Industrial wastewater treatment specialist, Aquatec Maxcon Pty Ltd, in conjunction with the Queensland Government, the University of Queensland and Ken Hartley Pty Ltd is proposing that low strength sewage can be effectively treated in a combination of innovative anaerobic and aerobic treatment. This design is proposed in their new and innovative Energy Recovery Sewage Treatment Technology (EnRec).
The EnRec proposal suggests that anaerobic treatment technology, in the form of an Anaerobic Migrating Bed Reactor (AMBR), when combined with a small secondary aerobic plant, improves energy efficiency, minimises greenhouse impacts, produces low volumes of solid waste and effectively cleans sewage for release back into the environment (Hartley [b], 2002). To determine the feasibility of this method, Aquatec Maxcon has constructed an EnRec pilot plant out at the Bundamba Wastewater Centre.
This report investigates the appropriate methods that can be used to assess the settling characteristics of the EnRec sludge granules that form in these Anaerobic Migrating Bed Reactors (AMBR). The settling characteristics are critical in determining the operating loading rates to the plant (to avoid granular washout) which in turn determines reactor volume. Reactor volume is the major factor in evaluating the full scale operating costs of the plant.
It is crucial to the overall operation of the treatment plant that the AMBR reactors are operated at correct loading rates. Correct loading will;
- promote micro-organism (sludge granule) aggregation,
- provide adequate separation of the solid, liquid and gaseous phases within the sludge due to hydraulic turbulence, and most importantly,
- prevent the washout of granular solids.
The reliability of using sedimentation techniques to accurately determine the settling characteristics of anaerobic particles was achieved by running preliminary tests on well defined anaerobic granular sludge from Golden Golden Cannery. The settling rates were determined by using a settling column and theory of sedimentation.
Preliminary analyses of EnRec sludge show that the sludge particles, ranging in size from 20µm to 1000 µm, will typically settle at rates between 5m/hr and 25m/hr. However, results further reveal that 70-80% of these particles actually have settling velocities in the range of 8m/hr – 12.5m/hr. These results correlate nicely with data provided by Aquatec Maxcon, which estimates that EnRec sludge has settling velocities in excess of 5m/hr.
For comparative reasons, settling characteristics of the flocculant EnRec sludge, and granular Golden Circle were compared. Results show that GC sludge settles much more rapidly than EnRec sludge, having settling velocities ranging from 50m/hr to 165m/hr. GC particles are also much larger, having a maximum size of approximately 4000µm.
Because this inquiry is based over two university semesters, refinement of settling column experimental and analytical methods will be done next semester to get more accurate and reliable results. Settling rates will also be investigated using a fluidised bed reactor at the university. Results obtained from the fluidised bed testing will be used to further validate the settling characteristics of the EnRec sludge. Appropriate recommendations can then be made to Aquatec Maxcon regarding the required operating conditions, in terms of reactor capacity and loading rates, of their full-scale anaerobic sewage treatment plant.