There are many processes and treatments that wastewater sludge goes through to come out with biosolids, which can then be used for land application on agricultural lands, ranches, forestlands, farms, and even gardens. One of the most popular treatment being used is lime stabilization—a process regulated and sanctioned by the US Environmental Protection Agency (EPA). The treatment through lime stabilization controls conditions wherein pathogens thrive and grow. Through the lime stabilization process, it is ensured that the product will be Class A biosolids.
Compared to other treatment options, lime stabilization is cheaper and therefore, is more cost effective. It is used to produce both Class A biosolids and Class B biosolids. Remember that Part 503 of EPA regulations has established two classes—Class A and Class B—to categorize biosolids? This also specify the treatment that biosolids must receive before beneficial use or disposal.
For Class A biosolids
For biosolids to be categorized as Class A, there should be extremely low pathogen concentrations and it must have few or no restrictions. Biosolids can become Class A through lime stabilization by using the pH elevated requirements for Class B biosolids (elevated to more than 12 for 2 hours) and combining it with elevated temperatures (70C for 30 minutes) or other EPA-approved time/temperature processes.
For Class B biosolids
Compared to Class A biosolids, Class B biosolids have higher concentration of pathogens, but they are low enough for some beneficial use, including land application with restrictions. To meet Class B requirements with lime stabilization, the pH of the biosolids must be elevated to more than 12 for 2 hours and subsequently maintained at more than 11.5 for 22 hours.
Part 503 of the EPA regulations also include the requirements for reducing the biosolids’ capacity to attract disease vectors such as rodents and insects. Through lime stabilization, vector attraction reduction can be reduced. What the treatment process does is to raise the pH level to 12 or higher for 2 hours and subsequently maintained above pH 11.5 for another 22 hours without alkali addition.
If you encountered a lime treatment facility, this could either produce Class A or Class B biosolids. As a result, the disposal and recycling options are increased.
The main reason why lime stabilization process is being utilized is because it is a cheaper option compared to the other processes that reduce the level of pathogens and vector attraction. The lower capital requirement is enough to encourage treatment facilities to consider lime stabilization as the treatment process of choice for producing biosolids.