Sludge　dewatering　has　proven　to　be　an　effective　method　to　reduce　the　volume　of　sludge.　In　this　study,　drinking　water　treatment　sludge　(DWTS)　was　treated　by　ultra-sonication　under　variable　conditions　comparing　two　sonoreactor　types　(bath　and　probe),　four　frequencies　(25,　40,　68,　160　kHz)　and　four　energy　density　levels　(0.03,　1,　3,　5　W/mL).　The　effects　of　these　conditions　were　studied　using　specific　resistance　to　filtration　and　capillary　suction　time　as　measures　of　dewaterability,　and　floc　size,　the　Brunauer,　Emmett　and　Teller　(BET)　specific　surface　area　and　Zeta　potential　to　determine　treated　sludge　characteristics.　The　results　indicated　that　the　dewaterability　of　sonicated　sludge　improved　at　relatively　low　energy　densities　of　0.03　and　1.0　W/mL,　while　an　optimum　for　sonication　duration　(within　10　min)　was　also　identified.　Higher　frequencies　(tested　up　to　160　kHz)　with　acoustic　energy　density　of　0.03　W/mL　also　reduced　the　dewatering　property.　At　higher　energy　densities　of　3.0　and　5.0　W/mL,　dewaterability　of　sludge　deteriorated　regardless　of　ultra-sonication　time,　with　an　increase　of　solubilized　organic　matter　content　and　severely　changed　floc　characteristics.　The　deterioration　of　the　dewatering　capacity　was　closely　related　to　the　considerably　reduced　floc　sizes,　dissolution　of　proteins　and　polysaccharides,　and　to　the　Zeta　potential　of　sonicated　sludge　flocs.　The　dewaterability　was　not　correlated　with　BET　specific　surface　area.　Mechanistic　explanations　for　the　observations　were　discussed　by　analyzing　corrosion　patterns　of　aluminum　foil　as　a　measure　for　cavitation　field　distribution.