Enhanced anaerobic treatment of WWTP sludge: an efficient way towards sludge minimization
Abstract:An innovative process for sludge treatment was tested on a full-scale plant (2,500 p.e.) for a duration of 4 months. It consists of a 40 min thermal pre-treatment at 175°C, followed by solids dewatering and mesophilic fixed-film methanisation of the centrate. Hydraulic retention time (HRT) in the anaerobic reactor was 2.9 days. Under the operating conditions of this study, an overall TS removal efficiency of 65% was achieved by the process, with a HRT of 3 days. Compared with conventional anaerobic digestion, this implies a drastic capacity increase or footprint reduction. A 42 % reduction of sludge production as TSS was obtained for the integrated system (WWTP + sludge treatment process). Hydrolysed solids are hygienised and show very good dewatering properties.
The impacts of the process effluent recycle to the WWTP aeration tank on the wastewater treatment performance were investigated: sludge volume index decreased from 279 to 195 mL/g TSS and heavy metals as well as some micropollutant concentrations in the activated sludge increased. The nitrogen load from the effluent recycle was entirely removed by the activated sludge, as well as 75% of the soluble COD. Accordingly, activated sludge aeration time increased by 17%.
Thus, this process is a very promising technical option for sludge minimisation. Operating conditions need to be carefully selected to find a compromise between the targets in terms of sludge minimisation, quality of produced sludge and the quality of treated water.
Document Type: Research Article
Publication date: January 1, 2004
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