Towards optimized drum composting: evaluation of the radial mixing performance of a model substrate on the laboratory scale

ABSTRACT

The rotating drum composter (RDC) is one of the most widespread reactor systems for biowaste treatment, worldwide. Nevertheless, knowledge on optimum operating conditions including, e.g. fill level, turning frequency, and mixing tool configuration is sparse. This study investigated the effect of static mixing tools (SMTs) on mixing in a rotating drum at high fill levels (60–80%). The methodological approach encompassed mixing experiments in a laboratory RDC using soaked wheat grains as a model material. The temporal course of material blending was quantified in terms of the entropy of mixing using digital image analysis. Experiments without SMTs showed the evolution of unmixed cores. With a single SMT, mixing was superior even at fill levels >70% while peripheral unmixed zones persisted when overly long SMTs were used. The results of this study may help to derive optimal process conditions for RDCs operated at high fill levels.

GRAPHICAL ABSTRACT

KEYWORDS:

• Rotating drum composter
• entropy of mixing
• composting
• biowaste
• static mixing tools

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This project ;[HA project no. 388/13-27] is funded in the framework of Hessen ModellProjekte, financed with funds of LOEWE – Landes-Offensive zur Entwicklung Wissenschaftlich-ökonomischer Exzellenz, Förderlinie 3: KMU-Verbundvorhaben (State Offensive for the Development of Scientific and Economic Excellence) by HA Hessen Agentur GmbH (Wiesbaden, Germany).