Biogas valorization and efficient energy management – Best practices for improved sludge digestion

This review covers state-of-the-art technologies for advanced anaerobic digestion of municipal sewage sludge. It is based on an extensive review of literature and available data, focussing on processes which have been realized in full-scale plants. The review includes information on single-stage mesophilic digestion, thermophilic digestion, temperature-phased digestion, high-load digestion and other process modifications, as well as mechanical, thermal, chemical, and biological disintegration methods. All processes are described with a set of key performance indicators such as degradation rate of volatile solids, biogas yield, return load, effects on dewatering, and capital costs.

Benefits and drawbacks of thermal pre-hydrolysis for operational performance of wastewater treatment plants

This paper presents benefits and potential drawbacks of thermal pre-hydrolysis of sewage sludge from an operator’s prospective. The innovative continuous Thermo-Pressure-Hydrolysis Process (TDH) has been tested in fullscale at Zirl wastewater treatment plant (WWTP), Austria, and its influence on sludge digestion and dewatering has been evaluated. A mathematical plant-wide model with application of the IWA Activated Sludge Model No.1 (ASM1) and the Anaerobic Digestion Model No.1 (ADM1) has been used for a systematic comparison of both scenarios – operational plant performance with and without thermal pre-hydrolysis. The impacts of TDH pre-hydrolysis on biogas potential, dewatering and return load in terms of ammonia and inert organic compounds (Si) have been simulated by the calibrated model and are displayed by Sankey mass flow figures. Implementation of full scale TDH process provided higher anaerobic degradation efficiency with subsequent increased biogas production (+75-80%) of waste activated sludge (WAS). Both effects – enhanced degradation of organic matter and improved cake’s solids content from 25.2 to 32.7% TSS – promise a reduction in sludge disposal costs of about 25%. However, increased ammonia release and generation of soluble inert Si was observed when TDH pre-hydrolysis was introduced to WWTP.

Evaluation of reflection and refraction in simulations of ultraviolet disinfection using the discrete ordinates radiation model.

Simulations of UV disinfection systems require accurate models of UV radiation within the reactor. Processes such as reflection and refraction at surfaces within the reactor can impact the intensity of the simulated radiation field, which in turn impacts the simulated dose and performance of the UV reactor. This paper describes a detailed discrete ordinates radiation model and comparisons to a test that recorded the UV radiation distribution around a low pressure UV lamp in a water-filled chamber with a UV transmittance of 88%. The effects of reflection and refraction at the quartz sleeve were investigated, along with the impact of wall reflection from the interior surfaces of the chamber. Results showed that the inclusion of wall reflection improved matches between predicted and measured values of incident radiation throughout the chamber. The difference between simulations with and without reflection ranged from several percent near the lamp to nearly 40% further away from the lamp. Neglecting reflection and refraction at the quartz sleeve increased the simulated radiation near the lamp and reduced the simulated radiation further away from the lamp. However, the distribution and trends in the simulated radiation field both with and without the effects of reflection and refraction at the quartz sleeve were consistent with the measured data distributions.

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