Wastewater, pH Balanced For Treatment
By Daniel Theobald, "Wastewater Dan"
Water Online's "Peer Perspectives" is a Q&A series that provides unique insight into the issues facing water and wastewater professionals by speaking directly to you, the reader. For this installment we spoke to Daniel Theobald, wastewater consultant and owner of Environmental Services. An accomplished writer and blogger for the industry, Dan was recently enlisted by the Water Environment Federation to revise its Manual of Practice (MOP-29) for biological nutrient removal (BNR).
In talking with Dan about important issues facing wastewater operators, his point of emphasis turned to pH control — a broader topic in that it affects all types of wastewater treatment, yet one that is too often overlooked. Since pH control became an overriding theme during our discussion (much the same as it does in practice), we narrowed our focus to shine a light on the subject. Read on for 7 key questions and answers regarding pH and wastewater.
Why is controlling pH an important procedure in treating wastewater?
As a chemical component of the wastewater, pH has direct influence on wastewater treatability — regardless of whether treatment is physical/chemical or biological. Because it is such a critical component of the makeup of the wastewater, it is therefore critically important to treatment.
What steps are needed to control pH?
First of all, you have to identify the parameters — the pollutants or impurities — that are actually in the wastewater. Once the pollutants are identified, you should determine the starting and the ending pH values, along with a specific treatment procedure; then you have to select the appropriate chemicals best suited for treatment.
How do starting and ending pH values impact the treatment procedure?
It takes residence or contact time during wastewater treatment for the pH to adjust appropriately. A very narrow pH range (i.e., 7.0 to 8.0) requires less contact or residence time as compared to a wider pH range (i.e., 7.0 to 10.0), so the procedure is affected by the required pH adjustment range.
Why is chemical selection an important consideration in controlling pH?
Different chemicals have varying reaction times, which in turn have a major effect on pH adjustment and control. Therefore, the equipment residence or contact time is very relevant in relation to the chemical used for treatment.
Does the pH change immediately? If not, what are some considerations?
Actually, pH virtually never changes immediately. The rate of change depends on chemical reaction times, which are directly associated with tank volume, the amount of mixing, and all other aspects of the treatment procedure. Often, the pH can change after wastewater leaves the treatment tank. In those instances, the reaction time exceeds residence or contact time.
Can pH be controlled manually, or is automated instrumentation required?
Rigorous precision of pH control is often required for treatment, and it seldom occurs by attempting to control pH manually. There are multiple interferences when attempting to control pH manually, so automation is recommended.
Can equipment selection influence the overall outcome?
Absolutely. Equipment, instrumentation, and specific procedures are all very influential. For equipment, tank size and mixer selection, as well as location and use, are all influential. For instrumentation, including controllers, the type and settings are paramount. Individual procedures, especially specific chemical use, will also impact the overall outcome.
Ultimately, rigorous pH control improves wastewater treatment and simultaneously reduces chemical usage and the associated cost, therefore increasing profitability.
Comments are welcome, so please share your thoughts on this article and the subject of pH control below. For the opportunity to participate in your own Peer Perspectives Q&A, or for other editorial concerns or questions, e-mail editor@wateronline.com.