Category: Chemistry

BOD Loading

BOD Loading

BOD Loading

10/21/25

“How can we quantify the amount of organic matter entering a treatment system over time?”

Every day, wastewater treatment plants use microorganisms to break down organic matter in water. Plant operators need to estimate how much organic matter is entering a treatment system over time to design their system properly. But how can we do this? Well, we know that we already have a unit, biological oxygen demand, to estimate organic pollutant concentration. And we know that the influent water stream will contain a certain concentration of organic contaminants. So what if we were to multiply the influent volume flow by its BOD concentration (milligrams of oxygen microorganisms need to use to consume pollutants per liter)? Well, this will give us a variable called BOD Loading, measured in mass of oxygen needed for pollution cleaning per time, that plant operators can use for design calculations.

Sludge Dewatering

Sludge Dewatering

Sludge Dewatering

10/20/25

“Why do we need to remove water from sludge?”

Sludge is a mixture of solid waste and water created after an industrial or water treatment process. The more water a body of sludge has, the more volume and weight it will take up, and the more difficult it is to handle. Draining water from the sludge will make it lighter and easier to operate. Sludge Dewatering is an essential tool for sludge operators. 

Image credit: https://caryloncorp.com/

Electrodialysis

Electrodialysis

Electrodialysis

10/17/25

“How can we use electric potential to desalinate water?”

Saltwater is much more common than freshwater in the world. Consequently, we could greatly increase our water supplies by converting saltwater to freshwater. But traditional reverse osmosis techniques are incredibly energy-intensive. Is there an easier way to desalinate water? Well, we know that salts have an electrostatic charge. So what if we were to place the water stream between a cathode and an anode and insert an alternating series of membranes that only allow cations or anions to pass? Well, this will create streams of purified water, separated from saltwater. This process, called Electrodialysis, is a smart way to desalinate water and make it useful for people. 

Image credit: https://static.wixstatic.com/

Chemical Dissociation

Chemical Dissociation

Chemical Dissociation

10/16/25

“Why do some ionic compounds dissolve in water?”

Ionic bonds hold together many compounds. But when placed in water, the water molecules can overpower the bonds and tear apart the compounds. This Chemical Dissociation process is a powerful effect that’s responsible for a plethora of important physical phenomena, ranging from carbonate equilibria to ion exchange.

Carbonate Equilibria

Carbonate Equilibria

Carbonate Equilibria

10/14/25

“How does the interaction between carbon dioxide and water keep pH levels stable?”

Water (H2O) can absorb carbon dioxide (CO2).  Some of this CO2 will react with the H2O to form carbonic acid (H2CO3), and some carbonic acid will reversibly decompose into a hydrogen ion (H+) and bicarbonate (HCO3-), and some of the bicarbonate will further reversibly decompose into a hydrogen ion and carbonate (CO3). The more basic a specific body of water is, the more likely these decompositions will occur. At pH levels below ~6.3, carbonic acid predominates. At pH levels between 6.3 to 10.3, bicarbonate predominates. At levels above 10.3, carbonate predominates. This balance is described as the Carbonate Equilibria. The balance of these chemicals holds a massive influence over a water body’s alkalinity and potential for certain treatment methods. 

Air Stripping (Water Treatment)

Air Stripping (Water Treatment)

Air Stripping (Water Treatment)

10/13/25

“How can we use air blowers to remove volatile organic compounds from water?”

Toxic volatile organic compounds (VOCs) might seep into water during the water cycle. According to Henry’s Law, low air pressure can remove these VOCs from water. So what if we were to push water into a tower with air from a giant air blower coming from the bottom and move it down while exposing as much surface area as possible to the low-pressure air to filter out the VOCs? This is the idea behind Air Stripping, a common method for treating VOCs in human-use water. 

Image credit: https://hydroquipinc.com/

Mass Transfer

Mass Transfer

Mass Transfer

10/12/25

“How does mass move from one phase/substance to another?”

Substances in different phases or substances may come into contact with each other. This can cause the mass of a certain substance in one phase or concentration to move to another, such as through diffusion (one substance moving from a single concentration in another to uniform distribution), convection (mass transport by bulk motion of a surrounding fluid), absorption (chemical penetration of one substance into another), or distillation (separation of different components by different boiling points). This Mass Transfer is foundational to understanding how chemical engineering systems operate.

Detention Time (Wastewater Treatment)

Detention Time (Wastewater Treatment)

Detention Time (Wastewater Treatment)

10/10/25

“How can we quantify the amount of time wastewater spends in a tank or basin?”

Wastewater is kept in tanks and basins as part of treatment processes. The amount of time it spends in these is given by the Detention Time, equivalent to the volume of wastewater divided by its flow rate.

Chlorine Disinfection for Water

Chlorine Disinfection for Water

Chlorine Disinfection for Drinking Water

10/09/25

“How can we use chlorine to make water safe to drink and swim?”

All sorts of pathogens harmful to human health reside in water. We need to disinfect water before we drink it. But what chemical should we use? Well, it turns out that chlorine is an incredibly useful tool. We can add chlorine in the form of chlorine gas (Cl2), sodium hypochlorite (NaOCl), and calcium hypochlorite (Ca(OCL)2) to water. The chlorine will then react with the water to form hypochlorous acid (HOCL) and hypochlorous acid (HCL). Hypochlorous acid may then dissociate into hydrogen ions (H+) and Hypochlorite ion (OCl-). The dissociation process is pH level and temperature dependent, and the HOCL and OCL- amounts are equal at pH levels of 7.5 and 20 degrees Celsius. Below a pH of 7.5, HOCL is dominant, and OCL- is dominant above 7.5. HOCL and OCL disinfect water by breaking down the cell walls and internal components of pathogens. HOCL is 80 times more effective at destroying E.coli than OCL- is. In Chlorine Disinfection for Drinking Water, there are at least some chlorine residuals left after the process ends. The amount of time and residual concentration the water is in contact with the chlorine is incredibly important for the disinfection process. Chlorine disinfection is used at a wide range of scales, from swimming pools to gargantuan treatment plants.