Which process best describes making sludge particles come together by neutralizing their charges?

Which process best describes making sludge particles come together by neutralizing their charges?

• A. Coagulation
• B. Filtration
• C. Oxidation
• D. Sedimentation

Answer: (A)

Neutralizing the charges on sludge particles is coagulation. In wastewater, many solids are colloidal and carry negative surface charges, which makes them repel each other and stay dispersed. Adding a coagulant introduces positively charged ions that neutralize these surface charges, reducing electrostatic repulsion. With the repulsion lowered, particles can come close enough for weak attractive forces to act, allowing them to collide and stick together into small aggregates called microflocs. This sets the stage for the next step, where gentle mixing helps these microflocs grow into larger flocs that settle more readily or can be removed by filtration. Filtration relies on passing water through a barrier to trap solids, not on changing particle charges. Oxidation chemically alters pollutants and is not about bringing particles together. Sedimentation is the gravity-driven settling of already formed flocs after coagulation and flocculation, not the charge-neutralizing process itself.

Neutralizing the charges on sludge particles is coagulation. In wastewater, many solids are colloidal and carry negative surface charges, which makes them repel each other and stay dispersed. Adding a coagulant introduces positively charged ions that neutralize these surface charges, reducing electrostatic repulsion. With the repulsion lowered, particles can come close enough for weak attractive forces to act, allowing them to collide and stick together into small aggregates called microflocs. This sets the stage for the next step, where gentle mixing helps these microflocs grow into larger flocs that settle more readily or can be removed by filtration.

Filtration relies on passing water through a barrier to trap solids, not on changing particle charges. Oxidation chemically alters pollutants and is not about bringing particles together. Sedimentation is the gravity-driven settling of already formed flocs after coagulation and flocculation, not the charge-neutralizing process itself.