Dewatering investigation of digested THP sludge

Lee, K.1, Ledoux, S.1, Kelleher, K.1, Murthy, S.2, Higgins, M.3 and Fountain, P.1, Thames Water Utilities, UK, 2DC Water, USA, 3Bucknell University, USA



Despite the increase in thermal hydrolysis pre-treatment (THP) plants used for treating sewage sludge, little is understood about the dewatering characteristics of digested THP sludge.  A joint collaborative field research between DC Water and Thames Water Utilities using belt filter presses (BFPs) was conducted to assess the loading capacity, polymer consumption, polymer-sludge mixing effects, BFP capture rate and cake quality of digested THP sludge.  Digested THP sludge from 2 sewage treatment works was studied throughout the trials.  Operating parameters which were recorded included dry solids of sludge and cake, and flowrates of feed sludge, polymer and polymer dilution water.  Filtrate from the BFPs was also analysed.  The results demonstrated that the dewatering characteristics of sludge from both sites were similar in respect to cake dry solids.  However, there were variations in polymer consumption and filtrate quality.  In comparison with conventional mesophilic anaerobic digested sludge, digested THP sludge had higher BFP throughput rates, whilst achieving higher cake dry solids.

Key words

Thermal hydrolysis pre-treatment, THP, belt filter press, loading capacity, polymer consumption, BFP capture rate, cake dry solids


At present, Thames Water (TW) has one operational Cambi’s thermal hydrolysis pre-treatment (THP) plant, which is located in Chertsey.  Prior to April 2011 Chertsey STW was not equipped with a dewatering facility.  Its digested sludge was stored in lagoons and tankered to nearby STWs and mixed with indigenous sludge for dewatering.  As such, Chertsey STW digested THP sludge dewatering characteristics were not known.  Cambi claims that its digested THP sludge dewaters to 30 – 40 % cake solids (Cambi, n.d.).  Conventionally digested sludge typically dewaters to 19 – 25% cake DS based on TW’s dewatering experience.  As limited published data on cake quality of digested THP sludge is available, it was essential that the dewaterability of digested THP sludge was understood as TW are retrofitting 5 STWs with THP process.

DC Water had intended to install Cambi’s THP at its Blue Plains Advanced Wastewater Treatment Plant in Washington, D.C.  As with TW, DC Water did not have experience in sizing its dewatering plant.  As such, a joint collaborative research between DC Water and TW was commissioned and a 2-week field investigation took place in October 2010.

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