Optimization of primary sludge fermentation for volatile fatty acids production required for biological phosphorus removal in WWTPs.

摘要

Phosphorous removal from domestic and industrial wastewaters has become an increasingly important component of wastewater treatment, because the control of point-source phosphorus discharges is regarded as the most effective method in limiting the eutrophication problem.;Several research works have highlighted the dependence of biological phosphorus removal mechanisms on the presence of readily biodegradable components, in particular volatile fatty acids. Fermentation of primary sludge with the aim of maximising volatile fatty acids production is a new aim in biological wastewater treatment.;The main objective of the present thesis has been to study the primary sludge fermentation-elutriation process for volatile fatty acids production. For that purpose, batch and continuous experiments were conducted in order to determine the influence of the most important operational and environmental parameters.;Batch-flow laboratory bench-scale experiments were carried out with primary sludges from two major wastewater treatment plants located in Valencia (Spain). Solids concentration, solids retention time and temperature effects were studied.;Continuous-flow experiments were also conducted in a pilot plant, located in the Cuenca del Carraixet wastewater treatment plant (Valencia). Solids concentration, solids retention time and hydraulic retention time effects were studied for two different configurations: primary settler with sludge recirculation ("APT") and completely mixed prefermenter.;Results indicated the importance of wastewater characteristics on volatile fatty acids production. Higher volatile fatty acids production was observed at higher solids concentrations. Solids retention times above 6 days scarcely improved volatile fatty acids production.;Solids retention time has a great influence on sludge sedimentation characteristics. Solids retention times above 4 days dropped drastically the efficiency in solids separation at the primary settler.;Gas chromatographic analysis shown inhibition of propionic acid degradation at high solids concentrations. This inhibition meant a bigger percentage of propionic acid and a decrease in acetic acid percentage.;The obtained experimental results were validated by DESASS developed by CALAGUA research group in order to obtain kinetics and stoichiometric parameters for primary sludge fermentation process. The obtained experimental data were validated using only one set of kinetics and stoichiometric parameters, showing a great consistency between the model and the experimental results.