In the last blog post, we examined the relationship between emission and production of chemicals, using year-over-year ratios to gauge environmental control behavior over time.
Another way to measure mitigation efforts across industries and companies is to look at total waste chemical amounts, and the portion of that waste that is released into the air or water. By dividing the released volume by the total, we get a sense of how well a company or an industry is doing in capturing and safely sequestering chemicals, whether through recycling or re-use.
Here we are not weighting by toxicity or economic value of the assessed chemicals. There is a higher incentive to capture rather than release a chemical that is highly harmful, and therefore more tightly regulated. Equally, a company is more likely to capture an expensive fugitive compound and re-use it. Capturing cheaper chemicals may be possible but not economical.
There’s finally a technical differentiation. Not all chemicals are equally susceptible to capture. Some are more easily caught by scrubbing, filtering and other techniques than others.
Looking at some examples, we see three types of behavior. In the first one, an industry reduces both total waste chemical output, and the release of that output into the air and water. An example is the cement industry, which reduced both its production waste of its top 5 regulated chemicals, and their release into the environment. The drop in both measures, shown in the chart below in thousands of pounds per year, started in the middle of the first decade of the 21st century and has trended lower since.
Cement production over this period has been increasing slowly but steadily. The drop in waste and in emission is therefore not driven by lower production. The industry was under pressure to reduce its greenhouse gas emissions, as well as improve its overall environmental footprint. There have been experiments with altering the rate of clinker to gypsum, which improves the energy efficiency of the manufacturing process. Also, the organic chemicals that are used in the grinding process to prevent clumping, and as sealants have been recycled and mixed in with solid fuel for burning. Since 2009, the energy recovery to waste production ratio for the cyclical and linear hydrocarbons that are either used or generated by the manufacturing process has stayed in the high 90s percentile.
Another type of observed behavior is a divergence between waste production and emission. Power generators using fossil fuels have increased the output of waste chemicals in their production process, but the release of these same top five toxic compounds into the environment has dropped.
Over the last ten years, the use of coal as a fuel to generate electricity dropped by 45%, while natural gas use increased by 51%. Total electricity generated by natural gas-fueled plants surpassed coal-fired output in the fourth quarter of 2015 and the two lines have continued to diverge.
A closer look at the top five pollutants shows that waste production of hydrochloric and sulfuric acid dropped significantly during the last ten years, which is mostly explained by the fuel switch. But the emissions of these acids dropped by even more. One driver is that the coal-fired plants that remain in operation are the newest ones, with the most advanced control equipment. The most significant advances were made in the middle of the last decade, with the ratio of disposal to waste production for sulfuric acid dropping by 10% in 2015 and 20% in 2016. Since then, the decrease in emissions relative to waste production has been muted.
The last example is from an industry where the rate of disposal to waste production is steady and low. In paper manufacturing, the main waste product is methanol, and the rate of disposal to production for this chemical in the industry hovers between 5% and 7%.
The ability of paper mills to capture this chemical reduces the overall emission ratio for the top five regulated chemicals to a fraction of those for the other industries mentioned here. The paper mills do not do better than power generators when it comes to sulfuric acid or ammonia, but their high rate of capture for methanol drives their overall emission-to-waste ratio much lower than in other industries.
This view of the data allows for broad comparisons between industries – who is doing more to mitigate the release of pollutants overall – but also creates the possibility of looking at best practices – who is more effectively controlling a particular chemical. What can be done across industries can be done across companies within an industry, or it can be done for a portfolio of facilities in multiple industries.