Decreasing activated sludge thermal hydrolysis temperature reduces product colour, without decreasing degradability

Activated sludges are becoming more difficult to degrade in anaerobic digesters, due to the implementation of stricter nitrogen limits, longer sludge ages, and removal of primary sedimentation units. Thermal hydrolysis is a popular method to enhance degradability of long-age activated sludge, and involves pressure and heat treatment of the process fluid (150-160 degrees C saturated steam). However, as documented in this study, in a full-scale system, the use of thermal hydrolysis produces coloured, recalcitrant compounds that can have downstream impacts (e.g., failure of UV disinfection, and increased effluent nitrogen). The coloured compound formed during thermal hydrolysis was found to be melanoidins. These are coloured recalcitrant compounds produced by polymerisation of low molecular weight intermediates, such as carbohydrates and amino compounds at elevated temperature (Maillard reaction). By decreasing the THP operating temperature from 165 degrees C to 140 degrees C, THP effluent colour decreased from 12,677 mg-PtCo L(-1) to 3837 mg-PtCo L(-1). The change in THP operating temperature from 165 degrees C to 140 degrees C was shown to have no significant impact on anaerobic biodegradability of the sludge. The rate and extent of COD biodegradation remained largely unaffected by the temperature change with an average first order hydrolysis rate of 0.19 d(-1) and conversion extent of 0.43 g-COD(CH4)g-COD(-1).     

Carbon Fiber as an Electrode Material

A new type of carbon electrode is introduced. The electrode consists of a bundle of carbon fibers, each fiber having a diameter of approximately 8 jim. In contrast to most electrodes, this electrode is flexible. The fabrication of the electrode is described, and a method is given to determine the apparent stimulating area.     

Evaluation, selection and initial performance of a large scale centralised biosolids facility at Oxley Creek Water Reclamation Plant, Brisbane.

Recent upgrades to Brisbane City Council's Water Reclamation Plants (WRP) for improved nutrient removal has led to a significant increase in sludge production, and loss in potential anaerobic degradability. This increase in sludge production brought forth an economic driver for an improved, integrated biosolids handling strategy. The solution adopted by Brisbane Water, was a centralised thermal hydrolysis facility at Oxley Creek WRP to process the waste activated sludges generated at a total of five WRPs in the region. The thermal hydrolysis process uses high temperature and pressure to make non-degradable material more readily digestible by anaerobic bacteria and hence achieve greater efficiency in the overall anaerobic digestion process. Dewaterability is also improved, as the thermal hydrolysis process releases some of the bound water from the waste activated sludge. The viability of this solution is linked primarily to the reduction in mass and volume of biosolids which leads to lower transportation and disposal costs. After four months of operation, the Oxley Creek thermal hydrolysis plant has resulted in a 70% reduction in biosolids quantities (bulk volume) and disposal costs. The process is currently being optimised. Savings to date have reached about AUD 80,000 per month. Technical and operational issues which emerged during commissioning are also described.