Evaluation of the mechanical properties and failure mechanism of fibres formed in municipal wastewater systems

The rainwater axial pumps are specially designed to operate in municipal wastewater systems. The fibres and wastes are discharged during storms with this type of pumps. Several problems have occurred in service due to the fibres clogging up the impeller. Therefore, the chemical compositions of the waste, microscopic analyses, tensile and shearing tests were performed on the debris collected into the rainwater pumps in order to determine it structure and mechanical properties. The failure mechanism of fibres was also determined. It was confirmed that the tensile and shear strength of wet fibres are higher than the dry ones. Also, the value obtained by shearing tests is higher than the values obtained by tensile tests for both wet and dry fibres. This approach represents a useful engineering tool for determination of mechanical properties and failure mechanism of fibres formed in the municipal wastewater systems that lead to clogging up the impeller. (paper)