In　order　to　verify　whether　a　conventional　wastewater　treatment　process　can　provide　sufficient　protective　screen　of　heavy　metals,　a　long-term　regular　monitoring　of　the　influent,　effluent,　and　water　at　different　stages　of　a　domestic　wastewater　treatment　plant　was　conducted,　targeting　As,　Cd,　Cr,　Cu,　Hg,　Pb　and　Zn.　For　most　of　the　heavy　metals,　more　than　50%＇s　removal　efficiency　could　be　obtained　by　the　whole　treatment　process,　in　which　a　fraction　of　heavy　metals　was　removed　by　the　primary　settling　tank,　while　the　following　biological　unit　made　great　contribution　to　heavy　metal　removal.　Through　a　series　of　adsorption　experiments　using　quartz　sand,　kaolin　of　known　size　distribution　as　inorganic　adsorbents　and　laboratory-cultured　activated　sludge　as　organic　adsorbent　for　adsorbing　model　of　As　and　Cr,　it　was　found　that　the　adsorption　of　heavy　metals　by　the　inorganic　adsorbents　well　followed　by　the　Langmuir　isotherm　with　the　saturation　capacity　proportional　to　the　specific　surface　area　of　the　solid　particles,　indicating　a　single-layer　adsorption　property.　However　for　the　activated　sludge,　its　adsorption　isotherm　showed　a　property　of　multilayer　adsorption　and　the　adsorption　capacity　was　one　order　higher　than　the　inorganic　particles.　The　different　behavior　between　the　activated　sludge　and　the　organic　particles　for　heavy　metals　adsorption　explained　the　mechanism　of　heavy　metals　decay　in　the　different　stages　of　the　conventional　wastewater　treatment　plant　and　indicated　that　the　activated　sludge　in　the　biological　treatment　plant　played　an　important　role　for　heavy　metals　removal.　Models　obtained　from　the　adsorption　experiment　were　practical,　and　can　provide　an　approach　to　predicting　the　contents　of　heavy　metals　in　the　WWTP＇s　effluent.　©　Trade　Science　Inc.