Reduction of the Production of Biological Sludge in a Wastewater Treatment Plant

The present work consisted on determining the conditions that allowed to reduce the production of biological sludge in a wastewater treatment plant (WWTP) of the activated sludge type, for this, the Organic Loading Rate (O.L.R.) and the Carbon/Nitrogen ratio (C/N) were the state variables studied.

Biological sludge is an unavoidable residue of the wastewater treatment process, so it is important to establish guidelines that make their management more efficient, by defining the optimal parameters of O.L.R. and C/N ratio can be established operating criteria to obtain a minimum volume in the production of biological sludge.

Different values were established for the state variables, with this different scenarios were created using the Activates Sludge Model 1 (ASM1) of the International Water Association (IWA) to determine the impact of these variables on sludge production, the model was calibrated using water characterization and sludge production data from a real WWTP, the scenarios were simulated using GPS-X software.

The ASM1 model is fed with water quality parameters, these parameters are: Biochemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Suspended Solids (TSS), Volatile Suspended Solids (VSS), Total Ammoniacal Nitrogen (TAN) and Total Kjeldahl Nitrogen (NTK); from the latter two, the nitrogen value of nitrates and nitrites (NOx-N) was inferred.

In activated sludge reactors, O.L.R. is the relationship between the organic substrate and the biomass, therefore, having a low O.L.R. implies having abundant biomass with a slow metabolism, but without inhibiting its activity, this favours a minimum production of biological sludge, although this implies high solid retention times (SRT).

On the other side, the amount of organic substrate required for nitrate reduction is usually expressed by the theoretical C/N ratio, which indicates the amount of carbon needed for denitrification, and is determines by the relationship between COD and NOx-N.

Optimum values O.L.R. and C/N ratio were determined in order to reach a minimum production of biological sludge, to implement operating conditions that reduce the production of sludge are favorable in terms of public health and economic, since a minimum cost is achieved in its handling and disposal.