I would like to know the ideal pH of the influent water for aerobic and anaerobic reactors (For example Aerobic - SBR; Anaerobic UASB). I would also like to know what could be the ideal pH inside the reactors. If the pH is higher or lower than the ideal, what could be the solution.
Hi, Arun
for anaerobic system:
The stability of the anaerobic process is very fragile. The balance between several microbial populations must be maintained. The hydrolysis and fermentation phases have the most robust organisms. They have the broadest environment range in which they thrive. They react quickly to increased food availability. Thereby, increasing the amounts of their products. The volatile fatty acid concentration rises very quickly. This is kept in check by the buffering action of the system provided by carbon dioxide in the form of biocarbonate alkalinity.
The pH range is, therefore maintained under normal circumstances. However, during shock loading the acid concentration can overcome the buffering action and raise the pH out of the narrow acceptable limits of the acetogens and the methogens. When this happens methane production stops and the acid levels rise to the tolerance level of the acid formers. At this point the system fails.
As has been previously stated the methanogens are pH sensitive. They operate in a pH range of 6.5 to 7.5. Movement to either side of this range quickly affects their metabolic rates and slows or stops methane production.
best regards
randa.
it should be nearly 6.5-7.5 but italso depends on which types of waste water
Ideal pH for any biological treatment is around neutrality, it may range between 6.5 to 7.5.
For aerobic treatment pH range is between 6 to 8 but for anaerobic pH is a major key parameter, it ranges from 6.5 to 7.5. However, if this can be keep at 7.0 is the best. This is because in anaerobic treatment, growth of methanogenic bacteria should be in equilibrium with acidogenic bacteria. If pH decreases to acidic methogens cannot survive.
To add to what Randa said, pH is easy to measure, and certainly should be near neutral, but it is a poor parameter for dynamically monitoring the health of the digester, because, as she indicated, an increase in fatty acids can overcome the buffer system. _After_ the buffer is depleted, the pH will shift decidedly acidic, but the low pH at that point will tell you pretty much the same thing that the reduced amount and increased CO2 in the gas evolved will tell you: that the digester is failing.
Thus you should of course measure the pH, but if you are interested in process control you should be monitoring the buffer system, usually through one of the many means of titration or with more expensive equipment.
David William House, author, The Complete Biogas Handbook, www.completebiogas.com
I have observed that anaerobic (methanog) fludizied beds could exhibit a robust methanogenesis with pH up to 8.3 - 8.5.
So, in my own experience, the range of pH is 6.5 to 8.3.
However, the parameter most important for anaer (meth) processes is the buffer or alkalinity, rather than pH.
A combination of pH 7.5 with a buffer concentration (alkalinity) of 2000 mg CaCO3/L is typical of robust methanogenic processes. Alkalinity is made up of bicarbonate anions, carbonate, phosphate anions. It is expressed on calcium carbonate basis. Hydroxyl anion is also a contributor to alkalinity, but at pH of 7.5 its concentration is negligible.
The volatile fatty acids anions (from HAc, HPr, HBu, HVal, etc., collectively known as VOA) also contribute to akalinity when determined by titration with sulfuric acid. It is called intermediate alkalinity IA according to the former article of Ripley and Converse, JWPC of the 80's. Please also check an article of mine published in Environmental Technology in 1991 or 1992 where I have re-explained Ripley and Converse concepts and provided the complete reference to their article.
A robust methanogenic process will exhibit a good amount of bicarbonate-carbonate alkalinity, and a low VOA alkalinity.
Ripley and Converse recommends using the indicator alpha, defined as the ratio of Intermediate Alkalinity / Partial alkalinity. If alpha is lower than 0.6, the methanogenesis is OK. If alpha is larger than 0.6, start worrying on organic acids accumulation and try strategies of stop feeding, adding bicarbonate alkalinity, and so on, in order not to have an abrupt increase of the acidogenesis and inhibition of methanogenesis.
Partila alkalinity is the alkalinity determined by titration with sulfuric acid from the initial sample pH down to pH 5.75. Intermediate alkalinity is the Total Alkalinity (determined by titration with sulf acid from the initial sample pH down to pH 4.1) minus Partial alkalinity.
Thus, based on this elementary chemistry concepts, the indicator alpha measures the ratio of organic acid alkalinity to bicarbonate alkalinity. if the
I have successuflly used the alpha indicator in my research. It is more rapid and more economic thant the chromatographic determination of VOAs. I can take corrective measures to the process almost in real time. A skilled operator can perform the alkalinity determinations and the alpha calculation in less than 15 minutes.
As food for thought, typically a sound methanogenic process cannot be judged by only one variable performance. A battery of variables are needed to determine whether the methanogenesis is sound or not.
Usually, the minimum battery of values consists of values in the recommended ranges of pH, alpha, total alklinity, biogas productivity, and methane content in biogas. If you have more time, more money and chromatography available, the the pool of VOA (the sum of organic acids concentrations based on COD) can be used as a part of that battery.
Kind regards,
Professor Dr. Héctor M. Poggi-Varaldo.
I have observed that anaerobic (methanog) fludizied beds could exhibit a robust methanogenesis with pH up to 8.3 - 8.5.
So, in my own experience, the range of pH is 6.5 to 8.3.
However, the parameter most important for anaer (meth) processes is the buffer or alkalinity, rather than pH.
A combination of pH 7.5 with a buffer concentration (alkalinity) of 2000 mg CaCO3/L is typical of robust methanogenic processes. Alkalinity is made up of bicarbonate anions, carbonate, phosphate anions. It is expressed on calcium carbonate basis. Hydroxyl anion is also a contributor to alkalinity, but at pH of 7.5 its concentration is negligible.
The volatile fatty acids anions (from HAc, HPr, HBu, HVal, etc., collectively known as VOA) also contribute to akalinity when determined by titration with sulfuric acid. It is called intermediate alkalinity IA according to the former article of Ripley and Converse, JWPC of the 80's. Please also check an article of mine published in Environmental Technology in 1991 or 1992 where I have re-explained Ripley and Converse concepts and provided the complete reference to their article.
A robust methanogenic process will exhibit a good amount of bicarbonate-carbonate alkalinity, and a low VOA alkalinity.
Ripley and Converse recommends using the indicator alpha, defined as the ratio of Intermediate Alkalinity / Partial alkalinity. If alpha is lower than 0.6, the methanogenesis is OK. If alpha is larger than 0.6, start worrying on organic acids accumulation and try strategies of stop feeding, adding bicarbonate alkalinity, and so on, in order not to have an abrupt increase of the acidogenesis and inhibition of methanogenesis.
Partila alkalinity is the alkalinity determined by titration with sulfuric acid from the initial sample pH down to pH 5.75. Intermediate alkalinity is the Total Alkalinity (determined by titration with sulf acid from the initial sample pH down to pH 4.1) minus Partial alkalinity.
Thus, based on this elementary chemistry concepts, the indicator alpha measures the ratio of organic acid alkalinity to bicarbonate alkalinity. if the
I have successuflly used the alpha indicator in my research. It is more rapid and more economic thant the chromatographic determination of VOAs. I can take corrective measures to the process almost in real time. A skilled operator can perform the alkalinity determinations and the alpha calculation in less than 15 minutes.
As food for thought, typically a sound methanogenic process cannot be judged by only one variable performance. A battery of variables are needed to determine whether the methanogenesis is sound or not.
Usually, the minimum battery of values consists of values in the recommended ranges of pH, alpha, total alkalinity, biogas productivity, and methane content in biogas. If you have more time, more money and chromatography available, the pool of VOA (the sum of organic acids concentrations based on COD) can be used as a part of that battery.
Kind regards,
Professor Dr. Héctor M. Poggi-Varaldo.
pH has a significant impact on the microbial makeup of a wastewater system. Most biological wastewater treatment is accomplished at pH range of 6.5 - 8.5, which is where a majority of our common environmental microbes thrive.
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