The effect of operational temperature on dewatering characteristics of digested sludge

Dewatering properties and sludge structure of anaerobically digested sludge were studied in relation to an increasing operational temperature. Sludge samples were taken from 5 pilot-scale CSTR reactors treating municipal sewage sludge with working volume of 20 L and operating at 33, 35, 37, 39 and 55 degrees C, respectively. The main parameters of interest were capillary suction time (CST), concentration of extracellular polymeric substances (EPS), charge density of the extracted EPS, filterability (dry solids content after vacuum filtration), compactibility (dry solids content after pressing) and concentration of fine particles in the liquid phase (turbidity). Sludge from the reactor working at 55 degrees C (thermophilic) contained the most fine particles in the liquid phase, which remarkably deteriorated filterability of the sample, however when subjected to an external pressure, the sludge reached the highest dry matter content of the sludge cake. Sludge originating from the reactor working at 37 degrees C reached the best filtration properties

New perspectives in anaerobic digestion

The IWA specialised group on anaerobic digestion (AD) is one of the oldest working groups of the former IAWQ organisation. Despite the fact that anaerobic technology dates back more than 100 years, the technology is still under development, adapting novel treatment systems to the modern requirements. In fact, most advances were achieved during the last three decades, when high-rate reactor systems were developed and a profound insight was obtained in the microbiology of the anaerobic communities. This insight led to a better understanding of anaerobic treatment and, subsequently, to a broader application potential. The present "state-of-the-art" paper, which has been written by members of the AD management committee, reflects the latest achievements and sets future lines for further development

Influence of temperature fluctuation on thermophilic anaerobic digestion of municipal organic solid waste

A laboratory-scale experiment was carried out to assess the influence of temperature fluctuation on thermophilic anaerobic digestion of municipal organic solid waste (MOSW). Heating failure was simulated by decreasing temperature suddenly from 55 °C to 20 °C suddenly; 2 h time is needed for temperature decrease and recovery. Under the conditions of 8.0 g/(L·d) and 15 d respectively for MOSW load and retention time, following results were noted: (1) biogas production almost stopped and VFA (volatile fatty acid) accumulated rapidly, accompanied by pH decrease; (2) with low temperature (20 °C) duration of 1, 5, 12 and 24 h, it took 3, 11, 56 and 72 h for the thermophilic anaerobic digestion system to reproduce methane after temperature fluctuation; (3) the longer the low temperature interval lasted, the more the methanogenic bacteria would decay; hydrolysis, acidification and methanogenesis were all influenced by temperature fluctuation; (4) the thermophilic microorganisms were highly resilient to temperature fluctuation