Methane Production from the Cambi Solidstream Centrate in an Upflow Anaerobic Sludge Blanket Reactor

Kjorlaug, O., Janka, E., Bakke, R., Nilsen, P.J.

IWA Specialist Conference On Sludge Management, SludgeTech 2017

Abstract

As a consequence of population growth and urbanization, recovering energy from the growing waste streams has become an important topic. With the treatment of sewage inevitably comes the production of sludge that has to be handled in a sustainable way. The increasing amount of sewage also represents an opportunity for resource recovery and energy in the form of methane that would otherwise be wasted. Upflow Anaerobic Sludge Blanket Reactors (UASB) has successfully been used to produce methane directly from the sewage entering some wastewater treatment plants; while Anaerobic Digestion (AD) in Continuous flow Stirred Tank Reactors (CSTR) of the sludge produced by wastewater treatment is the most common way to recover energy. Cambi SolidStream offers an upgrade to this process improving both dewatering and biogas production by high-temperature treatment and subsequent dewatering of the digested sludge. The high-strength centrate is returned to the digester to boost biogas production. Full scale results show 90% Chemical Oxygen Demand (COD) reduction of the centrate in a CSTR within 13 days. An alternative way of producing methane from the centrate was explored in this study by the application of UASB reactors. Initial results show that the Cambi SolidStream centrate can be efficiently treated in an UASB reactor with a total COD degradation of 57% at 1.5 days Hydraulic Retention Time (HRT) and Organic Loading Rate (OLR) of 18.4 g COD/L d. The concentration of propionate and acetate in the reactor can be used as state indicators to monitor the process. Dilution of the centrate or longer HRT may be necessary to avoid propionate accumulation and improve COD reduction. If the microbial community can be further adapted to the centrate so that dilution could be avoided, UASB treatment will be an efficient process to produce methane from the SolidStream centrate and represents a good alternative to returning it to anaerobic digestion in a CSTR.

Download the paper.