Florida Wastewater Practice Test

What is the purpose of adding lime to green sludge before drying?

1. To enhance disinfection

2. To minimize odor release

3. To increase pH and aid in dewatering

4. To reduce heavy metals content

The correct answer is: To increase pH and aid in dewatering

Adding lime to green sludge serves multiple important purposes, with one of the primary goals being the increase of pH levels, which significantly aids in the dewatering process. When lime is introduced, it reacts with the water content in the sludge, leading to a rise in pH. This elevated pH helps to flocculate (clump together) the particles in the sludge, making it easier to remove water. This improvement in dewatering efficiency is crucial as it reduces the volume of sludge that needs to be managed and processed further, contributing to cost savings and environmental benefits in wastewater treatment operations. Additionally, higher pH levels create an environment that may help stabilize the organic matter within the sludge, reducing potential issues during subsequent processing stages. Furthermore, while lime can also have ancillary effects such as odor control and reducing the bioavailability of certain heavy metals, its primary function in this context focuses on enhancing the physical properties of the sludge for more efficient dewatering.