Wach, Mathias (2014)

Theme

The effect of operating conditions on hydrolytic activity and performance of hybrid rotating biofilm reactors for wastewater treatment

Subject

Wastewater is a complex myriad of macromolecules which require degradation prior to assimilation for bacterial growth and population maintenance, which is the essence of biological wastewater treatment. Despite the importance of this step in the breakdown of complex organic molecules – little is known about the regulation or activity of these enzymes in wastewater treatment.  The student will be attempting to further understand this process in both biofilm and suspended growth biological reactors. The student will master routine wastewater analysis and biochemical-enzyme linked tests on model substrates to assess the activity of these proteins under different conditions of wastewater treatment. Other ‘culture independent’ molecular approaches will also be undertaken. The student will then experiment in ways to ‘harness’ these enzymes to boost performance. The student will have to operate ‘chemostat’ style biofilm reactors operating real wastewater from Cranfield University Sewage Treatment Works. The student will conduct a small, concise and targeted survey of existing knowledge which will form the introduction to the Masters assignment. The principal findings of the experimental work from this study will be to appear in a series of short chapters which will form the bulk of the Masters thesis (which the student will contribute in its entirety). However publication in one or more academic journals will be encouraged for dissemination of results beyond a thesis. All necessary support to achieve these objectives will be provided.

Abstract

Five, bench scale, rotating biological mesh media reactors were operated with municipal settled sewage containing organic loading rates (OLRs) from 11.6 up to 231.7 g sCOD/m²/d. Measurements of sCOD, NH4+, NO3-, NO2- and sTN showed evidence of nitrification at the time of sampling. Using a microtiter plate reader, the extracellular enzymatic activity was investigated for the substrates p-nitrophenyl phosphate di (tris) salt (APA), p-nitrophenyl α-D-glucopyranoside (α-GLC), l-leucine-p-nitroanilide (L-AMP) and p-nitrophenyl butyrate (LIP). Colorimetric results were then processed to convert to enzyme production rate (v0) using the Beer-Lambert law with a pH correction factor. Nonlinear least-squares data fitting was used to generate the Michaelis–Menten curves and their v0/Km/vmax values. Post assay investigations on the sludge density showed a correlation (r = -0.53) with OLR. Further, microtiter results showed an extracellular enzymatic activity order of LIP>L-AMP>APA>α-GLC. APA and α-GLC essays showed several late absorbance losses due to inhibition, most likely cause by natural substrate or product inhibition. Indications for patterns and correlations between the OLR and enzymatic kinetic parameters Km and vmax were found.

Supervisors