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Getting back to basics: What is pH?

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The most used measure in wastewater treatment, and for good reasons

The “potential of hydrogen” or “pH” is the measure of free hydrogen activity in water and thereby indicative of the measure of its free acidity or free alkalinity. Gauged on a numeric scale of 0-14, solutions with a pH of less than 7.0 are acids. Solutions with a pH greater than 7.0 are bases and solutions with a pH of 7.0 are neutral.

The pH is the most used measurement in wastewater treatment. Dependence on pH is found at every phase of water supply and wastewater treatment, including acid-base neutralization, water softening, precipitation, coagulation, disinfection and corrosion control.

In the simplest terms, bases are used to neutralize acids, while acids are used to neutralize alkalis. The terms “alkali,” “alkaline,” “caustic” and “base” are often used interchangeably.

The pH of common solutions vary dramatically such as lime juice having a pH of <2.5 to Milk of Magnesia having a pH of >10.0.

The best pH for a wastewater treatment process depends on the water’s ultimate use.

For example, the pH value for discharging treated wastewater into an environmental water stream, be it ocean, river or creek, often requires regulated pH ranges between 6.0 and 9.0. In comparison, pre-treated wastewater being discharged into a municipal sewer systems requires regulated pH ranges between <6.0 and >9.0.

Optimum pH also varies dependent upon wastewater treatment requirements, especially when treatment process tanks receive untreated wastewater from production processes or upon the available wastewater treatments available, and the need for tightly maintained set points.

For certain wastewater treatment processes a pH as low as 3.0 is maintained, while others specify a precise pH value as high as 11.0.

Consider the following in regards to controlling pH in treatment tanks to sustain unique wastewater treatments during a continuous or batch process.

Continuous pH adjustment

In continuous pH adjustment, the treatment tank operates full at all times. Consequently, one gallon entering the tank displaces one gallon exiting the tank discharge. As the influent flow enters the treatment tank it mixes with the tank contents. If the influent pH varies from that of the tank contents, which is likely, then the influent flow will be pH adjusted through the resultant chemical reaction that occurs as the influent mixes with the contents.

An equal and opposite reaction takes place within the tank contents. This opposite reaction is sensed by the pH probe which delivers a continuous pH feed-back signal to the pH controller. The controller triggers the appropriate metering pump to bring the tank water level back into set-point range.

If the influent flow was alkaline, for example, the result would be a steady rise in the tank pH as measured by the pH probe at the tank discharge location. The pH controller would then signal to operate the acid metering pump at an appropriate rate to return the pH to set-point range.

A major advantage to this layout is simplicity and relatively high flows. However, since the tank is always full there is no guarantee, regardless of tank size or control-system proficiency, that the effluent will always be in set-point range. Recognize, the pH control uses a feed-back loop, which does nothing until an out of set-point value is sensed.

If influent flow and chemistry are high enough or strong enough then the effluent pH diverge from and remain out of the pre-programed set-point ranges. Therefore, a pH control backup measure such as regular monitoring may be advised.

Batch adjustment of pH

Here there is a treatment tank, mixer, acid and caustic metering pumps, pH probe and controller, level sensor and discharge valve. Influent flow enters the tank anywhere convenient and exits the tank near the bottom.

In batch pH adjustment, untreated influent enters and fills the tank to the high tank-level point. For the untreated waste, the pH adjustment process occurs much in the same way that a continuous system performs. The difference, however, is that a large volume is treated in one cycle. Once the tank contents are within the discharge range for a minimum working period of time the effluent discharge valve opens thereby allowing the tank to empty. Once the tank is empty, the cycle repeats.

The batch advantage is that no effluent is removed from the tank until the discharge criteria is met. Batch systems are far more suitable for smaller treatment volumes and effluents that may be characterized by large swings in influent pH, concentrated discharges, or erratic flow rates.

The throughput of many designed pH neutralization / adjustment systems is limited by several major drawbacks. These flaws pertain to pH probe response time, mixing efficiency, tank design, chemical metering precision, chemical reaction times and pH control interaction.

So-called “advanced-procedure” pH controls address each of these deficiencies individually and harmoniously. With the use of advanced procedure pH controls, consistent, reliable results are achievable.

Certain general steps for controlling pH have been described. If you have specific pH or other wastewater queries, please submit a question.

This article is originally from Water/Waste Processing and this great article is written by Daniel L. Theobald. Daniel L. Theobald, also known in the industry as “Wastewater Dan”, proprietor of Environmental Services, is a professional wastewater and safety consultant/trainer. He has more than 24 years of hands-on industry experience operating many variants of wastewater treatment processing units and is eager to share with others his knowledge about water conservation (www.ConserveOnWater.com). To read more of Daniel’s article, please click here.

Egypt: Nanotechnology Comes to AUC

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This article details research being carried out at the Yousef Jameel Science and Technology Research Center (YJSTRC) at The American University in Cairo (AUC), Egypt, in the nanoscience and other technology-oriented fields. AUC says their new research includes “…the development of novel diagnostic tests for sensitive detection of the hepatitis C virus; detection of cancer biomarkers, as well as creating a new generation of nanodevices that include smart bricks with tiny sensors, which can analyze building safety and warn of fires and earthquakes.” The AUC is using a variety of nanoparticles, including gold and nanocrystals, to develop unique diagnostic tests for detection of the hepatitis C virus. Sherif Sedky, a physics professor and associate director of YJSTRC, added that they “…are also working on developing energy harvesters that could convert wasted energy into a useful one, which could then be used to charge devices implemented inside the human body, as well as developing miniaturized antennas and high precision motion systems that are suitable for space applications.” The projects are funded by grants from YJSTRC and the Arab Science Technology Foundation in the United Arab Emirates. The article can be viewed online at the link below.

Some Back Ground of Me

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I was inspired to choose chemical engineering when I first saw the chemical formula from my father’s chemistry book. The chemical formula shapes look fascinating and interesting to me.

My father is an organic chemistry lecturer in Universiti Teknologi Malaysia (UTM). When I was 14, I read his organic chemistry book and willingly learnt from it by myself. When I was 17, I wanted to have a career associated with chemistry. Back then, my first choice was chemical engineering and my second choice was biochemistry. To be honest, I was unaware of what chemical engineers do and what the industry is like. I could not imagine it due to lack of exposure and information.

After completing my high school education, I pursue my A-Levels and took 3 core subjects which are essential for engineering: Physics, Chemistry and Mathematics. Then I continued my degree in chemical engineering. I managed to get a place in Bradford University, United Kingdom. I was unlucky because in our contract, practical training or sandwich course is not included by our sponsors. Therefore, we don’t have any valuable practical and industry exposures. That doesn’t matter and I keep on studying until I graduated in 1999.

To be continued in the next post…

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