Proceedings

The sludge produced from wastewater treatment has considerable costs associated with it in terms of
transportation and treatment. Therefore accurate predictions of future sludge dry solid production are
critical for planning budgets and capacities of sludge treatment centres. Southern Water currently have
sludge make figures (g/head/d) for different wastewater treatment processes, that are used with the
population equivalent for a treatment works to give its theoretical dry solids mass of sludge. This paper
presents the source of the sludge make figures and how well they represent reality by comparing theoretical sludge production against actual sludge production data from a number of wastewater treatment works with different process configurations. Empirical calculations of primary and secondary sludge production show that the sludge make figures are based on primary clarifier efficiency and the cell yield coefficients for the different biological processes. The cell yield coefficients though do not take into account the inert solids fraction or the organic matter that is not biological in the secondary sludge. When the theoretical sludge production was compared against actual sludge production data there was a reasonably good correlation at a majority of the works analysed. The accuracy of the various methods of measuring actual sludge production was found to be highly variable though due to instrumental error, human error and process operation problems.

KEYWORDS
Wastewater, sludge production, biomass yield