Strategies For Enhancing pH Control Systems In Wastewater Treatment
By Emily Newton
Managing pH in wastewater treatment is a crucial undertaking for water utilities. Solid contaminants often receive more attention, as they’re more obvious threats, but sub-optimal pH levels can be dangerous, too.
Making water more acidic or alkaline can boost the efficacy of certain disinfectants. It also makes removing contaminants, like heavy metals and bacteria, easier. Extremes on either side of the pH spectrum may also corrode pipes or foster microbial growth that may impact the environment or degrade critical infrastructure.
Balancing these considerations requires careful attention to several factors in the water treatment process. Here’s how to lower pH in wastewater using different strategies.
Sulfuric Acid Treatment
The first step in managing pH levels in water treatment is to choose the ideal additive. Sulfuric acid is the most conventional choice. It’s so popular that the U.S. EPA calls it essential for pH adjustment, and it’s easy to see why. Sulfuric acid is effective and widely available.
Sulfuric acid’s dissolving ability lets it remove contaminants on top of reducing water’s alkalinity. Because it’s one of the most widely produced chemicals in the world, it’s also easy to source and is relatively low-cost. It’s less caustic compared to other acids that do the same, which makes it safer to handle and reduces environmental hazards.
Despite these benefits, sulfuric acid has several downsides that water treatment plants should be aware of. Most notably, too much of it can lead to calcium tie-up, blocking membrane treatments and other processing steps. Higher concentrations may also corrode metal pipes over time, and special handling is necessary to keep plant employees safe.
CO2 Treatment
Carbon dioxide is an increasingly popular alternative way to lower pH in wastewater. Unlike sulfuric acid, CO2 isn’t corrosive or caustic, making it safer to handle. Injecting it into wastewater creates carbonic acid with no harmful byproducts, providing similar anti-alkalinity benefits.
CO2 is more widely available than sulfuric acid, as it’s a byproduct of many natural and industrial processes. Consequently, it’s generally more cost-effective than sulfuric acid treatments. Carbonate scaling is not as common as the corrosion sulfuric acid may cause, so CO2 treatment is less likely to damage water infrastructure.
Storing CO2 involves pressurized containers, which introduces storage and transport risks. However, these are no more severe than sulfuric acid’s requirements. Carbonate scaling is also harder to remove, but it’s less common and preventable by keeping pH levels low enough. Consequently, maintenance costs are often lower with CO2 treatment.
Additive-Free Approaches
Wastewater processing facilities may also forgo additives altogether. Some mechanical processes can make water more acidic or alkaline as necessary without introducing a potentially hazardous substance. Reverse osmosis and electrocoagulation are the two main methods in this approach.
Reverse osmosis is already a common way to remove contaminants. It can help control pH levels by filtering out substances that contribute to an overly acidic or alkaline makeup. Because these filters have a pore size of 0.0001 microns, they can remove most pH-affecting contaminants.
Electrocoagulation causes contaminants to bind by running an electric current through the water. This coagulation creates larger particles, enabling easier filter-based removal.
These two processes have similar benefits and downsides regarding pH control. Both remove the need for chemicals with specific handling requirements but introduce costs and maintenance concerns from specialized equipment. Consequently, treatment plants with smaller budgets or lower processing volumes may not find them cost-effective.
Batch vs. Continuous Processing
Apart from additives, utilities can also improve pH control in wastewater treatment by choosing the best processing method. The primary choice here is between batch and continuous processing.
As the name implies, batch processing treats water in controlled batches, one at a time. The size of each can vary depending on the facility’s throughput. In all cases, the tank only releases water and refills once the current load reaches optimal pH levels for a predetermined time.
Continuous processing, by contrast, keeps treatment tanks at maximum capacity at all times. As soon as one gallon of pH-adjusted water leaves, another gallon of untreated water enters. This requires a linear filtering and pH control setup.
Studies show that continuous processing is more efficient, both in terms of energy consumption and in minimizing the water’s chemical oxidation demand. However, batch processing is more effective at preventing nitrification and offers more assurance about specific pH levels.
In light of these pros and cons, batch processing is ideal for small-volume operations or those with high pH variability. Continuous alternatives are suitable for larger, more predictable water treatment.
Glass Electrode vs. Metal Electrode vs. Semiconductor Testing
Regardless of how facilities reduce pH in their wastewater, they must have a reliable way to monitor these processes. Consequently, choosing the right testing method is another area where utilities can optimize their pH control processes.
Electrode tests are the most popular pH measurement methods, and glass electrodes are the dominant choice under this umbrella. Glass-electrode tests are more cost-effective than metal-electrode options because they don’t require frequent component switching. They’re also less likely to interact with suspended solids in the water, producing more reliable results, especially at scale.
Metal-electrode tests are more accurate than older paper indicator alternatives but are falling out of fashion in light of glass-electrode methods’ efficiency and reliability. However, a new option has emerged in semiconductor testing. The computer chips this method uses provide the highest level of reliability and are smaller, enabling less disruptive testing, but they cost more.
Hybrid Approaches
A hybrid approach is often the most beneficial way forward in many of these pH control strategies. Combining two or more methods instead of choosing one over another can balance each system’s benefits and downsides for optimal results.
Alkalinity reduction methods benefit the most from this hybrid philosophy. That may look like using reverse osmosis to filter water before treating it with sulfuric acid or CO2. Alternatively, facilities may use electrocoagulation to make reverse osmosis more effective.
Hybrid approaches are particularly valuable for facilities managing different kinds of wastewater. Industrial wastewater streams could go through batch processing, given their higher likelihood of containing dangerous contaminants, while residential wastewater flows through more energy-efficient continuous processes. Water utilities should review their current workloads and compare each method’s costs to find if hybrid solutions are ideal.
Automation
Whatever approach a treatment facility takes should be automated as much as possible. Automation is key to managing pH in wastewater treatment because it minimizes human error and improves process efficiency.
Automated solutions are already common in pH monitoring, but processing plants can also apply them to filtering and treatment. Automatically adding additives to water ensures the exact amount necessary is used each time, preventing overcorrection. It also reduces safety concerns around hazardous materials, as almost all workplace accidents stem at least partially from human error.
Across all use cases, automation is most effective when paired with Internet of Things (IoT) sensors. These devices can feed automated systems real-time data to enable more precise controls and make them more adaptable to changing conditions. For example, IoT-connected pH sensors could inform robotic solutions when to add more CO2 or run water through reverse osmosis again when pH levels still aren’t optimal.
Explore These Methods To Control pH In Wastewater Treatment
The best pH control method varies among treatment plants. Wastewater processing organizations should consider the kinds of materials they manage, their throughput volume, and budgets to determine the best way to lower pH in wastewater.
Learning about each strategy’s advantages and disadvantages is the first step in making an informed decision. Once businesses know when each method is most appropriate, they can find the ideal solution for their needs.
Emily Newton is an industrial journalist. She regularly covers stories for the utilities and energy sectors. Emily is also editor in chief of Revolutionized (revolutionized.com).