The role of biosolids product and process energy use of water content, based on market externalities: PAPER & PRESENTATION
Panter, K., Consultant, UK
(free)
Traditionally sewage treatment plant (STP) is designed with the objective of meeting the final effluent limits in mind and any route for sludge/residuals that occur is often decided by others and sometimes at a later date. Fundamentally, this approach lacks holistic approach and needs to be altered. The recommended approach will be to incorporate the strategy for sludge treatment and disposal simultaneously along with sewage treatment
The traditional approach ignores the actual outputs from STPs and a key role (and true cost) that sludge treatment and disposal /recycling plays in designing a successful STP. Virtually all the BOD load entering from the sewers is either oxidised (high energy use) or converted into sludge (containing energy) in STPs. The sludge so produced has to be converted to a useful form for reuse or destroyed. The sludge contains energy as carbon, and major and minor nutrients.
There are 3 areas to follow that impact on overall energy neutrality and at the same time total economy. These are 3 aspects to analyse: (i) energy flow; (ii) solids flow and (iii) water balance. The first two have been widely studied but the third one is generally ignored. However, the cost of water transport and/or treatment is the major cost of sludge management and is often one of the largest user of energy. The amount of water in the final product of biosolids to be recycled or disposed is driven by local circumstances where the externalities of marketing or processing can differ widely from country to country. This paper addresses that gap in our thinking with worked examples.
First the energy flow in sewage treatment have addressed in 4 scenarios: primary; Primary plus secondary; enhanced primary and 100% secondary. Results from an AECOM study for Sydney water show the energy flows from sewage to digested cake production 1.
