Improving sludge dewaterability and energy balance of wastewater treatment

A process for treating primary sludge in a wastewater treatment plant, comprising the steps of:

• admixing an organic coagulant and/or polymer to wastewater, wherein the organic coagulant and/or polymer is admixed to the wastewater before and/or during the primary treatment, and wherein the organic coagulant or polymer is selected from polyacrylamide, polyamine, polyDADMAC, melamine formaldehydes, natural polymers, starch, cellulose, hemicellulose alginate, guar gum, pectin, chitin and cationic or anionic derivatives thereof;
• allowing a primary treatment of the wastewater in the presence of the organic coagulant or polymer;
• separating solids as a primary sludge from said primary treatment;
• anaerobically digesting said primary sludge to provide a digested primary sludge and biogas;
• and
• dewatering the digested primary sludge to provide a dewatered primary sludge cake, wherein an additional organic coagulant and/or polymer is added before and/or during the dewatering, and wherein the additional organic coagulant and/or polymer is selected from polyacrylamide, polyamine, polyDADMAC, melamine formaldehydes, natural polymers, natural polysaccharides, starch, cellulose, hemicellulose alginate, guar gum, pectin, chitin, chitosan, or cationic or anionic derivatives thereof.