal and storage of carbon dioxide offers the most realistic way to mitigate the final slice of emissions expected to remain by the 2040s from sources that don’t currently have a decarbonisation solution, like aviation and agriculture.
It stresses that the potential of these technologies is “not an excuse to delay necessary action elsewhere” and cannot replace efforts to reduce emissions from sectors like road transport or power, where removals would be a more expensive alternative.
The critical role these technologies will play in meeting climate targets means government must rapidly kick start the sector so that it becomes viable by the 2030s, according to the report, which was commissioned by government in November 2020.
Early movement by the UK to develop the expertise and capacity in greenhouse gas removal technologies could create a comparative advantage, with the prospect of other countries needing to procure the knowledge and skills the UK develops.
The Commission recommends that government should support the development of this new sector in the short term with policies that drive delivery of these technologies and create demand through obligations on polluting industries, which will over time enable a competitive market to develop. Robust independent regulation must also be put in place from the start to help build public and investor confidence.
While the burden of these costs could be shared by different parts of industries required to pay for removals or in part shared with government, the report acknowledges that, over the longer term, the aim should be to have polluting sectors pay for removals they need to reach carbon targets.
Polluting industries are likely to pass a proportion of the costs onto consumers. While those with bigger household expenditures will pay more than those on lower incomes, the report underlines that government will need to identify ways of protecting vulnerable consumers and to decide where in relevant industry supply chains the costs should fall.
Chair of the National Infrastructure Commission, Sir John Armitt, said taking steps to clean our air is something we’re going to have to get used to, just as we already manage our wastewater and household refuse.
"While engineered removals will not be everyone’s favourite device in the toolkit, they are there for the hardest jobs. And in the overall project of mitigating our impact on the planet for the sake of generations to come, we need every tool we can find," he said.
“But to get close to having the sector operating where and when we need it to, the government needs to get ahead of the game now. The adaptive approach to market building we recommend will create the best environment for emerging technologies to develop quickly and show their worth, avoiding the need for government to pick winners. We know from the dramatic fall in the cost of renewables that this approach works and we must apply the lessons learned to this novel, but necessary, technology.”
The Intergovernmental Panel on Climate Change and International Energy Agency estimate a global capacity for engineered removals of 2,000 to 16,000 megatonnes of carbon dioxide each year by 2050 will be needed in order to meet global reduction targets.
Yesterday Summit Carbon Solutions received "a strategic investment" from John Deere to advance a major CCUS project (click here). The project will accelerate decarbonisation efforts across the agriculture industry by enabling the production of low carbon ethanol, resulting in the production of more sustainable food, feed, and fuel. Summit Carbon Solutions has partnered with 31 biorefineries across the Midwest United States to capture and permanently sequester their CO2 emissions.
Cory Reed, President, Agriculture & Turf Division of John Deere, said: "Carbon neutral ethanol would have a positive impact on the environment and bolster the long-term sustainability of the agriculture industry. The work Summit Carbon Solutions is doing will be critical in delivering on these goals."
McKinsey highlights a number of CCUS methods which can drive CO2 to net zero:
- Today’s leader: Enhanced oil recovery Among CO2 uses by industry, enhanced oil recovery leads the field. It accounts for around 90 percent of all CO2 usage today
- Cementing in CO2 for the ages New processes could lock up CO2 permanently in concrete, “storing” CO2 in buildings, sidewalks, or anywhere else concrete is used
- Carbon neutral fuel for jets Technically, CO2 could be used to create virtually any type of fuel. Through a chemical reaction, CO2 captured from industry can be combined with hydrogen to create synthetic gasoline, jet fuel, and diesel
- Capturing CO2 from ambient air - anywhere Direct air capture (DAC) could push CO2 emissions into negative territory in a big way
- The biomass-energy cycle: CO2 neutral or even negative Bioenergy with carbon capture and storage relies on nature to remove CO2 from the atmosphere for use elsewhere