Large　amounts　of　drinking　water　treatment　sludge　(DWTS)　are　produced　during　the　flocculation　or　flotation　process.　The　recycling　of　DWTS　is　important　for　reducing　and　reclaiming　the　waste　residues　from　drinking　water　treatment.　To　improve　the　coagulation　step　of　the　DWTS　recycling　process,　power　ultrasound　was　used　as　a　pretreatment　to　disintegrate　the　DWTS　and　degrade　or　inactivate　the　constituents　that　are　difficult　to　remove　by　coagulation.　The　effects　of　ultrasound　pretreatment　on　the　characteristics　of　DWTS,　including　the　extent　of　disintegration,　variation　in　DWTS　floc　characteristics,　and　DWTS　dewaterability,　were　investigated.　The　capacity　of　the　recycling　process　to　remove　particulates　and　organic　matter　from　low-turbidity　surface　water　compared　to　a　control　treatment　process　without　DWTS　was　subsequently　evaluated.　The　coagulation　mechanism　was　further　investigated　by　analyzing　the　formation,　breakage,　and　re-growth　of　re-coagulated　flocs.　Our　results　indicated　that　under　the　low　energy　density　applied　(0.03-0.033　W/mL)　for　less　than　15　min　at　a　frequency　of　160　kHz,　the　level　of　organic　solubilization　was　less　elevated,　which　was　evidenced　by　the　lower　release　of　proteins　and　polysaccharides　and　lower　fluorescence　intensities　of　humic-　and　protein-like　substances.　The　applied　ultrasound　conditions　had　an　adverse　effect　on　the　dewaterability　of　the　DWTS.　Ultrasound　pretreatment　had　no　significant　impact　on　the　pH　or　surface　charge　of　the　DWTS　flocs,　whereas　particle　size　decreased　slightly　and　the　specific　surface　area　was　moderately　increased.　The　pollution　removal　capacity　decreased　somewhat　for　the　recycled　sonicated　DWTS　treatment,　which　was　primarily　ascribed　to　organic　solubilization　rather　than　variability　in　the　floc　characteristics　of　sonicated　DVVTS.　The　main　coagulation　mechanism　was　floc　sweeping　and　physical　adsorption.　The　breakage　process　of　the　flocs　formed　by　the　recycling　process　displayed　distinct　irreversibility,　and　the　flocs　were　stronger　and　more　resistant　to　breakage　compared　to　those　from　the　control　treatment.　(C)　2015　Elsevier　B.V.　All　rights　reserved.