Rapid sand filtration is a purely physical drinking water purification method. Rapid sand filters (RSF) provide rapid and efficient removal of relatively large suspended particles. Two types of RSF are typically used: rapid gravity and rapid pressure sand filters. For the provision of safe drinking water, RSFs require adequate pre-treatment (usually coagulation-flocculation) and post-treatment (usually disinfection with chlorine).
with great suddenness the car in front stopped abruptly, and we almost hit it Synonyms short, suddenlyRelated Words surprisingly, unexpectedly; directly, immediately, incontinently, instantaneously, instantly, promptly, pronto, right, right away, right off, straightaway; fast, full-tilt, posthaste, quick, quickly, rapidly, readily, snappily, ...
something that makes a strong impression because it is so unexpected discovering that I had a long-lost sister was an absolute bombshell Synonyms surprise, jar, jaw-dropper, jolt, stunnerRelated Words shock, thunderclap; eye-opener, revelation, shocker; amazement, marvel, wonder; fillip, kick, kicker, twist, wrinkle.