Waste2value

Energy recovery by anaerobic co-digestion of sewage sludge and thermally hydrolyzed biowaste.

The management of biowaste is a major concern affecting large cities, as it accounts for around 40% of all urban waste. On the other hand, the management of sludge generated in wastewater treatment plants (WWTP) is one of the most complex environmental problems associated with the treatment of this water, due to the high volume produced.

The proposed work aims to valorize biowaste and sewage sludge by means of anaerobic co-digestion of both wastes after a thermal hydrolysis pretreatment of the biowaste.

Anaerobic digestion tests will be carried out in batch mode, in 120 mL vials, to determine the optimal conditions for the thermal hydrolysis of biowaste. Subsequently, batch co-digestion tests of the hydrolyzed biowaste with different proportions of sewage sludge (10:90, 15:85 and 20:80 v:v) will also be carried out, and then tested in semicontinuous mode, and compared with sewage sludge mono-digestion. Laboratory-scale continuously stirred tank reactors (CSTR) with a working volume of 2 L will be used in the anaerobic co-digestion of hydrothermally pretreated biowaste and sewage sludge. Experiments at mesophilic (35 ± 1 ºC) conditions will be carried out. The organic loading rate (OLR) will be increased to determine the operating conditions allowing the maximum biogas production. The parameters to be analyzed to monitor the discontinuous and continuous tests will be: pH, total and volatile solids, total chemical oxygen demand and total Kjeldahl nitrogen. Then the samples will be centrifuged and then filtered (0.45 mm) to determine soluble alkalinity, chemical oxygen demand, ammoniacal nitrogen, and individual volatile fatty acids concentrations (C2-C7, including isoforms) by GC-FID. In addition, biogas production will be determined. Biogas composition will be analyzed by GC-TCD with the aim of knowing methane production.