Open Collections

Evaluation of low power sonication on anaerobic digestion of municipal waste sludge and energy recovery

University of British Columbia

Ultrasound is one of the emerging pre-treatment technologies to enhance anaerobic digestion process, however high energy input requirement is a concern. This study investigated a low power sonication pre-treatment on anaerobic digestion under thermophilic (55⁰C) and mesophilic (35⁰C) digester temperatures. Low ultrasonic densities (0.08 to 0.25 W/mL) and specific energies (1,211 to 15,094 kJ/kg total solids (TS)) were applied to thickened waste activated sludge (TWAS) from Kelowna’s wastewater treatment plant (WWTP) to determine optimal sludge disintegration (solubilisation) conditions. At 0.25 W/mL and 11,343 kJ/kg TS, maximum solubilisation of organic matters and highest particle size reduction were observed. Following solubilisation, anaerobic digesters utilizing a mixture of primary sludge and pre-treated TWAS indicated that at shorter digestion solid retention times (SRT), the sonication effect on biogas production under mesophilic conditions was more pronounced. In an organic loading rate range of 1.8~6.8 g volatile solids (VS)/L of digester/d), corresponding to SRTs of 20-5 days, thermophilic digesters exhibited process instability with an increase in organic loading as well as ultrasound intensity applied due to reduced microbial diversity of methane formers at elevated temperatures. On the other hand, thermophilic digesters were more successful in fecal coliform destruction than mesophilic digesters due to elevated temperatures. Sonication enhanced dewaterability for mesophilic digesters (sonicated at 4163 and 8153 kJ/Kg TS) at higher SRTs and all thermophilic pre-treated digesters at 20 day SRT. However, sonication did not reduce odour causing volatile sulfur compounds in headspace of digesters. In an energy feasibility study, at 20 day and 10 day SRTs for all the digestion systems, the energy balance came out positive due to higher volume of biogas (methane) generated. Overall, among all digestion systems, the mesophilic digester (sonicated at 4063 kJ/kg TS) showed the highest stability at the shortest SRT of 5 days with significant (80%) increase in gas production and organic removal efficiency over control (un-pre-treated) digester. However, the results also indicated that at longer (safer) SRTs 10 and 20 days, low power sonication pre-treatment (2042 to 8153 kJ/kg TS) did not represent substantial benefits in terms of organic removals, biogas production, fecal coliform destruction or enhancement in dewaterability.

Text

2015-06-08

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/53774

Civil Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/