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Kelly

Kelly Hopewell

Year of Award: 2015 Award State: Queensland Environment > General
To investigate the emergent sludge pre-treatment and stabilisation - USA, Chile
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Wastewater treatment plants are increasingly being regarded as opportunities for resource recovery, and the optimal management of biosolids provides advantages in the goal of achieving sustainable environmental outcomes. Currently, around 300,000 dry tonnes of biosolids are produced in Australia every year (ANZBP 2016). The majority of biosolids in Australia (~55%) is applied to land to return valuable nutrients and micro-nutrients to agricultural soils (e.g. carbon, nitrogen, phosphorus, potassium, calcium and magnesium) (ANZBP 2016)

The carbon in sludge is also valuable as it can be used as a potential source of energy generation (electricity and heat). One method for ensuring the biosolids meets the appropriate regulations, and also ensures use of available energy in the wastewater is called Anaerobic Digestion (AD). Anaerobic digestion is a biochemical process in which bacteria (under conditions without oxygen) can ‘digest’ or degrade organic matter to produce methane (a ‘biogas’ which can be used to produce electricity). Often, an added benefit of reducing the organic content, is improvement to the ‘dewaterability’ of the biosolids, which reduces the volume of water that needs to be trucked away with the biosolids.

Originally, the aim of this project was to:

  1. Investigate methods to improve the ‘degradeability’ of sewage sludge using pretreatment to increase biogas production, increase pathogen destruction and improve sludge dewaterability, and to
  2. Explore if any sludge stabilization methods that do not require a separate digestion step, can produce stabilised biosolids and safe for land application

On further consideration and research prior to the trip, the project narrowed to focus on the first aim (pre-treatment technologies), rather than the second aim (main stream sludge stabilisation), however, a slight change was permitted to the original itinerary that allowed investigation of additional aims:

  1. Gain a greater understanding of an biosolids dewatering and drying options, to allow comparison with current conventional dewatering equipment and drying beds
  2. Investigate ways to improve the ‘degradeability’ of the sludge by using high rate treatment options in the mainstream treatment plant.

A variety of methods are used to pre-treat sludge prior to anaerobic digestion, and examples of this were seen in the UK and Chile. Other methods of increasing biogas production are to use high-rate treatment mainstream processes as seen in the UK, USA and Chile. Overall, the fellowship allowed visits to a variety of treatment processes; however, the most promising technology for a vast improvement in volatile solids destruction extent (rather than rate) seems to be high tech options like thermal hydrolysis. Other trends that appear to be developing in Europe and the USA are improvements in dewatering equipment (e.g piston press), centralized sludge processing centers and co-digestion.

 

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