Efficient methods and apparatus for separating both settleable-particles and finer-non-settlable-particles from particle-laden fluid are provided by combining many successive settling, filtration, and treatment stages in one basin. A sludge and finer-particle removal system combined into the one basin is configured with a common gantry drive having many arms hanging from an overhead beam, each arm carrying a particle remover configured for the corresponding stage. In one stage, a practical method of removing sludge from between closely-spaced settler flow trays is provided by one pair of arms that straddle the trays and move an array of pushers during movement of the common gantry drive. During that movement the common gantry drive also removes the finer-non-settleable-particles from all downstream stages of filtration and treatment, and each stage continues operating while the common gantry drive operates to perform the respective removal.